Synthesis and characterization of pH/temperature-sensitive block copolymers via atom transfer radical polymerization

In order to prepare well-defined pH-sensitive block copolymers with a narrow molecular weight distribution (MWD), we synthesized a pH-sensitive block copolymer via atom transfer radical polymerization (ATRP) of sulfamethazine methacrylate monomer (SM) and amphiphilic diblock copolymers by the ring-opening polymerization of d,l-lactide/ɛ-caprolactone (LA/CL), and their sol–gel phase transition was investigated. SM, which is a derivative of sulfonamide, was used as a pH responsive moiety, while PCLA–PEG–PCLA was used as a biodegradable, as well as a temperature sensitive one, amphiphilic triblock copolymer. The pentablock copolymer, OSM–PCLA–PEG–PCLA–OSM, was synthesized using Br–PCLA–PEG–PCLA-Br as an ATRP macroinitiator. The number average molecular weights of SM were controlled by adjusting the monomer/initiator feed ratio. The macroinitiator was synthesized by the coupling of 2-bromoisobutyryl bromide with PCLA–PEG–PCLA in the presence of triethyl amine catalyst in dichloromethane. The resultant block copolymer shows a narrow polydispersity. The block copolymer solution shows a sol–gel transition in response to a slight pH change in the range of 7.2–8.0. Gel permeation chromatography (GPC) and NMR were used for the characterization of the polymers that were synthesized.