SYNTHESIS AND CHARACTERIZATION OF NEW SILOXANE-MODIFIED ADDITION POLYIMIDES

A new series of polyimides was synthesized by addition polymerization of 4,4'-(bismaleimido)diphenylmethane, 1,4-piperazine and an amino-ter minated polydimethylsiloxane. The synthesis was carried out in m-creso l solution following a two-step procedure. Copolymers containing 15 an d 20 wt.-% of the polydimethylsiloxane elastomer were prepared, togeth er with the unmodified base copolymer. Infrared spectroscopy,C-13 and H-1 NMR, thermal and thermogravimetric analyses were used to character ize the copolymers. The DSC curves of all the samples showed an exothe rm in the temperature range 230-280 degrees C, attributable to curing and addition reactions involving the chain-end groups. Different glass transition temperatures (T-g) were observed, depending on the elastom er content. Thermogravimetric analysis indicated that nd significant c hanges occur in the thermal stability of rubber-modified copolymers.