A model, together with a comparison with previously published experimental data, is presented for initiator efficiency in seeded styrene emulsion polymerization systems in the absence of secondary particle formation. The data had shown that a number of previous models are inapplicable, viz., those assuming that the rate-determining step for free-radical entry into a particle is either diffusional capture, surfactant displacement, or colloidal entry. The data support the supposition that the rate-determining step for freeradical capture by latex particles is aqueous-phase propagation to a critical degree of polymerization, whereupon capture (irreversible adsorption) of the resulting oligomeric free radical by a particle is essentially instantaneous. Mutual aqueous-phase termination of smaller species also occurs. When account is taken of the fact that the rate coefficients for (a) the first aqueous-phase propagation step and (b) aqueous-phase termination are both in the diffusion limit, this model is in qualitative and quantitative accord with the experimental dependences of the entry rate coefficient on the concentrations of initiator, of surfactant, of aqueous-phase monomer, and of latex particles as well as on particle size and on ionic strength. For styrene emulsion polymerization initiated by persulfate, the critical oligomer size for entry was found to be dimeric.

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SYNOPSISThe exit or desorption of free radicals from latex particles is an important kinetic process in an emulsion polymerization. This article unites a successful theory of radical absorption (i.e., initiator efficiency), based on propagation in the aqueous phase being the rate determining step for entry of charged free radicals, with a detailed model of radical desorption. The result is a kinetic scheme applicable to true "zero-one" systems (i.e., where entry of a radical into a latex particle already containing a radical results in instantaneous termination), which is still, with a number of generally applicable assumptions, relatively simple. Indeed, in many physically reasonable limits, the kinetic representation reduces to a single rate equation. Specific experimental techniques of particular significance and methods of analysis of kinetic data are detailed and discussed. A methodology for both assessing the applicability of the model and its more probable limits, via use of known rate coefficients and theoretical predictions, is outlined and then applied to the representative monomers, styrene and methyl methacrylate. A detailed application of the theory and illustration of the methodology of model discrimination via experiment is contained in the second article of this series.

The ability of terminal model kinetics to predict copolymer microstructure was tested for the styrenemethyl methacrylate system copolymerized at 40 O C at various fractions of monomers. NMR studies (in the accompanying paper) showed that previous peak assignments of the spectra of statistical styrenemethyl methacrylate copolymers were incorrect. The peak areas obtained for all copolymers were described in terms of triad sequences and were also adequately predicted by the terminal model utilizing reactivity ratios calculated from a nonlinear least squares fit to the copolymer composition data determined by 'H NMR. The nonterminal model behavior of the kinetics of the rate of polymerization described elsewhere can be successfully modeled by the 'restricted" penultimate model of Fukuda et al. We show that all current data can also be explained by various "bootstrap" or monomer-polymer complex models. Further model discrimination awaits new independent experimental results. IntroductionThe kinetic model that is most widely used to model free radical copolymerizations is the terminal model, also known as the Mayo-Lewis model.' For most copolymer systems the copolymer composition has been shown to be well fitted by the terminal model equation.2 Recently, however, there have been numerous reports of the inability

The novel radical polym erization of an unsaturated m onom er in the hydrophobic p a rt o f vesicles is attempted using the experience gathered from kinetic a n d thermodynamic studies o f the e m ulsion polym erization process. The influence of the m onom er content of the system and also the in itia tio n of the polym erization are discussed. A free radical polym erization of styrene in d io ctadecyldim ethylam m om um brom ide vesicles is performed. Evidence of the form ation of polymer-containing vesicles is o b tain e d by means of electron microscopy and the comparison of the diffusion rate of a paramagnetic pro be over the bilayer of vesicles and polymer-containing vesicles.