Spectroscopic Investigation of Guest–Guest Interactions in the Nanoporous-Crystalline δ and ε Forms of Syndiotactic Polystyrene

Abstract

The study of guest−guest interactions in cocrystalline polymer samples is in general complicated by their possible occurrence in both amorphous and crystalline phases. In this paper we show that polarized FTIR spectra of axially oriented films allow discrimination between spatially ordered and disordered guest−guest hydrogen bonds occurring in crystalline and amorphous polymer phases, respectively. In particular, the possible formation of hydrogen bonds between alkyl-esters of para-hydroxybenzoic acid (parabens, relevant antimicrobial molecules), when absorbed in s-PS films exhibiting nanoporous-crystalline monoclinic δ and orthorhombic ε phases, has been studied. X-ray diffraction patterns show the formation, for high guest uptake, of triclinic δ and orthorhombic ε cocrystalline forms. Infrared linear dichroism measurements show that for δ form films the parabens are present as isolated guests of the cavities of the crystalline form, while guest−guest hydrogen bonds between parabens are observed only in the amorphous phase. Analogous measurements for ε form films show that, on the contrary, guest−guest hydrogen bonds occur prevailingly in the channels of the crystalline phase, with guest molecular planes being roughly parallel to the polymer host helical axes.

Axial Orientation of Co-Crystalline Phases of Poly(2,6-Dimethyl-1,4-Phenylene)Oxide Films

“…As is well established for s-PS, polarized FTIR spectra of axially stretched films can be powerful tools to study the relative orientations of polymer chain axes and guest molecules in CC phases by evaluating the amount and sign of linear dichroism of guest peaks [ 28 , 33 , 38 , 39 , 40 , 41 ]. The dichroism of the FTIR peaks of guest molecules absorbed in oriented amorphous phases is instead negligible for both PPO [ 42 , 43 ] and sPS [ 44 , 45 ].…”

“…Hence, high dichroic ratios can be achieved only when guest molecules are prevailingly present in CC phases, rather than in the corresponding amorphous phases. This is easily achieved for s-PS due to the largely higher solubility and slower thermal removal of guest molecules in CC phases [ 38 , 39 , 40 , 41 ].…”

Monomeric and Dimeric Carboxylic Acid in Crystalline Cavities and Channels of Delta and Epsilon Forms of Syndiotactic Polystyrene

“…This wide availability of guests has opened the possibility of applications of CC polymer films in many different fields, including fluorescence [ 24 , 25 ], photoreactivity [ 26 ], magnetism [ 27 ] and ferroelectricity [ 28 ]. CC s-PS films [ 29 , 30 , 31 , 32 ] and fibers [ 33 ] have also been proposed for antimicrobial applications, by using poorly polar antimicrobials as guests, such as carvacrol [ 29 , 32 ], eugenol, parabens [ 30 ] and hexanal [ 31 ].…”

Simultaneous Time‐Resolved SAXS and WAXS Study on Guest Exchange Process of Syndiotactic Polystyrene with Aromatic Compounds: Size and Shape Effects of Target Molecules

“…A new kind of functional materials would be developed by combining the characteristics of a host polymer lattice and those of a doped guest compound. The potential as novel functional polymer materials attracts strong attention, and many studies are actively being carried out …”

“…The potential as novel functional polymer materials attracts strong attention, and many studies are actively being carried out. [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] The guest molecules can be replaced smoothly when exposed to a vapor or a liquid of the substitute. [28][29][30][31] By using this unique phenomenon, we can form sPS crystalline complexes even with chemical compounds that are difficult to incorporate into the crystalline region by ordinary methods such as solution-cast and solvent-induced crystallization.…”