| Summary: | 碩士 === 義守大學 === 生物技術與化學工程研究所 === 101 === The effect of poly(propylene glycol) as hydrophobic chain ends of amphiphiles on the formation of lyotropic liquid crystalline phases was investigated. The branching structure of poly(propylene glycol) is suitable for the formation of reversed phase. Poly(propylene glycol)s of different molecular weights are commercially available. Different phases can be expected to occur by adjusting the molecular weight of the poly(propylene glycol) chain. Glycerol is employed as the hydrophilic head group in this study. Poly(propylene glycol) monobutyl ethers of molecular weights 340 and 1000 are used to obtain the designed amphiphiles, poly(propylene glycol)-glycerol (PPG-Gly 340 and 1000).
The proposed amphiphiles were synthesized firstly by the reaction of poly(propylene glycol) monobutyl ether with succinic anhydride to convert the hydroxyl end groups to carboxylic acid (PPG-acid). PPG-acid was connected with solketal by ester linkage. The protecting isopropylidene group can be removed by treating with 70% acetic acid to obtain PPG-GLY.
PPG-Glys with PPG of molecular weights 340 and 1000 do not exhibit lyotropic liquid crystalline phases by optical microscopy. It indicates that the flexibility of PPG leads to isotropic structure. The effect of PPG was further investigated by the mixing of PPG-Gly 340 or 1000 with 1-monoolein since the lyotropic liquid crystalline behaviour of 1-monoolein is well characterized. On the addition of PPG-Gly 340, the hexagonal phase cannot be detected by optical microscopy. By adding PPG-Gly 1000, The reversed hexagonal phase (H2) forms at considerable lower temperature (~55℃) and the appearance range (~20℃) is enlarged significantly. The longer hydrophobic chain of PPG-Gly 1000 can fill the energetically unfavorable space of H2 structure with less energy cost and facilitate the formation of reversed hexagonal phase. This result supports our initial hypothesis that the flexible ether linkage in poly(propylene glycol) can be expected to reduce the packing constraint. The small-angle X-ray diffraction patterns show that the addition of PPG-GLY and PPG-acid (340 and 1000) do not change the Pn3m structure of the 1-monoolein reversed cubic phase. However, the internal dimension of the Pn3m structure is modulated. On the addition of 4 mole% PPG-GLY 1000, the saturated water content decreased from 48% to 42.5%. The lattice parameter falls from 123 Å to 111 Å. The cross section area of hydrophilic head group increases from 16.7544 Å2 to 20.8243 Å2.
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