Some Aspects Of Emulsion Polymerisation Of Vinyl Acetate.

The emulsion polymerisation of vinyl acetate wasinvestigated using a wide range of sodium laurylsulphate, (SLS), as emulsifying agent, potassiumperoxydisulphate initiation and at two temperatures,58°C and 6S°C.Vinyl acetate was found to polymerise appreciablyeven below the cmc of (SLS). The form of dependence ofrate of polymerisation on the exponent of the emulsifierwas studied. The rate of polymerisation Rp , was foundto show a diminishing dependence on the exponent of theemulsifier concentration contrary to the Sinith-Ewartscheme of ideal emulsion polymerisation of water insolublemonomers. A greater dependence of R on the exponent ofthe emulsifier concentration was found below the cmc thanabove the cmc of (SLS). The form of dependence was alsoaffected by temperature. The exponent of the emulsifierconcentration increased with temperature below the cmc of(SLS) and decreased with temperature above the cmc of (SLS).This shows that R is less dependent on the [So] atincreased temperatures.Viscosity studios were carried out and the intrinsicviscosity was found to be dependent on molecular weightand chain branching. The occurence of branching isfavoured especially at high temperature. Higher intrinsicviscosity values were obtained for polyvinyl acetatevisamples produced below the cmc than above the cmc of(SLS), suggesting that the molecular weight of thepolyvinyl acetate samples formed while polymerisingvinyl acetate below the cmc of (SLS) as emulsifier arehigher than when polymerising above the cmc.Temperature was found to enhance the occurence ofbranching hence polyvinyl acetate samples obtainedabove the crno are expected to have higher molecularweights at 58°C. The interaction between the polymerand the solvent molecules in the viscosity study werefound to be less for polymers produced below the cmcof (SLS) due to the greater molecular weight.Tests on tensile mechanical properties were alsocarrie . out on the polyvinyl acetate samples obtainedfrom emulsion polymerisation. These properties werefound to be affected by the presence of branches andmodification of the macromolecular structures of thepolymer. The solvent used was also found to cause somemodifications on the polymer structures. The values ofthe tensile mechanical properties were relatively high.TENSILE strength and initial modulus of the polymersobtained showed opposite trends of variation to that of(%) elongation for different (%) conversion. The observationsfrom the variation of intrinsic viscosity and the tensilemechanical properties showed that these properties areaffected by modifications in the polymer chain.

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