UV-curing acrylic adhesives characterized by relatively high elastic modulus at room temperature and high T_g can achieve significantly higher initial adhesive strength by changing the adherend’s surface morphology from a flat to sawtooth structure. However, with the sawtooth structure, the rate of deterioration accelerates over storage time causing the adhesive strength to decrease significantly under reliability test storage onditions of 60℃/90％RH. In order to secure considerable improvement of the initial adhesive strength and suppress the adhesive strength deterioration, we verified the effect of crosslink density on adhesives by studying the relationship between crosslink density and adhesive reliability. The results revealed that, even in the case of the sawtooth structure, the degradation of adhesive strength after reliability testing can be suppressed by reducing the crosslink density of the adhesives. This is presumed to be because the flexibility of the adhesive interface increases at the adhesive terminals in response to stress occurring in the adhesive interface under 60℃/90％RH storage conditions. Accordingly, to simultaneously achieve higher reliability and increased adhesive strength, it is essential to choose the sawtooth structure for the adherend's surface morphology and use adhesives with a lowered crosslink density.

The acrylic polymers obtained from continuous radical polymerization at high temperature（＜150℃）have several unique features such as low molecular weight and narrow composition distribution even with a small amount of initiator and/or transfer agent, thus resulting in a low impurity. Due to high polymerization temperature, the polymerization is quite fast, and residual monomer and solvent could be easily removed from the polymer. We found that application of these acrylic polymers to plastici plasticizers of sealants raise weatherability and soil resistance（bleed resistance）. Another application to the base resin of sealants revealed the compatibility of low viscosity（easy handling）with good weather ability.