title: Synthesis and characterization of biocompatible, thermoresponsive ABC and ABA triblock copolymer gelators.
abstract: The synthesis of doubly thermoresponsive PPO-PMPC-PNIPAM triblock copolymer gelators by atom transfer radical polymerization using a PPO-based macroinitiator is described. Provided that the PPO block is sufficiently long, dynamic light scattering and differential scanning calorimetry studies confirm the presence of two separate thermal transitions corresponding to micellization and gelation, as expected. However, these ABC-type triblock copolymers proved to be rather inefficient gelators: free-standing gels at 37 degrees C required a triblock copolymer concentration of around 20 wt%. This gelator performance should be compared with copolymer concentrations of 6-7 wt% required for the PNIPAM-PMPC-PNIPAM triblock copolymers reported previously. Clearly, the separation of micellar self-assembly from gel network formation does not lead to enhanced gelator efficiencies, at least for this particular system. Nevertheless, there are some features of interest in the present study. In particular, close inspection of the viscosity vs temperature plot obtained for a PPO43-PMPC160-PNIPAM81 triblock copolymer revealed a local minimum in viscosity. This is consistent with intramicelle collapse of the outer PNIPAM blocks prior to the development of the intermicelle hydrophobic interactions that are a prerequisite for macroscopic gelation.
authors.affiliation: Department of Chemistry, Dainton Building, University of Sheffield, Brook Hill, Sheffield, South Yorkshire, S3 7HF, UK.
authors.forename: Chengming
authors.initials: C
authors.lastname: Li
authors.forename: Niklaas J
authors.initials: NJ
authors.lastname: Buurma
authors.forename: Ihtshamul
authors.initials: I
authors.lastname: Haq
authors.forename: Colin
authors.initials: C
authors.lastname: Turner
authors.forename: Steven P
authors.initials: SP
authors.lastname: Armes
authors.forename: Valeria
authors.initials: V
authors.lastname: Castelletto
authors.forename: Ian W
authors.initials: IW
authors.lastname: Hamley
authors.forename: Andrew L
authors.initials: AL
authors.lastname: Lewis
mesh_terms: D000180:Acrylic Resins / Q000737:chemistry; D001672:Biocompatible Materials / Q000138:chemical synthesis*; D005782:Gels; D057927:Hydrophobic and Hydrophilic Interactions; D008689:Methacrylates / Q000737:chemistry; D008823:Micelles; D010767:Phosphorylcholine / Q000031:analogs & derivatives / Q000737:chemistry; D011108:Polymers / Q000138:chemical synthesis* / Q000737:chemistry; D011109:Polymethacrylic Acids; D011409:Propylene Glycols / Q000737:chemistry; D013696:Temperature
chemical_list: D000180:Acrylic Resins; D001672:Biocompatible Materials; D005782:Gels; D008689:Methacrylates; D008823:Micelles; D011108:Polymers; D011109:Polymethacrylic Acids; D011409:Propylene Glycols; C115766:poly(2-methacryloyloxyethyl-phosphorylcholine); D010767:Phosphorylcholine; C052970:poly-N-isopropylacrylamide; C012504:polypropylene glycol