A novel temperature responsive copolymer, poly[2-(2-methoxyethoxy)ethyl methacrylate-co-oligo(ethylene glycol) methacrylate-co-N-hydroxymethyl acrylamide] [P(MEO 2 MA-co-OEGMA-co-HMAM)], was synthesized by atom transfer radical polymerization. pH responsive poly(methacrylic acid) (PMAA) was synthesized by reversible addition-fragmentation chain transfer polymerization. After the hydroxyl groups on P(MEO 2 MA-co-OEGMA-co-HMAM) were transformed into azide groups and the carboxyl groups on PMAA were transformed into alkyne groups respectively, a novel temperature and pH responsive hydrogel was fabricated by click chemistry between the azide-P(MEO 2 MA-co-OEGMA-co-HMAM) and alkyne-PMAA in the presence of CuSO 4 and sodium ascorbate in aqueous solution. The rheological kinetics of gel formation demonstrated that gelation had commenced within 5 min at 25 ∘ C, since then the storage modulus (G ′ ) was higher than the loss modulus (G ′′ ). SEM images of hydrogel morphology and the swelling ratios of hydrogel at different temperatures and pH proved that the formed hydrogel had temperature and pH sensitivities. Bovine serum albumin was used as a model to evaluate the sustained release of the hydrogel; the results indicated that the hydrogel was a promising candidate for controlling protein drug delivery.
A well-defined temperature responsive ABA triblock copolymer, poly(2-(2-methoxyethoxy) ethyl methacrylate-co-N-hydroxymethyl acrylamide)-b-poly(ethylene glycol)-b-poly (2-(2-methoxyethoxy) ethyl methacrylate-co-Nhydroxymethyl acrylamide) [P(MEO 2 MA-co-HMAM)-b-PEG-b-P(MEO 2 MA-co-HMAM)], was synthesized by atom transfer radical polymerization (ATRP). The synthesized triblock copolymer was characterized by 1 H nuclear magnetic resonance (NMR), Fourier transform infrared (FTIR) spectroscopy and Gel Permeation Chromatography (GPC). The aqueous solution phase behaviors of the triblock copolymers were investigated by UV transmittance measurements, surface tension measurement, laser particle size and viscosity analysis. The micellization of temperature responsive triblock copolymer was investigated by fluorescence probe technique, dynamic light scattering (DLS) and transmission electron microscopy (TEM). The results showed that the molecular weight of the poly(ethylene glycol) (PEG), the Nhydroxymethylacrylamide (HMAM) content, and the degree of polymerization (DP) of the P(MEO 2 MA-co-HMAM) block for the synthesized triblock copolymers could all affect the lower critical solution temperature (LCST) of the triblock copolymer aqueous solution. The higher the molecular weight of the PEG and the HMAM content for a given triblock copolymer are, the higher the LCST of its aqueous solution. The higher the DP of the P(MEO 2 MA-co-HMAM) block is, the lower the LCST of the copolymer aqueous solution. Sol-gel transition temperature (T sol-gel ) for the triblock copolymer determined by vial inversion test further indicated that it is dependent on the molecular weights of the PEG, the DP of the P(MEO 2 MA-co-HMAM) blocks and the concentration of the copolymer aqueous solution. Copolymer hydrogels loaded with bovine serum albumin (BSA) were used for the release study. The results revealed that 1) the hydrogels had sustained release for the BSA, 2) the release rate for the BSA is dependent of the length of the PEG chain, and 3) the longer the PEG chain is, the faster the release rate of the hydrogel for the BSA.
A series of well-defined novel amphiphilic temperature-responsive graft copolymers containing PCL analogues P(αClεCL-co-εCL) as the hydrophobic backbone, and the hydrophilic side-chain PEG analogues P(MEO 2 MAco-OEGMA), designated as P(αClεCL-co-εCL)-g-P(MEO 2 MA-co-OEGMA) have been prepared via a combination of ring-opening polymerization (ROP) and atom transfer radical polymerization (ATRP). The composition and structure of these copolymers were characterized by 1 H NMR and GPC analyses. The self-assembly behaviors of these amphiphilic graft copolymers were investigated by UV transmittance, a fluorescence probe method, dynamic light scattering (DLS) and transmission electron microscopy (TEM) analyses. The results showed that the graft copolymers exhibited the good solubility in water, and was given the low critical temperature (LCST) at 35(±1)°C, which closed to human physiological temperature. The critical micelle concentrations (CMC) of P(αClεCL-co-εCL)-g-P(MEO 2 MAco-OEGMA) in aqueous solution were investigated to be 2.0 × 10 −3 , 9.1 × 10 −4 and 1.5 × 10 −3 mg·mL −1 , respectively. The copolymer could self-assemble into sphere-like aggregates in aqueous solution with diverse sizes when changing the environmental temperature. The vial inversion test demonstrated that the graft copolymers could trigger the sol-gel transition which also depended on the temperature.
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