Synthese von hochmolekularem Polyglycolid unter Einsatz von überkritischem Kohlenstoffdioxid als Reaktionsmedium

Schmidt, Christian

Methods for synthesizing polyglycolide (PGA) with a preferably high molecular weight using supercritical carbon dioxide (scCO 2 ) were investigated. To perform the ring-opening polymerization (ROP) of the cyclic monomer diglycol ide various different catalytic systems are available. Conventional metal-organic, enzymatic an d organocatalysts were examined and compared concerning their activity towards the poly merization and potential side reactions. In addition, the physiological innocuousness of the ma terials is of high importance and strongly influences the choice of suitable solvents and cata lysts within the process. To obtain PGA with a preferably high molecular weight the influence of the relevant reaction parameters of the different catalytic systems was determined. By vari ation of these parameters the impact on molecular weight and conversion was determined, all owing to compare the influence of different catalysts upon the polymerization. High reaction temperatures, which are required for metal-organic catalyzed ROP, result in a strong thermal decomposition of the polymer, which can be avoided by utilizing scCO 2 as reaction medium. Especially by using diphenyl bismu th bromide very high molecular PGA with no visible thermal decomposition can be obtained. H owever, as most metal-organic catalysts serve as transesterification agents synthesizing PG A with a well-defined polymer architecture is hindered. This can result in disadvantageous eff ects on the processability of the material and the formation of insoluble polymer fractions, i ndicating cross-linked macromolecules. Enzymatic and organocatalysis on the other hand all ow for PGA synthesis at low temperature. Due to the high selectivity of enzymes side reactio n can be avoided leading to uniform polymer architectures. Therefore, the materials show enhanc ed solubility. Combining enzymatic catalysis with a non-harmful reaction medium such a s scCO 2 a new and sustainable route to synthesize PGA for medical applications at benign t emperatures is given. Utilizing organocatalysis shows similar advantages for PGA sy nthesis as the reaction can be performed at ambient temperatures resulting in completely sol uble polymer samples. However, liquid CO 2 is to favor over scCO 2 as lower temperatures are advantageous for the rea ction, allowing to use a non-toxic reaction medium at low temperatures . In addition, possibilities to improve the processab ility of PGA by block copolymerization with polyethylene glycol (PEG) were studied. Especially by using PEG 400 higher thermal stabilities and improved rheological behavior were observed, re quiring for only 4.8 wt% of PEG in the copolymer. It can be assumed that these copolymer m aterials are suitable for conventional injection moulding techniques. Thus, the polymer properties can be adjusted accord ing to the requirements. By choosing the catalytic system and reaction conditions the synthe sis of PGA over a broad range of molecular weight can be realized. Utilizing enzymes and organ ocatalysts is of special interest for synthesis of materials for biomedical applications as a non-toxic reaction medium is used and polymers with a uniform architecture are obtained. Applications for the materials are found e.g. in the area of tissue-engineering and drug-delivery .

Methods for synthesizing polyglycolide (PGA) with a preferably high molecular weight using supercritical carbon dioxide (scCO 2 ) were investigated. To perform the ring-opening polymerization (ROP) of the cyclic monomer diglycol ide various different catalytic systems are available. Conventional metal-organic, enzymatic an d organocatalysts were examined and compared concerning their activity towards the poly merization and potential side reactions. In addition, the physiological innocuousness of the ma terials is of high importance and strongly influences the choice of suitable solvents and cata lysts within the process. To obtain PGA with a preferably high molecular weight the influence of the relevant reaction parameters of the different catalytic systems was determined. By vari ation of these parameters the impact on

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Schmidt, Christian: Synthese von hochmolekularem Polyglycolid unter Einsatz von überkritischem Kohlenstoffdioxid als Reaktionsmedium. 2015.

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