Polyurethanes by ring‐opening polymerization initiated from alcohol moiety‐tethering acylazide

Abstract

An orthogonal agent having both alcohol and acylazide groups was used to construct novel polyurethanes by a simple synthetic process. Ring‐opening polymerization (ROP) of δ‐valerolactone from the orthogonal agent afforded a crystalline polymer having acylazide initiation end, while that of δ‐decanolactone resulted in an amorphous polymer. Since acylazide groups undergo thermally induced Curtius rearrangements to yield isocyanate groups, simple heating of above polymers gave macromonomers having both an isocyanate initiation end and an alcohol termination end, which afforded corresponding polyurethane by self‐polyaddition in a bulk condition without any additives. Meanwhile, kinetic analysis of the Curtius rearrangement revealed that a quantitative conversion was reached within a short reaction time, for example at 110°C for 30 min, or at 100°C for 1 h. Moreover, obtained polyurethane species showed unique self‐immolative type thermal degradation behavior. Considering the above, this orthogonal agent turned out to be useful to construct various polyurethane structures by a facile synthetic process, which would contribute to precise polymer synthesis and sequence defined polymer synthesis.

Tailored Polyurethane Synthesis from AB-Type Monomers

“…First of all, O2 was synthesized by the straightforward synthesis as follows; (1) the main framework construction by the reaction between methyl 4-hydroxybenzoate and allyl glycidyl ether (60% yield); (2) hydrolysis of methyl ester (94% yield); and (3) converting carboxylic acid to acylazide by diphenyl phosphoryl azide (DPPA) (74% yield). − In a similar manner, O3 and O4 were successfully synthesized by a facile process . Here, O3 was synthesized from methyl vanillate, which is derivatized from a biobased vanillin molecule, meaning that O3 and resulting polyO3 can be considered as a biobased material.…”

“…Analogous to previous reports, the kinetic and thermodynamic analyses of the Curtius rearrangement of O2 to O2_NCO were carried out as follows. ,− O2 was dissolved in PhCl- d 5 at 0.10 M concentration, heated to 100 °C (Scheme ), and then the time-course change of the reaction was followed by 1 H NMR measurements after 5, 10, and 15 min (Figure ). As a result, the signals of O2_NCO were clearly observed and increased according to the heating time, while those of O2 decreased, without any other signal emerging such as polyO2 .…”

“…Moreover, the activation energy, enthalpy, and entropy were calculated based on these kinetic constants, and all the parameters are summarized in Table . Furthermore, it was also calculated that the conversion reaches over 99% at 110 °C within 25 min, while at 100 °C, it takes 67 min, meaning that for the polymerization experiment, heating at 110 °C for 30 min or 100 °C for 70 min would be considered as a sufficient reaction time for completing the Curtius rearrangement, which did not differ much from O1 . Meanwhile, the Curtius rearrangement of O2 turned out to be around 15% slower than that of O1 (Table ).…”

“…According to this idea, Akae and co-workers developed polyurethane synthesis based on a basic AB-type monomer O1 (named as an orthogonal agent 1) featuring both alcohol and acylazide groups without any side chain functionality (see Figures B and A). , There, an acylazide group was used as the precursor of an isocyanate since the former can transform into the latter rapidly by a simple heat-induced Curtius rearrangement in a quantitative yield and the former is more stable than the latter, enabling a flexible molecular design on the former. So far, it turned out that O1 affords the corresponding polyurethane structure by self-polyaddition.…”

“…(A) Multiple polyurethane synthesis by O1 (previous works). , (B) Schematic of the flexible polyurethane design by the postpolymerization modification method. (C) Abstract of this work.…”