Omar García-Valdez

Modification of chitosan with polystyrene and poly(n-butyl acrylate) via nitroxide-mediated polymerization and grafting from approach in homogeneous media

Chitosan (CTS) modification with polystyrene (PS) and poly(n-butyl acrylate) (PnBA) via nitroxide-mediated polymerization (NMP) and a grafting from approach is reported. CTS was first functionalized with glycidyl methacrylate (GMA) and then converted into a macroalkoxyamine by intermolecular 1,2 radical addition of either 2,2,5-trimethyl-3-(1-phenylethoxy)-4-phenyl-3-azahexane (TIPNO-based alkoxyamine the “Universal Alkoxyamine”, UA) or the SG1-based BlocBuilder (BB) alkoxyamine. Graft polymerizations of styrene and n-butyl acrylate were conducted, using homogeneous media to ensure uniform grafting onto the CTS backbone. The graft modified CTS based materials were analysed by 1H-NMR, TGA and FT-IR.

Graft modification of cellulose nanocrystals via nitroxide-mediated polymerisation

Cellulose nanocrystals (CNC) have become the subject of increasing research interest because of their unique physical, chemical and mechanical properties, including being a renewable material. While CNC shows promise as a reinforcing material in polymer-based composites, the hydrophilic surface of CNC makes dispersibility in most hydrophobic polymers very difficult which limits potential applications. In this study, we report the first graft modification of CNC using nitroxide-mediated radical polymerisation. The CNC surface was first functionalised with the nitroxide SG1 (4-(diethoxyphosphinyl)-2,2,5,5-tetramethyl-3-azahexane-N-oxyl), yielding a CNC-macroalkoxyamine. Poly(methyl acrylate) and poly(methyl methacrylate) chains were then grafted from the CNC-macroalkoxyamine surface to yield polymer graft modified CNC.

Grafting CO2-responsive polymers from cellulose nanocrystals via nitroxide-mediated polymerisation

Cellulose nanocrystals (CNC) are a renewable resource possessing extraordinary physical, mechanical, and optical properties. CNC are readily dispersible only under hydrophilic environments, such as aqueous media and very polar solvents. Different approaches have been attempted to alter the surface properties and thereby improve CNC dispersibility in organic solvents and polymers (hydrophobic media), including functionalisation with small molecules and grafting of polymer chains to the CNC surface. However, when hydrophobic polymer chains are grafted on the CNC surface, the CNC are irreversibly altered toward increased hydrophobicity, which can be undesirable for some applications. Grafting stimuli-responsive polymer chains to the CNC surface offers a solution to this problem. We have synthesized stimuli-responsive CNC whose surface properties can be reversibly switched using only carbon dioxide (CO2) as the trigger to conduct the switching process. The surfaces were modified using surface-initiated nitroxide mediated polymerisation (SI-NMP) with CO2-responsive polymers poly(dimethylaminoethyl methacrylate) (PDMAEMA), poly(diethylaminoethyl methacrylate) (PDEAEMA) and poly(dimethylaminopropyl methacrylamide) (PDMAPMAm).

CO2-Responsive Graft Modified Chitosan for Heavy Metal (Nickel) Recovery

Chitosan was chemically functionalized with poly(diethylaminoethyl methacrylate) (PDEAEMA) using a grafting to approach to produce a CO2-responsive material for adsorbing metals from wastewater streams. A need for improved economical and greener approaches to recover heavy metals from wastewater streams exists due to increasing resource scarcity. Chitosan is currently used as an adsorbent for heavy metals but suffers from some properties that can be disadvantageous to its effectiveness; it is difficult to effectively disperse in water (which limits available surface area) and to regenerate. We set out to improve its effectiveness by grafting CO2-responsive tertiary amine containing polymers onto the chitosan backbone, with the goals of preparing and assessing a new type of adsorbent based on a novel concept; using carbon dioxide switchable polymers to enhance the performance of chitosan. PDEAEMA chains prepared by nitroxide-mediated polymerization were grafted onto chitosan functionalized with glycidyl methacrylate. In carbonated water, the grafted chitosan displayed improved dispersibility and exhibited a Ni(II) adsorption capacity higher than several other chemically functionalized chitosan variants reported in the literature with the regenerated material having a higher capacity than all physical and chemical derivatives reported in the literature. The results of this study validate the continued development of this material for applications in heavy metal removal and recovery from wastewater streams.