Kathleen Lava

Poly(2-cycloalkyl-2-oxazoline)s: high melting temperature polymers solely based on Debye and Keesom van der Waals interactions

The synthesis of new 2-cycloalkyl-2-oxazoline monomers, namely 2-cyclobutyl (cBuOx), 2-cyclopentyl (cPentOx) and 2-cyclohexyl-2-oxazoline (cHexOx) is described. Their microwave-assisted cationic ring-opening polymerisation allowed the synthesis of well-defined homopolymers. The resulting homopolymers are crystalline and have high chemical resistance to organic solvents. The highest melting point was registered for cPentOx (306 °C), followed by cHexOx (251 °C) and cBuOx (243 °C). The crystal structure of the homopolymers was put into evidence by X-ray diffraction and appeared to be similar to that of the poly(2-isopropyl-2-oxazoline). The absence of any hydrogen bonding or π–π interactions, makes these compounds a special class of high performance polymers which possess high Tm solely based on Debye and Keesom van der Waals interactions of the side-chains. The copolymerization of cPentOx with 2-ethyl-2-oxazoline (EtOx) and cBuOx, respectively are also reported indicating the formation of near ideal random copolymers. Furthermore, the copolymers of cPentOx with cBuOx with compositions in the range from 0 to 100% revealed a linear dependence of melting temperature with the weight fraction of comonomer. For cPentOx-EtOx copolymers containing up to 25 wt% EtOx a linear decrease of the melting temperature with composition was registered, most likely due to the disturbance of the cPentOx crystalline domains. Further, increasing the EtOx wt% revealed a complex non-linear dependence of glass transition temperature on composition, whereby the glass transition temperature of some copolymers was lower than for pure PEtOx.

Blend electrospinning of dye-functionalized chitosan and poly(ε-caprolactone): towards biocompatible pH-sensors

Fast-response and easy-to-visualize colorimetric nanofibrous sensors show great potential for visual and continuous control of external stimuli. This makes them applicable in many fields, including wound management, where nanofibers serve as an optimal support material. In this paper, fast responding and user-friendly biocompatible, halochromic nanofibrous sensors are successfully fabricated by incorporating the halochromic dyes Methyl Red and Rose Bengal inside a chitosan/poly(ε-caprolactone) nanofibrous matrix. The commonly applied dye-doping technique frequently suffers from dye-leaching, which not only reduces the sensors sensitivity over time but can also induce adverse effects. Therefore, in this work, dye-immobilization is accomplished by covalent dye-modification of chitosan before blend electrospinning. It is shown that efficient dye-immobilization with minimal dye-leaching is achieved within the biomedical relevant pH-region, without significantly affecting the halochromic behavior of the dyes. This is in contrast to the commonly applied dye-doping technique and other dye-immobilization strategies stated in literature. Moreover, the nanofibers show high and reproducible pH-sensitivity by providing an instantaneous color change in response to change in pH in aqueous medium and when exposed to acidic or basic gases. The results stated within this work are of particular interest for natural (bio)polymers for which covalent modification combined with electrospinning provides a universal method for versatile dye-functionalization of large area nanofibrous membranes with proper dye-immobilization.