Bespoke Degradable Polymers: Modifying Cyclic Allyl Sulfide Lactones to Tune Polymer Degradation Rates and Lower Critical Solution Temperatures

Abstract

A method is presented to modify the degradation rates of copolymers made through vinyl- and radical ring-opening copolymerization. Six (including five novel) 7-membered cyclic allylic sulfide (CAS) lactones with varied functionality (H, ethyl, decyl, phenyl, furyl, and benzo) at the 2 (or 2/3) position were synthesized. Their radical copolymerization with hydroxypropyl methacrylamide (HPMAm), N-isopropylmethacrylamide, and oligo(ethylene glycol) methyl ether methacrylate (OEGMA) led to the inclusion of primary alkyl, secondary alkyl, benzyl, and phenyl esters into the backbone. The choice of CAS lactone comonomer allowed tuning the LCST-type cloud point of OEGMA copolymers, with substituents decreasing the cloud point in the order H < ethyl < decyl ≪ phenyl ∼ benzo. Hydrolytic degradation rate coefficients determined on HPMAm copolymers varied by a factor of 3.3, with better alcohol leaving groups leading to faster degradation. Backbone phenyl esters degraded through aminolysis, while benzyl and aliphatic esters were stable. Selective degradation was also achieved in block copolymers containing (oxo)esters in one block and thioesters (from thionolactone copolymerization) in the other. These findings demonstrate the tuning of physical properties and degradation behavior through the choice of comonomer enabling the design of degradable polymers with tailored properties.