Visible-Light-Curable Solvent-Free Acrylic Pressure-Sensitive Adhesives via Photoredox-Mediated Radical Polymerization

Abstract

Owing to their excellent properties, such as transparency, resistance to oxidation, and high adhesivity, acrylic pressure-sensitive adhesives (PSAs) are widely used. Recently, solvent-free acrylic PSAs, which are typically prepared via photopolymerization, have attracted increasing attention because of the current strict environmental regulations. UV light is commonly used as an excitation source for photopolymerization, whereas visible light, which is safer for humans, is rarely utilized. In this study, we prepared solvent-free acrylic PSAs via visible light-driven photoredox-mediated radical polymerization. Three α-haloesters were used as additives to overcome critical shortcomings, such as the previously reported low film curing rate and poor transparency observed during additive-free photocatalytic polymerization. The film curing rate was greatly increased in the presence of α-haloesters, which lowered the photocatalyst loadings and, hence, improved the film transparency. These results confirmed that our method could be widely used to prepare general-purpose solvent-free PSAs—in particular, optically clear adhesives for electronics.

Initiator‐Activation Strategy‐Enabled Organocatalyzed Reversible‐Deactivation Radical Polymerization Driven by Light

“…Because the redox potentials of initiators could reflect their ability of electron acceptance in the catalytic cycle, we investigated the half‐peak potential [19] of TsCl by cyclic voltammetry (CV). Compared to diethyl 2‐bromo‐2‐methylmalonate, ethyl‐bromoisobutyrate and ethyl 2‐bromopropionate ( E p/2 =−0.75 to −0.85 V vs. SCE), [4c, 20] TsCl exhibits a more negative half‐peak potential ( E p/2 =−0.98 V vs. SCE), suggesting that the alkyl bromides are easier of being reduced to generate active carbon radicals in the photoredox‐mediated O‐ATRP as realized in many examples, [4a–e] and meanwhile implying that sulfonyl chlorides are more difficult initiators in terms of electron acceptance.…”

A Water‐Soluble Organic Photocatalyst Discovered for Highly Efficient Additive‐Free Visible‐Light‐Driven Grafting of Polymers from Proteins at Ambient and Aqueous Environments

“…To achieve this, water‐soluble and weakly electron‐donating sulfonate moiety was introduced in one of four donor groups of "4DP‐IPN" with a strongly twisted donor–acceptor structure that has been known for highly efficient organic PC for various organic reactions and polymerizations. [ 43–51 ] Most excitingly, the discovered PC exhibited unique “oxygen‐acceleration” behavior in PET‐RAFT polymerizations of a variety of acrylates and acrylamides in both DMSO and aqueous conditions without any additives, which is apparently distinct from previously reported systems. [ 30,31 ] Combined experimental and theoretical studies suggested that molecular oxygen acts as an electron shuttle to catalyze the electron transfer between the PC in the excited state and the chain‐transfer agent (CTA) (Figure 1d).…”

The Effect of Type-I Photoinitiators on the Kinetics of the UV-Induced Cotelomerization Process of Acrylate Monomers and Properties of Obtained Pressure-Sensitive Adhesives

“…Increasingly, in the last decade, publications on ecological methods of PSAs preparation have been made, of which the most important are photopolymerization processes. Back et al reported on a new pro-ecological method of obtaining solvent-free PSAs via visible-light-driven photocatalytic radical polymerization [ 10 ] and photoredox-mediated radical polymerization [ 11 ]. Instead, Beak at al.…”