A rapid oxygen-initiated and -regulated controlled radical polymerization was conducted under ambient temperature and atmosphere. The reaction between triethylborane and oxygen provides ethyl radicals, which initiate and mediate the radical polymerization. The controlled radical polymerization was achieved using RAFT chain transfer agents (CTA) without any process of removing oxygen, providing well-defined polymers with almost full conversion (>95 %) in a short period (15 min). High-throughput screening was used to discover the suitable conditions for various CTA and monomers. To show the versatility of this method, a polymer library containing 25 well-defined polymers with different compositions (block and statistical copolymers) and molecular weights were synthesized in 1 h via high-throughput synthesis technique. A polymer-painting technique was developed using this method, forming films with spatial control and excellent control in molecular weight and dispersity.
Boron-containing polymers have been demonstrated to be useful polymeric materials. However, the synthesis of boronic acid-or ester-containing polymers is highly challenging due to their instability and difficult characterization. This paper introduces N-methyliminodiacetic acid (MIDA) as a unique protecting group for the boronic acid to stabilize boron-containing polymers. The synthesized MIDA boronate stabilized polymers show remarkable stability to the air, moisture, and chromatography. Therefore, they could be used as a versatile platform for synthesizing other boronic acid-or ester-containing polymers. Postpolymerization modification also incorporates different functionalities by using this platform by Suzuki−Miyaura coupling. Both stability and versatility make MIDA boronate stabilized polymers have great potential applications in material and biomedical fields associated with borane chemistry.
The regulation of polymer topology and the precise control over the monomer sequence is crucial and challenging in polymer science. Herein, we report an efficient solution-phase synthetic strategy to prepare regio- and sequence-controlled conjugated polymers with topological variations via the usage of methyliminodiacetic acid (MIDA) boronates. Based on the solubility of MIDA boronates and their unusual binary affinity for silica gel, the synthesized regio- and sequence-defined conjugated oligomers can be rapidly purified via precipitation or automatic liquid chromatography. These synthesized discrete oligomers can be used for iterative exponential and sequential growth to obtain linear and dendrimer-like star polymers. Moreover, different topological sequence-controlled conjugated polymers are conveniently prepared from these discrete oligomers via condensation polymerization. By investigating the structure-property relationship of these polymers, we find that the optical properties are strongly influenced by the regiochemistry, which may give inspiration to the design of optoelectronic polymeric materials.
Compared with linear thermoplastic polymers, thermoset polymers with three-dimensional network structures exhibit improved solvent tolerance, heat resistance, and mechanical strength. The radicalmediated process is widely used to cross-link the linear polymer chains; however, this process requires high temperature (>150 °C) or UV irradiation to generate highly energetic radicals, unavoidably leading to undesired side reactions and uncontrolled cross-linking behavior. This work proposes and achieves a carbene-mediated polymer cross-linking with diazo-based compounds by C−H activation and an insertion mechanism under relatively mild conditions. A simple route containing only one or two steps is established to synthesize three generations of diazo-based cross-linkers 1G, 2G, and 3G. The cross-linker 1G exhibits the lowest cross-linking efficiency due to the undesired self-coupling of carbenes. After optimizing the chemical structure and increasing the numbers of diazo moieties, the cross-linking efficiency significantly improves for 2G and 3G cross-linkers. These cross-linkers are applicable for any polymers containing C−H bonds. They are useful in a wide range of applications, from the adhesion of low surface energy ultrahigh molecular weight polyethylene (UHMWPE) to polymer modification by co-cross-linking. This versatile, convenient, and practical carbene-mediated cross-linking strategy provides new opportunities for modification, cross-linking, and adhesion in polymer science.
Organoboron chemistry has been widely explored and developed in synthetic chemistry for over half a century and provides various elegant synthetic protocols in polymer synthesis. Compared with most trivalent bare organoboron compounds, Ncoordinated organoboron shows better performances, such as air and moisture stability. This review summarizes the application of various N-coordinated boranes and boronic acid/esters in polymer synthesis and materials science. We introduce the significance of N-coordinated boranes and boronate esters for controllable polymer synthesis and systematically summarize the structures and properties of polymers containing N-coordinated boronate esters. Furthermore, we highlight the effect of N→B dative bonds on improving the performance of self-healing materials. We hope that, through this review, more researchers will realize the advantages of N-coordinated organoboron and promote the development of this direction in polymer synthesis and materials science.
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