The structural and conformational changes in solid-phase chlorinated polyethylene samples of different average molecular masses were studied with infrared spectroscopy. Characteristic absorption bands for both chlorinated polyethylene and chlorinated high-molecular-mass polyethylene, containing 1-56% Cl, were identified. The chlorine content in the macromolecular chains, ranging from 1 to 15%, was associated with the presence of single chloromethylene groups and short syndiotactic structural sequences of poly(vinyl chloride) derived from them. Higher degrees of chlorination, ranging from 20 to 56%, resulted in an increase in the relative part of the heterotactic structures with 1,2-, 1,3-, and 1,2,3-modes of mutual location of the chlorine atoms within a fragment. Moreover, solid-phase chlorinated polyethylenes with chlorine concentrations as high as 56% were polymers with a mixed amorphous-crystalline structure. On the basis of the intensity ratio of the absorption at 610 cm(-1) to the absorption at 660 cm-1 for the corresponding characteristic absorption bands, the substitution of the hydrogen atoms for chlorine ones occurred predominantly in the trans-methylene groups, which were located within the amorphous and intermediate phases of polyethylene with chlorine concentrations as high as 20%. Consequently, the relative part of the gauche chlorinated methylene groups increased. A trans-to-gauche conformational change was thought to have taken place during the solid-phase chlorination of polyethylene under the influence of the bulky chlorine atoms. These changes were facilitated by the corresponding segmental mobility of the macromolecular chains. (C) 2004 Wiley Periodicals, Inc.