Heterogeneous reactions of polymers: 3. Conformational analysis of heterogeneously chlorinated polyethylenes

Abstract Conformational features of chlorinated polyethylenes prepared by chlorination under heterogeneous conditions are deduced from their i.r. spectra in the 600–700 cm −1 region. The concentration of vicinal chlorides in materials obtained this way is estimated by 1 H-n.m.r. The effect of the reaction kinetics on the concentration of vicinal chlorides is discussed. It is shown that while conformational transitions do take place during heterogeneous chlorinations at room temperature of the low density polyethylenes, they do not occur during chlorinations of the highly crystalline high density polyethylene films. In such materials the distribution of conformers is determined by the initial conformation of the polymeric precursors and it deviates strongly from the thermodynamic equilibrium. Freezing of the thermodynamically unfavourable conformations in such materials is attributed to the low mobility of the chlorinated chains restricted by the adjacent crystalline regions. Thermal treatment of the products, above the melting temperature of the crystallites, leads to a thermodynamic distribution of the conformers. However, when such treatment is conducted under isometric conditions in a press, the conformational transitions remain severely restricted.