Solvent-Free Aqueous Dispersions of Block Copolyesters for Electrospinning of Biodegradable Nonwoven Mats for Biomedical Applications Dedicated to Prof. Darrell Reneker on the Occasion of his 85th birthday Kathrin Bubel, Daniel Grunenberg, Gleb Vasilyev, Eyal Zussman, Seema Agarwal, Andreas Greiner* Biodegradable block copolyesters are processed from water to water-stable electrospun fibers without use of any organic solvent, which is of major importance for a variety of applications. The copolyesters (poly(e-caprolactone-b-methoxypolyethylene glycol)) (PCL-b-MPEG)) are emulsified in water at 90 8C in presence of poly(ethylene oxide) (PEO) using melt dispersion method. Dramatic increase in viscosity is observed upon addition of PEO to aqueous dispersions of copolyesters. Evidence of structure formation in aqueous PCL-b-MPEG/PEO dispersions is adduced using rheological studies. PCL block length dependent water stable nanofiber non-wovens are obtained upon electrospinning of the dispersions. 1. Introduction Electrospinning of biodegradable and biocompatible poly- mers is a promising way for the preparation of water stable polymer fibers and nanofiber-based non-wovens, which can, for example, be used for biomedical and agricultural applications. [1–11] Due to their large specific surface and microporous structure, the electrospun fibers can be employed as scaffolds for tissue engineering, or drug eluting wound dressings, as well as for biotechnical plant protection by the release of insect pheromones. [12–20] However, by using polymeric solutions of polylactide (PLA), poly(e-caprolactone) (PCL) or other aliphatic poly- esters with a general overall solid content of 5–15 wt.-% as electrospinning feed, the required quantity of organic solvents, like chloroform or dimethyl formamide, is rather high. [21–27] For a sustainable approach to electrospinning, organic solvents should be completely avoided. [28] A possible solution could be melt electrospinning which requires rather drastic processing conditions and yields fibers with larger diameter. [29,30] A relatively new K. Bubel Fachbereich Chemie, Philipps-Universit€ at Marburg, Hans-Meerwein-Strasse, Marburg 35032, Germany Prof. A. Greiner, D. Grunenberg, Prof. S. Agarwal Faculty of Biology, Chemistry and Earth Sciences, Macromolecular Chemistry II, Bayreuth Center for Colloids and Interfaces, Universit€ at Bayreuth, Universit€ atsstrasse 30, Bayreuth 95440, Germany E-mail: greiner@uni-bayreuth.de Dr. G. Vasilyev, Prof. E. Zussman Faculty of Mechanical Engineering, Technion-Israel Institute of Technology, Haifa 32000, Israel Full Paper ß 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim DOI: 10.1002/mame.201400116 1445 Macromol. Mater. Eng. 2014, 299, 1445–1454 wileyonlinelibrary.com