Jeanne François

Hydrolysis of polyacrylamide and acrylic acid-acrylamide copolymers at neutral pH and high temperature

Abstract The hydrolysis of acrylamide-acrylic acid copolymers has been studied as a function of pH and of the initial composition of the samples. Our experimental results confirm the intramolecular catalysis by neighbouring undissociated carboxylate groups for 3 et al. , and the catalysis of OH − ions with autoretarded kinetics for pH > 11. In the range of neutral pH, the observed kinetics cannot be simply explained by the superposition of these two mechanisms. Nevertheless, some empirical laws can be established from experimental data. A simulation based on a Monte Carlo method is proposed in order to predict the hydrolysis of these copolymers in different conditions.

Hydrophobically end-capped poly (ethylene oxide) urethanes: 1. Characterization and experimental study of their association in aqueous solution

Abstract Three hydrophobically end-capped poly (ethylene oxide) urethanes have been characterized carefully by n.m.r., size exclusion chromatography (s.e.c.) and light scattering in tetrahydrofuran. Their associative behaviour in aqueous solutions has been studied by several techniques. Hydrophobic substance solubilization and surface tension measurements have shown the formation of hydrophobic microdomains above a critical concentration; s.e.c., light scattering and viscometry have allowed us to determine the molecular weights and dimensions of the aggregates. Slight differences in the hydrophilic-lipophilic balance may induce large discrepancies in the associative behaviour but it remains difficult to determine the exact role played by the chemical nature of the hydrophobic moieties.

Microstructure of acrylamide-acrylic acid copolymers: 1. As obtained by alkaline hydrolysis

Abstract Kinetics of alkaline hydrolysis of high molecular weight commercial polyacrylamide were studied by two different methods proposed by Fuoss and Higuchi. Compositional triad distributions and cotacticity parameters are determined from results obtained by 13C (1H) nuclear magnetic resonance of carbonyl and methine resonance patterns of partially hydrolysed polyacrylamides. It is established that acrylate monomers tend to occur as isolated groups along the molecular chain but it is not possible to assert whether there is racemization or not during the reaction.

Hydrophobically end-capped polyethylene-oxide urethanes: 2. Modelling their association in water

Abstract Associative thickeners of the end-capped polyethyleneoxide urethane type are well known to form aggregates in aqueous solutions but there is a lack of studies dealing with the determination of the association mechanisms and with the size and form of these aggregates. We show for a given example that a combination of light scattering and viscosity experiments may produce a rather good description of these phenomena by interpreting them through theories of association and models of branched polymers. It is concluded that the aggregates look like statistically branched polymers, the junction points being formed by the association of approximately four hydrophobic chain ends.

Spectroscopic study (u.v.-visible and electron paramagnetic resonance) of the interactions between synthetic polycarboxylates and copper ions

The interactions of poly(methacrylic acid) (PMA), poly(acrylic acid) (PAA) and a copolymer of acrylamide and acrylic acid (CAMAA) with copper (II) ions in aqueous solutions were studied by electron paramagnetic resonance (e.p.r.) spectroscopy as a function of the degree of neutralization cr. A procedure for decomposition of the e.p.r. spectra was developed in order to evaluate the fraction of free copper and bound copper ions. When a loss of the e.p.r. signal intensity is observed in the solutions containing polymer with respect to the one of the reference copper salt solutions without polymer, this effect is attributed to the formation of a binuclear polymer/copper complex (copper: carboxylates, 2/4), inactive in e.p.r. The complex visible in e.p.r, is assumed to be mononuclear (copper: carboxylates, 1/2). This indicates that the main PMA/copper complex is binuclear. PAA and copper interactions lead to both bi-and mono-nuclear complexes, but this last species is preponderant at the higher ct values. In the case of CAMAA of lower charge density and where the charges are quenched, only a mononuclear complex was found. The constants of formation of the mono-and bi-nuclear complexes were evaluated by assuming that the system was ruled by a series of equilibrium laws: copper hydrolysis, polymer ionization and polymer/copper complexation. The peculiar behaviour for PAA may be explained by considering that the constant of formation for the binuclear complex decreases when the intramolecular monomer concentration is lowered by the chain expansion

Properties of ethylene oxide-propylene oxide statistical copolymers in aqueous solution

Abstract This paper presents a thermodynamic study of aqueous solutions of ethylene oxide-propylene oxide statistical copolymers. In a first step, copolymer samples are carefully characterized by elemental analysis, 1 H and 13 C nuclear magnetic resonance, gel chromatography and light scattering. Secondly, the lower critical solution temperature is studied as a function of copolymer composition and concentration. This phase separation behaviour as well as the temperature dependences of intrinsic viscosity, second virial coefficient, Flory interaction parameter χ and partial specific volume are discussed in the background of different polymer theories.

Interactions between partially hydrolyzed polyacrylamide and ionic surfactants

Abstract We have studied the micellar properties of the surfactant and also the polymer conformation in a mixture of sodium dodecyl sulphate or dodecylbenzene sulphonate and partially hydrolysed polyacrylamide. The results are interpreted in terms of electrostatic interactions and by taking into account the site binding of the counter-ions either on the polyions or onto the micelles.

Relation between physical gelation and tacticity in polystyrene

Abstract In order to throw some light on the physical gelation of polystyrene in solution, we have prepared samples of differing tacticities by means of epimerization of an isotactic sample. After careful characterization by 1H nuclear magnetic resonance, light scattering, viscometry and gel permeation chromatography, the gelation propensity has been studied by differential scanning calorimetry and the ball-drop method in carbon disulphide (CS2) and in diethyl malonate. For a fraction of isotactic triads higher than 58%, gelation characteristics remain those of isotactic polystyrene. Between 58 and 35%, no gelation occurs whatsoever. Below 30%, the gelation characteristics of atactic polystyrene are retrieved only in CS2. The main conclusion is that the gelation phenomenon in atactic polystyrene in CS2 is due to the syndiotactic sequences.

Effect of additives on solution properties of ethylene oxide-propylene oxide statistical copolymers

Abstract In this paper, the effect of different additives on the solubility and intrinsic viscosity [η] of ethylene oxide-propylene oxide statistical copolymers in water is studied. In the case of mineral additives, the order of ‘salting out’ is the same as for ethylene oxide homopolymer. If one excepts the case of sodium iodide, the variations of the viscosimetric expansion can be plotted on the same curve as a function of reduced temperature for different salts. Organic additives have an increasing or decreasing effect on the lower critical temperature (LCST′) of the copolymers according to their polarity. The relation between the variations of [η] and LCST′ is much more complex than for mineral additives since [η] at a given temperature depends on the free energy of mixing of the two solvents.

Interactions between aluminium ions and acrylic acid-acrylamide copolymers in aqueous solution: 2. Phase separation

Abstract The stability of aqueous solutions of acrylic acid-acrylamide copolymers (with acrylate content τ varying from 0.3 to 27%) towards Al species has been investigated at different pH values. In our previous work, an electrostatic interaction model was proposed which predicted first that the polymer stability is at a minimum at pH 5 (due to the presence of Al polycations) and secondly that there is no interaction between polymer and Al at pH 7 (due to the presence of non-ionic Al(OH)3 species). The second prediction is incorrect and phase diagrams were established at pH 5 as well as at pH 7, and allowed us to determine: (a) the critical concentration C∗ a of the Al (for which polymer precipitation occurs) as a function of polymer concentration and (b) the C∗ a dependence on τ. The fraction of precipitated polymer was evaluated using two techniques (potentiometric titration of the supernatant and carbon titration in the precipitated phase). This was compared, at low pH (≤5) with the calculated results of the electrostatic interaction model. An interesting result was the finding of gel formation at pH 5, for one of our polymer samples in the presence of Al.