Olefin copolymers thermoplastic elastomers

Keywords Catalyzed olefin polymerization, Chain shuttling catalysis, Chain transfer, Olefin block copolymers, Thermoplastic elastomers... 

Thermoplastic Olefin. These thermoplastic elastomers are primarily blends, or block or graft copolymers, of ethylene/propylene rubber with polypropylene. 

In 1982 numeroU.S. Patentent applications for blends of linear low-density polyethylenes, LLDPE, with other polyolefins, co-polyolefins, and olefinic elastomers have been filed. For example, ethylene copolymers, thermoplastic elastomers (TPO), EPDM, EPR, EVAc, maleated polypropylene, and PP-MA have been used... 

Ethylene-cyclo-olefin copolymers have been known since 1954 (DuPont USP2 721 189) but these materials only became of importance in the late 1990s with the development of copolymers of ethylene and 2-norbomene by Hoechst and Mitsui using metallocene technology developed by Hoechst. The product is marketed as Topas by Ticona. By adjustment of the monomer ratios polymers with a wide range of Tg values may be obtained including materials that are of potential interest as thermoplastic elastomers. This section considers only thermoplastic materials, cyclo-olefins of interest as elastomers are considered further in Section 11.10. 

Obviously, there exists severe interplastics competition, e.g. PP vs. ABS, clarified PP vs. PS, PA, PVC, HDPE and PS (Table 10.7). A wide range of cross-linked and thermoplastic elastomer applications, from footware to automotive parts and toothbrushes, are adopting new metallocene-catalysed polyolefin elastomers (POEs). These low-density copolymers of ethylene and octene were first accepted as impact modifiers for TPOs, but now displace EPDM, (foamed) EVA, flexible PVC, and olefinic thermoplastic vulcanisates (TPVs). Interpolymer competition may also result from... 

Thermoplastic elastomers (TPEs) are either block copolymers (SBS, SEES, SEPS, TPU, COPA, COPE) or blends, such as TPO (elastomer/hard thermoplastic, also referred to as thermoplastic olefin) and TPV (fhermoplastic vul-canizafe, blend of a vulcanized elastomer and a hard fhermoplastic). These types represent the majority of fhe TPEs other types are either specialty or small-volume materials. 

The living character of organolithium polymerizations makes such processes ideally suited for the preparation of pure as well as tapered-block copolymers. Diene-olefin pure-block copolymers have become important commodities because of their unique structure-property relationships. When such copolymers have an ABA or (AB) X [A = polyolefin, e.g., polystyrene or poly(a-methylstyrene) B = polydiene, e.g., polybutadiene or polyisoprene and X = coupling-agent residue] arrangement of the blocks, the copolymers have found use as thermoplastic elastomers (i.e., elastomers that can be processed as thermoplastics). 

Olefinic thermoplastic elastomers are block copolymers or blends of polyolefins — commonly, polypropylene, which forms the hard crystalline block, and another olefin block, most commonly ethylene or EPDM. Some less common soft segments include natural rubber, nitrile rubber, and EVA. Olefinic thermoplastic elastomers exhibit better processability than neoprene and have excellent resistance to oils. Therefore, they offer attractive replacements for neoprene in oil-resistant wire and cable insulation. 

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). 

The category of elastomers includes a wide range of products, such as natural rubber (NR), styrene-butadiene rubber (SBR), styrene-butadiene-styrene copolymer (SBS known as thermoplastic rubber), styrene-isoprene-styrene copolymer (SIS), polyurethane rubber, polyether-polyester copolymer, olefinic copolymers, ethylene-propylene rubber (EPR) and so on (see also Table 3.16). 

Let us first review the various thermoplastic elastomers used in automotive applications. These are styrenic block copolymers (SBCs), thermoplastic olefins (TPOs) (cross-linked... 

A patent on reactor-blended thermoplastic olefinic elastomer, R-TPO, was disclosed. Thus, PE was polymerized in the presence of an active catalyst and an already polymerized olefinic copolymer (e.g., ethylene-co-1-butene) or the sequence was reversed. The blend had superior resistance to environment stress cracking, and the blown film showed few fish eyes... 

While the range of the new metallocene-based polymers includes such specialty polymers as cyclo-olelin copolymers (COC), syndiotactic polystyrene, ethylene/ styrene copolymers, which are stiU in the developmental stage, commercially, the most prominent candidates are the elhylene/a-olefin copolymers such as ethylene/ butylene or hexene copolymers (Exxon s Exact ) or ethylene/l-octene copolymers (Dow s Engage and Affinity ). Depending on the comonomer content, these copolymers have been classified as plastomers or elastomers. At comonomer levels of >25 %, the copolymers exhibit the characteristics of thermoplastic elastomers such as high softness, toughness, flexibility, and resilience and hence been referred to as polyolefin elastomers (POE). CompositionaUy, these POEs usually contain 65 % ethylene and 35 % octene-1, hexene-1, or butene-1 as comonomers. 

A polymer is a material composed of large macromolecules. These macromolecules are formed by chains of hundreds or thousands of connected (polymerized) monomer molecules. The three main classes of polymers are thermoplastics, elastomers and thermosets. They differ in the degree of cross-linking of their macromolecules -from no cross-linking (thermoplastics) to moderate cross-linking (elastomers, rubbers) to high cross-linking (thermosets). Thermoplastics commonly used in microfluidics include materials like polymethylmethacrylate (PMMA), polycarbonate (PC), polyethylene terephthalate (PET) or cyclic olefin copolymers (COC). Silicones (like poly-dimethylsiloxane, PDMS) are a typical class of elastomers. Thermosets include photoresist materials like SU-8 and others. 

---