Abstract
<p class="1Body">The reaction of trimethylolpropane (TMP) and diphenyl carbonate gives three types of TMP-based six-membered cyclic carbonates (TMPCs) via phosgene-free route. TMPC having one hydroxyl group (TMPC-OH) reacted with terephthaloyl chloride or trimesoyl chloride to give bifunctional (Ph-TMPC<sub>2</sub>) or trifunctional cyclic carbonate monomers (Ph-TMPC<sub>3</sub>), respectively. The ring-opening polyaddition of Ph-TMPC<sub>2</sub> and conventional diamines efficiently proceeded without the cleavage of ester bonds to afford linear polyhydroxyurethanes (PHUs) with well-controlled molecular weights and polydispersities via isocyanate-free route. Moreover, the polyaddition of Ph-TMPC<sub>2</sub> and diamine at TMPC<sub>2</sub>/diamine feed ratio of 1.1 afforded PHUs having cyclic carbonate terminals, the hydroxyl side chains of which were easily reacted with acetic anhydride to give acetylated PHUs with cyclic carbonate terminals. On the other hand, the polyaddition at Ph-TMPC<sub>2</sub>/diamine feed ratio of 0.91 gave PHUs with amine terminals. The copolymerization of Ph-TMPC<sub>2</sub>, Ph-TMPC<sub>3</sub> and diamine gives PHUs comprising covalently-bridged networked structures. After DMF solutions of Ph-TMPC<sub>2</sub>, Ph-TMPC<sub>3</sub> and diamines were simply kept at 60 °C overnight, networked PHU films with well transparency were successfully fabricated. The PHU films prepared at different diamines showed similar transparency and thermal stability, while the mechanical properties were significantly affected by the methylene spacers of diamines.</p>
Highlights
Poly(hydroxyurethane)s (PHUs) have been attracting great interest as the promising alternatives of widely-used polyurethanes because PHUs can be synthesized by ring-opening polyaddition of bifunctional cyclic carbonates and diamines without using toxic isocyanates (Nohra, 2013; Kathalewar, 2013)
TMP was reacted with 4 equiv. of diphenyl carbonate (DPC) at 140 °C for 1-2 days and TMP-based six-membered cyclic carbonates (TMPCs)-OH was obtained in 56.6 % yield after purification by column chromatography
Fourier translation infra-red (FT-IR) spectrum of the solids exhibits no absorption at around 3500 cm-1 based on hydroxyl groups, while the characteristic absorption of ester bonds appears at 1756 cm-1 (Figure S3)
Summary
Poly(hydroxyurethane)s (PHUs) have been attracting great interest as the promising alternatives of widely-used polyurethanes because PHUs can be synthesized by ring-opening polyaddition of bifunctional cyclic carbonates and diamines without using toxic isocyanates (Nohra, 2013; Kathalewar, 2013). Five-membered cyclic carbonates (5-CCs) can be derived from epoxides and CO2 under mild conditions (Fleischer, 2013; Sheng, 2015) and numerous 5-CCs-derived PHUs have been synthesized using bisphenol A (Ochiai, 2014; Lambeth, 2013; Ochiai, 2007; Ochiai, 2005; Kihara, 1996) and bio-based polyols (Kathalewar, 2015; Maisonneuve, 2014; Annunziata, 2014; Guillaume, 2013; Guillaume, 2011) as starting materials. The ring-opening reaction of 6-CCs with amines requires the lower energy compared to 5-CCs because of the larger ring strain energy of 6-CCs (Tomita, 2001). This implies that PHUs can be synthesized at milder conditions. 6-CCs are generally synthesized using toxic phosgene or its derivatives (He, 2011; Maisonneuve, 2014; Tomita, 2001), which hinders the practical usage of 6-CCs and their application to PHU materials
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