Structural Feature and Internal Motion of Hyperbranching Cluster System with Low Polydispersity and Featured Pattern in Dilute Solutions

This work reports the structural feature and internal motion of one novel hyperbranching cluster system in dilution solution. The cluster system is composed of HB-PS300-g-PtBA(45) hypergraft copolymer chains with uniform subchain, high molar mass and low polydispersity (M-w=1.73x10(6) g/mol and approximate to 1.07), where HB-PS and PtBA represent hyperbranched polystyrene core and poly(tert-butyl polyacrylate) graft, respectively. In the selective solvent of PS blocks (cyclohexane, T-theta=34.5 degrees C), the aggregation kinetics and structural feature are found to be precisely tunable for assembled clusters by the aggregation temperature (11 degrees C<17 degrees C) and time (0 h<24 h). An interesting structural evolution kinetics is observed, namely, the fractal dimension (d(f)) of clusters is found to first increases and then decreases with t, eventually, it reaches a plateau value of d(f)approximate to 3.0, corresponds to a uniform spherical structure. By using dynamic light scattering (DLS) to monitor the number and strength of relaxation modes in Gamma(q) with Gamma being the decay rate and q being the scattering vector, it is quantitatively revealed that the relaxation, intensity contribution and mode origin of internal motions of clusters are neither similar with previously reported cluster systems with high polydispersity, nor with the classical linear chain systems. In particular, in the broad range of 2.0<6.0, we have observed that the reduced first cumulant [Gamma* = Gamma(q)/(q(3)k(B)T/eta(0))] does not display an asymptotic behavior. Whereas, a better asymptotic behavior is observed by plotting Gamma(q)/q(4) versus qR(h). For the first time, our observation provides direct evidence supporting that, for hyperbranching cluster system with low polydispersity and high local chain segment density, the hydrodynamic interaction is greatly weakened due to the enhanced hydrodynamic shielding effect.

Automated summary

This study reports the structural features and internal motion of a novel hyperbranching cluster system in dilution solution. The aggregation kinetics and structural features of the cluster system can be precisely controlled by adjusting the aggregation temperature and time. The internal motion of the clusters is quantitatively analyzed using dynamic light scattering, revealing unique characteristics compared to other cluster systems and classical linear chain systems.