Ordered structural evolution and relaxation behaviors of a series microphase separated

A series of ``hairy-rod'' polyimides, BBPA(n), with multiple alkyl side chains were synthesized. It was found that these polyimides possess a micro-phase separation between the backbones and side chains. This led to the formation of ordered structures in two different length scales, of which both are hexagonal packing: one is attributed to the alkyl side chains on the sub-nanometer scale, and another is for the whole polymer chains on the nanometer scale. The development of the hexagonal structure on the sub-nanometer scale was critically dependent upon the lengths of the alkyl side chains. Three relaxation processes were captured by dynamic mechanical analysis (DM), i.e., segmental motion of the backbones, $\alpha $; the melting of the side chain crystals, $\beta _{1}$, which exits only for the materials with longer side chains (n = 18,16); and the subglass relaxation of side chains, $\beta _{2}$. The peak relaxation temperature of the $\alpha $ process decreases with increasing the length of side chain, while the one of the $\beta _{2}$ process increases. The activation energy of the $\alpha $ relaxation is relatively independent on the length of side chain, whereas, $\beta _{2}$ process shows the increasing of activation energy with increasing the length of side chain.