Synthesis and characterization of well-defined block and statistical copolymers based on lauryl methacrylate and 2-(acetoacetoxy)ethyl methacrylate using RAFT-controlled radical polymerization

摘要

Four well-defined diblock copolymers and one statistical copolymer based on lauryl methacrylate (LauMA) and 2-(acetoacetoxy)ethyl methacrylate (AEMA) were prepared using reversible addition-fragmentation chain transfer (RAFT) Polymerization. The polymers were characterized in terms of molecular weights, polydispersity indices (ranging between 1.12 and 1.23) and compositions by size exclusion chromatography and H-1 NMR spectroscopy, respectively. The preparation of the block copolymers was accomplished following a two-step methodology: First, well-defined LauMA homopolymers were prepared by RAFT using cumyl dithiobenzoate as the chain transfer agent (CTA). Kinetic studies revealed that the polymerization of LauMA followed first-order kinetics demonstrating the "livingness" of the RAFT process. The pLauMAs were subsequently used as macro-CTA for the polymerization of AEMA. The glass transition (T-g) and decomposition temperatures (ranging between 200 and 300 degrees C) of the copolymers were determined using differential scanning calorimetry and thermal gravimetric analysis, respectively. The T(g)s of the LauMA homopolymers were found to be around -53 degrees C. Block copolymers exhibited two T(g)s suggesting microphase separation in the bulk whereas the statistical copolymer presented a single T-g as expected. Furthermore, the micellization behavior of pLauMAb-pAEMA block copolymers was investigated in n-hexane, a selective solvent for the LauMA block, using dynamic light scattering. pLauMA-b-pAEMA block copolymers formed spherical micelles in dilute hexane solutions with hydrodynamic diameters ranging between 30 and 50 nm. (C) 2008 Wiley Periodicals, Inc.