1993 рік

The gelation behaviour of a series of polystyrene (PS)-poly(vinyl methyl ether) (PVME) blends that had been exposed to electron beam radiation was determined. The gel fraction produced by electron beam irradiation of this blend was determined as a function of dose, blend composition and morphology. The effect of morphology was examined by irradiating miscible blends and blends that had been phase separated by spinodal decomposition. The results indicate that PS does not offer any protection from radiation crosslinking in the miscible blends. In fact, the addition of a small amount of PVME to pure PS greatly increased the gel content, suggesting that a significant amount of grafting is occurring between the blend components. Phase separation of these blends has been shown to significantly influence the effect of blend composition on the gel content, primarily by altering the localized composition of the blend.

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The intrinsic viscosity of polystyrene in cyclohexane is measured as a function of molecular weight at the critical temperature, 32.9°C. The results are plotted in the form of [r/] 1/3 versus N 1/3 (I-r/] = intrinsic viscosity, N = number of links in a polymer molecule). The scaling law for the collapsed state in the form of R ~ N 1/3 (R -- end-to-end distance) seems to have been obeyed.

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Poly(1,4-butylene isophthalate)s containing sodium sulfonate groups were prepared from dimethyl isophthalate, 3,5-bis(carbomethoxycarbonyl) benzenesulfonate (5SIPNa) and 1,4-butanediol. Polymers of fairly high molecular weight were obtained with a content of ionic comonomeric units up to 16.7 mol%; however, increasing amounts of 5SIPNa led to a decrease in the molecular weight and to an increase in the COOH/OH terminal-group ratio. The ionomer samples were characterized for chemical structure, terminal groups, the concentration of sulfonate groups, solubility and their thermal properties. Results from different methods of terminal-group and sulfonate-group analysis were compared. Solubility was found to be strongly affected by the introduction of sulfonate groups, and samples containing 16.7 mol% of SO3Na groups were water dispersible. D.s.c. studies on samples containing sulfonate groups, either in the free acid or sodium salt form, suggested that the effects on glass transition temperature and crystallization were due to the introduction of bulky sulfonate groups into the polymer backbone rather than to ionic interactions. Thermogravimetry showed that SO3H groups decreased the thermal stability significantly, while SO3Na groups had only a limited effect with respect to pure poly(1,4-butylene isophthalate).

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Time-resolved simultaneous small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD) experiments using synchrotron radiation were made in order to study the isothermal crystallization behaviour of poly(aryl ether ether ketone) (PEEK). Two types of long period (LB and L~), the scattering invariant Q, and the linear degree of crystallinity within the lamellar stacks XCL were estimated from the Lorentz-corrected plot and the correlation function. As a result, the average lamellar thickness Ic was calculated as the product of L~c and XCL during crystallization at temperatures of 230-310°C. The bulk degree of crystallinity (by weight), ~kc, was determined by WAXD. It was found that both long periods decreased, Q increased and lc remained approximately constant with time. The decrease in the long period was explained by the lamellar insertion within the lamellar stacks, whereas the increase in Q was attributed to the increase in the bulk-volume degree of crystallinity Xc, rather than XCL, In addition, the values of the long period and of Q were found to increase with temperature as a result of the thicker lamellae. Finally, our results support the model of two populations in lamellar thickness, namely the primary lamellae which are developed first in bundle-like stacks, and the narrower, secondary lamellae (as a small fraction) that are inserted later between the primary lamellae under various spatial restrictions.

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We report for the first time a non-linear optical polymer exhibiting optical transparency down to 307 nm. From the Maker fringe measurements, the non-linear optical d33 coefficient of poled aromatic polyurea films was found to be 14 times that of potassium dihydrogen phosphate (KDP) at 1.064 #m fundamental radiation. Aromatic polyurea forms flexible, colourless and transparent films and thermogravimetric analysis showed high thermal stability. The non-linear efficiency and optical transparency make aromatic polyurea a potentially useful material for non-linear optics.

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A series of aliphatic polyesters of 3,3'-thiodipropionic acid and linear glycols containing a different number of ethylene oxide groups has been prepared and characterized. These polymers show low values of glass transition temperature and appear, at room temperature, as highly viscous liquids, in which LiC104 can be dissolved easily. The resulting transparent semi-solid solutions behave as polymer electrolytes with high ionic conductivity, which has been investigated as a function of LiC104 concentration, temperature and chemical structure, i.e. the number of thioether sulfur and ether oxygen atoms in the backbone. The main factors that affect conductivity are the glass transition temperature and the solvating capacity for the lithium ions. It was found that both the oxygen and sulfur atoms contribute to solvating lithium ions.

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Heating measurements of amorphous and isothermally crystallized (260-320°C) samples were carried out using time-resolved small-angle X-ray scattering (SAXS) to study the melting behaviour of poly(aryl ether ether ketone) (PEEK). In the amorphous sample, the scattering maximum became detectable after the cold crystallization, with the peak position qm,x decreasing with temperature. The latter was also seen in crystallized samples. Two types of long period (L~ and LMc ) were determined, by using Bragg's law and the correlation function, respectively. These values are inversely proportional to q .... and therefore they all increased with temperature. In the crystallized samples, two stages of increase in the long period were found: below the lower melting temperature of the double endotherms (Tin,, determined by d.s.c.), the increase was small, while above Tin,, both of the long periods increased rapidly. In addition, the invariant Q was found to increase with temperature but reached a maximum near the onset temperature of the last endotherm. These results were consistent with the hypothesis of sequential melting of lamellar bundles consisting of two populations of thickness. In the crystalline specimens, the increase in Q was mainly due to the thermal expansion, whereas in the amorphous sample, the larger increase in Q was additionally attributed to the broad cold crystallization.

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Dilute solutions of poly (~-methylvinylacetophenone) (PM VAP) were exposed to long-wave (2/> 300 nm ) u.v. radiation under high vacuum conditions. The low molecular weight products, analysed by mass spectrometry, were ethane, methane and CO, and their appearance indicates that PMVAP decomposes via Norrish type I (~ cleavage) reactions. The relatively higher ethane yield reflects the greater difficulty of H abstraction by methyl radicals, substitution at the ~-C atom forcing the methyls to abstract at the less reactive secondary C atoms. Random chain scission also occurs, and has been attributed to the fl scission of macroradicals, which are formed by abstraction reactions involving methyl radicals, and more importantly, carbonyl triplets (photoreduction). Spectroscopic evidence supports the proposed chain scission mechanism.

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An improved method for obtaining cross-sectional images of thin polymer films by transmission electron microscopy is described. Two examples are described in order to demonstrate the simplicity and flexibility of the technique, In the first example, the structure of a highly ordered block copolymer on a solid surface is examined. In the second example, the behaviour of colloidal gold particles at the interface between immiscible polymers is considered.

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Characterization of the crystalline and amorphous orientation of a uniaxially deformed low-density polyethylene (LDPE) film has been accomplished by combining pole figure X-ray diffraction and birefringence measurements. Characterization of the crystalline regions of the extruded film reveals the existence of a row-nucleated morphology with the a axis preferentially oriented in the plane containing the machine (MD) and transverse (TD) directions and the b axis strongly oriented along the film normal. This morphology is embedded in an amorphous matrix, biaxially oriented in nature. Low uniaxial extension along the MD produces two major orientational states in the crystalline regions which seem independent of the corresponding amorphous orientation. The pole figure analysis clearly shows that the c axis weakly orients towards the MD. Upon further uniaxial extension, it begins to tilt progressively away from the stretching direction inducing a complementary orientational behaviour between the c and b crystallographic axes on account of the stationary a-axis orientation perpendicular to the stretching direction. At higher draw ratios, the c axis gradually realigns itself with the stretching direction and uniaxial orientational states in all regions of the microstructure are obtained, indicating the existence of a fibrillar-type morphology. Quantification of the induced orientation was carried out and compared in terms of Hermans, Nomura/Kawai and White/Spruiell orientation functions.

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