Synthesis And Self-assembly Of Diblock Copolymers

There was a great interest in microcontainner or micelles prepared fromamphiphilicblock copolymer PEG-PCL as prospective drug delivery systems.They showed notoxicity, prolonged circulation time in vivo due to theshielding effect of poly(ethyleneglycol) chains against the phagocytosis ofthe mononuclear phagocytic system (MPS),and sustained release of drugmolecules due to the controlled degradation of thebiodegradable polymers.The incorporated drug molecules in microcapsules can be released by adiffusion mechanism plus degradation of the biodegradablepolymers.Although polymeric micelles and nanoparticles have been widelyinvestigated ascolloidal drug carriers, the correlation between thephysicochemical characteristics of thecarrier and their biological fate is stillpoorly understood. Therefore in this paper theself-assembling of a series ofPCL and PEG dicopolymers was studied indetail and the main conclusionsare as follows:Synthesize the diblock copolymers under the condition of have no thewater and have no oxygen and catalyst is Sn(Oct)2. Among them PEGmolecular weight fixedly is 5000, a molecular weight distinguishes to2000,3000 and 5000, presenting the trend of the gradual aggrandizement.The method of synthesize PEG-PLA is totally same to the and PEG-PCL.measurese the molecular weight and molecular weights of the member todistribute of PEG-PCL by NMR and GPC, design standard match at thebeginning.The micelle formation of a series of amphiphilic block copolymers inaqueousand solutions was studied by fluorescent probe technique usingpyrene as a "modeldrug". These copolymers were synthesized frompoly(ethylene glycol) (PEG) and ε-caprolactone (ε-CL) . The critical micelleconcentration (cmc) was found to decrease with increasing PCLcontent.Slef-assembly of amphiphilicblock copolymer in the water is the result thattwo kinds of functions compete together:the hydrophile segment candissolve in the water the function makes the diblock copolymers totallyscatter stability in the water,the hydrophobe segment can't dissolve in thewater the function makes the diblock copolymers totally sink to accumulateout from the water totally, as a result making they to come together formingnuclear, the hydrophile segment solve in solvent scatter stability in the water.Therefore to evaluate the hydrophile segment and hydrophobe segment ofamphiphilicblock copolymer opposite length and absolute lengths isimportance to the self-assembly of diblock copolymers.To on fixing the PEG length, the cmc value of the diblock copolymerswith the increment but decreases of the PCL content, for example, thelength of the increment PCL chain segment.This is to comprehend of,because increment hydrophobe segment of PCL has to make the functionthat oneself come together.When the PCL content is low in 50%, the cmc islong to PEG chain and equal sensitive of the variety of the PCLcontent( PCL to PEG opposite length).But when PCL content over 50%, thecmc lowers with the increment but slownesses of the content of PCL,explain within the scope of this to cmc influence, the PCL content is a moreimportant decision factor of more absolute than PEG segment length。The morphology of the diblock copolymer micelle in the block-selectivesolvent was detected by AFM .It is observed that the morphology of micelleis changed.The size of the diblock copolymer micelle in the block-selective solventis measured by dynamic light scattering(DLS). It is observed that the size ofmicelle is changed.Observe the morphology and the size of diblock copolymermicelle ,they are maked by the different method.Discover that size ofmicelles with the PCL segment content increment and bigger,while takingethanol and waters as to selective solvent, because the ethanol makecopolymer deposit, the chain segment of the polymer is in the hybridsolvent of the ethanol and water the occurrence is mutually the degree ofdecrease change wants to compare the hybrid solvent of DFM and water isweak, so it is easy to become the micelles and easy gathering ,the size ofthe micelles is distributes the asymmetry. compare Method of (a) with ( b),because the latter is to join the selectivity melting to the polymer aqua ,make the ability of the polymer deliquescence descend, not only a processfor add in the polymer aqua is very quick and then took place the muddy,but also the dialysis time also appears to certainly precipitate Comparing tomethod( a) .,the micelles prepare by the method( b) is bigger and theheight is also high.