Intrinsic viscosity variation in different solvents for dendrimers and their hybrid copolymers with linear polymers

Abstract

The intrinsic viscosity of narrow molecular mass distribution polystyrene standards, poly-(benzyl) ether dendrimers, and their hybrid block copolymers was measured in a variety of solvents. The relative change in the intrinsic viscosity for all these polymers was almost equivalent, indicating that poly(benzyl ether) dendrimers expand and contract quite readily with a change in solvent. The intrinsic viscosity maximum for all polymers was found to occur at essentially the same solvent solubility parameter demonstrating that the thermodynamic interaction with the selected range of solvents was also equivalent. The intrinsic viscosity for hybrid copolymers in a good solvent for both components was found to fall well below the intrinsic viscosity for neat polystyrene at intermediate molecular masses. Below and above this mass range the intrinsic viscosity was quite similar to polystyrene. Yet, the transition for intermediate to high molecular mass behavior was quite sharp as seen through a rapid intrinsic viscosity rise at 60-70 kDa. A poorer solvent for the dendrimer, one where the dendrimer intrinsic.viscosity was found independent of generation number, produced the same intrinsic viscosity for the hybrid copolymer and virgin polystyrene. This unique behavior is due to novel interactions between the linear polystyrene block and the highly branched dendritic block which is a function of the solvent environment.