Eur. J. Lipid Sci. Technol. 2013, 115, 41 54 41
Review Article
The thiol-ene (click) reaction for the synthesis of plant oil
derived polymers
O
uz Türünç and Michael A. R. Meier
Karlsruhe Institute of Technology, Institute of Organic Chemistry, Karlsruhe, Germany
This review covers the discovery and development of radical thiol-ene addition reactions as
functionalization and polymerization method. First, some general and important developments
within the field of polymer chemistry are introduced. However, the utilization of this efficient
coupling procedure for the syntheses of materials derived from plant oils are the focus of this
manuscript. Applications of this unique reaction will also be discussed in terms of green chemistry
requirements as well as reaction conditions and efficiency.
Keywords: Thiol-ene / Fatty acid / Renewable raw materials / Polymer chemistry / Double bond
Received: April 17, 2012 / Revised: May 21, 2012 / Accepted: June 11, 2012
DOI: 10.1002/ejlt.201200148
fatty acids more than 50 years ago, the potential of these
1 Introduction
compounds for renewable polymers was prominently realized
in the last couple of years and receives a steadily growing
It has been many years since human beings began using plant
interest. Therefore, this review provides an overview on the
and animal products for purposes other than nutrition, such
development and current knowledge of the radical addition of
as paints or clothing. Since that time, the methods and knowl-
thiol compounds to alkenes and the exploitation of this reac-
edge used to produce valuable products from such resources
tion for the syntheses of polymers synthesized from plant oils
have steadily developed. Eventually, the discovery of fossil oil
and their derivatives.
and its exploitation, including the improved knowledge about
petroleum chemistry and chemical engineering, provided
cheap raw materials for the chemical industry and resulted 2 Discovery and development
in a   plastic revolution  . However, due to the recent aware-
ness of not only the greenhouse effect, but also accumulation The earliest report on the addition of mercaptans to unsatu-
of plastic waste in almost every part of the world as well as rated compounds dates back to 1905 [2]. In this report,
environmentally unsound production technologies, mankind Posner discussed that mercaptans add to double bonds in
has started to search for sustainable, environmentally-friendly an anti-Markovnikov manner and that the structure of the
feed-stocks and technologies to improve the ecological unsaturated compounds strongly influences the outcome of
impact of the chemical industry. Today, carbohydrate- and the reaction. Interestingly, two diunsaturated compounds,
plant oil-based polymers and synthesis technologies are being limonene and 1,4-cyclopentadiene were also utilized and
extensively researched and even commercialized to some only monoaddition products were observed. In the fol-
extent. lowing decades, a number of papers reported non-distillable
Plant oils, providing linear carbon chains with carboxylic liquid residues upon allyl mercaptan synthesis and later on,
acid end-group as well as double bonds in different positions the utilization of diolefins and dithiols to yield polymeric
and numbers with high purity, are very useful renewable raw alkylene sulfides with molecular weights of up to about
materials [1]. Moreover, thiol-ene addition reactions are 1300 Da; subsequently, Marvel and Chambers extended
known for being one of the most efficient and simple modi- the concept of this reaction in order to obtain higher mol-
fication and polymerization methods for alkenes. Although ecular weight polymers in 1948 [3]. After optimization, the
the exploitation of this efficient reaction was first applied to UV-initiated polymerizations of hexamethylenedithiol and
1,5-hexadiene resulted in polymers with up to 12 14 kDa
molecular weight and a melting range of 74 76 8C. X-ray
Correspondence: Professor Michael A. R. Meier, Karlsruhe Institute of
analysis of some of the polymers was conducted to show the
Technology, Institute of Organic Chemistry, Fritz-Haber-Weg 6, 76131
crystalline nature of the polymers, which agreed with the
Karlsruhe, Germany
E-mail: [e-mail] sharp melting peaks of the polymers and, therefore, with
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42 O. Türünç and M. A. R. Meier Eur. J. Lipid Sci. Technol. 2013, 115, 41 54
the anti-Markovnikov selectivity of this new addition 1-hexene was found to be 8 times more reactive than
polymerization. trans-2-hexene and 18 times more reactive than trans-3-hex-
It was already known in the 1950s that thiols add to a ene against monofunctional thiol addition, revealing the
double bond in the form of thiyl radicals and that the reaction strong effect of the position of the double bond in the alkene
involves radical chain propagation steps, when Walling and compound.
Helmreich [4] reported on the overall mechanism and the In the following decades, the addition of thiol compounds
reversibility of some of the reactions involved in 1959. The to unsaturations took its place among the most common
mechanism comprises the in situ formation of thiyl radicals, organic reactions and a number of reviews were published;
which add to the double bond and yield a carbon radical, for example, in 1970 Griesbaum reviewed reversibility, reac-
which subsequently abstracts a hydrogen atom from another tion rate, and reactant structure-reactivity in detail [7]. Until
thiol compound resulting in the final addition product. A new the beginning of the 90s, the mechanism of the free radical
thiyl radical is generated during this last step allowing the addition of thiols to unsaturations was clear: formation of a
radical chain mechanism to propagate. (Eq. 1 4) thiyl radical with the help of a radical initiator, e.g., the
addition of peroxides, azo compounds, etc. or exposure to
R-SHðþI Þ!R-S ðþIHÞ (1)
UV irradiation; addition of the thiyl radical to the unsaturated
substrate to form a carbon radical, which is reversible;
!
R-S þH2CźCHR R-S-CH2-C HR (2)
abstraction of an hydrogen from another thiol compound
by the carbon radical to form the final product (Eq. 1 4).
R-S-CH2-C HRþR-SH
Nevertheless, for the primary radical formation reactions, it
was also reported that apart from an external radical initiator,
!R-S-CH2-CH2RþR-S (3)
this reaction can also precede UV- and thermal-initiator-free
and under dark conditions, though the initiation mechanism
2 R-S-CH2-C HR
for these reactions remained unclear. Two postulations were
earlier discussed in the literature in order to give an expla-
!R-S-CH2-CðHRÞ-CðRHÞ-CH2-S-R (4)
nation to this phenomenon, one of them being a   Molecule-
Assisted Homolysis  (MAH), as first suggested by Pryor et al.
2 R-S !R-S-S-R (5)
[8] in 1974. Nuyken and Völkel, in 1990, reported the syn-
Their earlier experiments, which demonstrated a rapid thesis of telechelics from aromatic and/or aliphatic dithiols
cis trans isomerization of olefins during the addition of meth- and diolefins via spontaneous addition under UV radiation,
anethiol to cis- and trans-2-butene at 60 8C, made them citing Pryor s work (MAH) as the mechanism [9]. In their
conclude that the addition reaction (2) is reversible. following report, the high thermal stability of the telechelics
Additionally, the experiments confirmed that the addition synthesized in this way was measured and 5% weight loss-
to a-olefins is generally more rapid, more exothermic, and temperature (T5%) was detected from 190 up to 390 8C in the
less reversible than the addition to 1,2-disubstituted olefins. case of norbornadiene and 1,3-benzenedithiol, depending on
Moreover, from their additional experiments about the the molecular weight [10]. In 1991, Klemm et al. [11, 12]
relative reactivities of olefins towards dodecanethiol, the designed some reactions in order to clarify the self-initiation
authors concluded from their data that: (1) the reactivity is mechanism of thiol-ene polymerization, shortly after their
increased if the radical is stabilized by resonance, (2) elec- report on the linear photopolymerization of dithiols and
tron-donating groups on the olefin increase the rate, (3) diolefins, and to find a potential inhibitor against the high
cyclopentene is more reactive than cyclohexene, and (4) reactivity of the homogenous thiol-ene mixtures. In their
terminal double bonds are more reactive than internal ones. setup, Klemm and coworkers measured the UV-absorption
In 1964, Testa transferred this last feature to oleochemistry spectra of a dithiol and diolefins, and compared them to the
and utilizied thiol-ene reaction as a cis trans isomerization spectra taken after 1 min and 2 h after mixing these substan-
tool for unsaturated fatty acids, e.g., methyl oleate [5]. The ces. A new batochromicly shifted absorption band, which was
experiments showed that methyl oleate isomerizes to methyl attributed to a complex, formed between the dithiols and
elaidate with the ratio of 1 to 3, respectively, when the diolefins. This complex was described as an   Electron
reaction is initiated by benzophenone at 25 8C. Hoyle Donor Acceptor Complex  (EDA), whose formation was
et al. [6] compared the reactivities of the alkene compounds not detected in the presence of DABCO as an inhibitor.
against thiol-ene literature and their laboratory results by Very recently, the mechanism of the self-initiated thiol-ene
means of structure and the reactivity order was given as reaction was clarified by Metzger et al. [13] The kinetic study
follows: Norbornene > Vinyl ether > Propenyl > Alkene of the cis trans isomerization of methyl oleate in the presence
Vinyl ester > N-Vinyl amides>Allyl ether of dodecanethiol was conducted, focusing on the initiation of
Allyltriazine Allylisocyanurate > Acrylate > Unsaturated the radical chain mechanism. The initiation was found to be a
ester > N-substituted maleimide > Acrylonitrile Meth- complex reaction: the EDA complex of the thiol and ene
acrylate > Styrene > Conjugated dienes. In addition, forms in a pre-equilibrium (6) and then reacts with another
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Eur. J. Lipid Sci. Technol. 2013, 115, 41 54 The thiol-ene (click) reaction for the synthesis 43
thiol to give, in a MAH of the sulfur-hydrogen bond, an alkyl than mercapto propionates for both alkenes. In addition,
radical (7) and a sulfuranyl radical (8) that subsequently compared with those of linoleate, the higher isomerisation
dissociates to the thiyl radical and thiol (9), catalyzing the rate of oleate was attributed to a somewhat more restricted
cis trans isomerization. The experimentally found activation rotation along the unreacted linoleate C C bond, which

energy of the isomerization, in good agreement with the would have an effect on the overall addition rate of thiols
computational calculations carried out, is 82 kJ/M. The because of the fact that trans- is more reactive than a cis-alkene
results thus clearly revealed the thermal generation of thiyl [16].
radicals. Therefore, many well known thermally initiated Not only the structure of the thiols and the unsaturated
thiol-ene addition reactions as well as the low shelf-life compounds, but also the reaction conditions play an import-
stability of alkene and thiol mixtures can now be explained. ant role in the overall success of this reaction. For instance,
Lin et al. studied the addition of thiols to vinyl ethers and the
reactions were optimized by means of temperature and sol-
vent under initiator-free conditions [17]. Interestingly, the
reaction was found to be very   sluggish  in common organic
solvents and moderate in neutral ionic liquids, but good
yields were obtained under the solvent-free conditions in
5 h. In addition, a temperature value of 40 8C resulted in
the best yields for both aromatic and aliphatic thiol com-
pounds; lower and higher temperatures somewhat lowered
the reaction yields. On the other hand, the first systematic
study on the efficiency of the initiation reaction depending on
the type of initiation was reported by Yagci s group in 2010
[18]. The thiol-ene reactions between a library of several ene
groups such as allyl bromide, methyl acrylate, and methyl
methacrylate with thiol end-functional polystyrene using
both cleavage (Type I) and H-abstraction (Type II) type
initiators, and the classical thermal radical initiation was
studied. From the results, the authors concluded that the
thiol-ene coupling reactions have the characteristics of a
  click  reaction and when the reactions are initiated using
Apart from the discussion of the self-initiation mechan- the photochemical and thermal radical initiators, the use of
ism, the thiol-ene addition reaction was already exploited for Type I photoinitiators, such as (2,4,6-trimethylbenzoyl)di-
diverse functionalization protocols. For example, in 1998, phenylphosphine oxide or 2,2-dimethoxy-2-phenyl aceto-
Boutevin et al. [14] employed this chemistry in order to phenone (DMPA), leads to highest efficiencies. Moreover,
introduce thiol functionality to phosphorous compounds. the authors indicated that either or both radicals formed from
The terminal alkene of the phosphorous containing com- such Type I photoinitiators may add to a C C double bond

pounds was transformed into thiols via the addition of thio- directly, whereas ketyl radicals from Type II photoinitiators
acetic acid and subsequent transesterification with methanol; are usually not reactive toward double bonds.
the resulting compound was grafted onto polybutadiene Easy post polymerization modification of polymer back-
telechelics in the presence of AIBN. Another interesting bones is an important and challenging concept in polymer
application of this reaction in organic chemistry came from science. Thiol-ene addition reactions helped polymer chem-
de Meijere et al. in 1998: the thiophenol addition to the ists to perform such modifications in a highly efficient man-
double bonds of bicyclopropylidene, methylenespiropentane, ner. A number of thiol compounds bearing diverse functional
and some others in deuterobenzene occurred at RT in the groups can be introduced onto a polymer chain that bears
dark and exothermally, and completed within 1 h [15]. non-activated mono-substituted double bonds as functional
Bicyclopropylidene and methylenespiropentane reacted with groups. In 2008, Schlaad s group applied this chemistry also
complete retention of both three-membered rings; methyl- for the modification of polybutadiene that bears vinyl side-
1
enespiropentane gave exclusively the anti-Markovnikov type groups with different monothiol compounds [19]. The H-
adducts and methylenecyclopropane gave 91% of the anti- NMR analysis of the final polymers showed that up to about
Markovnikov product. Aliphatic and functionally substituted 80% functionalization with complete double bond conver-
thiols added also quantitatively onto bicyclopropylidene, but sion could be achieved when a 2-fold excess of corresponding
heating and longer reaction times (2 to 4 h) were necessary. thiol compound with respect to the double bonds was used
Last but not least, Johansson et al. studied the coupling of under irradiation with UV (>300 nm). They observed that
mercapto acetate and propionate esters to methyl oleate and the intermediate carbon radical may add, prior to proton
linoleate; mercapto acetates showed higher reaction rates transfer, to an adjacent double bond under the formation
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44 O. Türünç and M. A. R. Meier Eur. J. Lipid Sci. Technol. 2013, 115, 41 54
of a six- or five-membered cyclic unit. Interestingly, this side molecule proceeded quite well, whereas the polymer-polymer
reaction was partially suppressed when solely UV light was conjugations were mostly unsuccessful as the starting
used and similar results were obtained when sun light was materials were taken close to equimolar. The reason for
used as UV source. In order to provide spacing between the the failure was ascribed to head-to-head couplings that result
vinyl groups and to avoid this side reaction, Schlaad s group from Eq. 4 and 5, which interrupt the propagation cycle of the
also applied this chemistry to poly[2-(3-butenyl)-2-oxazo- thiol-ene process and lowers the overall coupling efficiency.
line]s, which was obtained via living/controlled cationic ring Nevertheless, it was also found that the thermal and photo-
opening polymerization [20]. The reactions proceeded chemical initiation showed similar results.
smoothly with 1.2 1.5 equivalents of mercaptan with respect
to double bonds under UV light. In the following years, the
3 Applications of thiol-ene reactions to plant
same group reported on the side-chain modification of vinyl-
oils and fatty acid derivatives
functional peptide homo and copolymers [21] as well as on
the surface-modifications of glass [22] and gold and silicone The relatively low cost, ready availability, renewability, and
substrates [23] via thiol-ene chemistry. the potential biodegradability of materials derived from plant
Thiol-ene chemistry was not only exploited in the con- oils make vegetable oils advantageous starting materials for
struction of linear polymers, but also for the synthesis of many applications [31] (Scheme 1). This class of renewable
dendrimers, which generally requires highly efficient linking raw materials possesses great potential as sustainable resour-
reactions. Rissing and Son, for instance, used tetravinyl silane ces for the polymer industry, since the synthetic potential of
and a number of thiol compounds in order to synthesize a naturally occurring fatty acids can be exploited for monomer
series of multifunctional organosilicon thioethers under UV and polymer synthesis without many reaction steps [32 34].
light [24]. High yields were obtained in 2 4 h reaction time. The possibility to use the plant oil directly, without chemical
Perhaps the most famous application of the thiol-ene chem- modification or further functionalization, most often leads to
istry is the synthesis of dendrimers by Hawker in 2008. In cross-linked structures (thermosets, coatings, resins . . .).
their report, Hawker and co-workers utilized this chemistry Moreover, thermoplastic materials can be prepared from fatty
for the synthesis of up to 4th generation dendrimers with acids and their derivatives, resulting in polymers with tune-
diverse peripheral functionalities [25]. This reaction was able properties and linear or hyperbranched architectures.
classified as one of the click reactions by the authors, the The functionalization of fatty acids and their esters via the
concept of which was introduced by Sharpless et al. in 2001 addition of sulfur, phosphor but also carbon radicals onto a
C C
for highly efficient and orthogonal reactions [26].  bonds has been known for long time [35]. This review
Subsequently, a large number of articles were published intends to provide an overview on the radical addition of
utilizing thiol-ene reactions in the scope of click chemistry thiols to plant oil derivatives, since this reaction received
[27 29] although not all of the described procedures actually increased interest in recent years. Although the reactions
fulfilled the requirements. In 2010, Koo et al. [30] briefly of unsaturated fats and oils were known, the first systematic
studied the efficiency of both thermal and UV initiated thiol- investigations were reported by Koenig and co-workers in the
ene addition reactions as a polymer-polymer conjugation tool 50s [36]. In their first report, mercaptoacetate was added to
for star-shaped polymer synthesis. The authors prepared undecenoate 1, oleate 2, elaidate 3, and ricinoleate 4, all both
macromonomers bearing single thiol or alkene end-groups, in the acid and ester form, yielding diverse diester and (or)
employing thermally decomposing initiators. The ESI-MS diacid compounds (Scheme 2). It was also shown that
studies revealed that conjugation of a polymer with a small Lauroyl peroxide enhanced the rate of the addition reaction.
Scheme 1. Chemical structures of common fatty acids utilized for polymer synthesis [31 34].
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Eur. J. Lipid Sci. Technol. 2013, 115, 41 54 The thiol-ene (click) reaction for the synthesis 45
Scheme 2. Modification of fatty acids with mercapto acetate [36].
In addition, this reaction was extended to include both study, hydrogen sulfide (H2S) was added to linseed oil, and
aliphatic and aromatic thiols: the resulting (alkylthio)- and the alkali-resistance and pencil hardness of the films prepared
(arylthio)-undecanoic acids were converted to, for example, therefrom were found to increase with the sulfur content.
sulfoxides, sulfones, and esters in the presence of peracetic Shortly after, the authors reported on the kinetics of the
acid [37]. Noteworthy, the authors were able to synthesize addition of H2S to conjugated and nonconjugated FAME
fatty thiol compounds with addition of thioacetic acid to 2; and the reactivity order given was as: methyl oleateffimethyl
the obtained thiolacetate was later hydrolyzed to mercaptans linoleate 5ffimethyl linolenate 6 >> methyl 9,11-trans,-
and further functionalized to disulfide products by iodine trans-octadecanedienoate > methyl b-eleosteorate [40].
oxidation (Scheme 3) [38]. In contrast to Koenig s method The use of fatty acids or plant oils is not only interesting
to couple 2, which yields a diester, Schwab and co-workers for the synthesis of polymeric materials, but also some other
used 1,6-hexanedithiol under UV irradiation, but the isolated application possibilities of thiol-ene modified plant oil deriva-
diester yield was less than 20% (by weight) [39]. In the same tives were reported. For instance, the pre-treatment of
Scheme 3. Modification of oleic acid with thioacetate [38].
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46 O. Türünç and M. A. R. Meier Eur. J. Lipid Sci. Technol. 2013, 115, 41 54
Aluminium metal sheets with linseed oil was applied as resistance and hardness with adhesion and flexibility regard-
an environmentally friendly alternative to the toxic and less of functionality. In addition, FT-IR spectroscopy was
carcinogenic chromium-based surface pre-treatments [41]. used to delineate between homopolymerization and thiol-ene
For this purpose, Aluminium substrates were treated reactions, and it was found that acrylates gave significant
with g-mercaptopropyltrimethoxysilane in buffer solution homopolymerization together with thiol-ene, whereas vinyl
prior to the plant oil solution with 4 wt% benzophenone, and allyl ethers copolymerized with cis-unsatuations and
as photoinitiator, under UV light. The Tof-MS [42] and thiols.
XPS [43] spectra of the substrates as well as the wash In contrast to Black and Rawlings work, for which com-
solutions, respectively, revealed that the unsaturated fatty mercial thiol compounds were used in order to cure func-
acids reacted and were bound onto the metal surface. The tionalized triglycerides, Webster and co-workers synthesized
same group reported on the kinetics of thiol-ene addition their own multifunctional thiol as well as mono-substituted
reactions of mono- and poly-unsaturated fatty acids, e.g., 2 ene compounds via BF3-catalyzed ring opening reaction of
and 5, and two different three-functional thiol compounds, epoxidized soy bean oil by appropriate thiols and alcohols,
trimethylolpropane trimercaptoacetate and trimethylolpro- respectively [46]. Due to the very low Tgs, the UV polymeri-
pane trimercaptopropionate, under UV conditions. The zation of the thiol- and ene-components could exhibit tack-
important result of this study for the application of thiol- free and good film properties only if allyl triazine was incorp-
ene reactions on plant oils is that trans isomers result in orated into the coating formulation. Hence, it was also shown
higher reaction rates, which is not the case for the natural that better coating material properties could be obtained by
plant oils. Thus, some additional driving force should be the addition of multifunctional, hyperbranched acrylates.
applied for these applications. For instance, Bantchev et al. Instead of thiol- or ene-functionalization of epoxidized plant
[44] modified corn and canola oils with butanethiol. In order oils, a direct exploitation can be achieved by a polyamine
to better understand how the reaction parameters influence cross-linker. In order to get both components renewable, a
this reaction, the temperature, oil/butanethiol ratio, presence polyamine was prepared from grapeseed oil via thiol-ene
of photoinitiator, and type of oil were varied. The conversion addition of cysteamine chloride and cross-linked with epoxi-
of double bonds and the yields were quantified by NMR dized linseed oil [47]. Upon the polyamine synthesis, three
and GC. The results revealed that the double bond conver- equivalents of cysteamine chloride per double bonds present
sion was higher at lower temperatures. This phenomenon on triglyceride in the presence of 0.1 equivalents of DMPA
was attributed to the entropically favored dissociation of were necessary in order to achieve 87% conversion of the
the carbon radical (back reaction of (2)). The presence of internal double bonds. The DSC analysis of this fully plant
DMPA as photoinitiator did not have an extraordinary effect oil-based material showed the polymer to have a Tg value of
on the double bond conversion, but an increase of the initial 38 8C and thermomechanical analysis showed classical
thiol to double bond ratio from 1:1 to 6:1 ratio resulted thermoset amorphous polymer that has a storage modulus
in threefold increase in the formation of sulfide modified of about 109 Pa below 45 8C in the glassy state. Another
vegetable oil. important area of plant oil utilization is the synthesis of
UV-curable coatings, which are typically aimed to be polyurethanes. Boutevin and co-workers synthesized a polyol
volatile organic compound (VOC)-free systems, offer rapid via thiol-ene coupling of rapeseed oil with mercaptoethanol
ambient crosslinking as well as reduced energy consumption. and polymerized it with different diisocyanates to yield poly-
However, and even though superior properties are often urethane elastomers [48]. Before the polymerization, the
obtained for thiol-ene resins (i.e., a lack of oxygen inhibition, authors optimized their reaction conditions with 2 and the
uniform networks, delayed gel points, reduced polymeri- reactions were studied by means of NMR, FT-IR, and LC-
zation shrinkage and stress, lack of toxicity concerns that MS as well as iodine titration. Best yields were obtained after
are typically associated with low molecular weight acrylates) 1-h reaction time for a thiol/ene ratio of 3, without solvent by
the unpleasant smell of low molecular weight thiols limits the using maximum UV irradiation intensity. The side reactions
commercial utilization. Nonetheless, Black and Rawlings (esterification between alcohol group of mercaptoethanol and
utilized castor oil in a thiol-ene UV curable coating formu- 2; disulfide formation; inter-and intra-molecular couplings)
lation for the benefits of renewable resource utilization, fatty were observed. Since all side products formed during the
acid plasticization, for VOC-free coalescence, and the oppor- thiol-ene grafting anyhow bear alcohol groups, they could
tunity of dried films via auto-oxidation [45]. To achieve this, still incorporate into polyurethane formation. It was also
the authors prepared allyl, acrylate, and vinyl ether deriva- shown that the higher the polyunsaturation, the lower the
tives of castor oil and blended them with multifunctional rate of thiol-ene reaction.
thiols to yield films with about 40% vegetable oil content When thiol-ene addition reactions were used for the syn-
without VOCs. The prepared films were evaluated for their thesis of linear polymers, two distinct approaches are realized,
gel content and by dynamic mechanical thermal analyses as already mentioned above. The first is the modification of
(DMTA). The results showed that each bio-based monomer an unsaturated monomer by a monofunctional thiol com-
exhibited excellent thin film performance, high solvent, pound into a polycondensable monomer, which has been
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Eur. J. Lipid Sci. Technol. 2013, 115, 41 54 The thiol-ene (click) reaction for the synthesis 47
Scheme 4. Syntheses of telechelics from 1 and 7 [49, 50, 51].
applied for more than 50 years on fatty acids, albeit the derived monomers suitable for polyesters synthesis was pub-
importance and exploitation of this method for renewable, lished in 2010 (Scheme 5) [52]. Owing to the terminal
tailor-made plastics were only realized in the last few years. position of the double bond present in 1, highly efficient
For instance, thiol-ene reactions have often been applied for thiol-ene additions were observed. After optimization,
the syntheses of telechelics, prepolymers, and macromono- >95% conversions at 35 8C within 2 h without any solvent
mers from 1 and its derivative, 10-undecenol 7, by Boutevin and additional initiator were observed. However, an inert
and coworkers (Scheme 4). The authors prepared an isocya- reaction atmosphere was found necessary to reach almost
nate terminated compound via the coupling of 1 with 2- complete conversion when 1:1 equivalents of the thiol and
mercaptoethanol and subsequent treatment with thionyl ene components were used.
chloride and sodium azide to obtain the final product [49]. The thus obtained monomers were then polymerized
On the other hand, the authors were also able to synthesize a using 1,5,7-Triazabicyclo[4.4.0]dec-5-ene (TBD) as a cata-
diol [50] and mercapto-alcohol [51] from 7 when a dithiol lyst at 120 8C under continuous vacuum, yielding hyper-
compound was used in stochiometric or excess amounts, branched and linear polyesters having 4 10 kDa molecular
respectively. weight. TGA and DSC analyses of the final polymers showed
One of the first reports on the systematic modification of 1 that these plant oil-derived polyesters have comparable ther-
with different thiol compounds in order to obtain plant oil- mal properties to the currently available petroleum-derived
Scheme 5. Synthesis of new polycondensable monomers from 1 [52].
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48 O. Türünç and M. A. R. Meier Eur. J. Lipid Sci. Technol. 2013, 115, 41 54
Scheme 6. Carboxyl monomers from sunflower and castor oils [53].
commercial ones. Polyanhydrides are another important class the reaction required higher amounts of photoinitiator. These
of biodegradable polymers, offering, for instance, fast degra- diols were then polymerized with MDI in DMF solution
dation properties for controlled drug delivery applications. 3- using tin(II)-2-ethylhexanoate as catalyst, to produce the
Mercaptopropionic acid addition to 2 and 1, as well as to corresponding thermoplastic polyurethanes having molecular
undecenoic acid triglyceride, resulted in di- and tri-functional weights in the range of about 36 83 kDa. The polymers were
carboxylic acid derivatives, which were first acetylated and characterized and revealed good thermal and mechanical
finally melt polymerized at higher temperatures under properties; for instance, the polyurethane from 1 exhibited
vacuum (Scheme 6) [53]. The thiol-ene addition reactions a Tg value of 56 8C and Tm value of 141 8C (second run), and
were carried out under UV radiation (365 nm) in the pres- T5% of 274 8C which are comparable to the commercially
ence of DMPA as photoinitiator and the monomers were available thermoplastic polyurethanes. In addition, cytotox-
purified with simple workup procedures to yield the carboxy icity tests revealed that these materials are promising for
monomers in good to high yields. The thermal properties of biomedical purposes. Similarly, Cramail et al. reported on
the resulting polymers were studied by means of DSC and the syntheses of diols from castor and sunflower oil [55]. The
TGA. The polyanhydride synthesized from 1, for instance, addition of mercaptoethanol to the 2-diesters, which were
exhibited Tg and Tm values of 38 and 72 8C (second run), derived via esterification of 2 with pentane diol or PEG diols,
and T10% and Tmax values of 279 and 413 8C, respectively. In was performed via both UV- and thermal initiation at differ-
addition, the polyanhydride synthesized from 1 and its tri- ent temperatures and thiol/ene ratios. The conversions were
1
glyceride was subjected to hydrolytic degradation and drug determined by H-NMR and the best results were achieved
release essays in phosphate buffer solution (pH 7.4) at 37 8C. under the following conditions: UV-initiation at 225 nm, and
The polymers exhibited fast degradation and release a thiol/ene ratio of 6 at 0 8C for 2 h. Interestingly, the pres-
properties. ence of benzophenone as photoinitiator did not have a
Just like epoxy resins, polyurethanes are one of the most remarkable effect on the final conversion, which is about
important materials for the plastic industry. Therefore, it 89 90% after 2 h. Finally, the obtained diol compounds were
would be very important to study polyurethanes synthesized polymerized with isophorone diisocyanate to yield linear
from plant oils even if it is only limited to the synthesis of polyurethanes (Scheme 7). The characterization of the
polyols from fatty acids and (or) triglycerides and cure obtained polyurethanes gave, for example, 35 kDa molecular
with non-renewable isocyanates. For instance, the syntheses weight and a Tg value of 28 8C, when it is synthesized from
of linear and branched diol compounds from 1 and 2, res- mercapto ethanol-modified pentamethylene dioleate.
pectively, and their polymerization with 4,4 -methylenebis- Another interesting application of 1 was reported very
(phenylisocyanate) (MDI) to yield partially renewable recently by Gandini et al. with the synthesis of polymers with
polyurethanes were reported in 2011 [54]. Linear diols were thermoreversible character [56]. The authors prepared
produced via mercaptoethanol addition to 1 and subsequent monomers from 1 through thiol-ene addition, bearing either
reduction or after esterification of 1 with allyl alcohol. The two furans or a combination of furan and a protected mal-
thiol-ene addition reactions were performed at RT without eimide end-group that can later be polymerized via Diels
deoxygenation, in small amount of acetonitrile as solvent, Alder reaction. The difunctional monomers with Diels-Alder
under UV irradiation (9W, 365 nm), and DMPA was used as moieties were prepared via 2-furylmethanethiol addition to
photoinitiator where necessary. When the same methodology the esterification product of either 1 with allyl alcohol, or 1
was applied to 2 a branched diol compound was formed and with 2-furylmethanol, or 7 with 4-maleimidobutyric acid (the
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Eur. J. Lipid Sci. Technol. 2013, 115, 41 54 The thiol-ene (click) reaction for the synthesis 49
Scheme 7. Polyurethane synthesis from 2 [55].
Scheme 8. Syntheses of the Diels Alder condensable polymers [56].
monomers were represented by 8, 9, and 10, respectively, at therefore the diene/dithiol ratio is an important parameter
Scheme 8). The thiol-ene addition reactions were carried out for this reaction. That means, in contrast to some of the
in excess of thiol compounds under nitrogen atmosphere and grafting reactions, the dithiol compound cannot be taken
365 nm UV irradiation for 4 h at RT. Later on, 8 and 9 were in excess amount in order to compensate the lower reaction
polymerized with 1,6-bismaleimidohexane and 10 was self- rates with internal alkenes, and hence this polymerization
polymerized. The highest molecular weight, about 17 kDa reaction is limited to the use of 1 and its derivatives bearing
with 1.8 PDI, was reported for 10, having a Tg value of 2 8C, terminal double bonds. For example, Lluch and coworkers
which was then depolymerised at 110 8C. Such polymers are prepared the allyl ester of 1 and polymerized it with a dithiol
expected to be used as amendable, recyclable, and controlled compound, e.g., 3,6-dioxa-1,8-octanedithiol under UV radi-
phase-changing systems. ation (365 nm) in the presence of DMPA for 2 h [57]. An
Another approach towards thermoplastics via step- important feature of this reaction is that telechelics could be
growth polymerization is the synthesis of monomers in the formed in a one-pot process. The polymerization of the diene
form of a,v-dienes that can be polymerized by a dithiol and dithiol compound was carried out with the excess of
compound. It should be noted that such a polymerization diene monomer in order to obtain polymers having double
reaction follows typical step-growth polymerization rules; bonds at the chain terminus; the subsequent addition of
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50 O. Türünç and M. A. R. Meier Eur. J. Lipid Sci. Technol. 2013, 115, 41 54
Scheme 9. Telechelics synthesis via thiol-ene addition [57].
mercaptoethanol resulted in alcohol-functional telechelics that the polyanhydride degraded much faster than the poly-
(Scheme 9). The telechelic diols were then reacted with ester, as expected. Interestingly, copolymers of 11 and 12
4,4 -methylenebis(phenylisocyanate) and 1,4-butandiol as showed tuneable degradation behavior. As biodegradability
chain extender to obtain multiblock copolymers with Tg has been discussed as a desired property for plastic materials,
and Tm values of 45 and 9 8C, respectively. it is not always desired. Especially polyethylene or polypro-
The polymerization of a,v-diene and dithiol compounds pylene, and their analogues, are preferred for the applications
was also applied for the syntheses of a new class of biopol- that request long-lasting use and actually are the commodity
ymers from fully renewable diene compounds. The conden- plastics produced in highest volume. Although such polymers
sation of 1 with its acid chloride derivative or with 1,3- would not be biodegradable, their production from renew-
propanediol resulted in two monomers with anhydride and able resources would still be a greener choice. Considering
ester moieties, 11 and 12, respectively; the monomers were their long linear aliphatic chain, fatty acids seem to be a
polymerized via both thiol-ene and Acyclic Diene Metathesis perfect renewable feed-stock for this kind of polymers.
(ADMET) polymerization reactions (Scheme 10) [58]. Recently, a catalytic process realized the migration of the
1
The final polymers were characterized by GPC and H- double bond present on 2 to the chain-end and a subsequent
NMR. The GPC calculations showed that the polyanhydride selective transformation to a methyl ester at the terminus,
had a molecular weight of 5.4 KDa with a PDI of 2.29, yielding a C19 linear diester product [59]. The polyconden-
whereas the polyester had a molecular weight of about 12 sation of this product with its corresponding dialcohol
KDa with a PDI of 2.00. The relatively lower molecular resulted in a polymer with polyethylene-like behavior. In
weight and higher PDI of the polyanhydride were explained 2011 Meier et al. reported the syntheses of two new com-
1
by H-NMR analysis, which clearly showed the formation of pletely renewable diene monomers from 1 derivatives, bear-
thioester and free carboxylic groups, which resulted from the ing either no other functional group or a single ether in the
transesterification reaction between anhydrides and thiols. middle of two linear C11 chains (Scheme 11) [60]. With both
The polymers formed via ADMET polymerization were sub- ADMET and thiol-ene polymerization of these monomers,
jected to stability tests under acidic (0.3 M H2SO4 in THF) the authors achieved linear aliphatic polymers that have only
and enzymatic conditions (immobilized lipase from candida ethers and sulfide-ethers on their main chain. Noteworthy,
Antarctica) at 37 8C in order to compare their degradation neither of the polymers with 1,4-butanedithiol moiety was
rates. The stability tests were preferred to be applied on the soluble in THF, but those with 2-mercaptoethylether were
ADMET polymers, since the thiol-ene polymerization of 11 soluble and had molecular weights within the range of 17
was not successful as described above. The results revealed 24 kDa. The highest melting temperature reached was 80 8C
ß 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.ejlst.com
Eur. J. Lipid Sci. Technol. 2013, 115, 41 54 The thiol-ene (click) reaction for the synthesis 51
Scheme 10. Syntheses of the biopolymers from 1 [58].
Scheme 11. Syntheses of the renewable polyethylene-like polymers [60].
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52 O. Türünç and M. A. R. Meier Eur. J. Lipid Sci. Technol. 2013, 115, 41 54
Scheme 12. Synthesis of monomers via the Ugi reaction and their thiol-ene polymerization [61].
Scheme 13. Side-chain functionalization of the unsaturated polyesters via thiol-ene addition [63].
with a degree of crystallinity Xcź42%, when compared to polyamides with aliphatic, cycloaliphatic, and aromatic side
LLDPE. groups were obtained.
So far, it was shown that the thiol-ene addition reaction is A different approach to the application of thiol-ene reac-
a very versatile tool for the polymerization of a,v-diene tion on fatty acid-derived polymers is side-chain functional-
monomers bearing, for example, ester, ether, and anhydride ization. The ring-opening polymerization of unsaturated
functional groups in the main chain. Nevertheless, very lactones that are synthesized from hydroxy fatty acids
recently, Meier et al. reported the synthesis of a number of resulted in unsaturated linear polyesters. The double bonds
new a,v-diene monomers bearing amide groups both in the remaining on the main chain were directly utilized for the
main as well as the side chain via the Ugi four-component thiol-ene addition by butyl-3-mercaptopropionate, mer-
reaction; the polymerization of these monomers via thiol-ene capto-1-hexanol, and N-acetylcysteamine (Scheme 13)
addition reaction led to the formation of poly-1-(alkyl-carba- [63]. In the last two cases, more than 95% coupling yield
moyl)carboxamides (Scheme 12) [61]. The Ugi four-com- was achieved at 80 8C in the presence of AIBN as thermal
ponent reactions consist of the reaction of an aldehyde (or initiator and a small amount of THF was added to improve
ketone), a primary amine with a carboxylic acid and an the miscibility. In contrast to the native crystalline polymer
isonitrile to form substituted a-amino acylamides, e.g., two that melts at 48 8C, the modified polymers were amorphous
substituted amide groups, under release of 1 equivalent of materials.
water [62]. Noteworthy, this reaction proceeds without any
metallic or organic catalyst, yielding moderate to high-yields, 4 Conclusions
depending on the monomers. Using 1 as carboxylic acid,
10-undecen-1-al as aldehyde, and diverse primary amines On the way to develop sustainable chemical production tech-
and isonitriles, the authors were able to synthesize partially nologies, the urgent shift from the currently used petroleum-
renewable a,v-diene monomers with easily tuneable peptide based feedstock to the renewable ones and the application of
like side chain (Scheme 12). Hence, applying thiol-ene as highly efficient and green procedures are needed. To achieve
well as ADMET polymerization reactions, linear aliphatic this, as this feature review article discusses, the use of the of
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Eur. J. Lipid Sci. Technol. 2013, 115, 41 54 The thiol-ene (click) reaction for the synthesis 53
[16] Samuelsson, J., Jonsson, M., Brinck, T., Johansson, M.,
thiol-ene addition reaction with plant oils and their fatty acid
Thiol-ene coupling reaction of fatty acid monomers.
derivatives, which naturally possess double bonds, is a
J. Polym. Sci. A Polym. Chem. 2004, 42, 6346 6352.
possibility.
[17] Lou, F.-W., Xu, J.-M., Liu, B.-K., Wu, Q. et al., Highly
selective anti-Markovnikov addition of thiols to vinyl ethers
The authors have declared no conflict of interest.
under solvent- and catalyst-free conditions. Tetrahed. Lett.
2007, 48, 8815 8818.
[18] Uygun, M., Tasdelen, M. A., Yagci, Y., Influence of type of
References
initiation on thiol-Ene   click  chemistry. Macromol. Chem.
Phys. 2010, 211, 103 110.
[1] Biermann, U., Bornscheuer, U., Meier, M. A. R., Metzger,
[19] ten Brummelhuis, N., Diehl, C., Schlaad, H., Thiol ene
J. O., Schäfer, H. J., Oils and fats as renewable raw materials
modification of 1,2-polybutadiene using UV light or sunlight.
in chemistry. Angew. Chem., Int. Ed. 2011, 50, 3854 3871.
Macromolecules 2008, 41, 9946 9947.
[2] Posner, T., Beiträge zur Kenntniss der ungesättigten
[20] Gress, A., Völkel, A., Schlaad, H., Thio-click modification of
Verbindungen. II. Ueber die Addition von Mercaptanen
poly[2-(3-butenyl)-2-oxazoline]. Macromolecules 2007, 40,
an ungesättigte Kohlenwasserstoffe. Ber. Dtsch. Chem. Ges.
7928 7933.
1905, 38, 646 657.
[21] Sun, J., Schlaad, H., Thiol ene clickable polypeptides.
[3] Marvel, C. S., Chambers, R. R., Polyalkylene Sulfides From
Macromolecules 2010, 43, 4445 4448.
Diolefins and Dimercaptans. J. Am. Chem. Soc. 1948, 70,
[22] Bertin, A., Schlaad, H., Mild and versatile (bio-)functional-
993 998.
ization of glass surfaces via thiol ene photochemistry. Chem.
[4] Walling, C., Helmreich, W., Reactivity and reversibility in
Mater. 2009, 21, 5698 5700.
the reaction of thiyl radicals with olefins. J. Am. Chem. Soc.
[23] Madaan, N., Terry, A., Harb, J., Davis, R. C. et al., Thiol-
1959, 81, 1144 1148.
ene-thiol photofunctionalization of thiolated monolayers
[5] Testa, A. C., Photosensitized cis trans isomerization of
with polybutadiene and functional thiols, including thiolated
methyl oleate. J. Org. Chem. 1964, 29, 2461 2962.
DNA. J. Phys. Chem. C. 2011, 115, 22931 22938.
[6] Hoyle, C. E., Lee, T. Y., Roper, T., Thiol-enes: Chemistry of
[24] Rissing, C., Son, D. Y., Thiol ene reaction for the synthesis
the past with promise for the future. J. Polym. Sci. A Polym.
of multifunctional branched organosilanes. Organometallics
Chem. 2004, 42, 5301 5338.
2008, 27, 5394 5397.
[7] Griesbaum, K., Problems and possibilities of the free-radical
[25] Killops, K. L., Campos, L. M., Hawker, C. J., Robust,
addition of thiols to unsaturated compounds. Angew. Chem.
efficient, and orthogonal synthesis of dendrimers via thiol-
Int. Edit. 1970, 9, 273 287.
ene   click  chemistry. J. Am. Chem. Soc. 2008, 130, 5062
[8] Pryor, W. A., Coco, J. H., Daly, W. H., Houk, K. N., Radical 5064.
generation from polymolecular reactions of closed shell mol-
[26] Kolb, H. C., Finn, M. G., Sharpless, K. B., Click chemistry:
ecules. Molecule-assisted homolysis (MAH). Hydrogen
Diverse chemical Function from a few good reactions.
atom transfer from a Diels-Alder adduct to an alkene.
Angew. Chem. Int. Ed. 2001, 40, 2004 2021.
J. Am. Chem. Soc. 1974, 96, 5591 5593.
[27] Kade, M. J., Burke, D. J., Hawker, C. J., The power of thiol-
[9] Nuyken, O., Volkel, T., Telechelics via addition of dithiols
ene chemistry. J. Polym. Sci. A Polym. Chem. 2010, 48, 743
onto alkadienes. 1. Radical mechanism. Makromol. Chem.
750. Hoyle, C. E., Bowman, C. N., Thiol-ene click chem-
Rapid Commun. 1990, 11, 365 373.
istry. Angew. Chem. Int. Ed. 2010, 49, 1540 1573.
[10] Nuyken, O., Volkel, T., Pohlmann, T., Telechelics via
[28] Barner-Kowollik, C., Inglis, A. J., Has click chemistry lead to
addition of dithiols onto diolefins. 3. Heat-resistant polysul-
a paradigm shift in polymer material design? Macromol.
fides from 1,3-benzenedithiol and norbornadiene macromol.
Chem. Phys. 2009, 210, 987 992. Lodge, T. P., A virtual
Chem. Phys. 1991, 192, 1959 1968.
issue of macromolecules:   Click chemistry in macromolecu-
[11] Klemm, E., Sensfuß, S., Holfter, U., Schütz, H., lar science  . Macromolecules 2009, 42, 3827 3829.
Untersuchungen zur linearen thiol-en photopolymerisation.
[29] Iha, R. K., Wooley, K. L., Nystroem, A. M., Burke, D. J.
Makromol. Chem. 1990, 191, 2403 2411.
et al., Applications of orthogonal   click  chemistries in the
[12] Klemm, E., Sensfuß, S., Investigations on the mechanism of synthesis of functional soft materials. Chem. Rev. 2009, 109,
autoinitiation in thiol en-polymerization. Makromol. Chem. 5620 5686.
1991, 192, 159 164.
[30] Koo, S. P. S., Stamenović, M. M., Prasath, R. A., Inglis, A. J.
[13] Biermann, U., Butte, W., Koch, R., Fokou, P. A., et al., et al., Limitations of radical thiol-ene reactions for polymer-
Initiation of radical chain reactions of thiol compounds and polymer conjugation. J. Polym. Sci. A Polym. Chem. 2010, 48,
alkenes without any added initiator: Thiol-catalyzed cis/trans 1699 1713.
isomerization of methyl oleate. Chem. Eur. J. 2012, 18, 8201
[31] Metzger, J. O., Fats and oils as renewable feedstock for
8207.
chemistry. Eur. J. Lipid Sci. Technol. 2009, 111, 865 876.
[14] Boutevin, B., Hervaud, Y., Moulédous, G., Grafting phos- Metzger, J. O., Bornscheuer, U., Lipids as renewable resour-
phonated thiol on hydroxy telechelic polybutadiene. Polym. ces: current state of chemical and biotechnological conver-
Bull. 1998, 41, 145 151. sion and diversification. Appl. Microbiol. Biotechnol. 2006, 71,
13 22.
[15] Kozhushkov, S. I., Brandl, M., de Meijere, A., Surprisingly
facile addition of thiols to the double bonds of bicyclopro- [32] Türünç, O., Meier, M. A. R., in: N. T. Dunford (Ed.), Food
pylidene and other methylenecyclopropanes. Eur. J. Org. and Industrial Bioproducts and Bioprocessing Wiley-Blackwell,
Chem. 1998, 1998, 1535 1542. Oxford, UK 2012.
ß 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.ejlst.com
54 O. Türünç and M. A. R. Meier Eur. J. Lipid Sci. Technol. 2013, 115, 41 54
[33] Meier, M. A. R., Metzger, J. O., Schubert, U. S., Plant oil [49] Boutevin, B., Chaib, M., Robin, J.-J., Synthesis of mono-
renewable resources as green alternatives in polymer science, dispers macromolecular diisocyanate. Polym. Bull. 1991, 26,
Chem. Soc. Rev. 2007, 36, 1788 1802. 177 179.
[34] Metzger, J. O., Organic reactions without organic solvents [50] Ameduri, B., Berrada, K., Boutevin, B., Bowden, R. D.,
and oils and fats as renewable raw materials for the chemical Synthesis of telechelic monodispersed diols. Polym. Bull.
industry. Chemosphere 2001, 43, 83 87. 1992, 28, 497 503.
[35] Metzger, J. O., Riedner, U., Free-radical additions to unsa- [51] Ameduri, B., Berrada, K., Boutevin, B., Bowden, R. D.,
turated fatty-acids. Fat Sci. Technol. 1989, 1, 18 23. Synthesis of a telechelic monodispersed mercapto-alcohol.
Polym. Bull. 1993, 31, 1 7.
[36] Koenig, N., Swern, D., Organic sulfur derivatives. 1.
Addition of mercaptoacetic acid to long-chain monounsatu- [52] Türünç, O., Meier, M. A. R., Fatty acid derived monomers
rated compounds. J. Am. Chem. Soc. 1957, 79, 362 365. and related polymers via thiol-ene (click) additions.
Macromol. Rapid Commun. 2010, 31, 1822 1826.
[37] Koenig, N., Swern, D., Organic sulfur derivatives. 2.
Sulfides, sulfoxides and sulfones from thiols and 10-undece- [53] Lluch, C., Lligadas, G., Ronda, J. C., GaliÄ…, M., Cadiz, V.,
noic acid. J. Am. Chem. Soc. 1957, 79, 4235 4237.   Click  synthesis of fatty acid derivatives as fast-degrading
polyanhydride precursors. Macromol. Rapid Commun. 2011,
[38] Koenig, N., Sasin, G., Swern, D., Organic sulfur derivatives.
32, 1343 1351.
5. Preparation and properties of some long-chain mercapto
acids and related compounds. J. Org. Chem. 1958, 23, 1525 [54] González-Paz, R. J., Lluch, C., Lligadas, G., Ronda, J. C.
1530. et al., A green approach toward oleic- and undecylenic acid-
derived polyurethanes. J. Polym. Sci. A Polym. Chem. 2011,
[39] Schwab, A., Gast, L., Free radical addition of hydrogen
49, 2407 2416.
sulfide and thiols to linseed oil and methyl oleate. J. Am.
Oil Chem. Soc. 1968, 45, 461 464. [55] Palaskar, D. V., Boyer, A., Cloutet, E., Le Meins, J.-F., et al.,
Original diols from sunflower and ricin oils: Synthesis,
[40] Schwab, A., Gast, L., Cowan, J., Free radical addition of
characterization, and use as polyurethane building blocks.
hydrogen sulfide to conjugated and nonconjugated methyl
J. Polym. Sci. A Polym. Chem. 2012, 50, 1766 1782.
esters and to vegetable oils. J. Am. Oil Chem. Soc. 1970, 47,
371-. [56] Vilela, C., Cruciani, L., Silvestre, A. J. D., Gandini, A.,
Reversible polymerization of novel monomers bearing furan
[41] Bexell, U., Olsson, M., Johansson, M., Samuelsson, J.,
and plant oil moieties: A double click exploitation of renew-
Sundell, P.-E., A tribological study of a novel pre-treatment
able resources. RSC Adv. 2012, 2, 2966 2974.
with linseed oil bonded to mercaptosilane treated aluminium.
Surf. Coat. Tech. 2003, 166, 141 152. [57] Lluch, C., Ronda, J. C., GaliÄ…, M., Lligadas, G., Cádiz, V.,
Rapid approach to biobased telechelics through two one-pot
[42] Bexell, U., Olsson, M., Sundell, P. E., Johansson, M. et al.,
thiol ene click reactions. Biomacromolecules 2010, 11, 1646
A ToF-SIMS study of linseed oil bonded to mercapto silane
1653.
treated aluminium. Appl. Surf. Sci. 2004, 231 232, 362 365.
[58] Türünç, O., Meier, M. A. R., Thiol-ene vs. ADMET: A
[43] Bexell, U., Berger, R., Olsson, M., Grehk, T. M. et al.,
complementary approach to fatty acid-based biodegradable
Bonding of vegetable oils to mercapto silane treated metal
polymers. Green Chem. 2011, 13, 314.
surfaces: Surface engineering on the nano scale. Thin Solid
Films 2006, 515, 838 841. [59] Quinzler, D., Mecking, S., Linear semicrystalline polyesters
from fatty acids by complete feedstock molecule utilization.
[44] Bantchev, G. B., Kenar, J. A., Biresaw, G., Han, M. G., Free
Angew. Chem. Int. Ed. 2010, 49, 4306 -4308. Cole-Hamilton,
radical addition of butanethiol to vegetable oil double bonds.
D. J., Nature s polyethylene. Angew. Chem. Int. Ed. 2010, 49,
J. Agric. Food Chem. 2009, 57, 1282 1290.
8564 8566.
[45] Black, M., Rawlins, J. W., Thiol-ene UV-curable coatings
[60] Türünç, O., Montero de Espinosa, L., Meier, M. A. R.,
using vegetable oil macromonomers. Eur. Polym. J. 2009, 45,
Renewable polyethylene mimics derived from castor oil.
1433 1441.
Macromol. Rapid Commun. 2011, 32, 1357 1361.
[46] Chen, Z., Chisholm, B. J., Patani, R., Wu, J. F. et al., Soy-
[61] Kreye, O., Türünç, O., Sehlinger, A., Rackwitz, J., Meier, M.
based UV-curable thiol-ene coatings. J. Coat. Technol. Res.
A. R., Structurally diverse polyamides obtained from mono-
2010, 7, 603 613.
mers derived via the Ugi multicomponent reaction. Chem.
[47] Stemmelen, M., Pessel, F., Lapinte, V., Caillol, S. et al.,
Eur. J. 2012, 18, 5767 5776.
A fully biobased epoxy resin from vegetable oils: From the
[62] Pirrung, M. C., Sarma, K. D., Multicomponent reactions
synthesis of the precursors by thiol-ene reaction to the study
are accelerated in water. J. Am. Chem. Soc. 2003, 126, 444
of the final material. J. Polym. Sci. A Polym. Chem. 2011, 49,
445.
2434 2444.
[63] Ates, Z., Thornton, P. D., Heise, A., Side-chain function-
[48] Desroches, M., Caillol, S., Lapinte, V., Auvergne, R.,
alisation of unsaturated polyesters from ring-opening
Boutevin, B., Synthesis of biobased polyols by thiol ene
polymerisation of macrolactones by thiol-ene click chemistry.
coupling from vegetable oils. Macromolecules 2011, 44,
Polym. Chem. 2011, 2, 309 312.
2489 2500.
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