Templated Fabrication of Polymeric Nanocages Using Polymeric Micelles as Reusable Template and One Pot Condensation Reactions of Alcohols and Ketones
|Course||Polymer Chemistry and Physics|
|Keywords||Nanoparticles Polymeric micelles Preparation of template One-pot Condensation reaction Template Self-assembly Core-shell structure Template synthesis Radical initiator AIBN Hollow ball Nanofibers Benzyl alcohol Template polymerization Synthesis Preparation Material Hydrophobic nature Nanowires illustration|
1. Templated fabrication of polymeric nanocages using polymeric micelles as reusable template. Due to their unique structure and properties, nano-materials become a hot subject in material science. In this thesis, we tried to prepare polymeric nanoparticles with varied morphologies using block copolymer micelles as reusable template. Firstly, we synthesized PEO-b-P4VP block copolymer with different structure parameters through ATRP. When the mixture of the copolymer with a radical initiator AIBN (2,2’-Azobisisobutyronitrile) in methanol was added with water to the water/methanol volume ratio of 9/1, the micelles with PEO as the shell and P4VP as the core formed; AIBN was largely located within the P4VP core due to its hydrophobicity. Subsequently, after further addition of a water soluble monomer 4VP (4-vinylpyridine) and a water soluble crosslinker MBA (N,N’-Methylene bisacrylamide) into the system, and increased the temperature to 70℃, radical copolymerization of 4VP and MBA occurred. The free radical polymerization should mainly take place at the core-shell interface, initiated by core-localized AIBN, forming nano cages surrounding the P4VP core. When the weight ratios of MBA/AIBN/block copolymer are high enough, particle-particle coupling took place. Modulated by PEO shell, the coupling resulted in linear or branched nanofibers rather than irregular clusters. After removal of the template, polymeric hollow spheres can be prepared. After separation of block copolymer from the nanoparticles, the block copolymer can be used as the template again. This method can prepare polymeric nanoparticles with varied morphologies simply and conveniently.2. One pot condensation reactions from ketones and aromatic alcohols in the presence of CrO3. Polymer loaded catalysts are very attractive since they are expected to combine the advantages of both homogeneous and heterogeneous catalysts. We planned to use PEO-b-P4VP (poly (ethylene oxide)-block-poly (4-vinylpyridine) loaded CrO3 to oxidize benzyl alcohol. After the reaction and the recovery of the polymer, we found that PEO-b-P4VP had been oxidized. Although we failed in developing such the polymer loaded catalysis systems, we found a new reaction that is significant forα,β-unsaturated ketones preparation. When reacting acetone and benzyl alcohols at 56℃in the presence of CrO3 for around 10 hours, the condensation product benzalacetone was the main product. Then we optimized the reaction conditions through reaction time, reaction temperature and the ratio of different substrates. We found that the condensation reactions occurred effectively among a wide combination of ketones and alcohols. The procedure is simple and the yields can be high up to 98%. A probable mechanism is proposed that during the alcohol/ketone condensation reactions ketones reacted with the intermediate of the oxidation reaction of the aromatic alcohols by CrO3, leading toα,β-unsaturated ketones. The process represents a step towards wider range of available substrates and reduced cost of production, and has the potential to be adapted to industrial production of benzalacetones and chalcones.