Synthesis And Characterzaion Of Biodegradable Block Copolymer And Their Self-assembly Behavior

Biodegradable aliphatic polyesters and their amphiphilic block copolymers have been extensively application in drug delivery and controlled release systems, sutures, scaffold for tissue engineering due to their excellent biodegradable, biocompatible and permeable properties. In recently years, the self-assembled behavior in selective solvents of biodegradable amphiphilic block copolymers have been attracted much attention in advanced materials and controlled drug delivery systems. On the one hand, amphiphilic block copolymers can self-assemble to nanoparticles for drug release carrier; on the other hand, amphiphilic block copolymers can also self-assemble to form various aggregates micelles by changing the composition and properties. The emphasis of this thesis focuses on three sections:(1) A series of poly(ε-caprolactone)-b-poly(ethylene oxide)-b-poly(ε-caprolactone) (PCL-PEG-PCL) amphiphilic triblock copolymers are synthesized by a ring-opening polymerization ofε-caprolactone in the presence of hydroxyl-terminated poly(ethylene oxide) with stannous octoate catalyst. The PCL-PEG-PCL block copolymers are characterized by 1H NMR, gel permeation chromatographies (GPC) and infrared (IR). The results indicate that the molecular weights of PCL-PEG-PCL copolymers calculated by 1H NMR is similar to the designed.(2) The self-assembled behavior of PCL-PEG-PCL in different pH aqueous media is investigated. The results manifest that, in acidic aqueous media, PCL-PEG-PCL block copolymers are easily self-assemble to form unstable and associated large-compound micelles aggregates, and in neutral aqueous media, PCL-PEG-PCL block copolymers are self-assembled to spherical shape micelles aggregates while it is self-assembled to flowerlike micelles aggregates in alkaline aqueous media. The morphological difference of flowerlike aggregates is not discovered by adjusting the block ratios of PEG/PCL. The morphology and sizes of PCL-PEG-PCL micelles aggregates are characterized by ZeTa granulometer, scanning electron microscope (SEM) and transmission electron microscope (TEM).(3) Amphiphilic diblock copolymers poly(ε-caprolactone)-b-methoxy poly (ethy- lene glycol)(MPEG-PCL) synthesized in our laboratory is employed to systematically investigate the self-assembled behavior in aqueous media. The morphological and sizes of MPEG-PCL micelles aggregates are controlled by adjusting the block ratios, different temperature, initiale concentration. The results indicate that, base on variation range, the sizes of obtained spherical shape micelles aggregates increased as the increase of the length of PCL chains and initial concentration of block copolymer while the temperature have no obvious difference on sizes. The morphology and sizes of MPEG-PCL micelles aggregates are also characterized by ZeTa granulometer, scanning electron microscope (SEM) and transmission electron microscope (TEM).