Design of crosslinked networks with hydroxyurethane linkages via bio‐based alkyl methacrylates and diamines

Abstract

A hybrid methodology is used to combine the favorable properties of non‐isocyanate polyurethanes (NIPUs) in the side chains with poly(methacrylates) as the backbone into thermoset hybrid resins with hydroxyurethane linkages (HNIPU)s. Using NIPUs linkages avoids the use of toxic isocyanates in the poly(urethane) segments. The backbone is synthesized from cyclic carbonated copolymer templates derived from atom transfer radical polymerization (ATRP) of an alkyl methacrylate (C13MA with average side‐chain length of 13)/glycidyl methacrylate (GMA) mixtures (initial GMA mol fraction = 0.1–0.4). The resulting flexible resins with pendent epoxy functional groups were subsequently carbonated and then reacted with 1,10‐diaminodecane (90°C, 24 h) to form rigid side chains via hydroxyurethane linkages. Manipulating template functionality (2–11 urethane linkages out of 35 backbone units) yielded crosslinked networks with Young's moduli from 0.1 to 71.9 MPa while decreasing tensile elongation at break from 105% to 10%. Swelling ratios (SR) of the networks in tetrahydrofuran (THF) decrease as urethane linkage concentration increases, indicating tighter networks, consistent with the rheologically obtained molecular weight between crosslinks. Gel content indicated less than 15% of the networks are soluble in THF. The HNIPU networks derived show their ready tunability by simply changing the precursor functionality.

Utilizing bio‐derived amine‐terminated thermoplastic polyhydroxyurethanes as crosslinkers for hybrid thermosets

“…In the case of excess diamine, amine‐terminated urethane linkages can be formed that do not contribute to the crosslinked networks. This can lead to reduced tensile strength and lower gel content in the final product 3 . Additionally, the excess diamine can react with the ester groups of methacrylates, leading to the formation of amides, 42–44 resulting in a network having lower crosslinking density with unreacted free species due to the aminolysis of the ester groups.…”

“…Annual GHG emissions of PUs in the United States alone are estimated to be 7.8 million metric tons 2 . Furthermore, conventional PUs are synthesized via polyaddition reactions between poly‐isocyanates and polyols 3 . Synthesis of isocyanates involves the use of phosgene, an extremely toxic and lethal gas, making the process hazardous.…”

“…Various synthetic pathways can be employed to obtain non‐isocyanate polyurethanes (NIPUs) 7,8 . Despite the wide choice of methods, many still generate significant amounts of side products such as HCl, alcohols, and water 3,7,9 . The polyaddition of cyclic carbonate functional groups with di‐ or polyamines, resulting in poly(hydroxy urethanes)s (PHUs), is considered one of the most promising synthesis routes.…”

“…To enhance the properties of bio‐based NIPUs, hybrid NIPUs have gained increasing prominence 19 . The definition of hybrid NIPUs varies, as it could refer to a chemical structure that is hybridized with an inorganic polymer, such as through the introduction of moisture‐sensitive silanes, or it may refer to the incorporation of desired functionality through a different polymerization method, such as the combination of radical polymerization and polyaddition 3,20–22 …”

“…We recently investigated crosslinking of carbonated copolymers with different diamines to form crosslinked networks bonded via urethane linkages. However, due to the presence of only two urethane linkages in the side chains, they do not strongly qualify as NIPUs 3,23 …”