1992 рік

The morphology and temperature dependence of the lateral growth rate G are reported for isotactic polystyrene crystallized from 0.1% dimethyl phthalate solution at high supercoolings. The outline of a lamella is a rounded hexagon for the highest temperature and a ragged circle for lower temperatures. The edges of the lamellae become ragged and overgrowth is pronounced with decreasing temperature. A linear relationship is found between log(G/r/) and 1~TAT over a wide range of supercooling (AT= T~a - T) from 70 to 170 K, where r/is a retardation factor of Arrhenius form with an activation energy of 8400 K, and ~ is the equilibrium dissolution temperature. The value of ~d is determined to be 200°C by differential scanning calorimetry. In these high supercoolings, the nucleation theory of polymer crystallization loses its validity; in fact, the slope of the plot of log(G/r/) versus I/TAT is four times as large as the value predicted by nucleation theory. Possible growth mechanisms at high supercoolings are discussed on the basis of the morphology

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Blends of a thermotropic liquid-crystalline polymer with poly(phenylene ether) are investigated in the melt and solid state. Melt flow properties are examined using a number of different flow regimes - ranging from simple shear to flows with an extensional component. The blends are shown to be largely immiscible in the molten state, with the addition of liquid-crystalline polymer reducing the blend viscosity. This viscosity reduction is seen to be more effective in the case of flows that contain an extensional flow history. The morphology associated with these blends is oriented liquid-crystalline polymer fibrils suspended in a poly(phenylene ether) matrix. Thermal and mechanical analysis indicates that the two polymers are practically immiscible in the solid state with the possibility of slight intermixing. Crystallization data indicates that the presence of the LCP phase may encourage crystallinity of the poly (phenylene ether) phase

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Thermodynamic analysis of the system isotactic polypropylene/n,n-bis(2-hydroxyethyl) tallowamine was performed using Flory's equation of state theory adapted to the polymer/oligomer system using parameters determined in the first paper in this series. The estimated results were in good agreement with those from melting temperature depression and cloud point measurements. The equilibrium phase diagram was estimated even in the experimentally unavailable region. When the estimated phase diagram could be compared with the experimental data, the agreement was good. The interaction parameter for this system increased greatly with temperature resulting in upper critical solution temperature behaviour. The increased end group polarity of n,n-bis(2-hydroxyethyl) tallowamine resulted in much greater enthalpic interactions than the n-alkane and n-fatty acid systems covered in the second paper in this series.

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Thermally stimulated currents (t.s.c.s) and a.c. dielectric spectroscopy were used to study poly(butylene terephthalate) (PBT) and blends of PBT with segmented copoly (ester-ether) elastomers. The high sensitivity of t.s.c, and a.c. dielectric techniques as compared to d.s.c, was useful for the study of these blends where the elastomer phase was present at only 20%. The techniques together cover a frequency range of 5 x 10-3-10 s Hz allowing detailed characterization of amorphous relaxations in these phase separated blends. Two separate glass transitions for the PBT/copoly(ester-ether) blends were observed, unchanged from the original pure components, indicating that they are immiscible and that ester exchange during processing was minimal. Peak assignments are made using a new analysis scheme by comparing activation energies (Ea) determined by the t.s.c, thermal sampling technique with predicted values using the activated states equation. With this method all values of E a agree with the zero activation entropy prediction except those measured in the vicinity of glass transitions.

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A new poly (amide ester )-ester copolymer was synthesized by reacting two oligomers, namely, oligo (amide ester) and oligo ester. Depending on the molar ratio of the two oligomers, a behavioural pattern of elastomeric to elastoplastic material was observed. D.s.c. studies revealed two glass transition temperatures : one at -40 to -50°C and another at 40 to 50°C, showing the presence of two different segments in the polymer backbone. Electron microscopic studies could not distinguish and differentiate the phase separation behaviour of the segments in the polymer. Mechanical studies showed that the polymer has a tensile strength at break of 6-20 MPa with an elongation as high as 160%.

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The molecular mechanism of real rubber vulcanizates, both unfilled and filled, is discussed in relation to the classical non-Gauss/an theory, in which the deviation from theory at large deformation seems to be attributable to the concept of fixed crosslinks in the theory. A new slider model that possesses the characteristic viscous property is introduced to represent physical crosslinks. The slider model is effectively available for interpreting the typical phenomena observed in real rubber vulcanizates, such as the crossing of the stress strain curves measured at different temperatures and the Mullins softening under cyclic deformation.

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Fourier transform infrared (FTi.r.) microspectroscopy was applied to evaluate the microscopic orientation of extrusion moulded sheets of a thermotropic liquid crystalline polymer, consisting of 4-hydroxybenzoic acid units, biphenol units and benzene dicarboxylic acid units. The polarized i.r. spectra were measured in the microscopic area down to 40 pm using a redundantly apertured i.r. microscope equipped with a wire-grid polarizer. It was shown that Beer's law held in the absorbance range below 2.5, and the polarization properties of oriented samples were accurately measured by FTi.r. microspectroscopy. The orientation profiles of the polymer sheets were obtained by plotting the dichroic ratio of the 1602 cm-1 band against distance from the centres of sheets. In the case of the sheet 0.68 mm thick, the central region is nearly isotropic, but the dichroic ratio increases markedly toward the surface of the sheet. In the thinner sheet (0.255 mm), the polymer chains in both surface and central regions are highly oriented in the extrusion direction, and the dichroic ratio gradually increases on approaching the surface. At the same sheet thickness, the degree of orientation decreases as the extrusion temperature is lowered. The orientation profiles obtained by polarized FTi.r. microspectroscopy are in accordance with the morphological structures studied by scanning electron microscopy

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A new procedure for analysing the structure of linear low-density polyethylene (LLDPE) based on differential scanning calorimetry (d.s.c.) has been developed. LLDPE with heterogeneous and homogeneous distributions of comonomer units have been annealed in stages at decreasing temperatures starting from the melt. With this new procedure, it has been possible to show on d.s.c, thermograms the appearance of various families of macromolecules in the case of heterogeneous copolymers. In the case of more homogeneous copolymers, various families are still present in the material but in a smaller number. Furthermore, using the various melting peaks that appeared on the d.s.c, thermogram during the heating of the annealed polymer and with the help of a calibration curve, it has been possible to determine qualitatively the composition of the LLDPE.

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The phase-transfer-catalysed chlorinations of poly(2-methylstyrene), poly(3-methylstyrene), poly(2,4- dimethylstyrene ) and poly (2,5-dimethylstyrene) using sodium hypochlorite in chloroform/dichloromethane mixtures are compared with that for poly(4-methylstyrene). Over the range of conditions employed, the chlorination of poly(2-methylstyrene) is barely detectable and the polymers with methyl substituents in the meta position show a lesser tendency to undergo chlorination than those with methyl substituents in the para position. In all cases concomitant modification of the molecular weight distributions of the polymers are minimal when the reactions are carried out at an aqueous phase pH of 8.5 and with a chloroform-rich organic phase. With a dichloromethane-rich organic phase, polymer chain scission is marked. The experimental observations are discussed both in terms of a compatible mechanism and of inductive effects involving the phenyl ring substituents.

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The cure of tetraglycidyl-4,4'-diaminodiphenylmethane with 27 wt% diaminodiphenylsulphone at 160°C was studied using near i.r. spectroscopy. The changes in concentrations of epoxy, hydroxyl, ether and primary, secondary and tertiary amine groups during cure were calculated and empirical reaction rate curves derived for the various functional groups involved. An autocatalytic reaction mechanism was observed for both the primary and the secondary amine group reaction with epoxide. The secondary amine-epoxy reaction showed a substitution effect and is affected by the changes in rheological properties of the resin during gelation and vitrification. Two separate epoxy-hydroxyl reactions are observed, as well as a cyclization reaction due to impurities.

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