Study On Nematic Liquid Crystalline Polymer As A New β-nucleator 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 nucleator of polypropylene (PP) is reported. Therefore, it is important to study on LC nucleator not only because it has theory and science values, but also it is hopeful to synthesize high efficient and multifunctional nucleator for PP.In this paper, six new nematic monomers were synthesized, which include4-(ethoxybenzoyloxy)-biphenyl-4’-allyloxybenzoate (M1),4-(ethylbenzoyloxy)biphenyl-4’-allyloxybenzoate (M2),4-allyloxybiphenyl-4’-[(p-ethoxybenzoyloxy)]benzoate (M3), n-pentylbenzoate (M4),4-(ethoxybenzoyloxy)phenyl-4’-allyloxybenzoate (M5),4-allyloxybiphenyl-4’-ethoxybenzoate (M6). The homopolymers P1～P6were prepared by graft polymerization reaction with the corresponding monomers M1～M6and PMHS, respectively. The copolymers P1-1, P2-1and P2-2were obtained by reacting with M1and4-hydroxyl-4’-allyloxybiphenyl (N1), M2and N1, M2and4-allyloxybenzoic acid (N2) and PMHS, respectively. Moreover, the PP blends containg different content of P1, P2and P2-1were obtained. The chemical structures and mesomorphic properties of all the monomers, homopolymers and copolymers were investigated by FT-IR and1H-NMR spectronscopy, polarizing optical microscopy (POM), differential scanning calorimetry (DSC). In addition, crystallization structure and morphology of PP containg LC polymer as nucleator were characterized with wide angle X-ray diffraction (WAXD), POM and DSC.M1～M6all exhibited typical nematic schlieren texture, thread texture and droplet texture. 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. Moreover, Tm and Ti of the monomers containing ethoxy group were more than those of the monomer containing ethyl group. All the homopolymers and copolymers exhibited nematic textures. Their glass transition temperature (Tg) was lower than102℃, while Ti; was greater than250℃, this is consistent with our idea on LC polymer as new nucleator. β-Form with bright color was induced for the PP blends containing three LC nucleator. The relative content of P-form (Kβ) showed an increase firstly, then a decrease with increasing the content of LC nucleator from0to1.4%. For P1/PP blends, the heterogeneous nucleation effect was best and Kpβ was54%when the mass fraction of P1was1.0%and the crystalline temperature (Tc) was130℃. For P2/PP blends, Kβ was35%when the mass fraction of P2was0.8%and Tc was125℃. For P2-1/PP blends, Kβ was52%when the mass fraction of P2-1was1.0%and Tc was130℃.Compared with pure PP, the LC nucleator in the PP blends can efficiently enhance the crystallization temperature and crystalline velocity, and the spherulites became small. In addition, a crystal showed a black and white morphology, and clear spherulite boundaries, while β-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 of β-crystal began outward along from a parallel assembly into a beam, and then branched outward growth. Moreover, the morphology of β-spherulites disappeared at about156℃, and that of α-spherulites disappeared at about172℃.DSC curves of PP blends containing LC nucleator showed a typical melting transition of P-crystal at about150℃beside a melting transition of α-crystal at about165℃. The enthalpy change of β-crystal showed an increase firstly, then a decrease with increasing the content of LC nucleator. Compared with pure PP, crystallization peak of PP blends with LC nucleator shifted to high temperature, and peak shape narrowed.