Synthesis and characterization of novel temperature-responsive gels derived from poly(ethylene glycol) for in situ gelatin applications

We report the development of two new triblock copolymers that form gels from aqueous solutions reversibly in response to high temperatures above their critical gel concentrations (CGC). The polymers are composed of temperature-responsive random copolymers of 2-(2-methoxyethoxy)ethyl methacrylate (MEO2MA) and oligo(ethylene glycol) methacrylate (OEGMA) (Mn = 475 g/mol) (P(MEO2MA-co-OEGMA)) terminal segments, and hydrophilic poly(ethylene) glycol (PEG) or P(OEGMA) central segment.;Variations of atom transfer radical polymerization (ATRP) were used to synthesize P(MEO2MA)-PEG-P(MEO2MA) (6000-4000-6000) and P(MEO2MA)-P(OEGMA)-P(MEO2MA) (9000-24000-9000). The low critical solution temperature (LCST), CGC, and gel strength of the polymers were identified by measuring the thermal and rheological behaviors of the polymers at various polymer concentrations using a particle size analyzer or differential scanning calorimeter (DSC), and a rheometer, respectively. The LCST of the polymers closely matched the LCST of the composing temperature-responsive terminal segments, P(MEO2MA-co-OEGMA), whose LCST was controlled by manipulating the initial monomer compositions. The CGC of the P(MEO 2MA)-PEG-P(MEO2MA) and P(MEO2MA)-P(OEGMA)-P(MEO 2MA) were approximately 25 and 35 w/w%, respectively. The latter gel showed less gel rigidity which was expected due to the bulky P(OEGMA) structure.