Search for: All records

Photoinduced electron/energy transfer (PET)-reversible addition–fragmentation chain transfer polymerization (RAFT) and conventional photoinitiated RAFT were used to synthesize polymer networks. In this study, two different metal catalysts, namely, tris[2-phenylpyridinato-C2,N]iridium(III) (Ir(ppy)3) and zinc tetraphenylporphyrin (ZnTPP), were selected to generate two different catalytic pathways, one with Ir(ppy)3 proceeding through an energy-transfer pathway and one with ZnTPP proceeding through an electron-transfer pathway. These PET-RAFT systems were contrasted against a conventional photoinitated RAFT process. Mechanically robust materials were generated. Using bulk swelling ratios and degradable cross-linkers, the homogeneity of the networks was evaluated. Especially at high primary chain length and cross-link density, the PET-RAFT systems generated more uniform networks than those made by conventional RAFT, with the electron transfer-based ZnTPP giving superior results to those of Ir(ppy)3. The ability to deactivate radicals either by RAFT exchange or reversible coupling in PET RAFT was proposed as the mechanism that gave better control in PET-RAFT systems. 

Model poly(n-butyl acrylate) (PBA) networks were prepared by photoinduced atom transfer radical polymerization (photoATRP), followed by curing of polymer stars via atom transfer radical coupling (ATRC) with a nitrosobenzene radical trap. The resulting nitroxyl radical installed thermally labile alkoxyamine functional groups at the junctions of the network. The alkoxyamine crosslinks of the network were degraded back to star-like products upon exposure to temperatures above 135 °C. Characterization of the degraded products via gel permeation chromatography (GPC) confirmed the inversion of polymer topology after thermal treatment. 

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 Mw = 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. 

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).