Heterogeneity in the distribution of entanglement density during polymerization in disentangled ultrahigh molecular weight polyethylene

Ultrahigh molecular weight polyethylene is an engineering polymer that is widely used in demanding applications because of its unparallel properties such as high abrasion resistance, high-modulus and high-strength tapes and fibers, biaxial films, etc. In common practice, to achieve the uniaxial and the biaxial products, solution processing route is adopted to reduce the number of entanglement per chain. Another elegant route to reduce the number of entanglement is controlled polymerization using single-site catalytic system. In this publication, we address different polymerization conditions, temperature and time, to control molecular weight and the resultant entangled state. With the help of rheological studies, we show that heterogeneity in the distribution of entanglement along the chain during polymerization occurs. Because of living nature of the catalytic system, with increasing polymerization time molecular weight increases whereas the number of entanglement per unit chain decreases. These findings suggest that most of the entanglement is established at the initial stages of polymerization. © 2011 American Chemical Society.