| 초록 |
The poly(N-isopropyl acrylamide-co-methoxy polyethyleneglycol monomethacrylate, NIPAM-co-MPEG) with different length of ethylene oxide (EO) were synthesized from their monomers, NIPAM and MPEGs. The numbers of repeating units of EO were 6, 10, 24, and 46. The chemical structure and mole ratio of the monomers was determined by FT-IR, 1H-NMR and 13C-NMR spectroscopy. The amide and ester peaks was identified in the FT-IR spectra, which are specific to the NIPAM and MPEG components, respectively. 1H peaks of the O-CH2 and O-CH3 of the copolymer appeared at 3.6 ppm and 3.3 ppm. The d-spacing increased with the number of EO and the values of the copolymers were in the range of 0.437 – 0.452 nm. The low critical solution temperature (LCST) of the copolymers were 34 oC for poly(NIPAM-co-6MPEG), 36 oC for poly(NIPAM-co-10MPEG) and 58 oC for poly(NIPAM-co-24MPEG). The transition temperatures of the poly(NIPAM-co-10MPEG) were 37 oC for 2.5 mol %, 39 oC for 5 mol %, and 44 oC for 7.5 mol %. The stabilizing effect is more pronounced with increasing amount of 10MPEG. An increase in the amount of 10MPEG increases the LCST of the NIPAM copolymers. In addition to the increasing critical temperature, the sharpness of the light blockage curves is smoothed in case of 10 mol % of 10MPEG. The change of chemical shift for –OCH3 proton exhibited a larger than those of the other protons of the poly(NIPAM-co-10MPEG). With increasing solution temperature, the spin-lattice relaxation time ( T1 ) for the protons in side chain increased, while that for the protons in the backbone chain decreased. The larger value in activation energy for the methoxy group in the MPEG implies that more significant structure change occur in the methoxy group through the phase transition than in the methyl group. NMR results indicate the fact that conformational change in side chain –OCH3 group is more significant that those in the backbone of the copolymer during the phase separation. Increasing temperature tends to break the hydrogen bonds and some of the water molecules are released out of the hydrated shell as a result of hydrogen bond breaking, so the structure of the hydrated shell is destroyed and T1 value for methoxy group decreases. Evidence for water release could be obtained by measuring the change of the integral intensity for water protons at 4.8 ppm relative to the integral intensity for CH at 3.8 ppm. Then, it forms hydrophobic bonding because the hydrophobic interactions of the methyl group in NIPAM and ethylene group in MPEG are more pronounced with increasing the solution temperature. |
