Accession Number : AD0675960

Title :   THE EQUILIBRIUM MELTING OF HOMOPOLYMERS.

Descriptive Note : Technical rept.,

Corporate Author : RENSSELAER POLYTECHNIC INST TROY N Y DEPT OF CHEMISTRY

Personal Author(s) : Prime,Robert B.

Report Date : 01 SEP 1968

Pagination or Media Count : 175

Abstract : Three polyethylenes of different molecular weight distribution and four fractions of polyethylene were crystallized to extended chain crystals. The molecular weight distribution was compared with the crystal size distribution revealed by electron microscopy. The melting of the crystals was recorded as a function of temperature and time by dilatometry and differential thermal analysis. The morphology of partially molten samples was analyzed by electron microscopy after quenching. The following results were obtained: In all samples eutectic separation occurred up to a molecular weight of 10,000. Larger molecular weights collect in mixed crystals. The melting of homopolymers undergoing eutectic separation can be calculated using a melting equation based on the Flory-Huggins theory of mixing. A computer program was developed for the necessary calculations. Wherever the mixed crystals start to melt, experimental data show a more abrupt melting at a lower temperature than calculated data assuming eutectic separation. The morphological studies show that melting begins from the ends and thinner portion of a lamella and proceeds in a direction perpendicular to the chain direction. Multiple peaks before final melting peak are caused by low molecular weight fractions which possibly form narrow distribution mixed crystals. (Author)

Descriptors :   (*POLYMERS, MELTING), (*POLYETHYLENE PLASTICS, MELTING), MOLECULAR WEIGHT, CRYSTALS, ELECTRON MICROSCOPY, DIFFERENTIAL THERMAL ANALYSIS, EUTECTICS, THESES

Subject Categories : Plastics
      Atomic and Molecular Physics and Spectroscopy

Distribution Statement : APPROVED FOR PUBLIC RELEASE