PET-RAFT Increases Uniformity in Polymer Networks

Abstract

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 energytransfer 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.

Gelation in Photoinduced ATRP with Tuned Dispersity of the Primary Chains

“…An expected difference in ESR between networks with [HDDA] 0 = 1.5 and 3 was clearly visible. However, no difference in swelling was observed for networks with [HDDA] 0 = 3 prepared at various catalyst concentrations as all samples 40 However, given the larger measurement error in networks with [HDDA] 0 = 1.5, this discrepancy is not substantial. These results were further supported by a rheological analysis of the shear storage moduli (G′) of dried networks (Figure 4b).…”

“…38 Konkolewicz and Matyjaszewski employed degradable crosslinkers to compare the structure and mechanical properties of networks prepared by ATRP and RAFT. 39,40 However, an interdependence between gelation kinetics, primary chain dispersity, and physical properties of networks from RDRP has not yet been studied.…”

“…For example, Appel et al proposed a gel point normalization method in order to account for crosslinks lost due to intramolecular cyclization and rationalize the synthesis of branched/network architectures by RAFT . Konkolewicz and Matyjaszewski employed degradable crosslinkers to compare the structure and mechanical properties of networks prepared by ATRP and RAFT. , However, an interdependence between gelation kinetics, primary chain dispersity, and physical properties of networks from RDRP has not yet been studied.…”

PET‐RAFT polymerization under flow chemistry and surface‐initiated reactions

“…For instance, Jin and co-workers 37,100 used PET-RAFT polymerization for 3D printing under ambient conditions and visible light. Shiwanka et al 101 demonstrated that PET-RAFT polymerization had higher potential in forming a more uniform network than conventional RAFT polymerization, which swelling ratio experiments can verify. Jianzhi et al 102 reported a bilayer hydrogel for wound dressing obtained using PET-RAFT polymerization.…”

Recent developments in visible light induced polymerization towards its application to nanopores

“…107 Since then zinc tetraphenylporphyrin (ZnTPP) was frequently used as metal-based photo catalyst in visible light induced PET-RAFT. 36,[114][115][116][117][118] Very recently Wanasinghe et al 116 used both Ir(ppy) 3 and ZnTPP to analyze bulk swelling ratios and homogeneity of polymer networks, whereby better results were reported using ZnTPP. Corrigan et al 119 used ZnTPP as photoredox catalyst for a PET-RAFT polymerization at low-intensity yellow light irradiation, ambient temperatures, and in an open reaction vessel in the presence of oxygen.…”