1994 рік

Polyurethanes from a system consisting of ethylene oxide endcapped poly(propylene oxide) polyol (PPO-EO), 4,4'-diphenylmethane diisocyanate (MDI) and ethylenediol (EDO) have been synthesized using a one-step process. The morphology of these polyurethanes has been investigated by a variety of techniques. Hard-segment-rich spberulites, with sizes of 10 #m in diameter, consisting of scattering fibrils, have been observed. The melting points of these spherulites lie in the range 220-260°C. The degree of microphase separation and the crystallinity of the polyurethanes increases with an increase in the hard-segment content. In addition, a relationship between the microstructure and the mechanical properties of these materials has been found.

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A novel approach to prepare composites of different porosity and morphology is demonstrated. Instead of blending two polymers, hydrophilic and hydrophobic monomers are solubilized in microemulsions and then polymerized to obtain composites with the desired properties. This technique is exemplified by the polymerization of microemulsions containing styrene and acrylamide as the hydrophobic and hydrophilic monomer, respectively. Different types of surfactants were used in formulating the microemulsions: anionic sodium dodecyl sulfate (SDS), cationic cetyltriethylammonium bromide (CTAB) and zwitterionic octadecyl dimethyl betaine (C18DMB). The clear or bluish microemulsions were stable at room temperature and at the polymerization temperature of 55°C. No gross phase separation was observed during polymerization. The morphology and thermal behaviour of the composites resulting from microemulsion polymerization are strongly influenced by the surfactant, which is trapped inside the solid. C18DMB produced the largest pore size and most rigid composite. Use of SDS or CTAB led to a random copolymer, poly(styrene-coacrylamide), with a single glass transition temperature (Tg) of 151 + 2°C, which is intermediate between the Tg values of the two homopolymers. The composite obtained using C18DMB was more heterogeneous, with polystyrene-rich and polyacrylamide-rich domains in addition to the copolymer. The Tg values of the polystyrene-rich (89+ I°C) and polyacrylamide-rich (171+ I°C) domains are lower than those of the corresponding homopolymers (99+ I°C and 175+1°C, respectively). Apparently, C18DMB acts as a plasticizer in the composite.

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High molecular weight semicrystalline poly(aryl ether ketone)s have been prepared from hydroquinone and 1,3-bis(4-chlorobenzoyl)benzene in diphenylsulfone and anhydrous potassium carbonate with or without toluene. The use of this solvent system, instead of a combination of dimethylacetamide, diphenylsulfone and toluene, results in the elimination of SRN1 (radical nucleophilic, unimolecular substitution) processes and the formation of high molecular weight polymer takes place entirely via SNAR (nucleophilic aromatic substitution) reactions

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Partial Least Squares modelling techniques have been used to calibrate Raman spectra in terms of the density of poly(ethylene terephthalate), with a standard prediction error of 0.0024 gcm- 3. The calibration, which utilizes, primarily, the bands at ~ 1730, 1094, 997, and 860 cm -1, spans isotropic, uniaxial and biaxially oriented samples with a single model; this is superior to univariate calibrations which require separate models for isotropic and oriented samples. Hierarchical Cluster Analysis and Principal Components Analysis were also used for exploratory analysis of the spectra; these methods grouped samples in terms of their density and orientation characteristics, and also identified the bands which responded most significantly to morphology changes. It was shown that the 1615 cm- 1 ring-stretching mode differentiated the samples on a basis other than simply by density or orientation alone; further work, however, is needed to understand this behaviour. The potential power of multivariate analysis techniques for correlating Raman spectra and polymer morphology was clearly demonstrated.

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We have measured the surface wettability of poly(ethylene terephthalate) (PET) film drawn to different draw ratios at strain rates of 0.56 and 0.01 s 1 and a draw temperature of 90°C. The probe liquid was demineralized water. We believe that the observed changes in advancing and receding work of adhesion--and in the wetting hysteresis indicated by their difference--reflect a lowering of the energy state of the film surface during drawing, due to increases in 'amorphous orientation' and the onset of crystallization. Orientation-induced interaction between PET molecules may reduce the availability of sites that would otherwise interact with water.

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A diblock copolymer based on poly(p-benzamide) (PBA) and poly(2-phenylene-(5-benzimidazole))isophthalamide (PABI) was synthesized by direct coupling reaction between acylchloride and amino end groups of the two homopolymers. Soxhlet extraction with N,N'-dimethylacetamide completely removed unreacted PABI and allowed determination of copolymer content and composition of the unextracted fraction (by u.v. data and viscosity measurements). Preliminary results on phase behaviour are given and analysed in terms of block length

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The protonation behaviour of emeraldine (EM) films by two polymeric acids, poly(acrylic acid) (PAAc) and poly(styrenesulfonic acid) (PSSAc), was studied by X-ray photoelectron spectroscopy (X.p.s.). The EM-PAAc films were prepared by direct protonation of EM films in aqueous PAAc medium, by blending of EM and PAAc in N-methylpyrrolidinone (NMP) and by near-ultra-violet light-induced surface graft copolymerization of EM film with acrylic acid. EM-PAAc salts were also prepared by direct polymerization of aniline in PAAc solutions. Relatively weak charge-transfer interactions or low protonation levels were observed in all cases, even in the presence of a large excess of PAAc units. However, in the presence of a strong acid such as PSSAc, almost all the amine nitrogens in the surface region of the EM film, in addition to the imine nitrogens, were susceptible to protonation. Furthermore, deprotonation of the PSSAc protonated EM film, but not the PAAc protonated EM film, was accompanied by a substantial increase in the intrinsic oxidation state of the EM film, leading to the 75% intrinsically oxidized nigraniline state. Lower extent of surface hydrolysis reaction was also observed during protonation by the polymeric acid than by mineral acids.

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We carried out the dynamic vulcanization of poly(butylene terephthalate) (PBT) with ethylene rubber having an epoxy group and investigated the morphology-mechanical properties relationship. The curing agent for the rubber used was adipic acid (AA). The AA-loaded (0.1 phr) 50/50 PBT/rubber blend had a two-phase structure of densely dispersed rubber particles in a PBT matrix and it showed excellent elastic behaviour, i.e. strain recovery after large deformation. To understand the elastic character, we constructed a two-dimensional model with five rubber inclusions in a PBT matrix and carried out an elastic-plastic analysis on the deformation mechanism by the finite-element method (FEM). FEM analysis revealed that, even in the highly deformed states in which almost the whole matrix has yielded due to the stress concentration, the ligament matrix between rubber inclusions in the stretching direction is preserved within the elastic limit to form an elastic field by interconnecting cured rubber particles. The tensile dilatometry test and transmission electron microscopy observation clearly showed internal cavitation of rubber particles. Insufficient strain recovery seems to be caused by the cavitation.

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Scanning transmission electron microscopy (STEM) dark field images reveal that within the essentially amorphous matrix of quench-cooled isotactic polypropylene (iPP) there exist microcrystalline regions, 100 to 200 A in size, that have the ~-monoclinic crystal form (a = 6.67 + 0.01, b =20.89 + 0.05, c= 6.48 +0.01 A, /~=98.4+0.6°). Regions of lower crystalline order are also observed which, according to micro-micro diffraction, also possess the c~-monoclinic crystal structure but with substantially larger unit cell constants (a = 7.03 ± 0.01, b = 2 i. 1 ± 0.1, c = 6.47 + 0.02 &, fl = 99 ± 2°). Differential scanning calorimetry studies indicate that during quench cooling to the glassy state iPP samples attain a low degree of crystalline order to an extent that depends on sample mass. Upon heating from the glassy state, these samples exhibit exothermic transitions, between - 15 and 120°C, that correspond to the formation and subsequent perfection of the microcrystalline regions observed by STEM dark field.

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This paper is devoted to a molecular description of the deformation of amorphous isotropic poly(ethylene terephthalate) (PET) films at temperatures slightly above the glass transition temperature under constant load. The deformation is qualitatively described by chain relaxation phenomena occurring before stress-induced crystallization, which are followed by the equilibration of a rubber-like network. The junction points include both trapped entanglements and crystalline units. The structure of this network is characterized by the number of segments between crosslinks. This parameter is calculated by comparing the predictions of the rubber elasticity theory (without Gaussian approximation) with the experimentally observed draw ratios under given conditions of temperatures and loads. It is shown that light loads induce soft networks leading to high draw ratios. The predictions of the molecular orientation derived from this treatment are in good agreement with birefringence data on a large variety of samples.

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