Terpolymers, vulcanization

Compression set resistance at 200 °C was compared between a TecnoflonT poly(VDF-ter-HFP-ter-1 -hydropentafluoropropene) terpolymer vulcanized with HMDA-C, and TecnoflonT vulcanized with piperazine carbamate [131]. The results are included in Fig. 12 [131]. Curves 3 and 4 are both poly(VDF-co-HFP) copolymer vulcanizates with piperazine carbamate in the presence of trimethylenediamine carbamate and MgO for curve 3, and bisphenol in the presence of MgO for curve 4. The compression set resistance is better for curve 4, than curve 2, which is better than curve 3, and finally the worst compression set resistance is obtained for Tecnoflon T vulcanized with HMDA-C. 

Fig. 12 Compression set versus ageing time at 200 °C for several vulcanizates Tecno-flonT(poly(VDF-ter-HFP-ter-TFE) terpolymer) vulcanized with HMDA-C curve 1) TecnoflonT vulcanized with piperazine carbamate curve 2) Tecnoflon (poly(VDF-co-HFP) copolymer) vulcanized with piperazine carbamate and trimethyldiamine carbamate curve 3) Tecnoflon cured with bisphenolAF curve 4) (Reprinted with permission of Hiithig Fach Verlag) [131]...

Fig. 30 Variation of the gel fraction (full line o) and the crosslink density ( ) of irradiated poly(VDF-ter-HFP-ter-TFE) terpolymer vulcanized with HMDA-C, and variation of the crosslink density of pure terpolymer rubber (broken line) versus radiation dose (Reprinted with permission of Kluwer) [49]...

Dithiophosphates. These compounds (13) are made by reaction of an alcohol with phosphoms pentasulfide, then neutralization of the dithiophosphoric acid with a metal oxide. Like xanthates, dithiophosphates contain no nitrogen and do not generate nitrosamines during vulcanization. Dithiophosphates find use as high temperature accelerators for the sulfur vulcanization of ethylene—propylene—diene (EPDM) terpolymers. 

Ethylene-propylene-diene terpolymers (EPDM), with their inherent complexity in structural parameters, owe their tensile properties to specific structures dictated by polymerization conditions, among which the controlling factor is the catalyst used in preparing the polymers. However, no detailed studies on correlation between tensile properties and EPDM structures have been published (l,2). An unusual vulcanization behavior of EPDMs prepared with vanadium carboxylates (typified by Vr g, carboxylate of mixed acids of Ccj-Cq) has been recently reported Q). This EPDM attains target tensile properties in 18 and 12 minutes at vulcanization temperatures of 150 and l60°C respectively, while for EPDMs prepared with V0Cl -Et3Al2Cl or V(acac) -Et2AlCl, about 50 and 0 minutes are usually required at the respective vulcanization temperatures, all with dieyclopentadiene (DCPD) as the third monomer and with the same vulcanization recipe. This observation prompted us to inquire into the inherent structural factors... 

The EPM rubbers, being completely saturated, require organic peroxides or radiation for vulcanization. The EPDM terpolymers can be vulcanized with peroxides, radiation, or sulfur. 

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 ... 

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

Table 15.14. Comparison of the typical properties of the dynamically vulcanized ethylene terpolymer/PVC blends vs. similar elastomeric blends based on polypropylene...

The blends of EPDM terpolymers and isotactic PP with curing agents, such as peroxide, phenol resins, and sulfur, are termed as thermoplastic vulcanized elastomer (TPV) since the rubber domains are vulcanized. Polyolefin copolymers, such as random copolymer of propylene with ethylene, copolymers of other olefins, elastomeric PP, and elastomeric PE, are developed with recent advances of... 

We will now report the results of autohesion for homogeneous, symmetric joints of polyisoprene rubber (IR) and styrene-butadiene copolymer (SBR) both vulcanized by a sulfur-based system (Section 24.2.1), and of ethylene-propylene diene terpolymer (EPDM) crossHnked by an electron beam (Section 24.2.2). 

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. 

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