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ETHYLENE–NORBORNENE COPOLYMERS

489

ETHYLENE–NORBORNENE
COPOLYMERS

Introduction

Copolymers made from

α-olefins and cyclic olefins have been known for nearly

50 years (1,2). Ethylene–norbornene (Et–Nb) copolymers are specifically de-
scribed in the patent literature as long ago as 1973 (3), with further patent fil-
ings since then (4–6). The general class of thermoplastic cyclic olefin copolymers
(COCs) includes products from Mitsui Chemicals (7), Japan Synthetic Rubber (8),
Nippon Zeon (9), and Ticona (10). Some of these products are manufactured by
ring-opening metathesis and others by addition polymerization. Only the COCs
made by Ticona, a division of Celanese AG, under the trademark Topas, are Et–
Nb copolymers. These products, for which Ticona started up a 30,000-t plant in
September 2000 (11), are described in this article.

Properties

Ethylene–norbornene copolymers are made by the direct addition of ethylene and
norbornene, using metallocene catalysts. Although regularly alternating copoly-
mers have been made with semicrystalline characteristics, all Et–Nb products
presently available are completely amorphous random copolymers, varying only
in melt flow and glass-transition temperature (T

g

). The bridged ring structure of

norbornene makes the resins quite stiff, and their completely amorphous nature
ensures high transparency. In general, the resins are stiff, strong, glass-clear, and
water-white. They have low elongation at break, negligible moisture absorption
and transmission, very low dielectric loss, and low density. The glass-transition

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

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ETHYLENE–NORBORNENE COPOLYMERS

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Norbornene, mol %

250

200

150

100

50

0

0

20

40

60

80

Current

Product Range

T

g,

°C

Fig. 1.

Effect of norbornene content on T

g

.

temperature increases linearly with norbornene content, as shown in Figure 1.
The commercially available products range in T

g

from about 65

◦

C to about 180

◦

C.

Subject to some limitations, conventional thermoplastic processing methods may
generally be employed with all of these products.

Because of the bulkiness of norbornene, Et–Nb copolymers remain amor-

phous down to very low levels of norbornene, where a clear elastomeric polymer
is obtained. In the current commercial range of products, all grades on offer ex-
hibit high rigidity, with tensile (Young’s) modulus values ranging from 2600 to
3200 MPa. Specific gravity values fall in a narrow spread from 1.00 to 1.02, and
light transmission is around 92%. Typical values for a range of physical properties
are shown in Table 1 for the announced commercial grades of Topas COC resins
(12). These materials have excellent chemical resistance to aqueous fluids (acids
and bases) and many polar solvents (alcohols and ketones), but are attacked by
nonpolar solvents (hexane, toluene, oleic acid, and methylene chloride) and some
oils and fats. The chemical resistance of the copolymers may be summarized as
follows (13).

The commercially important properties of Et–Nb copolymers include low

density, high transparency and low color, high moisture barrier and low moisture
absorption, low optical distortion, excellent feature replication, resistance to po-
lar solvents, high purity, shatter resistance, good biocompatibility, extremely low
dielectric loss, high temperature capability, and compatibility with polyethylenes.
The resins also have the low shrinkage and warpage typical of amorphous
polymers.

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ETHYLENE–NORBORNENE COPOLYMERS

491

Table 1. Properties of Et–Nb Copolymers, Commercial Grades of Topas

Property

8007

5013

6013

6015

6017

T

g

,

◦

C

80

140

140

160

180

Melt flow (260

◦

C), g/10 min

30

55

16

16

12

Density, g/mL

1.0

1.02

1.02

1.02

1.02

M

w

(PS), g/mol

93,200

80,500

65,400

80,200

82,500

H

2

O absorption, %

<0.01

<0.01

<0.01

<0.01

<0.01

Mold shrinkage, %

0.6

0.6

0.6

0.6

0.6

Tensile strength, MPa

a

66

66

66

66

66

Elongation @ break, %

10

3

4

4

4

Tensile modulus, MPa

a

2600

3100

3200

3200

3200

Charpy impact, kJ/m

2b

13

15

15

15

15

Notched Charpy impact, kJ/m

2b

2.6

1.7

1.7

2.0

2.0

HDT

c

@ 0.46 MPa

a

,

◦

C

75

130

130

150

170

Dielectric constant @ 1–10 kHz

2.35

2.35

2.35

2.35

2.35

Comparative tracking index, V

>600

>600

>600

>600

>600

Volume resistivity,

·cm

>10

16

>10

16

>10

16

>10

16

>10

16

Light transmission, %

92

92

92

92

92

a

To convert MPa to psi, multiply by 145.

b

To convert kJ/m

2

to ft

·lbf/in.

2

divide by 2.4.

c

Heat-deflection temperature.

FDA Drug and device master file numbers respectively are DMF 12132 and

MAF 1043. All grades, save only the highest temperature one, comply with U.S.P.
Class VI requirements. The FDA has issued a regulation, 21 CFR 177.1520, for
Et–Nb copolymers in dry food contact (14). The 80

◦

C T

g

grade complies with food

contact requirements under conditions of use C through H, while the 140

◦

C and

160

◦

C T

g

grades comply under conditions of use A through H. A Food Contact

Substance Notification, FCN 000075, became effective on August 22, 2000 for
the polymers in direct food contact with all food types as films, sheets, and ar-
ticles made therefrom (15). The afore mentioned properties, usually in various
combinations, are the drivers for current and developing applications for Et–Nb
copolymers.

Manufacturing

Although, strictly speaking, Et–Nb products are copolymers of ethylene and nor-
bornene, the manufacturing process starts with ethylene and a high purity dicy-
clopentadiene (DCPD) stream. The DCPD is cracked at a temperature in excess
of 160

◦

C to yield cyclopentadiene (CPD) (eq. (1)), which reacts with ethylene to

give norbornene (bicyclo[2.2.1]-2-heptene) via Diels–Alder condensation (eq. (2)).
Cyclopentadiene boils at 42

◦

C, whereas norbornene melts at 47

◦

C.

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ETHYLENE–NORBORNENE COPOLYMERS

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The norbornene product then reacts in solution with ethylene to form the

copolymer, using a zirconium metallocene procatalyst/methylaluminoxane cocat-
alyst system (eq. (3)).

Subsequent removal of catalyst and solvent yields a very pure polymer.

Processing

Many processing methods have been employed with Et–Nb copolymers. These
include injection molding, injection and coinjection blow molding, compression
molding, cast film and sheet extrusion and coextrusion, blown film extrusion and
coextrusion, tubing extrusion and coextrusion, extrusion compounding, film sol-
vent casting, mono- and biaxial (tenter) orientation of film, and thermoforming
of film and sheet. In co-extrusion and coinjection molding, a tie layer is normally
required except for polyethylenes and high ethylene copolymers. Unless the pari-
son is quite small, presently available polymer grades do not have sufficient melt
strength for extrusion blow molding. Typical starting conditions for molding and
extrusion are given in Tables 2 and 3 where the higher temperatures apply to
polymers of higher T

g

. For processes involving a free surface, such as extrusion or

blow molding, an external processing aid should be dusted on the polymer pellets
to obtain the best product esthetics. For both extrusion and molding, low com-
pression screws are recommended. A special screw design for film extrusion is
shown in Figure 2 (16). In both extrusion and molding, it is important that the
forming surface be maintained near the T

g

of the polymer grade being processed.

For higher T

g

grades, this requires oil-heated tooling for molding and oil-heated

take-off rolls for film casting. Manufacture of blown films requires a shorter tower
and a lower nip than those that are used in conventional olefin processing.

Post-processing assembly procedures such as lamination, machining, or di-

amond turning, and joining by solvent, friction, and ultrasonic bonding have all
been satisfactorily demonstrated with Et–Nb copolymers. Machining lubricants
should be water-based and should contain no oil. Also, relatively slow speeds and
shallow cuts should be used to avoid cracking the part.

Applications

Rigid and flexible packaging are currently the leading uses for Et–Nb copoly-
mers. This category includes both film and container applications in pharmaceu-
tical, medical and diagnostic, and food packaging end uses. Pharmaceutical blister
packaging requires high moisture barrier, transparency, and thermoformability.

metering section

shear section

mixing
section

2 D

3 D

6 D

8 D

5 D

3,5 D

1,5 D

metering section

flat compression section

feed section

decompression section

T

6

210 C

T

5

200 C

T

4

190 C

T

3

180 C

T

2

170 C

T

1

50 C

Fig. 2.

Special screw design for film extrusion.

493

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ETHYLENE–NORBORNENE COPOLYMERS

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Table 2. Injection-Molding Conditions for Et–Nb Copolymers

Feed Zone

<80

◦

C

Barrel Zone 1

230

◦

C–270

◦

C

Barrel Zone 2

245

◦

C–290

◦

C

Barrel Zone 3

260

◦

C–300

◦

C

Barrel Zone 4

270

◦

C–300

◦

C

Nozzle

270

◦

C–300

◦

C

Melt

260

◦

C–310

◦

C

Max barrel residence

<15 min

Injection pressure

50–110 MPa

a

Hold pressure

30–50 MPa

a

Back pressure

0.7 MPa

a

Screw speed

50–150 rpm

Injection speed

Moderate to fast (2–10 cm/s)

Mold temperature

110

◦

C–150

◦

C

Nozzle type

Open

Screw suckback

None or minimum

Cushion

Small

Screw type

Low compression

Screw turn on inject

No

Ram speed

Moderate to fast

a

To convert MPa to psi, multiply by 145.

Table 3. Extrusion Conditions for Et–Nb Copolymers

L/D ratio

>25

Compression ratio 2.0–2.5
Casting roll

Close to HDT of polymer (50

◦

C–70

◦

C up to 160

◦

C–175

◦

C)

Feed Zone

<50

◦

C

Zone 1

210

◦

C–240

◦

C up to 255

◦

C–275

◦

C

Zone 2

220

◦

C–250

◦

C up to 275

◦

C–300

◦

C

Zone 3

230

◦

C–270

◦

C up to 275

◦

C–300

◦

C

Zone 4

230

◦

C–270

◦

C up to 275

◦

C–300

◦

C

Die

230

◦

C–270

◦

C up to 275

◦

C–300

◦

C

Melt

230

◦

C–270

◦

C up to 290

◦

C–310

◦

C

These requirements are met with a multilayer structure containing a thicker cen-
tral layer of the copolymer with thin outer layers of polypropylene (17). Such film
structures are made by lamination or coextrusion, respectively using appropriate
adhesive or tie layers. Other uses for these films include packaging of personal
care and consumer products as in, for instance, blister bottles.

Medical and diagnostic packaging applications include syringes, vials, and

tubes made by injection or injection blow molding (18,19). Here the key properties
include moisture barrier, transparency, shatter resistance, bioinertness, and abil-
ity to undergo terminal steam- or gamma-sterilization. Cuvettes and micro-titer
(multiwell) plates are other important diagnostic/analytical uses for the copoly-
mers (20,21). Resistance to dimethyl sulfoxide is an important attribute in these
applications, as are clarity and transparency, especially in the near uv region.
Low shrinkage and dimensional stability provide the ability to mold very flat

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ETHYLENE–NORBORNENE COPOLYMERS

495

three-dimensional structures that can be accurately and consistently positioned
in automated analytical equipment.

Food packaging uses may include both mono- and multilayer films, primarily

using the copolymer in a blend with polyethylene (22). Suitable blend components
include low density, linear low density, and plastomer polyethylenes as well as
ethylene vinyl alcohol copolymers. These blends exhibit improved stiffness, re-
duced friction and blocking, and improved hot tack and ultimate seal strength
performance over the respective unmodified polyethylenes, with no loss, or even
an improvement in clarity and oxygen permeation. Uses for the blends are in
packaging of fresh-cut produce and standup pouches.

Biaxially oriented cast films have been shown to have improved mechani-

cal properties, with modulus increased 1.5 times, tensile strength 2.5 times, and
elongation 20 times (23). Films have been drawn down to about 7

µm using draw

ratios between 3:1 and 4:1 in machine and transverse directions. These films can
be metallized on both sides and because of their extremely low dielectric loss and
higher temperature capability, can provide superior capacitor performance in a
smaller package.

High transparency, low birefringence, and high Abb´e number combine with

low moisture absorption to make the Et–Nb copolymers extremely suitable for
precision optical applications as well as more mundane uses where temperature or
solvent resistance issues preclude the use of other materials such as polycarbonate
or polymethyl methacrylate. Superior reproduction of surface features also makes
the resins suitable for production of diffraction optics. Current applications include
lenses for use in light-emitting diodes, compact disc (CD) readers, and automotive
rain sensors. Light guides capable of resisting higher temperatures such as are
experienced during wave soldering are another current optical application (24).

Work in the mid-nineties showed that excellent audio CDs could be made

from a high flow Et–Nb copolymer. However, cycle times comparable to those ob-
tainable with CD-grade polycarbonate were not achieved. As optical storage media
standards move to higher and higher data density, renewed interest has arisen
in COC resins for such applications, based on their excellent feature replication,
superior birefringence, and higher transparency to the lower wavelength lasers
required to read the smaller pits accurately. Et–Nb copolymers are candidates for
these high data density applications (25).

The two key control parameters available in manufacture of the copolymers

are T

g

and molecular weight. This capability has been exploited to produce a new

class of toner binder resins for electrophotographic printing (26). The new binder
resins offer significant performance benefits over existing materials especially
where high process speed or improved image quality is required. Control of T

g

allows precise matching to the fuser temperature requirements of specific printer
designs. The single-site metallocene catalysts used in manufacture of the Et–Nb
resins allow a narrow molecular weight distribution with a polydispersity index
(M

w

/M

n

) of close to 2.0. This enables undesirable oligomer content to be kept to

a minimum and also facilitates design of appropriate bimodal molecular weight
compositions to meet the requirements of different printing processes, especially
in regard to providing a large antioffset window. The high clarity and colorless-
ness of the base copolymer resin provide high color fidelity in the finished print.
Making toner binder resins of very low molecular weight ensures good pigment

496

ETHYLENE–NORBORNENE COPOLYMERS

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dispersability and also facilitates grinding the finished toner into relatively uni-
form small and approximately spherical particles.

The Et-Nb copolymers presently on the market are all neat polymers. No

compounds of these resins are commercially available at this time. However, glass-
fiber-reinforced formulations have been developed (27), as have impact-modified
and flame-retarded compositions (28). The glass-reinforced formulations had high
flow and the ability to fill long thin sections. Complex three-dimensional parts
showed very little warpage, reflecting the low shrinkage of the base resin. Rein-
forcement with glass fibers significantly increased notched impact strength. Im-
provements in tensile strength and modulus were on a par with those obtainable
with polypropylene. Flame-retarded compositions were based on halogenated and
nonhalogenated flame-retardant packages, and yielded both V-0 and V-2 perfor-
mance.

As the unique property profiles of cyclic olefin polymers and copolymers, and

particularly those of Et-Nb copolymers, become more widely known and under-
stood, new applications and most likely, new formulations will continue to develop.
This process will undoubtedly be furthered by any cost improvements obtainable
via scale economies in production of the base resin, for which the U.S. developmen-
tal price in 2001 ranges between $5.70/kg and $6.60/kg at truckload quantities.

BIBLIOGRAPHY

1. U.S. Pat. 2721189 (Oct. 18, 1955), A. W. Anderson and N. G. Merckling (to E. I. du Pont

de Nemours & Co., Inc.).

2. G.B. Pat. 951022 (Apr. 24, 1962) (to Montecatini Societa Generale per L’Industria

Mineraria e Chimica).

3. D.D.R. Pat. 109224 (July 10, 1973), J.-P. Koinzer, U. Langbein, and E. Taeger (to VEB

Leuna).

4. Eur. Pat. 0156464 (Feb. 1, 1985), H. Kajiura, H. Oda, and S. Minami (to Mitsui Petro-

chemical Industries, Ltd.).

5. Eur. Pat. 0283164 (Mar. 1, 1988), N. Ishimaru and co-workers (to Mitsui Petrochemical

Industries, Ltd.).

6. Eur. Pat. 0407870A2 (July 4, 1990), M.-J. Brekner and co-workers (to Hoechst

Aktiengesellschaft).

7. Apel Product Bulletin, Mitsui Petrochemical Industries (undated).
8. Report IV-B-2, Nippon Chemtec Consulting (Dec. 1992).
9. Zeonex Product Brochure, Nippon Zeon Co. Ltd., Jan. 2000.

10. Topas

®

COC Product Bulletin, Ticona GmbH (Sept. 1997).

11. Ticona press release (Sept. 2000).
12. R.R. Lamonte and D. McNally, Plastics Eng. 56, 6, 51 (2000).
13. D. McNally, in New Polymer Technologies ’98 Conference, Philadelphia, Pa., 1998.
14. Title 21, Code of Federal Regulations, 177.1520.
15. USFDA Food Contact Substance Notification 00075.
16. E. Beer and W. Hatke, Plastics Special 6, 1999.
17. E. Beer and K. Trombley, in Blister-Pack 2000 Conference, Jamesburg, NJ, May 17,

2000.

18. Schott Pharmaceutical Packaging, American Association of Pharmaceutical Scientists

Conference and Exhibition, Philadelphia, Nov. 15, 1999.

19. Ticona press release (Jan 15, 2001).

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EXTRUSION

497

20. U.S. Pat. 5910287 (June 8, 1999), P. J. Cassin and co-workers (to Aurora Biosciences

Corp.).

21. U.S. Pat. 6063338 (May 16, 2000), A. A. Pham and co-workers (to Aurora Biosciences

Corp.).

22. R.R. Lamonte, in 10th Worldwide Flexible Packaging Conference, Amsterdam,

Nov. 2000.

23. T. Weller, in New Plastics ’98 Conference, London, Jan. 22, 1998.
24. Ticona press release (Feb. 26, 2001).
25. A. Tullo, Chem. Eng. News 77, 14, 51 (2000).
26. K. Berger, T. Nakamura, and M. Bruch, in International Conference on Digital Printing

Technologies, Vancouver, Oct. 15, 2000, pp. 623–626

27. V. Sullivan, Glass Reinforcement of COC, private communication, 1997.
28. T. Wehrmeister, Flame Retardation of COC, private communication, 1997.

D

ONAL

M

C

N

ALLY

Ticona