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No abstract available

No abstract available

[en] Short communication. 2 figs

[en] Abstract only. 1 ref

[en] If sodium dodecyl sulphate, SDS, is added to a latex of poly(vinyl acetate), PVAc in water, to give an overall SDS concentration greater than 4.5 mM, the polymer latex particles swell reversibly to a final volume of the particles up to fifty times their original volume. 96% of the increase is due to water carried in with the SDS. The swelling is attributed to the formation of polymer micelle complexes (PMCs) along the polymer chains. The charges on these PMCs repel, thus expanding the particles. Entanglement of higher molecular weight chains inhibit swelling beyond an equilibrium value. If, however, the swollen particles are irradiated in a gamma source and then dialysed, they shrink only slightly to approx. forty times the original volume indicating that the charges are attached irreversibly to the PVAc chains. The maximum effect is observed at 12 kGy (dose rate 0.12 Gy/s) and at a molecular ratio PVAc : SDS of 12; both of which indicate that grafting has occurred. The stabilised lattices show a remarkable increase in colloidal stability towards coagulation in sodium chloride solution. The stabilised particles do not coagulate in salt solution 400 times as concentrated as that in which as-prepared unstabilised lattices coagulate. In 2% VAc monomer / 20 mM SDS solution the nonstabilised expanded dose particles contract as the PMCs are displaced by monomer but stabilised particles remain the same size

No abstract available

[en] Full text: Synthetic polymer chains can be prepared more or less singly by the technique of microemulsion polymerisations (MEP), so that each microlatex particle formed contains only one polymer chain. Below T_g, these polymeric particles can be called single chain polymer glasses (SCPG). The conformation of a polymer in a single chain glass is in the compact form, in contrast to the expanded random coil conformation evident in conventional multichain polymer glasses (MCPG). The question is whether the physical properties of single chain glasses are identical with those of multichain glasses. Experiments show that single chain polystyrene glasses (SCPS) display properties quite different from those of ordinary polystyrene (PS). This is apparent from measurements of their DSC, FTIR, WAXD, PALS and density. Such measurements all point to the one conclusion: that SCPS as prepared are more random than ordinary PS. Monomers other than styrene were also covered. Copolymers and crosslinked polymers were studied. The process of the particle formation was also studied. The formation of the superchain-like structure during the heating of some virgin SCPG is proposed to be responsible for the exhibition of a first-order-like DSC exotherm near Tg. It was found that there are two prerequisites for the formation of such superchain-like structure. That is, the phenyl ring in the monomer is essential and the compression factor must be more than one. The triad SSS is found to be the minimum length for such structure formation. It was also found that at the stage of conversion 47%, MEP starts to differ from the conventional emulsion polymerisation

[en] Anionic surfactants form polymer micelle complexes (PMCs) along the chains of hydrophobic/hydrophilic polymers in an aqueous latex. The charges on these PMCs repel each other allowing access by the solution and causing the particles to swell to up to sixty times their volume in the poly(vinyl acetate) (PVAc) / sodium dodecyl sulphate (SDS) system. Swelling starts at 4.5 mM SDS which is well below the critical micelle concentration (8.3 mM). The particle size was measured by Dynamic Light Scattering (DLS) and verified by weighing the sediment after ultracentrifuging. We attributed the limitation of swelling to the presence of entanglements which were not loosened during swelling. The fully swollen material contained 1.8% PVAc, 1.6% SDS and 96.6% water. If the SDS concentration was lowered by dialysis or by dilution, the SDS of the PMCs dispersed and the particles reverted to slightly less than their original size, ie the swelling was reversible. The somewhat smaller size was accounted for by the leaching into the solution of low molecular weight polymer as individual chains incorporating PMCs along their length and thus similar to a polyelectrolyte. With sodium tetradecyl sulphate the threshold is 1 mM and the particles swell up to 200 fold. Prolonged attack by free radicals either by irradiation or by chemical sources would be expected to give a more or less continuous array of single charges along the chain and this might be more effective in loosening entanglements. Alternatively or additionally, the radicals might cause main chain scission. Both would lead to faster dissolution. The results obtained have some ramifications for polymerisation at surfactant concentrations above the critical micelle concentration