Rheology of side chain dendritic polymers

We have presented the first rheological studies conducted on a series of si de chain dendritic polymers (SCDP) which are produced by copolymerization o f dendritic dilos of the second, third, and fourth generation with differen t semiregid and flexible diisocyanates. The SCDPs, consisting of polyuretha ne main chain and polyether side chains, obeyed time/temperature superposit ion. The shift factors as a function of temperature were fitted to the so-c alled WLF equation. Some results suggested that the dendritic side groups h ave a distinct effect on the elastic part of the complex modulus, whereas t he effect on the viscous part seemed to be small. At low frequencies, SCDPs behaved almost Like classical viscous liquids (theory: G' similar to omega (2) and G " similar to omega; experiment: G' similar to omega(1.5-1.8) and G " similar to omega). At the intermediate frequencies, the experimental ex ponent was 0.8, which is higher than the theoretical value of 0.5 predicted within the Rouse model. The zero shear viscosities were generated from the low limiting values of eta'(omega). For the dendritic macromonomers the vi scosity increased with the generation number. For the dendritic polymers, h owever, the reversed trend was observed; the relative increase of the visco sity upon polymerization is smaller for dendritic polymers of higher genera tion side groups. These results were discussed in terms of the shielding ef fect of the dendritic side groups. Furthermore, it was demonstrated that th e rheology of the SCDPs can be regulated by the choice of the diisocyanate, i.e., by changing the flexibility of the main chain.