Controllable Degradation of Polyurethane Thermosets with Silaketal Linkages in Response to Weak Acid

Abstract

Polyurethane (PU) thermosets offer great favors to our daily life on account of their excellent mechanical, physical, and chemical properties as well as appreciable biocompatibility. Nevertheless, PU waste is increasingly causing environmental and health-related problems as it is mostly resistant to chemical degradation under mild conditions. Herein, we report a kind of PU thermoset with silaketal leakages in its main chains to enable polymer degradation in response to weak acids, even in edible vinegar. The degradation rate is significantly influenced by the alkyl substituents on the silicon atoms, with entire degradation in hours, days, weeks, or months. Besides controllable degradation, investigations are also provided into the recycling of PU thermosets by means of thermal reprocessing based on carbamate bond exchange or repolymerization of degradation residuals. Because of the controllable degradation and easy recycling, this particular kind of PU thermoset exhibits great potential in manufacturing green polymer products that can be decomposed by nature or reutilized after disposal.

Catalyst-Free, Mechanically Robust, and Ion-Conductive Vitrimers for Self-Healing Ionogel Electrolytes

“…Stress relaxation tests were performed between 60 to 180 °C, as the materials maintained in the rubbery state (Figure S9). The activation energy for CP3 calculated from Figure C and Figure S13 is about 174 kJ/mol, which is significantly higher than the values observed for other catalyst-promoted Si–O-based systems. ,− Since we were not using catalysts to promote Si–O metathesis, as expected, our values (174 kJ/mol) were higher by at least a factor of 2 and revealed vitrimeric behavior at around 160–180 °C, comparable to other catalyst-free Si–O systems. , We also proved material stabilities up to 300 °C by TGA analysis (Figure S11). Because of the silyl ether bond exchange reaction, the materials could self-heal after being damaged.…”

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

“…For example, as early as 1954, it was known that strong acids or bases could catalyze Si–O exchange in siloxanes (Si–O–Si groups) such as polydimethylsiloxane (PDMS) (Figure a). − Later, Guan and co-workers reported alcohol-induced Si–O bond exchange in trialkoxysilane crosslinked materials (Figure b) as well as a proposed direct Si–O bond metathesis in mono-silyl ether-crosslinked materials (Figure c). , Additionally, Du Prez and co-workers proposed an associative silanol-induced siloxane exchange process to achieve similar material remodeling (Figure d) . While these studies provide strong precedent for Si–O bond exchange in crosslinked materials, we note that there are no reports on Si–O bond exchange in BSEs (Figure e) despite their use as cleavable functionalities in polymers and related systems. − ,− Moreover, BSEs could offer greater control over the rate of network reconfiguration than other Si-based systems. We posit that the Si substituents in BSE-based materialswhich are known to dramatically influence the rate of Si–O bond cleavage and of which hundreds of variants are readily synthesized from commercially available precursors ,, will provide a route to control CAN stress relaxation dynamics.…”

Neighboring Group Effects on the Rates of Cleavage of Si–O–Si-Containing Compounds

“…In turn, this determines the suitability of the specific functional group [R 3 SiOR′, R 2 Si­(OR′) 2 , RSi­(OR′) 3 , Si­(OR′) 4 ]; R′ = C and/or Si] for myriad applications (e.g., protecting group chemistry, silicone polymers, surface modifications, sealants, sol–gels). The lability of the Si–O-containing moiety influences the utility of these siloxy compounds by impacting features such as cure rates, dynamics of covalent adaptable network reorganization, release rates, and postuse degradation in the environment …”