Abstract
Guest molecular features determining the formation of α and β phases of poly(2-6-dimethyl-1,4-phenylene) oxide (PPO) are explored by collecting literature data and adding many new film preparations, both by solution casting and by guest sorption in amorphous films. Independently of the considered preparation method, the α-form is favored by the hydrophobic and bulky guest molecules, while the hydrophilic and small guest molecules favor the β-form. Furthermore, molecular modeling studies indicate that the β-form inducer guests establish stronger dispersive interactions with the PPO units than the α-form inducer guests. Thus, the achievement of co-crystalline (and derived nanoporous crystalline) α- and β-forms would result from differences in energy gain due to the host–guest interactions established at the local scale.
Highlights
CC PPO films were prepared by immersion of amorphous PPO films in the liquid guest at room temperature, and this method is indicated in Table 1 as guestinduced crystallization (GIC)
This study aimed to establish guest molecular features determining the formation of α or β CC and nanoporous crystalline (NC) phases of PPO
This aim was pursued by collecting literature data and by adding many new film preparations to evaluate the influence of the chemical nature of the guest on the formation of α or β phases
Summary
Poly(2-6-dimethyl-1,4-phenylene) oxide (PPO), is always amorphous by melt processing (Toi et al, 1982; Guerra et al, 1991; Tsujita, 2003; Yang and Knauss, 2015; Minelli et al, 2017), while it can be crystallized by solution processing as by sorption of guest molecules in amorphous samples (Alentiev et al, 1998; Khulbe et al, 2000; Khayet et al, 2004; Sterescu et al, 2007; Daniel et al, 2011; Nagendra et al, 2019; Alentiev et al, 2021). The CC forms of Class ii can be divided into two subclasses (α and β) with different values of the chain periodicities (c = 0.528 nm and c = 0.547 nm) and different polymer packing (with main equatorial reflections at 2θCuKα ≈ 4.5°, 7.1°, 11.2°, 14.9°, and 5.2°, 7.7°, 12.8°) (Daniel et al, 2011; Nagendra et al, 2019) Both the CC α- and β-forms can be obtained by guest-induced crystallization of amorphous samples or solution processing. The CC phases of Class i become amorphous (Barrales-Rienda and Fatou, 1971; Horikiri, 1972; Hurek and Turska, 1984; Tarallo et al, 2012), while the CC phases of Class ii can produce two different nanoporous crystalline (NC) forms, i.e., crystalline forms with a density lower than that of the corresponding amorphous phase. The aim is to try to establish, with the support of molecular modeling, guest molecular features determining the formation of α or β crystalline phases
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