Long-term efficiency for reducing entanglements of nascent polyethylene
by a polystyrene modified Ziegler-Natta catalyst
Abstract
The weakly entangled UHMWPE was synthesized by a Ziegler-Natta catalyst,
where the titanium tetrachloride was anchored on the polystyrene (PS)
modified silica. The PS chains were incorporated into silica pores
through the in-situ free-radical polymerization of styrene. This
incorporated PS was proved to be coated on the surface of pore walls.
The self-diffusion coefficients and crystallization of probed molecules
were investigated by the pulsed field gradient NMR and thermoporosimetry
to address the swollen behavior of the coated PS phase. This swollen PS
formed numerous horizontal isolators to compartmentalize the active
sites and adjacent chains. The ubiquitous isolators effectively limited
the formation of chains overlaps during the polymerization, showing a
long-term efficiency to reduce the entanglements of nascent UHMWPE with
an exceptional activity. The toughness/stiffness/strength balance of
weakly entangled UHMWPE was significantly improved, since the enhanced
chain diffusion rate limited the formation of forming defects.