In Situ Polymerization via an Environmentally-borne Initiation Stimulus.

[摘要] The utilization of an environmentally-borne stimulus, atmospheric oxygen, has been convincingly demonstrated as a useful means for initiating in situ polymerization.As molecular oxygen is both ubiquitous and capable of participating in reduction-oxidation reactions, it particularly well-suited for affording radicals capable of initiating radical-mediated polymerization.The thiol–ene reaction is extraordinarily resistant to oxygen inhibition and thus useful as an oxygen-mediated polymerization reaction.In order to utilize oxygen as a polymerization stimulus, three initiating systems were developed, including those based on alkylboranes, oxidoreductase enzymes, and thiones.These systems are capable of solidifying thiol–ene monomer formulations within seconds, minutes, or hours, respectively, upon oxygen exposure. The interest in in situ oxygen-mediated polymerization is largely driven by two emerging applications.The first of these, self-healing materials suitable for space exploration applications, requires a reactive liquid, sandwiched between a solid support structure, that is able to flow and polymerize immediately after being punctured by space debris, thus sealing the resultant hole.To demonstrate the suitability of oxygen-mediated polymerization for self-healing materials, high-velocity ballistics testing, monitored by videography and thermal imaging, was performed and established that a reactive liquid monomer formulation can polymerize within seconds of oxygen exposure to afford a solid polymeric material capable of sealing the projectile-induced puncture.The second application is for next-generation surgical adhesives and sealants that would be suitable as emergency hemostats and other medical procedures.As a demonstration that oxygen-mediated polymerization is a useful mechanism for producing these materials, formulations based on chitosan, a polysaccharide known for its biocompatibility and bioadhesion, were produced that afford solid hydrogels within a minute of oxygen exposure.In addition to the alkylborane- and oxidoreductase-based systems, thiones were employed to initiate bulk thiol–ene polymerization.Although thiones were shown to be capable of generating radicals in the presence of atmospheric oxygen and thiol groups, the reaction extents achievable were lower than desired owing to unwanted side reactions quenching radical production and, subsequently, suppressing polymerization.Despite this limitation, the development of approaches to suppress the quenching reaction will afford a rapid and efficient method of utilizing oxygen as an environmentally-borne polymerization initiation stimulus.

[发布机构] University of Michigan

[效力级别] Oxygen-mediated polymerization

[关键词] Polymers;Oxygen-mediated polymerization;Self-healing materials;Hydrogels;Engineering (General);Materials Science and Engineering;Chemistry;Science (General);Engineering;Science;Macromolecular Science and Engineering