Photosensitive polyrotaxanes: New comb-like polymethacrylamides containing 1,3- diphenyl-2-propen-1-one (chalcone) functions and noncovalently bound cyclodextrin in the side-chains
The synthesis and free radical polymerization of a methacrylamide monomer, 5, bearing non-covalently attached cyclodextrins and the chalcone function with a barrier group, is described. The first step of preparation of the monomer was the condensation of 4-(N-methacryloyl-6-aminohexanoylamino)- acetophenone, 1, with 4-nitrobenzaldehyde. The resulting 1-(N-methacryloyl-6- aminohexanoyl-4-aminophenyl)-3-(4-nitrophenyl)-2-propen-1-one, 2, was reduced with tin(II) chloride dihydrate to the corresponding 1-(N-methacryloyl-6-aminohexanoyl- 4-aminophenyl)-3-(4-aminophenyl)-2-propen-1-one, 3. After this, the aminochalcone was condensed with a barrier group, triphenylacetyl chloride, yielding 1-(N-methacryloyl-6-aminohexanoyl-4-aminophenyl)-3-(N’-triphenylacetyl- 4-aminophenyl)-2-propen-1-one, 4. Monomer 4 was copolymerized with methyl methacrylate to the model polymer poly[4-co-methyl methacrylate], 6, and also complexed with dimethylated β-cyclodextrin to the semi-rotaxane (4 / 2,6-Me2-β- CD) 5, which was copolymerized with methyl methacrylate, yielding a polyrotaxane (5-co-methyl methacrylate) 7, containing a cyclodextrin ring in the side-chain. The semi-rotaxane 5 and both copolymers 6 and 7 were characterized spectroscopically and also by means of differential scanning calorimetry, gel permeation chromatography and thermogravimetrical analysis, and - in the case of 5 - by mass spectrometry. Furthermore, the UV-induced E/Z-isomerization of both polymers 6 and 7 was examined in tetrahydrofuran solution. A retarding effect of the noncovalently attached cyclodextrin was finally detected.