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-terminated polydimethylsiloxane. The synthesis was carried out in m-cresol solution following a two-step procedure. Copolymers containing 15 and 20 wt.-% of the polydimethylsiloxane elastomer were prepared, together with the unmodified base copolymer. Infrared spectroscopy,C-13 and H-1 NMR, thermal and thermogravimetric analyses were used to characterize the copolymers. The DSC curves of all the samples showed an exotherm 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 elastomer content. Thermogravimetric analysis indicated that nd significant changes occur in the thermal stability of rubber-modified copolymers.