1992 рік

Novel, anionic surface-active monomers, sodium di(10-undecenyl)sulphosuccinate (DUSS) and sodium n-undecy110-undecenylsulphosuccinate (MUSS) were prepared. The monomers were soluble in both water and apolar organic solvents on heating. DUSS and MUSS in water exhibited Kraft points at about 39°C and 48°C, respectively. The critical micelle concentrations for aqueous solutions of DUSS and MUSS at 50°C were determined to be 2.4 x 10- 5 and 1.2 x 10- 5 tool 1 - 1, respectively. Polymerization of the monomers in darkness and under u.v. irradiation at 50°C were studied using three different solvents, namely water, n-hexane and dioxane, giving aqueous micelles (or vesicles), reversed micelles and isotropic solution, respectively. Only traces of polymers were formed for the polymerizations in darkness, while the polymerizations under u.v. irradiation gave polymers, except for the polymerization of MUSS in dioxane. The solvents used for the polymerization were observed to exert an effect on the solubility of the polymers of DUSS and only the polymer obtained from the polymerization in water was soluble in solvents such as water and N,N-dimethylformamide. Thus, the monomer aggregation, especially for the aqueous system, was found to affect the structure of the resulting polymers.

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ct-Terthienyl and 2,5-di(2-thienyl )pyrrole, n-alkylated at the r-position of the central ring, have been oxidized electrochemically or chemically to afford electroactive polymers which were characterized by cyclic voltammetry, spectroelectrochemistry and FTi.r. These systems, which can be viewed as ~-linked alternating copolymers of bithiophene with a 3-alkylthiophene or 3-alkylpyrrole, display superior effective degrees of conjugation compared with homopolymers of similarly substituted 3-alkylheteroaromatics. Chemically generated materials are soluble in a variety of organic solvents, but fail to produce coherent films when cast from these due to lower degrees of polymerization than similarly produced 3-alkylthiophene homopolymers. Electrogenerated polymers are insoluble despite apparently comparable degrees of polymerization as determined by FTi.r. end-group analysis. Oxidation potentials of the monomers are reduced in proportion to the number of alkyl substituents.

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Diblock macromonomers possessing central vinylbenzyl groups were synthesized by anionic addition in a three-stage process using styrene, 1,4-divinylbenzene, and t-butyl methacrylate monomers. Upon addition of 1 ,Cdivinylbenzene monomer to polystyryl anion in tetrahydrofuran at - 78”C, aggregates of polystyryl anions were formed in spite of variations in reaction time and feed mole ratio of the living ends to 1,4-divinylbenzene. However, upon reaction in toluene, linear polystyryl anions possessing terminal vinylbenzyl groups were formed. Anionic propagation of t-butyl methacrylate monomer with linear polystyryl anions end-capped with 1,4-divinylbenzene led to the formation of poly( styrene-block-t-butyl methacrylate) diblock macromonomers possessing central vinylbenzyl groups.

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The kinetics of strain-induced crystallization of swollen, crosslinked polyethylene fibres have been measured under low draw conditions (~ = 1.2 or 1.4) using dynamometry in combination with birefringence. Crosslinking was carried out in dicumyl peroxide to produce a range of chemical and trapped entanglement concentrations. Avrami analysis showed that transformation proceeds by heterogeneous nucleation followed by one-dimensional growth of c-axis oriented crystallites. Growth rates and the size of the corresponding critical nuclei show a strong dependence on crosslink density and entanglement concentration at high crosslink concentration. When entanglement concentration is comparable to the crosslink concentration, the effects of the two constraints become indistinguishable. The latter observation is in line with published results for flow-induced crystallization under comparably low stress levels showing that growth rates are relatively insensitive to entanglement concentration. At higher crosslink concentrations, growth rate decreases in a non-linear fashion indicating potential thermodynamic as well as mobility effects. A physical model illustrates the role of chain constraints on the kinetics of oriented crystallization

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Blocked copolymers from aliphatic diacids and diol-terminated aromatic polyester blocks have been prepared and studied. The preparations of such block copolymers with good molecular weights proved difficult, but a final carbonation reaction enabled the preparation of materials with values of [q] above 1.0. The mechanical and thermal properties of these have been studied and reported.

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A theoretical analysis of the possible conformations of poly(p-phenylene terephthalate) (PPTA) and poly(p-phenylene isophthalate) (PPIA) is performed on the basis of molecular mechanics and molecular dynamics trajectories. An algorithm for creating long polymer chains up to 150 monomers used for the calculation of the small-angle X-ray form factor is introduced. Three different methods to determine the experimentally accessible property, persistence length, are presented. The results of all three methods agree very well with the experimental result for the persistence length of PPTA; in addition, the relationship between stiffness and persistence length is elucidated by comparison of the two different conformations of PPTA and PPIA.

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Grafting of maleic anhydride (MAH) onto ethylene-propylene rubber (EPR) was performed by melt mixing in a laboratory-scale internal mixer with the addition of an initiator (dicumyl peroxide, DCP) and an ingredient (stearamide, SA) for the suppression of side reactions of cross-linking and chain scission. Effective suppression of side reactions was realized for systems of moderate or low DCP contents upon addition of SA, but no apparent changes could be identified at high DCP loadings. Within the confidence level of Fourier-transform infrared spectroscopic measurements, the extent of grafting appeared to be little affected by the addition of SA. Possible reaction paths in the present system are discussed. In particular, SA is considered as a chain transfer agent which tends to suppress the more populated reaction path, whether it be cross-linking or chain scission.

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When selective solvents are used for the dissolution of block copolymers, their solid-state structure may be partly preserved in solution. At room temperature, polystyrene-block-poly(ethylene-co-propylene) dissolves in decane, a selective solvent for the aliphatic block, to form a solution of metastable micellar structures with polystyrene core. These convert to stable micelles at elevated temperature; the molar mass of the micelles is reduced several times after the heat treatment. The change of the structure is explained by the existence of a frozen state of the micellar core at room temperature. A possible connection with the glass transition of the core is discussed. Static and dynamic light scattering, small-angle X-ray scattering, differential scanning calorimetry and viscometry have been used to characterize equilibrium and nonequilibrium micelles. A pronounced mutual interaction of micelles has been observed by light scattering even at a concentration as low as 5 x 10-4g cm -3. The concept of sticky chains is introduced to explain the association of the micellar shells. The behaviour of micelles in another selective solvent, diisopropylether, is simpler, both effects observed in decane being absent

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Liquid-crystalline (LC) copolymers with redox-active groups were prepared by copolymerization of mesogenic and ferrocene-containing monomers (up to 10%). In these copolymers the ferrocene groups can be oxidized reversibly to prepare ionomers, while retaining the LC phase. It is thus possible to vary the amount of ionic groups in the ionomers by a redox reaction. The oxidized (charged) polymers show a strong excess X-ray scattering at small angles. This is typical for ionomers and is assigned to the scattering of ionic aggregates. Dynamic mechanical measurements show that these aggregates are effective as crosslinking points. Thus an oxidation-reduction reaction can be used to transfer an uncrosslinked polymer (reduced ferrocene groups, uncharged) reversibly into an oxidized polymer that acts like a weakly crosslinked gel

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A new method to prepare polymer composites based on concentrated emulsions was developed in this laboratory. The composite is synthesized starting from a concentrated emulsion of a hydrophobic phase, containing a hydrophobic monomer, dispersed in a continuous hydrophilic phase, containing a hydrophilic monomer. Of course, inverted dispersions in which the hydrophilic phase is dispersed in a hydrophobic phase are also possible. The concentrated emulsions have the same appearance and behaviour as a gel; the volume fraction of their dispersed phase is very large (it can be as large as 0.99). Not all pairs of monomers can lead to concentrated emulsions. In addition, concentrated emulsions prepared and stable at room temperature may not remain stable at the polymerization temperature of 50°C. The present paper contains a large number of experiments whose goal is to identify the conditions under which a coupling between two monomers can lead to hydrophilic-hydrophobic or hydrophobic-hydrophilic composites. The nature of the hydrophilic and hydrophobic monomers (particularly their polarity), the pH and the ionic strength are found to be important factors in the formation at room temperature and stability at 50°C of the concentrated emulsions. It is found that the instability at 50°C of the concentrated emulsions (expressed as weight per cent of bulk phases separated from the emulsion after heating for a certain time) can be correlated with the interfacial tension at 25°C between the hydrophilic and hydrophobic phases free of surfactant. The larger this interfacial tension, the higher the stability of the concentrated emulsion. Hence, the lower the polarity of the hydrophobic monomer and the higher the polarity of the hydrophilic monomer, the more stable the emulsion. The film-forming capability of the surfactant is also important. Improved mechanical strength of the interfacial film is achieved using blends of non-ionic surfactants or mixtures of ionic surfactants and long-chain alcohols as dispersants. Increased stability is exhibited by adding methyl cellulose in the aqueous continuous phase when hydrophobic monomers with higher polarity are employed in the dispersed phase. High temperatures and higher volume fractions of the dispersed phase decrease the stability of the emulsion. Several hydrophilic-hydrophobic polymer composites have been prepared on the basis of the above observations.

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