Self-assembly of supramolecules consisting of octyl gallate hydrogen bonded to polyisoprene-block-poly(vinylpyridine) diblock copolymers

Synchrotron radiation was used to investigate the self-assembly in two comb-shaped supramolecules systems consisting of octyl gallate (OG)(x) i.e., 1-octyl-3,4,5-trihydroxybenzoate, hydrogen bonded to the pyridine groups of polyisoprene-block-poly(vinylpyridine) diblock copolymers. In the case of the 1,2-polyisoprene-block-poly(4-vinylpyridine)(OG)(x) system, self-assembly was only observed for x greater than or equal to0.5, where x denotes the number of OG molecules per pyridine group. For x = 0.5, 0.75, 1.0, and 1.2 the system self-assembled in the form of hexagonally ordered cylinders of P4VP(OG) throughout the entire temperature range of 25-200 degreesC investigated. For the 1,4-polyisoprene-block-poly(2-vinylpyridine)(OG)(x), system, on the other hand, a considerably more complex phase behavior was found, including the formation of cubic, hexagonally ordered cylinders and lamellar morphologies. In this case several order-order transitions were observed as a function of temperature, including a lamellar to lamellar transition involving a collapse of the layer thickness. The absence of hydrogen bonding between the octyl gallate molecules and the pyridine groups at elevated temperatures is argued to be a key factor for many of the phenomena observed.