1999 рік

The transverse stretching, under a constant drawing force, of a one-way drawn poly(ethylene terephtalate) film has been studied. This type of stretching leads to an equilibrium deformation under load which increases mainly with the applied stress and to a lesser degree with temperature. The crystalline phase of such samples has been characterized using wide-angle X-ray diffraction. The orientation of the chain axis and the normal to the phenylene ring have been analysed as well as the crystalline size, as a function of the draw ratio and the stretching temperature. The crystallinity is constant during stretching. The orientation distribution of the chain axes as well as the length of the crystals shows that the crystals which were preferentially oriented with their c-axes along the first stretching direction rotate rapidly towards the actual draw direction and grow up in length as the stretching proceeds. At the same time, the length of the crystals aligned along the other direction of the film plane decreases rapidly, indicating a break-down of some of these crystals. The orientation in the crystalline phase is uniquely controlled by the draw ratio. No relaxation with temperature is observed. This stretching method is compared with the constant speed drawing of one-way drawn films, where no rotation of large crystallites can be detected.

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Poly(amic diethyl ester) [PAE] precursors of four different polyimides with various chain rigidities were synthesized and thermally converted to the polyimides in thin films: rodlike poly(p-phenylene pyromellitimide) [PMDA-PDA] and poly(4,4⬘-biphenylene pyromellitimide) [PMDA-BZ], pseudo-rodlike poly(p-phenylene biphenylenetetracarboximide) [BPDA-PDA] and semiflexible poly(4,4-oxydiphenylene pyromellitimide) [PMDA-ODA PAE]. For the polyimide films, water sorption behaviors were investigated by gravimetry and then compared with those of the polyimides prepared from the corresponding poly(amic acid) [PAA] precursors. In addition, their morphological structures were examined by X-ray diffraction. For all the polyimides, both water sorption and morphological structure were dependent upon the history of precursor origin. All the polyimides except PMDA-ODA revealed relatively higher diffusion coefficient of water, higher water sorption, lower intermolecular packing order and lower population of a more ordered phase in the PAE-derived polyimide films than the corresponding PAA-derived polyimide films. For PMDA-ODA, the variations in the water diffusion and sorption due to the precursor origin were relatively small in spite of a relatively large change in the morphological structure. Overall, the effect of precursor origin on the water diffusion and sorption is significantly high in the rodlike or pseudo-rodlike polyimides having a high chain rigidity and high intermolecular packing order, but relatively low in the semiflexible polyimide with a relatively low chain rigidity. In comparison, regardless of the precursor origins, the diffusion coefficient of water was in the decreasing order PMDA-ODA > PMDA-PDA > PMDA-BZ > BPDA-PDA and, however, the water sorption was in the decreasing order PMDA-PDA > PMDA-BZ > PMDA-ODA > BPDA-PDA. These water diffusion and sorption behaviors were understood by considering their chemical affinities to water in addition to the morphological structures.

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The relationship between the crystallisation behaviour and physical ageing history of poly(ethylene terephthalate) is reported. It is shown that short term ageing can enhance the subsequent rate of crystallisation, but longer ageing times can retard the crystallisation process. It is suggested that physical ageing favours the formation of ordered domains.

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Polyacrylamides (PAAms), polyacrylonitriles (PANs) and poly(methyl methacrylate)s (PMMAs) were synthesized by using Ce(NH4)2(NO3)6, Ce(SO4)2·4H2O and KMnO4 in combination with nitrilotriacetic acid (NTA) and diethylenetriamine pentaacetic acid (DTPA), which have strong chelating properties, as redox initiators. Polymerizations were carried out in the aqueous acidic solutions at 258C and 558C in the presence of air. The chain structures of the resulting products were studied by Fourier-transform infrared (FTIR) spectroscopic measurements. From the comparison of the spectroscopic results with gravimetric and viscometric data it was concluded that both the differences between the solubility behaviour in aqueous solutions of MMA, AN, AAm and their polymers, and catalyst–activator– monomer combinations were important parameters effecting the polymerization mechanisms, conversions and the structures of the polymers. The FTIR and viscosity results indicated that PAAms obtained in our experimental conditions formed crosslinked structures with sulphated complexes of Ce(III) and MnSO4 produced by the redox reactions between catalysts (MnO42 and Ce(IV)), NTA and AAm. Further, it was observed that PAN chains were terminated by hydrated and sulphated complexes of Ce(III) while the termination of PMMA radicals took place by primary radicals because PMMAs were formed by emulsion polymerization kinetics.

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Using polymerization solutions containing 0.1 M aniline and 1 M HCI or 1 M HC104, which happened to give the same pH (0.2), we investigated the effects of different counter-anions on the primary and higher order structures as well as on electrochemical responses of the obtained polyamline (PAn) films. From time developments of polymerization current and u.v.-visible absorption spectra as well as the results of atomic force microscopic (AFM) observation, we found that in both media the higher order structure of the PAn films developed in almost the same manner from grainy to fibrillar texture and finally to bundles of the fibrils. The primary structures as judged from the spectra were not very different, but the structural size was somewhat larger for the films prepared in HC104 than the ones prepared in HCl. The apparent acid dissociation constants of the resulting PAn films were again not so different, reflecting little differences in their primary structures. However, the electrochemical responses of the former were much slower than those of the latter, especially when the transition from the oxidation to reduction form was compared, reflecting differences especially in the structural size and compactness of their higher order structures.

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Isothermal miscibility maps for blends of styrene–acrylonitrile (SAN) copolymers with methyl methacrylate (MMA) copolymers containing ethyl acrylate (EA) and n-butyl acrylate (nBA) have been determined. The miscibility region for MMA-nBA copolymers is larger than that for MMA-EA copolymers. Binary interaction energies for monomer unit pairs were calculated from critical molecular weight experiments and data from the miscibility maps using with the Flory–Huggins theory combined with the binary interaction model. Spinodal temperatures predicted from the lattice-fluid theory of Sanchez and Lacombe, using these experimental interaction energies, are similar to the experimental phase separation temperatures.

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Dianhydrides of specific molecular architecture was designed and synthesized based on 2,2 0 -disubstituted 4,4 0 ,5,5 0 -biphenyltetracarboxylic dianhydrides (2,2 0 -disubstituted BPDAs). Eight dianhydrides were polymerized with two 4,4 0 -diamino-2,2 0 -disubstituted biphenyl diamines (trifluoromethyl disubstituted groups, or PFMB, and methyl disubstituted groups, or DMB) to obtain two series of PFMB- and DMB-based aromatic polyimides. As the backbone structures of these two series of polyimides are unchanged throughout each series, the effects of the 2,2 0 -disubstituted groups of both the dianhydride and diamine constituents on the solubility and thermal and optical properties as well as the relaxation behavior of these polyimides can be identified. It was found that the PFMB-based polyimides with 2,2 0 -disubstituted BPDAs show excellent solubility while the DMB-based polyimides with the same dianhydrides are less soluble. The same trends can be found for both thermal and thermo-oxidative stability and optical transparency in the ultraviolet and visible light regions. These two series of polyimides exhibit glass transition temperatures (Tg) which show a competition between chain rigidity and linearity with regards to molecular packing. When the size of the 2,2 0 -disubstituted groups is small and their shape is close to spherical, the Tg initially increases with the size of these 2,2 0 -disubstituted groups. This is because of the fact that the steric hindrance of these groups prevents the appearance of a cisconformation of BPDA. However, once these groups possess large size and exhibit anisotropic shapes, their effect on the molecular packing becomes dominant and the Tg starts to decrease. Further, this is the first time that three relaxation processes (the b 1, b 2, and a processes) were observed above room temperature in these aromatic polyimides. We have identified that the b 1 process is attributed to the local motion of the diamine constituents while the b 2 process is caused by the local motion of the dianhydride constituents. The a process is associated with the glass transition. The cooperativity of the molecular motion associated with the b 1 and b 2 processes are also discussed.

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Performance of carbon black reinforced elastomers strongly depend on the adhesion at the filler–matrix interface. Surface characteristics of carbon blacks can be changed by use of a number of different techniques each with certain advantages and disadvantages and as regards to these, plasma surface modification is a novel one. This study aims to check the limits of applicability of plasma surface modification of carbon black to be used in the tire manufacturing industry. For this purpose, RF range cold plasma has been utilized in styrene or butadiene atmospheres. Tensile strengths and percent elongations of vulcanizates are found to respond differently if modified fillers are used as compared with those prepared by the unmodified fillers. Glass transition temperatures of vulcanizates are found to correlate well with the results of mechanical properties. Findings are also supported by the SEM pictures.

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A series of poly(methy1 methacrylate)-g-poly(dimethylsiloxane) and poly(methy1 methacrylate)-g-poly(trifluoropropylmethylsiloxane) copolymers have been synthesized via the 'macromonomer’ method by which monofunctional polysiloxane macromonomers are copolymerized with methyl methacrylate. The graft copolymers have been characterized by gel permeation chromatography, 'H n.m.r. spectroscopy and differential scanning calorimetry. Dynamic contact angle (DCA) analysis afforded advancing and receding water contact angles over 15 days immersion in water. The initially hydrophobic polymer surfaces rapidly rearrange in the presence of water to more hydrophilic surfaces. The effects of varying the amount and type of siloxane in the copolymer on DCA results are discussed. The fouling and fouling release behaviour of coatings formulated from the graft copolymers have been evaluated in Chesapeake Bay. Fouling and fouling release behaviour are discussed in the light of DCA results.

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Blends of nylon 6 and ethylene–propylene rubber, grafted with maleic anhydride, (EPR-g-MA) were prepared using a melt blending process. For certain compositions, nylon 6 forms finely dispersed particles due to the reaction of the polyamide amine end groups with the grafted maleic anhydride, that have the potential to reinforce the elastomer matrix. This study focuses on the effects of the content of nylon 6 on the rheological, morphological and mechanical properties of such blends where nylon 6 is the dispersed phase. Transmission electron microscopy was used to determine blend morphology. Mechanical properties were examined by stress–strain measurements and dynamic mechanical thermal measurements; the modulus is compared to values calculated from theory. The addition of magnesium oxide causes significant improvement in tensile properties of these blends.

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