INFLUENCE OF POLYMERIZATION CONDITIONS ON MELT CRYSTALLIZATION OF PARTIALLY ALIPHATIC POLYIMIDES

A homologous series of polyimides (PIs) was prepared in N-methyl-2-pyr rolidone (NMP) from 3,3',4,4'biphenyltetracarboxylic dianhydride (BPDA ) and alpha,omega-diaminoalkanes containing 4-10 carbon atoms. For thi s series the well known odd-even effect was found. Whereas the PIs bas ed on even numbered aliphatic diamines all rapidly crystallize from th e melt, the PIs based on 1,7-diaminoheptane (C7) and 1,9-diaminononane (C9) stay amorphous upon cooling from the melt. The chemical structur e of the synthesized PIs was confirmed by solid state C-13 n.m.r. and FTi.r. spectroscopy. The PI based on BPDA and 1,8-diaminooctane (DAO) was selected for a study on the relation between chain architecture an d crystallization behaviour. This specific polymer was both prepared i n NMP and in m-cresol. In NMP the poly(amic acid) intermediate was exp ected to generate a more branched PI structure than in m-cresol, where this intermediate has never been detected. Furthermore, for both the NMP and the vn-cresol synthesized PI the residual amine endgroups were blocked, since it is known that these endgroups may generate branchin g and/or crosslinking. The endcapped poly(BPDA-DAO) synthesized in m-c resol exhibited the most optimal crystallization behaviour, which is i n line with its expected, predominantly linear character. (C) 1998 Els evier Science Ltd. All rights reserved.