Synthesis And Properties Of Polyesters Based On Coffeic Acid

Degradable P(DHCA-co-LCA) polyesters were synthesized by melt polycondensation of 3,4-dihydroxycinnamic acid (DHCA, coffeic acid) and lithocholic acid (LCA). The structure and molecular weight of P(DHCA-co-LCA) polyesters were characterized by Fourier transform infrared (FT-IR), nuclear magnetic resonance (1H-NMR) and gel permeation chromatography (GPC). The glass transition temperatures (Tg), thermal and photosensitive properties of the polyesters were investigated by differential scanning calorimeter (DSC), thermo gravimetric analyzer (TGA), UV spectroscopy and fluorescence spectroscopy. It was found that obvious changes of Tg could not be observed when the ratio of LCA increased. The photoreactivity of P(DHCA-co-LCA) depended on their compositions which could be tuned by varying the monomer feeding ratio. The presence of LCA in copolymer enhanced the solubility and thermal stability. In addition, the strongest fluorescence emission occurred at certain amount of LCA in the copolymers. Accelerated hydrolysis experiments revealed that the degradation rate of P(DHCA-co-LCA) was slower than that of PDHCA.P(DHCA-co-LCA) micelles with different diameters were prepared by mixing N,N-dimethylformamide as a good solvent and water as a poor solvent. The average diameters and morphologies of the micelles prepared under various conditions were evaluated by laser light scattering (LLS) and transmission electron microscopic (TEM). The uniform micelles with a smooth surface were obatined. The size varied from about 251nm to 440nm by altering the concentration of the polyesters and the LCA in feed. The photo-cross-linking induced size decrement of the micelles depending on the LCA in feed. Accelerated hydrolysis experiments showed that P(DHCA-co-LCA) micelles have good degradable performance.P(DHCA-co-LCA)-b-PEG polyesters were synthesized by melt polycondensation of DHCA, LCA and poly(ethylene glycol) (PEG). It was proved that Tg and fluorescence emission intensity of the polyesters decreased with increasing PEG content. P(DHCA-co-LCA)-b-PEG polyesters could be photo-crosslinked under UV light (λ>310nm) and its reversible photo-cleavage could take place under UV light of 254nm. The micelles with smooth surface were obtained by self-assembly and possessed a certain photosensitivity based on LLS and TEM results. The sizes of micelle depended on PEG in feed, polyester concentration and water content in the mixed solution. Accelerated hydrolysis experiments showed that P(DHCA-co-LCA)-b-PEG micelles have good degradable performance and the degradation rate of P(DHCA-co-LCA)-b-PEG micelles was faster than that of P(DHCA-co-LCA).