We propose a new method for the determination of reactivity ratios based on a nonterminal model of copolymerization kinetics. Within the context of this model, we derive simple, reactivity-ratio-dependent expressions whose solution relies solely on monomer consumption information spanning the full range of conversion. Utilizing this method, reactivity ratios are obtained for the aluminum chelatecatalyzed copolymerization of phenyl glycidyl ether and allyl glycidyl ether (r PGE = 1.56 ± 0.01 and r AGE = 0.66 ± 0.03) with monomer consumption monitored by in situ 1 H NMR spectroscopy. Additionally, this approach is applied to experimental data extracted from the literature for other copolymerization systems encompassing a range of monomer types (styrenics, isoprene, lactones, lactide, and other cyclic ethers) and polymerization type (anionic, coordination, and zwitterionic) to obtain reactivity ratios under the mechanistic assumption of nonterminal model copolymerization kinetics. We present the nonterminal model of copolymerization as the first method that should be utilized before more complex frameworks (e.g., terminal or penultimate model of chain copolymerization) are used to understand copolymerization kinetics.

Membranes are a critical component of many energy generation and storage technologies, including artificial photosynthesis systems that reduce atmospheric CO 2 to high-value products. In this study, we used in situ ATR FTIR spectroscopy to monitor the crossover of three commonly-reported CO 2 reduction products-methanol, sodium formate and sodium acetatethrough Nafion ® 117, a common cation exchange membrane. Measurement errors for the permeation of mixtures of solutes are discussed. Permeabilities from one-, two-, and three-solute mixed solutions were measured using a standard diffusion cell, and ATR FTIR spectra were used to obtain time-resolved concentration data that were fit to a model describing transport of ions and small molecules through hydrated polymer films. The permeability of Nafion ® 117 to methanol measured using this methodology was in agreement with literature reports. The sorption of methanol, sodium formate, and sodium acetate, and mixtures thereof, were measured using a desorption technique. From the measured permeabilities and solubilities, diffusivities of each solute were calculated. Differences in permeability among the solutes were found to be primarily due to differences in their solubility in Nafion ® 117.