Study On Liquid Crystalline Polysiloxanes As β Nucleator To Induce Crystallization Behavior Of PP

Liquid crystalline polymers (LCP) have some advantages, such as high modulus and strength, and they were used widely in polymer composite materials. To the best knowledge, little research on LCP nucleators of polypropylene (PP) is reported. Therefore, it is significant to study on LCP nucleators not only because it has important theory and science values, but also it is hopeful to synthesize high efficient and multifunctional nucleators used in PP.In this paper, four new nematic monomers were synthesized.The homopolymers P1 was prepared by graft polymerization reaction with the corresponding monomer and PMHS. The copolymers P11-15 and P11-10 were obtained by the copolymerization of M1, 4-hydroxyphenyl-4'-undecylenate (Ni) and PMHS. The PP blends containg different content of nucleators Pi, P11-15 and P11-10 were obtained. The chemical structures and mesomorphic properties of M1-M4, P1, P11-15 and P11-10 were investigated by FT-IR spectronscopy, polarizing optical microscopy (POM), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Moreover, the influence of P1, P11-15 and P11-10 as new nucleator to the crystallization structure, properties and morphology of PP was dicussed with POM, DSC and wide angle X-ray diffraction (WAXD).M1 exhibited enantiotropic nematic threaded textures, and monotropic fan-shaped texture of smectic A (SA) phase, schlieren texture texture of smectic C (SC) phase, and mosaic textures of smectic B (SB) phase on cooling process. M2 exhibited enantiotropic mosaic textures of SB phase, break fan-shaped textures of Sc phase, fan-shaped textures of SA phase and nematic schlieren textures on heating and cooling cycles. M3 and M4 only exhibited nematic threaded textures and droplet textures. The melting point (Tm) and clearing temperature (Ti) of the monomer containing ethoxy group were greater than those of the monomer containing ethyl group. Moreover, with increasing the rigidity of the mesogenic cores, Tm and Ti of the corresponding monomer increased, and mesophase range widened because the Ti increased greater than Tm.The homopolymer (P1) and copolymers (P11-15 and P11-10) showed nematic phase. P1, P11-15 and P11-10 were semicrystallinity polymers, and DSC curves of the polymers showed the melting transition and nematic to isotropic phase transition. TGA showed that the temperatures at which 5% weight loss occurred (Td) were greater than 370℃for P1, P11-15 and P11-10, this indicated that they had a good thermal stability.Compared with pure PP, the PP blends with the LC nucleators could efficiently enhance the crystallization temperature, crystalline velocity, and the spherulites became smaller. Moreover, Three LC nucleators all inducedβ-form in PP with bright color. For blends P1/PP, the heterogeneous nucleation effect was best and the relative content ofβ-form (Kp) was 70% when the mass fraction of P1 was 1.0% and the crystalline temperature (Tc) and time (t) was 125℃and 1h, respectively. For blends P11-15/PP, the nucleation effect was best and Kβwas 59% when the mass fraction of P11-15 was 1.0%, Tc and t was 130℃and 1h, respectively. For blends P11-10/PP, the nucleation effect was best and Kβwas 60% when the mass fraction of P11-10 was 1.0%, Tc and t was 130℃and 1h, respectively.POM observation revealed thatβ-spherulites had bright color morphology, and exhibited a sheaf-like structure, while a-spherulites showed the black and white morphology, and exhibited an emanant structure. The a-spherulites had a clear rotundity, and morphology disappeared at 171℃. However, theβ-spherulites had an obscure boundary, and morphology disappeared at 158℃.The kinetics of the PP blends with a different mass fraction of LC nuceator was studied. There nucleators could enhance the crystallization temperature of PP blends. However, the blends with higher Kp exhibited a lower crystallization temperature than the blends with lower Kβdue to the relatively slower crystalline velocity, lower melting point and the special structure or growth way forβ-form. The non-isothermal crystallization kinetics was studied for 1.0% P11-15/PP. Jeziorny method and the Mo Zhishen method had the same conclusion, and could describe well the non-isothermal crystallization kinetics for 1.0% P11-15/PP, but Ozawa method is not fit for the process.