POLY(METHYLPHENYLSILYLENEMETHYLENE) - THE CARBOSILANE ANALOG OF POLY(ALPHA-METHYLSTYRENE)

The carbosilane analog of poly(alpha-methylstyrene), poly(methylphenyl silylenemethylene) (PMPSM) has been prepared by ring-opening polymeriz ation of 1,3-dimethyl-1,3-diphenyl-1,3-disilacyclobutane (1), using va rious transition-metal-based catalysts in bulk and in solution. PMPSM samples from polymerization in bulk and in solution, respectively, wer e characterized by GPC coupled with on-line low-angle laser light scat tering (LALLS) and viscometry. Absolute molecular weights were in the range of 200 000; however, polymerization in solution afforded higher yields of PMPSM. Polymerizations generally yielded atactic PMPSM with strictly alternating SiR(1)R(2)/CH2 backbone structure and monomodal m olecular weight distribution. Radical and cationic initiators proved t o be unable to effect polymerization. Polymerization of pure trans-1 a fforded PMPSM without isotactic triads. Stereoregularity as well as po lymer yields increased when polymerization was performed at low temper atures (-32 degrees C). Thermal properties of PMPSM were investigated. TGA analysis evidenced better thermal stability of PMPSM than poly(al pha-methylstyrene). PMPSM shows a T-g at 28 degrees C, which lies betw een the glass transition of poly(alpha-methylstyrene) and that of poly (methylphenylsiloxane), suggesting that poly(silylenemethylenes) may s tructurally be ranged between the analogous carbon-based polymers and the highly flexible poly(siloxanes).