Phase Separation Kinetics in Block Copolymer Based Pressure Sensitive Adhesives

Blends of styrene-based block copolymers and low molecular weight, high-T_g resins (tackifiers) have been used as pressure-sensitive adhesives (PSA). Although tackifiers are well-established ingredients of PSAs, very little work has been published about the effect of tackifiers on phase separation kinetics in block copolymer (BCP) melts. We report time-resolved small-angle X-ray scattering (SAXS) and rheological analysis of styrene-diene BCP based PSAs aimed at studying the ordering of polystyrene domains at different tackifier contents in PSA blends. We observe that increasing tackifier content leads to a decrease in the order-disorder temperature (ODT) of BCP blends. The addition of small amounts of tackifier enhances the ordering of polystyrene domains in a bcc structure, but higher tackifier content disrupts the order. We also observe a shift from a ‘nucleation and growth’ mechanism to a ‘spinodal decomposition’ mechanism of microphase separation in PSA melts with increasing tackifier content. Ongoing work is aimed at correlating the X-ray scattering and rheological analysis of PSA blends with varying tackifier content.