Unsaturated terpolymers

Copolymerization of ethylene with propylene results in a random, noncrystalline copolymer that is a chemically inert and rubbery material. EPM is a saturated copolymer that can be cross-linked through the combination of the free radicals generated by peroxides or radiation. To incorporate sites for vulcanization, an unsaturated terpolymer can be prepared from ethylene, propylene, and a small amount (3 to 9%) of a nonconjugated diene (EPDM). The diene is either dicyclopentadiene, ethylidene nor-bomene, or 1,4-hexadiene. The resulting unsaturated terpolymer can be vulcanized by traditional techniques. Each of the termonomers confers different characteristics on the final elastomer. 

The A and B cure systems can be used in epichlorohydrin homopolymer (CO). The B and D cure systems can be used in unsaturated terpolymers (GECO). In addition, GECO can be cured with sulfur and peroxide cure systems. 

Organic peroxides are used in the polymer industry as thermal sources of free radicals. They are used primarily to initiate the polymerisation and copolymerisation of vinyl and diene monomers, eg, ethylene, vinyl chloride, styrene, acryUc acid and esters, methacrylic acid and esters, vinyl acetate, acrylonitrile, and butadiene (see Initiators). They ate also used to cute or cross-link resins, eg, unsaturated polyester—styrene blends, thermoplastics such as polyethylene, elastomers such as ethylene—propylene copolymers and terpolymers and ethylene—vinyl acetate copolymer, and mbbets such as siUcone mbbet and styrene-butadiene mbbet. 

EPDM is a terpolymer of ethylene, propylene, and a small amount (<10%) of an unsaturated diene third monomer to provide a cure site. Unlike the elastomers previously discussed, the unsaturation in EPDM is not in the main chain, but it is pendent to the chain. Peroxide cure gives superior aging resistance and low compression set. 

The terminal double bond is active with respect to polymerisation, whereas the internal unsaturation remains in the resulting terpolymer as a pendent location for sulfur vulcanisation. The polymer is poly(ethylene- (9-prop5iene- (9-l,4-hexadiene) [25038-37-3]. 

Some of the terpolymers containing high levels of AGE give superior sour gasoline and ozone resistance, particularly dynamic ozone resistance. Since the unsaturation is not in the polymer backbone, it can be, and apparentiy is, sacrificed under sour gasoline or ozone aging. This protection scheme is limited with the peroxide and sulfur cure systems as they involve the aHyl functionaUty of the polymer. The protection is maximized when a dinucleophilic curative, such as trithiocyanurate, is used. 

EPDM terpolymer of ethylene, propylene and a diene with the residual unsaturated... 

New copolymers based on a copolymerization of isobutylene and p-methyl-styrene with improved heat resistance have been reported [64]. Once copolymerization was accomplished, the polymer was selectively brominated in the p-methyl position to yield a terpolymer called EXXPO. In contrast to butyl and halobutyl, the new terpolymer has no unsaturation in the backbone and therefore shows enhanced thermal stability and resistance to oxidation. Useful solvent-based adhesives can be formulated using the new terpolymer in combination with block copolymers [65]. The hydrocarbon nature of the new terpolymer results in excellent compatibility with hydrocarbon resins and oils. 

Epichlorohydrin is also available as a terpolymer with a small amount of unsaturated allyl glycidyl ether. There is no ISO designation for the terpolymer, but ETER is used by ASTM. 

As with EPDM, the unsaturation is pendant to the main chain and this allows vulcanisation with sulphur, whilst preserving the stability of the main chain. The ability to be cured by sulphur also allows the terpolymer to be used in blends with other polymers, e.g., nitriles. 

The absence of any polar grouping gives this material superior low temperature performance when compared to the epichlorohydrin terpolymers, but this is at the expense of oil resistance. The unsaturated nature of the main chain confers excellent resistance to oxygen, ozone and UV light. 

Several polymers based on 1,3-dienes are used as elastomers. These include styrene-1,3-butadiene (SBR), styrene-1,3-butadiene terpolymer with an unsaturated carboxylic acid (carboxylated SBR), acrylonitrile-1,3-butadiene (NBR or nitrile rubber) (Secs. 6-8a, 6-8e), isobutylene-isoprene (butyl rubber) (Sec. 5-2i-l), and block copolymers of isoprene or... 

Z. Zhou, N. Liu, and H. Huang, Reactivity of acrylonitrile-butadiene-styrene terpolymer grafted with long-chain unsaturated carboxylic acids, Polymer, 45(21) 7109-7116, September 2004. 

Copolymers of itaconic esters with butadiene have not yet been used technically. On the other hand, acrylonitrile containing copolymers with other components have been studied from several points of view. Standard Oil Co. has claimed a terpolymer of isobutylene, butadiene, and acrylonitrile, and BASF a similar product of butadiene, acrylonitrile, and styrene. The films from these combinations are said to have high flexibility and cold resistance. However, all butadiene containing copolymers are not light fast. Copolymers of butadiene, acrylonitrile, and unsaturated dicarboxylic esters are suggested for plasticizing PVC, but they must be thermally degraded before they are combined with the polymer. 

EPDM - ASTM abbreviation for a terpolymer of ethylene, propylene, and a diene with the residual unsaturated portion of the diene in the side chain. 

EPDM terpolymers of ethylene, propylene, and a small percentage of a non-conjugated diene, which makes the side chains unsaturated. 

The novelty of isobutene-triene copolymers does not allow us to present a complete series of results since further work is in progr However, some interesting features shown by these copolymers, e. g. radical and Diels-Alder curing, hi efficiency in radical grafting, possibility of easy and controlled halogenation, allow us to expect a parallel behavior in terpol3nners containing similar unsaturations and hence permit us to draw some conclusions which comjdete thc obtained from the terpolymers study. 

As a ctmsequence of the situation depicted above, terpolymers based on ethylene and propylene are expected to contain different amounts of brandiing or gel even when they contain only single olefinic unsaturation. It has been calculated that in the case of terpo mers ba d on S-ethylidene-24iorbomene (ENB) the gel point is passed at about 02 wt % of ENB. 

Improved ABS-similar resins can be obtained by grafting SAN onto ethylene-propylene-diene terpolymers (EPDMs) which contain, usually, a much lower degree of unsaturation than polybutadiene, thus achieving hi er thermal-oxidative resis-tance However, only EPDMs containing a sufficient amount (7—10 double bonds per 1,000 C atons) of reactive unsaturations, e.g. ethylidene or isopropylidene groups, display a grafting efficiency sufiident to bring about compatibility of the ssy i se with the rubbery one and hence satisfactory final properties. 

Table 8. Relative rate constants foi the reactions of methyl radicals with isooctane and the model compounds simulating the unsaturation present in some ethylene-propylene based terpolymers...

Figure 12 shows the behavior of different terpolymers as a function of the unsaturation and the peroxide content in the formulation. The unusual trend of (V)-EPTM can be explained by the existence of another cross-linking mechanian (self-vulcanization) besides the radical one (see the next Section), while the high yield of cross-links displayed by 5-methylene-2-norbomene-EPDM is due to the high reactivity of the radical originating from the methylene double bond which undergoes, preferentially, addition reactions instead of coupling processes ... 

Another calculation was made in order to distinguish between the amount of t-butoxy radical reacting with ethylene-propylene units and that reacting with the unsaturations of some terpolymers. The results (Table 12) indicate that there is al-wsys a significant amount of t-butoxy radicals which react with the H atoms of the saturated back-bone, while in the case of (III)-EPTM 34% of (CH3)3C0 reacts with flie unsaturation when the termonomer content is only 0.1 M. The sune result k achieved in the case of ENB-EPDM when the termonomer content is four-fold end hence agrees with the experimental data of Fig. 11. However, the formation of abundant amounts of tertiary alkyl type radkals, e.g. CH2-C(CH3)-CH2, when the termonomer concoitration is low, explain the poor yield of grafting... 

The interesting behavior own mainly by (V)-EPTM was not confirmed by terpolymers containing 5,6-dimethylene-24ioibomene (X) or 5- 2 -vinyl-3 -butenyl)-2-norbomene (XI), both being model compounds of triene (V). In fact, the first EPTM contains two conju ted double bonds in obligatory dsoid conformation which were found very reactive toward methyl free radicals. The second EPTM has one bis-allylic hydrogen atom in the unsaturated system ... 

Table 18. Vulcanization kinetic parameters of some unsaturated ethylene-propylene-based terpolymers ... 

Aside from the possibility of distinguishing between two cross-linking mechanisms with other appropriate analyses (see previous Section), the data of Table 18 indicate that covulcanization processes occur, under the adopted conditions, when the cross-linking reaction rate constant of a given terpolymer is > 03 kg m min . High rate constants imply, in principle, the possibility of obtaining high values of the tensile properties (Fig. 20), even when the unsaturation concentration is low. 

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