ORIGINAL CONTRIBUTION ABA triblock copolymers of poly(N-isopropylacrylamide-co-5,6-benzo-2-methylene -1,3-dioxepane) (A) and poly(ethylene glycol) (B): synthesis and thermogelation and degradation properties in aqueous solutions Gabriel Turturicǎ 1 & Maria Andrei 1 & Paul O. Stǎnescu 1 & Constantin Drǎghici 2 & Dumitru Mircea Vuluga 2 & Anamaria Zaharia 3 & Andrei Sârbu 3 & Mircea Teodorescu 1 Received: 15 October 2015 /Revised: 5 January 2016 /Accepted: 7 January 2016 /Published online: 21 January 2016 # Springer-Verlag Berlin Heidelberg 2016 Abstract Novel hydrolytically degradable thermosensitive triblock copolymers with poly(ethylene glycol) (PEG) middle-chain and random copolymers of N - isopropylacrylamide and 5,6-benzo-2-methylene-1,3- dioxepane as side blocks were synthesized by the reversible addition–fragmentation chain transfer (RAFT) copolymeriza- tion of the two monomers in the presence of the bisester of [S- 1-dodecyl-S′-(α,α′-dimethyl-α″-acetic acid)] trithiocarbonate and α,ω-dihydroxy PEG of 10,000 Da molecular weight as the RAFT macroagent. The polymers prepared were structur- ally characterized by gel permeation chromatography (GPC), 1 H NMR and differential scanning calorimetry (DSC) analy- ses, and their thermosensitive behavior was evidenced by rhe- ological measurements on 10 wt% aqueous solutions. The polymer aqueous solutions displayed enhanced viscosity at low temperatures due to the association of the hydrophobic dodecyl trithiocarbonate end groups, which was decreased by free radically removing the RAFT groups in the presence of tributyltin hydride. The gelation temperature, defined as the temperature at which the viscoelasticity moduli become equal each other, ranged between 36 and 43 °C depending on the aqueous solvent (distilled water or phosphate buffer saline (PBS)) and the presence of hydrophobic dodecyl end groups. The degradable character of the triblock copolymers prepared was proved by the hydrolysis of the in-chain ester groups in 1- N KOH solution at room temperature. A partial degradation of the polymer also occurred in the gel formed at 37 °C from a 10 wt% PBS solution, as proved by both GPC and 1 H NMR measurements. Under these conditions, the gel completely dissolved and lost its thermogelation ability up to 60 °C in less than 24 days. Keywords Poly(N-isopropylacrylamide) . Poly(ethylene glycol) . 5,6-Benzo-2-methylene-1,3-dioxepane . Block copolymers . Injectable hydrogels . Degradation Introduction Polymers displaying a lower critical solution temperature (LCST) in aqueous solutions have attracted a lot of interest within the last decades due to their potential for synthesizing Bsmart materials^ with applications in various fields, like con- trolled drug and cell delivery, tissue engineering, valve and actuators, flow modifiers in oil industry, smart clothing fabri- cation, catalysts, etc. [1–10]. As temperature is a very effective stimulus, those with a LCST below the body temperature have been largely researched for their biomedical applications as injectable hydrogels. These hydrogels are initially fluid Electronic supplementary material The online version of this article (doi:10.1007/s00396-016-3831-9) contains supplementary material, which is available to authorized users. * Mircea Teodorescu mirceat@tsocm.pub.ro 1 Department of Bioresources and Polymer Science, Faculty of Applied Chemistry and Materials Science, Polytechnic University of Bucharest, 1-7 Gh. Polizu Street, 011061 Bucharest, Romania 2 Center of Organic Chemistry of the Romanian Academy, 202B Splaiul Independentei, 060023 Bucharest, Romania 3 National Institute of Research and Development for Chemistry and Petrochemistry—ICECHIM, 202 Splaiul Independentei, 060021 Bucharest, Romania Colloid Polym Sci (2016) 294:743–753 DOI 10.1007/s00396-016-3831-9