ABSTRACT:The copolymerization reactivity ratios of acrylic acid and acrylamide are found at pH 5 and pH 2. Automatic continuous online monitoring of polymerization reactions (ACOMP) has been used for the first time to monitor the synthesis of polyelectrolytic copolymers. The composition drift during the reactions revealed that at pH 5, the acrylamide participates more in the copolymer, and at pH 2, the acrylic acid incorporates in the system at a higher ratio. The copolymerization data were analyzed by a recent error in variables (EVM) type calculation method developed for obtaining the reactivity ratios by on-line monitoring and gave at pH 5 reactivity ratios r Aam ¼ 1.88 6 0.17, r Aac ¼ 0.80 6 0.07 and at pH 2 r Aam ¼ 0.16 6 0.04, r Aac ¼ 0.88 6 0.08. The results show that the reactivity ratios depend strongly on the pH of the medium. The effect of polyelectrolytic interactions on the reactivity ratios is discussed in detail.

Despite their importance in biological and technological contexts, copolymeric polyelectrolytes (or "copolyelectrolytes") continue to present challenges to theorists and experimentalists. The first results of a unified approach to the kinetics and mechanisms of copolyelectrolyte synthesis and the physical characteristics of the resulting polymers are presented. The free radical copolymerization of 4-vinylbenzenesulfonic acid sodium salt and acrylamide was monitored using automatic continuous online monitoring of polymerization reactions (ACOMP), from which the average bivariate composition and mass distributions were determined. Composition drift was related to the evolution of conductivity. In some cases bimodal populations of copolyelectrolyte and homopolymeric poly(acrylamide) resulted, i.e., blends of copolyelectrolyte and neutral homopolymer. The end-product scattering behavior depended on whether the end-product was bimodal or not, as demonstrated using automatic continuous mixing (ACM) in conjunction with light scattering and viscosity. Negative light-scattering third virial coefficients were found for bimodal end-products. This combined approach may allow connecting the synthesis kinetics to the resulting "trivariate" distribution of composition, molar mass, and linear charge density, which in turn controls the properties of end-product solutions, such as chain conformations, interparticle interactions, viscosity, interactions with colloids and other polymers, phase separation, etc. Unified results may allow testing and improvement of existing polyelectrolyte theories, development of new quantitative physicochemical models, provide advanced characterization methods, set the stage for studying more complex copolyelectrolytes, such as hydrophobically modified ones, and provide tools for ultimately controlling and tailoring the synthesis and properties of copolyelectrolytes.

The possibility of controlling the composition of acrylic acid/acrylamide copolymers by controlling the pH and the ionic strength of the reaction medium is investigated. The reactivity ratios of charged monomers depend on the pH of the medium, acrylic acid is the more reactive monomer below pH 3 and acrylamide above pH 4. The working pH was set at 3.6, a candidate for the crossover point, where no composition drift is expected. Copolymerization kinetics is investigated at this pH at various ionic strengths and a reaction without composition drift up to 80% conversion was achieved. All the chains produced in this reaction contain 30% ± 3% acrylic acid. Copolymer conversions, molecular weights, and composition distributions were measured through Automatic Continuous Online Monitoring of Polymerization (ACOMP) system. The copolymerization data were analyzed by a recent error in variables method (EVM) and reactivity ratios are calculated. The results show that in salt free conditions, the reactivity ratios depend on the ionic monomer concentration (ionic strength) in addition to the pH of the reaction medium. The effect of polyelectrolytic interactions on the reactivity ratios and the resulting composition drift during the reaction, sequence length distribution, and Stockmayer bivariate distribution are discussed in detail. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Acrylamide/N,NЈ methylene bisacrylamide gels were prepared at different voltages electrochemically. The dependence of the swelling properties on the preparation voltage was investigated. A set of gel samples was swollen as prepared and another set was swollen after being dried to constant weight. Swelling versus time curves were all in stretched exponential form, rather than pure exponential form, indicating that the gels are of heterogeneous nature. Maximum swelling increased with the preparation voltage in both gel types.