This work explores the concept of structurally tailored and engineered macromolecular (STEM) networks by proposing a novel metal-free approach to prepare the networks. STEM networks are composed of polymer networks with latent initiator sites affording post-synthesis modification. The proposed approach relies on selectively activating the fragmentation of trithiocarbonate RAFT agent by relying on visible light RAFT iniferter photolysis coupled with RAFT addition–fragmentation process. The two-step synthesis explored in this work generates networks that are compositionally and mechanically differentiated than their pristine network. In addition, by careful selection of crosslinkers, conventional poly(ethylene glycol) dimethacrylate (M_n = 750) or trithiocarbonate dimethacrylate crosslinker (bis[(2-propionate)ethyl methacrylate] trithiocarbonate (bisPEMAT)), and varying concentrations of RAFT inimer (2-(2-(n-butyltrithiocarbonate)-propionate)ethyl methacrylate (BTPEMA)), three different types of primary (STEM-0) poly(methyl methacrylate) (PMMA) networks were generated under green light irradiation. These networks were then modified with methyl acrylate (MA) or N,N-dimethylacrylamide (DMA), under blue light irradiation to yield STEM-1 gels that are either stiffer or softer with different responses to polarity (hydrophilicity/hydrophobicity).

Degradable polymers are crucial in order to reduce plastic environmental pollution and waste accumulation. In this paper, a natural product, tannic acid was modified to be used as a polymer star core. The tannic acid was modified with atom transfer radical polymerization (ATRP) initiators and characterized by ¹H NMR, FT-IR, and XPS. Twenty-five arm polymer stars were prepared by photoinduced ATRP of poly(methyl methacrylate) (PMMA) or poly(oligo(ethylene oxide) methacrylate) (molar mass M_w = 300 g/mol) (P(OEO₃₀₀MA)). The polymer stars were degraded by cleaving the polymer star arms attached to the core by phenolic esters under mild basic conditions. The stars were analyzed before and after degradation by gel permeation chromatography (GPC). Cytotoxicity assays were performed on the P(OEO₃₀₀MA) stars and corresponding degraded polymers, and were found to be nontoxic at the concentrations tested.