Differential scanning calorimetry of copolymer of isotactic polypropylene backbone with grafted poly(ethylene-co-propylene) branches

A series of graft polymers having polypropylene (PP) backbone and poly(ethylene-co-propylene) (EPR) side chains was prepared. PP backbone molecular weight (M-n) was 28-98 kg/mol, EPR side chain M-n was 2.6-17 kg/mol, and EPR content was 0-16 wt %. In this work, thermal analysis of the copolymers was performed using differential scanning calorimetry (DSC). Nonisothermal crystallization was performed at different cooling rates. The DSC thermograms revealed multiple melting peaks for slowly cooled samples, most likely the result of the melting of thinner tangential lamellae followed by the melting of thicker radial lamellae. Equilibrium melting temperature (T-m(0)) was determined using the linear Hoffman-Weeks method. Another approach was also used for determining T-m(0): melting temperature (T-m) and crystallization temperature (T-c) were plotted as functions of logarithmic cooling rate. Linear relationships were observed for all samples with the cross points as T-m(0)'s. As cooling rate decreased, T-m and enthalpy of fusion (Delta H-f) increased. T-m and T-m(0) increased with increasing PP M-n. T-c and T-m were unaffected by the grafting of EPR onto the PP backbone. T-m(0) and Delta H-f decreased as EPR content increased. (c) 2006 Wiley Periodicals, Inc.