(582e) Tuning Compositional Drift in the Bulk Living Copolymerization of Styrene and Isoprene

The local and long range ordering of polymer materials has a profound impact on their properties. In general, the nature of a polymer chain’s chemistry depends on how the monomers are incorporated during the polymerization and how the monomers are incorporated can be manipulated to achieve desired polymer properties. Compositional control in living chain copolymerization is tied to the intrinsic reactivity (or relative reactivity) of the two monomers. This relative reactivity is typically described with a terminal model of copolymerization kinetics and the reactivity ratios, for instance r_S and r_I for the copolymerization of styrene and isoprene, describe the tendency of a propagating chain end species to self-propagate and enchain its own type of monomer over that of the other monomer. In this way, reactivity ratios represent the compositional drift that results from the difference in monomer reactivity during the copolymerization and have been a common metric for classifying or discerning between the four well established types of copolymerization; gradient, blocky, alternating and random. Reactivity ratios are distinct for pairs of monomers under specific reaction conditions. They are temperature and solvent dependent and may be influenced by the presence of additives. Here, we leverage this solvent dependence to tailor the compositional drift in copolymerizations of styrene and isoprene. Copolymerizations of styrene and isoprene are conducted with varied quantities of a polar modifier and monitored with either in situ Attenuated-Total-Reflectance Fourier Transform Infrared (ATR FTIR) or ¹H Nuclear Magnetic Resonance (NMR) spectroscopy. Compositional profiles for each copolymerization and reactivity ratios are extracted. General guidelines for synthesizing SI copolymers with desired compositional profiles. Copolymer glass transition temperatures are determined and related to the copolymer overall composition and compositional profile.