I. Hernández-Fuentes

Influence of the electropolymerization parameters on the generation of polyfurane perchlorate doped films

Chemical and electrochemical parameters have been modified in the potentiostatic electropolymerization of polyfurane films doped with perchlorated anions (PFuClO4) in order to systematize the formation of this conducting polyaromatic compound in aprotic media. The study revealed a strong correlation between the electrochemical generation of black, adherent, ordered and conducting PFuClO4 films and the applied overpotential. Moreover, dopant concentration must be equal to or lower than monomer concentration due to the inhibition effect of the ClO4− anion.

Network defects in polyacrylamide gels

The weight conversion at the gel point (αGw) was determined by the gas bubble method in two sets of polyacrylamide (PAA) gels crosslinked with N,N′-methylene-bisacrylamide (BA). αGw remained practically constant when the crosslinker ratio was C = 10% (w/w) and the total concentration of comonomers in the feed ranged from CT = 5 to 10 g/100 ml. When CT was kept constant at 5 g/100 ml and C changed from 0 to 25% (w/w), αGw showed a minimum at C = 7%. By comparing the experimental values of αGw with those calculated for an ideal network, it was concluded that the crosslinking efficiency of BA is very low. The dependence on C of αGw and other properties like the elastic phantom modulus, |ƒph∗|, and the polymer volume fraction at swelling equilibrium, v2so, was explained in terms of the formation of network defects: the formation of BA sequences longer than unity and that of intramolecular cycles both have an increasing contribution at C > 7% but can be neglected at lower values of C.

Polyacrylamide networks. sequence distribution of crosslinker

The crosslinking copolymerization of acrylamide (AA) and N,N′-methylene-bis-acrylamide (BA) has been studied by high resolution 1H-NMR with copolymerization in situ. This procedure allows calculation of the copolymer composition at zero degree of conversion and as a function of the polymerization time. Monomer reactivity ratios were calculated by the Kelen-Tudos method in the pre-gel state and during gelation. Sequence distributions of both comonomers were then characterized.

Polyacrylamide gels. Process of network formation

Abstract This paper refers to the crosslinking copolymerization of acrylamide (AA or monomer-1) and N,N′-methylene-bisacrylamide (BA or monomer-2) in aqueous solution at 22°, covering a broad range of comonomer concentrations. The extent of reaction, pT, the composition of the remaining comonomer mixture, f2, and the copolymer composition, F2, have been determined by high resolution 1H-NMR with polymerization in situ. The non-linear regression fit of f2 as a function of pT yields almost the same values for the reactivity ratios for any of the studied comonomers feeds. The instant copolymer composition changes with the copolymerization time due to a shift in the residual comonomer composition and, to a smaller extent, to changes in the comonomer relative reactivities. This effect contributes to the heterogeneity of the final network.

Polyacrylamide networks. Kinetic and structural studies by high field 1H-NMR with polymerization in situ

Abstract The crosslinking polymerization of acrylamide (AA) and N,N′-methylene-bis-acrylamide (BA) in aqueous solution at 22°C has been studied by H.R. 1H-NMR spectroscopy. The initial comonomer mixture was placed inside the NMR spectrometer probe head and the polymerization was followed for 10 hr. This procedure allows measurement of the instant composition of the residual comonomer mixture even during and after gelation and therefore to calculate the composition of the formed copolymer or network. When the reaction was finished, the structure of the most mobile part of the network was also analyzed.

Limits of the dilute regime for the solution viscosity of PMMA in good and in poor solvents

Abstract The concentration ( c ′) marking the first deviation from linearity in the Huggins plot of specific viscosity η sp / c vs c ) has been determined for PMMA in chloroform, benzene (good solvents), acetonitrile, chlorobutane (poor solvents) and acetonitrile/chlorobutane mixtures (cosolvent). The dependence of c ′ on polymer chain length and on solvent quality is given. The results are analysed in terms of the influence on c ′ of incipient coil overlap, peripheral entanglements and other interactions, such as polymer association.

Preparation and conformational analysis of severely hindered β-diketones. Dipole moment determinations and theoretical calculations.

Abstract Several β-diketones bearing bulky substituents at the intercarbonyl positions have been prepared by alkylation of the cobalt(II) complexes of the unsubstituted diketones. Agreement between experimental and calculated dipole moments is fairly good thus rendering Molecular Mechanics a safe tool for the conformational analysis of the title molecules. The most populated conformations have been evaluated for nine ϱ-diketones bearing 1- and 2- adamantyl, tert -butyl, cyclohexyl, 1-phenylethyl and benzhydryl groups as well as two methyl groups and one methyl plus one 1-adamantyl groups.

Partial specific volume and specific refractive index increment of some poly(carbonate)s and poly(thiocarbonate)s

Abstract Partial specific volume and specific refractive index increment of a series of poly(thiocarbonate)s and poly(carbonate)s were determined by densimetry and refractometry measurements, in benzene and/or 1,4-dioxane. The effect of the size and nature of the side groups on partial specific volume is analyzed. Poly(thiocarbonate) with a phenyl side group exhibits a more contracted state than the alkyl substituted poly(thiocarbonate)s. The value of the refractive index increment of poly(carbonate)s and poly(thiocarbonate)s carrying the same side group show similar values.

Partial specific volume of hyaluronic acid in different media and conditions

Density measurements of hyaluronic acid in different media and conditions have been made in order to determine the partial specific volumes, v0(2). We have studied the effects of temperature, type of cation, cation concentration, pH and solvent polarity on v0(2).

Cosolvency, coil expansion and dimensions of PMMA in mixed solvents

Abstract Limiting viscosity numbers ([ν]) and Schulz-Blaschke constants ( k s ) of PMMA samples (differing in molecular weight) have been determined at 25°C (as a function of mixed solvent composition) for the following mixtures: acetonitrile+1-butanol, acetonitrile+pentyl acetate, and 1-chlorobutane+pentyl acetate. The first two mixtures are powerful cosolvents of PMMA and the third one is a ‘co-nonsolvent’ of the polymer. The samples are predominantly heterotactic. Their k s values at θ indicate some association tendency of the polymer. Unperturbed dimensions and coil expansion coefficients have been obtained from [ν], as a function of solvent mixture composition. All the pure liquids are poor or non-solvents of PMMA (at 25°C), but the cosolvent pairs behave as very good solvents for the polymer. The mechanism of such cosolvency is analysed in terms of the different molecular interactions present in these systems.