Question

When a saturated paraffin such as polymethylene is chlorinated, chlorine replaces hydrogen at random. Invariably, small amounts of chlorine (10–50 wt% Cl) cause a lowering of softening point. Large amounts (about 70%) raise the softening point. Rationalize on the basis of intermolecular forces.

Answer 1

Small amounts of Cl replaces small amounts of hydrogen, then polymer has large number of non polar bonds C-H and fewer number of polar bonds C-Cl. So weak London disperson forces are predominant intermocular forces. Hence softening point will be lowered.

Large amounts of (about 70%) of Cl will replace 70 % of H atoms. Then polymer will have 70% polar C-Cl bonds and it has dipole-dipole moilecular attraction forces as predominant inter molecular forces.

Hence softening point will be raised.