Carbonate-siloxane block polymers

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). 

Electrical properties have been reported on numerous carbon fiber-reinforced polymers, including carbon nanoflber-modified thermotropic liquid crystalline polymers [53], low-density polyethylene [54], ethylene vinyl acetate [55], wire coating varnishes [56], polydimethyl siloxane polypyrrole composites [50], polyacrylonitrile [59], polycarbonate [58], polyacrylonitrile-polycarbonate composites [58], modified chrome polymers [59], lithium trifluoromethane sulfonamide-doped polystyrene-block copolymer [60], boron-containing polyvinyl alcohols [71], lanthanum tetrafluoride complexed ethylene oxide [151, 72, 73], polycarbonate-acrylonitrile diene [44], polyethylene deoxythiophe-nel, blends of polystyrene sulfonate, polyvinyl chloride and polyethylene oxide [43], poly-pyrrole [61], polypyrrole-polypropylene-montmorillonite composites [62], polydimethyl siloxane-polypyrrole composites [63], polyaniline [46], epoxy resin-polyaniline dodecyl benzene sulfonic acid blends [64], and polyaniline-polyamide 6 composites [49]. 

In case of direct copolymerization (Scheme 103) only 52-58% of the siloxane was incorporated into the polymer structure. The PC glass transition temperature (148 °C) was not altered by incorporation of siloxanes. Alternatively, either living PC or living polysiloxane was used to initiate ROP of cyclic siloxane or cyclic carbonate, respectively. Block copolymers were obtained by ROP of cyclic carbonate with BPA, which resulted in hydroxy-terminated PCs, followed by reaction of chlorosilane-terminated polysiloxane. Block copolymers showed good optical clarity and lowered glass transition temperature (110 °C). 

One of the most important uses of end-functionalized polymers is the preparation of block copolymers.73,74 The reactions are identical to the chain extensions already mentioned, except that the sequences being joined are chemically different. In the case of the -OSilCR Y chain ends mentioned above, R is typically (CH2)3 5 and Y can be NH2, OH, COOH, CH=CH2, and so on The siloxane sequences containing these ends have been joined to other polymeric sequences such as carbonates, ureas, urethanes, amides, and imides. 

In addition to the D units [Me2Si(Oo.s)2 ] and bisphenol A (BPA) carbonate units [21 ], the nature of the polymer synthesis (85) gives rise to single BPA units [22] isolated between two silicone blocks. The Si NMR spectrum of a sample polymer with average silicone block length hpDMs = 10 is shown in Fig. 17. Peaks A and A correspond to silicon atoms adjacent to polycarbonate blocks. The peak B corresponds to the second siloxane units in the silicone block and the rest of the... 

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