Arturo Horta

Synthesis and solution properties of comb-like poly(mono-n-alkyl-itaconates): 2. Poly(monododecyl itaconate)

Abstract The monoester of itaconic acid with n-dodecyl alcohol was synthesized and polymerized. Polymer fractions were characterized by viscometry, size exclusion chromatography (s.e.c.) and light scattering. Thermodynamic and dimensional parameters were determined and calculated. The results found are 67 A for the statistical segment length l and 8 A for the chain diameter d . These results are compared with those reported previously for a similar compound.

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.

Direct estimation of the true Mark-Houwink-Sakurada parameters from gel permeation chromatography, intrinsic viscosity and one average of molecular weight

A method is described for the simultaneous determination of the true constants in the Mark-Houwink viscosity equation and the absolute calibration of gel permeation chromatography data. In this method, polydisperse samples can be used. The experimental data required on each sample are its gel permeation chromatogram, its intrinsic viscosity and one average of molecular weight, Mw or Mn. The method does not require any calibration curve for another polymer (e.g. polystyrene monodisperse standards). The method is applied to the system poly(N-vinyl-3,6-dibromocarbazole) in tetrahydrofuran at 25°C. The procedure may be especially useful in those cases in which, due to the existence of secondary exclusion mechanisms resulting from polymer-stationary phase or polymer-solvent interactions, the hydrodynamic volume universal calibration concept is not valid.

The pH inside a swollen polyelectrolyte gel: poly(N-vinylimidazole).

The pH inside a dissolved polyelectrolyte coil or a swollen ionic polymer network is not accessible to direct measurement. It is here calculated through a simple model, based on Donnan equilibrium, counterion condensation (for charge density exceeding the critical value), and balance of mobile ions, without any assumption on the pKa of the ionizable groups. The data needed for the calculation with this model are polymer concentration, pH value in the initial solution, and pH value in the bath at equilibrium. All three can be determined experimentally by a batch method where the polymer is immersed in a different pot for each starting pH. The model is applied to a sample system, namely, chemically cross-linked poly(N-vinylimidazole) immersed in acidic baths of different pH values. The imidazole units are basic and become protonated by the acid, thus changing the pH of the initial bath. The model shows how the pH developed inside the swollen gel is several units higher than the pH of the bath at equilibrium, both with or without the correction for counterion condensation. Consequently, when the pKa of the polyelectrolyte is determined in the usual way (with the pH measured in the external bath), it gives an apparent value that is several units below the pKa determined from the actual pH inside the swollen gel at equilibrium. The inclusion of the counterion condensation decreases very slightly the polymer basicity. Surface effects and intramolecular association between protonated and unprotonated imidazole rings are discussed to explain the pKa behavior in the limit of low degree of ionization.

Synthesis, solution properties, and chain flexibility of poly (methyl dodecyl itaconate)

Abstract The dilute solution behavior of poly(methyl dodecyl itaconate) (PMeDoI) has been studied in THF and n-butanol at 298 K, by intrinsic viscosity, light scattering, and size-exclusion chromatography (SEC) measurements. The Kuhn-Mark-Houwink-Sakurada relationships were established. The flexibility factors [sgrave] and C∞ and the thermodynamic parameters B were calculated using the Stockmayer-Fixman equation. The A2 and the B values are indicative of the presence of the excluded volume effect. The results obtained are compared with those previously found for poly(mono dodecyl itaconate) (PMDoI) and discussed in terms of specific influence of the free carboxylic group in the poly(monoester).

Depression of the critical temperature in PMMA-cosolvent systems

Abstract A theoretical expression is developed to calculate the critical line of a polymer-mixed solvent system, at the limit of decreasing proportion of one of the solvents. This expression is written in terms of binary interaction parameters, and provides a criterion to predict whether or not the liquid mixture is expected to be a cosolvent of the polymer. The expression should be useful to describe powerful cosolvent systems, and it is applied to calculate the depression of the critical line in the system PMMA-acetonitrile + chlorobutane. Experimental cloud point data are determined on this system and the results are compared with the theory. Other cosolvents of PMMA are discussed.

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.

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.

Polymerization of N,N-dimethylacrylamide in Aerosol OT–water mixtures: from lamellae to segregation

The polymerizable N,N-dimethylacrylamide (DMAA) is added to the lamellar liquid crystalline system formed by the anionic surfactant Aerosol OT and water. Small angle X-ray scattering, gives the same bilayer thickness and hydrophilic group cross-sectional area as without DMAA, and an environment sensitive fluorescent probe indicates that DMAA is likely to be in the water layers between the AOT bilayers. This shows that the structure of the AOT bilayer in the lamellar phase is not affected by DMAA. However, DMAA induces instability of the lamellar phase, and a second phase, an isotropic solution, appears for larger DMAA contents The effect of DMAA in stabilizing this phase with respect to lamellae is much larger than that expected from a simple dilution with water. Furthermore, there is a combined influence of temperature and DMAA concentration on the coexistence of the lamellar and the isotropic phases. When an initiator is added and the monomer polymerizes the tendency to phase separate increases strongly. The lamellar spacing after polymerization is below the value predicted by the global AOT/H2O ratio. This indicates that the polymer segregates from the AOT phase and that the lamellar phase is osmotically compressed by the polymer rich phase