Polymerization of cystine-derived monomers

Abstract

Cystine was used as a platform chemical to prepare cyclic and acyclic monomers for entropy-driven ring-opening polymerization (ED-ROMP) via olefin or disulfide metathesis and for step-growth polymerization. The olefin ED-ROMP of an olefin/disulfide containing 16-atom macrocycle using the 3^rd generation Grubbs catalyst was examined in greater detail. Kinetic studies revealed that the catalyst turned inactive during the polymerization, which limited the achievable (apparent) polymer molar mass to ∼70 kg mol⁻¹. Such limitation could be overcome with the disulfide ED-ROMP of the same macrocycle to yield polymers with molar masses of up to 180 kg mol⁻¹. The step-growth polymerizations of acyclic diene and dithiol monomers via olefin metathesis or oxidation were far less effective and yielded just low molar mass polymers or oligomers; photopolymerization of a thiol–ene monomer produced a polyester with a molar mass of 35 kg mol⁻¹.