Mesomorphic Phase Behaviour of Hydrogen-bonded Supramolecular Copolymers Containing Dendritic and Linear Side Chains

The self-assembled structure, from hydrogen-bonded copolymers containing poly(4-vinylpyridine) (P4VP), linear surfactant pentadecylphenol (PDP) and dendritic molecules, 1-[4'-(3", 4", 5"-tridecyloxybenzoyloxy) phenyleneoxycarbonyl]-3-[(4"-hydroxyphenyl) oxycarbonyl] benzene (12CBP), was investigated. The ternary complex system is named as P4VP(12CBP)(x)(PDP)(y) (x + y = 1) which was prepared via solution blending method. It has been reported that P4VP(12CBP)(x) possess hexagonal columnar structure at x >= 0.3 and P4VP(PDP)(x) possess lamellar structure. Despite the different shapes and self-assembled properties from 12CBP and PDP, FTIR, DSC, POM and SAXS studies revealed that the ternary supramolecular copolymer system forms a homogeneous phase, instead of phase separation. At x >= 0.5, P4VP(12CBP)(x)(PDP)(y) possesses a homogeneous hexagonal columnar phase. Each column is constructed with P4VP as polymer backbone tethered with mixed side chains. The lattice parameter is smaller than that of the corresponding P4VP(12CBP)(x+y) and decreases gradually with decreasing x. In this case, the P4VP polymer chains are surrounded by 12CBP and PDP molecules which would induce "defects" from shape difference of the molecules. While the results show that such kind of "defects" didn't prevent the columnar phase formation. The formation of each column with randomly distributed 12CBP and PDP would increase the system entropy. Meanwhile, smaller PDP provides more free volume, especially in alkoxy segment, and further increases the conformational entropy of the side chains. At x < 0.5, P4VP(12CBP)(x)(PDP)(y) is amorphous with layer like fluctuation, instead of columnar phase. In this case, the relative grafting density of the linear side chains is larger than that of dendritic side chains, which could not stabilize the columnar phase formation. Meanwhile the existence of small amount of 12CBP tends to interrupt the lamellar mesophase formation. AFM topographies of P4VP(12CBP)(x)(PDP)(y) thin films also support the formation of homogeneous phase. The typical fingerprint patterns from hexagonal columnar phase are gradually interrupted with decreasing x. At x < 0.5, only irregular morphology could be detected. So the surface patterns of such kind of supramolecular copolymer thin films could be easily controlled by varying x and y.