Considerations on the Crystallization with Chain Folding in Polymers

Abstract

In 1962 Flory (J.A.C.S. 84, 2857) showed that the fraction of stems in a lamellar polymer crystal, that is connected by folds in one of the lamellar end planes, is about 1/2. It is here emphasized that the derivation of this ratio is rigorous, and does not allow deviations such as discussed in literature of late. In extending the arguments to solution-grown crystals it is argued, that also here folding must be considered as a compromise, resulting from the inability of the chains to make large movements in lateral directions in the solution. Chain folding is furthermore shown to be promoted by the local flow pattern resulting from the overcrowding in the amorphous or the solvent phase. The fraction of the stems connected to tie molecules at one of the crystal faces in a melt grown crystal is found to be close to 1/4. It is shown that crystallization can proceed without anisotropy being induced in the amorphous phase.