The -, -, and -polymorphs of polypropylene-polyethylene random copolymer modified by two kinds of -nucleating agent

The -, -, and -polymorphs of polypropylene random copolymer with two kinds of -nucleating agent (TMB-5 and WBG-2) have been studied via wide-angle X-ray diffraction and differential scanning calorimetry. It was found that the addition of 0.5wt% -nucleating agent (-NA) hardly induces appreciable -modification content, until -NA content is up to 1wt%. It seems that low amount of -NA is not enough to counterbalance the nucleation ability and high content of defects (stereo- and regioerrors) of co-PP, and only - and -modifications are obtained in the samples. Moreover, the relative amount of -crystal depends on the crystallization temperature. Although TMB-5 has better heterogeneous nucleation effect than WBG-2, the ability to form stable -polymorph of WBG-2 is stronger than that of TMB-5. Since large amount of -nucleation sites overcome the defects of co-PP molecular chain and curb the formation of -crystal, competitive growth of - and -polymorphs ultimately leads to the coexistence of - and -modification.