Facile synthesis of dendrimer-like star-branched poly(isopropylacrylamide) via combination of click chemistry and atom transfer radical polymerization

Abstract

We report a facile synthesis method of dendrimer-like star-branched poly(N-isopropylacrylamide) (PNIPAM) via the combination of click chemistry and atom transfer radical polymerization (ATRP) by employing the arm-first approach. First, the α-azido-ω-chloro-heterodifunctionalized building block, N3-PNIPAM-Cl (G0-Cl), was synthesized via ATRP by 3-azidopropyl 2-chloropropionate as the initiator. Taking advantage of click chemistry, the first generation (G1) of dendrimer-like star-branched PNIPAM, G1-(Cl)3, was facilely prepared via the click coupling reaction between G0-Cl and tripropargylamine. For the construction of second generation (G2) dendrimer-like star-branched PNIPAM, G2-(Cl)6, terminal chloride moieties of G1-(Cl)3 were first converted to azide, and then reacted with excess tripropargylamine to give G1-(alkynyl)6; G2-(Cl)6 was subsequently prepared via click reaction between G1-(alkynyl)6 and G0-Cl. Gel permeation chromatography (GPC) and matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry were employed to confirm the successful construction of dendrimer-like star-branched polymers. The unique thermal phase transition behavior of this dendrimer-like star-branched polymer in aqueous solutions was further investigated by turbidimetry and micro-differential scanning calorimetry (Micro-DSC).