ABSTRACT
Polyethylene is a semicrystalline solid and the degree of crystallinity is dependent upon defects on the polymer chain that interfere with the ability of the chain to be arranged in a crystal. Unlike many polymers the applications of polyethylene can be divided into two major areas, durables and nondurables. The main cause for rejection of a polyethylene molecule from a crystal is the presence of imperfections, which are usually branch points, on the chain backbone. Blown films made from high-density homopolymers tend to be very splitty in the machine direction, because of the lack of tie-molecules and the fact that the high-density polyethylene (HDPE) tends to be oriented in the machine direction. Without copolymerization of other α-olefins with ethylene two very different types of ethylene polymers can be made: low-density polyethylene, which is made at very high pressures using a free-radical initiator, and HDPE, which is made using various metal-complex catalysts.
