title: Biodegradable thermogelling poly(ester urethane)s consisting of poly(lactic acid)--thermodynamics of micellization and hydrolytic degradation.
abstract: Multiblock poly(ether ester urethane)s comprising of poly(lactic acid) (PLA), poly(ethylene glycol) (PEG), and poly(propylene glycol) (PPG) segments were synthesized, and their aqueous solutions exhibited thermogelling behavior at critical gelation concentrations (CGC) ranging from 7 to 9 wt%. The chemical structures and molecular characteristics of the copolymers were studied by GPC, 1H NMR, 13C NMR and FTIR. The thermal stability of the poly(PEG/PPG/PLA urethane)s was studied by thermogravimetry analysis (TGA), and the PLA contents were calculated based on the thermal degradation profile. The results were in good agreement with those obtained from the 1H NMR measurements. The critical micellization concentration (CMC) of these water-soluble poly(ether ester urethane)s was determined at different temperatures using a dye solubilization method. The thermodynamic parameters for micelle formation were calculated, indicating that the process is largely entropy-driven. Interestingly, it appears that there exists a requirement for the system to possess a minimum gain in entropy before the thermogelling effect can be observed. Dilute copolymer solutions showed a lower critical solution temperature (LCST) behavior similar to pNIPAM dissolved in aqueous solutions. The thermogels hydrolytically degraded to polymer fragments corresponding to the constituent segment blocks within 3 months.
authors.affiliation: NUS Graduate School for Integrative Sciences & Engineering (NGS), National University of Singapore, Centre for Life Sciences, 28 Medical Drive, Singapore 117456, Singapore.
authors.forename: Xian Jun
authors.initials: XJ
authors.lastname: Loh
authors.forename: Yun Xuan
authors.initials: YX
authors.lastname: Tan
authors.forename: Ziyun
authors.initials: Z
authors.lastname: Li
authors.forename: Lin Shin
authors.initials: LS
authors.lastname: Teo
authors.forename: Suat Hong
authors.initials: SH
authors.lastname: Goh
authors.forename: Jun
authors.initials: J
authors.lastname: Li
mesh_terms: D001673:Biodegradation, Environmental; D005782:Gels / Q000737:chemistry*; D006868:Hydrolysis; D019344:Lactic Acid / Q000737:chemistry*; D008422:Materials Testing; D008823:Micelles; D015394:Molecular Structure; D008970:Molecular Weight; D044367:Phase Transition; D011091:Polyesters / Q000737:chemistry / Q000378:metabolism*; D011092:Polyethylene Glycols / Q000737:chemistry; D011108:Polymers / Q000737:chemistry*; D011140:Polyurethanes / Q000138:chemical synthesis / Q000737:chemistry*; D011409:Propylene Glycols / Q000737:chemistry; D013816:Thermodynamics; D013818:Thermogravimetry; D014783:Viscosity
chemical_list: D005782:Gels; D008823:Micelles; D011091:Polyesters; D011108:Polymers; D011140:Polyurethanes; D011409:Propylene Glycols; D019344:Lactic Acid; D011092:Polyethylene Glycols; C033616:poly(lactide)