Eve Marchal

Poly(sulphopropylbetaines): 3. Bulk properties

The bulk properties of a series of five atactic aliphatic and aromatic poly(sulphopropylbetaines) have been studied by u.v. and broad line n.m.r. spectroscopy, differential scanning calorimetry (d.s.c.), X-ray scattering (WAXS, SAXS) and thermally stimulated depolarization currents (t.s.d.c.). The high density in dipolar units N+(CH2)3SO−3 affords a number of specific properties to these poly(zwitterions): very high glass transition temperatures (d.s.c., n.m.r.); (ii) a strong polarity typified by an apparent local dipole moment of about 5.5 D (u.v.) and a dielectric increment at Tg > 1 × 102 (t.s.d.c.); (iii) the ability to dissolve LiClO4 in stoichiometric amounts to yield amorphous microphase separated blends (WAXS, SAXS) without much change in chain dynamics (slight increase in Tg and in n.m.r. linewidth); (iv) a very high affinity for water which behaves as a very efficient plasticizer with 6.5 moles of ‘unfreezable bound water’ per monomeric unit.

Poly(ammonioalkanesulfonate) Blends with Polar Organic Species and Alkali Metal Salts: Structure, Glass Transition and Ionic Conductivity

Because the dipole moment of its zwitterionic side group is very high (μ∼23 D), poly[3-(N,N-diethyl-N-(5-methacryloyoxy-3-oxopentyl)-ammonio) propanesulfonate] affords a unique polar host matrix possessing a strong solvation power towards a variety of polar or ionic guest species. Water, glycerol, liquid ethylammonium nitrate, triethylammoniopropanesulfonate are all good plasticizers with a fairly similar efficiency of ΔTg∼−2°C/mol% of additive, while a dizwitterion behaves as a weak antiplasticizer. The stoichiometric blends of the polyzwitterion with alkali metal salts of low enough lattice energy such as thiocyanates, trifuoromethanesulfonates, iodides, perchlorates, tetrafluoro or tetraphenylborates, are amorphous systems showing a single glass transition, with plasticization or antiplasticization effects depending on the salt nature. Microphase separation systematically occurs in these binary systems but long-range order is observed only in some cases, with development of lamellar (I−) or hexagonal (SCN−) structures. Conductivity increases and the dielectric constant of the material decreases as salt is added. The activation energies of the conductivity are not strongly affected either by the state of the material, glassy or viscoelastic, or by the salt nature.

Thermally stimulated depolarization currents used in the study of chemical relaxation

Abstract An equilibrium reaction between two species, A and B, which carry different dipole moments can give a specific peak in thermally stimulated depolarization current (TSDC) diagrams of solids if the orientation of B is slow with respect to the chemical reaction. The expression for the current is derived: dipole moments and the thermodynamic kinetic parameters can be obtained from the TSDC relative to the chemical reaction and that due to dipolar disorientation. An experimental illustration is given for an aromatic poly(sulphopropylbetaine) in which a thermally induced conformational change of the zwitterionic group is observed: using three approximations, the dipole moment μ ≈ 12 D in the low T curled conformation and μ ≈ 23 D in the extended conformation. The rate constants of the forward and back reactions are determined as a function of temperature.

Thermally stimulated depolarization currents: A new analysis and significance of the compensation law

The model introduced by Ngai to predict the relaxation behavior of condensed matter is used here to derive the expression of thermally stimulated depolarization currents (TSDC). This is done via Ngai’s second universality equation and by assuming that the stretching index β is temperature dependent. The four parameters involved in the model can, in principle, be determined from TSDC data. Two parameters are determined for polyisoprene below its glass transition temperature Tg. Furthermore, expressing that a compensation law holds for the α relaxation of polymers around Tg, the variation of β with T is given. This relation leads to a Williams–Landel–Ferry‐type expression of the macroscopic relaxation time near and above Tg, a well‐known experimental observation, and gives a strong support in favor of the model.

Intramolecular dipolar coupling enhancement of the first-order molecular hyperpolarizability in a polar solvent

Abstract The effect of intramolecular coupling on the first-order molecular hyperpolarizability in a bis-chromophoric system was theoretically and experimentally investigated. According to finite-field calculations using AM 1 parameters, the effective hyperpolarizability of a bis-chromophore is essentially a vectorial addition of that of the corresponding monomers. However, the EFISH-derived effective hyperpolarizabilities of the bis-chromophores do not follow the additive model. Interestingly, the effective hyperpolarizabilities of the bis-chromophores are significantly enhanced as the solvent polarity increases, which is not observed in those of the corresponding monomeric counterparts.

A new way of interpreting thermally stimulated depolarization currents of polymers using the coupling model in a broad temperature range

Abstract A recently published analysis [E. Marchal, J. Chem Phys. 96 (1992) 4676] of thermally stimulated depolarization currents using the coupling model of Ngais group is extended by introducing a continuous time or temperature-dependent change of origin of time while keeping the parameters of the model constant. This allows non-linearity to be addressed in a coherent way. A clear significance appears for the compensation law when fractional polarization is carried out for the α-process related to the glass transition. Using the values of the parameters of the model determined from dynamical measurements, a test of the model is enabled. Above the glass transition, the same procedure is used. This provides an alternative way of expressing the Williams-Landel-Ferry behviour, and has the advantage of avoiding any discontinuity. Finally, at the compensation temperature reported for conductivity measurements the relaxation function is an exponential in the light of the above scheme and conforms to the prediction of the model.

Combined isothermal and thermally stimulated depolarization measurements in polymers interpreted with the modified coupling model of relaxation

In Ngai’s coupling model, the relaxation rate of bulk amorphous polymers has a power law time dependence which can be measured by isothermal depolarization. We propose a method by which the time needed for one experiment is considerably shortened without loss of information. At temperatures below and above the liquid glass transition we have previously modified Ngai’s model by introducing a parameter t′ which replaces the physical time, while the other parameters of the model are constant. The above experimental method can be used to probe the hypothesis. This is illustrated for an amorphous poly(ethyleneterephtalate) sample studied below Tg. Above Tg the thermally stimulated depolarization current was analyzed for polystyrene. At the α−β bifurcation temperature it appears that t′=t.

Thermally stimulated depolarization currents of polymers: a new analysis and significance of the compensation law

The model introduced by K.L. Ngai to predict the relaxation behavior of condensed matter is used to derive the expression of thermally stimulated depolarization currents. A test to probe a possible common origin of two relaxation processes is suggested. Furthermore, physical aging is qualitatively taken into account. The compensation law then appears as a consequence of the variation with T of the stretching index n of the model.<<ETX>>

High dielectric constant values in some polyampholytes as observed by thermally stimulated depolarization

Thermally stimulated depolarization currents of three aromatic and three aliphatic poly(sulphopropylbetaines) are described in the range −190 to +180°C. No particular relaxation common to all six polymers due to the presence of the zwitterionic group is revealed at low temperatures. A peak in the 100–170°C region occurs for all the samples. It is related to a glass transition in two cases. Very high dielectric constant increments, Δε > 100, are obtained for this peak in four cases. For these hygroscopic polymers water acts as a plasticizer for this peak without changing Δε.

Interpretation of thermally stimulated depolarization currents using a modification of the coupling model

Thermally stimulated depolarization currents are analyzed in the framework of Ngais coupling model modified by introducing a continuous time-or temperature dependent change of the origin of time while keeping the parameters of the model constant in the whole temperature range. There is no need to define the glass transition temperature. The relaxation time at the compensation temperature can be calculated. Furthermore the analysis gives an explanation for the /spl alpha/-/spl beta/ bifurcation. The few available results are consistent with the scheme but there is a need for more experimental work to know how universal the formalism is.