1992 рік

The melting-point depression of a random copolymer with comonomer exclusion from the crystalline phase is investigated. The analysis is based on simulation results obtained with an extended Sadler-Gilmer crystallization model. Apparent copolymer melting points T,p(l) of lamellae of finite thickness I are observed. Further thickening is entropically suppressed. It is shown that the average lamellar thickness and the minimum thermodynamically stable thickness converge at Tzp. The fine-grained nature of the model reveals an entropic contribution to the melting-point depression, which is due to the so-called blind attachment of chain segments to the growth face. Our new ‘kinetic’ melting-point equation is compared with the ‘equilibrium’ result by Flory and shows a considerably stronger melting-point depression.

Детальніше...  

The aqueous solubility of gelatin and the sodium salt of carboxymethylcellulose (CMC) together with the sol~-gel transition of gelatin and its crosslinking reaction with glutaraldehyde is exploited to synthesize interpenetrating complexes of these two macromolecules. This material exhibits swelling properties, typical of ionic hydrogels, which vary as a function of CMC content. Several compositions were cast into films. The protein component contributed more towards the mechanical properties of these films. The gels responded to an electric stimulus by a change in dimensions. The striking compositional resemblance of this system to cartilage tissues is discussed.

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Several series of copolymers of different geometry were synthesized from zwitterionic surfactant monomers and polar non-ionic comonomers. Bulk properties were investigated by d.s.c, and X-ray scattering. The copolymers were amorphous, but exhibited superstructures up to high comonomer contents. Solubility of the copolymers was determined as a function of geometry and composition. From the results, a main chain spacer model has been derived. All water-soluble copolymers exhibited characteristic features of classical polysoaps, as shown by surface tension measurements and by solubilization of pyrene. But gradual differences depending on the polymer geometry were observed for the solubilization sites

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Radii of gyration Rg and hydrodynamic radii Rh of star-shaped polystyrenes with different arm numbers and their arm polymers were measured in toluene solution by static and dynamic light scattering. Rh depends on the number of arms f stronger than Rg. The ratios g~=Rg(star)/Rg(arm) and g~ = Rh (star)/Rh (arm) were compared with other experimental and computer simulation results to examine the universality of these ratios. Universality of the relation of gg versus number of arms f is confirmed. No clear indication of failure of g~ in universality is observed, and it was suggested that g~ is not sensitive to systems. Experimental results were also compared with available theories. The renormalized two-parameter theory by Douglas and Freed for static quantities gg and gA (= A2(star)/A2(linear), where A2 is the second virial coefficient) reproduces the experimental data very well at lower fs and agreement in g~ is excellent over a wide range of f.

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Intramolecular ether cyclization occurs much more readily than previously recognized in the cure of N,N-diglycidyl epoxies with aromatic amines. Even at a modest reaction temperature of 120°C, the polymer from N,N-diglycidylaniline (DGA) and aniline was shown by 13C n.m.r, spectroscopy to contain morpholinyl and perhydro-l,4-oxazepinyl end groups which accounted for 6 and 4%, respectively, of consumed epoxy groups, whereas intramolecular amine cyclization to give the simple perhydro- 1,5-diazocine isomers accounted for 19%. ortho-Methyl substituents in the amine had little steric influence on the extent of ether cyclization, but electronegative substituents had a very marked effect such that it was increased to 28% with 2,4,6-trichloroaniline and 26% with 3,5-bis(trifluoromethyl)aniline. The polymer from DGA and aniline was linear and had a completely random tacticity: variation of reaction temperature and reactant ratio led to only modest improvements in molecular weight (maximum value about 3000) because of the relative ease of chain termination by ether cylization. Two new thermal reactions of the polymer are proposed to explain n.m.r, spectral and g.p.c, data, a cleavage reaction to give secondary amine and tetrahydroquinolyl end groups, and water elimination from adjacent hydroxyl groups to form an in-chain morpholine ring. The reactions were surface- and temperature-dependent. Polymer degradation also occurred slowly in tetrahydrofuran solution at room temperature.

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This paper describes the rational design of four different types of functionalized polymers with interesting material properties. (i) Liquid crystalline (LC) side-group polymers with a high spontaneous polarization in the ferroelectric chiral smectic C* phase can be prepared by a proper selection of the chiral groups. The additional functionalization with non-linear optical chromophores makes these materials interesting for non-linear optics. (ii) Chiral LC polymers, which are functionalized with crosslinkable groups, can be converted into LC elastomers. The mechanical orientability of these elastomers leads to new piezoelectric materials. (iii) The incorporation of ferrocene units into a LC matrix allows the reversible formation of LC ionomers by a redox reaction. This leads to a gelation of the LC polymer system. (iv) The curing (dense crosslinking) of a polymer matrix is one possibility to stabilize the polar order of dye molecules, which is necessary for frequency doubling. This can lead to large and stable non-linear optical coefficients.

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This paper reports the phase diagrams of PBZT/nylon/MSA, PBZT/NaAMPS polymer/MSA, PBZT/HAMPS monomer/MSA and PBZT/PPTA-PS/MSA, with PBZT = poly(p-phenylene benzobisthiazole), MSA = methanesulphonic acid, NaAMPS = sodium 2-acrylamido-2-methylpropanesulphonate, HAMPS = 2-acrylamido-2-methylpropanesulphonic acid and PPTA-TS = poly(p-phenyleneterephthalamido) propanesulphonate). The ternary phase diagram of rigid-rod polymer PBZT and amorphous nylon in MSA solvent was found to follow Flory's prediction of a rod/coil/solvent ternary system very well. Flory's theory assumes no interaction between the rod and the coil, and the PBZT/nylon system fits this model nicely. When sulphonated polymers, such as NaAMPS polymer and PPTA-PS, were used instead of nylon in a ternary solution, it was found that the phase behaviour deviated from Flory's theory. This deviation could be due to the possible coil rod intermolecular interaction in the ternary solution. Flory's formalism was used to analyse these data. It was found that for the PBZT/nylon/MSA system, the X 3 value was consistent with the contour length of the coil molecules as predicted by Flory's theory. However, both PBZT/HAMPS monomer/MSA and PBZT/NaAMPS polymer/MSA systems showed an X3 value of unity. The ternary phase diagram of the PPTA-PS system showed an X 3 value between 1 and 5. This suggests that the degree of intermolecular interaction between rod and coil plays an important role in determining the phase behaviour of a rod/coil/solvent ternary system

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A photochromic p,p'-bis(chloromethyl)azobenzene (CAB) was prepared as a crosslinking agent. Three poly(tertiary aminostyrene)s prepared via living anionic polymerization were used as reactive polymers: poly(N,N-dimethyl-4-vinylphenylamine) (PPA), poly(N,N-dimethyl-4-vinylbenzylamine) (PBA) and poly((N,N-dimethyl-4-vinylphenethylamine) (PPTA). Films were cast from tetrahydrofuran solution of CAB and the polymers. The crosslinking reaction proceeded during the evaporation of solvent and the annealing of the films at 90°C for > 10 h. The result of the swelling test led us to conclude that all the CAB added to the polymer was consumed in the crosslinking reaction. Photochemical isomerization was studied for CAB incorporated in three polymers by cross linkage. The conversions for photochemical isomerization of CAB in three crosslinked films were 35-10% in the stationary state under u.v. irradiation below the glass transition temperature. This indicated that the thermal freedom of CAB was depressed by crosslinking in the glassy state.

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Poly(maleic anhydride) was reacted with long-chain aliphatic amines in a 1:1 molar ratio (as per monomer unit) resulting in the formation of amphiphilic polymers bearing the carboxylic group on their polymer backbone. On the other hand, poly(acryloyl chloride) was interacted with ~o-amino or ~o-hydroxy carboxylic acids affording polyamphiphiles with the carboxylic polar group at the tail of the pendant group. In addition, the carboxylic group was replaced by the extremely polar quaternary group at the end of the lipophilic chain. Liquid crystalline textures were exhibited by these polymers as determined by optical microscopy and d.s.c, studies while the supramolecular structures, formed through hydrogen bonding of carboxylic groups, were responsible for the formation of mesomorphic phases.

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Phase separation has been studied in a mixture composed of a crystalline polymer, poly (vinylidene fluoride ) (PVDF), and a mesomorphic polymer, hydroxypropyl cellulose (HPC). The mixture was first studied in solution in a common solvent of the two polymers: the ternary phase diagrams showed a large incompatibility between the two polymers with different chemical structures. Then the solvent was evaporated, and phase separation was studied in the resulting solid biphasic films. The determination of binary phase diagrams as a function of temperature revealed that each phase was composed mainly of one polymer. We also studied the influence of various parameters on the size of the droplets in these films: the proportions of the two polymers (the size of the droplets was larger when the two polymers were in equal proportions, and decreased when the quantity of polymer in the droplets decreased), the polymer concentration in the initial ternary solutions (the size of the droplets increased with polymer concentration ), the evaporation rate of the solvent (the size of the droplets in the solid films decreased when the evaporation rate was increased) and the molecular weight of PVDF (the size of the droplets decreased when the molecular weight of PVDF was increased). We have tried to explain the variations observed using ternary phase diagrams, Binder's theory concerning mixtures of two polymers in the melt and by macromolecular diffusion phenomena

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