The Study On The Synthesis Of Star-shape Block Copolymers And Their Micelles Properties

In this article firstγ-Aminopropyl triethoxysilane(KH-550) was reacted with oxiranem ethanol, and then the mixture of silsesquioxane (POSS-OH),which contained several hydroxyl groups, was prepared via reaction of hydrolysis and polycondensation with acid as catalyst. With POSS-OH as core initiator, stannous octoate as catalyst, star PCLs were synthesized by ring-opening polymerization(ROP) ofε-caprolactone. Then after the star PCLs converted into a macromolecular initiator , N-isopropylacrylamide was grafted to star PCLs through atom transfer radical polymerization (ATRP),and ultimately star-shaped block copolymer was synthesized .In this paper ,the relation between molecular weight, Polydispersity of star PCLs and amount of caprolactone was investigated, as well as the DMF solvent effect to ATRP. At the same time, thermal properties of the star PCLs and star-shaped block copolymer were investigated.POSS-OH, star PCLs and star-shaped block copolymers were characterized through methods of FTIR, NMR, DSC, TG and GPC. POSS-OH was a mixture composed by a series of ladder and cage-type silsesquioxane , which had a good thermal stability and contained more active hydroxyl. GPC analysis showed that: When the amount of POSS-OH was certain, the molecular weight of star-shaped PCLs can be controlled by the amount of CL; when other factors were same, after NIPAM reached a certain value, increased the amount of NIPAM, however, reduced molecular weight. DSC analysis showed that: when the arm of the star PCLs were shorter, the melting point were far less than the linear PCL; the melting point of star PCLs increased with increasing molecular weight; melting point of star-shaped block copolymer was close to the star-shaped PCLs, and its LCST was 29.8℃.Star block copolymer POSS-PCL-PNIPAM micelles were prepared by method of dialysis. The morphology and thermo-sensitive of micelles were studied by TEM, LLS and UV ,at the same time the drug release of micelles which loaded ibuprofen were investigated. The results showed that: POSS-PCL-PNIPAM micelles with core-shell structure had regular spherical structure. In dispersion state micelles had a single peck, a smaller radius and a good mono-disperse; micelles exhibited obvious thermosensitive, the LCST was approximately 30℃, but the phase transition temperature was expressed as a wide temperature range, the size of micelle had gone through a first down and then up process with increasing temperature; As the PCL content in the copolymer increased, the drug content and the drug loading efficiency of micelles was increasing. The much bigger concentration of electrolyte, the more easily micelle precipitated, the ratio of PNIPAM in the star-shaped block copolymer was smaller, the more unstable in deionized water; POSS-PCL-PNIPAM micelles for drug release demonstrated the rapid release of temperature-induced .