No abstract

No abstract

Blends of polycarbonate (PC) and poly(alkylene terephthalate) (PAT) such as poly(butylene terephthalate) (PBT) and poly(ethylene terephthalate) (PET) were investigated. It was learned that processes of phase separation in blends consisting of PC and PAT can cause variations in properties of both the amorphous and crystalline phases. In PC/PBT blends the DSC technique did not detect crystalline portion of PBT with its concentrations up to 20 wt %. For PBT ϭ 40 wt %, it forms a continuous phase, and blend's crystallinity is close to the additive values. The glass transition temperature (T g ) shifts to the lower temperature region. The relaxation spectrometry revealed strong adhesion between phases in the blends over the temperature range from the completion of ␤-transition to T gPAT . This interaction becomes weaker between T gPAT and T gPC . Temperature-dependent variations in the molecular mobility and interphases interactions in the blends affect their impact strength. Over the temperature range where interphases interactions occur and the two components are in the glassy state, the blend is not impact resistant. Over the temperature range between T gPAT and T gPC the blends become impact-resistant materials. This is because energy of crack propagation in the PAT amorphous phase-being in a high-elastic state-dissipates. It is postulated that the effect of improving the impact strength of PC/PAT blends, which was found for temperatures between the glass transition temperatures of the mixed components, is also valid for other binary blends.

ABSTRACT:The possibility of modifying polycarbonates by using dian (Bisphenol A) polysulphone-polydimethyl siloxane block copolymers having multiblock structure and triblocks with end polydimethyl siloxane or a polysulphone block structure was shown. In triblock copolymers the polydimethyl siloxane blocks have a constant molecular weight equal to 2500, while in polyblocks it was assumed to be 2500 and 10,000. The molecular weight of polysulphone blocks varied between 700 and 9000 in triblocks or between 500 and 4500 in polyblocks. It was found that block copolymers of both multiand triblock structure with polydimethyl siloxane end blocks of concentration 45-68 wt % are created with PC microheterogenous blends. These blends, in a wide temperature interval (from cryogenic to the glass transition temperature of PC), have high impact strength when multiple crazes are created independently on testing temperature.

Methylene diphenyl diisocyanate (MDI) affects the morphology, rheological, mechanical, and relaxation properties, as well as tendency to crystallize of PET in PET/PC/(PP/EPDM) ternary blends produced by the reactive extrusion. Irrespective of the blend phase structure, the introduction of MDI increases the melt viscosity (MFI dropped), resulting from an increase in the molecular weight of the polymer chains; the PET crystallinity was also reduced. MDI favors compatibility of PET with PC in PET/PC/(PP/EPDM) blends. This is explained by intensified interphase interactions on the level of segments of macromolecules as well as monomer units. The presence of MDI causes a substantial rise in the dynamic shear modulus within the high-elastic region of PET (for temperature range between T g,PET and that of PET cold crystallization); the processes of PET cold crystallization and melt crystallization become retarded; the glass-transition temperatures for PET and PC become closer to each other. MDI affects insignificantly the blend morphology or the character of interactions between the disperse PP/EPDM blend and PET/PC as a matrix. PP/EPDM reduces the intensity of interphase interactions in a PET/PC/(PP/ EPDM), but a rise in the degree of material heterogeneity. MDI does not change the mechanism of impact breakdown in the ternary blends mentioned above. Increased impact strength of MDI-modified materials can be explained by higher cohesive strength and resistance to shear flow at impact loading.

Itaconic acid (IA) was grafted onto polypropylene/low-density polyethylene (PP/LDPE) blends. The ratio of polymeric components was varied from 100 : 0 to 0 : 100. The effect of the variation in the ratios of the components on grafting efficiency and concomitant side processes was studied. Grafting of IA (1 wt %) was initiated by 2,5-dimethyl-2,5-di(tert-butyl peroxy)-hexane (0.3 wt %) and was carried out in an extruder reactor equipped with a dynamic mixer. An increase in the PP content of the blend led to a lower yield of the grafted product. With low concentrations of LDPE in the blend (up to 25 wt %), grafting efficiency was observed to increase, and this increase was greater in comparison with the additive rule. Between 25 and 99 wt % of LDPE in the blend, grafting efficiency rose monotonically with LDPE concentration. At or below an LDPE content of 25 wt %, the melt flow index (MFI) of [PP/LDPE]-g-IA would increase unlike with PP-g-IA systems. But a small quantity of PP (below 25 wt %) in the [PP/LDPE]-g-IA blends would result in a decreased MFI unlike with LDPE-g-IA. The dependence of swell index and melt strength on the ratio of polymeric components in [PP/LDPE]-g-IA blends also was investigated.

A novel method was applied to study the topological and molecular structures of multicomponent rubber. This method is based on the thermomechanical analysis of a solid polymer. A diblock amorphous structure was found for the studied rubber network. These blocks differ a great deal in their glass transition temperature. The methodology of how to calculate the crosslink density in each block, the molecular weight distribution of the chains between the junctions of the network, and the shares of low-temperature (soft) and high-temperature (hard) blocks in a structure of the rubber network were also shown. Based on these data it is possible to calculate the number-average and weight-average molecular weight and the polydispersity coefficients of the chains between the junctions of the network.

No abstract