1994 рік

Ultra-thin, highly oriented polyethylene (PE) films drawn from the melt have been investigated using scanning force microscopy (SFM) to study their surface morphology. The results obtained from SFM measurements exhibit the lamellar morphology and evidence for extended chain crystals of the films. Morphological defects, such as structural thickness modulations of lamellae and steps on lamellar crystals of ~< 1 nm height, were obtained. The fact that the lamellar crystals protrude out of the film surface is explained by a combination of film processing and crystal growth effects. On a molecular scale, high resolution SFM investigations of the crystalline parts of the film show extended PE chains with an intermolecular distance repeat of 0.56-1- 0.1 nm.

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Compression creep measurements on acrylonitrile-butadiene-styrene (ABS) polymers were conducted to compare with the results of the impression creep tests at similar stress levels and testing temperatures. The creep curves of ABS polymers obtained from the compression tests were similar to those from the impression tests, namely they all exhibited transient and steady-state stages. The stress and temperature dependences of the steady-state strain rate obtained from the compression tests were in general agreement with the corresponding quantities obtained from the impression tests at temperatures below 353 K; however, they deviated from each other at higher temperatures

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The longitudinal sound velocities in crosslinked polyacrylate hydrogels were measured as a function of water content in the gel in the temperature range 30-I00°C. The sound velocity changed drastically around a water content of 40--50 wt %. Above this range, the sound velocity decreased monotonically and approached that of pure water. The maximum sound velocity was observed around 74°C for a water content above 50 wt%, while for a water content less than ca. 40 wt% the temperature dependence curve of the sound velocity became concave. The amount of water bound to the gel was estimated and was discovered to vary depending on the ratio of sodium polyacrylate to polyacrylic acid and the temperature

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Poly(spiro[2,4]hepta-4,6-diene) (PSHD) was exposed to oxidants such as bromine, iodine and antimony pentachloride either in solution or as a film. Bromine was rapidly added to the C--~C bonds of the polymer. Heating the brominated polymer to elevated temperatures resulted in dehydrobromination and the formation of a conjugated, unsaturated polymer backbone, recognizable by the formation of a black, insoluble product. Exposure of PSHD to iodine or antimony pentachloride led to the formation of a black product with a metallic appearance. The conjugation length of the resulting oxidized polymer was rather short. From optical absorption spectra a length of six to eight C~---~C bonds could be deduced. Infra-red spectra indicated that oxidation was accompanied by a cleavage of the cyclopropyl groups. The oxidized polymer was electrically conducting. Maximum conductivities of 10- 5 S cm- ~ were obtained when PSHD was exposed to iodine vapour for several hours. From electron spin resonance studies it could be derived that the conductivity is due to an electron-hopping process.

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Films of polystyrene-polybutadiene-polystyrene triblock copolymer were cast from toluene solutions using the technique of 'roll-casting', which leads to microphase separation of the block copolymer into globally oriented structures that are often termed 'single crystals'. The thermal expansion of unannealed films was found to be dominated by molecular stresses resulting from the casting process. The angular dependence of the thermal expansion coefficient of annealed films, which were free of any preferred molecular orientation, was governed by the supramolecular structure and was found to be in good agreement with theoretical predictions related to traditional composite materials.

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We investigate the miscibility of a polystyrene/poly(vinyl methyl ether) (PS/PVME) blend using nuclear magnetic resonance spectroscopy. We examine 1H spin-lattice relaxation times in both the laboratory (Tin) and rotating (T~pH) frames at various temperatures. At temperatures lower than the glass transition temperature (T~) of the blend, the observed 1H relaxation time of PS is equal to that of PVME, showing that the 5/5 PS/PVME blend is miscible on a scale of 20-30 A. At temperatures much higher than T~, the observed ~H relaxation curve (T~pH) of PS apparently differs from that of PVME. They are not single exponentials. The non-exponential decays are analysed taking into account spin diffusion; the ~H spin diffusion rate between PS and PVME is found to be ~ 1000s -~ at 38°C. This spin diffusion rate is too slow for the T~pH values of PS and PVME to coincide with each other. This is attributed to the fast molecular motion of PVME. The IH relaxation curve of the phase-separated blend formed by heating above the lower critical solution temperature is markedly different from that of the homogeneous blend. On the assumption that IH spin diffusion does not occur between phase-separated domains, we analyse the ~H relaxation curve of each component polymer and obtain the stoichiometry of the phase-separated domains. We conclude that the phase separation of the 5/5 PS/PVME blend is initiated by spinodal decomposition; the phase separation rate is 0.5 min-t at 140°C.

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The surface modification of polytetrafluoroethylene (PTFE) by microwave plasma treatment was investigated by means of contact angle measurement and e.s.c.a, studies. Various gases (e.g. 02, O2/N~, NH3) were used. The influence of the various plasma parameters, such as power, gas flow, distance between the sample and the centre of the discharge, treatment time, etc., has been evaluated. No modification was induced by 02 and O2/N2 treatment, whatever the treatment conditions. NH 3 plasma irradiation, however, rendered the PTFE surfaces more hydrophilic, leading to an increase of the polar component of the surface energy from 4.5 to ~ 57 mJ m- 2 under optimized treatment conditions. NH3 treatment led to defluorination, crosslinking, hydrocarbon (CC,CH) bond formation, and incorporation of nitrogen-containing groups, as confirmed by e.s.c.a. Oxygen was also detected at the surface of treated PTFE. Correlations between the contact angle, defluorination rate, and surface nitrogen and oxygen contents, have been established. Optimization of operational NH 3 plasma parameters, leading to the best wettability of the treated samples, is also reported.

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Three -(AB),- type multiblock copolymers, consisting of soft segments of polyolefin and hard segments of poly(ethylene terephthalate) (PET), were synthesized through melt polycondensation by reacting a hydrogenated hydroxy-terminated polybutadiene and dimethyl terephthalate with a stoichiometric excess of ethylene glycol. The synthesized copolymers are not soluble in toluene, m-xylene, m-cresol or phenol/tetrachloroethane because of the very different solubility behaviour of the two incompatible blocks. These copolymers exhibit two clear melting temperatures as determined by differential scanning calorimetry and two glass transition temperatures as observed by dynamic mechanical analysis. The melting temperatures of the polyolefin and PET blocks increase with increasing weight fraction of the corresponding block. The glass transition temperatures of the polyolefin and PET blocks are around -17°C and 79°C, respectively. As the PET weight fraction is decreased to 15%, its glass transition temperature (tan t~ peak) becomes broader because of interference by the melting transition of the polyolefin block

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Water structures in polymeric matrices were studied using Fourier transform infra-red (FTi.r.) spectroscopy. The infra-red spectra of water sorbed in many polymers imply systematic changes. As the polymer becomes more hydrophilic, among the three bands corresponding to the normal vibrational modes of an isolated water molecule the va(OH ) and v,(OH) bands gradually shift to lower frequencies, while the 6( / HOH) band moves to a higher frequency. Using these shifts, we have deduced the heat of water sorption for several hydrophobic polymers. Moreover, it has been found that the atom with the largest electronegativity in the polymers increases the bending frequency shift, A6(/_HOH), more than the stretching frequency shifts, Ava(OH ) and Av,(OH). Eventually, it was concluded that water molecules sorbed in solid polymers, in almost all cases (for both hydrophilic and hydrophobic materials), form either strong or weak hydrogen bonds with particular site atoms in the polymers. Various water structures in these polymeric matrices were discussed in terms of the FTi.r. data that were obtained.

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Wide angle X-ray diffraction has been used to investigate polymorphism in isotactic polypropylene (IPP) mouldings produced by conventional injection moulding and by shear controlled orientation injection moulding (SCORIM). y Phase was found to form in highly oriented IPP produced by SCORIM, with a marked enhancement of the preferred orientation of the ~ phase and percentage crystallinity when compared with conventionally moulded IPP.

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