The development of degradable and recyclable polymers holds a lot of promise with applications to a diverse array of fields starting from packaging, biomedical engineering to sustainability challenges. This thesis expands the space of such materials by exploring three structurally distinct S- containing cyclic monomer systems.

The first part of the thesis addresses the established difficulty of homopolymerizing the well-known thionolactone, dibenzo[c,e]oxepine-5(7H)-thione (DOT). Cationic ring-opening polymerization (CROP) under ambient conditions, afforded the homopolymers with near-quantitative conversions and molar masses up to 50 kg/mol. Thermal and nucleophilic depolymerization yielded the thiolactone isomer of DOT as the major degradation product, leading a crucial step towards chemical recyclability.

The second study investigates an activated ester derived from lipoic acid (a naturally occurring cyclic disulfide): pentafluorophenyl (PFP) lipoate, as a modifiable and degradable scaffold. It was homopolymerized by additive-free UV irradiation and the homopolymer further yielded a series of polylipoamides and hydrogels. The lipoamide polymers had distinct thermal properties and thermoresponsive behaviour, while the hydrogels showed tunable swelling and mechanical properties. Both polymers and crosslinked materials with degradable disulfide linkages in the backbone underwent successful degradation under oxidative or reductive conditions.

Next, a novel lipoate monomer 4-acetamidophenyl 5-(1,2-dithiolan-3-yl)pentanoate (ADP) was synthesized by covalent conjugation of lipoic acid to a commercially available drug. Its copolymerization with hydrophilic comonomers afforded a series of thermoresponsive copolymers, one with a cloud point close to body temperature (36.2 °C). These polymers selectively released the attached drug under mild basic conditions while remaining stable under acidic conditions. The disulfide backbone of the polymers was also degraded by reductive means, establishing proof-of-concept for a stimuli-responsive drug-delivery platform.

Overall, this thesis provides access to different degradable, modifiable and recyclable materials from structurally diverse cyclic monomers under various polymerization strategies with relevance to chemical recycling, functional materials design, and drug delivery.