In general, second-generation acrylic adhesives (SGAs) attract attention due to their advantageous properties, such as room temperature curing using redox reaction, balanced shear/peel adhesive strengths. The current SGAs consist of acrylic monomers and elastomers and make phase structures in micrometer scale via polymerization-induced phase separation.
In this study, functional methacrylic tri-block copolymers (BCPs) were used as the toughening modifiers for room temperature polymerized blends. In specific, poly (methyl methacrylate/glycidyl methacrylate)-b-poly (lauryl methacrylate)-b-poly (methyl methacrylate/glycidyl methacrylate) triblock copolymers [(P(MMA/GMA)-b-PLMA-b-P(MMA/GMA)] were utilized as the BCPs. Meanwhile, methyl methacrylate (MMA) monomer was used as main component and was copolymerized with small amount of methacrylic acid (MAA) to produce the matrix polymer. Cumene hydroxy peroxide and trimethyl thiourea were used as the redox reaction initiator. The glycidyl groups in the hard-block chains of the BCPs reacted firstly with the carboxy groups of the MAA, then produced the methacrylated BCPs, which co-polymerized with the MMA.
The phase structures and physical properties of the blends were studied in relation to the amounts of functional groups in both the BCPs and the matrices. In the case of methacrylic polymer matrices without MAA, the PMMA matrix / BCP blends formed phase structures in micrometer scale via polymerization-induced phase separation. On the other hand, in the case of methacrylic polymer matrices with MAA, self-assembled nanostructures with tens of nanometers scale, such as curved lamella, cylinders, and spheres, were observed in the blends. When the hard-block chains of the BCPs and the methacrylic matrix polymers have high compatibility, the hard-block chains are sufficiently diffused in the matrix. As a result, the interfacial curvature increases between the matrix and the immiscible PLMA domains, which produces spherical micelles. Meanwhile, when the compatibility of the hard-block chains with the matrix decreases, the hard-block chains shrink in the matrix, and the interfacial curvature between the matrix and the immiscible PLMA domains decreases. Using the mechanism several nano-micelle shapes, such as spherical, cylindrical, and lamella was controlled. Then, fracture toughness and toughening mechanisms were examined.

Hajime Kishi

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