(255cj) Single Polymerization Determination of Reactivity Ratios Via in Situ Spectroscopic Techniques and a Simple Nonterminal Model for Chain Copolymerization

Here, we propose a new method for the determination of reactivity ratios based on a non-terminal model of copolymerization kinetics. We propose this non-terminal model of copolymerization as an initial method that should be utilized before more complex frameworks (e.g. terminal or penultimate model of chain copolymerization) are used to understand copolymerization kinetics. The ability to synthesize tailored polymer materials with specified functionalities and material properties is fundamental to understanding and ultimately controlling structure-property relationships. Through precise control over the distribution of monomers along the polymer chain, a wide variety of polymer architectures (block, random, gradient etc.) can be achieved with consequently varying and tunable physical properties. Importantly, during the simultaneous copolymerization of two (or more) monomers, the resulting polymer chains typically exhibit a composition gradient along the chain due to the monomer reactivity ratios straying from unity. However, as many ionic and coordination polymerizations exhibit ideal or close to ideal copolymerization, the product of their reactivity ratios is unity or close to unity. The implication of this behavior is that the enchainment of monomer is dictated by the monomers themselves and is independent or predominantly independent of the identity of the reacting chain end. Thus an analytical solution can be derived from the coupled ordinary differential equations and ultimately the determination of reactivity ratios can be achieved from kinetic polymerization data that span the full range of conversion. This nonterminal model removes the need to perform the more labor-intensive processes in order to perform techniques such as Mayo-Lewis or Fineman-Ross.We utilize monomer consumption data obtained with in situ ¹H NMR spectroscopy to obtain reactivity ratios for the aluminum-chelate catalyzed copolymerization of phenyl glycidyl ether and allyl glycidyl ether (r_PGE = 1.56 ± 0.01 and r_AGE = 066 ± 0.03). Furthermore, we apply this approach to other copolymerization whose experimental data is readily available in the literature. These copolymerization systems include a range of monomer types (styrenics, isoprene, lactones, lactide, and other cyclic ethers) and polymerization routes (anionic, coordination and zwitterionic). For systems where reactivity ratios have been determined via other methods we find good agreement using the nonterminal model proposed here.