Radiation‐induced emulsion polymerization of vinyl acetate and styrene

Abstract

SynopsisStudies have been made of the 7-induced emulsion polymerization of styrene and comparisons made with chemically initiated emulsion polymerization. The polymerization proceeded smoothly to high conversions at 0 and 60°C, the reaction showing a high G (monomer) value. Complete conversions were obtained with total doses of less than 0.05 Mrad. In accordance with the behavior expected of systems having a constant rate of initiation, the molecular weight was found to decrease with decreasing temperature. The molecular weight and particle size distributions were narrower than those obtained in chemically initiated emulsion polymerizations at the same temperature. The radiation-induced emulsion polymerization of vinyl acetate proceeded smoothly at temperatures in the range 0-50°C to give polymers of much higher molecular weight than these obtained from chemically initiated polymerizations a t the same temperature. Complete conversion was attained after a dose of 0.02 Mrad for latices approaching 50% solids. The elimination of ionic endgroups in the poly(viny1 acetate) radicals tends to drive the polymerization from the aqueous phase, resulting in faster rates and higher molecular weights than are obtained from chemically initiated systems. Rates of polymerization were found to be independent of temperature and the molecular weight of the polymer to be independent of dose rate. Latices of poly(viny1 acetate) of high solids content were evaluated for latex and film properties and found to have improvements over commercially available samples in both areas, especially in clarity of film and scrub resistance. A number of acrylate and maleate esters were copolymerized with vinyl acetate in a radiation-initiated emulsion system. High molecular weight copolymers were produced after low dose.The use of high energy radiation to initiate emulsion polymerization systems has obvious advantages. The comparatively high yield of free radical from the radiolysis of water (4-7 per 100 eV) plus the large kinetic chain lengths found in emulsion polymerization ensure the efficient use of the radiation. I n addition there are a number of other potential advantages over chemical initiation. The flux of radicals is constant throughout the reaction and not diminishing exponentially as in the case of chemical initiation. This leads to greater ease of removal of residual monomer * Present address:

Emulsion Polymerization of Vinyl Acetate

“…Stannett 94 reported an order of dependence of 0.79 at 30°C over a similar range of γ dose rates to that used in this work.…”

“…The other references to post-irradiation behaviour only mention whether or not there was significant post irradiation polymerization 93,94 .…”

“…Stannett et al 94 determined polymerization rates and viscosity average molecular weights between 0°C and 50°C for ab-initio and seeded homopolymerizations. The polymerizations were monitored by dilatometry; however, no account was taken of the small, but non-negligible, non-linearity of the contraction due to polymerization in systems such as this where the monomer has significant water solubility.…”

Photo‐induced emulsion polymerization of vinyl acetate in the presence of poly(oxyethylene)10 nonyl phenyl ether ammonium sulfate, an anionic emulsifier (I)

“…It was reported that the dependence of the rate of polymerization on ionic strength, based on the fact that the dependence of adsorption rate of the charged polymeric radicals to the already existing polymer particle on ionic strength, approaches first order when ionic strength is below 0.01. 26…”

“…The low power dependence DP on the concentrations of emulsifier and initiator was attributed to the frequent chain transfer to monomer, followed by the large desorption of oligomeric radical from the polymer particle due to high water solubility of the monomer. 26…”