Enzo Butta

Molecular motions in glassy polymers with aromatic groups either in the side chain or in the backbone

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.

Secondary mechanical relaxation effects in some cycloalkyl side groups containing polymers

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.

Polycarbonate-linear low density polyethylene blends: Thermal and dynamic-mechanical properties

Blends of polycarbonate (PC) and linear low density polyethylene (LLDPE) of different compositions, in the form of slabs obtained by melt extrusion, have been examined by differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA).DSC measurements show that the melting, crystallization and glass transition temperatures of the two polymeric components in the blends are slightly affected by the composition. On the contrary, large differences are observed in the melting behaviour of layers cut at various depths, parallel to the slab surfaces of samples. This supports the occurrence of different crystal morphologies and distribution of the two components within the samples. The study of the crystallization kinetics from the melt blends shows that the crystallization processes of LLDPE are affected by the presence of PC.The dynamic mechanical analysis indicates that modulus, transitions and relaxational behaviour of the polymer components are scarcely affected by the composition. Some variations of the damping factor have been interpreted as due to the phase heterogeneity of the system, arising from the processing conditions and rheological behaviour of the blends.

Co-operative and group motions in poly-3,3-bis(chloromethyl)oxetane

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.