Alternating Sequence Control for Carboxylic Acid and Hydroxy Pendant Groups by Controlled Radical Cyclopolymerization of a Divinyl Monomer Carrying a Cleavable Spacer

Abstract

By utilizing features of the hemiacetal ester (HAE) bond: easy formation from vinyl ether and carboxylic acid and easy cleavage into different functional groups (-COOH and -OH), we achieved control of the alternating sequence of two functional pendant groups of a vinyl copolymer. Methacrylate- and acrylate-based vinyl groups were connected through HAE bonds to prepare a cleavable divinyl monomer, which was cyclo-polymerized under optimized conditions in a ruthenium-catalyzed living radical polymerization. Subsequent cleavage of the HAE bonds in the resultant cyclo-pendant led to a copolymer consisting of alternating methacrylic acid and 2-hydroxyethyl acrylate units as analyzed by C NMR spectroscopy. The alternating sequence of -COOH and -OH pendants specifically provided a lower critical solution temperature (LCST) in an ether solvent, which was not observed with the random copolymer of same composition ratio.

Unprecedented Sequence Control and Sequence‐Driven Properties in a Series of AB‐Alternating Copolymers Consisting Solely of Acrylamide Units

“…Furthermore, Figure C shows the 13 C NMR spectrum of the obtained copolymer in comparison with the random copolymer, and the spectra exhibit almost identical shapes and peak‐splitting patterns. Peculiar peaks specifically due to the alternating sequence were not observed, though 13 C NMR spectroscopy of the alternating copolymer was different from random ones, and it clarified the sequence in previous works of sequence control …”

“…Thus, we tried to control the polymerization with various conditions of reversible deactivation radical polymerization. First, atom transfer radical polymerization (ATRP) conditions were applied to the cyclopolymerization of 1 under dilute conditions ([ 1 ] 0 =100 m m ; [initiator] 0 =2.0 m m ), which are similar to those of the cyclopolymerization of the methacrylate–acrylate divinyl monomer in our previous study . However, the conversion of the vinyl groups in 1 reached a plateau less than 50 % during the early stages of the reaction, affording low‐molecular‐weight polymers using any iron and copper catalyst in conjunction with various ligands and additives (Supporting Information, Table S1, Entries 2–9).…”

“…Forschungsartikel 5232 www.angewandte.de ditions ([1] 0 = 100 mm ;[ initiator] 0 = 2.0 mm), which are similar to those of the cyclopolymerization of the methacrylateacrylate divinyl monomer in our previous study. [24,26] However,the conversion of the vinyl groups in 1 reached aplateau less than 50 %d uring the early stages of the reaction, affording low-molecular-weight polymers using any iron and copper catalyst in conjunction with various ligands and additives (Supporting Information, Table S1, Entries 2-9). This could be reasonably interpreted in terms of catalyst poison by the nitro group.…”

“…We have recently developed a method to control the alternating sequence in copolymers by selective radical cyclopolymerization and the cleavage of the cyclo‐spacer in the resulting repeat units . The spacer of the divinyl monomer can either be cleaved or transformed, and the design determines the pendant groups in the resulting alternating sequence.…”

Orthogonal Click Postfunctionalization of Alternating Copolymers Prepared by Nitroxide‐Mediated Polymerization

“…Iterative multi‐step approaches provide excellent sequence‐fidelity but are tedious to conduct and therefore limited to oligomers and smaller polymeric chains . Template‐based strategies, polymerizations based on multicomponent reactions, and the polymerization of sequence‐controlled precursors allow for higher molecular weights but are limited to relatively simple repetitive patterns. Also pinpoint functionalization of polymer chains has been achieved by time‐resolved addition of co‐monomers .…”