Manabu Adachi

Effects of Compatibility of Acrylic Block Copolymer and Tackifier on Phase Structure and Peel Adhesion of Their Blend

The effect of compatibility of polymer and tackifier on the adhesion properties of pressure-sensitive adhesive tape was investigated. For this purpose, a model pressure-sensitive adhesive tape was prepared. A mixture of poly(methyl methacrylate)-block-poly(butyl acrylate)-block-poly(methyl methacrylate) triblock copolymer and a similar diblock copolymer was used as the base polymer. And three kinds of tackifiers, namely a rosin phenolic resin (A), a special rosin ester resin (B) and a hydrogenated cycloaliphatic resin (C) were used. The compatibility with the base polymer was in the order of tackifier A > B > C. Transmission electron microscopy studies confirmed that the tackifier A had good compatibility, where agglomerates of the tackifier with a size of about 10 nm only were observed. Larger and distinct agglomerates of tackifier were observed for tackifier B and the size increased with the tackifier content. The tackifier C formed domains with a mean size of several tens μm. Dynamic mechanical analysis indicated that both the glass transition temperature and modulus increased at low temperature and the modulus at high temperature decreased by the addition of tackifier for tackifiers A and B. This tendency was more remarkable for tackifier A as compared to tackifier B. An increase of the glass transition temperature was never observed for tackifier C. The peel adhesion was in the order of tackifier A > B > C. It was found that the compatibility of tackifier and base polymer had strong effect on adhesion properties.

Effects of Polystyrene Block Content on Morphology and Adhesion Property of Polystyrene Block Copolymer

Effects of polystyrene block content on adhesion property and phase structure of polystyrene block copolymers were investigated. Polystyrene-block-polyisoprene-block-polystyrene triblock and polystyrene-block-polyisoprene diblock copolymers with different polystyrene block contents in the range from 13 to 35 wt% were used. In the case of the low polystyrene block content (below 16 wt%), a sea-island structure was observed: near-spherical polystyrene domains having a mean diameter of about 20 nm were dispersed in polyisoprene matrix. The phase structure changed from a sea-island structure to a cylindrical structure with an increase of polystyrene block content (over 18 wt%). Peel strength decreased with an increase of polystyrene block content and the pure triblock copolymers had lower peel strength than their blends with the diblock copolymers. Pulse nuclear magnetic resonance studies indicated that molecular mobility of polyisoprene phase decreased with an increase of polystyrene block content, and the molecular mobility was lower in the pure triblock than in the blend. Thus, the peel strength was found to be related to molecular mobility. The adhesion strength of the block copolymer depended on the molecular mobility: high molecular mobility can promote interfacial adhesion.