PC siloxane block copolymers

In order to improve the low-temperature notched impact strength of polycarbonate while still maintaining the transparency, new polycarbonate-poly(dimethyl siloxane) block copolymers were developed (Maruvada et al. 2005). These PC-siloxane block copolymers were transparent as long as the siloxane block length was kept short (<10 units), so that fine siloxane rubber domains (10-40 nm) were... 

Siloxane blocks (see the section PC Siloxane Block Copolymers ). 

For a given notched-lzod value, a higher melt flow can be obtained via use of a copolymer than with the corresponding BPA homopolymer (e.g., Lexan resins). For example, Lexan SP grades possess almost twice the melt flow index (MFI) of the BPA homopolymer resins at a 640 J/m (12 ft Ib/in) notched Izod. The tradeoff for the increased flow is a corresponding decrease in the distortion temperature under load (DTUL) of 20°C, as shown in Fig. 14.7. These resins are being supplanted by the siloxane-BPA polycarbonate (see the section PC Siloxane Block Copolymers ), which provide an even better balance of melt flow and ductility without a significant loss in heat performance. 

PEST Blends PET with PDMS and MABS PEST and/or PC with siloxane-based vinyl-grafted copolymer PEST/PC/PPE/star-block copolymer PEST and siloxane-acrylic elastomer impact and embrittlement resistance chemical, weather, and low temperature impact resistance impact modified engineering resins impact strength at low temperature Sauers Barth, 1970 Kongo et al., 1987 Hoxmeier, 1994 Yamamoto eta/., 1992, 1994... 

Abbreviations HIPS, high-impact polystyrene ABS, acrylonitrile-butadiene-styrene graft copolymer EPDM, ethylene propylene-diene copolymer CTBN, carboxyl terminated butadiene nitrile telomer M = 5000 g/mol) PC, polyearbonate SBS, styrene-butadiene-styrene triblock copolymer SIS, styrene isoprene styrene tribloek copolymer SEBS, SBS with hydrogenated center block PU, segmented (block copolymer) polyurethanes PDMS, poly(dimethyl siloxane) FIFE, polytetralluoroethylene. 

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). 

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