Abstract
A homologous series of polyimides (PIs) was prepared in N-methyl-2-pyrrolidone (NMP) from 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA) and α,ω-diaminoalkanes containing 4–10 carbon atoms. For this series the well known odd-even effect was found. Whereas the PIs based on even numbered aliphatic diamines all rapidly crystallize from the melt, the PIs based on 1,7-diaminoheptane (C7) and 1,9-diaminononane (C9) stay amorphous upon cooling from the melt. The chemical structure of the synthesized PIs was confirmed by solid state 13C 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 and crystallization behaviour. This specific polymer was both prepared in NMP and in m-cresol. In NMP the poly(amic acid) intermediate was expected 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 m-cresol synthesized PI the residual amine endgroups were blocked, since it is known that these endgroups may generate branching and/or crosslinking. The endcapped poly(BPDA-DAO) synthesized in m-cresol exhibited the most optimal crystallization behaviour, which is in line with its expected, predominantly linear character.
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