G. Pezzin

Molecular weight dependence of some rheological and thermal properties of perfluoropolyethers

The glass transition temperatures and the viscosities (over a very large temperature range) have been measured as a function of molecular weight, for two different series of perfluoropolyethers. The results have been interpreted according to well-known free-volume models. The Williams-Landel and Ferry equation describes the viscosity data with values of fg (the fractional free volume at Tg) close to 0.04 and with values of αf (the free-volume expansion coefficient) close to 7 × 10−4°C−1. The critical molecular weight, Mc, is approximately 5000–6000 for perfluoropolyethers from hexafluoropropene and 7800 for perfluoropolyethers from tetrafluoroethene.

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.

The glass transition temperature of polymer-diluent systems

Abstract The theoretical treatment proposed by Couchman to describe the compositional dependence of T g for polymer-diluent systems has been applied, in its several forms, to selected pairs for which heat capacity data are found in the literature. The most accurate equation gives the least satisfactory description of the experimental T g data. This result seems to be accounted for by the assumption, first suggested by Couchman, that in some cases the entropy of mixing is not continuous at T g .

An investigation of the viscoelastic properties of molten polypropylene

Two series of polypropylene samples of different molecular weight, the first obtained directly from polymerization reactions and the second from controlled thermal degradation, were studied by dynamic testing in the melt state. Several viscoelastic parameters were determined, and correlated with weight-average molecular weightMw. It is found that theMw-dependence of the two series is rather different.

Rheological characterization of highly branched poly(ethyleneterephthalate)

Linear and highly branched poly(ethyleneterephthalate) samples were synthesized and characterized in terms of intrinsic viscosity, molecular weight and melt viscosity over a wide range of shear rates at several temperatures, in the range from 265° to 295 °C. Linear samples exhibited Newtonian behavior over a wide range of shear rates, while the branched ones became shear thinning at relatively low shear rates. Our experimental data, as well as data previously reported, were found to be described by a proposed correlation between the melt viscosity ratio and a branching index. Moreover, the activation energy for melt flow was found for the highly branched samples to be a little higher than that of the linear samples.

Glass transition of binary systems: peculiarities at low temperature

Abstract The present paper refers to the well known fact that the glass transition-composition curves of miscible binary systems (e.g. polymer-diluent and polymer-polymer mixtures) often exhibit a singular point when the Tg values of the two components are far apart. Two different equations apparently apply above and below the temperature of this singularity. Starting from Couchmans entropic treatment of the glass transition of mixtures, and from Angells suggestion for the calculation of T0 (‘ideal glass transition temperature’ of the component with higher Tg), it is shown that below T0 an equation should be applicable to binary mixtures which differs considerably from the equations normally used in the literature. The new equation gives a satisfactory description of selected experimental data in the proximity of the component with lower 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.

Linear and branched poly(butyleneterephthalate): Activation energy for melt flow

AbstractPoly(butyleneterephthalate) (PBTP) samples of different molecular weights, both linear and branched, were synthetized by mass polymerization and studied in the molten state with a melt-flow-index apparatus at different temperatures in the range 245–270 °C. In our experimental conditions (