Isothermal crystallization kinetics of compatibilized blends of polyolefines with a semiflexible liquid crystalline polymer

Abstract

SUMMARY A study of the isothermal crystallization behaviour and an analysis of the kinetic parameters of compatibilized blends of polyolefines (isotactic poly(propy1ene) (iPP) and high density polyethylene (HDPE)) with a semiflexible liquid crystalline polymer (LCP) SBH 1 : 1 : 2 of Eniricerche, Italy are presented in this work. The compatibilizers are ad hoc synthesized graft copolymers of the liquid crystalline polymer grafted to functionalized poly(propy1ene) (PPAA) or polyethylene (PEox) -PP-g-SBH and PE-g-SBH copolymers, respectively. It has been established that the LCP dispersed phase in the blends plays a role in nucleation for the polyolefine matrix crystallization. This effect is more pronounced in the poly(propy1ene) matrix than in the polyethylene matrix, due to the lower crystallization rate of the former. The addition of PP-g-SBH copolymers (2.5-10 wt.-%) to 90/10 and 80/20 iPP/SBH (w/w) blends provokes a drastic increase of the overall crystallization rate of the iPP matrix and of the degree of crystallinity. Contrarily, the addition of PEg-SBH copolymers (2.5-8 wt.-%) to 80/20 HDPE/SBH (w/w) blends almost does not change or only slightly decreases the PE overall crystallization rate. Moreover, the interpretation of the Avrami exponents indicates that the iPP crystallization mechanism in the compatibilized iPP/SBH blends remains unchanged only until a degree of conversion of 0.7 and changes above this value; the PE crystallization mechanism and the degree of crystallinity in the compatibilized HDPE/SBH blends do not alter. The results were interpreted in terms of some differences in the compatibilization mechanism and efficiency of both types of graft copolymers (PP-g-SBH and PE-g-SBH). The relationships between blend morphology and nucleation phenomena are discussed.

Synthesis and Structural Elucidation of 2′-Deoxy-4′-thio-L-threo-pentofuranosylpyrimidine and -purine Nucleosides

“…The kinetics parameters of isothermal crystallization were determined by the following modified Avrami equation:1, 2, 4, 5, 14–21 where X ti is the relative crystallinity at crystallization time t i , K is a crystallization kinetic constant, and n is the Avrami exponent.…”

Effect of the dispersion of the chromophore on the optical performances of polarizers from polyethylene and 5”-thio- (3-butyl)nonyl-2,2’:5’,2”-terthiophene

“…The temperature was gently allowed to rise until 0°C for 5 min, and after all the CuCN was dissolved, the system was cooled to -78°C and 8 mL of trans-2-nonenal (48.3 mmol) was added. After stirring for 1 h at -78°C the reaction mixture was quenched with a 10% solution of NH 4 Cl/NH 4 OH, extracted with diethyl ether and dried over Na 2 SO 4 . After solvent evaporation, the product was purified by flash chromatography on silica gel using pentane/diethyl ether 9:1 as eluent.…”

“…Increasingly important applications of these systems are modern opto-electronic materials formed by host olefin polymers blended with highly conjugated guest polymers, aromatic or inorganic molecules [1]. In addition, chain orientation and extension of the host polymer system can also be used to generate and to enhance for instance the optical [2], electrical [3] and thermal [4] properties of the binary devices.…”

“…Studies of the dispersion of the guest in the host polymeric phase have shown that the presence of phase-separated regions inside the device due to the tendency of the guest molecules to aggregate may yield materials with poor mechanical [4], electronic and optical [5] properties. In particular the dispersion of organic dichroic guest molecules in polyethylene was shown to affect the optical properties of linear absorbing polarizers [6,7] due to the heterogeneity related to the immobilization of the dispersed guest molecule during tensile deformation of the host polyethylene matrix.…”

Melting behavior in blends of isotactic polypropylene and a liquid crystalline polymer

“…When the thermoplastic polymer is semicrystalline, such as iPP, even low levels of LCP can significantly affect the morphology and the blend properties. This is because the complex crystallization behavior of this type of system depends on the influence of the dispersed component on the nucleation of the polymer matrix 21–24. It has been widely observed that the crystallization of iPP generally occurs on the surface of heterogeneities.…”