STRUCTURE AND PROPERTIES OF POLYETHYLENE A long chain aliphatic hydrocarbon. The flexibility of the C-C bonds lead to low values for the glass transition temperature. There is no solvent at room temperature. Excellent high-frequency insulator because of its non-polar nature.

Different grades of PE are due to Variation in the degree of short chain branching in the polymer. Variation in the degree of long chain branching. Variation in the average molecular weight. Variation in the molecular weight distribution (which may in part depend on the long chain branching). Presence of a small amount of comonomer residues. The presence of impurities or polymerisation residues, some of which may the long chain branching be combined with the polymer.

Effect of Branching ‘back-biting’ mechanism during polymerisation

The presence of these branch points is bound to interfere with the ease of crystallisation. The branched high-pressure polymers have the lowest density. the least opacity (since the growth of large crystalline structures is impeded) A lower melting point, yield point, surface hardness Young’s modulus in tension. The more the branching and the lower the crystallinity, the greater will be the permeability to gases and vapours.

Effect of long chain branches is on flow properties. Unbranched polymers have higher melt viscosities than long-branched polymers of similar weight average molecular weight.