PERFECTLY ALTERNATING SEGMENTED POLYIMIDE-POLYDIMETHYL SILOXANE COPOLYMERS VIA TRANSIMIDIZATION

New strategies for the synthesis of perfectly alternating segmented po lyimide-polydimethyl siloxane copolymers were developed by utilizing a transimidization method. Imide oligomers endcapped with 2-aminopyrimi dine were reacted with aminopropyl terminated (dimethyl siloxane) olig omers to afford perfectly alternating segmented imide siloxane copolym ers. The polymerization was conducted in solvents such as chlorobenzen e and chloroform. High molecular weight, fully imidized perfectly alte rnating segmented imide siloxane copolymers were obtained within 2 h a t temperatures of 60-110-degrees-C. The mechanism of the reaction was further elucidated via model compounds and NMR characterization. The b lock copolymers exhibited two T(g)S due to the microphase separation o f the polyimide and polysiloxane phases. The T(g) of the polyimide pha se was a function of the length of the polyimide block. However, parti al phase mixing was also evident from the DSC results on the imide sil oxane copolymers prepared with low molecular weight polyimide. segment s. Thermooxidative stability and tensile properties of the perfectly a lternating segmented imide siloxane copolymers were found to be princi pally dependent on the amount of poly(dimethyl siloxane) incorporated in the copolymer and did not correlate with the poly(dimethyl siloxane ) or polyimide block lengths. The stress-strain behavior of both solve nt cast films or molded films is also reported. (C) 1994 John Wiley & Sons, Inc.