Concetta D'Aniello

Photoisomerization patterns based on molecular complex phases of syndiotactic polystyrene

Syndiotactic polystyrene (s-PS) films presenting molecular-complex crystalline phases with norbornadiene (N), possibly suitable for data storage systems with molecular size marks, have been thoroughly investigated. In particular, a procedure suitable for obtaining polymer films containing N molecules only in the crystalline phase and the long-term stability of this s-PS/N molecular-complex crystalline form have been investigated by thermogravimetric, infrared linear dichroism and X-ray diffraction experiments. The possible loss of guest molecules during photoisomerization processes from N to quadricyclane (Q) has also been studied. Moreover, the N and Q patterns obtained by photoisomerization and their long-term stability have been investigated by Fourier transform infrared microscopy.

Influence of the crystallinity on the transport properties of isotactic polypropylene

Samples of polypropylene of varying crystallinity were obtained by blending isotactic with atactic polypropylene, and the crystallinity determined by X-ray diffraction and differential scanning calorimetry. Crystallinity ranged between 20 and 75%. The transport properties of dichloromethane were analysed varying the activity of the vapour. We observed that the sorption decreases, as the crystallinity increases, proportionally to the decrease of the amorphous fraction. As matter of the fact, the specific sorption, normalized by the amorphous fraction, does not depend on the crystallinity. At variance, a simple correlation between the thermodynamic diffusion coefficient and the crystallinity was not obtained; at low values of this parameter, up to 40%, the zero concentration diffusion coefficient is independent of it. A sharp transition separates a range of crystallinities, in which the diffusion parameter decreases, increasing the crystallinity, due to the tortuosity of the path, and shows that the presence of the impermeable crystals is important only for values higher than 50%.

Transport properties of the mesomorphic form of poly(ethylene terephthalate)

The mesomorphic form of poly(ethylene terephthalate), present in samples drawn at 60°C at a draw ratio of 4, was studied by analysing the transport properties of dichloromethane vapours. The reduced sorption with respect to the amorphous sample indicates that the mesophase is impermeable to the vapours at low activity, and this allows the determination of the fraction of mesophase in the drawn samples.

Transport properties of dichloromethane in glassy polymers. VI. Poly(ethylene terephthalate)

Sorption and diffusion of dichloromethane vapor in amorphous poly(ethylene terephthalate) (PET) were investigated, with the aim of studying how aging phenomena, at different temperatures, influence the transport properties. It has been found that aging produces the appearance of non-Fickian behavior in the sorption curves as well as the reduction of the diffusion coefficients. Furthermore, aging at 60°C reduces the sorption of vapor at low activity, and this led to the hypothesis of the presence of ordered domains in the aged samples. In this case, the process of solvent-induced crystallization is favored, and it appears at lower activity.

Cold crystallization of isotactic polystyrene

Abstract Thermal crystallization from the glassy state was investigated for isotactic polystyrene (iPS) at three temperatures (140°C, 170°C, and 200°C) for different times. The crystallized samples were analyzed by x-ray diffraction, differential scanning calorimetry (DSC), and transport properties of dichlo- romethane vapor. X-rays and DSC give very similar values of crystallinity. At variance, sorption measurements indicate a fraction of amorphous phase much lower than the previous. The presence of a mesophase, impermeable to the vapors at low activity, was hypothesized. Its value is constant for annealing at 140°C, whereas it decreases with time at 170°C and 200°C, in correspondence with an increase of the crystalline fraction.

Three different co-crystalline phases of syndiotactic polystyrene with a nitroxide radical

Extensive crystallization studies have been conducted on syndiotactic polystyrene in the presence of the nitroxide radical compound 2,2,6,6-tetramethylpiperidinyl-N-oxyl (TEMPO). Depending on the selected crystallization conditions, three different co-crystalline phases are obtained: beside the known intercalate structure (guest layers intercalated with layers of alternated enantiomorphous helices), a δ-clathrate structure (isolated guests imprisoned into cavities formed between the same kinds of layers), and a e-clathrate structure (guests confined into channels). All three s-PS/TEMPO co-crystalline phases exhibit a long-term stability for temperatures below 60 °C. The control of the polymorphism of the co-crystals, associated with the control of film morphology (axial and/or uniplanar orientations) allows a control of concentration and orientation of the radical guest molecules, which can be helpful for the preparation of new organic magnetic materials.

Transport properties of dichloromethane in polymeric blends Part I Low density polyethylene-isotactic polypropylene

Low density polyethylene (LDPE) and either isotactic polypropilene (IPP) or a copolymer of isotactic polypropilene with 3% of ethylene (CPP) were blended, and analyzed with X-rays, differential thermal calorimetry, dynamic mechanical analysis, and transport properties of dichloromethane vapour at different activities. The results show that polyethylene and polypropylene crystallize in different domains in the usual crystalline forms (orthorhombic and monoclinic respectively). Also the amorphous phases are not miscible; moreover in the blend LDPE-IPP, in which PE crystallize less, the transport of the vapours occurs mainly through polyethylene, whereas the opposite is true in the blend LDPE-CPP, in which polypropylene crystallizes less. The sorption properties are in agreement with the additivity of sorption of the two amorphous phases.

Transport properties of poly(ethylene terephthalate) crystallized from the glassy state

Poly(ethylene terephthalate) was crystallized from the glassy state at 120 and 200°C. The structural organization of samples, after the primary and secondary crystallizations, was analyzed by density, X-rays, infrared and transport properties of dichloromethane vapor. The values of crystallinity derived with different methods do not agree, indicating that the crystallized samples cannot be considered simply biphasic. Since the fraction of the impermeable phase is much higher than the fraction of the crystalline phase, it suggested that the presence of mesomorphic form, impermeable to the vapors at low activity. With this hypothesis, the complete composition of the crystalline samples, in terms of fraction of crystalline, amorphous and mesomorphic form was derived. A value of density of the mesomorphic form of 1.39 g/cm3 was also derived.

Cast-extruded syndiotactic polypropylene films: preliminary structural and mechanical results

Syndiotactic polypropylene (sPP) was cast-extruded with a laboratory single screw extruder, obtaining a crystalline and still highly transparent film. The structural studies showed that the film crystallized at room temperature in the disordered helical form I, containing a fraction of a mesophase with the chains in trans-planar conformation. X-ray patterns, taken either along the extrusion direction (MD) or along the orthogonal directions (TD and ND), indicated a low orientation of the c axis parallel to the machine direction (MD) and a partial orientation of the a axis along the transverse direction (TD). Mechanical properties performed in either direction showed a very similar behaviour, but a different strain at the breaking point. The mechanical parameters were derived in both directions.

STRUCTURAL CHANGES DURING ANNEALING OF THE CRYSTALLINE HELICAL FORM OF SYNDIOTACTIC POLYPROPYLENE

A sample of syndiotactic polypropylene was quenched from the melt at 0°C and kept at this temperature for 1 min. Upon heating to room temperature, it shows the disordered crystalline form I, with the chains in helical conformation. In addition, it also contains a fraction of trans-planar mesophase, formed during the short time at 0°C. It was annealed at increasing temperatures, up to 120°C, and the structural changes analyzed by x-rays and FTIR measurements. Annealing up to 90°C results in a progressive decrease in the trans-planar mesophase, and also the melting of the more disordered and smaller helical crystals. In this range, the structural parameters such as crystallinity and crystal perfection smoothly increase, whereas a steeper increase is observed after 90°C when the disordered phases have disappeared. Afterwards, the formation of the more ordered form I, characterized by a peak at 18.8° of 2θ in the x-ray diffractogram, becomes possible. The content of the mesophase was determined by measurements of sorption of a vapor at low activity; it was 30% in the initial sample. This value decreased up to the annealing temperature of 90°C, where the value of the crystallinity was found coincident with the fraction of impermeable phase derived by sorption. In addition, transport properties confirm that the disappearance of the mesophase allows the formation of the ordered crystalline form I.