Seminar Series
Nitroxide‐Mediated Polymerization of 2‐(Diethylamino)ethyl Methacrylate in Bulk and Solution
Ali Darabi
ABSTRACT 2‐(Diethylamino)ethyl methacrylate (DEAEMA) is a pH‐responsive methacrylate‐based monomer containing a tertiary amine group that has been used in synthesizing different types of CO2‐switchable polymers such as CO2‐switchable latex, CO2‐switchable surfactant, and CO2‐swicthable block copolymers. In this study, nitroxide‐mediated polymerization (NMP) of DEAEMA has been investigated in bulk and solution using monocomponent and bicomponent initiating system. In monocomponent initiating system, n‐hydroxysuccinimidyl BlocBuilder (NHS‐BB) was employed as alkoxyamine while in bicomponent initiating system n‐tertbutyl‐n‐(1‐ diethylphosphono‐2,2‐dimethylpropyl) nitroxide (SG1) was used as nitroxide and 2,2'‐azobis[2‐(2‐imidazolin‐2‐yl)propane]dihydrochloride (VA‐044) as initiator. The effect of several parameters including monomer concentration, temperature, initiator concentration, free nitroxide in the system, and polymerization medium on the kinetic of the reaction has been studied in detail.
Seminar Series
Investigation of Copper Wire‐Mediated Controlled/Living Radical Polymerization: Development of Greener Solvent Systems & Grafting to
Cellulose via Thio‐Bromo Click Reaction
Oxana Shibaeva ABSTRACT Copper wire mediated controlled living radical polymerization (CLRP) is a powerful tool that provides numerous opportunities for the development of new materials. It requires low catalyst loading and mild reaction conditions, but does involve use of organic solvents. There is a need for greener solvent systems to replace traditional volatile organic solvents without detrimentally affecting polymerization. The effects of greener solvents on control over polymerization and polymer characteristics were investigated with polyethylene glycol (PEG) and polypropylene glycol (PPG) for copper wire mediated CLRP. Polymerization of low molecular weight poly(methyl acrylate) (PMA) with bromine chain‐end functionality was initiated by ethyl 2‐bromoisobutyrate (EBiB). Two effective green solvent systems were established, 75‐25 PEG‐Ethanol and 75‐25 PPG‐Ethanol. Both provide good control over polymerization, livingness, narrow dispersity (~1.1), high retention of chain‐end functionality (>90%), and can be recycled, which should be considered for an industrial scale implementation. Furthermore, utilization of a bromine chain‐end functionality of synthetic homopolymer (PMA) synthesized via copper wire mediated CLRP with EBiB was evaluated for grafting to cellulose substrates, microcrystalline cellulose and cellulose acetate. Cellulose was functionalized with thiol groups using ring opening reaction with ethylene sulfide. The grafting via thio‐bromo click reaction was investigated, where grafting of EBiB was performed first to evaluate the reaction and then repeated with PMA. One‐pot and two‐pot reactions were performed. In one‐pot reaction, functionalization of cellulose and grafting were performed in the same reaction solution to avoid exposure of thiols to oxygen. In a two‐pot reaction, functionalized cellulose was purified before grafting. Nuclear Magnetic Resonance analysis showed that grafting of EBiB had low degree of substitution (DS) of 0.026 (1 unit per 39 AGU units), whereas grafting of polymer chains to cellulose substrate was not successful.
Seminar Series
Redispersible Polymer Latexes Based on CO2 Switchable Amidine Chemistry
Xin Su
ABSTRACT The development of redispersible polymer latexes is of significant interest from scientific and industrial viewpoints. The research is focused on preparing stimuli‐responsive polymer latexes that can switch between aggregated and dispersed states using CO2 as a trigger. The polymer latex is prepared using switchable amidine chemistry. Amidine groups can react with dissolved CO2 in the continuous water phase to produce the corresponding cationic amidinium bicarbonate; these charged groups then provide stabilization of the latex particles. Measurements of particle size and zeta potential were used to study the aggregation and redispersion of the latexes. The latex is aggregated by heating and bubbling with argon to remove CO2 and convert the active cyclic amidinium groups to their neutral form. When treated with sonication and bubbling with CO2, the aggregated polystyrene latex can be redispersed successfully, as evidenced by recovery of the original latex particle size and zeta potential from the large aggregated polymer particles. Research is ongoing to identify optimal redispersing conditions for the aggregated latexes.
Seminar Series
Novel Poly(lactic acid) foams: Micro to Sub‐micron size transition
Praphulla
ABSTRACT Chemical modification of poly(lactic acid) (PLA) through a reactive extrusion process was performed in presence of a free‐radical initiator and multi‐functional chain extender; to prepare formulations that are suitable for foaming. Batch foaming, using nitrogen as the blowing agent, was done at various temperatures to differentiate the effect of chain branching and nucleation on the cell size of reactively modified foams. Depending on the conditions very fine, sub‐micron size foams were obtained in reactively modified PLA.
Seminar Series
Thermo responsive “smart” catalysts for living radical miniemulsion polymerization: Catalyst activation, removal, and recycle
Elijah Bultz
ABSTRACT
A thermoresponsive ruthenium catalyst containing PEGylated triphenyl phosphine derivatives has been used to conduct transition metal mediated living radical polymerizations (ATRP) in miniemulsion, allowing for easy removal of the metal catalyst post‐polymerization. The polymerizations of butyl methacrylate in miniemulsion catalyzed by RuCp*Cl(PPh3)2 ‐(non‐thermoresponsive) or the RuCp*Cl(PPEG) (thermoresponsive) were compared, with the PEG containing ligand found to be significantly more active than the triphenyl phosphine ligand. The reaction temperature was near the cloud point of the thermoresponsive catalyst allowing it to transfer into the monomer droplets upon heating and mediate the polymerization. The polymerization showed good control with molecular weight distributions increasing shifting to higher molecular weights at increasing conversions and relatively low polydispersities. Following polymerization the reaction mixture was cooled allowing the catalyst to desorb from the particles. The latex was precipitated in methanol, producing a colorless polymer product that contained less than 10 ppm of residual metal as measured by ICP‐AES. This approach may facilitate the development of waterborne ATRP processes yielding final latexes that are metal‐free and enabling catalyst recycle. Furthermore, improvements in the catalytic activity were investigated by the addition of cocatalysts including amines or ferrocene. Addition of ferrocene allowed for significant improvements in the rate and the final achievable conversion from a concerted cocatalytic cycle with the ruthenium catalyst allowing for faster activation and deactivation of the growing polymers.
Seminar Series
Chemical analysis of biopolymers associated with membrane fouling
and their removal by biofiltration during water treatment
Xinhai (August) Guo
ABSTRACT The application of membrane filtration for drinking water treatment is limited by membrane fouling due to the accumulation of biopolymers. Biofiltration may be an effective pretreatment to reduce the biopolymers, thus improving the performance of membrane filtration. Biological treatment and the microbial community associated with drinking water treatment systems can potentially play a positive role on chemical contaminant removal and biopolymer reduction. The efficacy of biofiltration to remove biopolymers is being investigated. The specific biopolymers include total polysaccharides (PS), acidic polysaccharides (APS), proteins (PN) and humic substances (HS), and their presence in raw water and treated effluent following biofiltration and prior to membrane filtration. Methods developed for the analysis of extracellular polymeric substances (EPS) associated with microbial flocs and biofilms in wastewater were adapted to analyze surface waters and drinking water where biopolymers are found in significantly lower concentrations. Freeze‐drying was found to be an effective method for concentrating water samples and to recover and analyze neutral and acidic polysaccharides, but did not work for protein quantification. EPS from the biofilter media was also analyzed as part of the characterization of the microbial community associated with biofiltration, PN/PS ratios of EPS from biofilters ranged from 0.3‐0.6, potentially suggesting loosely‐bound EPS dominated biofilter environment. Results of water samples suggested that biofiltration was an ineffective pretreatment for polysaccharides removal in the untreated water. Higher concentration of polysaccharides present in effluent samples might come from the loosely‐bound EPS developed in the biofilters. Therefore, further optimization for biofilter is required to achieve better effluent quality for the purpose of membrane fouling control. Keywords: Drinking Water; Biofiltration; Polysaccharides; Chemical Analysis; Freeze drying