Benzoic acid (BA) and its derivatives are very attractive because of their pharmacological properties, such as antioxidant, radical-regulating, antiviral, antitumor, anti-inflammatory, antimicrobial ...and antifungal. Syndiotactic polystyrene (sPS) and poly(2,6-dimethyl-1,4-phenylene)oxide (PPO) films exhibiting co-crystalline phases with BA were prepared and characterized by WAXD, FTIR and polarized FTIR measurements. The FTIR measurements clearly showed that BA was present mainly as a dimer in the crystalline channels of the ε form of sPS as well as in the α form of PPO, as generally occurs not only in the solid state but also in organic dilute solutions. BA was instead present as isolated molecules in the crystalline cavities of the δ form of sPS. In fact, the FTIR spectra of BA guest molecules exhibited vibrational peaks close to those of BA in its vapor phase. Hence, the nanoporous-crystalline δ form of sPS not only avoids additive aggregation but also leads to the separation of dimeric molecules and the segregation of monomeric BA.
Extensive characterizations, mainly by wide-angle X-ray diffraction (WAXD) and Fourier transform infrared (FTIR) techniques, are reported for co-crystalline (CC) ...poly(2,6-dimethyl-1,4-phenylene)oxide (PPO) films with many different low-molecular-mass guest molecules. These characterizations are also reported for the corresponding nanoporous crystalline (NC) phases, as obtained by suitable guest-removal procedures. Two well-separated NC forms, hereafter named α and β, are obtained by guest removal from two well-separated groups of CC forms. α and β NC forms can be easily recognized by reflections in WAXD patterns as well as by suitable FTIR crystalline peaks. Density and degree of crystallinity measurements confirm that both NC phases exhibit a density definitely smaller than for the amorphous phase (ρam = 1.04 g/cm3 > ρβ = 0.95 g/cm3 > ρα = 0.93 g/cm3). Density functional theory calculations combined with geometrical analysis on PPO model systems indicate conformations suitable to fit the observed chain periodicities of the two crystalline forms (c = 5.28 and 5.47 Å, for α and β NC forms, respectively).
Graphene oxide efficiently promotes high regio‐ and enantioselective ring opening reactions of aromatic epoxides by indoles addition, in solvent‐ and metal‐free conditions. The Friedel–Crafts ...products were obtained with enantioselectivity up to 99 % ee. The complete inversion of stereochemistry indicates the occurrence of SN2‐type reaction, which assures high level of enantioselectivity.
Do not pass GO: Graphene oxide efficiently promotes highly regio‐ and enantioselective ring opening reactions of aromatic epoxides by addition of indoles, in solvent‐ and metal‐free conditions. The Friedel–Crafts products were obtained with enantioselectivity up to 99 % ee. The complete inversion of stereochemistry indicates the occurrence of SN2‐type reactions, which assures high level of enantioselectivity.
Monolithic aerogels can be easily obtained by drying physical gels formed by linear uncross‐linked polymers. Preparation methods, structure, and properties of these physically cross‐linked polymeric ...aerogels are reviewed, with particular emphasis to those whose cross‐linking knots are crystallites and, more in particular, crystallites exhibiting nanoporous‐crystalline forms. The latter aerogels present beside disordered amorphous micropores (typical of all aerogels) also all identical nanopores of the crystalline phases. Their outstanding guest transport properties combined with low material cost, robustness, durability, and ease of handling and recycle make these aerogels suitable for applications in chemical separations, purification, and storage as well as in biomedicine. Scientific, technological, and industrial perspectives for monolithic nanoporous‐crystalline polymeric aerogels are also discussed.
Monolithic aerogels can be obtained by drying physical gels formed by linear uncross‐linked polymers. Particularly relevant are aerogels, the cross‐linking knots of which are nanoporous crystalline, which beside disordered amorphous micropores (typical of all aerogels and shown by scanning electron microscopy) also present all identical crystalline nanopores.
Films and fibers of syndiotactic polystyrene (sPS), being amorphous or exhibiting nanoporous crystalline (NC) or dense crystalline phases, were loaded with salicylic acid (SA), a relevant ...non-volatile antimicrobial molecule. In the first section of the paper, sPS/SA co-crystalline (CC) δ form is characterized, mainly by wide angle X-ray diffraction (WAXD) patterns and polarized Fourier transform infrared (FTIR) spectra. The formation of sPS/SA δ CC phases allows the preparation of sPS fibers even with a high content of the antibacterial guest, which is also retained after repeated washing procedures at 65 °C. A preparation procedure starting from amorphous fibers is particularly appropriate because involves a direct formation of the CC δ form and a simultaneous axial orientation. The possibility of tuning drug amount and release kinetics, by simply selecting suitable crystalline phases of a commercially available polymer, makes sPS fibers possibly useful for many applications. In particular, fibers with δ CC forms, which retain SA molecules in their crystalline phases, could be useful for antimicrobial textiles and fabrics. Fibers with the dense γ form which easily release SA molecules, because they are only included in their amorphous phases, could be used for promising SA-based preparations for antibacterial purposes in food processing and preservation and public health. Finally, using a cell-based assay system and antibacterial tests, we investigated the cellular activity, toxicity and antimicrobial properties of amorphous, δ CC forms and dense γ form of sPS fibers loaded with different contents of SA.
New polymeric materials based on syndiotactic polystyrene (s-PS) are presented. These materials are able to absorb rapidly and efficiently volatile organic compounds from water and air, also when ...present at very low concentrations and can be considered as the first example of polymeric molecular sieves, as they display a high sorption selectivity similar to zeolites. To our knowledge, this is the first case of polymeric semicrystalline material whose sorption ability is higher for the crystalline phase than for the amorphous phase. Moreover, these new molecular sieves are hydrophobic and hence seem particularly suitable for water and moist air purification.
Research work focused on experiments and modeling aimed to understand the properties of these materials in term of chemical structure will be reviewed. In particular, different aspects relative to the structure, absorption properties, host–guest interactions, penetrant diffusion and molecular guests mobility of these new polymeric materials will be covered.
For poly(2,6-dimethyl-1,4-phenylene)oxide (PPO) films exhibiting nanoporous-crystalline (NC) phases,
orientation (i.e., crystalline polymer chain axes being preferentially perpendicular to the film ...plane) is obtained by crystallization of amorphous films, as induced by sorption of suitable low-molecular-mass guest molecules. The occurrence of
orientation is relevant for applications of NC PPO films because it markedly increases film transparency as well as guest diffusivity. Surprisingly, we show that the known crystallization procedures lead to
oriented thick (50-300 μm) films and to unoriented thin (≤20 μm) films. This absence of crystalline phase orientation for thin films is rationalized by fast guest sorption kinetics, which avoid co-crystallization in confined spaces and hence inhibit formation of flat-on lamellae. For thick films exhibiting
orientation, sigmoid kinetics of guest sorption and of thickening of PPO films are observed, with inflection points associated with guest-induced film plasticization. Corresponding crystallization kinetics are linear with time and show that co-crystal growth is poorly affected by film plasticization. An additional relevant result of this study is the linear relationship between WAXD crystallinity index and DSC melting enthalpy, which allows evaluation of melting enthalpy of the NC α form of PPO (ΔH
= 42 ± 2 J/g).
Crystalline modifications, exhibiting largely different X-ray diffraction patterns, have been obtained for poly(2,6-dimethyl-1,4-phenylene)oxide (PPO), by gel desiccation procedures as well as by ...solvent-induced crystallization of amorphous films. The choice of the solvent allows controlling the nature of the crystalline phase. Both amorphous and semicrystalline samples of this commercial thermoplastic polymer exhibit a high uptake of large guest molecules (like, e.g., benzene or carbon tetrachloride), both from vapor phases and from diluted aqueous solutions. Surprisingly, the semicrystalline PPO samples present guest solubility much higher than fully amorphous PPO samples. These sorption experiments, as well as density measurements and classical Brunauer–Emmett–Teller (BET) experiments, clearly indicate that the obtained PPO crystalline phases are nanoporous. For these thermally stable PPO-based materials exhibiting nanoporous crystalline and amorphous phases, many applications are predictable.
Poly(2,6-dimethyl-1,4-phenylene)oxide (PPO) is a high-performance commercial thermoplastic polymer that exhibits cocrystalline phases (CC) with many low molecular mass guest molecules as well as ...nanoporous crystalline (NC) phases. In this paper, preparation and characterization, mainly by WAXD and FTIR techniques, of PPO films exhibiting the CC phase with carvacrol (a relevant natural antimicrobial) are reported. The study shows that the relative intensities of two O–H out-of-plane deformation peaks (at 698 and 717 cm−1) of carvacrol are highly sensitive to its concentration in CC films. The reported data can be rationalized by assuming that 698 and 717 cm−1 peaks are due to isolated and hydrogen-bonded guest molecules, respectively, and by preferential inclusion of carvacrol in the cavities of the NC phase. Polarized FTIR spectra of axially stretched CC PPO/carvacrol films show that the guest peak at 717 cm−1 is not dichroic, while the guest peak at 698 cm−1 is markedly dichroic. This confirms that the O–H out-of-plane deformation peak at 698 cm−1 is due to isolated guest molecules, which are mainly enclosed in the cavities of the axially oriented CC phase.Preparation and characterization of poly(2,6-dimethyl-1,4-phenylene)oxide (PPO) films exhibiting the cocrystalline phase with carvacrol, a relevant natural antimicrobial, are reported. The relative intensity and linear dichroism of two O–H out-of-plane deformation peaks (at 698 and 717 cm−1) of carvacrol can be rationalized by assuming that these peaks are due to isolated and hydrogen-bonded guest molecules, respectively, and by slower desorption of carvacrol when included as isolated molecules in the cavities of the polymer host crystalline phase.
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