Structural development and adhesion of acrylic ABA triblock copolymer gels

Relationships between the structure, properties, and processing techniques of model polymer gels are investigated. The mechanical properties of the gels are determined by a thermally reversible aggregation of the syndiotactic PMMA end blocks of an acrylic triblock copolymer, which is diluted with a selective solvent for the center block. The adhesive and mechanical properties of these gels are related to their structural features, which are quantified by small-angle X-ray scattering experiments. The gels are significantly strengthened by the addition of low molecular weight isotactic PMMA homopolymers. These polymers form complexes with the syndiotactic PMMA end blocks of the triblock copolymer. In addition, we employ an axisymmetric adhesion test to demonstrate that the equilibrium gelation process can be utilized to reproducibly control the structure and adhesive properties of "dried" polymers. Acrylic acid moieties increase the adhesive performance of these materials without affecting their structure. By employing a unique gel casting process, a network structure with the desired properties can be formed, giving materials that are ideally suited for use as pressure-sensitive adhesives.