A new general approach to determine more accurate comonomer reactivity ratios in controlled/living radical copolymerization systems

摘要

In controlled/living radical copolymerization (atom transfer radical copolymerization in this study) and in any other living chain-growth copolymerization, the possible preferential addition of one of the comonomers onto the (macro)initiator-derived (macro)radical can affect the copolymer composition, especially at low conversion; this results in inaccurate comonomer reactivity ratio estimation by the classic approach. A new general approach is introduced in this article, which allowed us to exclude the influence of the possible preferential addition of one of the comonomers onto the (macro)initiator-derived (macro)radical on the copolymer composition at any conversion. According to this approach, copolymer chain grown during time t (t ≠ 0) is considered to be, in fact, the macroinitiator terminated with one of the comonomers under study, which will further grow during the time interval δt′ = t′ - t where any reaction time t′ is considered to be grater than reaction time t, i.e. t′ > t from a comonomer mixture with composition of f(t) where f(t) is the molar ratio of comonomer i to comonomer j in the comonomer mixture at time t. In such a situation, it is possible to obtain individual comonomer conversions x _i(δt′) and x_j(δt′), the overall comonomer conversion xov(δt′), and the cumulative average copolymer composition for the copolymer formed during δt′, from which more accurate comonomer reactivity ratios can be calculated by the various low- or high-conversion methods, depending on the overall comonomer conversion.