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

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 AB_n 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 (R_g) are found to be scaled to the macromonomer molar mass (M_macro) and the total molar mass (M_hyper) as [η]=Kη,AB4MhyperνMmacroμ (ν ≈ 0.40, μ ≈ 0.25, and K_η, AB4 ≈ 1.72 × 10^–2 mL/g) and Rg=HR,AB4MhyperαMmacroβ (α ≈ 0.52, β ≈ 0.20, and H_R, 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 M_macro-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 M_macro independence for the AB₃ system (μ ≈ 0 ≈ β). A combination of experimental observation and Langevin dynamics simulation of AB_n 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 AB_n LHP systems (n > 4).