Study On Liquid Crystalline Polyacrylates As A New Nucleator To Induce Crystallization Behavior Of PP

Liquid crystal (LC) polymers 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 LC nucleators of polypropylene (PP) is reported. Therefore, it is significant to study on LC nucleators not only because it has important theory and science values, but also it is hopeful to synthesize high efficient and multifunctional nucleators on PP.In this paper, eight new nematic acrylate monomers (M1～M8) were synthesized. The homopolymers P1～P4 were prepared by free radical reaction with M1～M4;. The copolymers P1-1～P1-2 and P4₁～P4-2 were obtained by the copolymerization of M1 and 4-(2-(acryloyloxy)ethoxy)benzoic acid (Ni) or M4 and 4-(6-(acryloyloxy)hexyloxy)benzoic acid (N2) with different mass fraction. 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). The effect of the flexible spacer and rigid mesogenic core on the phase transition temperature and phase types is discussed. Moreover, crystallization structure and morphology of PP containg liquid crystaliine polymer as a nucleator were characterized with wide angle X-ray diffraction (WAXD), POM and DSC.M1～M8 all exhibited typical nematic threaded texture, schlieren texture or droplet texture on heating and cooling cycles. All the homopolymers and copolymers exhibited nematic textures. DSC curves of the homopolymers and copolymers showed glass transition temperature (Tg) or melting temperature (Tm) and clearing temperature (Ti). TGA showed that the temperatures at which 5% weight loss occurred (Td) were greater than 300℃for P1～P4, P1-1, P1-2, P4-1 and P4-2, except P3, this indicated that these polymers had a good thermal stability.The crystallization behavior of PP blends were studied by means of wide angle X-ray diffraction (WAXD), polarized optical microscopy (POM) and differential scanning calorimetry (DSC) by the homopolymers P1 and the copolymers P1-1 and P1-2.Compared with pure PP, the LC nucleator in the PP blends could efficiently enhance the crystallization temperature, crystalline degree and velocity, and the spherulites became small. Moreover, Three LC nucleators all inducedβ-form with bright color. For blends P1/PP, the nucleation effect was best and the relative content ofβ-form (Kβ) was 21% when the mass fraction of P1 was 0.8% and the crystalline temperature (Tc) was 125℃. For blends P1-1/PP, the nucleation effect was best and Kβwas 25% when the mass fraction of P1-1 was 1.2% and Tc was 120℃. For blends P1-2/PP, the nucleation effect was best and Kβwas 18% when the mass fraction of P1-1 was 1.2% and Tc was 130℃.POM observation revealed thatβ-spherulites had bright color morphology, and exhibited a sheaf-like or helix-like structure, whereas,α-spherulites showed the black and white morphology, and exhibited an emanant structure. The a-spherulites had a clear rotundity disappeared at 171℃. However, theβ-spherulites had an obscure boundaries and disappeared at 156℃.The kinetics of the PP blends with a different mass fraction was studied. There nucleators could enhance the crystallization temperature of blends PP. However, the blends with higher Kβexhibited a lower crystallization temperature than the blends with lower Kβdue to the lower melting point and the special structure or growth way forβ-form. The non-isothermal crystallization kinetics was studied for 1.2%P1-1/PP. Jeziorny method and the Mo Zhishen method had the same conclusion. Jeziorny method showed that Z increased with increasing the cooling rate, but Zc held a constant.