Synthesis, Characterization and Sensor Application of Novel PCL-Based Triblock Copolymers

In this study, novel triblock copolymers, including poly(<i>N</i>-isopropylacrylamide)-<i>block</i>-poly(<i>ε</i>-caprolactone)-<i>block</i>-poly(<i>N</i>-isopropylacrylamide) (PNIPAM-<i>b</i>-PCL-<i>b</i>-PNIPAM), poly(<i>N</i>-vinyl-pyrrolidone)-block-poly(<i>ε</i>-caprolactone)-block-poly(<i>N</i>-vinyl-pyrrolidone) (PNVP-<i>b</i>-PCL-<i>b</i>-PNVP), poly(<i>N</i>-isopropylacrylamide-<i>co</i>-<i>N</i>,<i>N</i>-dimethylaminoethyl methacrylate)-<i>block</i>-poly(<i>ε</i>-caprolactone)-<i>block</i>-poly(<i>N</i>-isopropylacrylamide-<i>co</i>-<i>N</i>,<i>N</i>-dimethylaminoethyl methacrylate) (P(DMAEMA-<i>co</i>-NIPAM)-<i>b</i>-PCL-<i>b</i>-P(NIPAM-<i>co</i>-DMAEMA)), and poly(<i>N</i>,<i>N</i>-dimethylacrylamide)-<i>block</i>-poly(<i>ε</i>-caprolactone)-<i>block</i>-poly(<i>N</i>,<i>N</i>-dimethylacrylamide) (PDMA-<i>b</i>-PCL-<i>b</i>-PDMA), were synthesized via a combination of ring-opening polymerization (ROP) and reversible addition-fragmentation chain transfer (RAFT) polymerization. The synthesis was performed using novel bifunctional PCL-based RAFT macro chain transfer agents (macroCTAs; MXTPCL-X1 and MXTPCL-X2) with a <i>m</i>-xylene-bis(2-mercaptoethyloxy) core. Initially, <i>m</i>-xylene-bis(1-hydroxy-3-thia-propane) (MXTOH), which has not previously been used in lactone polymerization, was synthesized via the reaction of <i>α</i>,<i>α</i>'-dibromo-<i>m</i>-xylene with 2-mercaptoethanol in the presence of sodium in ethanol. Subsequently, Sn(Oct)₂-catalyzed ROP of <i>ε</i>-caprolactone (<i>ε</i>-CL) using MXTOH as an initiator yielded PCL-diol (MXTPCLOH). The resulting PCL-diol underwent further functionalization through esterification and substitution reactions, leading to the formation of PCL-based RAFT macroCTAs. Triblock copolymers were synthesized using these macroCTAs with AIBN as an initiator. The synthesized products, along with their intermediates, were characterized using FTIR and ¹H NMR spectroscopy. The number average molecular weight (M_n) and polydispersity index (<i>Ð</i>) of PCL-based macroCTAs were determined by using GPC analysis. The sensor capabilities of the synthesized novel triblock copolymers were investigated on the determination of syringic acid and it was determined that the most sensitive polymer was PNVP-<i>b</i>-PCL-<i>b</i>-PNVP (MXTP2). The working range was between 1.5 µg/mL and 15 µg/mL and the limit of detection (LOD) was found to be 0.44 µg/mL using DPV on MXTP2 polymer sensor.