G. Marchionni

Some physical chemical properties of α–ω dihydroperfluoropolyethers

Abstract This paper describes the physico-chemical characterization and some properties of several α–ω dihydroperfluoropolyethers. Characterization has been carried out on the following properties: vapour pressure, density and viscosity as a function of temperature, glass transition temperature, refractive index and dielectric constant. The boiling point T b and the vaporization enthalpy Δ H v (calculated from vapour pressure data by means of the Clausius–Clapeyron equation) increase with the number of the backbone atoms N ; both T b and Δ H v are higher than the corresponding values for compounds with the non-polar chain end CF 3 and the difference decreases, but does not disappear, when the number of chain atoms is as large as 10–15. The cohesive energy density and the solubility parameter δ are also found to be larger. It is shown that the increase with respect to CF 3 terminated homologues has to be attributed, as expected, to the polar component due to the CF 2 H end group. The p – V – T properties can be predicted through a modified Peng–Robinson equation, where the critical temperature and pressure are obtained by group contributions. The comparison with the experimental data shows that the best group contribution data are those reported by Joback. The density increases and the expansion coefficient decreases with increasing chain length, as expected; at the same chain length the density is lower for materials with a CF 2 H end group; the difference decreases with increasing N . The viscosity also increases with molecular weight; its dependence on temperature is described by the well-known Arrhenius equation. The activation energy is a function of Δ H v , as predicted by the hole theory of Eyring for simple liquids. The glass transition temperatures are very low and depend both on the chain length and on the structure of the compound. While the refractive index is a weak function of chain length and structure, the dielectric constant is a strong function of both variables; a relationship between the dielectric constant and the polar component of the solubility parameter is suggested. Finally the group contributions of the CF 2 H group to the molar volume, vaporization energy, molar refractivity and molar polarizability have been determined, so that these data can be used to predict properties of new molecules.

Solution properties of perfluoropolyether polymers

Abstract Solution properties of fractions of a perfluoropolyether copolymer (PFPE Z) having the structure CF3(OC2)F4)p(OCF2)qOCF3have been studied in two solvents, 1,1,2-trichloro-1,2,2-trifluoroethane (CFC 113) and perfluoroheptane, over a large molecular weight range. Two series of fractions having p/q ratio equal to 0.54 and 1.27 were considered. The fractions, which were characterized by light scattering, vapour pressure osmometry and viscosimetry, were found to be narrow. The coefficients of the Mark Houwink—Sakurada equation, [η] = KMa, were determined for both solvents in the molecular weight range between 8000 and 200 000. CFC 113 turned out to be a theta solvent (the Flory polymer—solvent interaction parameter χ is close to 0.5) while perfluoroheptane behaves as a good solvent (χ = 0.28). The coil expansion factor α3 in perfluoroheptane was also measured. The relationship between the hydrodynamic radius and the molecular weight was determined from dynamic light scattering. Finally, a parameter related to the chain stiffness, the characteristic ratio C∞, was also determined. In the molecular weight range explored it was found that the stiffness is independent of the p/q ratio. PFPE Z polymer has a chain flexibility similar to that of poly(oxyethylene) and larger than that of poly(tetrafluoroethylene).

Thermodynamic and other physical properties of several hydrofluoro-compounds

Abstract Reported here are several physical properties of the following hydrofluoro-compounds: (1) hydrofluoropolyethers (HFPE) of general formulae: HF 2 CO(CF 2 O) n (CF 2 CF 2 O) m CF 2 H; (2) an experimental (HFPE) sample: CH 3 O(CF 2 O) n (CF 2 CF 2 O) m CH 3 ; (3) a linear hydrofluorocarbon (HFC): CF 3 CHFCHFCF 2 CF 3 ; a cyclic HFC: c-CF 2 CF 2 CF 2 CHFCH 2 ; hydrofluoroethers (HFE): C 4 F 9 OCH 3 , C 4 F 9 OC 2 H 5 and C 7 F 15 OC 2 H 5 . The properties of the HFPE series are monotonic functions of molecular weight M . Some of the properties of the HFC and HFE samples differ substantially from the molecular weight dependence shown by the HFPE series, indicating that the overall number and geometry of the H substitution, as well as the molecular geometry of the sample, could perhaps play some role in the control of physical properties.

The viscosity–molecular weight relationships for diolic perfluoropolyethers

Abstract It is shown that for diolic perfluoropolyethers having short chain lengths the “anomalous” (non monotonic) relationship between isothermal melt viscosity and molecular weight, reported in recent papers, is not anomalous at all but fully explainable when one takes into account the fact that the glass transition of the samples Tg is itself a function of the molecular weight. For low molecular weight polymers the viscosities have to be compared not at the same T but at the “normalised” temperature T−Tg.

Structure–Property Relationships in Perfluoropolyethers: A Family of Polymeric Oils

Among the different classes of fluorinated organic molecules the perfluoropolyethers (PFPEs), composed entirely of carbon, fluorine and oxygen, represent a well known family that is of interest to the researcher and the user for the novelty and uniqueness of their chemical and physical properties. PFPEs have therefore become, in the past two decades, very important technically and commercially for a variety of applications, the most diffuse of which is related to their use as high quality lubricants.

Peculiarities of the glass transition temperature of binary polymeric systems: entropic and enthalpic treatments

Abstract The concentration dependence of the glass transition temperature T g of binary polymeric systems, for the Couchman entropic and enthalpic treatments, has been described by taking into account the temperature dependence of the specific-heat increments Δc p ( T ) and presence of a characteristic temperature T o . It is shown that at T o the analytical equations undergo a sudden change. Comparison of the equations obtained with a set of experimental data on the poly(vinyl chloride)-dibutyl phthalate system appears to be satisfactory. The treatment allows one to characterize a binary system with suitable thermodynamic parameters.

Free-radical and ion chemistry of fluoro derivatives : the mechanism of γ-radiolysis of perfluoropolypropene and perfluoropolytrimethylene oxides

Abstract The radiation chemistry of perfluoropolypropene and perfluoropolytrimethylene oxides has been investigated by ESR spectroscopy of the intermediate free radicals and by NMR spectroscopic detection of the major changes occurring in the structure of the oligomers. The major radiolytic products have been related to CC and CO bond scissions and to a minor participation of CF bond cleavage. The results have been rationalized in terms of ionic and free-radical reactions stemming from the formation of primary ether cation-radicals.

Synthesis of low molecular weight perfluoro oxymethylene vinyl ethers

Abstract Perfluoro oxymethylene vinyl ethers have been formed by a multi-step synthesis. The key intermediates are low molecular weight perfluoropolyether (PFPE) fluoroformates CF 3 O(CF 2 O) n COF ( I ) n =1–6 obtained from the photo-oxidation of perfluoro propene (HFP) in perfluorohexane. Under certain conditions the light-mediated fluorination of PFPE fluoroformates ( I ) gives PFPE hypofluorites CF 3 O(CF 2 O) n CF 2 OF ( II ), which can be added to sym dichlorodifluoroethene to form the dichloro adduct CF 3 O(CF 2 O) n CF 2 OCFClCF 2 Cl ( III ) which, after dechlorination, gives the desired vinyl ethers CF 3 O(CF 2 O) n CF 2 OCFCF 2 ( IV ). Every reaction step has to be properly controlled as far as the reaction variables are concerned. A mechanistic scheme is presented that is consistent with the observed experimental data.

Synthesis and characterization of perfuoropolyethers from perfluoromethylvinylether

Abstract The synthesis of a novel perfluoropolyethers (PFPEs) family has been carried out by the low temperature photooxidation of perfluoromethylvinylether. The macromolecular chains are terpolymeric in nature, being constituted by random sequences of the following groups: the regular –CF 2 CF(OCF 3 )O–, the orthoestereal –CF(OCF 3 )O–, and the acetalic –CF 2 O–. The presence of an ethereal oxygen in the short side chains represents the main structural difference with other PFPE families studied up to date [G. Marchionni, G. Ajroldi, G. Pezzin, in: S.L. Aggarwal, S. Russo (Eds.), Comprehensive Polymer Science, 2nd suppl., Pergamon Press, London, 1996.] Several fractions have been obtained, in the present work, by a single sample of the new PFPE, and some of their most important physical and molecular properties have been determined by a variety of different techniques. The properties change regularly with chain length, as expected. The group contribution analysis previously applied by our group to other families of PFPE has been found to be applicable also to chains of infinite length of the present family, which contains oxygen in the side chain.

Heat capacities of perfluoropolyethers

The heat capacities at constant pressure of liquid perfluoropolyethers with different chain structures were determined above the glass transition temperature up to 480 K by means of differential scanning calorimetry (DSC). The group contributions of the O,CF2, and CF(CF3) were calculated as a function of the temperature. Anomalous behavior of ethereal oxygen in a perfluorinated chain, as previously found for group contributions to the glass transition and to the vaporization energy, was observed also for heat capacity where the oxygen contribution is consistently lower for perfluorinated polyoxides in comparison to the hydrogenated homologous. The jump in cp at the glass transition follows a regular behavior in the sense that ΔCp/beadmole is within the average range found by Wunderlich for the majority of polymers. Moreover, data obtained in the present work allow the prediction of cp of perfluoropolyethers of whatever structure between Tg and 480 K.