Study of structure and thermal properties of polypropylene and chlorinated polypropylene by infrared spectroscopy and differential scanning calorimetry

Abstract The infrared spectra of chlorinated polypropylene (CPP) are interpreted and tentative assignments of C—Cl stretching vibration of CPP are proposed. Recently, infrared spectrophotometry has been applied as a useful tool for the investigation of polymer transitions. The solid‐state transition in isotactic polypropylene (IPP) was studied by infrared method in the range of −50° to 30°C; and from the temperature dependence of the peak absorbance, transition at ‐10°C was detected. This temperature of ‐10°C agrees well with the T g 2 detected by other methods. From these results, it is presumed that T g 2 is attributed to a motion (thermal expansion) of IPP segments in either crystalline and amorphous region. The thermal transition of chlorinated isotactic polypropylene (CIPP) was also examined with differential scanning calorimetry and infrared method, and two thermal transitions were observed. A higher transition ( T H ) has a minimum at a degree of chlorination of about 39 wt‐%; and a lower transition ( T L ) changes linearly with increasing degree of chlorination. Infrared results indicate that T H may be associated with a motion (thermal expansion) in chlorinated segments, and T L may be associated with a motion in unchlorinated segments. These results of infrared studies also suggest that CIPP may have a block structure.