Add time:07/11/2019         Source:sciencedirect.com

Based on a model amidation reaction of benzoic acid triethylene glycol (TEG) ester with lithium anilide, which proceeded as rapidly as that of the methyl ester and faster than that of the ethyl ester, we considered that a TEG ester AB2 monomer would have sufficient reactivity to undergo chain-growth condensation polymerization. Indeed, condensation polymerization of 5-(methylamino)isophthalic acid TEG ester proceeded in a chain-growth polymerization manner in the presence of 1,1,1,3,3,3-hexamethyldisilazide (LiHMDS) and an initiator at −40 °C to afford a well-defined hyperbranched polyamide (HBPA) bearing many hydrophilic TEG ester moieties. The Mn values of the HBPA increased in proportion to the feed ratio of monomer to the initiator, with retention of low polydispersity (Mn = 6120–42200, Mw/Mn = 1.10–1.20). The degree of branching (DB) remained in the range of 0.48–0.51, irrespective of the feed ratio. A 0.25 wt% aqueous solution of HBPAs with different Mn values showed thermoresponsive behavior with a lower critical solution temperature (LCST) in the range of 35–37 °C, which is close to human body temperature, as in the case of poly(N-isopropylacrylamide).

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