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

Research progress on the conformational properties of comb-like polymers in dilute solutions

As a special type of branched polymers, comb-like polymers simultaneously possess the structural characteristics of a linear backbone profile and crowded sidechain branches/grafts, and such structural uniqueness leads to reduced interchain entanglement, enhanced molecular orientation, and unique stimulus-response behavior, which greatly expands the potential applications in the fields of super-soft elastomers, molecular sensors, lubricants, photonic crystals, etc. In principle, all these molecular features can be traced back to three structural parameters, i.e., the degree of polymerization of the backbone (Nb), the degree of polymerization of the graft sidechain (Ng), and the grafting density (σ). Consequently, it is of great importance to understand the correlation mechanism between the structural characteristics and physicochemical properties, among which, the conformational properties in dilute solution have received the most attention due to its central position in polymer science. In the past decades, the development of synthetic chemistry and characterization techniques has greatly stimulated the progress of this field, and a number of experiments have been executed to verify the conformational properties; however, due to the complexity of the structural parameters and the diversity of the chemical design, the achieved experimental progress displays significant controversies compared with the theoretical predictions. This review aims to provide a full picture of recent research progress on this topic, specifically, (1) first, a few classical theoretical models regarding the chain conformation are introduced, and the quasi-two-parameter (QTP) theory for the conformation analysis is highlighted; (2) second, the research progress of the static conformation of comb-like polymers in dilute solution is discussed; (3) third, the research progress of the dynamic conformation in dilute solution is further discussed. The key issues, existing controversies and future research directions are also highlighted. We hope that this review can provide insightful information for the understanding of the conformational properties of comb-like polymers, open a new door for the regulation of conformational behavior in related applications, and promote related theoretical and experimental research in the community.

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

Post-polymerization modification (PPM) is one of the most powerful strategy for preparing polymers with functional groups that cannot be synthesized by direct polymerization. So far, numerous experimental efforts have been devoted to the stability issue of monomer structures during the PPM process, but little attention was paid to chemical linkages. However, for hyperbranched polymers, a minor change of linkage unit could lead to a significant influence on the overall stability and performance of polymer materials. In this work, we investigated the chemical stability of long-subchain hyperbranched polystyrenes with ester, aryl ether, and carbon-carbon bonds as branching linkages under a few most popular PPM conditions, including NaOH hydrolysis reaction, TFA-promoted hydrolysis reaction, BBr3-catalyzed methoxy-hydroxyl conversion reaction, and LiAlH4 carbonyl reduction reaction. Related results are summarized into a synthetic route map that can provide practical and intuitive guidance for preparing functional long-subchain hyperbranched polystyrenes and other type of polymers by PPM for future applications.