1999 рік

The variation in the oxidation state of the titanium species after reaction with various alkylaluminiums was investigated by X-ray photoelectron spectroscopy (XPS). The reaction of an MgCl 2-supported Ziegler catalyst with alkylaluminium was observed to induce a chemical shift to lower binding energy and a broadening of the full width at half maximum intensity (FWHM), depending upon the kind of alkylaluminium. The polymerization kinetics was examined for slurry and stopped-flow polymerization to estimate the relationship between polymerization stages. The catalyst activation and the decay during the polymerization were found to be related to the variation in the titanium species arising from various alkylaluminium compounds.

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Constitutive equations are derived for the viscoelastoplastic response of glassy polymers under isothermal loading. The model is based on a concept of adaptive links (a version of the theory of temporary networks), where active chains are modeled as elastoplastic elements. Breakage and reformation of adaptive links reflect the viscoelastic behavior, whereas irreversible deformations of links are responsible for plastic effects. Stress–strain relations in finite viscoelastoplasticity are developed with the use of the laws of thermodynamics. These relationships are essentially simplified at small strains, when geometrical and physical nonlinearities are neglected. The model is applied to the analysis of uniaxial extension of a viscoelastoplastic bar. Fair agreement is demonstrated between experimental data for polycarbonate and poly(methyl methacrylate) at elevated temperatures and results of numerical simulation.

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Contact mode imaging of plasma-treated poly(ethylene terephthalate) films using bare silicon nitride tips yields poor image resolution because of tip-induced disruption of the surface structure. Deposition of a hydrophobic self-assembled monolayer onto the tip enables the minimisation of the interfacial free energy of the tip-sample contact, with such good effect that images are obtained in contact mode with comparable resolution to that observed in tapping mode. Control of tip chemistry therefore presents an important strategy for the imaging of delicate polymer structures by scanning force microscopy.

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The initiation mechanisms of 1,1,2-trimethylpropyl peroxypivalate 1a and 1,1,2,2-tetramethylpropyl peroxypivalate 1b in the radical polymerization of styrene and methyl methacrylate (MMA) have been studied using the nitroxide trapping technique. Thermolysis of 1 generated t-butyl and the corresponding t-alkoxyl radicals, i.e. 1,1,2-trimethylpropoxyl 2a and 1,1,2,2-tetramethylpropoxyl radicals 2b. Both t-alkoxyl radicals underwent very fast unimolecular processes (b-scission) essentially to the exclusion of intermolecular processes (addition and H-abstraction), in contrast to other t-alkoxyl radicals such as t-butoxyl radicals. The extent of b-scission of 2a and 2b to form alkyl radicals R· were 97.6 and 99.7% in styrene and 98.4 and 99.7% in MMA, respectively. Alkyl radicals formed in the reaction then underwent selective tail addition to monomers or were trapped by the nitroxide. From the relative yields of products arising from the competitive addition/trapping reactions of alkyl radicals, the absolute rate constants for the addition of isopropyl radicals to the two monomers at 60°C are estimated to be 4.7 х 10 5 l mol ¹1 s ¹1 to styrene and 1.3 х 10 6 l mol ¹1 s ¹1 to MMA, respectively.

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The physical aging in poly(methyl methacrylate) during annealing just below T g was investigated by light scattering and oscillating-DSC in which a sinusoidal temperature rise was imposed over the conventional linear temperature rise. Light scattering intensity decreased monotonously with increasing scattering angle. The intensity was found to increase rapidly and then to decrease gradually with annealing time t a. The correlation length and the mean-square density fluctuations by Debye–Bueche plot increased at an early stage and then decreased with t a. The width of the glass transition, obtained by the Fourier transform treatment of the oscillated DSC heat flow, increased with t a at an early stage and then decreased. The endothermic peak, given by the non-reversing part of the oscillating DSC heat flow, appeared even at an early stage of the aging. These results suggest that: (1) as-quenched PMMA glass is partially densified to yield an inhomogeneity in density with a correlation length about 200 nm; (2) by the annealing, the density fluctuations grow at first by a decrease in density at the low density regions and an expansion of the low density regions to increase the correlation length; and (3) the densification then proceeds at the low density regions to reduce the correlation length and to get higher density as a whole, by approaching a rather homogeneous glassy state.

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Copolymerization of styrene with styrene-terminated polystyrene macromonomer (SSTM) by CpTiCl3 –methylaluminoxane (MAO) catalyst was investigated. SSTM was prepared by a reaction of living polystyrene initiated with sec-butyllithium (s-BuLi) and p-chloromethyl styrene at 2788C. The synthesized SSTM has a high terminal functionality and a narrow molecular weight distribution. Graft copolymers of polystyrene consisted of syndiotactic main chain and atactic side chain were synthesized by CpTiCl3 –MAO catalyst. The synthesized graft copolymer was confirmed to have highly syndiotactic sequence on the main chain.

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The kinetic of photoinitiated polymerization of a dimethacrylate oligomer was studied by using isothermal photocalorimetry. The reaction was realized with 2,2-dimethyl-2-hydroxyacetophenone (Darocur 1173) as radical photoinitiator. Two kinetic models were applied. First, it was shown that an autocatalytic model can describe this reaction in a satisfying way. The reaction temperature does not influence the m and n orders of the reaction which were found to be constant and respectively equal to 0.8 and 2. The phenomenological rate constant k varies with temperature according to the Arrhenius law up to 80°C. Above this temperature, this law can again be checked if the initial variation of double bond concentration due to thermal polymerization is taken into account. In addition, by means of a mechanistic model, the k p and k t rate constants were calculated. Their evolution with conversion was studied at 50°C and well illustrates the importance of the reactive diffusion mechanism.

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Band broadening in size exclusion chromatography (SEC) causes errors in the calculated molar mass distribution even when molar-masssensitive detectors are used. These errors can be partially corrected by shifting the elution volume of the molar-mass-sensitive detector chromatogram relative to the concentration detector chromatogram, and then re-calculating the molar mass distribution. In this paper a computer simulation of multi-detector SEC of a polymer with a Flory–Schulz molar mass distribution and Gaussian band broadening is used to study the volume shift method of correcting for band broadening. The results are compared with those obtained by applying a conventional band broadening correction. In the case of SEC with a light scattering detector the results from the two methods are comparable. For SECviscometry with universal calibration the conventional method is significantly more accurate than the volume shift method. A method for calculating the volume shift required to correct for a known amount of band broadening is also presented.

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The synthetic process of hyperbranched aliphatic polyesters based on 2,2-bis(hydroxymethyl)propionic acid (AB2-type monomer) and 2ethyl-2-(hydroxymethyl)-1,3-propanediol (B3-type core) was investigated with in situ Fourier transform infrared (FT-IR) spectroscopic analysis. The experimental parameter was the stoichiometric ratio between monomer and core moiety corresponding to theoretical first, second and third generation. In the theoretical first generation, monomers were directly combined with a core molecule. In the theoretical second and third generation, oligomers derived from the reaction between monomers were gradually combined with a core moiety as the reaction time increased. The microstructure of the main product was surmised from the peak integration of in situ FT-IR spectra, the intensity of each repeating unit on 13C NMR spectra and the number average molecular weight.

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A series of novel polyimides have been synthesized from the condensation of 5-(perfluorononenyloxy)isophthalic acid bis(4-aminophenyl) ester (IV 3) with various aromatic tetracarboxylic dianhydrides. For comparison, the polyimides containing the bis(4-aminophenyl) ester unit were prepared from terephthalic acid bis(4-aminophenyl) ester (IV 1) and isophthalic acid bis(4-aminophenyl) ester (IV 2) with dianhydrides. The poly(amic acid)s had inherent viscosities of 0.97–1.98 dl g ¹1, depending on the diamines and dianhydrides. Perfluorononenyloxy groupcontaining polyimides (VII 3a–d) had lower dielectric constant (ranged from 2.73 to 2.56), lower moisture absorption, and better solubility than those of analogous polyimides (VII1a–d, VII2a–d) which do not contain perfluorononenyloxy group. Moreover, they maintained good mechanical properties (G⬘ close to 10 9 Pa) up to 270°C. The glass transition temperatures of these perfluorononenyloxy groups containing polyimides were in the range of 268–287°C by d.s.c. and 272–291°C by d.m.a., and the 10% weight loss temperatures in nitrogen and air were above 529 and 522°C, respectively.

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