Design, assembly and application of boronate ester polymer

In the last hundred years, polymer science has been flourishing. Industrial products of polymers have been used in many aspects of our life. Each new polymer and its assembly driving force indicates the blooming of the “new branch” of the towering tree of polymer. Researchers are always looking for new polymer and new self-assembly driving force to imbue the towering tree of polymer with magic. The traditional self-assembly driving forces are limited to noncovalent interactions, such as electrostatic interaction, hydrogen bond, π-effects or Van der Waals interaction. The bonding energy of noncovalent interaction is weak and directionless. Therefore, the as-formed assemblies have the problems of poor stability and low structural order. Compared with the good designability of the assembly building blocks, the driving forces of self-assembly is monotonous and limited. In recent years, interactions like coordination, dynamic covalent bond and host-guest recognition have been introduced into the self-assembly system, which leads to new methods of self-assembly. The structure of self-assembly which depends on strong bond is inert, so it is difficult to realize the intelligent characteristics including irritating response, self-regulation and self-evolution. The driving force of ideal self-assembly should simultaneously have the characteristics of weak bonding strength, directionality and tunable chemical bonds. Boronate ester polymers, which are formed by incorporating dynamic boronate ester bonds into the main chain, side chain or cross-linking point of polymers, can be described as a new polymer material with high synergy of “stability” and “dynamic”. Stability refers to the high-efficiency condensation ability of phenylboronic acid group with 1,2-diol or 1,3-diol structures and polymers, as well as the protection of polyhydroxy groups, especially phenolic hydroxyl groups. The dynamic feature of boronate ester polymer is due to their reversible cleavage and reformation under the stimulation of temperature, pH and guest molecules. Catechol group is one of the polyhydroxy functional groups used to construct boronate ester polymers. It can form coordination, hydrogen-bonding, electrostatic interaction, with metal ions, inorganic nonmetallic oxides, etc. The introduction of catechol as a building block into boronate ester polymer system could make surface engineering more intelligent. When nitrogen-containing functional groups are present in molecular chains, B-N coordination can also be formed between boronate ester polymer chains. These supramolecular driving forces can induce the self-assembly of boronate ester polymers in solution and interfacial. Boronate ester polymers not only have flexible designability of molecular structure, but also give full play to the intrinsic characteristics of boric acid groups, phenylboronic acid groups and polyol groups. From the molecular structure level, boronate ester polymer is a kind of multifunctional polymer. From the supramolecular point of view, the B-N coordination of boronate ester polymer and the strong interface binding force of catechol has a unique advantage in driving the ordering of polymer chains. Boronate ester polymers have been widely used in surface engineering, intelligent materials, biomedicine, energy storage and other fields, due to its wide range of molecular structure designability and unique B-N coordination between chain segments. In this review, starting from molecular block and self-assembly mechanism, the synthesis strategy, properties, supramolecular behavior and application fields of boronate ester polymers were summarized; the development direction of boronate ester polymer functional materials was prospected.