5 Polychlorotrifluoroethylene Polymers (PCTFE) and Copolymers with Ethylene (ECTFE)

Polychlorotr@oroethylene Polymers (PCTFE) 375

Pressures varied from 20 to 1500 lbf/in2 (0.14 to 10.5 MPa) and reaction times

were of the order of 5-35 hours. Reaction promoters included peroxides and salts

of persulphuric and perphosphoric acids. ‘Activators’, ‘accelerators’ and

buffering agents were also discussed in the patent. The process of manufacture of

Kel-F is understood to be based on this patent.

The major differences in properties between PTFE and PCTFE can be related

to chemical structure. The introduction of a chlorine atom, which is larger than

the fluorine atom, breaks up the very neat symmetry which is shown by PTFE

and thus reduces the close chain packing. It is still, however, possible for the

molecules to crystallise, albeit to a lower extent than PTFE. The introduction of

the chlorine atom in breaking up the molecular symmetry appears to increase the

chain flexibility and this leads to a lower softening point. On the other hand the

higher interchain attraction results in a harder polymer with a higher tensile

strength. The unbalanced electrical structure adversely affects the electrical

insulation properties of the material and limits its use in high-frequency

applications.

Because of the lower tendency to crystallisation it is possible to produce thin

transparent films.

The chemical resistance of PCTFE is good but not as good as that of PTFE.

Under certain circumstances substances such as chlorosulphonic acid, molten

caustic alkalis and molten alkali metal will adversely affect the material.

Alcohols, acids, phenols and aliphatic hydrocarbons have little effect but certain

aromatic hydrocarbons, esters, halogenated hydrocarbons and ethers may cause

swelling at elevated temperatures.

The polymer melts at 216°C and above this temperature shows better cohesion

of the melt than PTFE. It may be processed by conventional thermoplastics

processing methods at temperatures in the range 230-290°C. Because of the high

melt viscosity high injection moulding pressures are required.

PCTFE is more expensive than PTFE and its use is comparatively limited.

With the advent of FEP copolymers, TFE-ethylene copolymers and the

peffluoroalkoxy polymers the advantage of melt processability is no longer,

alone, a sufficient justification for its use. The particular advantages of the

material are its transparency in thin films and its greater hardness and tensile

strength as compared to PTFE and FEP copolymers. Examples of its use

include gas-tight packaging film for medical and military applications (the

main use), transparent windows for chemical and other apparatus where glass

or other materials cannot be used, seals, gaskets and O-rings and some

electrical applications such as hook-up wire and terminal insulators. Consumption, estimated at 350-400 tonnes per annum, is only about 1% that of

PTFE.

PCTFE is marketed by Hoechst as Hostaflon C2 and in the United States by

Minnesota Mining and Manufacturing (Kel-F) and Allied Chemical (Halon).

Typical values for various physical properties are given in Table 13.1.

Copolymers of chlorotrifluoroethylene and ethylene were introduced by

Allied Chemicals under the trade name Halar in the early 1970s. This is

essentially a 1:1 alternating copolymer compounded with stabilising additives.

The polymer has mechanical properties more like those of nylon than of

typical fluoroplastic, with low creep and very good impact strength. Furthermore the polymers have very good chemical resistance and electrical

insulation properties and are resistant to burning. They may be injection

moulded or formed into fibres.



376 Fluorine-containing Polymers

13.6 POLY(V1NYL FLUORIDE) (PVF)

Poly(viny1 fluoride) was first introduced in the early 1960s, in film form, by Du

Pont under the trade name Tedlar. Details of the commercial method of preparing

the monomer have not been disclosed but it may be prepared by addition of

hydrogen fluoride to acetylene at about 40°C.

CHGCH



+ HF



HgClz



CH2=CHF



on Charcoal



It may also be prepared by pyrolysis of 1,l-difluoroethane at 725°C over a

chromium fluoride catalyst in a platinum tube or by the action of zinc dust on

bromodifluoroethane at 50°C.

The polymers were first described by Newkirk." Polymerisation may be

brought about by subjecting acetylene-free vinyl fluoride to pressures to up to

1000 atm at 80°C in the presence of water and a trace of benzoyl peroxide.

Although poly(viny1 fluoride) resembles PVC in its low water absorption,

resistance to hydrolysis, insolubility in common solvents at room temperature

and a tendency to split off hydrogen halides at elevated temperatures, it has a

much greater tendency to crystallise. This is because the fluorine atom (c.f. the

chlorine atom) is sufficiently small to allow molecules to pack in the same way

as polythene.

PVF has better heat resistance than PVC and exceptionally good weather

resistance. It will burn slowly. Instability at processing temperatures makes

handling difficult but this problem has been sufficiently overcome for Du Pont to

be able to market their Tedlar film.

PVF film is now being used in the manufacture of weather-resisting laminates,

for agricultural glazing and in electrical applications.

13.7 POLY(VINYL1DENE FLUORIDE)

This melt-processable homopolymer was first introduced in 1961 as Kynar by the

Pennsalt Chemical Corporation (the company name being subsequently changed

to Pennwalt). Other companies now manufacturing similar polymers are

Dynamit Nobel (Dyflor), Kureha (KF), Solvay (Solef) and Atochem

(Foraflon).

The monomer is a gas boiling at -84°C which may be made by

dehydrochlorination of 1-chloro-1,l-difluoroethane:

CF2Cl.CH3



+CF2=CH2



or by dechlorination of 1,2-dichloro-1,l-difluoroethane:

CF2 C1 CH2 CY----+



CF, =CH2



Poly(viny1idene fluoride) is a crystalline polymer melting at 171"C. Amongst the

melt-processable fluoroplastics the polymer is of interest because of its good

mechanical properties and relatively low price. Tensile and impact strengths are

good and the material is flexible in thin sections. Although it has generally good

chemical resistance, strongly polar solvents such as dimethyl acetamide tend to



Other Plastics Materials Containing Tetrafluoroethylene 377

dissolve the polymer whilst some strongly basic primary amines such as

n-butylamine tend to cause embrittlement and discolouration. The polymer is

also attacked by some concentrated acids. A further disadvantage of the material

is that its dielectric properties are frequency dependent and this limits its use as

an electrical insulator. The high dielectric constant is a particular feature.

Of greater interest in recent years have been the peculiar piezolectric

propertie~"-'~ of poly(viny1idene fluoride). In 1969 it was observed" that

stretched film of the polymer heated to 90°C and subsequently cooled to room

temperature in a direct current electric field was 3-5 times more piezoelectric

than crystalline quartz. It was observed that the piezolectric strain coefficients

were higher in the drawn film and in the normal directions than in the direction

transverse to the film drawing.

The piezoelectric phenomena have been used to generate ultrasonic waves up

to microwave frequencies using thin poly(viny1idene fluoride) transducers. In the

audio range a new type of loudspeaker has been introduced using the transverse

piezolectric effect on a mechanically biased membrane. This development has

been of considerable interest to telephone engineers and scientists.

Poly(viny1idene fluoride) also has interesting pyroelectric properties showing

a stable and reversible polarisation which persists after several heating cycles. In

consequence the film is used in pyroelectric detectors. PVDF has a wide

processing window in that there is a big difference between the melt temperature

and the decomposition temperature. Thermal stability may, however, be

drastically affected by contaminants, and scrupulous cleanliness is important

when processing. The generation of HF should decomposition occur during

processing is an obvious hazard. Typical melt temperatures are in the range

24O-26O0C, with mould temperatures being anything from 30 to 120°C.

The polymer, like many fluorine-containing polymers has very good

weathering resistance and may also be used continuously up to 150°C. Outside

of the electrical field it finds use in fluid handling, in hot water piping systems,

in packaging and in chemical plant. A widely used specific application for PVDF

is in ultra-pure water systems for the semiconductor industry.

13.8 OTHER PLASTICS MATERIALS CONTAINING

TETRAFLUOROETHYLENE



In 1972 Du Pont introduced Teflon PFA, a copolymer of tetrafluoroethylene and

perfluoro(propy1 vinyl ether) (CF2=CFOCF2CF,CF3). Similar materials are

now also produced by Asahi Glass, Daikin, Hoechst and Monteflos and are

commonly referred to as PFA fluoropolymers. In 1994 Hoechst introduced

Hostaflon PFA-N, claimed to have significantly lower melt viscosities than

earlier grades of material.

Properties are similar to those of PTFE, and PFA fluoropolymers are generally

considered to be the best melt-processable alternative to PTFE yet available.

They are, however, more expensive than PTFE. Compared with the TFE-FEP

copolymers such as Teflon FEP the PFA fluoropolymers:

(1) Have a higher melting point (300-310°C).

(2) Have better processability.

(3) Retain a higher proportion of their room temperature stiffness and strength at

elevated temperatures.



318 Fluorine-containing Polymers

In addition, the polymers are noted for their outstanding flex life, toughness

and stress cracking resistance.

PFA fluoropolymers may be processed by injection moulding, extrusion,

extrusion blow moulding and transfer moulding. All machine parts coming into

contact with the melt should be made from highly corrosion-resistant high nickel

content alloys. Processing melt temperatures can be as high as 420°C and mould

temperatures may be in the range 50-250°C.

Applications include high-performance insulation for wire and cables

(particularly heater cables), and corrosion-resistant linings for pumps, valves,

pipes and other chemical equipment. Its availability in the form of film and tubing

has led to its demand for both corrosion protection and antistick applications.

Somewhat between PTFE and PFA materials is the product Hostaflon TFM,

which is a copolymer of TFE and a small amount of the perfluoro(propy1 vinyl

ether). It has improved impact strength and weldability and has been promoted

as a suitable material for forming into bottles. Yet another TFE-perfluoroalkoxy

copolymer was introduced by Du Pont in 1979 as Teflon EPE. This material had

a somewhat lower melting point (295°C) than the more common PFA

fluoropolymers but it is no longer marketed.

In 1989 Du Pont introduced Teflon AF, said to be a copolymer of

tetrafluoroethylene and trifluoromethyldifluorodioxol. This amorphous fluoropolymer has a similar heat and chemical resistance to PTFE but possesses several

notable properties, including:

High optical clarity (>95% in the visible range extending into the near

infrared together with a good level of transparency to ultraviolet light).

A very low refractive index (1.29-1.31).

The lowest dielectric constant (1.83-1.93) of any known plastics material. (It

is to be noted that this is in spite of the fact that the dielectric constant is more

than the square of the refractive index, indicating that polarisations other

than electronic polarisations are present-see Section 6.3).

Limited solubility in selected perfluorinated solvents (unique amongst

commercial fluoropolymers), enabling solution-cast ultra-thin coatings in the

submicrometre thickness range.

A high coefficient of friction.

At about &1500/lb it is one of the most expensive plastics materials

commercially available.

At the time of writing two grades of the material were available with different

comonomer ratios. Typical properties are given in Table 23.3.



Table 13.3 Typical properties of Teflon AF amorphous fluoropolymers

Grade



I



ASTMMethod



AF1600



AF2400



D34 18

D1708

D1708

D1708

D792

D3835



160

27

20.5

1.55

1.78

2657 at 250°C



240

24.6

6.1

1.54

1.67

540 at 350°C



I



Tg ("C)

Tensile strength (MPa)

Ultimate elongation (%)

Tensile modulus (GPa)

Specific gravity

Melt viscosity (Pa.s)

(at loo-')



Fluorine-containing Rubbers



379



The AF polymers are of potential interest in a number of high-technology

applications, including the following:

(1) For coating optical devices for use in chemically aggressive environments.

( 2 ) Fibre optics applications.

(3) Semiconductor and dielectric applications.

(4) Release film coatings of very low thickness.

( 5 ) Corrosion-resistant coatings and high-permeability separation membranes.

13.9 HEXAFLUOROISOBUTYLENE-VINYLIDENE FLUORIDE

COPOLYMERS

A 5050 mol/mol copolymer of hexafluoroisobutylene (CH2 =C(CF3)J and

vinylidene fluoride was made available by Allied Chemical in the mid-1970s as

CM-1 Fluoropolymer. The polymer has the same crystalline melting point as PTFE

(327°C) but a much lower density (1.88 g/cm3). It has excellent chemical

resistance, electrical insulation properties and non-stick characteristics and, unlike

PTFE, may be injection moulded (at -380°C). It is less tough than PTFE.

13.10 FLUORINE-CONTAINING RUBBERS

Fluorine-containing rubbers were originally developed during the search for fluidresisting elastomers which could be used over a wide temperature range. Much of

the initial developmental work was a result of contracts placed by the US Army and

Air Force. Whilst the current commercial materials are very expensive compared

with general purpose rubbers they find a number of both military and non-military

applications, particularly in the area of seals and O-rings.

In order to produce a rubbery material the polymer must have a flexible

backbone, be sufficiently irregular in structure to be non-crystalline and also

contain a site for cross-linking. These are of course requirements applicable

equally to any potential elastomer whether or not it contains fluorine.

The first material to be marked, Fluoroprene, was introduced by Du Pont in

1948. A polymer of 2-fluorobuta-1,3-diene it was the fluoro analogue of

polychloroprene. However, its properties were far from outstanding and

production was soon discontinued.

In the early 1950s the fluoroacrylate polymers Poly-IF4 and Poly-2F4 (known

initially as PolyFBA) and PolyFMFPA) were introduced. These materials had the

structures given in Figure 13.7.These materials are also no longer of commercial

significance.

Much greater success has been achieved with fluororubbers based on

vinylidene fluoride (see Table 13.4). The copolymer of VDF with hexafluoropropylene (HFP) (typified by Viton A) and the terpolymer of VDF, HFP

and TFE (typified by Viton B) are of similar importance and between them

probably hold about 95% of the fluororubber market. The terpolymers have

better long-term heat resistance, better resistance to swelling in oils and better

resistance to chemical degradation, particularly from oil additives. On the other

hand, the copolymers have a good balance of properties with a better retention of

tensile strength after high-temperature aging, and some copolymer grades have

outstanding compression set resistance. Polymers containing hydropenta-



380 Fluorine-containing Polymers

(CH2- CH),m



I

c=o

I



(CH,-CH),m



I

I



c=o



0



0



CH,



CH,



I



I

I



CF, -CF, -0 -CF,

(b)



Figure 13.7. (a) Poly 1F4,(b) Poly 2F4



fluoropropylene (early grades of Tecnoflon) appear to have been introduced

primarily to circumvent patents but are no longer of importance. On the other

hand DuPont have introduced Viton GLT, a terpolymer of tetrafluorethylene,

vinylidene fluoride and perfluoromethyl ether. All of the materials referred to in

this paragraph are collectively classified by ASTM as FKM rubbers.

Since their appearance in the 1950s the main developments with these

materials have been in their method of vulcanisation. Being saturated rubbers

they cannot be vulcanised with sulphur but they could be cross-linked by

irradiation or the use of peroxides. Until the 1970s, however, the only agents of

commercial importance were diamines and certain of their derivatives. Typical of

these materials were ethylenediamine carbamate, hexamethylenediamine carbamate and N,N'-dicinnamylidenehexane-1,6- diamine. Amongst the disadvantages

of these systems were the high level of compression set shown by the

vulcanisates, the generation of double bonds during vulcanisation providing a

possible site of degradation, and the generation of up to 2% of water during cure

which can cause both porosity and some de-vulcanisation.

Reduction in compression set began to be achieved in the late 1960s when it

was found that tropolene and phenanthroline not only accelerated amine cures

but were also effective with certain bisnucleophiles such as resorcinol,

hydroquinone and bis-phenol AF. In due course even better results were obtained

with quaternary ammonium or phosphonium salts being used in conjunction with

aromatic dihydroxy compounds.

As with the amine systems such systems still suffered the disadvantage that

water was split out during cure. This led to the availability in the late 1970s of

peroxide-curable materials containing a cure site of enhanced receptivity to attack

by aliphatic radicals. These peroxide-cured elastomers are claimed to have

superior resistance to steam, hot water and mineral acids than the earlier systems.

It has been estimated that about 75% of FKM consumption is for O-rings,

packings and gaskets for the aerospace industry, whilst automotive and other

mechanical goods accounts for about 12%. Although the parts are expensive,

motor manufacturers, are nowadays more appreciative of the demand by

customers for reliability and increased service intervals. For this reason FKM is

now used in valve stem seals, heavy duty automatic and pinion seals, crankshaft

seals and cylinder liner O-rings for diesel engines. Other uses include seals for

diesel engine glow plugs, seals for pilot-operated slide valves, protective suiting

and flue duct expansion joints.

As will be seen from Table 13.4 elastomers are also available which are

copolymers of vinylidene fluoride and chlorotrifluoroethylene. These materials



382 Fluorine-containing Polyniel-s

are notable for their superior resistance to oxidising acids such as fuming nitric

acid. Elastomeric copolymers of vinylidene fluoride and hydropentafluoropylene

have also been marketed (Tecnoflon by Montedison).

In attempts to further improve the stability of fluorine-containing elastomers

Du Pont developed a polymer with no C-H

groups. This material is a

terpolymer of tetrafluoroethylene, perfluoro(methy1 vinyl ether) and, in small

amounts, a cure site monomer of undisclosed composition. Marketed as Kalrez

in 1975 the polymer withstands air oxidation up to 290-315°C and has an

extremely low volume swell in a wide range of solvents, properties unmatched

by any other commercial fluoroelastomer. This rubber is, however, very

expensive, about 20 times the cost of the FKM rubbers and quoted at $1500/kg

in 1990, and production is only of the order of 1 t.p.a. In 1992 Du Pont offered

a material costing about 75% as much as Kalrez and marketed as Zalak.

Structurally, it differs mainly from Kalrez in the choice of cure-site monomer.

A terpolymer of tetrafluoroethylene, propylene and a cure site monomer

(suggested as triallyl cyanurate by one commentator) has now been marketed by

Asahi Glass as Aflas. This rubber may be cross-linked by peroxides to give

vulcanisates that swell only slightly in inorganic acids and bases but strongly in

chloroform, acetone and hydrocarbons. Compared with the Du Pont material

Kalrez, this rubber has a higher Tg(-2"C, c.f. -12°C) and a lower long time heat

distortion temperature (less than 200°C) and thus has a narrower temperature

range of application. It is stated to be significantly cheaper.

The excellent chemical resistance of Aflas has led to important applications in

oilfields and, more recently, in the car industry in place of FKM rubbers because

of the better resistance to new types of engine oils, transmission fluids, gear

lubricants and engine coolants.

In 1991 MMM announced Fluorel 11, a terpolymer of tetrafluoroethylene,

vinylidene fluoride and propylene. As might be expected from the structure, this

is intermediate between FKM and Aflas, having better resistance to many newer

automotive oils, lubricants and transmission fluids than the former but better heat

resistance than the latter.

In 1955 Barr and Haszeldine, working in Manchester, prepared nitrosofluoroelastomers of the general type:



Interest has continued with these materials because of their non-inflammable

nature (they will not bum, even in pure oxygen), their excellent chemical

resistance, including that of nitrogen tetroxide and chlorine trifluoride, a low Tg

of -5 1"C and an extremely low solubility parameter of 10.6MPa'''.

The earliest materials were copolymers of tetrafluoroethylene and trifluoronitrosomethane but they were cross-linked with difficulty and the

vulcanisates had little strength. Somewhat better results were obtained using

carboxynitrosopolymers of the type

-NO-



I



CF,



CF, -CF, -NO-



I



CF, (CF,), COOH



in which perfluoro(nitrosobutyric acid) was used as the cure site monomer.



Thermoplastic Fluoroelastomers



383



In general the nitroso rubbers also suffer from a poor resistance to ionising

radiation, sensitivity to degradation by organic bases, highly toxic degradation

products and an exceptionally high cost. The advent of the rubbers based on

perfluoro(methy1 vinyl ether) considered above and of the phosphonitrilic

elastomers considered below would appear to put the commercial future of these

materials in extreme doubt.

These last named materials may be considered as derivatives of the inorganic

rubber, polyphosphonitrilic chloride, discovered by Stokes in 1895. This was

prepared by the reaction of phosphorus pentachloride with ammonium chloride

as follows:

n PC1,



+



nNH, CI



__+



120T



3



(NPCl,),



+



4nHC1



This material had poor hydrolytic stability and was no more than a laboratory

curiosity. Treatment with sodium trifluoroethoxide and heptafluorobutoxide has

recently been found to yield a useful fluorophosphazene polymer:

n NaOCH,CF,



OCH,CF,



-



+ 2nNaC1

n NaOCH, (CF,), CF,H



OCH,(CF,),CF,H-,



The rubber has a very low Tg of -68"C, excellent hydrolytic stability and

excellent resistance to ozone, solvents and acids. In addition the rubber does not

burn even in an oxidising atmosphere. Although its properties are virtually

unchanged in the range -75 to + 120°C it does not possess the heat resistance of

other fluoroelastomers. This polymer was marketed by Firestone in the mid1970s as PNF rubber, but in 1983 the Ethyl Corporation obtained exclusive rights

to the Firestone patents and the polymer is now marketed as Eypel F.

In addition to the elastomers already described, others, have been produced on

an experimental scale. These include the perfluoroalkylenetriazines with their

unsurpassed thermal oxidative stability for an elastomer but with many offsetting

disadvantages, and poly(thiocarbony1 fluoride). It is probably true to say that

material does not have any outstanding desirable property that cannot now be

matched by an alternative and commercially available material.



13.11 THERMOPLASTIC FLUOROELASTOMERS

Over the past 40 years there have been a number of developments that have

resulted in the availability of rubbery materials that are thermoplastic in nature

and which do not need chemical cross-linking (vulcanisation or setting) to

generate elastomeric properties (see also Section 11.8 and 31.2). This approach

has been extended to the fluoroelastomers.



384 Fluorine-containing Polymers

The Japanese company Daikin Industries has marketed block copolymers of

the ABA type where B is a soft segment that is a terpolymer of vinylidene

fluoride, hexafluoropropene and tetrafluoroethylene and A is a hard segment

which is either a polyvinylidene fluoride segment or an ethylene, tetrafluoroethylene, hexafluoropropene copolymer. If desired, in order to enhance the

properties, the soft segment may be thermoset either by radiation or chemical

curing mechanisms. These polymers are made by free radical polymerisation of

the B monomers in the presence of organic iodides. At the end of this reaction

monomer(s) for the hard segment are charged into the reactor and the terminal

iodines cleaved by radicals leaving free radical ends which can initiate chain

extension polymerisation of the A segment monomers.

The polymers are marketed under the name Dai-el. Dai-el T530 has a hard

segment based on ethylene, tetrafluoroethylene and hexafluoropropene which

has a melting point of 220"C, tensile strength of 12 MPa, a resilience of 10% and

a 24 h compression set @50°C of 1 1 %. Dai-el T630, with the hard segment based

on vinylidene fluoride has a lower melting point of 160"C, a tensile strength of

only 2 MPa and a compression set (24 h @ 50°C) of 80%.



13.12 MISCELLANEOUS FLUOROPOLYMERS



In addition to the fluoroplastics and fluororubbers already described other

fluoropolymers have been marketed. Polymers of hexafluoropropylene oxide are

marketed by Du Pont (Krytox). These materials have a low molecular weight

(2000-7000) and are either oils or greases. The oils are uses as lubricants, heat

transfer fluids and non-flammable oils for diffusion pumps. The greases are also

used as lubricants. They have good heat and oil resistance but it is said that

explosions may result from contact with the surfaces aluminium or magnesium

cuttings.

Another Du Pont material (XR-resin) is prepared by copolymerisation of

tetrafluoroethylene and the following sulphonyl fluoride vinyl ether:



Saponification to the sulphonic acid yields the product marketed as Nafion.

This material is said to be permselective in that it passes cations but not anions.

It is used as a membrane material in electrochemical processes, in for example

the manufacture of sodium hypochlorite.

Very similar materials have been produced by Asahi Glass which are

copolymers of tetrafluoroethylene and o-carbalkoxy-perfluoroalkoxy vinyl

ethers of the general structure

CF2 =CF-(O-CF~-CF(CF~))-O-(CF~),-CO-OR

Films of the copolymers are, as with Nafion, saponified and used for

permselective membranes. They have a much higher tensile strength than

the Du Pont material and are also claimed to have a higher ion exchange

capacity.

An interesting aromatic fluoro compound is polytrifluoromethylstyrene, which

is claimed to have excellent optical properties (ref. 14).



Reviews



385



References

1 German Patent, 677,071; French Patent, 796, 026; British Patent, 465, 520 (IG Farben)

2. U.S. Patent, 2,230,654 (Kinetic Chemicals Inc.)

3. U S . Patent, 2,393,967 (Du Pont)

4. U.S. Patent, 2,534,058 (Du Pont)

5. THOMAS, P E., LONTZ, I. F., SPERATIC, c. A,, and MCPHERSON, I. L., SOC.Plastics Engrs J . , 12,(5) 89

.

(1956)

6. Technical Trade Literature, IC1 Ltd. (Plastics Division), Welwyn Garden City

7. BOWLEY, G. w., Plastics Progress 1957 (Ed. P. Morgan), Iliffe, London (1958)

8. WHITCUT, H. M., Plastics Progress I955 (Ed. P. Morgan) Iliffe, London, p. 103 (1956)

9. U S . Patent, 2,689,241 (M. W. Kellogg)

10. NEWKIRK, A. E., J . Am. Chem. SOC.,68, 2467 (1946)

11. KAWNI, H., Japan J . Appl. Phys., 8, 975 (1969)

12. ZIMMERMAN, R. L., SUCHICITAL, c., and FUKADA, E., J . Appl. Polymer Sci., 19, 1373 (1975)

13. SUSSNER, H., and DRANSFELD K., J. Polymer Sci. (Phys.), 16 529 (1978)

14. B ~ M E R ,B. and HAGEMANN, H ., Angew. Makromol. Chem., 109-110, 285 (1982)



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SCHILDKNECHT, c.E., Vinyl and Related Polymers, John Wiley, New York (1952)

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2nd Edn, pp. 805-831 (1966)

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COOK, D.



(1972)

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FITZ, H.,



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