Development of Myrcene-Based Resins with Amine Ended Poly(Propylene Glycol) Side Chains Bonded Through Hydroxyurethane Linkages

Hybrid non-isocyanate poly(urethanes) (HNIPUs) are designed from a precursor whose carbonate functionality is derived from epoxy-functional statistical copolymers. Specifically, a bio-based diene (β-myrcene) is copolymerized via conventional free radical polymerization with glycidyl methacrylate (GMA) at different molar ratios, producing flexible copolymers with epoxy pendant groups, which are then reacted with carbon dioxide to yield the precursors with cyclic carbonate functionality. Subsequent addition of an amine-terminated telechelic poly(propylene glycol) (PPG) forms urethane linkages in the side chains, whose concentration is tuned by varying the GMA initial molar fraction. The NIPUs are end-capped with silanes to enable moisture curing, resulting in HNIPUs with elongations at break up to 150%, and relatively low elastic moduli varying from 32 kPa to 50 kPa as the number of urethane side linkages increases from 6 to 22. The swelling ratio of the NIPUs is also measured in tetrahydrofuran (THF). As the number of urethane side chains increases, the swelling ratio of the NIPUs decreases (710% to 620%), indicating a higher crosslinking density. All samples have gel contents higher than 50% in THF, indicating non-crosslinked species in the hybrid samples which confirms the relatively low reported tensile moduli.