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Dispersions of high density polyethylene (HDPE) particles in polystyrene (PS) were produced by interfacially driven breakup of nanolayers in multilayered systems that were fabricated by means of layer-multiplying coextrusion. The droplet size distribution was controlled by the HDPE initial individual layer thickness: 14, 40 or 120 nm. These unique systems allowed us to demonstrate unequivocally for the first time that the HDPE pseudohexagonal phase formation required nucleation on foreign surfaces or on crystals formed in the orthorhombic form at atmospheric pressure. The dispersions of HDPE particles in the PS matrix were subjected to annealing at high pressure of 480 MPa at 235 °C, in conditions where the pseudohexagonal phase forms in HDPE. To reach the desired conditions the samples were first heated and then subjected to high pressure or they were first pressurized and then heated. The samples treated according to the first route melted and transformed into the pseudohexagonal phase from the molten s...

Isotactic copolymers of 1-propene and 1-hexene that contain over 10% and up to about 25% of hexane units in the chain have been shown to crystallize in an unusual crystal modification that differs significantly from the well-known structures of isotactic polypropylene (α, β, and γ phases) or of isotactic poly(1-hexene) (Macromolecules 2005, 38, 1232). The experimental data obtained by Poon et al. are reinterpreted and analyzed. The new crystal form has a trigonal unit-cell with parameters a = b = 1.717 nm, c = 0.65 nm, very similar to form I of isotactic poly(1-butene) (iPBu) (trigonal cell with parameters a = b = 1.770 nm, c = 0.65 nm). The chain conformation is the 3-fold helix of isotactic polypropylene. The side-chain material in the copolymer with the highest hexene content (25%) is about 12% less than in iPBu form I (all ethyl units). These copolymers of propene and hexene adopt a crystal structure isomorphous to that of a third polyolefin (polybutene) that, in terms of overall composition, is close...

A new plasticizer for poly(L-lactide) (PLA)-poly(propylene glycol) (PPG) is proposed. The advantage of using PPG is that it does not crystallize, has low glass transition temperature, and is miscible with PLA. PLA was plasticized with PPGs with nominal Mw of 425 and 1000 g/mol. Poly(ethylene glycol) (PEG), long known as a plasticizer for PLA, with nominal Mw of 600 g/mol, was also used to plasticize PLA for comparison. The thermal and tensile properties of PLA and PLA with 5-12.5 wt % of the plasticizers were studied. In blends of PLA with PPGs the glass transition temperature was lower than that of neat PLA. Both PPGs enhanced the crystallizability of PLA albeit less than PEG. All of the plasticizers increased also the ability of PLA to plastic deformation which was reflected in a decrease of yield stress and in an increase of elongation at break. The effect was enhanced by the higher PPG content and also by lower molecular weight of PPG. A phase separation occurred only in the blend containing 12.5 wt % of PPG with higher molecular weight. The evidences of crazing were found in deformed samples of PLA with low plasticizer content, whereas the samples with higher content of plasticizers crystallized due to deformation.

The solid state structure and properties of homogeneous copolymers of propylene and 1-hexene were studied by examining melting behavior, dynamic mechanical response, and morphology primarily with atomic force microscopy, wide- (WAXS) and small-angle X-ray scattering, and tensile deformation. Chain microstructure was analyzed by 13C NMR. The results indicate that copolymers used in this study have an essentially random distribution of comonomer. For copolymers with less than 10 mol% hexane, crystallinity decreases with increasing comonomer content, as expected for exclusion of comonomer from the polypropylene crystal. The peak melting and crystallization temperatures also decrease with increasing hexene content. Copolymers with more than 10 mol% hexane crystallize with a new crystal structure that permits incorporation of hexene units. This is inferred from a higher level of crystallinity than would be expected if comonomer were excluded from the crystal and better development of the crystals as the hexene...

A method of obtaining polymer with markedly decreased entanglements concentration in melt, via high-pressure crystallization of high-density polyethylene (HDPE), is elaborated. It is shown, by calculations and experiments, that melting of chain-extended crystals obtained in this process provides a chain-disentangled melt for a period of 20−30 min. The disentanglement is tested by means of spherulite growth rate measurements in a regime II melt crystallization. Spherulites grow faster from partially disentangled melt than from melt with normal concentration of entanglements: the growth rate is increased by 25−45%, and the conversion rate is also markedly higher. The difference is augmenting with decreasing undercoolingconsistently with conclusions made from nucleation theory including reptationand decaying with increasing time of melt annealing at 160 °C before crystallization, which is a result of entanglements reconstitution. The crystallization behavior in initially chain disentangled samples subjected...

Blends of polystyrene with of spherical shell particles composed of alternating shells of PS and lightly crosslinked polybutadiene of averaze sizes of 0.32 and 2.3 μm are prepared at particle weight fractions of 0,05 and 0,15. It is found that the craze flow stress increases systematically with decreasing particle volume fraction at constant particle size and that the blends with the small particles that are less potent craze initiators have higher flow stresses than blends with large particles