Study On Liquid Crystalline Polymer As A New Nucleator To Induce Crystallization Structure,Morphology And Property Of PP

Liquid crystalline polymers (LCP) have some advantages, such as high modulus, and they were used in polymer composite materials. Polypropylene (PP) with β-form have been studied for many years, the excellent mechanical performance make it possible to substitute some engineering plastics. However, to the best of our knowledge, little research on LCP as nucleators for PP is reported. Therefore, it is important to study on LCP nucleators not only because it has important theory and science values, but also it is hopeful to obtain efficient and multifunctional nucleators used in PP.In this paper, four new nematic monomers were synthesized, which include4-(4-amylbenzoyloxy)biphenyl-4’-allyloxybenzoate (M1),4-(4-amylbenzoyloxy)phenyl-4’-(4-(2-(acryloyloxy)ethoxy) benzoate (M2),4-(4-amylbenzoyloxy)phenyl-4’-(4-(6-(acryloyloxy)-hexyloxy) benzoate (M3),4-(4-amylbenzoyloxy)biphenyl-4’-(4-(6-(acryloyloxy)hexyloxy) benzoate (M4). The polymer P1was prepared by graft polymerization reaction with M1and PMHS. The polymer P2was prepared by free radical reaction with M2. In addition, the PP blends containg different content of nucleators P1and P2were obtained.The chemical structures and LC properties of M1～M4, P1and P2were investigated by FT-IR,1H-NMR, polarizing optical microscopy (POM), differential scanning calorimetry (DSC). The influence of P1and P2as new nucleator on the crystallization structure, morphology and thermal properties of PP blends was dicussed.M1～M4all exhibited typical nematic threaded texture and schlieren texture on heating and cooling cycles. With increasing length of the flexible spacer, the melting temperature (Tm) and clearing temperature (Ti) of the corresponding monomer decreased, and Tm decreased greater than Ti. With increasing the rigidity of the mesogenic cores,Tm and Ti of the corresponding monomers increased, and mesophase range widened because the Ti increased greater than Tm. The glass transition temperatures (Tg) of P1and P2were lower than95℃, while Ti were greater than200℃, this is consistent with our idea on LCP as new nucleator.P1and P2with low concentration in PP played a role in the heterogeneous nucleation effect, and the spherulites became smaller and more homogeneous. Moreover, β-form was induced in PP blends. The relative content of β-form (Kβ) showed an increase firstly, then a decrease with increasing the content of nucleators from0to1.2%. For blends PP/P1, the heterogeneous nucleation effect was best and Kβ was41%when the mass fraction of P1was0.3%and the crystalline temperature (Tc) was130℃. For blends PP/P2, Kβ was35%when the mass fraction of P2was0.8%, Tc was130℃.POM results revealed that P-spherulites had bright color morphology, and exhibited a sheaf-like or helix-like structure, whereas, a-spherulites showed the black and white morphology, and exhibited a cross-hatched radial grain structure. Moreover, the spherulite center of a crystal grew outward along the radial direction, while the spherulite center of β-crystal began outward along from a parallel assembly into a beam, and then branched outward growth. In addition, the morphology of β-spherulites disappeared at155℃, and that of a-spherulites disappeared at171℃.Compared with pure PP, the PP blends with the LCPs nucleators could efficiently enhance the crystallization temperature and velocity. In addition, the non-isothermal crystallization kinetics for0.3%PP/P1was studed with Jeziorny and Ozawa methods. The results showed that Jeziorny method could describe well the non-isothermal crystallization kinetics for0.3%PP/P1, but Ozawa method is not fit for the process.