Effect of Macromonomer Branching on Structural Features and Solution Properties of Long-Subchain Hyperbranched Polymers: The Case of Four-Arm Star Macromonomers
NR Hao and A Umair and M Zhu and XZ Duan and LW Li, MACROMOLECULES, 52, 6566-6577 (2019).
Following our recent work on AB(3) macromonomer systems (Macro- molecules, 2019, 52, 1065-1082), this work focuses on AB(4) 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 AB(4) 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 (eta) 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 eta = (K eta,AB4MhyperMmacro mu)-M-nu (nu approximate to 0.40, mu approximate to 0.25, and K-eta,K-AB4 approximate to 1.72 x 10(-2) mL/g) and R-g = (HR,AB4MhyperMmacro beta)-M-alpha (alpha approximate to 0.52, beta approximate to 0.20, and H-R,H-AB4 approximate to 1.54 x 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 (AB(2), AB(3), and AB(4)) and (ii) the AB(4) system presents M-macro-dependent solution properties (mu approximate to 0.25 and beta approximate to 0.20), which is similar to the result for the AB(2) system but totally different from the observed M-macro independence for the AB(3) system (mu approximate to 0 approximate to beta). 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).
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