In this paper, we show that mechanically stretching an immiscible blend made from a nematic side-chain liquid crystalline polymer and a conventional polymer is an efficient way to induce a rapid macroscopic orientation of the mesogenic groups along the stretching direction. The basic condition for this achievement is to perform the mechanical stretching at temperatures between the glass transition temperature and the clearing temperature of the nematic polymer in order to take advantage of the intermolecular co-operativity which is indispensable for a rapid alignment of the nematic domains. The alignment is monitored by determining the orientation of the mesogenic groups using the i.r. dichroism technique. The liquid crystalline polymers investigated are two nematic polyacrylates, and the conventional polymers used are a styrene-butadiene-styrene triblock copolymer, which is a thermoplastic elastomer, and a poly(vinyl chloride).
Samples of injection moulded poly(aryl-ether-ether-ketone) (PEEK) resin with molecular weights covering the range, M,= 15000-50000, have been subjected to a variety of thermal treatments, and the resulting material properties measured. It was found that crystallinity could be increased by annealing the mouldings, but also that an effective ceiling value depended on the molecular weight, i.e. the higher the Mw, the lower the maximum crystallinity. Tensile modulus and yield strength of the moulded polymer increased with increasing crystallinity, but the molecular weight had no detectable effect in these cases. In contrast, both crystallinity and molecular weight independently influenced the toughness. Toughness was found to increase with increasing molecular weight, and to decrease with increasing crystallinity. Implications of these effects on the injection moulding of components of PEEK are discussed
The crystallization behaviour of the poly(ethylene terephthalate-co-l,4-cyclohexylene dimethylene terephthalate) (P(ET/CT)) random copolyesters is studied by d.s.c, analysis. ET units can crystallize with complete rejection of the CT units from the crystals, whereas CT units can co-crystallize with incorporation of ET units to some extent, resulting in a minimum melting temperature at an intermediate composition of about 30--40 mol% CT. A good linear relation is found between the compositions at which the melting point exhibits a minimum experimentally in various random copolyesters and those at which the cohesive energies for two components estimated by group contribution methods are identical.
Poly(oxy-l,4-benzenediylcarbonyl) (POB) whiskers from p-acetoxybenzoic acid were prepared in mixtures of liquid paraffin having many branched carbons (LP) and completely linear paraffin (SW). The crystal shapes of the POB whiskers obtained were largely changed by the mixing ratio of LP and SW. When the content of SW in the solvents increased: (i) both the length and the width of the whiskers decreased; (ii) the tip angle of the whiskers increased; and (iii) radial growth of the whiskers increased. The size of the POB whiskers was attributed to both the number and the size of those lamellar crystals with screw dislocations (primary nuclei for whisker growth) which had formed in the early stages of polymerization. In SW, larger numbers of smaller lamellar crystals were formed than in LP, owing to the lower solubility of POB oligomers at 330°C in SW; that is, the higher supersaturated state of the POB oligomers produced a larger number of smaller primary nuclei for whisker growth. Hence, whiskers having smaller lengths and widths were obtained as the content of SW increased. The other characteristic changes in whisker shapes, i.e. tip angles and radial growth, also seemed to be attributable to the degree of supersaturation of the POB oligomers, though further study is required. The thermal properties of the whiskers were evaluated by differential scanning calorimetry and thermogravimetric analysis.
The compatibilization effect of poly(styrene-b-methyl methacrylate) on the immiscible polymer blend of polystyrene and poly(styrene-co-acrylonitrile) was examined by dynamic mechanical spectroscopy. Special regard was taken of additional relaxation processes in the flow region, which were analysed using weighted relaxation-time spectra. Furthermore, an important topic of our research was the characterization of the morphology by energy-specific transmission electron microscopy. By increasing the amount of compatibilizer, the average particle size decreases from large polystyrene domains (R~-0.2 #m) down to micellar dimensions (R = 60 nm). In this way, typical morphological structures in the blends were related with rheological behaviour. With a modified emulsion model from Choi and Schowalter, some correlations between particle size and trends in interfacial tension could be established dependent on compatibilizer concentration. Especially, it was found that the particle size reduction and the reduction of interracial tension occur in different ranges of block-copolymer concentration
The glass transition (~) and secondary transition (fl) are compared in various aliphatic polyamides swollen by water, alcohol and acid. For all these polymer-solvent systems, the evolution of the temperature T~ with the equilibrium sorption ratio presents two regimes. In the low-concentration regime, the dependence of T~ on the number n of absorbed solvent molecules per accessible amide group follows a master curve independent of the nature of the system. No master curve is, however, observed for the fl transition. In the second regime, above a critical ratio n* dependent on the nature of both the solvent and the polymer, T, levels off, and the maximum concentration of absorbed solvent is proportional to n*. These effects are explained in terms of solvent clustering around the amide groups
The probability of positronium (Ps) formation in semicrystalline poly(ethylene terephthalate) (PET), has been investigated by means of positron annihilation lifetime spectroscopy (p.a.l.s.). The p.a.l.s, data are correlated with the structural characteristics of the samples, such as crystalline content, interlamellar spacing and lamella thickness. The results show an approximately linear decrease of the intensity (I3) of the long-lived orthopositronium (o-Ps) component with an increase in the crystalline content up to 53%, while the lifetime remains practically constant. It seems that the other structural parameters do not affect the Ps formation. The decrease of I3 cannot be completely accounted for if one assumes that o-Ps localizes in the amorphous phase only. It is suggested that the o-Ps also forms in the crystalline regions, due to the inhomogeneous electron density distribution along the c-axis of the PET lattice.
Self-diffusion, viscosity and spin-spin relaxation have been measured for a series of low molecular weight liquid poly(propylene oxide) melts. The data are discussed within the framework of theories commonly invoked for polymer dynamics including the Rouse chain and free volume effects. The average diffusion coefficients of a range of bimodal blends have also been measured and the results interpreted using the Rouse model.
By means of the pulsed-field gradient nuclear magnetic resonance method, the tracer diffusion of homopolymer chains dissolved in the microphase domain of block copolymer mesophase has been studied for two systems: poly(dimethylsiloxane) (PDMS) in polystyrene(PS)-b-PDMS in the presence of d6-benzene as a plasticizer, and poly(ethylene glycol) (PEG) in PS-b-poly(hydroxystyrene-g-PEG)-b-PS. Comparing the diffusion coefficient D of the tracers in the block copolymer matrices with the self-diffusion coefficient D s of the pure tracers, two regimes with a different dependence of D/D s on the molecular weight M of the tracers have commonly been found in the two systems. In the lower M regime (regime I), the ratio D/D s increased remarkably with increasing M, whereas in the higher M regime (regime II), the value of DID s was ~0.15 and was independent of M. This behaviour could be explained by the M dependence of the spatial distribution of the tracer chains in the microphase domain. In regime I, the tracers deeply penetrate into the brushes of the PDMS or grafted PEG with the depth decreasing with increasing M, while in regime II the tracer chains do not penetrate well into the PDMS or PEG brushes, but rather are interposed between the layers.
The dielectric relaxations of poly(dimethylphenyl methacrylate)s were studied over a wide frequency and temperature range by two methods. The ct relaxation, associated with the glass transition temperature, was studied by classical dielectric measurements. Thermal peak cleaning was used to deconvolute the global thermally stimulated current spectra over the range of low temperatures, corresponding to the fl relaxation. The ~ relaxation involves long-range, generalized and highly cooperative motions of the main chain. They are influenced by the steric hindrance and dipole~lipole interactions relative to the position of the CH 3 group of the aryl ring in the polymer repeat unit. As a first approximation it was assumed that the fl process was related only to local motions of the side group, but the activation parameters are too high to be consistent with this assumption. Therefore it was concluded that intermolecular factors and local motions of the main chain could also be involved