Vulcanization diene rubbers

Ethylene-propylene-diene rubber is polymerized from 60 parts ethylene, 40 parts propylene, and a small amount of nonconjugated diene. The nonconjugated diene permits sulfur vulcanization of the polymer instead of using peroxide. 

Ethylene—Propylene Rubber. Ethylene and propjiene copolymerize to produce a wide range of elastomeric and thermoplastic products. Often a third monomer such dicyclopentadiene, hexadiene, or ethylene norbomene is incorporated at 2—12% into the polymer backbone and leads to the designation ethylene—propylene—diene monomer (EPDM) mbber (see Elastomers, synthetic-ethylene-propylene-diene rubber). The third monomer introduces sites of unsaturation that allow vulcanization by conventional sulfur cures. At high levels of third monomer it is possible to achieve cure rates that are equivalent to conventional mbbers such as SBR and PBD. Ethylene—propylene mbber (EPR) requires peroxide vulcanization. 

Ethylene—Propylene (Diene) Rubber. The age-resistant elastomers are based on polymer chains having a very low unsaturation, sufficient for sulfur vulcanization but low enough to reduce oxidative degradation. EPDM can be depicted by the following chain stmcture ... 

Compatibilization along with dynamic vulcanization techniques have been used in thermoplastic elastomer blends of poly(butylene terephthalate) and ethylene propylene diene rubber by Moffett and Dekkers [28]. In situ formation of graft copolymer can be obtained by the use of suitably functionalized rubbers. By the usage of conventional vulcanizing agents for EPDM, the dynamic vulcanization of the blend can be achieved. The optimum effect of compatibilization along with dynamic vulcanization can be obtained only when the compatibilization is done before the rubber phase is dispersed. 

Naskar, M., Debnath, S.C., and Basu, D.K. Effect of Bis (Diisopropyl) Thiophosphoryl Disulfide on the Co-Vulcanization of Carboxyhc Acrylonitrile Butadiene Rubber and Ethylene Propylene Diene Rubber Blends. Rubber Chem. Technol. 75(3), 309-322, July/August 2002. 

The accelerated sulfur vulcanization of general-purpose diene rubbers (e.g., NR, styrene-butadiene rubber [SBR], and butadiene rubber [BR]) by sulfur in the presence of organic accelerators and other rubbers, which are vulcanized by closely related technology (e.g., ethylene-propylene-diene monomer [EPDM] mbber, butyl rubber [HR], halobutyl mbber [XIIR], nitrile rubber [NBR]) comprises more than 90% of all vulcanizations. 

Most accelerators used in the accelerated sulfur vulcanization of other high diene rubbers are not applicable to the metal oxide vulcanization of CR. An exception is the use of so-called mixed-curing system for CR, in which metal oxide and accelerated sulfur vulcanization are combined. Along with the metal oxides, TMTD, DOTG, and sulfur are used. This is a good method to obtain high resilience and dimensional stability. 

Some special vulcanizing agents can vulcanize diene rubbers such as NR, SBR, and BR. They are described in the following sections. 

Diene rubbers can be vulcanized by the action of phenolic compounds like phenol-formaldehyde resin (5-10 phr). Resin-cured NR offers good set properties and low hysteresis [54]. 

A high diene rubber can also be vulcanized by the action of a dinitrosobenzene, made in situ by the oxidation of a quinonediooxime (Figure 14.13) [56-60] incorporated into the rubber together with the vulcanizing agent lead peroxide. 

Another vulcanizing agent for diene rubbers is m-phenylenebismaleimide. A catalytic free-radical source such as dicumyl peroxide or benzothiazyldisulfide (MBTS) is commonly used to initiate the reaction [61]. Phenolic curatives, benzoquinonedioxime, and m-phenylenebismaleimide are particularly useful where thermal stability is required. 

These two rubbers are prepared by halogenation of the butyl. Halogenation gives increased cure reactivity. As a result, improvement occurs in vulcanization rates resulting in improved properties over butyl. The state of cure and reversion resistance and covulcanization with other diene rubbers can also be suitably monitored. CIIR and BIIR vulcanizates have lower gas permeability,... 

Abbreviations y x AFM AIBN BuMA Ca DCP DMA DMS DSC EGDMA EMA EPDM FT-IR HDPE HTV IPN LDPE LLDPE MA MAA MDI MMA PA PAC PB PBT PBuMA PDMS PDMS-NH2 interfacial tension viscosity ratio atomic force microscopy 2,2 -azobis(isobutyronitrile) butyl methacrylate capillary number dicumyl peroxide dynamic mechanical analysis dynamic mechanical spectroscopy differential scanning calorimetry ethylene glycol dimethacrylate ethyl methacrylate ethylene-propylene-diene rubber Fourier transform-infra-red high density polyethylene high temperature vulcanization interpenetrating polymer network low density polyethylene linear low density polyethylene maleic anhydride methacrylic acid 4,4 -diphenylmethanediisocyanate methyl methacrylate poly( amide) poly( acrylate) poly(butadiene) poly(butylene terephtalate) poly(butyl methacrylate) poly(dimethylsiloxane) amino-terminated poly(dimethylsiloxane)... 

In order to overcome thfe drawbadr, new types of multi-unsaturated hydrocarbon monomers have been synthedzed in recent years and their behavior in ethylene-propylene copolymerization has been extensively studied. Such mcmomers are characterized by the presence of one unconjugated double bond suitable for copolymerization and of a system of two or three cmijugated double bonds, the high reactivity of which makes them competitive with conventional diene rubbers in sulfur vulcanization despite their low concentration. 

Currently, vulcanization processes for natural rubber and other diene rubbers are being carried out by reacting nitrophenols with dusocyanates. In this way, cross-links of the urea type are produced, as shown in the following diagram ... 

Phenanthroline in the presence of heavy metals acts as an activator of the polymerization of vinyl compounds - and other olefins. " It also assists the dimerization of olefins in the presence of titanium catalysts. - It enhances the metal catalyzed oxidation of ascorbic acid and dimethyl sulfoxide. On the other hand, on its own it can inhibit several polymerization processes. - It also stabilizes butadiene and isoprene and prevents their dimerization. It prevents peroxide formation in ether, inhibits the vinylation of alcohol and stabilizes cumyl chloride. It accelerates the vulcanization of diene rubbers and copolymers. 1,10-Phenanthroline catalyzes the autooxidation of linoleic and ascorbic acids in the absence of metals. ... 

Dimethyldithiocarbamatocopper Dimethyidithiocarbamic acid copper salt EINECS 205-287-8 Hermat Cu NSC 32947 Wolfen. Accelerator for butyl rubber, ethylene-propylene-diene rubbers, for high-speed vulcanization of SBR, UR, EPDM. Solid mp >300 d = 1.75 slightly soluble in organic solvents. Akrochem Chem. Co. Akzo Chemie Vanderbilt R.T. Co. Inc. 

Cure-rate mismatch is extreme when the blends constitute high unsaturated diene mbbers like NR, and low unsaturation rubbers like EPDM. It involves the migration of polar curatives from the low unsaturation phase to a more polar high unsaturation phase, further undercuring the low unsaturation phase (11-13,34) and it has been shown that unvulcanized EPDM exists in the vulcanized blend with NR (35). Several approaches have been made to obtain a cocured blend vulcanizate of NR-EPDM without sacrificing the physical properties by (1) increasing the unsaturation of EPDM elastomer so that the cure rate becomes at par with NR or other diene rubbers... 

In addition to the components of the vulcanization system, several other additives are commonly used with diene rubbers. Rubbers in general, and diene rubbers in particular, are blended with many more additives than is common for most thermoplastics with the possible exceptions of PVC. The major additional classes of additives are ... 

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