CRYSTALLIZATION BEHAVIOR AND MORPHOLOGY OF PE-G-LCP COPOLYMERS

This study presents DSC and optical microscopy investigations on copol ymers of semiflexible liquid crystalline polymer SBH 112 grafted to fu nctionalized low molecular mass polyethlene (PEox) obtained by melt po lycondensation or reactive blending procedures. The crystallization be havior of the PE-g-SBH copolymers has been studied under nonisothermal measurement conditions carried out at different cooling rates. The cr ystallization temperature (T-er) of the PE component of the copolymers decreases steadily upon increasing the concentration of the SBH rafts . It was found that the copolymers prepared by reactive blending cryst allize at slightly higher T-er than those prepared by polycondensation and with a higher rate, confirmed by the determination of the crystal lization rate coefficients (CRC). The results have been interpreted by the fact that the PE crystallizable segments and SBH grafts of the co polymers obtained by reactive blending are longer than those of the co polymers Prepared by polycondensation. The overall nonisothermal cryst allization kinetics has been studied by the Harnisch and Muschik equat ion. The results show that the mechanism of the crystallization of the PE phase changes only when the SBH content overruns ca.50%. due to th e decrease of both nucleation and crystal growth rates. The morphology of the copolymers crystallized nonisothermally from melt has been exa mined by polarization microscopy. Fairly homogeneous morphology with t iny PE spherulites is observed for PE-g-SBH copolymers prepared bu pol ycondensation with SBH as the minor phase. No sign of the dispersed LC P domains call be recognized. On the contrary, the morphology of the c opolymers prepared by reactive blending is distinctly biphasic. The al legedly longer PE segments crystallize into tiny spherulites too. but the LC domains formed by the long SBH branches present in this type of copolymers appear clearly in the micrographs at room temperature. It is concluded that the copolymers prepared by reactive blending would b e moro effective as compatibilizers for PE SBH blends than those prepa red by polycondensation.