1994 рік

A new technique for preparing freely suspended submicron films of poly(3-nonylthiophene) (PNT) has been developed. These films were characterized by both i.r. and u.v. spectroscopy, allowing us to qualitatively analyse the effects of photo-oxidation and how these effects change with the period of time after the end of the irradiation treatment. Before these spectroscopic measurements were made, PNT was compensated with hydrazine in order to remove any chemical impurities resulting from the polymerization catalyst. The i.r. experiments indicate that when PNT was irradiated by light of wavelength longer than 466 nm, electrons were transferred from the PNT to oxygen. Thus, the photo-oxidation process resulted in the formation of positive polarons on the polymer chains, plus superoxide anions. In the dark, electrons were transferred back to the polymer chains, which therefore returned to their neutral state. This mechanism was supported by e.s.r, experiments. Irradiation by light of wavelength shorter than 466 nm induced i.r. absorptions due to both polarons and sulfonyl groups, as well as conjugation-breaking reactions. When impurities were not removed, the formation ofpolarons and sulfonyl groups was observed even if wavelengths shorter than 466 nm were excluded. These impurities also accelerated the conjugation-breaking reactions.

Детальніше...  

A thermally induced associative polymer was developed by grafting lower critical solution temperature side chains onto a water-soluble backbone. Based upon the thermodynamic properties of the pendent chains, acting as reversible crosslinkers with varying temperature, such a system was prepared from a poly(ethylene oxide)-modified poly(acrylic acid) (PAA-g-PEO). In aqueous solution this polymer provides an enhancement of the viscosity on heating, the extent of which can be controlled by polymer concentration, grafting ratio and salt concentration.

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Polyacrylonitriles prepared by aqueous free-radical slurry polymerization at 40°C using ammonium persulfate and sodium metabisulfite as redox initiator have been examined by FTi.r. and by high-field 13C and IH n.m.r. They have been shown to contain small quantities of acrylamide and acrylic acid units and to possess predominantly sulfonate and non-sulfur containing end-groups derived principally from transfer to bisulfite ion during the polymerization. Other end-groups present in low concentration are sulfate and hydroxyl; the former probably arises from initiation by sulfate radical anions and the latter either from transfer to water or by adventitious hydrolysis of some of the sulfate end-groups. Because they contain few groups capable of initiating intramolecular cyclization, the polyacrylonitriles are white with no sign of discoloration.

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We investigated the dielectric properties of crystalline poly(vinylidene fluoride) (PVDF)/poly(methyl methacrylate) (PMMA) blends in a wide range of frequency f at various temperatures T. A large peak of the dielectric loss e"(f) due to the interfacial polarization was found in the blend below the frequency region of the ~c process. Such a peak was not observed in neat PVDF. The difference may be ascribed to the existence of a large amount of PMMA at the crystal-amorphous interphase in the blend. We also demonstrated that a low Tpeak in e"(T), which was thought of as an interfacial peak, is not related to the cta process of PVDF in the interphase, but to the fl process of PVDF.

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Blends of polycarbonate (PC) and poly(acrylonitrile-butadiene-styrene) (ABS) of compositions ranging between 10 and 90% ABS have been investigated to study the effect of addition of ABS on the flow properties of polycarbonate. Torque data have been collected for these blends at temperatures in the range of 210-230°C and speed in the range of 40-80 rpm, on a Haake Torque Rheometer System 90. The recorded data have been interpreted in terms of shear rate, shear stress and viscosity. The viscosity of the blend has been found to decrease with shear rate, and the decrease is greater for compositions that are rich in ABS. The viscosity decreases with increase in temperature, although the activation energies show higher values for PC-rich compositions and relatively lower values for ABS-rich blends. Thus, the addition of small amounts of ABS to PC could result in materials having good properties along with improved processability

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The phase separation mechanism in poly(butylene terephthalate) (PBT)/polycarbonate (PC) and PBT/PC-copolymer (cPC) blends was investigated by time-resolved light scattering. The early stage of phase separation followed the linearized theory of spinodal decomposition. The temperature dependence of the apparent diffusion coefficient showed lower critical solution temperature (LCST) type phase behaviour (LCST= 198°C for PBT/PC and 228°C for PBT/cPC). Scaling rules were applied for the late stages to show serious deviations from theoretical expectations. Time variation of the scattering invariant showed that the deviations were caused by an ester exchange reaction. A plausible scenario is presented for the development of a bicontinuous two-phase structure in the melt-extruded blends

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A series of copolymers containing 1,4-phenylenevinylene (PV) and either 2-n-butoxy-5-methoxy-l,4- phenylenevinylene (BMPV) or 2-n-dodecyloxy-5-methoxy-l,4-phenylenevinylene (DDMPV) units were prepared in the form of thin films from their water-soluble sulfonium-salt precursor polymers. The electrical conductivity of the I2- and FeC13-doped copolymers exhibits a steep initial increase with an increase in the content of the BMPV or DDMPV units, followed by a slower increase to finally reach the values of that of the corresponding homopolymers, PBMPV and PDDMPV, respectively. The conductivities of the 12- and FeC13-doped, drawn BMPV copolymer films ranged from 35 to 266 S cm-1, and from 10-1 to 256 S cm-1, respectively, depending on the composition. PDDMPV films could be uniaxially drawn at 150-160°C to a draw ratio of 5, and gave an electrical conductivity value of 27 S cm- i when doped with 12, whereas I2-doped PDDMPV films, obtained from the precursor polymer that itself had been pre-drawn to the draw ratio of 5, exhibited a conductivity of 46 S cm- 1. PDDMPV was found to be soluble in p-xylene, but PBMPV was insoluble in this solvent. The presence of the long dodecyloxy group enables the precursor polymer of PDDMPV to form an ordered structure. The u.v.-vis, spectra of the dialkoxy substituted homopolymers and their corresponding copolymers were red-shifted relative to the parent PPV, suggesting a decreased bandgap, which was consistent with the electron-donating nature of the alkoxy substituents. In general, the electrical conductivities of the DDMPV copolymers were lower than those of the BMPV copolymers, which can be ascribed to the presence of longer insulating alkoxy groups in the former.

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The molecular structure of three isotactic polypropylenes polymerized using either slurry or bulk process and heterogeneous Ziegler-Natta catalysts without external donors was studied in this work. The influence of external donor addition was also examined. The samples were fractionated according to stereoregularity using a solvent gradient extraction method, and calorimetric properties, ~3C nuclear magnetic resonance (n.m.r.) pentad tacticities and molecular weights of the fractions were determined. Statistical analysis was also applied to the 13C n.m.r, results. The samples polymerized with the novel catalyst system had the conventional stereostructure arising from a catalyst-site-controlled propagation mechanism. When compared with commercial polypropylenes, the amount of clustered defects was increased in the products made with the novel catalyst system. The addition of an external donor diminished the amount of highly atactic material, but the isotacticity of long-chain material was also increased. Qualitatively similar defects were detected in all samples, only the amount of defects varied depending on the catalyst structure and polymerization process used. Surprisingly, the bulk polymerization process seemed to favour the formation of non-isotactic material

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The wetting characteristics of an amorphous poly(ethylene terephthalate) (PET) film by water were studied by the Wilhelmy plate technique in the dynamic and static modes. At room temperature, a dynamic hysteresis of 40 ° (0A = 80 °, OR = 40 °) was found. It was interpreted in terms of water adsorption~lesorption phenomena. The air-water and water-air equilibration processes of the PET surface were studied. The static mode was most useful for this purpose. It showed that it takes about 10 days to reach equilibrium at 20°C and that equilibration with water is only partially reversible. Surface restructuration was described by molecular modelling. The validity of this description was confirmed by a good quantitative agreement between experimental and calculated data. An increase of the temperature accelerates molecular rearrangements especially around the glass transition temperature of the polymer

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The morphology of poly(styrene-block-butyl methacrylate) (SBMA) copolymer with 42 wt% S was studied by transmission electron microscopy in a selective environment. Micelles with S cores were observed in dilute solutions in 2-propanol, a non-solvent for S and a theta solvent for the BMA blocks. The solvent influence on the final morphology of SBMA films was investigated. Films obtained from solution in tetrahydrofuran had ordered cylindrical structures. When 10% poly(phenylene oxide) (PPO), which has a preferential interaction with the S blocks, was added to the copolymer, the cylinders turned into spheres with PPO cores separated by the swollen S blocks from a BMA matrix. In PPO/SBMA 50/50 blends multilayer vesicles and lamellar structures coexist. For blends with SBMA content lower than 5%, micelles with BMA cores were observed in a PPO matrix.

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