Catalyst-Free Reactive Ester (Meth)Acrylates Enabling Crosslinking Below 100 °C

In the design of materials such as adhesives, resists, and coatings, crosslinked structures are one effective approach to achieving the desired mechanical strength and long-term reliability.
Acrylic resin compositions are widely used in these applications. Crosslinking is typically achieved either by forming dense network structures using multifunctional monomers, or by introducing reactive side chains into copolymers that subsequently form crosslinks.
For example, multifunctional isocyanate monomers form crosslinks through urethane or urea bonds by reacting with active hydrogen groups such as hydroxyl or amino groups present in the formulation. While these reactions can proceed at room temerature, they generally require metal catalysts such as tin compounds and inevitably suffer from short pot life.
Alternatively, (meth)acrylate monomers that contain a reactive group with a curing mechanism different from radical-polymerizable (meth)acryloyl groups can be copolymerized into acrylic polymers and crosslinked via their side-chain functional groups. Oxetane is one such example. Oxetane-based crosslinking proceeds via ring-opening polymerization and is not affected by oxygen inhibition; however, it requires the addition of a catalyst or initiator and heating above 100 °C.

Films prepared by coating a mixture of the MOI-DEM–containing copolymer and PEG600 were heated at temperatures ranging from 80 to 140 °C. Gel fraction measurements were used to evaluate the degree of crosslinking. As a comparative material, a copolymer containing AOI-BP—an in-house conventional material in which isocyanate ethyl acrylate is blocked with pyrazole—was evaluated. Upon deblocking, AOI-BP generates isocyanate groups that form urethane linkages with alcohol in the presence of a tin-based catalyst.
As shown in Figure 2, MOI-DEM achieved gel fractions exceeding 70% when heated at 80–100 °C. No further increase was observed above 100 °C, indicating that crosslinking reached saturation below 100 °C. In contrast, AOI-BP required both a catalyst and heating above 120 °C to achieve a comparable level of crosslinking.