Study On Liquid Crystalline Polymers As A New β-crystal Nucleating Agent To Induce Crystallization Behavior Of PP

Liquid crystalline (LC) polymers have some advantages, such as high modulus and strength, and they have been used widely in polymer composite materials. To the best knowledge, little research on LC nucleating agent of polypropylene (PP) is reported. Therefore, it is important to study on LC nucleating agent not only because it has theory and science values, but also it is hopeful to synthesize high efficient and multifunctional nucleating agent for PP.In this paper, five new nematic allyoxy monomers (M1-M5) were synthesized. The homopolymers P1-P5 were prepared by graft polymerization reaction with the corresponding monomers and PMHS, respectively. The copolymers LCP-OH(1)-LCP-OH(4) and LCP-COOH were obtained by the copolymerization of a monomer, intermediate (N1) and PMHS. Moreover, The PP blends containg different content of nucleators P2, LCP-OH(1) and LCP-OH(2) were obtained. The chemical structures and mesomorphic properties of all the monomers and polymers were investigated by FT-IR spectronscopy, polarizing optical microscopy (POM), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Moreover, crystallization structure and morphology of PP containg LC polymer as nucleating agent were characterized with wide angle X-ray diffraction (WAXD), POM and DSC.M1-M5 all exhibited typical nematic schlieren texture or droplet texture on heating and cooling cycles. With increasing the rigidity of the mesogenic cores, the melting point (Tm) and clearing temperature (Ti) of the corresponding monomers increased, and mesophase range widened because the Ti increased greater than Tm. All the homopolymers and copolymers exhibited nematic textures. Their glass transition temperatures Tg were lower than 80℃, while Ti were greater than 180℃, this is consistent with our idea on LC polymer as new nucleating agent. TGA showed that the temperatures at which 5% weight loss occurred (Td) were greater than 330℃for all the polymers, this indicated that they had a good thermal stability.Compared with pure PP, the LC nucleating agent in the PP blends could efficiently enhance the crystallization temperature and crystalline velocity, and the spherulites became small. Moreover, three LC nucleating agents inducedβ-form with bright color. For P2/PP blends, the heterogeneous nucleation effect was best and the relative content ofβ-form (Kβ) was 31% when the mass fraction of P2 was 1.0% and the crystalline temperature (Tc) was 130℃. For LCP-OH(1)/PP blends, Kβwas 36% when the mass fraction of LCP-OH(1) was 0.8% and Tc was 130℃. For LCP-OH(2)/PP blends, Kβwas 41% when the mass fraction of LCP-OH(2) was 1.0% and Tc was 130℃.In addition,β-form and a-form in PP has some difference:αcrystal showed a black and white morphology, and clear spherulite boundaries. P-crystal displayed bright color morphology, and obscure spherulite boundaries. Moreover, the spherulite center of a crystal grew outward along the radial direction, while the spherulite center ofβ-crystal began outward along from a parallel assembly into a beam, and then branched outward growth.The kinetics of the PP blends with a different mass fraction of LC nucleating agent was studied. There nuceating agents could enhance the crystallization temperature and velocity. In addition, the non-isothermal crystallization kinetics for 0.8%LCP-OH(1)/PP was studed with Jeziorny and Ozawa methods. The results showed that Jeziorny method could describe well the non-isothermal crystallization kinetics for 0.8%LCP-OH(1)/PP, but Ozawa method is not fit for the process.