Ethylene-propylene-diene terpolymer production

Thioureas mainly find use for the vulcanisation of CR, epichlorohydrin (ECO) and some ethylene propylene diene terpolymer (EPDM) compounds. They show high crosslinking activity, with usually adequate compound flow time before onset of the crosslinking. In EPDMs, the thioureas are used as activators for low activity third monomer types and, in the presence of calcium oxide desiccants, in free state vulcanisation of extrudates, etc. The use of thioureas can overcome the retardation caused by the desiccant. In this case some care must be taken otherwise overcompensation may occur. Thioureas are not used in food product applications and are a known health hazard, particularly for pregnant women. 

By rapid expansion of supercritical propane solution (RESS), and isobaric crystallisation (ICSS), isotactic polypropylene and ethylene-butylene copolymers were precipitated from the supercritical solution. The RESS process produced microfibres with a trace of microparticles, while the ICSS process produced microcellular products. Improvement in thermal stability was achieved by first synthesising a thermoplastic vulcanisate from polypropylene and ethylene-propylene-diene terpolymer from a supercritical propane solution, followed by RESS. 28 refs. 

Nowadays commercial mixtures of bitumens with uncured synthetic elastomers are produced, e.g. ethylene-propylene-diene terpolymers (EPDM), styrene-butadiene sequence copolymers (SBS), and ethylene-acrylic ester-acrylic acid terpolymers (AECM). Mixtures with some thermoplastics are also commercial products, e.g. polyethylene (PE), ethylene-propylene copolymers (EPM), alpha-olefinic copolymers, atactic polypropylene (aPP), and ethylene-vinyl acetate copolymers (EVA). 

Yamada and co-workers [6] determined the degradation products in the region of ethylene-propylene-diene terpolymer (EPDM). These are listed in Table 2.1. 

Table 2.1 Characteristic degradation products of ethylene-propylene-diene terpolymer or the region ...

The high diffusion speed of small molecules (even under nearcritical conditions) in comparison with ordinary solvents and the dissolution selectivity of such systems can be used in the extraction of low-molecular organic products out of amorphous polymeric materials. Some results for acrylonitrile containing (co-) polymers/blends and thermoplastic polymers like ethylene-propylene-diene terpolymers are reported. 

Krishen [42] obtained the products listed in Table 4.10 by pyrolysis of ethylene-butadiene rubber and ethylene-propylene-diene terpolymer. He showed that the 2-methyl-2-butene peak was linear with the natural rubber content of the sample. Styrene-butadiene rubber was determined from the peak area of the 1,3-butadiene peak. The ethylene-propylene-terpolymer content was deducted from the 1-pentane peak area of the pyrolysis products. 

During the stud5dng or operation of pol3mier-based products, the most accelerated modifications take place in the thin outer layer of material, because the absorption of light prevails. The correlation between oxidation level and exposure time (Fig. 6) illustrated by the accumulation of carbonyl stmcmres and the contact angle at the surface of ethylene-propylene-diene terpolymer demonstrates the proportionality between the concentration of collected oxidation products and the physical behavior of specimen [7]. The main carbonyl strucmres (Fig. 7) appeared... 

The isoprene units in the copolymer impart the ability to crosslink the product. Polystyrene is far too rigid to be used as an elastomer but styrene copolymers with 1,3-butadiene (SBR rubber) are quite flexible and rubbery. Polyethylene is a crystalline plastic while ethylene-propylene copolymers and terpolymers of ethylene, propylene and diene (e.g., dicyclopentadiene, hexa-1,4-diene, 2-ethylidenenorborn-5-ene) are elastomers (EPR and EPDM rubbers). Nitrile or NBR rubber is a copolymer of acrylonitrile and 1,3-butadiene. Vinylidene fluoride-chlorotrifluoroethylene and olefin-acrylic ester copolymers and 1,3-butadiene-styrene-vinyl pyridine terpolymer are examples of specialty elastomers. 

Terpolymerization, the simultaneous polymerization of three monomers, has become increasingly important from the commercial viewpoint. The improvements that are obtained by copolymerizing styrene with acrylonitrile or butadiene have been mentioned previously. The radical terpolymerization of styrene with acrylonitrile and butadiene increases even further the degree of variation in properties that can be built into the final product. Many other commercial uses of terpolymerization exist. In most of these the terpolymer has two of the monomers present in major amounts to obtain the gross properties desired, with the third monomer in a minor amount for modification of a special property. Thus the ethylene-propylene elastomers are terpolymerized with minor amounts of a diene in order to allow the product to be subsquently crosslinked. 

EPDM is a terpolymer produced from ethylene, propylene, and a diene monomer that is usually 5-ethylidene-2-norbornene (ENB), see Eigure 3.12. Good EPDM properties are attainable because the stereospecific Ziegler-Natta catalysts and the newer metallocene-type catalysts are used in the polymerization of these elastomers. Much proprietary knowledge is applied with the latest catalysts to help the EPDM producers achieve a competitive advantage in the marketplace. Today, about 20% of all EPDM goes into the production of TPOs (thermoplastic olefins) or TPVs (thermoplastic vulcanizates), mainly for nontire automobile uses. (About 13% of EPDM production is used in TPO manufacture while about 7% is consumed in TPV production.)... 

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