Anna Zheng,Bo Chen,Dihang Hu,Yong Guan,Dafu Wei,Shuzhao Li,Dandan Ji
This work confirms the new view of the initiation and propagation mechanism of the anionic polymerization previously proposed, based on the investigation of anionic bulk-polymerization of styrene and α -methyl styrene with the help of a self designed microflow device and characterized by GPC and in situ 7 Li NMR. It was found that n -BuLi tended to form the hexameric-aggregated structure and even to form the huge aggregated structure based on the former. These aggregations of initiators could directly initiate the anionic polymerization and form the supramolecule aggregations. The supramolecule aggregations inevitably blocked the diffusion of the monomers to the ion-pairs and resulted in a stationary-conversion platform. Then the aggregators were dissociated completely into equal binary-aggregated species, and the polymerization continued again rapidly before the termination. Tetrahydrofuran (THF) acted as the electron donator, which could push the electron cloud to Li cation and make the aggregated ring of the active species rather loosened and facilitated the monomer to insert in. Therefore, a little THF can greatly promote the anionic polymerization. However, further addition of THF might block the channel between the ion-pairs and decrease the propagation rate. It was also found that the aggregated structure of the active species during the anionic polymerization only depends on the initiator aggregations which were formed before the polymerization.
In this study, we designed and synthesized four α-ketone aryl thioesters photoinitiators ( PTEs ) with excellent cytocompatibility for LED photopolymerization using a simple one-step reaction. We investigated the potential photopolymerization initiation mechanisms of PTEs under 405 nm LED irradiation through ultraviolet–visible absorption spectroscopy, high-resolution mass spectroscopy, and electron spin resonance. Our findings revealed that PTEs can effectively initiate the photopolymerization of acrylate monomer tripropylene glycol diacrylate (TPGDA) under either 405 nm or 455 nm LED irradiation, achieving double bond conversions of approximately 80 % or higher after 180 s of irradiation. Remarkably, compared to the commercial photoinitiator 2,4,6-trimethylbenzoyl-diphenylphosphine oxide (TPO) and benzoyl methacrylate (MBF), PTEs exhibit certain advantage in initiating photopolymerization of triethylene glycol dimethacrylate (TEGDMA) widely used for dental materials under the irradiation of 405 nm. More importantly, MO-PTE has better cytocompatibility compared to TPO and exhibits a great potential in the fields of LED photopolymerization, biomaterials and food packaging.
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