Melting of a flexible-chain polymer crystallized in a porous medium

The melting of a flexible-chain linear polymer, polyethylene oxide with M = 40 000, introduced into porous substances with a pore diameter from 40 to 1440 Angstrom, was investigated. Depending on the character of the melting, this range of pore diameters can be divided into two regions, whose bounda ry lies between 110 and 320 Angstrom. In large pores, a high degree of crys tallinity (greater than or equal to 0.7) was attained. The shape of melting curves was explained by the presence of two types of regions: the highly o rdered and the relatively less ordered. In this case, the proportion of the less ordered regions was found to increase with overcooling upon the cryst allization, In large pores, the dependence of the melting point lowering, D elta T-m, on the reciprocal pore diameter d was linear, as predicted by Gib bs-Thomson relation. It was shown that the melting point lowering was due t o contributions from the lamellar and lateral surfaces of lamellar crystall ite. In this case, lamellar crystallite probably occupied only a part of th e cross-section of a pore. The rest of the cross-section was occupied with less ordered crystalline and/or amorphous regions. In smaller pores, the ma ximal degree of crystallinity was less than or equal to 0.3, Delta T-m(1/d) dependences deviated from the linear dependence obtained for wide pores. T he lamellar surface was found not to contribute to the lowering of the melt ing point. Measurements of the transverse NMR relaxation showed that, in su ch pores, the motion in the crystalline phase was more intense.