Intrahelical empty channels of nanoporous-crystalline α and β forms of PPO

• Published in: European polymer journal 2022-10, Vol.179, p.111568, Article 111568
• Main Authors: Golla, Manohar, Nagendra, Baku, Daniel, Christophe, Rizzo, Paola, Auriemma, Finizia, Tarallo, Oreste, Guerra, Gaetano
• Format: Article
• Language: English
• Subjects: Axially oriented amorphous and crystalline phases; Channels; Crystal structure; Crystallinity; Crystallization; Crystals; Dichroism; Film birefringence; Helices; Infrared linear dichroism; Intrahelical guest placement; Molecules; Phases; Polydimethyl phenylene oxide; Polymers; Vibration
• ISSN: 0014-3057; 1873-1945
• DOI: 10.1016/j.eurpolymj.2022.111568

[Display omitted] •First linear dichroism study on polyphenyleneoxide, by Polarized FTIR.•Signs of dichroism of peaks of α and β phases opposite with respect to amorphous phases.•Large crystalline polymer helices, with intrahelical guest location. A linear dichroism study of vibrational peaks of amorphous and semi-crystalline axially stretched poly(2,6-dimethyl-1,4-phenylene)oxide (PPO) films shows an unusual behaviour of co-crystalline and nanoporous-crystalline (α and β form) phases. In fact, signs of dichroism for all vibrational peaks of α and β phases are opposite with respect to those observed for amorphous phases. This behaviour indicates the occurrence in PPO α and β forms of large polymer helices, whose thermodynamic stability can be rationalized by placement of guest molecules in intrahelical channels. A large diameter helix, with chain periodicity of 1.06 nm, is compatible with layer-line position in WAXD patterns of axially stretched α form films. The occurrence for both α and β NC forms of PPO of intrahelical empty channels, can rationalize the very high guest diffusivity of semi-crystalline PPO films, which becomes particularly high when crystalline helical axes are preferentially perpendicular to the film plane.