向列相液晶共聚物作为β晶成核剂对等规聚丙烯结晶结构与热性能的影响

EFFECT OF NEMATIC LIQUID CRYSTALLINE COPOLYMER AS A β-FORM NUCLEATOR ON CRYSTALLIZATION STRUCTURE AND THERMAL PROPERTIES OF ISOTACTIC POLYPROPYLENE

采用接枝聚合的方法,合成了一种新型聚硅氧烷类向列相液晶共聚物(LCP-H4),然后将LCP-H4与PP在一定工艺条件下密炼共混,得到了一系列的共混样品,采用WAXD、POM与DSC等研究了LCP-H4作为成核剂对PP样品结晶结构、形态与热性能的影响.结果表明,具有独特"液晶"性能的LCP-H4为PP结晶提供了更多的带自由能的晶核与较多的活性点,起到了异相成核的作用,既提高了PP的结晶速度、结晶温度和结晶度,又减小了球晶的尺寸,同时也改变了PP的结晶结构、形态及热力学与动力学,诱导出了β晶.此外,随着增加LCP-H4的含量及结晶温度,对应PP试样的β晶含量(Kβ)呈现先增加后降低的趋势,当LCP-H4含量为0.9%,在128℃等温结晶1h,对应成核PP的Kβ最大,为54%.

A new nematic liquid crystalline copolysiloxane（LCP-H4） was prepared by graft polymerization,and a series of PP blends containing different mass fraction of LCP-H4 with propyloxy spacers were obtained by blending PP and LCP-H4 at a proper process program.The crystallization structure,morphology and thermal properties of PP with LCP-H4 as a nucleator were characterized with wide angle X-ray diffraction（WAXD）,polarizing optical microscopy（POM） and differential scanning calorimetry（DSC）.The experimental results showed that LCP-H4 with mesomorphism in the PP could supply many crystal nucleuses and active spots,play a role in the heterogeneous nucleation effect,efficiently enhance the crystallization velocity,temperature and degree of crystallinity,moreover,the spherulites became smaller and more homogeneous.The nucleated PP showed different crystallization structure,morphology,and thermodynamics and kinetics.β-phase in the PP was induced,the maximal relative content of β-form（Kβ） was 54% when the mass fraction of LCP-H4 was 0.9%,and the crystalline temperature and time were 128℃ and 1 h,respectively.In addition,the birefringence of β spherulites is stronger than that of α spherulites,this difference is related to their particular growth way and lamellar morphology.The trigonal β spherulite with the sheaflike grain growth is bright and colorful compared with the black and white monoclinic α one with the cross-hatched radial grain growth.Moreover,the molecular arrangement of β crystal is looser than that of α crystal.The melting point of α-and β-crystal was about 153oC and 166oC,respectively.