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. © 2014 American Chemical Society.
|Titolo:||Spectroscopic investigation of guest-guest interactions in the nanoporous-crystalline δ and ε forms of syndiotactic polystyrene|
|Data di pubblicazione:||2014|
|Appare nelle tipologie:||1.1 Articoli su Rivista|