Conformational Transition and Interchain Association of Hypergraft HB-PS-g-PtBA Copolymer Chains with Varied Copolymer Compositions and Block Lengths in a Selective Solvent

Understanding the correlation between the solutionphase behavior and topological effect of branched polymers is afundamental problem in polymer physics. In this work, four sets ofnarrowly distributed hypergraft HB-PS-g-PtBA copolymers wereprepared and studied, where PS and PtBA represent a polystyrenehyperbranched core and a poly(tert-butyl polyacrylate) periphery,respectively. The dispersity, branching pattern, block length, andcopolymer composition were precisely controlled. In particular, themass fraction (wt) of PtBA in HB-PS-g-PtBA was varied from 64 to6.5% in a wide range. By combining laser light scattering (LLS),small-angle neutral scattering (SANS), and theoretical analysis, thetemperature-dependent intrachain collapse and interchain associ-ation of HB-PS-g-PtBA chains were investigated in the temperature range lower than the theta point of the PS block in cyclohexane. Bymeasuring the apparent aggregation number (Nagg,app), the radius of gyration (< Rg,app >), hydrodynamic radius (< Rh,app >), form factor,aggregation pattern, existing species, segment density, internal structural features, and the degree of overlap (DO) of PtBA graftswere quantitatively analyzed. The result not only demonstrated that the hyperbranched topology can significantly suppress theaggregation tendency of the solvophobic hyperbranched PS core, irrespective of the copolymer composition, even though the wt ofthe PtBA solvophilic shell was decreased to as low as 15%, but also indicated that the DO value is the most important index that canreflect the ability of the graft layer in stabilizing the collapsed core structure.

Automated summary

This study investigates the solution behavior and topological effect of branched polymers, and finds that the hyperbranched structure can significantly suppress the aggregation tendency of the solvophobic core.