David Hunkeler

Inverse-emulsion polymerization of acrylamide using block copolymeric surfactants: mechanism, kinetics and modelling

A comprehensive experimental investigation of the inverse-emulsion polymerization of acrylamide was carried out using an oil soluble initiator and a block copolymeric surfactant whose hydrophobic moiety is poly(12-hydroxystearic acid) and whose hydrophilic moiety is polyethylene oxide. It was found that the initial polymerization rate was first order with respect to molar monomer concentration, first order with respect to molar initiator concentration, and zeroth order with respect to molar emulsifier concentration. Based on these experimental findings, a mechanism was proposed which includes initiation, propagation, transfer to monomer and termination. The elementary reaction scheme also includes transfer to impurities which are found in the surfactant. The kinetic model developed from the proposed mechanism is found to be in good agreement with the experimental conversion and weight-average molecular weight data. Compared with sorbitan esters of fatty acids, the copolymeric surfactant provides higher polymerization rates and very high and linear molecular weights. These are comparable to those obtained by solution polymerization, however the total monomer level in the recipe can be substantially greater. Furthermore, stable inverse-laticies can be produced at emulsifier levels as low as 2 wt%.

LIQUID CHROMATOGRAPHY OF MACROMOLECULES UNDER LIMITING CONDITIONS OF ADSORPTION. I. PRINCIPLES OF THE METHOD

A novel separation method for macromolecules, viz. liquid chromatography under limiting conditions of adsorption (LC LCA), is presented. LC LCA is designed for discrimination of complex polymers. It combines exclusion and adsorption mechanisms so that they mutually compensate. This results in the absence of separation of macromolecules according to their size or molar mass. In LC LCA, the eluent is a liquid moderately promoting adsorption of polymer species. The column packing attracts macromolecules and, if the sample were dissolved and injected in eluent, it would be retained within column. Therefore, the polymer is injected in a solvent that effectively suppresses adsorption. Experimental conditions can be identified with regard to the eluent, column packing, temperature as well as sample solvent, and injected sample volume under which macromolecules of various molar masses are eluted together with their initial solvent. in this way, binary polymer blends, with components exhibiting different adsorptiv...

Prediction of copolymer composition drift using artificial neural networks : copolymerization of acrylamide with quaternary ammonium cationic monomers

The free radical copolymerization of acrylamide with a quaternary ammonium cationic comonomer, diethylaminoethyl acrylate (DMAEA), has been investigated in inverse-emulsion. The copolymer composition was determined from residual monomer concentrations using an h.p.l.c. method. Both reactivity ratios were observed to change with conversion. Furthermore, the reactivity ratio of the cationic monomer was found to be a function of the ionic strength and monomer concentration and, to a limited extent, the polymer concentration and the organic-to-aqueous phase ratio. Therefore, the classical binary ultimate group copolymerization scheme cannot predict copolymer composition drift throughout the reaction. An artificial neural network (ANN) has been built to predict the copolymer composition. ANNs have the ability to map nonlinear relationships without a priori process information. The results show that an ANN can predict the copolymer composition very well as a function of reaction conditions and conversion. It is expected that for any system where the reactivity ratios are conversion dependent that an ANN, such as the one developed herein, will be preferable.

Heterophase water-in-oil polymerization of acrylamide by a hybrid inverse-emulsion/inverse-microemulsion process

Heterophase water-in-oil polymerizations of acrylamide have been conducted in the presence of blends of non-ionic stabilizers at moderate monomer concentrations (20%). The initial monomeric system is located outside the inverse-microemulsion domain, yet close to the inverse-macroemulsion/inverse-microemulsion phase boundary. A turbid, viscous and unstable dispersion is produced at the outset and during the intermediate stages of the polymerization. This evolves to an inviscid and non-settling system at high conversions. Transparent inverse latices can also be produced provided that the polymerizations are conducted semi-adiabatically. Small angle neutron scattering (SANS) studies of the initial monomer and reacting systems have found the latices to be particulate with a particle diameter of 150 nm, independent of conversion. The SANS intensities can be fitted using a polydispese spherical particles model. Therefore, these heterophase water-in-oil polymerization systems seem to follow an inverse-macroemulsion-like mechanism. The ‘hybrid inverse-microemulsion/inverse-macroemulsion’ polyacrylamides produced herein have a smaller radius of gyration in aqueous media relative to those produced by either solution polymerization or a true inverse-macroemulsion polymerization of the same weight-average molecular weight. This is likely due to a large number of intramolecular interactions, such as hydrogen bonds, which are induced by the collapsed nature of the polymer chains in the inverse-microemulsion droplets. The weight-average molecular weight, the radius of gyration and the particle diameter of the final latex are relatively independent of the polymerizations conditions such as initiator level, hydrophilic-lipophilic balance (HLB), temperature and physical changes occurring during polymerization. From a kinetic point of view, the molecular weights of these systems are controlled by transfer to monomer, while transfer to interfacial emulsifier is the polymerization rate controlling step. A reaction mechanism consisting of a number of elementary reactions has been proposed for these heterophase-water-in-oil polymerizations. Agreement with the experimental data is found to be good at different levels of initiator, HLBs and temperature. Despite the limitations of this heterophase water-in-oil polymerizations (the moderate emulsifier levels, low radius of gyration and its inability to increase the weight-average molecular weight beyond 106 daltons), this polymerization process can produce final latices that are transparent and non-settling with small particles (< 150 nm). This allows post-reaction chemical modification, e.g. by the Mannich reaction.

Inverse-emulsion copolymerization of acrylamide and quaternary ammonium cationic monomers with block copolymeric surfactants: copolymer composition control using batch and semi-batch techniques

Abstract An experimental investigation of the inverse-emulsion copolymerization of acrylamide and quaternary ammonium cationic monomers (dimethylaminoethylacrylate, DMAEA and dimethylaminoethylmethacrylate, DMAEM) has been carried out using both a block copolymeric surfactant (HB246) whose hydrophilic moiety is polyethylene oxide and whose hydrophobic moiety is poly(12 hydroxy stearic acid) and sorbitan monoleate (SMO). Our results indicate that the choice of surfactant influences strongly the quality of the copolymers produced. For example, more uniform copolymers of acrylamide and DMAEA can be synthesized using the block copolymeric surfactant (HB246) at faster production rates in comparison with sorbitan monoleate (SMO) when utilizing batch reactors. However, a composition drift is observed in the inverse-emulsion copolymerization of acrylamide and DMAEM using HB246. A possible explanation for this behaviour is either a reduced reactivity ratio (r2) or propagation constant (k22). However, physical effects such as a possible lower interfacial acrylamide concentration are not to be ruled out. It is also shown, for the first time, that copolymers of acrylamide and DMAEM of more uniform composition can be produced by implementing simple semi-batch policies with non time-varying feedrates. It is believed that these cationic copolymers would have a higher flocculation efficiency both in municipal and in industrial water treatment due to their more uniform distribution of the positive charge along the polyacrylamide backbone.

INVERSE-EMULSION STABILITY: QUANTIFICATION WITH AN ARTIFICIAL NEURAL NETWOR

ABSTRACT Due to the multiplicity of parameters governing emulsion stability, existing theories generally cannot quantitatively predict the phase separation in oil/water systems. In this work, an artificial neural network, which is known to have a strong nonlinear mapping ability, was used to “learif” the correlation between the factors influencing emulsion stability (phase ratio, surfactant concentration and comonomer concentrations) and the magnitude of phase separation. This has been applied to the water-in-oil copolymerizations of acrylamide with quaternary ammonium cationic monomers. It was found that the ANN can accurately predict the subset of the stability state (stable, metastable, unstable), along with the extent of oil separation for metastable systems.