The soapless emulsion copolymerization of methyl methacrylate (MMA) and n‐butyl acrylate (n‐BuA) at four levels of monomer feed composition (f10) was studied. Conversion (X), average particle diameter (Dp), molecular weight distribution (MWD), surface charge density, and glass transition temperature (Tg) of the copolymer as a function of reaction time (t) were measured. The copolymers obtained even at low conversion, except for the run of (f10) = 90 wt. percent MMA, exhibit two Tgs in their DSC thermograms. Phase separation is found to occur in the latex particles during polymerization. The heterogeneous distribution of monomers in particles, in which a relatively rich MMA region exists in the shell and a relatively rich n‐BuA region exists in the core of the particles, is assumed to arise from phase separation. The average copolymer composition and the fraction of the two domains are estimated. The polymerizatrion course and particle size growth follow the linear X vs. t2 and Dp3/2 vs. t relationships, respectively. Although the coagulation of particles happens after around 30 percent conversion, the polymerization behaviors, except for increasing rates, are not affected.

In this article the kinetics of chemical-controlled radicalchain copolymerization have been reduced to pseudohomopolymerization kinetics by introducing the apparent rate constants. The methods for the determinations of the values of the apparent rate constants, mode oftermination, and the methods for the calculation of molecular weights and distributions are proposed. The data required for these determinations and calculations are simply obtained by the usual steady-state method. According to the traditional kinetics along with the definitions of the apparent rate constants, these apparent rate constants as functions of traditional rate constants, monomer compositions, and copolymer compositions are derived. Further utilizing the theoretical expressions obtained, we show that the apparent rate constants are the general rate constants for both radical chain homo-and copolymerizations. The bulk radical copolymerizations of methyl methacrylate and styrene at various monomer feed compositions at 60°C are used to test the proposed model. The empirical apparent rate constants obtained are described well, by the following expressions, l/k," = -0.132 X IO-'(FIlf) + 0.428 X lo-' (Fdf) and kp/(k,")' = -0.138 x 104(F,/jl)2 + 0.354 X 104(F1F2/fif2) -0.114 X 104(F2/f)'and the mode oftermination based on the combination termination is p = 0.997 F l + 0.398 Fz + 0.039 (FIF,)) where k," and k? denote the apparent rate constants of propagation and termination, respectively. The termfi(= 1 -f2) stands for the mole &action of sytrene in the monomer soldtion fed. F, is the copolymer composition produced atfl. p is the mode of termination.

An environmentally friendly visible-light-driven photocatalyst, silver vanadates/SBA-15, was prepared through an incipient wetness impregnation procedure with silver vanadates (SVO) synthesized under a hydrothermal condition without a high-temperature calcination. The addition of mesoporous SBA-15 improves the formation of nanocrystalline silver vanadates. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) confirms the presence of Brønsted and Lewis acids on the SVO/SBA-15 composites. The results of photoluminescence spectra indicated that the electron-hole recombination rate have been effectively inhibited when SVO was loaded with mesoporous SBA-15. All the composites loaded with various amount of SVO inherit the higher adsorption capacity and larger mineralization yield than those of P-25 (commercial TiO2) and pure SVO. The sample loaded with 51% of SVO (51SVO/SBA-15) with mixed phases of Ag4V2O7and α-Ag3VO4exhibits the best photocatalytic activity. A favorable crystalline phase combined with high intensities of Brønsted and Lewis acids is considered the main cause of the enhanced adsorption capacity and outstanding photoactivity of the SVO/SBA-15 composites.

The soapless emulsion polymerization of methyl methacrylate (MMA) and n‐butyl acrylate (BA) containing various concentrations of sodium methacrylate (NaMA) or methacrylic acid (MMA) is studied. The hydrosoluble yields in final latexes are not larger than 1.3–5%, depending on the concentration of NaMA used. Below 25% conversion, the change of conversion with reaction time follows the square rule and the particle size is proportional to the 2/3 power of time. Above 25% conversion, serious gel effect occurs, and the conversion follows the seventh power on time and the growth of particle diameter obeys the 2.5 power on time. The multiple glass transition (Tg) occur below 20% conversion, where monomer droplets exist. NaMA added induces more Tgs. The effect of molecular weight of the copolymers obtained on Tg (even the molecular weight distributions were shown to be shouldertype bimodal) is estimated to be insignificant. Thus, the heterogeneity of copolymer compositions for multiple Tgs is ascribed to be caused from neither the molecular weight heterogeneity nor the shifts in compositions due to the difference of the monomer reactivity ratios. Referring to the results mentioned, we assume the sublayer surrounding the particle, rich with SO4− and COO− groups, and the concentration gradients of monomers in particles to illustrate particle morphology. In addition, the relatively hydrophilic sublayer is proposed to be closely relative with the occurrence of the composition heterogeneity in particles.

SynopsisIn this article the straight-line relationship between In A and In B, where A and B denote the concentrations of the two types of monomers in any reaction period, is examined to exist in the radical copolymerizations of 1.02 2 rIrz 2 0.25. Utilizing this observation, we propose an easy-touse compositions calculation method in which a single empirical parameter is included. The method is derived without involving the constant monomer reactivity ratios assumption. The copolymerizations of styrene-methyl methacrylate, vinyl chloride-vinyl acetate, methyl methacrylate-vinyl acetate, acrylic acid-acrylamide, methacrylic acid-methacrylamide, and sodium methacrylate-methacrylamide are investigated. The instantaneous and cumulative copolymer compositions and the residued monomer compositions computed by this proposal are in very good agreement with the experimental data.