Rosa M. Masegosa

Polymer viscoelasticity : stress and strain in practice

Structure of polymers crystalline and amorphous states in polymers rubber elasticity stress-strain relations for ideal solids and ideal liquids linear viscoelasticity - viscoelastic functions dynamic viscoelastic functions experimental determination of viscoelastic properties viscoelastic behaviour of polymers above the glass-transition retardation and relaxation spectra viscoelastic models molecular models of the viscoelastic polymers viscoelasticity of glassy and semicrystalline polymers flow behaviour of polymer melts and solutions yield crazing and fracture reinforced polymers multiaxial analysis of linear viscoelastic stress flexion and torsion of viscoelastic rods.

Polymethyltrifluoropropylsiloxane: polymer-solvent interaction, solubility and network swelling

Abstract The degree of swelling of polymethyltrifluoropropylsiloxane (PMTFPS) networks and the solubility of the linear polymer have been determined in a variety of solvents (hydrocarbons, halogenated hydrocarbons, ethers, ketones, esters, alcohols, nitriles and nitro compounds) at 25°C, and, in some of them (ethyl acetate (EtOAc), n-butyl acetate (BuOAc), tetrahydrofuran (THF) and butyl chloride (BuCl)), as a function of temperature (range 15–45°C). The polymer-solvent interaction parameter x has been obtained from the degree of swelling, applying Florys elasticity theory: x is practically constant in EtOAc, BuOAc and THF (good solvents), and varies appreciably with T in BuCl (poor solvent). From these x results, Hildebrands solubility parameter for PMTFPS has been obtained as δ=8.8 ( cal cm −3 ) 1 2 . The better solvents are aliphatic ketones and acetates, having -CH2CO- groups in the molecule. All solvents consist of polar molecules. It is argued that the polar trifluoropropyl side chain, being articulated, effectively shields the chain from interactions with the solvent unless the solvent molecules are sufficiently polar.

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.

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.

DYNAMIC-MECHANICAL AND LIGHT SCATTERING STUDY OF THE GLASS TRANSITION OF POLY(VINYLACETATE) AND A POLY(VINYLACETATE) +POLY(4-HYDROXYSTYRENE) BLEND

The dynamics of poly(vinylacetate) (PVAc) and of a blend of PVAc and 20% in weight of poly(4‐hydoxystyrene) have been studied in the glass transition region using dynamic‐mechanical and photon‐correlation spectroscopies. Both kinds of data show the overlapping of the main α relaxation with a faster one. The complex part of the elastic modulus shows the existence of a β’ sub‐Tg transition overlapping with the α one in the high‐frequency region. The light scattering data show some degree of overlapping of the α and β transitions. As a consequence, at least two Kohlraush–Williams–Watts terms are needed to describe the relaxation functions. The results show a good agreement with the predictions of the mode coupling theory except for the fact that the calculated critical temperature seems to be lower than the calorimetric glass transition temperature.

Polystyrene fluorescence in cosolvent mixtures

Abstract Fluorescence of atactic monodisperse and isotactic polystyrenes has been measured in liquid mixtures showing cosolvent behaviour, as a function of the solvent composition. Polymer intrinsic viscosities and solvent liquid viscosities have also been measured as a function of the solvent mixture composition. The ratio of excimer to monomer intensities changes slowly with solvent viscosity and is almost independent of the hydrodynamic volume of the coil. Three alternative mechanisms for intramolecular excimer formation were considered to explain the observed behaviour: (i) energy trapping by preformed dimers, the concentration of which is configuration-dependent; (ii) long-range excimer formation by chain recoiling, whose contribution depends on segment density; and (iii) segmental rotation to the sandwich conformation during the monomer excited-state lifetime, whose probability depends on solvent viscosity. It is concluded that, for atactic polystyrene, the largest contribution comes from the first mechanism, whilst for isotactic polystyrene, segmental rotation appears to be the predominant mechanism. Long-range excimers play a negligible role in the excimer formation process for either tactic form.

Swelling equilibrium and preferential sorption of crosslinked poly(methyl methacrylate) in the mixture acetonitrile + n-butanol

Measurements of preferential sorption,λ(Ν3), determined by refractometry, and swelling equilibrium,Ν3−1, of PMMA networks have been carried out in the cosolvent mixture MeCN+BuOH at 25‡ and 49 ‡C. With an intermediate mixture composition,Ν3−1 passes through a maximum at both temperatures. At 25 ‡C MeCN is preferentially adsorbed by the network over most of the composition range, but a small inversion is detected. At 49 ‡C MeCN is preferentially adsorbed over all the composition range.The behavior of the system crosslinked PMMA/MeCN + BuOH is compared with the results obtained for solutions of linear PMMA in mixtures formed by the same two solvents, MeCN and BuOH.