Gertjan Vancoillie

Direct nitroxide mediated (co)polymerization of 4-vinylphenylboronic acid as route towards sugar sensors

The controlled polymerization of the unprotected, commercially available, 4-vinylphenylboronic acid (4-VBA) monomer is reported by nitroxide mediated polymerization. The glucose responsive pH window of poly(4-VBA) is reported based on turbidimetry. Finally, poly(4-VBA) polymeric pH sensors have been developed by the incorporation of solvatochromic dyes.

Hydrogen bonded polymeric multilayer films assembled below and above the cloud point temperature

Polymeric multilayer films assembled via hydrogen-bonding are witnessing increased interest from the scientific community. Here we report on hydrogen bonded multilayers of tannic acid and neutral poly(2-oxazoline)s. Importantly we demonstrate, to the best of our knowledge, for the first time that a temperature responsive polymer, in this case poly(2-(n-propyl)-2-oxazline), can be assembled below and above its TCP with distinctly different growth mechanisms.

Synthesis and polymerization of boronic acid containing monomers

Boronic acid decorated copolymers have gathered significant interest in recent years. These (co)polymers are well-known for their saccharide responsive properties commonly applied in polymeric glucose sensors, cell capture and enzymatic inhibition. Despite this wide variety of applications, boronic acid containing monomers and resulting (co)polymers are also known for their notoriously difficult synthesis and purification. This review provides a condensed overview of the different synthetic pathways that have been reported for both monomer and (co)polymer synthesis. The first part of this review will focus on the synthesis of different boronic acid containing monomers bearing various polymerizable groups including (meth)acrylates, (meth)acrylamides and styrenics. These monomers show a wide variety in synthetic complexity but also in the Lewis acidity of the boronic acid moiety, which is of vital importance for success of the desired application. The second part will then discuss the main approaches for the (co)polymerization of these monomers divided into three groups, namely polymerization of unprotected boronic acid monomers, polymerization of protected boronate ester monomers and finally boronic acid incorporation through post-polymerization modification reactions. This review will complement the already numerous application-focused papers and provide a comprehensive overview of the currently used synthetic methodologies as guideline for boronic acid-containing (co)polymer research.

Dye immobilization in halochromic nanofibers through blend electrospinning of a dye-containing copolymer and polyamide-6

‘Smart’ materials can be defined as materials that respond to a certain stimulus with a change in their properties. A specific class herein is halochromic textiles, i.e. fibrous materials that change color with pH. Such halochromic textiles play an important role in the continuous monitoring and visual reporting of the pH with applications in various fields, such as wound treatment and protective clothing. pH-sensitive nanofibrous nonwovens have high sensitivity and a fast response time, and are mostly fabricated by introducing a pH-responsive dye via dye-doping of the feed mixture before fabrication. However, this method suffers from leaching of the dye, which is an undesirable effect that not only reduces the output signal strength but can also be detrimental to the environment by causing, for instance, toxicological responses. In this paper, a new strategy is demonstrated for the reduction of dye leaching in electrospun, nanofibrous materials. Through blend electrospinning of polyamide-6 (PA6) with a dye-functionalized copolymer, large sheets of uniform, halochromic nanofibrous material can be fabricated showing a fast pH-sensitive color change. Polymeric entanglements within the nanofiber are proposed to immobilize the dye-functionalized copolymer in the PA6 matrix, resulting in drastically reduced dye leaching. Such stable nanofibrous, PA6-based, halochromic materials are particularly interesting in the design of new colorimetric sensors applicable in several sectors, including the biomedical field, agriculture, safety and technical textiles.

RAFT polymerization of 4-vinylphenylboronic acid as the basis for micellar sugar sensors

Well-defined homo and mPEGylated block (co)polymers of the commercially available unprotected 4-vinylphenylboronic acid (4-VBA) monomer are reported based on reversible addition-fragmentation chain transfer (RAFT) polymerization. The polymerization kinetics are studied in detail for homo and block (co)polymerizations with different chain transfer agents (CTAs) to optimize the preparation of well-defined polymer structures, eventually leading to comparatively low dispersities (Đ ≤ 1.25). Subsequently, block (co)polymers with methoxy poly(ethylene glycol) mPEG-b-P(4-VBA) are prepared using a mPEG-functionalized CTA. The formed block copolymer mPEG114 -b-P(4-VBA)30 is demonstrated to be pH and glucose responsive as its micellization behavior is dictated by pH as well as the presence of glucose. The glucose-responsive pH window of mPEG114 -b-P(4-VBA)30 is found to be pH 9-10 based on the DLS and TEM measurement.

Synthesis of novel boronic acid-decorated poly(2-oxazoline)s showing triple-stimuli responsive behavior

Boronic acid-functionalized (co)polymers have gained increasing attention in the field of responsive polymers and polymeric materials due to their unique characteristics and responsiveness towards both changes in pH and sugar concentrations. This makes these (co)polymers excellently suited for various applications including responsive membranes, drug delivery applications and sensor materials. Unfortunately, boronic acid-based polymer research is also notorious for its challenging monomer synthesis and polymerization and its overall difficult polymer purification and manipulation. In light of this, many research groups have focused their attention on the optimization of various polymerization techniques in order to expand the field of BA-research including previously unexplored monomers and polymerization techniques. In this paper, a new post-polymerization modification methodology was developed allowing for the synthesis of novel boronic acid-decorated poly(2-alkyl-2-oxazoline) (PAOx) copolymers, utilizing the recently published PAOx methyl ester reaction platform. The developed synthetic pathway provides a straightforward method for the introduction of pH- and glucose-responsiveness, adding this to the already wide variety of possible responsive PAOx-based systems. The synthesized BA-decorated PAOx are based on the thermoresponsive poly(2-n-propyl-2-oxazoline) (PnPropOx). This introduces a pH and glucose dependence on both cloud and clearance point temperatures of the copolymer in aqueous and pH-buffered conditions, yielding a triply-responsive (co)polymer that highlights the wide variety of obtainable properties using this pathway.

Thermoresponsive polymeric temperature sensors with broad sensing regimes

Polymeric temperature sensors with a broad sensing regime in aqueous solution have been developed. Two strategies, namely including a monomer gradient within the polymer chain and incorporation of highly polar hydroxyl functional comonomers, are evaluated to obtain a broader sensing regime of the thermometer, which is mostly limited to 10 °C for LCST-type polymers.

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.

Responsive Boronic Acid-Decorated (Co)polymers: From Glucose Sensors to Autonomous Drug Delivery

Boronic acid-containing (co)polymers have fascinated researchers for decades, garnering attention for their unique responsiveness toward 1,2- and 1,3-diols, including saccharides and nucleotides. The applications of materials that exert this property are manifold including sensing, but also self-regulated drug delivery systems through responsive membranes or micelles. In this review, some of the main applications of boronic acid containing (co)polymers are discussed focusing on the role of the boronic acid group in the response mechanism. We hope that this summary, which highlights the importance and potential of boronic acid-decorated polymeric materials, will inspire further research within this interesting field of responsive polymers and polymeric materials.

Chapter 7:Polymeric Temperature Sensors

This chapter describes polymeric temperature sensors based on the combination of solvatochromic dyes and thermoresponsive polymers, which undergo temperature-induced phase transitions in solution. The concepts and synthesis of such polymeric sensors will be explained, followed by a discussion on how polymer structures influence the sensory properties. Moreover, the working mechanisms to translate the polymer phase transition into an absorbance or fluorescence output signal for different types of dyes will be discussed. Finally, selected potential applications of these polymeric temperature sensors will be highlighted.