Vittorio Frosini
University of Pisa
Network
Latest external collaboration on country level. Dive into details by clicking on the dots.
Publication
Featured researches published by Vittorio Frosini.
Molecular Crystals and Liquid Crystals | 1981
Vittorio Frosini; G. Levita; Domenico Lupinacci; Pierluigi Magagnini
Abstract The influence of the flexibility of the polymer main chain on the smectic ordering has been investigated, by means of optical, diffractometric and calorimetric techniques, in several polymers carrying rigid anisometric side-groups. The effect of the chemical structure of the sidegroups has been examined throughout: atactic polymers with biphenylyl side-groups may be amorphous or mesomorphous depending on the nature of the groups linking the biphenylyl moiety to the backbone chain. Correlations between the molecular weight and the stereochemical structure of the macromolecules and the occurrence of a thermotropic smectic phase in a series of polyacrylates and polymethacrylates, have been reported.
Molecular Crystals and Liquid Crystals | 1983
Vittorio Frosini; S. De Petris; Emo Chiellini; Giancarlo Galli; Robert W. Lenz
Abstract The thermal and dynamic viscoelastic behavior of some thermotropic liquid crystalline polyesters based on α, ω-bis(4-hydroxybenzoyloxy)alkanes and terephthalic acid is reported. Original samples obtained by solution polymerization followed by precipitation showed physical and dynamic-mechanical properties typical of semicrystalline polymers. Quenching of the polymers from the LC state gave rise to glass-like mesomorphic modifications that retained a glass transition at considerably higher temperature T 8m than that of the corresponding amorphous material T 8a. However, the formation of a new crystal form with respect to the original sample could not be prevented and the polymers so obtained were in fact partially mesomorphic and partially crystalline materials. All the quenched samples exhibited by dynamic-mechanical and calorimetric analyses a first order solid-solid transition independent of the length of the flexible spacer. Such a phenomenon was interpreted as an order-disorder transition of ...
Materials Science and Engineering | 1968
Mario Baccaredda; Enzo Butta; Vittorio Frosini; Silvano de Petris
Abstract Dynamic mechanical properties (sound velocity v and damping factor Q−1) have been determined, below the glass transition, over a wide range of temperature at acoustic frequencies ( ⋍ 10 kHz ), in polymers containing aromatic groups either in the side chain (polystyrenes, poly(vinyl benzoates), polyvinylpyridines, poly(vinyl nicotinates)) or in the backbone (poly(phenylene oxides)). The ortho and meta ring-substituted polystyrenes do not show any secondary mechanical relaxation effect in the glassy state; in all the other substituted polystyrenes a low-temperature damping peak (delta-process) is found at 90–100°K, the height and location on the temperature scale of which depend on the nature and position of the substituents. Para substitutions in the ring or α-substitutions in the main chain shift the delta-peak of the unsubstituted polystyrenes towards higher temperatures and increase apparent activation energies. Substitutions in β-position do not affect the delta-peak. Analogous results are found in poly(vinyl benzoates), which show also an additional relaxation effect (beta-process). The delta peak is connected with “wagging” motions of the ring and the beta-peak is associated with carbonyl group movements. A delta-process is also found in polyvinylpyridines and poly (vinyl nicotinates), which however is shifted towards higher temperatures as compared with the analogous phenomenon in polystyrene. In polymers with aromatic rings in the skeleton no damping peak is found at temperatures below room temperatures, but a relaxation effect is found, which covers a very wide temperature range and gives place to a flattened loss maximum at 400–450°K. Such a phenomenon is tentatively attributed to torsional oscillation of phenylene rings.
Molecular Crystals and Liquid Crystals | 1984
Mariano Pracella; Vittorio Frosini; Giancarlo Galli; Emo Chiellini
Abstract The isothermal crystallization and melting processes have been investigated in liquid crystal polyesters based on mesogenic bis(4-carboxyphenyl) terephthalate units and flexible alkylene spacers. The kinetic and thermodynamic parameters for the nucleation and growth of crystals from the smectic phase are presented and discussed with reference to the polymer chain structure.
Colloid and Polymer Science | 1966
Vittorio Frosini; Pierluigi Magagnini; Enzo Butta; Mario Baccaredda
SummaryThe dynamic mechanical properties at acoustic and low-ultrasonic frequencies (6–60 kHz) have been determined in polycyclopentylmethacrylate (PCPMA), polycyclohexylmethacrylate (PCHMA), polycyclohepthylmethacrylate (PCHpMA), polycyclooctylmethacrylate (PCOcMA), polycyclohexylacrylate (PCHA), polyvinylhexahydrobenzoate (PVHHBz), polyvinylcyclohexylether (PVCHE) and polyvinylcyclohexane (PVCH) Measurements were carried out by an electrostatic method (flexural vibrations) over the temperature range 60 °K to room temperature.All polymers, except for polyvinylcyclohexane, exhibit a γ-relaxation, connected with internal motion of the cycloalkyl ring, whose activation parameters depend exclusively on the nature of the ring.PVCHMA, PVCHA, PVHHBz, PVCHE and PVCH exhibit a further secondary relaxation effect (δ-process) at lower temperature, whose position on the temperature scale, strength (peak height) and activation parameters depend on the nature of the units to which the cyclohexyl ring is attached. The δ-process is attributed to some complex motion of the whole cyclohexyl ring, involving oscillatory rotation of the same around simple bonds which link it to the backbone chain. Contrarily to the δ-process of the phenyl side group containing polymers, the δ-process of the polymers here examined seems to be more sensibly dependent on intramolecuar effects.ZusammenfassungEs wurden die dynamischen Eigenschaften im akustischen und im Bereich langsamer Ultraschallfrequenzen (6–60 kHz) untersucht für Polycyclopentylmethacrylat (PCPMA), Polycyclohexylmethacrylat (PCHMA), Polycycloheptylmethacrylat (PCHpMA), Polycyclooctylmethacrylat (PCOcMA), Polycyclohexylacrylat (PCHA), Polyvinylhexahydrobenzoat (PVHHBz) Polyvinylcyclohexyläther (PVCHE) und Polyvinylcyclohexan (PVCH). Die Untersuchungen wurden mit einer elektrostatischen Methode (Biegeschwingung) über den Temperaturbereich von 60 °K bis Raumtemperatur durchgeführt.Alle Polymeren, außer Polyvinylcyclohexanen, zeigen eine γ-Relaxation verbunden mit internen Bewegungen des Cycloalkylrings, deren Aktivierungsparameter wesentlich von der Natur des Rings abhängen.PVCHMA, PVCHA, PVHHBz, PVCHE und PVCH zeigen einen weiteren sekundären Relaxationseffekt (δ-Prozeß) bei tieferen Temperaturen, dessen Lage in der Temperaturskala, Stärke (Peakhöhe) und Aktivierungsparameter von der Natur der Einheiten abhängen, an welchen der Cyclohexylring hängt. Der δ- Prozeß wird irgendeiner komplexen Bewegung des ganzen Cyclohexylrings zugeschrieben, eingeschlossen oszillatorische Rotation desselben um die Einfachbindung, die ihn mit der Hauptkette verbindet. Anders als der δ-Prozeß der Phenylseitengruppen enthaltenden Polymerenketten scheint der hier untersuchte δ-Prozeß emfindlicher von intramolekularen Effekten abzuhängen.
Molecular Crystals and Liquid Crystals | 1984
Mariano Pracella; S. De Petris; Vittorio Frosini; Pierluigi Magagnini
Abstract The kinetics of the isotropic-to-smectic A transition of poly(p-biphenylyl acrylate) has been investigated by differential scanning calorimetry. The parameter n of the Avrami equation has been found to be of ca. 3. The calculated formation energy of the nuclei is 40-50 KJ mole−1. From the thermal data, it is concluded that, in this polymer, a fraction of amorphous material is present together with the mesophase, and the relative amounts of the two phases varies with the thermal history.
Archive | 1972
B. A. Newman; Pierluigi Magagnini; Vittorio Frosini
The unusual properties of atactic poly(parabiphenyl acrylate reveal that some degree of order in this polymer exists. An x-ray study of this polymer and some related polymers confirm this and indicate that the order is one-dimensional. Some annealing studies show that the extent of this order can be increased by thermal treatments. A model of the molecular packing is suggested to account for these results.
European Polymer Journal | 1966
Mario Baccaredda; Enzo Butta; Vittorio Frosini
Abstract The dynamic mechanical properties (sound velocity, v, and damping factor, Q −1 have been determined in samples of poly-3,3-bis(chloromethyl)oxetane Penton at temperatures between 100° and 450°K, by an electrostatic method at medium frequencies (10–30 kHz). The νv - T curve shows a change of slope at about 270°K, corresponding to the dilatometric glass transition point. At still higher temperatures, in the neighbourhood of the melting point ( T m ⋍450° K ), a further decrease of the sound velocity is observed and is followed by softening of the sample. The damping factor vs. temperature curve has two maxima, one (γ), at about 230°K and another (α) at about 330°K. Whilst the latter is attributed to the relaxation process accompanying the excitation of co-operative motions of chain segments in the amorphous regions ( T g ), the low-temperature damping peak is tentatively assigned to particular motions of the CH 2 O group, on the basis of the good correspondence between the values of the activation parameters, ΔH′, ΔS′ and ΔF′, relative to the “γ” processes of Penton and of polyoxymethylene.
Archive | 1985
Vittorio Frosini; S. De Petris; Giancarlo Galli; Emo Chiellini
There is currently considerable interest in the solid state physics of thermotropic liquid crystalline (LC) polymers and much emphasis is placed on studies regarding the solid-solid transitions and the chain dynamics of these systems. Recently, evidence for the occurrence of supercooled mesomorphic structures in the glassy state of polymers quenched from the anisotropic melt has been presented.1 – 3
Advances in Liquid Crystal Research and Applications#R##N#Proceedings of the Third Liquid Crystal Conference of the Socialist Countries, Budapest, 27–31 August 1979 | 1981
Pierluigi Magagnini; Vittorio Frosini; Domenico Lupinacci; Bruno C O Dipartimento Bresci
Poly(p-biphenylyl acrylate) (PPBA) displays a thermodynamically stable smectic mesophase at temperatures below ca 270°. The X-ray diffraction diagram of this polymer shows a sharp reflection, with higher orders, corresponding to a spacing of 23,2 a. Optical observation and X-ray photographs of fibres of PPBA indicated good preferred orientation along the fibre axes. The structure is not influenced by the stereochemical configuration of the macromolecules, whereas the temperature of the smectic-isotropic transition of PPBA has been found to increase with decreasing degree of isotacticity. The smectic-isotropic transition of PPBA has been studied with different techniques, and the effect of the copolymerization, of the addition of a diluent and of the polymer molecular weight has been investigated. All the data indicate that the smectic-isotropic transition of PPBA resembles closely the fusion of semicrystalline polymers.