364

ENZYMATIC POLYMERIZATION

Vol. 2

ETHYLENE POLYMERS,
CHLOROSULFONATED

Introduction

Chlorosulfonated polyethylene (CSM) [68037-39-8] describes a group of curable,
halogenated olefin polymers, first introduced to the rubber industry by E. I. du
Pont de Nemours and Co. in 1951 (1–5) under the trade name of Hypalon. They
contain pendant chlorine and sulfonyl chloride groups and vary in consistency
from soft and elastomeric to hard and plastic. The chemical structure may be
represented by

Although the base resin is usually polyethylene, other base resins, ie,

polypropylene (6), ethylene propylene copolymers (7), and polymers containing
additional functionality (ie, vinyl acetate, acrylic or methacrylic acid, and maleic
anhydride graft) have been chlorinated and chlorosulfonated commercially. This
family of polymers is widely used in rubber and adhesive industries because of
the valuable properties that can be achieved when properly compounded and vul-
canized.

Chlorosulfonated olefin polymers may be prepared in polymer melts (8),

as slurries in a nonsolvent medium (9,10), or in a fluidized bed (11), but are
usually prepared by the interaction of ethylene polymers or copolymers with

Encyclopedia of Polymer Science and Technology. Copyright John Wiley & Sons, Inc. All rights reserved.

Vol. 2

ETHYLENE POLYMERS, CHLOROSULFONATED

365

chlorosulfonating agents in a homogeneous solution. Substitution of chlorine
atoms onto the polymer chains interrupts the regularity of the chain structure
so that the crystalline polymer becomes semiplastic to elastomeric and even-
tually hard and brittle as the substitution level increases. Introduction of the
sulfonyl chloride group provides a cross-linking site for vulcanization with con-
ventional rubber technology. These polymers are known for advantages in com-
bined heat and oil resistance compared with most other synthetic elastomers.
They also offer good mechanical toughness and are superior in color retention,
weatherability, flame resistance, abrasion resistance, and resistance to corro-
sive chemicals. In addition, it can be made to adhere well to metal and most
fabric reinforcements. Chlorination of the polymer, to sufficient levels, also pro-
vides for solubility in common solvents, and the sulfonyl chloride group or other
functionality offers unique advantages in specific adhesion to various substrates.
This combination provides for tough, abrasion-, chemical-, and oil-resistant coat-
ings and adhesives. The properties of these polymers vary widely with the
selection of the base resin, chlorine and sulfonyl chloride content, or other
functionality.

Olefin polymers containing only pendent chlorine groups may also be pre-

pared using this procedure. The properties are very similar to those of CSMs in
appearance and properties; however, the lack of sulfonyl chloride group makes
them more difficult to cure and less flexible in compounding techniques.

Polymer Properties

Polyethylene.

Chlorosulfonated polyethylene is one of a few examples of

a class of polymers, which is formed by chemical substitution on the backbone
chain of a preformed polymer. In addition, starting from one specific polyethylene,
a whole new series of polymers result, whose properties depend on the degree and
randomness of chlorine substitution. So, it is not surprising that the properties
of the modified polymer also depend, to a large extent, on those of the precursor
olefin resin.

Polyethylene is a saturated hydrocarbon and shows, in general, properties ex-

pected for high molecular weight paraffin. As such, it exhibits very low chemical re-
activity at low temperatures, but impurities, such as residual catalyst fragments,
may cause oxidative or free-radical attack, particularly at elevated temperatures.
Oxidative attack is prevented by the addition of small amounts of antioxidants, ie,
hindered phenol or alkyl phosphites. An excess of these residual antioxidants may
inhibit the chlorosulfonation reaction. The structure and morphological aspects
of polyethylene are tied to the synthesis technology. A large variety of synthesis
processes are used in polyethylene manufacture, including high pressure poly-
merization in supercritical ethylene (known as “free-radical” or “high pressure”
process) and solution-, slurry-, or gas-phase polymerization using Ziegler-type cat-
alysts (known as “low pressure” or “linear” process) (12). Control of the properties
is achieved by controlling molecular weight, molecular weight distribution, and
density. This is accomplished by choice of catalyst, reactor configuration, and tem-
perature profile. These structural properties are then carried over into those of the
resulting chlorosulfonated polymer, since neither chain scission nor cross-linking

366

ETHYLENE POLYMERS, CHLOROSULFONATED

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takes place during the chlorosulfonation process. Molecular weight and molecular
weight distribution of the polymer chains then have great influence on mechan-
ical and rheological properties of the polyethylene resin as well as the modified
polymer. The average molecular weights of commercial polyethylenes may vary
from about 500 for polyethylene waxes to

>10

6

for ultrahigh molecular weight

polyethylene grades.

The presence, shape, and length of side branches as well as the distribution of

branches along the molecular chain also significantly modify physical properties
of solid polyethylene polymers and their melts.

Depending on the catalyst system and polymerization conditions employed, a

wide variation in the degree and type of chain branch is observed. In high pressure,
free-radical polymerization (low density polyethylene, LDPE), these branches may
be linear or branched and may vary in length from 1 to 8 (short-chain branching)
or up to several thousand carbon atoms (long-chain branching). The broad molec-
ular weight distribution in these polymers is mostly because of the varying length
of chain branches. In low pressure, catalytic polymerization, polymer chains are
essentially absent of branching and are termed as linear or high density polyethy-
lene (HDPE) (13).

Alternatively, significant short-chain branching may be introduced deliber-

ately by copolymerization of ethylene with

α-olefins, ie, butene, hexene, octene,

etc. Branching is controlled by the type of catalyst,

α-olefin type, and composition.

Metalathene polymerization catalysts give a more select distribution of branching
than Ziegler catalysts. (13) These polymers are called linear low density polyethy-
lene (LLDPE).

According to ASTM D1248, polyethylene resins are divided into various

classifications based on properties. Two of the most easily measured character-
istics of polyethylene are melt index and density. The density determines the
type of resin and melt index determines the category. However, the shape of
molecular weight distribution curve has an important bearing on the proper-
ties of both the polyethylene and the resultant chlorinated polymer. The molec-
ular weight distribution is usually referred to as the polydispersity index or
weight to number-average molecular weight ratio. Polyethylene resins are gen-
erally categorized as narrow, intermediate, or broad based on these indices, but
the distribution may also be bimodal and/or skewed toward the high or low por-
tions of the distribution curve (13). The shape function of the distribution curve
may be determined by several methods; however, it is most easily determined by
gel-permeation chromatography (gpc). Polydispersity index can be readily calcu-
lated from gpc data, but is also indicated by the melt flow ratio (MFR), which
is the ratio of two melt indexes determined at different melt pressures. The
range of MFR may vary from 25 to 150 for commercial polyethylene resins. An-
other term often used to describe molecular weight distribution is stress expo-
nent, which is defined as the slope of the melt flow ratio curve over a specified
range.

Because of its exceptional symmetry, the polyethylene molecule fits so read-

ily into a crystalline lattice, in spite of its lack of molar cohesion, that its tendency
is to crystallize into spherulite structures on relaxation rather than revert to a
disordered state. However, the degree and type of chain branching that interrupts
the geometrical regularity of the polyethylene molecular structure causes a local

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ETHYLENE POLYMERS, CHLOROSULFONATED

367

reluctance to form crystallites so that both crystalline and amorphous regions
may be present. The density of the polyethylene is a function of the degree of
crystallinity. For HDPE, this crystallinity reaches levels of about 80%. The crys-
tallinity of LLDPE is usually below 40–45% (13). So, the size, structures, and level
of the crystallites for a given polymer depend on the degree, type, and uniformity
of branching.

In order to convert these crystalline polymers into elastomers it is necessary

to eliminate most of these areas of crystallinity. This may be accomplished by
increasing the concentration of

α-olefin comonomer as in the case of ethylene–

propylene elastomers; however, these polymers are similar to polyethylene in
chemical properties.

Chlorosulfonated Polyethylene.

The process of modifying polyethylene

with randomly spaced chlorine atoms represents a change in entropy conditions.
Although adding chlorine to the polymer chain greatly increases its polarity and
thus its molar cohesion, the increase in bulk, because of its large volume, prevents
temporary chain alignment by external tension, thus reducing the entropy factor.
As chlorine attachments to the chain are made, the adjacent chain segments, not
held in place by crystallites, begin to exhibit rapid local Brownian motions, typical
of molecules in the liquid state as may be seen in the polyethylene melt. This
rapid internal Brownian movement, together with the slow external Brownian
movement, or movement of entire polymer chains, due to high molecular weight,
creates the captive liquid or rubbery state.

Incorporation of chlorine atoms onto the polyolefin backbone then causes suf-

ficient molecular irregularity to break up crystalline chain segments of the base
resin. As the chlorine content is increased, the crystallites gradually disappear
and, eventually, the thermoplastic material becomes amorphous and behaves as
an elastomer because of the inherent flexibility of the polyethylene chain. Chloro-
sulfonated polyethylene resins made in slurry or fluidized beds generally have a
more blocky chlorine distribution, both intramolecularly and intermolecularly, so
that the same degree of amorphous characteristic is not always achieved. The in-
crease in molar cohesion, by the addition of chlorine atoms, increases the polymer
solubility parameter, and thus decreases its miscibility with paraffinic and aro-
matic oils. So, as chlorine content of the polymer increases, resistance to swelling
effect of oil increases.

The added pendant chlorine groups create intermolecular friction, due to

their polar nature, binding chains together, particularly at high substitution lev-
els, in a rigid network, reducing free volume, increasing short-range entangle-
ment, and thereby increasing the brittle point. The glass-transition temperature
(T

g

), which is closely related to the brittle point, is then a function of the chlo-

rine content ranging from

−35 to −40

◦

C at about 15–20% chlorine to

>80

◦

C at

chlorine levels above 65%. The low chlorine polymers retain some of the polyethy-
lene crystallinity and thus yield products that are thermoplastic. At the higher
chlorine substitution extremes polymer properties are achieved, which may be
generally associated with relatively high temperature rigid plastic material. In
between these extremes range a whole series of materials with intermediate
properties, which depend on the level of chlorination and the randomness of the
chlorine placement along the chain. In the range of 25–35 % chlorine, there is
a series of polymers along a more random chlorination line, whose transition

368

ETHYLENE POLYMERS, CHLOROSULFONATED

Vol. 2

80

60

40

20

0

−20

−40

7

9

8

10

Fig. 1.

Chlorine content vs T

g

for CSM with random chlorine substitution.

Chlorine

%;

T

g

,

◦

C.

temperature occurs in the range of

−20 to −30

◦

C. Glass-transition temperatures

in this range represent materials that behave like elastomers. The glass-transition
temperature of a chlorinated polyethylene polymer may be estimated by consid-
ering that it is a copolymer of ethylene and vinyl chloride. It then follows the
relationship (14)

T

g

= M

i

T

gi

where M

i

is the mole fraction of the ith component, T

g

the glass-transition tem-

perature of the copolymer in Kelvin, and T

gi

the glass-transition temperature of

the homopolymer of the ith component, ie,

T

g

= M

1

T

g1

+ M

2

T

g2

where T

g1

is the glass-transition temperature of polyethylene (

−80

◦

C), M

1

the

mole fraction of ethylene, T

g2

the glass-transition temperature of poly(vinyl chlo-

ride) (75

◦

C), and M

2

the mole fraction of poly(vinyl chloride).

At higher chlorine levels, where vicinal chlorine groups may occur, one may

also include a term for poly(vinylidine chloride) (T

g

= 226

◦

C). The relationship of

glass-transition temperature to chlorine content for a CSM with random chlorine
substitution is shown in Figure 1.

The optimum chlorine content for an amorphous elastomer is the minimum

amount required to destroy the crystalline segments. This optimum level depends
on the number and types of crystallites in the polyethylene precursor, the random-
ness of chlorine distribution along the chain, and chain-to-chain distribution. So,
for HDPE, the optimum chlorine level for elastomeric properties is at about 35%

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ETHYLENE POLYMERS, CHLOROSULFONATED

369

with even distribution along the chain. For low density base resin, the optimum
chlorine level is about 28–30%.

The flow behavior of CSM polymers under manufacturing and finished prod-

uct processing conditions is of primary practical importance in their commercial
acceptance. These properties are functions of the starting polyethylene parame-
ters and the chlorine content and distribution. For molten polymers and for elas-
tomers, viscosities differ with deformation conditions, and elastic effects accom-
pany the flow properties. Hence, both polymer melts and elastomers are generally
viscoelastic and greatly influenced by polymer chain lengths and by the distribu-
tion of chain lengths within the whole polymer. Melt index, as described earlier,
is a low average shear viscosity measurement (avg. shear rate

= 4 s

− 1

) mea-

sured at 190

◦

C. It serves the polyethylene industry as an imperical measure of

processing control parameters. It is not a fundamental quantity, however, and
its meaning is often ambiguous, but its measurement is convenient and well en-
trenched in the industry as a prediction of processing characteristics. Although
it is considered to be mostly responsive to the weight-average molecular weight
of the polyethylene, in most cases it is not because it is measured in the non-
Newtonian region of the flow curve. The shape and slope of the curve in this region
are strongly effected by the molecular weight distribution and this effect can be
overriding.

For the same reason of convenience and low cost, Mooney viscosity (avg.

shear rate

= 1.6 s

− 1

), usually measured at 100

◦

C, is an imperical control for the

rubber industry. It, too, is not a fundamental quantity and is usually measured in
the non-Newtonian part of the flow curve.

The Mooney viscosity of CSM is also related to the weight-average molecular

weight of the starting polyethylene and the chlorine content. However, differences
in molecular weight distribution, and especially in the shape function of the dis-
tribution curve, become an even more important factor in determining the final
chlorosulfonated polymer bulk viscosity and shear sensitivity.

Quantitizing the effect of these parameters is difficult because of the many

different possibilities in the shape function of the base resin molecular weight
distribution curve. When the distribution curve is monomodal and log normal,
the breadth of the molecular weight distribution is a function of the slope of a line
formed by measurement of melt flow at increasing load or shear rate. Extrapola-
tion of this slope defines a shear rate for measuring a base resin viscosity, which
correlates with Mooney viscosity of the chlorinated product.

Although both base resin and chlorinated product viscosities are related to

molecular weight, a higher shear rate is needed in the latter case to account for
the lower measuring temperature for Mooney viscosity. Substitution of chlorine
atoms onto the polymer chain increases polymer bulk and polarity, resulting in
greater chain entanglement and resistance of chains to flow past one another
causing viscosity increase at a predictable rate. Using these parameters, ie, ex-
trapolated melt viscosity and chlorine content, one can predict the final prod-
uct Mooney viscosity assuming log normal distribution and random chlorination
(15).

η

γ

= 3.5 + 1.06(0.56ln 86 + 2.66ln f )/f

M

v

= η

γ

[(

−1.7 + 5.9(%Cl)]

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ETHYLENE POLYMERS, CHLOROSULFONATED

Vol. 2

where

η

γ

is the polyethylene viscosity at a shear rate which corrects for measuring

temperature differences between Mooney viscosity and melt index of polyethylene
under standard conditions, f is the slope of melt index vs shear rate, and M

v

the

Mooney viscosity of the chlorinated product at 100

◦

C.

A more general approach for a polydisperse case uses an adaptation of a

model relating molecular weight distribution of the polyethylene to shear depen-
dence. This method concerns the relationship of elastic properties of polyethylene
melts to molecular weight. It postulates that bulk viscosity

η

γ

is a function of a spe-

cific molecular weight average M

w

∗

in the same manner that zero shear viscosity

is a function of weight-average molecular weight (16).

η

γ

= K(M

∗

w

)

a

when

η

0

= K(M

w

)

a

Where K and a are empirical constants depending on the nature of the polymer
and temperature. Then,

M

∗

W

=

i

= c − 1

i

= 0

W

i

M

I

+ M

c

∝

i

= c

where W

i

is the weight fraction associated with molecular weight M

i

and M

c

is the

critical molecular weight associated with the largest polymer molecule undergoing
Newtonian flow at

γ , and therefore must be determined for each shear rate of

interest.

For CSM, at a given chlorine content, the relationship of molecular weight

to viscosity is

Log

η(γ ) = −13,8615+3.4Log M

w

where

η(γ ) is the bulk viscosity of CSM at 100

◦

C in kPa’s and M

w

∗

is the molecular

weight average of the polyethylene used to manufacture the CSM.

To convert

η(γ ) to CSM Mooney viscosity (γ = 1.6 s

− 1

),

η(γ ) = 1.2894 ×

Mooney viscosity.

As expected, the viscosity of the polymer increases with increasing molecular

weight. The effect diminishes, however, until a critical molecular weight is reached
where chains become so long that they fail to undergo complete relaxation at a
given shear rate and the additive effect on viscosity becomes negligible. Polymer
chains longer than the critical molecular weight influence the whole polymer vis-
cosity as though they were of critical molecular weight. And chain entanglements
become unimportant to flow behavior if molecular weight

> M

c

. Thus, as chain

length, and the weight-average molecular weight, increases in the distribution
curve, its contribution to viscosity is increased until the critical molecular weight
is reached. Beyond that point chains contribute to viscosity as though they were
at the critical molecular weight. This gives added weight to contributions of low
molecular weight fractions as confirmed by experience. This relationship gives
added flexibility to design of chlorosulfonated polymers for specific application
without viscosity penalties.

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ETHYLENE POLYMERS, CHLOROSULFONATED

371

50

45

40

35

30

25

50

45

40

35

30

25

20

20

15

15

10

10

5

5

0

0

Chlorine, %

Oil Sw

ell, %

Fig. 2.

General relationships of oil swell and chlorine content on a cured linear-based

CSM.

To further interpret the results, the distribution curve may be divided into

three segments, ie, low, medium, and high, and a polydispersity index, M

w

/M

n

,

calculated for each segment (17).

M

w

= H

i

M

i

/H

i

and

M

n

= H

i

/H

i

M

i

where H is the height of the segment and M is the mass.

This model has, in fact, been found to give the most comprehensive rela-

tionship between polyethylene composition and Mooney viscosity of the resultant
CSM polymer. CSM polymers are generally categorized on the basis of base resin
type, ie, LDPE, HDPE, LLDPE or functionalized polyolefin, chlorine content, and
Mooney viscosity.

The chlorine atoms on the polymer backbone not only provide elastomeric

properties but also give useful improvement in chemical and mechanical prop-
erties. The chlorine atoms attached to the chain form centers of high cohesive
energy, which prevents infusion of oil, oxygen, acids etc from reaching the main
chain. Thus, oil, chemical, flame, and weather resistance improves with increasing
chlorine level. Conversely, heat resistance, low temperature flexibility, and elec-
trical resistance become poorer. When the chlorine atoms are more evenly spaced
along the chain, they are more effective and, thus, more efficient. Therefore, a
CSM with a homogeneous chlorine distribution would be expected to have better
resistance to low temperature brittleness and oil resistance than one with blocky
distribution, all other conditions being equal. Figure 2 shows the general relation-
ships of oil swell and chlorine content on a cured linear-based CSM, made under
homogeneous chlorinating conditions.

Table 1 shows a description of commercial CSM polymers produced by

DuPont Dow Elastomers under the trade name of Hypalon Acsium and Hypalon
CP. Toya Soda of Japan also offers similar but not all grades.

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ETHYLENE POLYMERS, CHLOROSULFONATED

Vol. 2

Table 1. Commercial CSM Polymers

Polyethylene

Hypalon type

Chlorine, %

Sulfur, %

Mooney viscosity

Melt index

Stress Exp.

From LDPE (branched)
20

29

1.2

28

10

NA

30

43

1.3

43

100

NA

From HDPE
45

24

1.0

37

2.5

1.44

623

24

1.0

21

14

1.72

LD-999

35

1.0

30

12

1.76

40 S

35

1.0

45

7

1.45

40

35

1.0

55

4

1.44

4085

36

1.0

90

2.5

1.25

610

35

1.0

130

0.75

1.30

48 S

43

1.0

62

14

1.76

48

43

1.0

90

17

1.28

From LLDPE
Acsium 6367

27

1.0

45

5.0

1.30

Acsium 6932

30

1.0

60

5

1.33

Acsium 6983

90

1.0

90

0.8

1.3

From polymers containing other functional groups
CP-770

44

2

NA

NA

NA

CP-826

28

0

NA

NA

NA

Preparation

Chlorosulfonated polyolefins are prepared by interaction of the base resin with
chlorine and either sulfur dioxide (18) or sulfuryl chloride in the presence of a
radical initiator (19). Sulfuryl chloride may be used alone as a chlorosulfonating
agent, but must be accompanied by a catalytic amount of pyridine or other organic
base. It has been proposed that the function of the organic base is to catalyze de-
composition of the sulfuryl chloride molecule to form SO

2

and Cl

2

. However, the

chlorosulfonation rate with base-catalyzed sulfuryl chloride is 5–10 times faster
than that with gaseous chlorine and sulfur dioxide. So it is possible that the mech-
anism is more complex. In the latter case, the ratio of sulfonyl chloride to chlorine
substituted onto the polymer backbone is, to some extent, a function of the amount
of organic base added. The reaction temperature (lower reaction temperatures
that result in higher sulfur utilities) also affects it (19).

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ETHYLENE POLYMERS, CHLOROSULFONATED

373

The chlorination reaction and the chlorosulfonation reaction are usually

carried out simultaneously in homogeneous solution, but may be carried out in
stages; that is, the resin may be partially chlorinated with elemental chlorine and
then chlorosulfonated to the desired composition with a chlorosulfonating agent
(20).

Many solvents have been used in laboratory preparations of CSM,

eg, chloroform, chlorobenzene, trichloroethane, tetrachloroethane (21), trichlo-
rofluoromethane, fluorobenzene (22), and carbon tetrachloride. Mixed sol-
vents, ie, chlorobenzene and carbon tetrachloride, have also been used
to achieve certain desired properties such as low temperature flexibility
(23).

For practical applications, the solvent used in the reaction must dissolve the

base resin and the final product, be inert to chlorination, and easily be separated
from the finished product without polymer degradation. The degree of compati-
bility of the solvent with the base resin and the various stages of finished product
may also substantially affect the chlorine distribution and thus the physical and
mechanical properties of the final product.

When a highly compatible solvent is used, the solvent surrounds each seg-

ment with an “envelope” of solvating molecules, which prevents contact with other
segments and other chains. The individual chain is then in a relatively elon-
gated condition, and the solvent can flow freely around the various chain parts.
When the chlorinating agent is dissolved in the solvent, equal exposure of all
chains and chain segments to molecular chlorine attack is afforded and there-
fore a more selective chlorine distribution along the chain and between chains
results.

In a solvent with poor compatibility, the chains are irregularly folded into

tight coils, and considerable amounts of solvent can be immobilized by the en-
tangled segments of the polymer. At a concentration where chains would still be
separate and discrete in a good solvent, they would have associated into networks
of relatively large size in a poorer solvent. These shapes and dimensions hin-
der attack of chlorine in hidden segments and chains, leading to a more blocky
distribution of chlorine atoms substituted along the chain and among the poly-
mer chains. In addition, as the polymer concentration is increased, chain-to-chain
bridging takes place much more readily in the tightly coiled chains so that the
bridged chains respond as though they are much higher in molecular weight. The
rate of increase in viscosity with concentration is then distinctly greater in a poorer
solvent. The higher viscosity causes the formation of larger gas bubbles during
chlorine gas addition and interferes with the mass transfer of chlorine from the
bubble to the main body of solution. Under this condition, a higher concentration
of chlorine at the bubble interface causes overchlorination of polymer chains in
that area compared to the remainder of the reaction mass. Thus, optimum con-
ditions for a homogeneous chlorine distribution are low solution viscosity, good
mixing, high reaction temperature, and a reaction solvent most compatible with
the polymer.

The effect of solvent compatibility on chlorine distribution may be illus-

trated by comparison of reaction in fluorobenzene, an excellent solvent for both
polyethylene and the chlorinated product, and in carbon tetrachloride, a poorer

374

ETHYLENE POLYMERS, CHLOROSULFONATED

Vol. 2

solvent. Blocky chlorine distribution may be shown by comparison of

H val-

ues; infrared absorption at 715 and 730 cm

− 1

and by nmr determination of

γ , or

greater protons. Chlorinated polymers prepared in fluorobenzene show about 1/3
as many

γ , or greater hydrogens as those prepared in carbon tetrachloride under

the same reaction conditions, indicating more selective distribution in the former
case.

In commercial solution processes, carbon tetrachloride has been the sol-

vent of choice, in spite of its solvency limitations. It is desirable because
it easily dissolves the polyolefin reactants as well as the chlorosulfonated
finished product. It is also stable under reaction conditions; it is inert to chlo-
rination and its boiling point is low enough to facilitate isolation of the poly-
mer from solvent by evaporation at temperatures low enough to prevent de-
composition of the chlorosulfonated product. In addition, it has always been
readily available and reasonably priced. However, because carbon tetrachloride
is toxic and a suspected carcinogen and because it is postulated that it can
take part in reactions that deplete atmospheric ozone, it has been the sub-
ject of increasingly stringent controls. Consequently, the use of carbon tetra-
chloride on a large scale has become increasingly undesirable for both safety
and environmental reasons. Its continued use requires that careful and strin-
gent containment is maintained (24). Trichloroethane or fluorobenzene have
been suggested as safe and environmentally friendly alternatives (24), but have
higher boiling points, thus difficult to remove from the polymer and not com-
pletely unreactive to chlorine. Chloroform, because of its very low ozone de-
pletion potential, is considered environmentally acceptable, but it is toxic and
a suspected carcinogen and it undergoes some chlorination to carbon tetra-
chloride under reaction conditions. Therefore, it too requires restricted contain-
ment.

Commercial processes consist of dissolving the base resin, usually polyethy-

lene, at a temperature above its Vicat softening point, in a glass-lined, stirred
kettle, fitted with an agitator and at least one condenser. For HDPE, the
dissolving temperature is at least 98

◦

C, but dissolution rate increases with

temperature. The chlorosulfonating agents together with a free-radical ini-
tiator, usually 2,2



-azobisisobutyronitrile, are added continuously during re-

action. The heat of reaction, 54–145 J/g (13–35 cal/g), depending on reac-
tants used, is removed from the reaction mass by condensing the solvent
vapors and returning the cooled reflux liquid to the reaction mass. The tem-
perature of the cooled reflux may affect composition control as it affects the
solubility of sulfur dioxide, ie, lower reflux temperatures and/or reaction tem-
peratures, at a given reaction pressure, favor higher sulfonyl chloride incorpo-
ration.

When the desired chemical composition is reached, as determined by infrared

analysis, the by-product HCl and unreacted SO

2

are removed by sparging with

an inert gas, ie, nitrogen, decreasing reactor pressure to atmospheric, pulling a
vacuum on the system, or combinations of these. Adding a small amount of an
aromatic epoxy resin then stabilizes the product. This resin reacts with residual
HCl remaining in the degassed solution as well as that, which may be formed
upon product storage. It also functions to prevent oxidative decomposition of the
sulfonyl chloride group during storage.

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ETHYLENE POLYMERS, CHLOROSULFONATED

375

The usual method for removing the solvent from the cement is by means

of steam-heated drum dryers, wherein a heated solution of the polymer is in-
troduced into the nip of rotary drum dryers and solvent is removed by evap-
oration. As the solvent evaporates at the drum surface, a thin film of poly-
mer is deposited, which continues to dry as the drum rotates. The dried film
is doctored from the drum surface with a knife blade; gathered into a rope and
cut into small chips. It is then dusted with talc, to prevent massing, and then
packaged.

Processing of Chlorosulfonated Polyethylene

As with most other elastomers, unvulcanized CSM is unsuitable for all but a few
applications. In order to make useful materials having the desired processing
characteristics, ultimate finished product properties, or cost control, it is usually
necessary to incorporate several compounding ingredients to improve their me-
chanical and chemical behavior. These include vulcanizing agents, accelerators,
accelerator activators, specific retarders, age resisters, processing aids, reinforc-
ing pigments, inert fillers, coloring dyes and pigments, and other special-purpose
materials, ie, blowing agents, abrasives, etc.

After the compounds have been properly mixed and shaped into blanks

for molding, or calendered, extruded, or fabricated into a composite item,
they must be vulcanized by one of many processes. During this vulcaniza-
tion process, the polymer chains are cross-linked into three-dimensional struc-
tures, transforming the soft, weak, plastic-like material into a strong elastic
product.

In most elastomers the reactive site for cross-linking is carbon–carbon dou-

ble bonds either in the backbone of the polymer chain or, as in the case of EPDM
elastomers, on the side chains. Vulcanization of these polymers usually involves
reacting sulfur or sulfur compounds with the double bond at elevated tempera-
tures to form sulfide or polysulfide cross-links. Metal oxides, ie, zinc oxide and
organic sulfur bearing accelerators (ie, thiuram polysulfides), are added to speed
up the curing process. For CSM, the major cross-linking site is the sulfonyl chloride
group, which offers a variety of cross-linking reactions. The most commonly used
cross-linking systems for CSM may be grouped into four general classes: sulfur
donor, ionic, organic (Maleimide), and peroxide. Although they may be fundamen-
tally different, these systems may also be viewed as the extreme end points of a
broad band of possible cure recipes. Consequently, practical curing systems may
incorporate various combinations of different types of vulcanizing agents offering
a synergistic effect in optimizing desired properties of a given final product for a
specific application.

CSM cure chemistry usually involves a cross-linking agent, an activator, an

accelerator, and often an activator/retarder for processing safety. Acid acceptors
must also be added to neutralize the by-products HCl and SO

2

, which may evolve in

the vulcanizing environment. The acid acceptors may also be involved in forming
a part of the cross-linking mechanism.

The cure system most widely employed for CSM is based on sulfur and

its derivatives, sometimes referred to as the sulfur or sulfur donor cure. Unlike

376

ETHYLENE POLYMERS, CHLOROSULFONATED

Vol. 2

elastomers, ie, natural rubber, which contains unsaturation, CSM may not be
cured with elemental sulfur alone, or with sulfur and a metal oxide, eg, lead ox-
ide or magnesium oxide, even at extended cure times. However, several sulfur
bearing organic compounds, eg, dipentamethylene thiuram hexasulfide (“Tetrone
A”), thiuram disulfide (“Thiuram M” or “Methyl tuads”), and tetramethylthiuram
disulfide (“TMTD”), have been found to give low level CSM cures when used alone.
When combined with PbO or MgO, high states of cure may be achieved. Addition
of finely divided elemental sulfur further enhances the state of cure. Lead com-
pounds have become increasingly restricted in rubber stocks because of health
hazards. Hydrotalcite (magnesium aluminum hydroxy carbonate) has no serious
health issues and has been found to perform in the same manner as PbO in CSM
compounds by trapping chlorides (25). Its use has been accepted by most of the
rubber industry.

Incorporation of elemental sulfur, activated by metal oxide, into the cur-

ing recipe allows further polysulfidic cross-links through the small amount
of unsaturation formed by SO

2

decomposition to further enhance the cross-

link density. Benzothiazyl disulfide (MBTS) is often added in practical sul-
fur recipes. It functions as a retarder–activator, ie, it improves processing
safety (scorch) while increasing cross-link density. The mechanism proba-
bly involves assisting in the decomposition of the polysulfide at a controlled
rate. When optimum heat resistance is desired, nickel dibutyl dithiocarbamate
(NBC) is often added. This material does not act as an antioxidant, which
is normally added to compounds for heat aging resistance. Several mecha-
nisms have been proposed for its effectiveness but it probably reacts with
any residual sulfonyl chloride group, which survives curing conditions, caus-
ing their elimination and the formation of a stable alkyl chloride in the
polymer chain. This reaction prevents further cross-linking during heat ag-
ing from the polymer radical and oxygen, which eventually causes brittle-
ness.

The Maleimide cure of CSM is also widely used particularly when low com-

pression set is needed along with good heat resistance. It can also give tight
cures with flexible cross-links, which are important for dynamic applications. The
fact that it can give heat resistance equivalent to the best mixed oxide (MgO

+

PbO) cures without the use of lead, and that it can be used in light colored ap-
plications has added substantially to its importance. The major disadvantage
is the sensitivity of uncured compounds to moisture, causing poor bin stability.
Water opens the Maleimide ring, which voids its use in the cross-links. Mixing
in additional Maleimide may reactivate a stock, containing Maleimide, which
has been exposed to moisture for an extended time and, therefore, rendered
inactive.

The Maleimide cure system is similar to the sulfur donor system in that

it involves the decomposition of the sulfonyl chloride cure site. In this case,
however, the Maleimide (meta-toluene-bis-maleimide, HVA-1 or meta-phenylene-
bis-maleimide, HVA-2) rather than sulfur, is involved in the cross-links, and
there is no evidence of a metal ionic bond. The reaction is usually initiated
with an amine involving either an amine-catalyzed decomposition of the sul-
fonyl chloride group or a path of radical anions. The most recently devel-
oped initiators, which have been found to give a balanced combination of

Vol. 2

ETHYLENE POLYMERS, CHLOROSULFONATED

377

excellent processing safety and cross-link density, are a butyraldehyde/aniline
condensation product (known as “Antox” special or “Vanax” AT) and N,N



-

diphenylpropylene diamine (GFI), all secondary amines. These amines are
antioxidants and therefore readily oxidized, which makes them less stable, par-
ticularly at elevated temperatures and in the presence of the sulfonyl chlo-
ride group (a strong oxidizing agent) and leads to decomposition. In completing
the cross-linking reaction, the polymer radical, thus formed, interacts with the
Maleimide.

Since SO

2

is released quantitatively in this cross-linking reaction, it is nec-

essary to include an SO

2

absorbing ingredient in the compound. For this reason

calcium hydroxide is usually added. Other SO

2

absorbers, eg, 1,3-bis (hydroxy-

methyl) urea, which are not too volatile, may be used as well.

Peroxide cures are used in cross-linking CSM as well as many other elas-

tomeric and nonelastomeric polymers. It is used in CSM when very low compres-
sion set is needed along with excellent heat aging and oil resistance. Its disad-
vantages include limited amount and types of plasticizers, requirement of high
amounts of acid acceptors, and high cure temperatures.

Hydrogen chloride, evolved at curing temperatures, inhibits the cross-linking

reaction. Therefore, sufficient quantities of an acid acceptor must be added to the
recipe to neutralize the HCl. Magnesium oxide is the most effective acid acceptor
because it does not react with the sulfonyl chloride group to cause scorch, but its
miscibility with the CSM polymer is poor. Therefore, relatively large amounts are
required for an efficient cure. This increases the cost and the compound viscos-
ity, which is already high due to the absence of plasticizer. Addition of a small
amount of pentaerythratol complexes with the MgO greatly improves its solubil-
ity in the polymer mass and therefore significantly reduces the amount of MgO
required.

Peroxide cures are usually temperature specific, and higher than normal

curing temperatures are usually required to achieve adequate properties. Addition
of a small amount of a co-agent, triallyl cyanurate or HVA-2, helps to activate the
cure by forming a complex with the peroxide.

Typical vulcanizable compounds will, in addition to the curatives, contain

certain plasticizers, fillers, processing aids, pigments, etc.

CSM does not crystallize upon elongation, but some reinforcement is devel-

oped through polar and hydrogen bonding effects. Thus, vulcanizates containing
no filler may still develop significant tensile strength upon extension. Additional
reinforcement may be achieved with certain carbon blacks and silicates. Surface
reinforcing furnace blacks give the best balance of properties and are widely used
as general-purpose fillers. Weathering of CSM with as little as three parts of car-
bon black is outstanding. Mineral fillers may be used to take advantage of CSM’s
nondiscoloring characteristics. Among mineral fillers, finely divided calcium car-
bonate gives the best heat resistance, and the best electrical properties and water
resistance is obtained with calcined clay. Titanium dioxide may be used when
white or pigmented end products are desired. The color of CSM products contain-
ing titanium dioxide does not fade. Flammability performance is improved by the
addition of hydrated silica and alumina Table 2.

The linear low density based CSM polymers have excellent dynamic prop-

erties over a broad temperature range. The pendent alkyl groups on the linear

378

ETHYLENE POLYMERS, CHLOROSULFONATED

Vol. 2

Table 2. Comparision of CSM Cure Systems

Compound Ingredients, phr

Sulfur donor Maleimide Peroxide

CSM (Hypalon 40)

100

100

100

N762 Black

35

35

Calcium Carbonate

–

–

40

Low MW Polyethylene

3

2

–

Paraffin wax

2

2

1

Magnesium Oxide

4

–

6

Calcium Hydroxide

–

4

–

HVA-2

1

3

–

Pentaerythratol-200 mesh

3

–

3

Sulfur

1

–

–

TMTD

1

–

–

MBTS

1

–

–

Triallyl cyanurate

–

–

3

Varox powder

–

–

6

Original Properties

a

100% modulus, MPa

b

6.6

6

7.5

200% modulus, MPa

b

18.2

16

19.5

Tensile strength, MPa

b

25.8

26.8

25

Elongation, %

340

360

300

Hardness, Shore A

73

70

76

Tear strength @ (RT) Die C, kN/m

c

39.4

46.6

34.7

Heat-aged

d

Properties

100% modulus, MPa

b

10.2

9

11

200% modulus, MPa

b

26.4

2 3

28

Tensile strength MPa

b

27

28.3

26.5

Elongation, %

250

267

220

Compression set, 22 h @ 70 C, %

34

23

46

a

Press cured 30 min @ 160

◦

C.

b

To convert MPa to psi, multiply by 145.

c

To convert kN/m to ppi, divide by 0.175.

d

After 7 days aging @ 120

◦

C.

backbone reduce the crystallinity of the base resin and allow rubbery products
at lower chlorine levels than linear-based polymers. High strength polymer prod-
ucts are produced with the heat and oil resistance near those of linear-based CSM,
but with low hysteresis, high resilience, high complex modulus, low damping, and
good flexibility at low temperatures. When properly compounded and cured, these
resins produce tan

δ values of 0.06–0.13 at 100

◦

C, dynamic ratio (E



/tan

δ) of 50–

70, and a brittleness temperature of

−75

◦

C. Gehman T50 values are

−30 to −40

◦

C

(26).

Economic Aspects

Production of chlorosulfonated polymers has declined somewhat in recent years
because of the increased competition from polymers with similar properties.

Vol. 2

ETHYLENE POLYMERS, CHLOROSULFONATED

379

Annual worldwide production of all products is now about 40,000 tons. The pri-
mary producer, with about 85% of world capacity, is DuPont Dow Elastomers, Inc.,
a joint venture of E.I. du Pont de Nemours & Co. Inc. and The Dow Chemical Co.,
with a single plant in the United States. The remaining capacity is provided by
Toyo Soda Manufacturing Limited, with one plant in Japan. DuPont Dow Elas-
tomers products are sold worldwide under the trade names of Hypalon, Acsium,
and Hypalon CP. Products similar to several grades of Hypalon products are made
by Toya Soda and sold under the trade names of CSM-CP and CSM-Ts. The ma-
terial cost variability is related mostly to the petroleum costs. Prices generally
range from $3 to $6 per kilogram.

Health and Safety Factors

Hypalon, Acsium, and Hypalon CP grades contain small amounts of carbon tetra-
chloride residue, normally

<0.2%, and traces of chloroform. These chemicals

are toxic and carcinogenic and carry time-weighted average exposure limits of
5 ppm. They are both regulated under the Occupational Safety and Health Act
as air contaminants. These contaminants diffuse from the product at measurable
rates if the product is not massed. So it is advisable to provide adequate ven-
tilation to keep concentrations at safe levels. Toya Soda chlorosulfonated prod-
ucts, CSM-CP and CSM-Ts, may contain up to 0.5% trichloroethane and small
amounts of tetrachloroethane. Both products contain

<1% epoxy resin as sta-

bilizer. These resins are regulated at

<1% level in some European countries.

Significant amounts of sulfur dioxide and hydrogen chloride as well as traces
of carbon oxy sulfide (COS) may be evolved during compounding in internal
mixers.

Disposal of Hypalon, Acsium, Hypalon CP, CSM- CP and CSM-Ts grades

should be in an approved landfill. Incineration is not recommended because of the
possible evolution of toxic gases. Additional information is available from DuPont
Dow Elastomers concerning these or other potential hazards when handling Hy-
palon products.

Uses

CSM products are classed as specialty elastomers but enjoy use in a broad spec-
trum of industrial, automotive, construction, coatings and miscellaneous appli-
cations. The applications for CSM depend only in part to its combination of oil
resistance and heat resistance. CSM is much more resistant to corrosive or oxi-
dizing chemicals, including ozone, than are CR or nitrile rubbers. It is tougher
than silicone and EPDM rubbers. It has good electrical insulation properties,
which are not as good as EPDM but better than many other elastomers. CSM also
has excellent radiation resistance needed in nuclear power applications and is
also color-stable and highly weather-resistant. Good flame resistance is obtained
with high chlorine grades of CSM. Chlorinated plasticizers, brominated resins,
and antimony trioxide synergists are commonly used as additives. Mineral fillers,

380

ETHYLENE POLYMERS, CHLOROSULFONATED

Vol. 2

excluding carbonates are preferred and hydrated alumna is frequently used when
smoke suppression is important.

In industrial hose, CSM is particularly useful because of its combination of

heat, oil, and chemical resistance and its outstanding ozone and weather resis-
tance. It is also preferred because of the frequent need for stable bright colors.
Hypalon 4085 and Hypalon 610 are often used in these applications because their
high compound Mooney viscosity prevents hose collapse or “flat spotting” during
curing.

In the electrical industry, CSM may be used as a protective jacketing or

sheathing over elastomers having superior insulation resistance but poor weather-
ability. It also finds considerable usage as an integral insulator for up to 600 V. This
combination of insulation resistance plus the long-term ozone resistance makes it
useful for high quality applications. In these cases, the lower viscosities of LD999
and Hypalon 40 are preferred for faster and smoother extrusions.

In the automotive industry, Hypalon 40 grades are used for fuel hose, power

steering hose, brake hose covers, vacuum tubing, and spark plug wire covers and
boots. The new Acsium grades are finding use in high performance timing belts and
accessory drive belts and in brake hose covers (26). Low permeability to moisture
and refrigerants make high chlorine grades qualify for air conditioning hose and
tubes. Chlorinated and chlorosulfonated maleic anhydride grafted polypropylene
is used as a primer for polypropylene bumpers.

Low chlorine CSM grades, based on linear polyethylene, eg, Hypalon 45,

have sufficient crystallinity to produce adequate tensile strength and elonga-
tion for uncured applications. They are generally compounded with white or
light-colored pigments and calendered into film for use as unsupported mem-
branes. Tensile strength of these sheets range from 9 to 12 MPa and Graves tear
strength of the order of 50–60 kN/m. These types are also used as binders for
magnetic door strips and signs because of its ability to accept very high loading
and specific adhesion to magnetic metal powders, as well as its excellent weather-
ability.

Hypalon CP grades are similar to CSM but have additional functionality,

ie, esters, acids, or maleic anhydride grafts, which set them apart for specific
applications. They add value as modifiers for adhesives, coatings, and inks because
of their low solution viscosity and increased solubility and compatibility. Hypalon
CP 826 promotes adhesion to polypropylene and finds use as a primer coating for
automobile bumpers.

A variety of miscellaneous end uses take advantages of CMS’s oil resistance,

colorability, and weather and ozone resistance. Grades based on LDPE find use
in numerous coating applications such as awnings, gas hose, escalator handrails,
and rubber boats. CSMs are also used for curb pump hose, mining cable jackets,
and appliance wire jackets. Grades based on ethylene vinyl acetate polymers are
used for traffic paints and marine paint.

BIBLIOGRAPHY

“Ethylene Polymers, Derivatives” in EPST 1st ed., Vol. 6, pp. 431–454, by P. J. Canterino,
Allied Chemical Corp.; “Ethylene Polymers, Chlorosulfonated Polyethylene” in EPSE 2nd

Vol. 2

ETHYLENE POLYMERS, CHLOROSULFONATED

381

ed., Vol. 6, pp. 513–521, by G. D. Andrews and Robert L. Dawson, E. I. du Pont de Nemours
& Co., Inc.

1. R. R. Warner, Rubber Age 26–29 (May 1952).
2. R. E. Brooks, D. E. Strain, and A. M. McAlevy, India Rubber World 968–974 (Mar.

1953).

3. U.S. Pat. 2212786 (Aug. 27, 1940), D. M. McQueen (to E. I. du Pont de Nemours & Co.,

Inc.).

4. U.S. Pat. 2416016 (Feb. 18, 1947), A. M. McAlevy, D. E. Strain, and F. S. Chance (to E.

I. du Pont de Nemours & Co., Inc.).

5. U.S. Pat. 2503253 (Apr. 11, 1950), M. L. Ernsberger and P. S. Pinkney (to E. I. du Pont

de Nemours & Co., Inc.).

6. U.S. Pat. 2982759 (May 2, 1961), R. O. Heuse (to E. I. du Pont de Nemours & Co., Inc.).
7. U.S. Pat. 2972604 (Feb. 21, 1961), W. B. Reynolds and P. J. Canterino (Phillips Petroleum

Co.).

8. U.S. Pat. 3347835 (Oct. 7, 1967), J. C. Lorenz (to E. I. du Pont de Nemours & Co., Inc.).
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10. U.S. Pat. 3296222 (Nov. 20, 1970), S. Dixon and R. E. Ennis (to E. I. du Pont de Nemours

& Co., Inc.).

11. U.S. Pat. 3542747 (Nov. 20, 1970) R. E. Ennis and J. W. Scott (to E. I. du Pont de

Nemours & Co., Inc.).

12. R. A. V. Raff and K. W. Doak, Crystalline Olefin Polymers, John Wiley and Sons, Inc.,

New York, 1965, pp. 307–405.

13. H. V. Boenig, Polyolefins: Structure and Properties, Elsevier, Amsterdam, the Nether-

lands, 1966.

14. A. B. Peterson, SPE Trans. 167–175 (July 1963).
15. E. G. Brehme, Hypalon Technical Bulletin H. P. 302, E. I. du Pont de Nemours & Co.,

Inc.

16. B. H. Bersted, J. Appl. Polym. Sci. 20, 2705 (1976).
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etalonage de Chromatographie par Permeation de Gel, Analusis, 1076, Vol. 4, No. 10,
pp. 450–455.

18. U.S. Pat. 3299014 (Apr. 15, 1967), J. Kalil (to E. I. du Pont de Nemours & Co., Inc.).
19. Jpn. Pat. 4544709 (Oct. 1, 1985), Y. Narui and co-workers (to Toya Soda Mfg.

Ltd.).

20. U.S. Pat. 3314925 (Apr. 15, 1967), K. F. King (to E. I. du Pont de Nemours & Co.,

Inc.).

21. U.S. Pat. 4871815 (Oct. 3, 1989), T. Nakagawa and co-workers (to Toya Sota Mfg.

Ltd.).

22. U.S. Pat. 5208290 (May 4, 1993), E. G. Brugel (to E. I. du Pont de Nemours & Co.,

Inc.).

23. T. Nakagawa, India Rubber World 104–111 (Jan. 1992).
24. Code of Federal Regulations, Title 29, Government Printing Office, Washington, D.C.,

Parts 1910–2000.

25. R. E. Fuller and K. S. Macturk, Rubber and Plastics News (Sept. 20, 1999).
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GENERAL REFERENCES

F. W. Billmeyer Jr., Textbook of Polymer Science, 2nd ed., John Wiley & Sons Inc., New York,
1971, pp. 147–149.

382

ETHYLENE POLYMERS, CHLOROSULFONATED

Vol. 2

D. W. Van Krevlen, Properties Of Polymers, 2nd ed., Elsevier Scientific Publishing Co., Inc.,
New York, 1976, pp. 129–172.
R. F. Ohm, Vanderbilt Rubber Handbook, 13th ed., Vanderbilt Rubber Co., Norwalk, Conn.,
1990, pp. 183–189.

R

OYCE

E

NNIS

Consultant