Chemical modification of PVC by different nucleophiles in solventon-solvent system at high temperature

摘要

Chemical modification of polyvinyl chloride by nucleophiles is a versatile method for preparation of new functional polymers. Modification of PVC was carried out using different nucleophiles (Nu) in ethylene glycol (EG)/N,N-dimethylformamide (DMF) (1:1by volume) solution. OH-, N-3(-), and SCN- were examined as nucleophiles in this study. The FTIR spectrum confirmed substitution of Cl by nucleophiles and also the elimination of HCl in the modification reaction of PVC. The glass transition temperatures (T(g)s) of modified-PVC samples were in the order N-3(-) SCN- OH- and were equal to 87.6, 86.8 and 78.15 degrees C, respectively. The T-5% (the temperature at which weight loss is 5%) of PVC was 266 degrees C, while after 1 h modification by OH- it reduced to 197 degrees C. After alkaline modification, the scanning electron microscopy (SEM) images not only showed an increase in surface roughness and porosity, but also revealed a relatively large drop in average particle size from 160 to 80 mu m. Molecular weight and molecular weight distribution were determined by gel permeation chromatography (GPC). The GPC results showed that the number average molecular weight (M-n) and weight average molecular weight (M-w) were decreased from 79,950 and 176,360 g mol(-1) in crude PVC to 45,370 and 99,930 g mol(-1), respectively, after 1 h modification by OH-. Alkaline treatment also decreased the mechanical strength of PVC.