Local Chain-Configuration Dependence of the Mechanisms of the Chemical Reaction of Poly(vinyl chloride). IX. Novel Results on Stereoselectivity of Chlorination Reaction G. MARTI ´ NEZ, 1 J. MILLA ´ N, 1 J. CONTRERAS 2 1 Instituto de Ciencia y Tecnologı ´a de Polı ´meros (CSIC), Juan de la Cierva 3, 28006 Madrid, Spain 2 Grupo de Polı ´meros, Departamento de Quı ´mica, Facultad de Ciencias, Universidad de los Andes, Me´rida 5101 A, Venezuela Received 16 April 2002; accepted 18 November 2002 ABSTRACT: A poly(vinyl chloride) (PVC) sample was chlorinated in solution in the presence of 2,2-azobisisobutyronitrile and by the fluid-bed method. The aim was to evaluate the scope of the stereoselectivity of the chlorination reaction. The quantitative microstructural analysis of the residual PVC with a degree of chlorination was followed by 13 C NMR spectroscopy. From the evolution of the content of isotactic (mm), hetero- tactic (mr), and syndiotactic (rr) triads and of mmmm, mmmr, and rmmr isotactic pentads in the unchlorinated parts of the polymer, it was unambiguously inferred that the chlorination reaction proceeds by a stereoselective mechanism in that the mr heterotactic triads are the most reactive structures followed by the isotactic triad at mmmr and rmmr pentads. This conclusion was confirmed on the basis of the Fourier transform infrared results. The results provide valuable information regarding the effect of tacticity and related local conformations in the chemical reactions of PVC. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 508 –519, 2003 Keywords: poly(vinyl chloride) (PVC); modification; microstructure; stereoselective chlorination; local chain configuration INTRODUCTION Chlorination of poly(vinyl chloride) (PVC) has been the subject of extensive research related to synthetic methods 1,2 and the possible arrange- ments of CH 2 , CHCl, and CCl 2 groups occurring in many sequence combinations along the poly- mer chain. 3–10 Chlorination of PVC with gaseous chlorine or with its mixture with inert gases 11 may be carried out in a fluidized phase, 9 in sus- pension, 3,4,6 or in solution. 12 The reaction initi- ated by organic peroxides or ultraviolet radiation 6 proceeds by radical mechanisms, whereas initia- tion by Lewis acids leads to an ionic process. 13 The hydrogen atoms of the methylene group in PVC are most susceptible to the attack by chlo- rine atoms—the rate of their chlorination being twice that of OCHClO groups; 4,14 therefore, in the first stage of chlorination the arrangements OCHClOCHClO are practically the only to be found. It is only at a later stage that OCCl 2 O groups are produced. 10 The distribution of the possible arrangements of the different groups has been investigated with infrared spectroscopy (IR) 14,15 and nuclear magnetic resonance (NMR). 7,8,10 However, the different researchers disagree par- ticularly with the abundance of 1,2- and 1,1-di- chloroethylenic units. More recently, Komoroski and coworkers 16,17 investigated the chlorination Correspondence to: G. Martı ´nez (E-mail: gmart@ictp. csic.es) Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 41, 508 –519 (2003) © 2003 Wiley Periodicals, Inc. 508