Isothermal growth, thickening and melting of poly(ethylene oxide) single crystals in the bulk. Part 4.—Dependence of pathological crystal habits on temperature and thermal history
Abstract
Characteristic features of isothermal growth, thickening and melting behaviour of melt grown single crystals of low molecular weight poly(ethylene oxide) fractions are described and discussed in terms of their relevance to basic concepts of polymer crystal growth. In the narrow temperature interval where transition from once folded to extended chain growth occurs, the crystal morphology displays some spectacular modifications. The dependence of the relevant crystal habits on temperature and on thermal history are analysed in terms of the probabilities of chain deposition in the once-folded and the fully-extended conformation, while defining a series of precisely determined transition temperatures at which these probabilities are equal. It will be concluded that in these systems crystal growth proceeds with regular chain folding, determined by the free energy balance relevant to the local environment of the depositing chains.