Diblock polystyrene-block-poly(hydrogenated isoprene) was fluorescence labelled by random covalent attachment of anthracene at the polystyrene block (the average number of anthracenes per copolymer chain was 0.88). Micellization of the labelled copolymer was studied in a broad composition range of the solvent mixture 1,4-dioxane/heptane. Micelles with polystyrene cores are formed in heptane-rich solvents (0-30 vol% 1,4-dioxane). In mixtures with 30-50 vol% 1,4-dioxane, the sample dissolves molecularly in the form of individual copolymer coils and in dioxane-rich solvents (more than 50 vol% 1,4-dioxane), micelles with polystyrene shells are formed. Micellar solutions were characterized by static and quasielastic light scattering and by sedimentation velocity measurements. The mobility of pendant fluorophores and polymer segments in micellar cores and shells in selective solvents and in individual copolymer coils in good solvents was studied by time-resolved fluorescence-anisotropy measurements.
The miscibility of binary polymer blend systems consisting of poly(vinyl methyl ether) (PVME) and polyacrylates has been studied. Based on film clarity, glass transition temperature and cloud-point studies, PVME is found to be miscible with poly(ethyl acrylate), poly(n-propyl acrylate) and poly(n-butyl acrylate) but not with poly(methyl acrylate). The phase diagrams of some of these blends are reported.
Simple, analytical expressions are derived for the surface composition and surface excess (adsorbed amount) of the lower surface energy component of a miscible polymer blend at equilibrium. In practical cases, the total surface excess is predicted to depend more strongly on the value of the Flory-Huggins interaction parameter between the segments of the two polymers than on the difference in surface energies between the components of the blend.
Kinetics of emulsion polymerization of vinyl acetate have been studied in the absence of emulsifiers using potassium persulphate as the radical generator. Uniformity of particle sizes, in batch operation, indicated that nucleation of stable particles occurs early in the polymerization. The polymerization rate was proportional to the 0.69 power of the initial monomer concentration. Particle sizes were consistent with the suggestion that particles are stabilized by initiator fragments. When polymerization was carried out in the presence of a dialysed seed latex, with no added emulsifier, the polymerization rate was found to depend on the initiator concentration raised to the power 0.60_+0.05 but was independent of the monomer-to-polymer ratio. New stable particles could be produced when the monomer-to-polymer ratio was high. The production of these new particles did not affect the polymerization rate significantly. Polymerization rate was insensitive to the stirrer speed unless the speed was very high. At high speed the polymerization rate was reduced.
The transesterification reaction in the molten state of ester groups of ethylene vinyl acetate copolymers and ethylene acrylic ester copolymers, in the presence of dibutyltin oxide as a catalyst, leads to crosslinking of the copolymer chains. The kinetics of this crosslinking reaction has been assessed by two different experimental methods: viscoelastic measurements of the dynamic storage modulus and thermogravimetric analysis coupled with gas chromatography which allows measurement of the evolved methyl acetate which is a volatile product of the crosslinking reaction. The equilibrium storage modulus calculated from theories of elastic modulus has shown that the kinetics of the crosslinking reaction may be determined through variations of the dynamic storage modulus
The value of the interaction parameter X in dilute polymer solutions is usually higher than would be expected on the basis of simple theory. This is caused by a large entropic contribution, for which there is, as yet, no theoretical explanation. In this paper the results are presented of a study of the behaviour of the energetic and entropic contributions to Z. It is shown that the two contributions are closely correlated and exhibit qualitatively similar molecular-weight dependences. These observations may guide future theoretical efforts towards the understanding of the thermodynamic phase behaviour of polymer solutions
Three triblock copoly(oxybutylene/oxyethylene)s, EssBIvEss, E71BzsE7a and E132B53E132, with similar composition (75-80 wt% E) but different chain lengths, were prepared by sequential anionic copolymerization, and their micellar and gelation properties in aqueous solution were determined. The methods used were light scattering intensity, photon correlation spectroscopy and gel permeation chromatography, together with observation of gelation. Measurements were made at 30°C over the full concentration range from dilute solution into the gel. The lower and upper temperature boundaries of the gel regions were identified. Phase separation was observed in dilute solutions of the copolymer of longest chain length (E132B53E132 ). Critical micelle and gel concentrations decreased markedly as chain length was increased, and micellar weights and sizes increased
Monomer reactivity ratios in free-radical copolymerization of styrene and 4-vinylpyridine monomers at 80°C in toluene solution under reduced pressure were determined for low and high conversions. Finemann-Ross, Kelen-TiJd6s, extended Kelen-Tfid6s and Mayo-Lewis methods were used for this purpose. The most reliable method was found to be the extended Kelen-Tfid6s method. By the use of this method, for conversions below 20%, monomer reactivity values of 0.700+0.005 and 0.335 +0.001 were calculated for 4-vinylpyridine and styrene respectively. For conversions greater than 20%, these values were found to reduce to 0.538 +0.004 and 0.277 + 0.001 respectively.
A newly designed viscometer was used to measure the viscosity of polymer solutions under high-temperature and low-shear-rate conditions. Rheograms of dilute and concentrated scleroglucan solutions were determined in the range of temperatures between 30 and 150°C. Rheological behaviour was correlated with macromolecule structural parameters. Intrinsic viscosity values versus temperature were analysed on the basis of Yamakawa's theory of semirigid chains. As the temperature increased, local molecular rigidity decreased. An Arrhenius equation form was found for the persistence length variation versus temperature. An apparent activation energy of 7.5 kJ mol-1 (1.8 kcal mol-1) was determined. This value was of the same order of magnitude as the hydrogen bond energy that stabilizes the scleroglucan triple-helix structure. On considering a model of rod particles, the scleroglucan molecule behaves like a rod-like polymer up to 130°C.
We report the chemical synthesis of an N-substituted water-soluble polyaniline derivative. This novel processable conducting polymer has been characterized by a wide range of techniques including visible absorption, FTi.r. and 1H n.m.r, spectroscopy, scanning electron microscopy, cyclic voltammetry in non-aqueous media, room temperature d.c. conductivity measurements, photon correlation spectroscopy and thermogravimetry.