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

The intrinsic viscosity of narrow molecular mass distribution polystyrene s tandards, poly(benzyl) ether dendrimers, and their hybrid block copolymers was measured in a variety of solvents. The relative change in the intrinsic viscosity fur all these polymers was almost equivalent, indicating that po ly(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 th at the thermodynamic interaction with the selected range of solvents was al so equivalent. The intrinsic viscosity for hybrid copolymers in a good solv ent for both components was found to fall well below the intrinsic viscosit y for neat polystyrene at intermediate molecular masses. Below and above th is 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 poo rer solvent for the dendrimer, one where the dendrimer intrinsic viscosity was found independent of generation number, produced the same intrinsic vis cosity for the hybrid copolymer and virgin polystyrene. This unique behavio r is due to novel interactions between the linear polystyrene block and the highly branched dendritic block which is a function of the solvent environ ment.