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

Abstract

Films exhibiting co-crystalline (CC) phases between a polymer host and low-molecular-mass guest molecules are relevant for many applications. As is usual for semi-crystalline polymers, axially oriented films can give relevant information on the crystalline structure, both by Wide Angle X-ray diffraction fiber patterns and by polarized Fourier-transform infrared spectroscopy. Axially oriented CC phases of poly(2,6-dimethyl-1,4-phenylene)oxide (PPO) with 1,3,5-trimethylbenzene (mesitylene) can be simply obtained by the stretching of CC PPO films. In fact, due to the plasticization effect of this highly boiling guest, PPO orientation can occur in a stretching temperature range (170–175 °C) nearly 50 °C lower than that generally needed for PPO films (220–230 °C). This low stretching temperature range allows avoidance of polymer oxidation, as well as formation of the mesomorphic dense γ PPO phase. Axially oriented CC phases of PPO with toluene, i.e., with a more volatile guest, can be instead obtained by the stretching (in the same low temperature range: 170–175 °C) of CC PPO blend films with polystyrene.

Segregation of Benzoic Acid in Polymer Crystalline Cavities

“…The polarized FTIR spectra of the axially oriented α PPO films before and after 8 wt% of BA uptake are shown in Figure 6 . In agreement with the literature [ 30 ], the FTIR peaks (at 773, 756, 495 and 414 cm −1 ) typical of the α NC host phase were dichroic (e.g., S p,495 = +0.33).…”

“…In this paper, we characterized films of sPS and PPO including BA molecules in their amorphous and crystalline phases. In particular, axially oriented sPS and PPO films [ 30 ] were used to obtain information on the crystalline structure by WAXD fiber patterns, as well as information on the aggregation and orientation of the guest molecules in the polymeric amorphous and crystalline phases, by polarized FTIR measurements. The present study shows that the NC δ form of sPS not only avoids additive aggregation but also leads to the separation of BA dimers and, hence, the appearance of vibrational peaks typical of vapor phase molecules.…”

Molecular Features Behind Formation of α or β Co-Crystalline and Nanoporous-Crystalline Phases of PPO

“…Table 1 collects in its last column the crystalline forms (α or β) of all films characterized in this study together with those already reported in the literature ( Khulbe et al, 2000 ; Daniel et al, 2011 ; Nagendra et al, 2019 ; Golla et al, 2020b ; Nagendra et al, 2021a ; Nagendra et al, 2021b ). In Table 1 , the guest molecules are ordered on the basis of their solubility parameter (second column) while the used crystallization methods are indicated in the fourth column.…”

Absorption and Isomerization of Azobenzene Guest Molecules in Polymeric Nanoporous Crystalline Phases

“…Axially amorphous oriented films were obtained by stretching PPO amorphous films in the temperature range 220-230 • C up to draw ratio 4-5. Films exhibiting axial orientation of α NC phase were obtained by axial stretching of PPO/mesitylene CC films at 170-175 • C up to draw ratio 4 and by subsequent mesitylene removing through sorption/desorption procedures of acetonitrile at room temperature for 2 h [71]. PPO/mesitylene CC films, with thickness of nearly 150 µm, were obtained by casting from 3.5 wt% mesitylene solution at room temperature.…”