Effect of Macromonomer Branching on Structural Features and Solution Properties of Long-Subchain Hyperbranched Polymers: The Case of Four-Arm Star Macromonomers

Abstract

Following our recent work on AB3 macromonomer systems (Macromolecules, 2019, 52, 1065–1082), this work focuses on AB4 systems to further explore the effect of macromonomer branching on structural features and solution properties of long-subchain hyperbranched polymers (LHPs). Compared with ABn macromonomers (n < 3), our results reveal that AB4 macromonomers tend to undergo less interchain coupling but more intrachain self-cyclization during “click” polyaddition process. Via the triple-detection SEC characterization of resultant LHPs, both intrinsic viscosity ([η]) and radius of gyration (Rg) are found to be scaled to the macromonomer molar mass (Mmacro) and the total molar mass (Mhyper) as [η]=Kη,AB4MhyperνMmacroμ (ν ≈ 0.40, μ ≈ 0.25, and Kη, AB4 ≈ 1.72 × 10–2 mL/g) and Rg=HR,AB4MhyperαMmacroβ (α ≈ 0.52, β ≈ 0.20, and HR, AB4 ≈ 1.54 × 10–3 nm). The obtained results clearly demonstrate that (i) the self-similar behavior of LHPs is almost independent of the detailed structures of the macromonomer (AB2, AB3, and AB4) and (ii) the AB4 system presents Mmacro-dependent solution properties (μ ≈ 0.25 and β ≈ 0.20), which is similar to the result for the AB2 system but totally different from the observed Mmacro independence for the AB3 system (μ ≈ 0 ≈ β). A combination of experimental observation and Langevin dynamics simulation of ABn dendrimers and LHPs unambiguously verifies our previously proposed conjecture; that is, the unique synergistic effect of segment back-folding and segment interpenetration exists only in moderately branched LHP systems but not in highly branched ABn LHP systems (n > 4).