Study On Liquid Crystalline Polysiloxane As A New Nucleator To Induce Crystallization Structure And Morphology 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, which include4-(pentylbenzoyloxy)phenyl-4’-allyloxybenzoate (M1),4-(pentylbenzoyloxy)biphenyl-4’-allyloxy-benzoate (M2),4-(undec-10-enoyloxy)biphenyl-4’-pentylbenzoate (M3),4-(pentylbenzoyloxy)biphenyl-4’-(undec-10-enoyloxy)benzoate (M4). The homopolymers P1, P2, P3was prepared by graft polymerization reaction with the corresponding monomer and PMHS. The copolymers P22was obtained by4-hydroxybiphenyl-4’-allyloxybenzoic acid (N2), M2, and PMHS. Moreover, the PP blends containg different content of nucleators P3, and P22were obtained.The chemical structures and mesomorphic properties of M1～M4, P1～P3and P22were investigated by FT-IR and’H-NMR spectronscopy, polarizing optical microscopy (POM), differential scanning calorimetry (DSC). Moreover, the influence of P3and P22as new nucleator on the crystallization structure and morphology of PP blends was dicussed with wide angle X-ray diffraction (WAXD), POM, and DSC.M1～M4exhibited thermotropic liquid crystalline compounds. M1and M2exhibited nematic schlieren texture. M3exhibited enantiotropic mosaic texture of smectic B (SB) phase, break fan-shaped texture of smectic C (Sc) phase, fan-shaped texture of smectic A (SA) phase and nematic schlieren texture on heating and cooling cycles. M4exhibited fan-shaped of a SA phase and nematic schlieren texture on heating cycle. DSC curves of P1, P2and P22only showed a glass transition, and those of P3showed the melting transition, not nematic to isotropic phase transition was seen. However, POM result that showed P1～P3and P22exhibited nematic texture.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, β-form with bright color was induced in PP with three LC nucleators. The relative content of P-form (Kβ) showed an increase firstly, then a decrease with increasing the content of LC nucleator from0to1.0%. For blends PP/P3, the heterogeneous nucleation effect was best and Kβ was45%when the mass fraction of P3was0.6%and the crystalline temperature (Tc) and time (t) was125℃and1h, respectively. For blends PP/P22, the nucleation effect was best and Kβ was29%when the mass fraction of P22was0.4%, Tc and t was125℃and1h, respectively.POM observation 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 an emanant 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 P-spherulites disappeared at about155℃, and that of a-spherulites disappeared at about171℃.DSC curves of PP blends containing P3and P22nucleators showed a typical melting transition of β-crystal at about150℃beside a melting transition of a-crystal at about165℃. The enthalpy change of β-crystal showed an increase firstly, then a decrease with increasing the content of LC nucleator.