Remolding and Deconstruction of Industrial Thermosets via Carboxylic Acid-Catalyzed Bifunctional Silyl Ether Exchange

Abstract

Convenient strategies for the deconstruction and reprocessing of thermosets could improve the circularity of these materials, but most approaches developed to date do not involve established, high-performance engineering materials. Here, we show that bifunctional silyl ether, i.e., R′O−SiR 2 −OR′′, (BSE)-based comonomers generate covalent adaptable network analogues of the industrial thermoset polydicyclopentadiene (pDCPD) through a novel BSE exchange process facilitated by the low-cost food-safe catalyst octanoic acid. Experimental studies and density functional theory calculations suggest an exchange mechanism involving silyl ester intermediates with formation rates that strongly depend on the Si−R 2 substituents. As a result, pDCPD thermosets manufactured with BSE comonomers display temperature-and time-dependent stress relaxation as a function of their substituents. Moreover, bulk remolding of pDCPD thermosets is enabled for the first time. Altogether, this work presents a new approach toward the installation of exchangeable bonds into commercial thermosets and establishes acid-catalyzed BSE exchange as a versatile addition to the toolbox of dynamic covalent chemistry.

Frontal Polymerizations: From Chemical Perspectives to Macroscopic Properties and Applications

“…In this concept, structurally robust materials undergo controlled disassembly reactions at targeted sites only in the presence of orthogonal chemistries. Indeed, several examples 170,172,173,175,391,392 demonstrated the feasibility of such a thermoset deconstruction strategy (section 4.1.3). Ideally, these smaller components may themselves act as monomers for future upcycling/polymerization reactions.…”

“…The resulting DCPD thermosetting copolymer exhibits robust mechanical properties until treated with fluoride, which induces Si–O fragmentation along the polymer backbone to provide soluble oligomeric products. A subsequent study demonstrated that deconstruction and remanufacturing of such materials also occurs via carboxylic acid catalyzed dynamic exchange of bifunctional silyl ether groups . These works highlight new directions for thermoset end-of-life management.…”

“…A subsequent study demonstrated that deconstruction and remanufacturing of such materials also occurs via carboxylic acid catalyzed dynamic exchange of bifunctional silyl ether groups. 173 These works highlight new directions for thermoset end-of-life management. One may rightly wonder, however, whether such transformations truly address the problem of polymer waste; on their own, these advances convert solid polymer waste into smaller, perhaps less inert oligomeric waste.…”

cis-Selective Acyclic Diene Metathesis Polymerization of α,ω-Dienes

“…Commercially available deca-1,9-diene ( 5 ) was transformed into all- cis polyoctenamer P5 , the cis variant of industrially produced vestenamer . To further explore the functional group tolerance of the cis -selective ADMET, polysiloxanes, which are common in coatings, ceramics, and dynamic covalent networks, , were targeted. Polysiloxanes P6a and P6b were isolated from monomers 6a and 6b with exquisite cis selectivity and M n values up to 17.6 kg/mol.…”

cis-Selective Acyclic Diene Metathesis Polymerization of α, ω-Dienes

“…Commercially available deca-1,9-diene ( 5) was transformed into all-cis polyoctenamer P5, 35 the cis-variant of industrially-produced vestenamer ® . 36 To further explore the functional group tolerance of the cis-selective ADMET, polysiloxanes which are common in coatings, ceramics, and dynamic covalent networks, 37,38 were targeted. Polysiloxanes P6a and P6b were isolated from monomers 6a and 6b with exquisite cis selectivity.…”