Small Angle Neutron Scattering Study of Conformation of Oligo(ethylene glycol)-Grafted Polystyrene in Dilute Solutions: Effect of the Backbone Length

Abstract

The conformation and clusterization of comblike polymers of polystyrene densely grafted with oligo(ethylene glycol) (OEG) side chains in 1.0 wt % solutions of D2O, toluene-d8, and methanol-d4 was investigated as a function of the degree of polymerization (DP) of the backbone by small angle neutron scattering (SANS). Each side chain had four EG repeat units, and the DP of the polystyrene backbone varied from 8 to 85. The global conformation of the polymers in toluene and methanol was shown to assume ellipsoidal, rigid cylindrical, or wormlike morphologies with increasing DP of the polystyrene backbone. At the same time, in D2O, the polymer conformation was described by the form factor of rigid cylinders. The second viral coefficient A2 was measured for the polymer with a DP of 85 in all three solvents, and the solvent quality of toluene, methanol, and D2O was identified to be good, marginal, and poor, respectively, for this polymer. Because of a poor solvent quality, the PS backbone (DP = 85) is partially collapsed in D2O, whereas it is moderately expanded in toluene and methanol. Polymers with a DP of 8 were found to form clusters in all three solvents, with the characteristic size between 100 and 200 Å and a fractal dimension of 2. With the increase in the DP, the clusters diminished in D2O and completely disappeared in toluene and methanol. This observation suggests that the clusterization of these short side-chain polymers is caused by end-group and hydrogen bonding interactions between different chains.