How Does the Branching Effect of Macromonomer Influence the Polymerization, Structural Features, and Solution Properties of Long-Subchain Hyperbranched Polymers?

Abstract

This work aims to elucidate how the branching effect of macromonomer influences the polymerization, structural features, and solution properties of AB n long-subchain hyperbranched polymers (LHPs). Our result reveals that compared with linear AB2 macromonomers, star AB3 macromonomers result in the suppression of chain extension, and the enhancement of macromonomer self-cyclization during the preparation of LHPs by “click” polymerization, due to the branching-enhanced steric hindrance effect. The combined triple-detection SEC and stand-alone LLS studies of unfractionated and fractionated AB3 LHPs unambiguously demonstrate their statistically fractal nature. Namely, the intrinsic viscosity ([η]) and radius of gyration (R g) are scaled to the macromonomer molar mass (M macro) and the total molar mass (M hyper) as [η] = K η ,AB3 M hyper νM macro μ (ν ≃ 0.39, μ ≃ 0, and K η ,AB3 ≃ 0.29 mL/g) and R g = H R ,AB3 M hyper α M macro β (α ≃ 0.47, β ≃ 0, and H R ,AB3 ≃ 3.6 × 10–2 nm). Surprisingly, [η] and R g are both almost independent of M macro (μ ≃ 0 ≃ β), indicating a similar draining property and local segment density for LHPs with different subchain lengths, which is different from the classic AB2 systems (μ ≃ 0.3 and β ≃ 0.1). A comparison of results for AB n LHPs (n = 2, 3) and short-subchain hyperbranched systems indicates that the fractal dimensions (f) for LHPs are generally smaller than short-subchain systems, whereas f is not sensitive to the local segment density or branching pattern. A combination of experimental observation and Langevin dynamics simulation of AB n dendrimers and LHPs further reveals (i) the segment back-folding phenomenon is prominent only for AB n (n ≥ 3) LHPs systems because it is mainly dominated by the macromonomer branching effect, rather than the internal subchain length, and (ii) the trend for segment interpenetration increases remarkably as M macro increases for both dendrimers and LHPs. The result also indicates that the unique synergistic effect of segment back-folding and segment interpenetration in AB3 system is the most probable reason for the observed M macro independent solution properties. Specifically, because of the unique synergistic effect, small macromonomer/oligomer chains can interpenetrate more easily into hyperbranched oligomer chains composed of longer subchains and subsequently “click” couple with the back-folded segments in the interior space of LHPs, which eventually could lead to a similar draining property and local segment density for AB3 LHPs with different subchain lengths.

Branched/Hyperbranched Copolyesters from Poly(vinyl alcohol) and Citric Acid as Delivery Agents and Tissue Regeneration Scaffolds

“…According to the viscosity trend and microstructure analysis, it seemed that only V3 could be considered as a true hyperbranched copolyester while both V1 and V2 could be regarded more as branched copolyesters only. [25] Figure 3b shows the size distribution profiles of the copolyesters studied at different pH (3)(4)(5)(6)(7)(8)(9). Distribution profile of linear PVA molecules at pH 7 was also included for reference.…”

Preparation of Functional Long‐Subchain Hyperbranched Polystyrenes via Post‐polymerization Modification: Study on the Critical Role of Chemical Stability of Branching Linkage

“…[26][27][28] In addition, we synthesized the AB n (n > 2) LHPs with AB n (n > 2) macromonomer for the first time, and studied the relationship between branching pattern and solution properties. [29,30] It is worth mentioning that in our recent work, AB 2 hyperbranched polystyrenesulfonate were successfully synthesized by soft sulfonation with acetyl sulfate as the the sulfonating reagent, using AB 2 hyperbranched polystyrene with total carbon branching linkage as the precursor. [31] The results clearly prove that the total carbon branching linkage has an incomparable stability advantage over ester linkage under the condition of sulfonated PPM, indicating that the stability of the branch point in the PPM process is very important.…”

“…Long‐subchain hyperbranched polymers (LHPs) with long linear chains between every two branching points have received considerable attention in the past two decades, since it can combine the excellent mechanical properties of linear polymers with the special physical properties of hyperbranched polymers. Three main methods have been reported to synthesize LHPs: (1) A 2 +B 3 approach, (2) self‐condensing vinyl polymerization (SCVP) approach, and (3) macromonomer AB n approach . In vein of the A 2 +B 3 approach, Long et al.…”

“…Three main methods have been reported to synthesize LHPs: (1) A 2 + B 3 approach, [20,21] (2) self-condensing vinyl polymerization (SCVP) approach, [22,23] and (3) macromonomer AB n approach. [24][25][26][27][28][29][30][31][32] In vein of the A 2 + B 3 approach, Long et al synthesized a series of LHPs such as hyperbranched poly(ether ester)s, and polysulfone ionomers by polycondensation of an A 2 chain and a B 3 monomer. [21] Alternatively, Gao et al [22] synthesized hyperbranched poly(tertiary amino methacrylate)s with hydrophilic core and hydrophobic shell via SCVP methodology.…”

“…adopted this AB 2 macromonomer approach to construct a number of LHPs model systems by the Williamson coupling reaction, and they established a few structure‐property relationships about the rheological properties and the phase behavior of LHPs; Our group synthesized LHPs with controllable branched subchain length by using the seesaw‐type macromonomer . In addition, we synthesized the AB n (n>2) LHPs with AB n (n>2) macromonomer for the first time, and studied the relationship between branching pattern and solution properties . It is worth mentioning that in our recent work, AB 2 hyperbranched polystyrenesulfonate were successfully synthesized by soft sulfonation with acetyl sulfate as the the sulfonating reagent, using AB 2 hyperbranched polystyrene with total carbon branching linkage as the precursor .…”