Guping He

Superhydrophobic Hierarchically Assembled Films of Diblock Copolymer Hollow Nanospheres and Nanotubes

Reported are the formation of rough particulate films from cross-linked diblock copolymer vesicles and nanotubes and the wetting properties of the resultant films. The diblock copolymers used were F66M200 and F95A135, where the subscripts denote the repeat unit numbers, whereas M, A, and F denote poly(2-cinnamoyloxyethyl methacrylate), poly(2-cinnamoyloxyethyl acrylate), and poly(2,2,2-trifluoroethyl methacrylate), respectively. The precursory polymers to F66M200 and F95A135 were prepared by atom transfer radical polymerization. In 2,2,2-trifluoroethyl methacrylate (FEMA), a selective solvent for F, vesicles and tubular micelles were prepared from F66M200 and F95A135, respectively. Photo-cross-linking the M and A blocks of these aggregates yielded hollow nanospheres and nanotubes bearing F coronal chains. These particles were dispersed into CH2Cl2/methanol, where CH2Cl2 was a good solvent for both blocks and methanol was a poor solvent for F. Casting CH2Cl2/methanol dispersions of these particles yielded films consisting of hierarchically assembled diblock copolymer nanoparticles. For example, the hollow nanospheres fused into microspheres bearing nanobumps after being cast from CH2Cl2/methanol at methanol volume fractions of 30 and 50%. The roughness of these films increased as the methanol volume fraction increased. The films that were cast at high methanol contents were superhydrophobic, possessing water contact angles of ∼160° and water sliding angles of ∼3°.

Enhanced copper-catalyzed “click” reaction between homopolymers with terminal azide and alkyne groups in the presence of water

Abstract We report here that the efficiency of the click chemistry between the terminal azide and alkyne groups of different polymer chains could be drastically increased with the addition of an optimum amount of water into a reaction system. That is, the efficiency was only slightly promoted by the addition of a small amount of water into the reaction mixture. However, the reaction efficiency was increased dramatically near the water volume fraction to lead the reaction mixture into nanosized phase separation. Further increasing in water content caused the polymer(s) to undergo macroscopic phase separation and the click reaction efficiency was decreased once again. The enhanced efficiency of click coupling reaction including conversion and rate was also demonstrated via in-situ 1H-NMR. The reaction kinetics as well as reaction rate constant for these reaction system with typical water content were also evaluated. This finding on enhanced click reaction is of practical value, because click reactions in polymer synthesis are generally more difficult to be carried out and proceed relative slowly at low yield in most case because of the strong steric hindrance effect from “large and long” polymer chains, as compared to “click” reactions which are employed for preparation of the low molecular weight organic compounds.