Polyolefin elastomers commercial production

Within the past five years, commercial interest in metallocene catalyst components for the polymerization of olefins has increased enormously. Commercial production of a rising number of polyolefin types from different companies is creating a burgeoning and highly diversified demand for metallocenes. New brand names (e. g., Metocene (Basell), Elite (Dow Chemical), Engage (DuPont), Exact (ExxonMobil), Luflexen (Basell), Apel (Mitsui Chemicals), Borecene (Borealis), Finathene (TotalFinaElf), Topas (Ticona), just to name a few) characterize polyolefins such as PE, elastomers, PP, cycloolefin copolymers (COCs) and PS from metallocene-type catalysts [1-3]. 

Butyl rubber is one of the older synthetic rubbers, having been developed in 1937. Because of the saturated nature of a polyolefin elastomer, the commercial polymer is actually a copolymer of isobutylene and isoprene. The isoprene is added to provide cure sites. In addition, halogenated (bromo or chloro) derivatives are available. The halogenated products improve the mixing and cure compatibility with the more common unsaturated rubbers such as natural or styrene-butadiene rubber. 

A series of compounded flame retardants, based on finally divided insoluble ammonium phosphate together with char-forming nitrogenous resins, has been developed for thermoplastics.23 These compounds are particularly useful as intumescent flame-retardant additives for polyolefins, ethylene-vinyl acetate, and urethane elastomers. The char-forming resin can be, for example, an ethyle-neurea-formaldehyde condensation polymer, a hydroxyethyl isocyanurate, or a piperazine-triazine resin. Commercial leach-resistant flame-retardant treatments for wood have also been developed based on a reaction product of phosphoric acid with urea-formaldehyde and dicyandiamide resins. 

Two of the most interesting aspects of the catalysts used in this work are their ability to copolymerize ethylene and a-olefins with polar monomers and their inertness toward impurities, allowing for a relatively straightforward production of these types of polymers in SCCO2. Although the activity of these catalysts is still rather low for commercial use, it may be expected that this will improve significantly in the near future. This would enable the development of clean polyolefin production based on C02-technology, for which future applications may be expected in the production of EPDM and other elastomers. 

Other thermoplastic elastomer combinations, in which the elastomer phase may or may not be cross-linked, include blends of polypropylene with nitrile (26), butyl (28), and natural (29) rubbers, blends of PVC with nitrile rubber and plasticizers (30-32), and blends ofhalogenated polyolefins with ethylene interpolymers (30). Commercially important products (33,34) based on blends of polystyrene with S-B-S and oil and also on blends of polypropylene with S-EB-S and oil are described later in this article. They are also considered as thermoplastic elastomer combinations. The oils nsed in these prodncts are nsnally hydrocarbons but blends with silicone oils have also been described (35). Collectively, all thermoplastic elastomers of this type (both bends and dynamic vnlcanizates) are referred to herein as hard polymer/elastomer combinations. 

ABS graft polymers and of a polymer/softener/soot/ mineral filler mixture. TG-DTA curves have also been used to evaluate antioxidation activities of various types of antioxidants [305], TG-DTA and PDSC are suitable for product quality control as exemplified by OIT measurements for commercial engineering plastics, polyolefins and elastomers [306], Applications of TG-DTA outnumber those of TG-DSC. 

Other elastomer blends of commercial utility have been cited in the literature [96-98]. Polyolefin blends have been utilized in many forms to achieve modifications yielding environmental stress rupture resistance and to improve impact strength, flexibility, and filler acceptance [99,100]. The addition of ethylene-propylene rubber (EPR) or blends of EPR and high-density PE to PP has been specifically utilized for improving the low-temperature impact strength [101]. Low-modulus materials can be produced from EPR-PP blends containing more than 50% of EPR. These products include those under the trade names TPR, Somel, and Telcar [102-105]. Addition of rubber inclusion has been shown to yield definite improvements in the environmental stress rupture resistance [106]. Other examples of commercial rubber-based blends are impact-PS, ABS and bisphenol A polycarbonate blends and polysulfone blends made of a block copolymer of polysulfone and nylon 6 [107]. 

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