Alexandra R. Albunia

Normal vibrational analysis of the syndiotactic polystyrene s(2/1)2 helix.

The full vibrational spectra of the gamma, delta, and epsilon crystalline phases of syndiotactic polystyrene (sPS), i.e., phases presenting the s(2/1)2 helical conformation, have been experimentally determined and compared with that calculated at the B3LYP/6-31G(d,p) level of theory for an infinite helix. The assignment of the different modes was highly facilitated and validated by the experimental evaluation of the direction of the transition moment vector of most IR peaks, which was made possible for the first time by measurements on sPS films with different uniplanar orientations of the crystalline phase. The normal vibration analysis of most representative modes of the periodic model allowed for a general description of each one to be obtained, which was further confirmed by the direct inspection of mode animations.

Ethylene removal by sorption from polymeric crystalline frameworks

The uptake and diffusivity of ethylene in amorphous and semicrystalline s-PS (syndiotactic polystyrene) films presenting different crystalline phases and different crystalline-phase orientations have been studied by gravimetric and Fourier transform infrared measurements. High solubility and low diffusivity of ethylene have been observed for the nanoporous host δ phase of s-PS, due to the formation of a co-crystalline phase, where ethylene molecules are oriented nearly perpendicular to the polymer helices. In addition, ethylene diffusivity can be minimized by suitable (002) uniplanar orientation of the host crystalline phase, i.e. by placing the crystalline polymer helices perpendicular to the film surface. Ethylene-desorption measurements conducted at different temperatures have allowed us to evaluate activation energies relative to ethylene diffusion. The reported results suggest that this cheap, robust and easy-to-process polymeric material is suitable for (also for repeated use) food packaging requiring ethylene removal.

Crystalline orientation and molecular transport properties in nanoporous syndiotactic polystyrene films

The orientation of the crystalline δ nanoporous phase in syndiotactic polystyrene films, obtained by different procedures, have been characterized. For both solution cast and biaxially stretched films a high degree of uniplanar orientation, corresponding to the tendency of the ac crystallographic planes, to be parallel to the film plane has been observed and rationalized. According to molecular dynamics simulations of diffusion of small molecules into the δ nanoporous phase, this uniplanar orientation would minimize the molecular diffusivity through the nanoporous crystalline phase.

Interactions of Volatile Organic Compounds with Syndiotactic Polystyrene Crystalline Nanocavities

The interaction of some volatile organic compounds, namely, 1,2-dichloroethane, 1,2-dibromoethane, and 1,1,2,2-tetrachloroethane, included in the δ crystalline phase of syndiotactic polystyrene (sPS) has been studied in terms of conformation, orientation, and dynamical behavior. By combination of X-ray diffraction (XRD), Fourier-transform infrared (FTIR), and solid-state (2)H NMR analyses, it has been shown that despite the differences in guest molecular properties (mass, boiling temperature, and volume), stable sPS/guest δ-clathrate cocrystals are formed since the nanoporous δ crystalline form has a flexible structure able to adapt itself to the guest molecule. As a consequence of inclusion, it has been shown that the guest diffusivity is strongly reduced and the dynamical processes are constrained, particularly when these guests are in trans conformation. This suggests the nanoporous sPS δ form to be an efficient tool for water and air purification through volatile organic compound absorption.

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.

The Effect of Inclusion of Dichloromethane in the -Clathrate Phase of Syndiotactic Polystyrene

Inclusion of molecules in the crystalline phases of s-PS induces on the guest long range order and strongly reduces the guest diffusivity and mobility with respect to a random dispersion at the molecular level in polymeric amorphous phases. Moreover, when included in highly oriented s-PS films, the degree of guest orientation is comparable to the host orientation and detailed information on directional properties within molecules can be unambiguously achieved. In this paper, the behavior of dichloromethane in the δ-clathrate phase of syndiotactic polystyrene is studied by combined FTIR and solid state 2H NMR techniques, defining the molecular orientation in the crystalline phase and the constrained reorientational dynamics of the guest molecules in the cavities.