des Hyperfrequences et des Semi-conducteurs US JL -59655 a-(Triethy1ammonio)alkane-a-sulfonates (H,C,),N ' -(CH,),-SO,-( n = 2-4), pyridinio-, 2,6-lutidin ioand Nmet hyl imidazol i n iopropa nesu If onates, and triet hylammon ioa I koxydicya noet henolates (H,C,),N'-(CH,),-0-CO-C-(CN),(n = 2, 3) have been studied by dielectric measurements (1 M Hz-1 GHz) in dilute aqueous or trifluoroethanol solution. Their intercharge distances have been derived from their dipole moments ( p in the range 18-30 D) calculated according to Buckingham's theory, and compared with the maximum and minimum intercharge distances estimated by molecular mechanics for the ideal fully extended and ion-pair conformations respectively. For identical tether length, stronger charge delocalization in the cationic (imidazolinium versus pyridinium) or anionic (dicyanoethenolate versus sulfonate) sites slightly increases the intercharge distance, while better specific solvation of the zwitterions by hydrogen bonding in the less dissociating trifluoroethanol does not result in any significant conformational change with respect t o aqueous solutions. Folding of the intercharge arm, negligible for 2-(triethy1ammonio)ethane-1 -sulfonate, progressively increases with its length, but the ion-pair conformation, where the intercharge distance becomes rapidly insensitive to the tether length, is never reached. This behaviour is in good agreement with the variations of the apparent ApK, values of the zwitterions (normalized to that of n-C,H,SO,H) measured by potentiometry in acetic anhydride-acetic acid (9:1, v/v) solution.4 (R = hexyl). In the present work, we focus our attention mainly on the calculation of the dipole moment from dielectric measurements in polar solvents for two series of low molecular weight zwitterionic species chosen as model compounds for the corresponding polymers of current interest in our laboratory: 8 , ' hydrophilic ammoniosulfobetaines studied in water and in trifluoroethanol (TFE) and hydrophobic ammonio-a1 kox ydicyanoe thenola tes studied in TFE solution. AmmoniosuifobetainesArnmonioal koxydicyanoethenolates n = 2; Et3N-CN3 t~ = 3; EtaN-CN4 O"\CH, n = 3; Py-s3 eN+-(CHJ1-S03-n =3;Lu-s3 \ CH3Critical comparison of the experimental data within these two series may afford useful information on a number of major factors controlling the characteristic zwitterion intercharge distance such as: steric hindrance and polarizability of the * 1 cal = 4.184 J.

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Linear triblock dimethyls iloxane-ethylene oxide PDMS-PEO-PDMS copolymers have been synthesized by hydrosilation polycondensation of a, -diallylpoly(ethylene oxide) (Mn = 6 X 10s and 10 X 103) and a,o!-dihydro(polydimethylsiloxane) (Mn = (1-4.5) X 103). Studies by dilatometry, differential scanning calorimetry, and X-ray scattering have shown that the copolymers are characterized by a periodic organization in lamellae or hexagonal cylindrical structures according to composition. PEO crystallizes within its own domains, with specific features such as a lower degree of crystallinity, a lower melting point with respect to that of the PEO precursor, and crystallinity independent of thermal conditions. Gas chromatography has allowed a semiquantitative estimation of the xpdms-peo interaction parameter and its dependence on temperature and composition. The values in the range 0.4-1.1 are in good agreement with the high incompatibility of the PDMS and PEO chains.

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Water sorption by amorphous (meth)acrylic poly(zwitterions)‐bearing quaternary ammonioalkoxydicyanoethenolate side groups , dipole moment μ(D) = 25.9 and 30.8 for p = 2 and 3, respectively was studied at 23°C over a broad range of water activity a (0.14–0.98). Water diffusion is nearly Fickian (Ds = 5.9 10−7 cm2.s−1 for a = 0.63) and the sorption isotherms may be quantitatively analyzed according to the Guggenheim‐Anderson‐De Boer equation for a multilayer process characterized by a number of site‐bound water molecules per monomeric unit, nm ⋑ 0.7. The Flory χ interaction parameter is a strongly increasing function of the water content in the glassy hydrated systems and it always remains higher than 0.75. Clustering of water molecules (Zimm‐Lundberg theory) is never observed. Differential scanning calorimetry allows to quantify nonfreezable bound water (type I) of strong plasticization efficiency, n(I) = 2.8 mol. of water per monomeric unit, and it points out the quasisimultaneous emergence of low amounts of freezable bound water (type II) crystallizing at −40°C and melting at −1°C and of bulkfree water (type III, n(II)/n(III) ⋑ 0.1). All these typical features distinguish these rather hydrophobic poly(zwitterions) from their hydrophilic homologues of the quaternary ammoniopropanesulfonate type . © 1995 John Wiley & Sons, Inc.