Pressure-sensitive adhesives from renewable triblock copolymers

ABA triblock copolymers were prepared using the renewable monomers menthide and lactide, by sequential ring-opening polymerizations. Initially, hydroxy telechelic polymenthide was synthesized by the diethylene glycol-initiated and tin(II) ethylhexanoate-catalyzed polymerization of menthide. The resulting 100 kg mol^-1 polymer was used as a macroinitiator for the tin(II) ethylhexanoate-catalyzed ring-opening polymerization of d,l-lactide. Two polylactide-polymenthide-polylactide triblock copolymers were prepared with 5 and 10 kg mol^-1 polylactide end blocks. Transesterification between the two blocks, and polylactide homopolymer formation were minimized, and triblock copolymers with narrow molecular weight distributions were produced. Microphase separation in these systems was corroborated by differential scanning calorimetry and small-angle X-ray scattering measurements. The triblocks were combined with up to 60 wt % of a renewable tackifier, and the resulting mixtures were evaluated using probe tack, 180° peel adhesion, and shear strength tests. Maximum values of peel adhesion (3.2 N cm^-1) and tack (1.1 N) were obtained at 40 wt % of tackifier. These new materials hold promise as renewable and hydrolytically degradable pressure-sensitive adhesives.