| Liquid crystalline polymers (LCP) have some advantages, such as high modulus and strength, and they were used in polymer composite materials. To the best knowledge, little research on LCP nucleators of isotactic 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, six new nematic monomers were synthesized, which include4-(4-(2-(acryloyloxy)ethoxy)benzoyloxy)phenyl-4’-ethoxybenzoate (M1),4-(4-(2-(acryloyloxy)ethoxy) benzoyloxy)phenyl-4’-ethylbenzoate (M2),4-(4-(2-(acryloyloxy)ethoxy)benzoyloxy)biphenyl-4’-ethoxybenzoate (M3),4-(4-(2-(acryloyloxy)ethoxy)benzoyloxy)biphenyl-4’-ethylbenzoate (M4),4-(4-(2-(acryloyloxy)ethoxy)benzoyloxy)biphenyl-4’-pentylbenzoate(M5),4-allyloxybiphenyl-4’-pentylbenzoate (M6). The polymers P1～P5were prepared by free radical reaction with M1～M5. The polymer P6was prepared by graft polymerization reaction with M6and PMHS. Moreover, The two series of PP blends containg different content of nucleators P2and P6were obtained. The chemical structures and mesomorphic properties of all the monomers and polymers were investigated by FT-IR,1H-MNR, polarizing optical microscopy (POM), and differential scanning calorimetry (DSC). The structure-property relationships of M1～M5and P1～P5are discussed. In addition, crystallization structure, morphology and thermal properties of PP blends containg P2or P6as a new nucleator were characterized with wide angle X-ray diffraction (WAXD), POM and DSC.M1～M6all exhibited typical nematic threaded texture, schlieren texture or droplet 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 core, Tm and Ti of the corresponding monomers increased, and mesophase range widened because Ti increased greater than Tm. All the polymers exhibited nematic textures. DSC curves of the polymers showed glass transition or melting transition and nematic to isotropic transition. The glass transition temperatures (Tg) of P2and P6were lower than75℃, while Ti were greater than200℃, this is consistent with our idea on LCP as new nucleator.P2and P6with low concentration in PP played a role in the heterogeneous nucleation effect, and the spherulites became smaller and more homogeneous. Moreover, β-form with bright color was induced. For P2/PP blends, the relative content of β-form (Kβ) was65%when the mass fraction of P2was1.2%and the crystalline temperature (Tc) was130℃. For P6/PP blends, Kβ was51%when the mass fraction of P6was0.3%and Tc was130℃.POM observation showed that β-form and a-form in PP has some difference:a crystal showed a black and white morphology, and clear spherulite boundaries, whileβ-form displayed bright color morphology, and obscure spherulite boundaries. Moreover, the spherulite center of a-form grew outward along the radial direction, while the spherulite center of β-form began outward along from a parallel assembly into a beam, and then branched outward growth.The kinetics of the PP blends with a different mass fraction was studied. P2and P6in PP could enhance the crystallization temperature and velocity of PP blends. However, the blends with higher Kβ exhibited a lower crystallization temperature than the blends with lower Kβ due to the lower melting point and the special structure or growth way for β-form. Jeziorny method showed that Z increased with increasing the cooling rate, but Zc held a constant. |
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