Robot Assisted Polyurethane Chain Extension of Dihydroxy Telechelic Depsipeptides
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Robot Assisted Polyurethane Chain Extension of Dihydroxy Telechelic Depsipeptides S. Baudis1, M. Balk1,2, A. Lendlein1,2,3, M. Behl1,2 Institute of Biomaterial Science, Helmholtz-Zentrum Geesthacht, Teltow, Germany 2 Tianjin University - Helmholtz-Zentrum Geesthacht, Joint Laboratory for Biomaterials and Regenerative Medicine, Teltow, Germany 3 Berlin-Brandenburg Center for Regenerative Therapies (BCRT), Teltow, Germany
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ABSTRACT Depsipeptide-based multiblock copolymers synthesized from dihydroxy telechelic oligodepsipeptide precursors are promising candidate materials for biomedical and pharmaceutical applications. High molecular weight polymers in polyaddition reactions e.g. of diols with diisocyanates can only be reached when reactive groups are equivalent and a high conversion for this step growth polymerization is obtained. However, in depsipeptide-based multiblock urethanes reported so far, the stoichiometric ratio of the diisocyanate compound exceeded the theoretical value of 100% by far. In order to investigate the influence of the dosing system in this unusual behavior of the stoichiometric reaction two dosing devices, a solid dosing unit (SDU) and a gravimetric dosing unit (GDU) were used for a gravimetric transfer of an oligo(3-sec-butylmorpholine-2.5-dione) (OBMD) as model oligodepsipeptide. The OBMD precursor, which was transferred as a solid or as a highly viscous solution, was reacted with an isomeric mixture of 2,2,4- and 2,4,4-trimethylhexamethylene diisocyanate (TMDI) as chain extender. Two series of 49 reactions were performed and the chain extension efficacy of the building block was compared between the SDU and GDU as well as with respect to the Carothers equation. When the GDU was used the chain extension yielded higher molecular weights, proving the high accuracy of the dosing device, and the molar ratio of TMDI required for the high-throughput synthesis of the depsipeptide-based multiblock copolymers was similar to depsipeptide-based multiblock copolymers created in a classical synthesis approach. INTRODUCTION Robot assisted synthesis [1, 2] of multiblock copolymers, in which reaction parameters have been varied gradually has become a promising option to investigate structure-property relationships and is helpful to gain an insight into the mechanism of multiblock copolymer formation [3, 4]. Recently, high throughput (HT) synthesis of polyester-diols with diisocyanates by polyaddition reaction was reported where the volumetric transfer of viscous polymer solution was quantified and the influence of the diol to isocyanate molar ratio on the molecular weight was investigated [5]. However, an optimization of a volumetric transfer is required for viscous solutions to ensure accurate quantitative amount of components. Hence, a gravimetric transfer is needed. Here, we investigated whether a polyaddition reaction of dihydroxy oligomers with diisocyanates can be performed by gravimetric controlled addition of the starting material with a robotic platform. Interesting for biomedical application are
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