Results are reported on the influence of composition and molecular mass of components on the isothermal growth rate of spherulites, on the overall kinetic rate constant, on the primary nucleation and on the thermal behaviour of poly(ethylene oxide)/poly(methyl methacrylate) blends. The growth rate of PEO spherulites as well as the observed equilibrium melting temperatures decrease, for a given Tc or ΔT, with the increase of PMMA content.Such observations are interpreted by assuming that the polymers are compatible in the undercooled melt, at least in the range of crystallization temperatures investigated. Thermodynamic quantities such as the surface free energy of folding σe and the Flory-Huggins parameter χ12 have been obtained by studying the dependence of the radial growth rate G and of the overall kinetic rate constant K from temperature and composition and the dependence of the equilibrium melting temperature depression ΔTm upon composition, respectively. 相似文献
Various numbers of diphenyl-siloxane groups were incorporated in α,ω-bis(aminopropyl)polydimethylsiloxane (APPS) to prepare
α,ω-bis(aminopropyl)-polydimethyldiphenylsiloxane (APPPS) oligomers of three different number-average molecular weights(Mn
= 547,772,1210 g mol−1).These APPPS oligomers were than used, together with 3,3′,4,4′-bezonphenone tetracarboxylic dianhydride (BTDA) and 2-2′-bis[4-(3-aminophenoxy)phenyl]
sulfone (m-BAPS), to synthesize a series of APPPS containing poly(imide siloxane) (PIS) copolymers. Microstructural studies
showed that at certain APPPS content, a critical microphase separation point existed, beyond which, microphase separation
began to develop. This critical point of microphase separation was found to be affected by the Mn of the APPPS oligomers (8.0,
4.3 and 2.1 mol% for Mn of 547, 772 and 1,210 g mol−1, respectively). Diphenyl-siloxane significantly improved compatibility between polyimide and polysiloxane segments. Physical
studies showed that the introduction of diphenyl siloxane changed the thermal stabilities and mechanical properties of the
PIS copolymers. These findings have potential applications for design purposes in engineering polymers. 相似文献
Summary: The effectiveness of some thermoplastic elastomers grafted with maleic anhydride (MA) or with glycidyl methacrylate (GMA) as compatibilizer precursors (CPs) for blends of low density polyethylene (LDPE) with polyamide‐6 (PA) has been studied. The CPs were produced by grafting different amounts of MA or GMA onto a styrene‐block‐(ethylene‐co‐1‐butene)‐block‐styrene copolymer (SEBS) (KRATON G 1652), either in the melt or in solution. A commercially available SEBS‐g‐MA copolymer with 1.7 wt.‐% MA (KRATON FG 1901X) was also used. The effect of the MA concentration and of other characteristics of the SEBS‐g‐MA CPs was also studied. The specific interactions between the CPs and the blends components were investigated through characterizations of the binary LDPE/CP and PA/CP blends, in the whole composition range. It was demonstrated that the SEBS‐g‐GMA copolymers display poor compatibilizing effectiveness due to cross‐linking resulting from reactions of the epoxy rings of these CPs with both the amine and the carboxyl end groups of PA. On the contrary, the compatibilizing efficiency of the MA‐grafted elastomers, as revealed by the thermal properties and the morphology of the compatibilized blends, was shown to be excellent. The results of this study confirm that the anhydride functional groups possess considerably higher efficiency, for the reactive compatibilization of LDPE/PA blends, than those of the ethylene‐acrylic acid and ethylene‐glycidyl methacrylate copolymers investigated in previous works.
SEM micrograph of the 75/25 LD08/PA blend (with 2 phr SEBSMA1). 相似文献
An experimental study was carried out in order to investigate the morphological, kinetic, structural and thermodynamic properties of nylon-6/rubber (namely ethylene-propylene copolymer (EPM) and ethylene-propylene copolymer functionalized by inserting along its backbone succinic anhydride groups (EPM-g-SA)) blends. The morphology and the overall kinetics of crystallization of the blends strongly depend on the type of copolymer added to nylon and on the blend composition. The EPM-g-SA acts as a nucleating agent for the Ny spherulites and at the same time causes a drastic depression of the overall kinetic rate constant. This decrease is related to the increase of the melt viscosity observed in Ny/EPM-g-SA blends. The crystalline lamella thickness of the Ny phase in the blends is lower than that of pure Ny crystallized at the same Tc suggesting that the presence in the melt of an elastomeric phase disturbs the growth of the Ny crystals. The rubber does not influence the thermal behaviour of the nylon. The results found lead to the conclusion that in the melt nylon-6 is incompatible with both EPM and EPM-g-SA copolymers. 相似文献
The sorption of n-alkanes, viz. hexane, heptane and octane by cross-linked natural rubber/poly(ethylene-co-vinyl acetate) (NR/EVA) blends has been studied at 28, 38, 48 and 58°C, with special reference to the effects of EVA content,
cross-linking systems, penetrant nature and temperature. The solvent transport was found to decrease with increase in EVA
content in the blends. The effects of blend ratio on the transport characteristics have been correlated with the phase morphology
of the blends, using scanning electron micrographs and optical micrographs. Among the three vulcanising systems, viz. sulphur
(S), dicumyl peroxide (DCP) and a mixed system (S + DCP) employed for the matrix, the DCP cross-linked blends exhibited the
lowest solvent uptake. Octane has been found to show higher interaction with the blends than hexane and heptane, probably
owing to the closer solubility parameter values. The computed transport coefficients, viz. diffusion coefficient and permeability
coefficient, were found to decrease with increase in EVA content in the blends. At room temperature, the mechanism of diffusion
was found to deviate slightly from the regular Fickian trend for all blend systems. The blend–solvent interaction parameter
and the activation energy for transport were also determined from the sorption data. 相似文献