X-ray diffraction study of bulk poly N-substituted maleimides

Abstract

A series of 7 aliphatic and 6 aromatic poly N-substituted maleimides (PNMI) was synthetized by free radical polymerization. The series was characterized by means of intrinsic viscosity, number average molecular weight and glass transition temperature measurements. The X-ray diffractograms of all samples show two rather broad maxima indicative of non-crystalline structures. The location of the innermost peak strongly depends on the length of the substituted groups and can be associated to intermolecular vectors. The observed linear increase of the spacing associated to the inner maximum with the number of methylene groups of the substituted aliphatic chain favours the idea of predominantly extended lateral conformations. The outer peak due is to intramolecular average distances along the backbone chain and slightly depends on the shape of the substituted groups. This repeat distance fits well with the assumption of a 4/1 helix for the chain conformation. In the aryl series a third maximum appearing as a shoulder on the outer peak suggests the presence of chain sequences coiled in 3/1 helices. The “chain bundle” dimensions calculated from the broadening of the innermost maximum are of the order of two intermolecular vectors suggesting, hence, the absence of a well defined short range order. A model for the packing of PNMI molecules with lengthy substituted groups is proposed.