Rachele Pucciariello

On melt-crystallization of polytetrafluoroethylene and of random fluorinated copolymers of tetrafluoroethylene

Through differential scanning calorimetry, isothermal crystallization from the melt of polytetrafluoroethylene (PTFE) has been investigated. PTFE was regarded as one of the polymers for which crystallization is so rapid that the samples crystallize during the cooling from the melt to the selected crystallization temperature. By contrast, we now report that a stochastic behavior is observed for isothermal melt-crystallization of PTFE. In fact, on cooling very quickly the samples from the molten state to the selected crystallization temperature, crystallization during the cooling is randomly observed. Therefore, repeating the experiments until crystallization on cooling was absent, it was possible to investigate isothermal melt-crystallization of PTFE. However, crystallization is very fast; in fact, crystallization kinetics can be followed just for very low undercoolings, while as the undercooling becomes as large as about 15°C, only secondary crystallization is observed. In both cases, the data have been examined through the well-known Avrami analysis, taking into account the different physical meaning of the obtained parameters. For the first cases (actual crystallization kinetics) very low, noninteger Avrami exponents have been obtained. They have been related to the fractal dimension of the crystallites and their values to the morphological observations on PTFE. For the second cases, the typical low values of Avrami exponents of secondary crystallization are obtained. Moreover, isothermal melt-crystallization of random fluorinated copolymers of tetrafluoroethylene with either hexafluoropropylene or perfluoromethylvinylether as comonomers has been studied and compared with that of PTFE.

Graft Copolymers of lignin from straw with 1-Ethenylbenzene: Synthesis and Characterization

The synthesis of copolymers between lignin from steam-exploded straw and 1-ethenylbenzene is described. Beforehand, lignin from steam-exploded straw was fully characterized by using elemental analysis, ultraviolet spectroscopy, gel permeation chromatography (GPC), Fourier transform infrared (FTIR), and both 1H and 13C nuclear magnetic resonance (NMR) spectroscopy. Using a previously described procedure utilizing calcium chloride and hydrogen peroxide as reagents the synthesis of the copolymers was performed. FTIR of the copolymers showed the presence of both lignin and polystyrene. GPC analysis showed the presence of a fraction with high molecular weights. These results were confirmed from both viscosity data and differential calorimetry.

Phase behavior of crystalline blends of poly(tetrafluoroethylene) and of random fluorinated copolymers of tetrafluoroethylene

In the present article, we investigate by differential scanning calorimetry (DSC) the thermal behavior (melting, crystallization, and crystal-crystal transitions) far from equilibrium of blends constituted of two crystalline polymers. In particular, the following blends are examined: PTFE-PFMVE, PTFE-FEP, and FEP-PFMVE where PTFE is poly(tetrafluoroethylene), PFMVE is poly(tetrafluoroethylene-co-perfluoro-methylvinylether), and FEP is poly(tetrafluoroethylene-co-hexafluoropropylene) The two last ones are random tetrafluoroethylene copolymers with small amounts of comonomer. Our results indicate that, under the experimental investigated conditions, the blends containing PTFE do not give cocrystallization on cooling from the melt, although under very rapid crystallization conditions, quenching, the presence of the copolymer would seem to slightly influence PTFE crystallization (lower peak temperatures are observed for the crystalline transitions and the melting with respect to those of the neat homopolymer). The behavior of the FEP-PFMVE blend is completely different; in fact, our results indicate the occurrence of cocrystallization, then miscibility in the crystalline phase, for almost all compositions and all investigated experimental conditions.

Phase Behavior of Blends of Poly(ϵ‐Caprolactone) and a Modified Montmorillonite‐Poly(ϵ‐Caprolactone) Nanocomposite

Blends between high‐molecular weight poly(ϵ‐caprolactone) (PCL) and an intercalated nanocomposite of poly(ϵ‐caprolactone)‐organophilic montmorillonite (OMONT), containing 30% by weight of the nanofiller (NPCL30) have been investigated. Such blends have been shown to have much improved mechanical properties with respect to the parent polymer. The detailed phase behavior, crystallization kinetics, and morphology of neat PCL and of blends containing 2, 9, and 15% by weight of OMONT have been studied by using differential scanning calorimetry (DSC). The thermal properties and the overall crystallization rate of pure PCL are strongly influenced by the presence of the montmorillonite nanoparticles. The study of the solid‐state dynamic‐mechanical properties revealed an enhancement of the storage modulus in particular above Tg and upon increasing the clay content. The enhancement of the modulus can be attributed to confined orientation of the polymer chains among the silicate galleries (intercalation). This is confirmed by the appearance in the sample with the highest clay content, of a second Tg peak at higher temperature indicative of a less mobile amorphous fraction.

Extreme thermal behaviors of polytetrafluoroethylene and random tetrafluoroethylene fluorinated copolymers

By differential scanning calorimetry (DSC), the thermal behavior of polytetrafluoroethylene (PTFE) and random fluorinated copolymers of tetrafluoroethylene-containing hexafluoropropylene (FEP copolymers) or perfluoroalkylvinylether (PFA copolymers) as comonomers was investigated. Rapid-melt crystallization was employed to provide new data about the problem of inclusion/exclusion of co-units from the homopolymer crystal lattice. Equilibrium melting points were determined and tested in light of random copolymer predictions. Both nonequilibrium and equilibrium behaviors seem to point to the inclusion of -CF 3 side groups and the exclusion of larger ones. Finally, a new value of the equilibrium melting point of PTFE is given, in good agreement with those present in the literature.

Effect of thermal history on the melting behavior and the crystal-crystal transitions of tetrafluoroethylene-perfluoroalkylvinylether copolymers

By differential scanning calorimetry (DSC), the effect of thermal treatments on the melting of tetrafluoroethylene-perfluoroalkylvinylether copolymers (PFA) with different contents of perfluoromethylvinylether as a comonomer has been investigated. Two melting peaks can be identified for all copolymers, whose presence, value, and extent depend upon the thermal treatments. The higher temperature one, scarcely influenced by the crystallization conditions (i.e., cooling rate and annealing), can be attributed to more perfect crystals present in the original samples. The lower temperature one is produced only by annealing (annealing peak) and can be interpreted as resulting from much poorer crystals grown among the larger ones. For the copolymer with the lowest content of comonomer, the effect of thermal treatments on the low-temperature (crystal-crystal) transitions has also been studied. The rejection of the counits from the crystals, at least in equilibrium conditions, is confirmed.

Melting behavior of ethylene-tetrafluoroethylene alternating copolymer

The melting behavior of the alternating copolymer of ethylene and tetrafluoroethylene (ETFE) was investigated by differential scanning calorimetry (DSC). A complex melting pattern is observed, strongly influenced by the thermal history. Three melting processes can be identified, whose heats of fusion and peak temperatures (Tm1′, Tm1, and Tm2 at increasing values) strongly depend upon thermal treatments. The higher-temperature melting peak Tm2 is not affected by the crystallization conditions (i.e., cooling rate and annealing); therefore, it can be attributed to more perfect crys+als present in the original sample. The peak at Tm1 increases when the cooling rate is decreased and upon prolonged and/or higher-temperature annealing, and it fastly merges to the higher-temperature peak at Tm2. The peak at Tm1 can be due to crystals that are able to recrystallize and perfect during thermal treatments. Lastly, the peak at the lowest-temperature Tm1′, produced only by annealing and strongly developing on increasing annealing time and temperature, is the so-called annealing peak that can be attributed to much poorer crystallites grown among the larger ones. The melting behavior of ETFE is compared with that of the ethylenechlorotrifluoroethylene (ECTFE) alternating copolymer.

Calorimetric study of the room-temperature transitions : of tetrafluoroethylene-hexafluoropropylene copolymer : thermal history and crystalline state

Abstract Differential scanning calorimetry reveals at least three very clear room-temperature transitions for native tetrafluoroethylene-hexafluoropropylene (TFE-HFP) copolymer, with a composition of 0.3 mol.% HFP, from aqueous dispersion polymerization. The influence of the thermal history on the room-temperature transitions was studied. The enthalpies and the temperatures of each transition were evaluated vs. the annealing temperature. The results are compared with those previously obtained for polytetrafluoroethylene (PTFE). As for the homopolymer, it is suggested that the native copolymer and the copolymer annealed at T ann

PIDOTIMOD, a new immunostimulating dipeptide, studied by molecular mechanics, normal mode analysis and dynamics calculations☆

Abstract A theoretical study of PIDOTIMOD, a new immunostimulating dipeptide, using a combination of molecular mechanics, normal mode analysis and dynamics methods, has been carried out. The results have been compared with the experimental ones obtained using NMR spectroscopy. Conformational calculations and NMR spectra identify two classes of conformers, trans and cis, around the peptide bond between the rings, with relative conformational populations of 0.55 and 0.45, respectively. The best agreement is obtained using a dielectric constant ϵ = 7 in the calculations. The conformational features show that the path connecting the trans and the cis forms may involve the rotation of the bridged peptide bond alone. From a dynamic point of view the conformers appear rather rigid, and only the oxo-prolyl ring and the carboxyl group show significant rigid body-like motions. Interesting correlations occur in the fluctuations of the torsion angles.

Substrate interaction with 5α-reductase enzyme: influence of the 17β-chain chirality in the mechanism of action of 4-azasteroid inhibitors

Abstract A series of steroidal compounds were synthesized in order to evaluate the possible influence of the configuration of a stereocenter in the 17β-side chain on the inhibitory activity on the enzyme 5α-reductase (5AR). For this purpose diastereomerically pure 4-azasteroids epimers at C-22 were prepared (compounds 1–11) and tested as inhibitors of 5AR in ‘in vitro’ tests. The obtained data showed that in most cases the couples of epimers possess a significant difference in their biological activity. We also considered, for the tested molecules, a series of chemico-physical parameters in order to find a possible correlation with their biological activity. The findings allowed us to propose a model of the binding site of 5AR which comprises also, for 4-azasteroid inhibitors, the configurational aspect of the 17β-side chain.