TECHNICAL FIELD

The present disclosure is generally related to silyl-containing thermosets.

DESCRIPTION OF RELATED ART

Thermosetting materials, commonly referred to as thermosets, are formed from the chemical reaction of two or more synthetic materials to generate a permanent three-dimensional network. Unlike thermoplastic materials, thermosets cannot be melted and reflowed into another form, which makes them useful for applications where thermal, chemical and/or UV-oxidative resistance are required. However, the cross-linked network of thermosets makes them difficult to degrade and destroy. Thermosets offer unique attributes and functional properties, which enables their utilization in numerous military and commercial applications. For example, thermosets are used to provide high-performance topcoats and primers for ships, aircraft and ground vehicles, adhesives for aircraft canopies, high-strength composites for ship hulls and the fuselage of aircraft, and high-temperature composites for aircraft exhausts.

Thermosets are currently degraded by using harsh chemicals, incineration, or physical methods. For instance, Navy aircraft topcoats and primers are often removed with methylene chloride, which solvates and swells the polymeric chains of the coatings so they can be easily removed via scraping or brushing. However, methylene chloride is highly toxic and carcinogenic to humans, and less toxic alternatives, such as peroxides and benzyl alcohols, have proven to be less effective at coating removal. Abrasive blasting is utilized to physically remove coatings, yet these methods present a health hazard due to the generation of microscopic particles. As a result, containment with sufficient ventilation, in addition to respirators, must be utilized by workers to reduce health risks.

Thermosets with bonds that can be selectively cleaved have been recently developed to enable these materials to be more easily degraded and destroyed. Examples include epoxies that contain alkene linkages, which were cleaved using harsh oxidizing reagents, such as permanganates, and epoxies that contain ester linkages, which were cleaved with strong acids or bases. However, in all cases, these reagents were slow to cleave the selective bonds in epoxy thermosets unless a large excess of reagent and heat were applied. Furthermore, bond cleavage within these epoxy thermosets was stoichiometric, meaning that only one bond was cleaved per chemical reagent, thus not sufficiently degrading the cross-linked system until a substantial number of bonds were broken. Conversely, thermoset components designed with an excess of selective cleavable groups may lack sufficient properties for many of the aforementioned applications, even though they are easy to degrade. To date, these limitations have prevented the development of durable, thermally stable, and rigid thermosets that can also be easily degraded and destroyed on-demand with mild and benign chemicals.

BRIEF SUMMARY

Disclosed herein are a process and a thermoset made thereby comprising: providing a polyfunctional compound selected from polyisocyanate, polyacrylate, and polyepoxy; and reacting the polyfunctional compound with a hydroxyl- or amine-terminated silyl-containing compound. The polyfunctional compound and the silyl-containing compound are at least difunctional.

