Estimating Monomer Sequence Distributions in Tetrapolyacrylates

Recently Ting et al. [ACS Macro Lett. 2013, 2, 770−774] described the syntheses of acrylic tetrapolymers with controlled molecular weights and tetramonomer compositions. Relative reactivity ratios of all monomer pairs were determined and used in the Walling–Briggs terminal copolymerization model along with Skeist’s equations to address the expected compositional drift in the monomer feed ratios. The anticipated control of monomer incorporation based on this approach was verified experimentally on several tetrapolyacrylates synthesized by RAFT polymerization, which additionally controlled their molecular weights. Their “new and simple paradigm combining both predictive models provides complementary synthetic and predictive tools for designing macromolecular chemical architectures with hierarchical control over spatially dependent structure–property relationships for complex applications” is extended here to the derivation of expected monad compositions, and diad, triad, and tetrad monomer sequence distributions. These were obtained directly from the comonomer reactivity ratios determined experimentally by Ting et al. Our motivation was twofold: (i) The similar chemical structures of the four acrylate monomers they selected (methyl, 2-carboxyethyl, 2-hydroxypropyl, and 2-propylacetyl acrylate) render the experimental determination of sequence distributions in the resulting tetrapolyacrylates problematic. (ii) Because they are spatially dependent structural parameters, the sequence distributions of monomer diads, triads, tetrads, etc., in co-, tri-, tetrapolymers, etc., are generally expected to correlate more closely with their properties than their overall compositions