Siloxane elastomers, thermoplastic

The same method was used to prepare thermoplastic siloxane elastomers based on poly(arylenevinylenesiloxanes) compounds [75]. The polyhydrosi-lylation was then performed between an a, (w-dialkenylarylenevinylene and an organosilicon compound containing two Si-H, in the presence of diCpPtCb as shown in Scheme 27. 

More recently, we have also reported the synthesis of thermoplastic siloxane elastomers based on hybrid polysiloxane/polyimide block copolymers (the hybrid polysiloxane being fluorinated or not) that were obtained through polyhydrosilylation of dienes with a,dihydrooligosiloxanes [76-78], as follows ... 

Linear polysiloxanes having reactive terminal groups are often condensed with reactive orgaiuc polymers. For example, hydroxy-terminated siloxanes can be condensed with a carboxy-terminated polyester, as illustrated in equation (28). The resulting polymers behave as thermoplastic elastomers, having some of the desirable properties of both siloxanes and polyesters. Similar condensation reactions have been used to synthesize siloxane copolymers with polyamides, polyethers, polycarbonates, and so on. 

Hybrid versions of silicone-thermoplastic semi-IPNs have been developed (19). A hybrid interpenetrating network is one in which the cross-linked network is formed by the reaction of two polymers with structurally distinct backbones. Hydride-functionalized siloxanes can be reacted with organic polymers with pendant unsaturated groups such as polybutadienes (5) in the presence of platinum catalysts. Compared with the polysiloxane semi-IPNs discussed earlier, the hydride IPNs tend to maintain mechanical and morphologically derived properties, whereas properties associated with siloxanes are diminished. The probable importance of this technology is in cost-effective ways to induce thermoset characteristics in thermoplastic elastomers. 

Starting from these aminofunctional siloxanes, PDMS-urea block copolymer can be obtained easily [6]. The synthesis is performed by polyaddition of aminoaikyl-terminated polydimethylsiloxanes with diisocyanates to yield thermoplastic silicone elastomers (TPSE). The reaction between the amino and the isocyanate group gives highly polar urea groups, which solidify at room temperature (Scheme 1). 

The title block copolymers with characteristics ranging from thermoplastic elastomers to polyethylene-like thermoplastics are obtained from ring opening polymerization of hexamethylcyclotrisiloxane with living a,(D-dilithiopoly-styrene. Chain scissions and oligomerizations which usually complicate siloxane polymerization are avoided, and molecular parameters regulating physical and mechanical properties are conveniently controlled to provide a unique family of thermoplastic materials. 

This interesting behavior of the ABA triblock copolymers is not a unique feature of the styrene-diene stmcture, but can be found in the case of other analogous chemical structures. Thus thermoplastic elastomers have been obtained from other triblock copolymers, where the dienes have been replaced by cyclic sulfides (Morton et al., 1971), cyclic siloxanes (Morton et al., 1974), or alkyl acrylates (Jerome, 2004) poly(alkyl methacrylate) end blocks have also been investigated (Jerome, 2(X)4). 

Chem. Descrip. Reactive epoxy-functional siloxane oligomer in water Uses Adhesion promoter between inorg. materials (glass, minerals, metals) and org. polymers (thermosets, thermoplastics, elastomers) surface treatment aid for mins. reinforcement aid for glass fibers primer for glass and metals surface modifier for org. materials additive for water-borne polymers... 

A rubbery/crystalline combination consisting of poly(dimethyl siloxane)/poly(diphenyl siloxane). The crystalline, high-melting diphenyl siloxane blocks alternate with rubbery dimethyl siloxane blocks, and the resulting copolymer behaves like a thermoplastic elastomer. 

Block polymers with dimethyl siloxane units are produced in large number, for example, with polyfstyrene) or poly(carbonate) blocks. Triblock polymers with central siloxane blocks and ""rigid outside blocks exhibit the typical properties of thermoplastic elastomers (see also Chapter 37.3.4). 

In its simplest terms, the titanate function (1) mechanism may be classed as proton-reactive through solvolysis (monoalkoxy) or coordination (neoalkoxy) without the need of water of condensation, while the silane function (1) mechanism may be classed as hydroxyl-reactive through a silanol-sUoxane mechanism requiring water of condensation. The silane s silanol-siloxane water of condensation mechanism limits its reactions to temperatures below 100 °C, thereby reducing the possibility of in situ reaction in the thermoplastic or elastomer melt above 100 °C as is possible with titanates. In addition, a variety of particulate fillers such as carbonates, sulfates, nitrides, nitrates, carbon, boron and metal powders used in thermoplastics, thermosets, and cross-linked elastomers do not have surface silane-reactive hydroxyl groups, while almost all three-dimensional particulates and species have surface protons, thereby apparently making titanates universally more reactive. 

A new, low-Tg siloxane thermoplastic elastomer with a functionalizable backbone was recently synthesized via sequential anionic ring-opening polymerization and coupling. The attachment of a photoresponsive liquid crystal led to a rapid thermoplastic photoactuator. Polystyrene was used as a hard glassy end block, and poly(vinylmethylsiloxane) served as the soft middle segment in this polystyrene-b-poly(vinylmethylsiloxane)-b-polystyrene ABA triblock copolymer. 

Polyaddition of organosilicon dihydrides, mainly dihydro(poly)siloxanes to dialkenyl-substituted organic compounds also known as hydrosilylation copolymerization, leads to polycarbosiloxanes with functionalized organic segments (359). Platinum-catalyzed polymerization hydrosilylation of a,allyl-substituted bisphenols, imides, or amides leads to the synthesis of block copolymers that are useful thermoplastic elastomers (Scheme 40). 

Marija Pergal, MSc, works at the Department for Polymeric Materials, Institute for Chemistry, Technology and Metallurgy since 2003 as Research Scientist. Since 2007 she is also Teaching Assistant for the course Chemistry of Macromolecules at Department of Chemistry, University of Belgrade. Her research interests are focused on synthesis and characterization of siloxane homopolymers and copolymers, especially thermoplastic elastomers based on poly(butylene terephthalate) and polyurethanes, as well as polyurethane networks based on hyperbranched polyester. In addition to physico-chemical, mechanical and surface properties of polymers, her particular interest is directed towards the study of biocompatibility of polymer materials. 

Block polymers containing polydimethylsiloxane soft blocks have been the subject of considerable recent synthetic activity. In particular, polydimethylsiloxane-b-polystyrene polymers have received considerable attention as thermoplastic elastomers. For the most part, anionic polymerization methods have provided the most successful routes to the preparation of these block polymers. Among the most notable papers in this field are those of Dean, Saam et al, Juliano, and Bajaj and coworkers. Recently Chaumont and his coworkers have prepared polydimethylsiloxane-b-polystyrene polymers by the platinum catalyzed condensation polymerization of a,o)-vinyl terminated polystyrene oligomers with a,o)-hydrogen terminated polydimethyl-siloxanes. 

The hydrosilylation reaction has also been employed in the reverse way. A poly(dimethyl-siloxane) backbone exhibiting a number of silane (Si-H) functions is reacted with a polystyrene or a poly(methyl methacrylate) fitted at its chain end with allyloxy groups. The latter species can be obtained readily by reacting a living anionic polymer first with oxirane and then with allyl bromide. The hydrosilylation reaction yields poly(dimethylsiloxane- ra/t-styrene) or poly(dimethylsiloxane-graft-mQthyl methacrylate), which have been characterized as such. They exhibit typical behavior of thermoplastic elastomers over a rather broad range of compositions. ... 

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