Probing by Time-Resolved FTIR Spectroscopy Mass Transport, Molecular Interactions, and Conformational Ordering in the System Chloroform−Syndiotactic Polystyrene

Abstract

The transport of chloroform in films of semicrystalline syndiotactic polystyrene (s-PS) in its nanoporous form (δ-form) has been investigated by gravimetric analysis and time-resolved FTIR spectroscopy. Experimental tests have been performed at 56 °C and at several vapor pressures ranging from 5 to 100 Torr. Sorption and desorption kinetics have been monitored with both techniques, and the dependence of diffusion coefficients with penetrant concentration was investigated, evidencing Fickian features typical of systems characterized by diffusivity increasing with concentration. Analysis of the vibrational spectrum of chloroform sorbed in the crystalline phase showed significant perturbations when compared to the spectrum of the isolated molecule or the molecule absorbed in amorphous s-PS. This perturbation has been attributed to host−guest molecular interactions whose strength was found to be relatively small. Conformational rearrangements of macromolecular chains in the amorphous phase were detected as a consequence of chloroform sorption. These rearrangements, which lead to an increase of the overall crystallinity degree, were quantified using the concept of critical sequence length (CSL). The kinetics of the conformational ordering process was found to parallel the sorption kinetics, and the associated increase of crystallinity was not reversible upon chloroform desorption.

Understanding at molecular level of nanoporous and co-crystalline materials based on syndiotactic polystyrene

“…Several FTIR studies [43,46,74,75] have given information about the nature of host-guest interactions in s-PS co-crystals.…”

“…It presents two identical cavities and eight styrene monomeric units per unit cell [16] and rapidly and selectively absorbs low-molecular-mass guest molecules even at very low activities, producing clathrate [28][29][30][31][32][33] and intercalate [34][35][36][37] co-crystals. Several recent studies have shown that the d crystalline phase is promising for applications in chemical separations [38][39][40][41] and air/water purification [42][43][44][45][46][47][48][49][50] as well as in sensorics [51][52][53][54][55][56]. It has been also found that the self-assembling of this polymeric framework and active guest molecules into co-crystals reduce guest diffusivity and prevent guest self-aggregation (without recurring to chemical reactions).…”

Guest Exchange Mechanism in the Clathrate Phase of Syndiotactic Polystyrene

“…21 However, we should be careful when comparing diffusion coefficients obtained under different experimental conditions as suggested by Musto et al 36 The diffusion of penetrant in the amorphous region is greatly influenced by the plasticizing effect. Therefore, the D a depends significantly on the kind and concentration of penetrant.…”

Study on δ-Form Complex in Syndiotactic Polystyrene-Organic Molecules System III. Fine Structures of Complexes with Xylene Isomers by Means of High-Resolution Solid-State 13C NMR Spectroscopy

“…Estimation of crystallinity of the δ-form complex is very difficult and only a few papers 17,22 have been reported the crystallinity. In the present study, we calculated approximate crystallinity of the δ-form complex (χ c δ ) as,…”