“Brill Transition” Shown by Green Material Poly(octamethylene carbonate)

Abstract

Poly­(octamethylene carbonate) (POMC), as the eighth member of the newly developed biodegradable aliphatic polycarbonate family, demonstrates a reversible crystal–crystal transition, which is highly similar to Brill transition extensively studied in the nylon family. With the dipole–dipole interaction in POMC much weaker than the hydrogen bonding, POMC exhibits its “Brill transition” temperature at around 42 °C, much lower than nylons. The two crystalline structures of POMC at below and above the transition temperature can be identified. The transition of POMC is largely associated with the reversible conformation change of methylene sequences from trans-dominated at low temperatures to trans/gauche coexistence at high temperatures.

Using Successive Self-Nucleation and Annealing to Detect the Solid–Solid Transitions in Poly(hexamethylene carbonate) and Poly(octamethylene carbonate)

“…For PC8, there is an α to β (Brill-like transition as reported in the literature) transition at ∼33 °C followed by the melting of the β crystals at ∼58 °C. These transitions are in line with those reported by Zhao et al in PC8 and by us in a preceding work …”

“…The Brill-like transition was attributed to the reversible transition from trans-dominated conformations (in the α phase (at low temperatures)) to the coexistence of trans/gauche conformations (in the β phase (at high temperature)) of methylene sequences. Additionally, a weakening of the dipole–dipole interaction of the carbonyl groups was also observed . These results were recently corroborated in PC8 by Pérez-Camargo et al Similar but even clearer changes were found in PC6-D at higher temperatures due to the dithiocarbonate groups .…”

“…These results were recently corroborated in PC8 by Pérez-Camargo et al Similar but even clearer changes were found in PC6-D at higher temperatures due to the dithiocarbonate groups . In both PC8 and PC6-D, an endothermic signal was clearly detected by using designed thermal protocols for amplification of the signals. , This demonstrated that solid–solid transitions signals could be enhanced with well-designed thermal protocols.…”

“…For the β phase or the Brill-like phase, the main reflections merged to a single one, at q = 15.5 nm –1 (2θ = 21.91°) with the characteristic d -spacing = 0.41 nm, which can be indexed to the (110)/(200) planes. In this case, the unit cell dimensions are a = 0.81 nm, b = 0.89 nm, c (chain axis) = 2.42 nm, and α = 31.9° . In both cases, the unit cell parameters have been estimated by taking the a -axis as a unique axis and selecting monoclinic angles lower than 90°.…”

“…The Brill transition has been widely studied in the polyamide family, ,,− and recently, a Brill-like transition has been reported for poly­(octamethylene carbonate) (PC8) and poly­(hexamethylene dithiocarbonate) (PC6-D) . In PC8, Zhao et al reported the convergence, upon heating, of the d 110 = 0.43 nm and d 200 = 0.38 nm, observed at low temperatures (in the denoted α phase), into a single d -spacing at 0.41 nm at ∼42 °C (in the denoted β phase). The β to α transition also occurs during cooling (reversible character), displaying a hysteresis effect.…”