K. Bouchal

Immobilized-metal affinity sorbents based on hydrophilic methacrylate polymers and their interaction with immunoglobulins

Abstract Hydrophilic homogeneous poly[2-(2-hydroxyethoxy)ethyl methacrylate- co -ethylene dimethacrylate] poly(DEGMA- co -EDMA) beads have been prepared as precursors for introducing the chelating groupings of ethylenediaminetriacetic acid, quinolin-8-ol, or N -(2-pyridylmethyl)glycine. The effect of the chelating ligand structure on coordination with Ni 2+ ions and that of the metal complexes on binding the model protein (horseradish-peroxidase-specific immunoglobulin IgG 1 ) was analyzed. It was found that the protein binding affinity and selectivity was the highest for IMA sorbents with quinolin-8-ol groups.

Molecular order and dynamic mechanical behavior of polyurethanes based on liquid crystalline diol

Abstract Synthesis of the liquid crystalline (LC) diol 6,6′-[ethylenebis(l,4-phenylene-oxy)]-dihexanol (I) is described. The structure of polyurethanes prepared from diol I and 4,4′-methylenedi(phenyl isocyanate) (MDI), 4,4′-methylenedi(cyclohexyl isocyanate) (HMDI), or 2(4)-methyl-l,3-phenylene diisocyanate (TDI) at 1:1 molar ratios of isocyanate and hydroxy groups is studied by dynamic mechanical spectroscopy, differential scanning calorimetry (DSC), polarizing microscopy, and x-ray scattering. The polymer prepared from HMDI and the diol (I/HMDI) shows, on cooling, thermal behavior typical of amorphous polymers. A frequency-temperature superposition could be applied to the mechanical data, and the horizontal shift factor satisfied the Williams-Landel-Ferry (WLF) equation. A more-complex thermal behavior was found for I/HMDI polymer during subsequent heating; above 70°C, the formation of an ordered structure takes place, and this structure melts at about 120°C. Complex thermal behavior is exhibited by I/...

Solubility and dynamic mechanical behaviour of polyurethane systems at the critical molar ratio of the reactive groups for gelation and at the gel point

Abstract The dynamic mechanical behaviour of fully cured soluble and insoluble polyurethanes from two poly(oxypropylene)triols and a diisocyanate with initial ratios r H = [OH]/[NCO] from 1.44 to 1.8 were investigated. The dynamic behaviour during the curing reactions of two samples with r H = 1 was also measured. From extraction experiments the critical ratios for gelation r H c of fully cured samples were determined. As expected, both critical gel (CG) samples in which the gel point was reached by changing the conversion exhibit a power-law rheological behaviour. On the other hand, both fully cured CG samples prepared at r H c show a small frequency dependence of the loss tangent so that critical power-law behaviour is not exactly obeyed. New conditions representing critical rheological behaviour are suggested.

Gelation and dynamic mechanical behavior of liquid crystalline networks

Abstract The dynamic mechanical behavior of polyurethane networks based on liquid crystalline (LC) diol, 6,6′-[ethylenebis(1,4-phenyleneoxy)]dihexanol (D), 2(4)-methyl-1,3-phenylene diisocyanate (DI), and poly(oxypropylene)triol (T) at the stoichiometric molar ratio of isocyanate (NCO) and hydroxy (OH) groups was studied. Samples were prepared at various initial molar ratios of the reactive groups [OH]T/[NCO]DI/[OH]D from 1/1/0 to 1/40/39. The gelation studies during the curing reaction in the LC and isotropic states showed that the critical gel structure at the sougel transition exhibits a power-law mechanical behavior; the relaxation exponent in the LC state is always higher than that in the isotropic state. From viscoelastic results, it follows that formation of the LC mesophase enhances the connectivity of the molecular structure at the gel point. Introduction of chemical cross-links in fully cured networks reduces the flexibility of the elastically active network chains (EANCs) and inhibits conformat...

Phase transition in swollen gels: 25. Effect of the anionic comonomer concentration on the first-order phase transition of poly(1-vinyl-2-pyrrolidone) hydrogels

Abstract The swelling and mechanical behavior of ionized networks prepared by radiation polymerization of 1-vinyl-2-pyrrolidone, sodium itaconate and of a crosslinker, 3,3′-ethylidenebis(1-vinyl-2-pyrrolidone), was investigated in water/acetone mixtures and aqueous NaCl solutions. In the molar fraction range of the ionic comonomer xs=0.022–0.15, the first-order phase transition (collapse) was found. The extent of the collapse (stepwise change in the gel volume) and the critical acetone concentration in the mixture at collapse slightly increase with increasing xs. The collapse is accompanied by a stepwise change in equilibrium modulus. The expected decrease in the swelling and increase in the modulus with increasing concentration of NaCl in aqueous solutions were found. The earlier suggested theory describing the swelling equilibrium of polyelectrolyte networks was applied to description of the collapse phenomenon in water/acetone mixtures and swelling in dependence on NaCl concentration; satisfactory agreement was obtained when an effective degree of ionization i (i

Phase transition in swollen gels 24: Effect of the concentration and structure of ionic comonomers on the collapse of poly(acrylamide) hydrogels

Abstract The swelling and mechanical behaviour of ionized networks of copolymers of acrylamide (AAm), methylenebisacrylamide and sodium 2-[(3-carboxypyridine-4-carbonyl)oxy]ethyl methacrylate (PyNa, molar fraction of salt x S =0–0.20) was investigated in water–acetone (w/a) mixtures and in aqueous NaCl solutions. In the range x S ⩾0.01 , a first-order phase transition (collapse) was found in w/a mixtures; with increasing x S , both the critical acetone concentration a c in the mixture at which collapse takes place and the extent of collapse (jump in the swelling ratio X ), Δ log X , increases. A comparison of these results with the results obtained for charged PAAm networks with sodium 2-[(2-carboxybenzoyl)oxy]ethyl methacrylate (BeNa) as ionic comonomer led to a conclusion that substituting benzoyl for pyridyl groups in the side chain slightly decreases Δ log X and the swelling degree in water, and does not change critical a c values. On the other hand, a comparison with charged PAAm networks with sodium methacrylate (MNa) as ionic comonomer showed that at constant x S , the swelling degree in water, the extent of collapse Δ log X and the concentration of elastically active network chains strongly decreased with the increased distance of the bound charge from the main chain (length of the side chain of the ionic comonomer). The expected decrease in the swelling degree of ionized networks with increasing NaCl concentration was found. The experimental swelling data in w/a mixtures and in aqueous NaCl solutions could be described by a theory proposed previously if an effective degree of ionization i is introduced ( i x S ). The mechanical behaviour of gels in w/a mixtures is predominantly determined by the degree of swelling. On the other hand, different dependencies of the reduced modulus on the swelling ratio X found in w/a mixtures and in aqueous NaCl solutions in the high swelling region suggests that contracted gels with different microstructure were formed during gel deswelling in bad solvents or salt in water.

Swelling and photoelastic behaviour of ionized hydrogels of poly(acrylic acid)

SummaryThe photoelastic and swelling behaviour of poly(acrylic acid) gels swollen in 1 M NaCl aqueous solution was studied as a function of crosslinking degree (1–5 wt.% ethylene glycol dimethacrylate) and degree of ionization αg = 0 − 1. The degree of swelling passes through a minimum at αg ≐ − 0.15 regardless of the degree of crosslinking, probably due to the formation of hydrogen bonds between ionized and nonionized carboxyl groups. In the same neutralization region, the equilibrium modulus reaches a maximum; on the other hand, the modulus related to the dry state is independent of α for all crosslinker concentrations. Thus the mechanical behaviour of poly(acrylic acid) gels is in accord with the Gaussian theory and no contribution of permanent physical interactions to the modulus is observed. The optical behaviour is more complex — the sign of the stress-optical coefficient Ce changes three times with increasing α due to the orientation of the side groups. The analysis of the optical data shows that the Ce value is controlled by the degree of swelling and by the ionization.

Dynamic Mechanical Behavior of Ordered Off-Stoichiometric Polyurethane Systems at the Gel Point Threshold

Dynamic mechanical and thermal behavior of ordered off-stoichiometric polyurethane (PU) systems, before and after the gel point, based on the mesogenic diol 6,6′;-[ethylenebis(1,4-phenyleneoxy)]dihexan-1-ol (D),2(4)-methyl-1,3-phenylene diisocyanate (DI), and poly(oxypropylene)triol (T) were studied. Polymer samples were prepared at various initial molar ratios of the reactive groups, r = [OH]T/[NCO]DI/[OH]D, ranging from 1/10/9 to 5/10/9 (the ratio [NCO]DI/[OH]D = 10/9 was constant); the total mole ratio of hydroxy (OH) and isocyanate (NCO) groups, rOH = [OH]/[NCO] = ([OH]D)/[NCO]DI,changed from 1 to 1.4. Dynamic mechanical measurements during the curing reaction showed that the power law parameters that characterize the critical gel state (gel strength S and relaxation exponent n) are dependent on the initial composition (the ratio r OH). The gel-point critical ratio of reactive groups rc OH, found during curing in the ordered state of the diol (at low curing temperature), has revealed that the critical gel (CG) structure is determined by a contribution of strong physical interactions as well as chemical junctions and does not correspond to pure chemical gelation (CG structure formed at low temperature exhibits flow at elevated temperatures in the isotropic state). This fact suggests that formation of the mesophase enhances the connectivity of the molecular structure at the gel point. Dynamic mechanical behavior of fully cured chemical networks (r OH < r OH c ) and un-cross-linked (r OH > r OH c ) samples (and a CG sample) has also been investigated. Decreasing the rOH ratio (increasing concentration of chemical cross-links in the systems) inhibits conformational rearrangements required for ordering; at the same time, the intensity of the slow relaxation process in the rubbery region decreases.