Huceste Çatalgil-Giz

In situ photon transmission technique for studying ageing in acrylamide gels due to multiple swelling

Abstract In situ photon transmission experiments were performed using an ultra-violet-visible (u.v.-vis) spectrometer during the multiple swelling of polyacrylamide (PAAm) gel in water. The transmitted light intensity, Itr decreased continuously as the PAAm gel swelled. The decrease in Itr was attributed to the increase in scattered light intensity which might have orginated from the contrast between ‘frozen blob clusters’ and holes in the swollen gel. It was observed that the correlation length, ξc, increased by 1 4 power of the swelling time. The sudden increase in the gel relaxation time, τ, was attributed to the rupture of the network structure after the eight swelling step during multiple swelling of the PAAm gel.

Electrochemically prepared acrylamide/N, N'-methylene bisacrylamide gels

Acrylamide/N,N′-methylene bisacrylamide gels were synthesized electrochemically at room temperature in the presence of an initiator only, without using chemical activator. Various electrode systems were examined and silver was chosen as a working electrode material. Working conditions were determined and the effect of bisacrylamide concentration and electrode voltage on gelation times was examined.

A New Model for the Evolution of the Molecular Weight Distribution of Polymers During Ultrasonic Chain Scission

A new model for ultrasonic scission of polymer chains has been developed. The model takes the coiled nature of the polymer chains into consideration. The time evolution of the molecular weight distribution for several values of the solvent quality parameter is obtained using the new model. It is seen that the model leads to higher scission rates and lower final molecular weights for better solvents in accord with the experiments. Simulated gel permeation chromatography results are also in line with the experiments.

Block Copolymer Synthesis and Chain Extension from TEMPO-Terminated Chains Formed by Ultrasonic Chain Scission

Long poly(ethyl methacrylate) (Mn 5 2,300,000) and polystyrene (Mn 5 1,200,000) chains were subjected to ultrasonic scission in the presence of a radical scavenger, 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO). This procedure yielded poly- mers with lower molecular weights and TEMPO terminal units. Application of these polymers in stable radical mediated polymerization of styrene resulted in chain exten- sion and block copolymers, depending on the precursor polymer. Block copolymer formation was evidenced by NMR measurement, and chain extension was shown by GPC analysis.

Statistical group transfer copolymerization. Monomer reactivity ratios for allyl methacrylate and n-butyl methacrylate

Abstract Statistical copolymerizations have been performed for allyl methacrylate-butyl methacrylate systems using 1-methoxy-2-methyl-1-trimethylsilyloxypropene (initiator) and tris (dimethylamino) sulphonium bifluoride (catalyst) in tetrahydrofuran solution. Soluble allyl copolymers have been obtained by this method. The copolymer compositions were determined by ultraviolet spectroscopy and the results evaluated by the Kelen-Tudos and Fineman-Ross methods. The reactivity ratios were found to be r AMA = 2.35, r BMA = 0.08 (Kelen-Tudos) and r AMA = 2.37, r BMA = 0.08 (Fineman-Ross).

Automatic, simultaneous determination of differential refractive index of a polymer and its corresponding monomer

The differential refractive index (dn/dc) of a polymer/ solvent pair is an important parameter in situations involving refractometric concentration determination, light scattering determinations of absolute molar mass, and so forth. It is well known that the dn/dc can be different for a polymer and its corresponding monomer. In this Note we present a rapid and accurate means of simultaneously determining the dn/dc for a monomer and a polymer and apply it to the case of acrylamide/polyacrylamide. Our motivation for developing this technique, instead of simply making separate determinations of dn/dc for the monomer and then the polymer, was based on concerns about the hygroscopic nature of the polyacrylamide (PAAm): PAAm normally contains 10–15% water by mass, and this is difficult to remove entirely and reliably. On the other hand, AAm is far less hygroscopic, so that if one commences with an accurate concentration of AAm in a polymerization reaction the concentration of AAm plus PAAm throughout the chain-growth polymerization reaction will remain constant; thus, the problem of an unknown amount of PAAm hydration starting from a “dry” powder is avoided. The technique involves continuous measurement of the monomer and total monomer/polymer concentration while the polymerization of the monomer proceeds. This method will be useful whenever detectors can be found that can distinguish between the concentration of the monomer and polymer, and the polymer can be produced in a homogeneous monomer/solvent system. A refractometric detector (RI) detects both the monomer and polymer. In the monomers with double bonds or conjugation, such as AAm, there is a strong ultraviolet absorbance that is lost upon polymerization. This allows an ultraviolet spectrophotometer (UV) to monitor the disappearance of the monomer during a polymerization reaction. Another possible scheme for distinguishing the monomer from the polymer is via evaporative light scattering, in which the monomer and solvent can be stripped via passage through a heated drift tube from droplets containing the monomer, solvent, and polymer. Any standard chromatography pump can be used to deliver reacting liquid to the detectors. RI and UV detectors and a chromatography pump are standard devices in polymer characterization laboratories, so application of this technique will not normally require any investment in additional equipment.

Dielectric spectroscopy study of EMA-EGDM crosslinking system at sol-gel transition

Ethyl methacrylate, ethylene glycol dimethacrylate free radical crosslinking co-polymerization reaction is studied by dielectric spectroscopy at various temperatures. A maximum in the dielectric constant was observed during the gelation reaction. At the same point, the dielectric loss switched from a linear decrease to a relatively constant behavior. Parallel experiments, performed with a magnetic stirrer, showed that this maximum is consistent with the gel-point. In the ethyl methacrylate homopolymerization reactions the dielectric constant did not go through a maximum but decreased monotonically. The evolution of the dielectric constant is found to depend on the extent of the reaction, but not on time and temperature separately.

Dielectric investigation of the sol-gel transition in the acrylamide/N,N′ methylenebisacrylamide system

The acrylamide/N,N′-methylenebisacrylamide gelation process was studied by time dependent measurement of real ϵI and imaginary ϵII parts of the complex dielectric permittivity. The measurements were carried out in the frequency interval 500 Hz to 13 MHz. Strong relaxation behavior of ϵI and ϵII was observed in all dielectric spectra during the transformation from the sol to the gel state. At all frequencies a maximum in the imaginary part of dielectric constant ϵII was observed. The gel point was found by extrapolating this maximum to zero frequency. The behavior of ϵI and ϵII related to the gelation mechanism is discussed.

Preconcentration of copper ion in aqueous phase on methacrylate polymers

Copper was preconcentrated from aqueous solutions by adsorption on polymethyl methacrylate, polymethacrylonitrile, and their copolymers prepared by group transfer polymerization. Atomic absorption spectrometry was used to determine the metal ion. The copper (II) ion was collected from aqueous solutions starting from pH 2. In both homopolymers and copolymers, an increase of retention starting from pH 2 to 7 was observed. Below pH 2, no retention was observed. The retention of the ion from the aqueous phase on the polymers was above 90% at pH 7.

Ultrasonic Chain Scission of Polyacrylamide in Solution: Online Monitoring Results and Comparison with Theoretical Models

Abstract Ultrasonic processing of a water soluble polymer, polyacrylamide, is investigated and molecular weight evolution during ultrasonic degradation was monitored online by light scattering and viscometry. The resulting Data were compared to various theoretical models. Initially the scission was very rapid but as the limiting molecular weight was approached it slowed down. This slowing down was too pronounced to be described by a first order model. Only the Giz, Ovenall/Harrington/Madras and Tang models, adequately accounted for this slowing down and gave good fits to the data.