The Brill Transition in Long-Chain Aliphatic Polyamide 1012: The Role of Hydrogen-Bonding Organization

Abstract

The effect of hydrogen-bond (H-bond) organization, evaluated by the crystal perfection index (CPI), on the Brill transition of long-chain polyamide 1012 upon heating was investigated with variable-temperature wide-angle X-ray diffraction (WAXD), small-angle X-ray scattering (SAXS), and Fourier transform infrared spectroscopy (FTIR). A sufficiently high cooling rate was required to prepare samples with randomly distributed H-bonds (i.e., a low CPI) because this inhibits the reorganization of the 2-D hydrogen sheet structure during cooling from melts. The Brill temperature (T B) values of the T210 and T270 samples, which were prepared by cooling from 210 and 270 °C at a rate ranging from 5 to 100 °C/min, were determined. The T B values of the T270 samples determined by WAXD and FTIR show a significant linear decrease with the decreasing CPI, whereas that of the T210 samples remains constant because its CPI is independent of the applied cooling rate. Both the T210 and the T270 samples quenched by a liquid nitrogen bath are γ-phase at ambient temperature, suggesting that the critical cooling rate required to reduce the CPI depends on the content of hydrogen-bonded H-bonds at each temperature for the melts. The T B gap between the T210 and T270 samples with a similar lamellar thickness is caused by the content of randomly distributed H-bonds.

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

“…As the more perfect and bigger the crystals are, the T B will be found in a higher position. However, recently, it has been pointed out that the amorphous phase may also play a key role, as well as the hydrogen bond organization …”

“…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).…”

“…They quenched and subsequently cold-crystallized the samples at different T c , obtaining that as T c increases, the T B increases. 25 Recently, Wang et al 26 studied the effect of hydrogen bond organization by measuring the crystal perfection index (CPI) in PA1012. They found that the T B values, after cooling at different rates (i.e., ranging from 5 to 100 °C/min) from the melt (i.e., 270 °C), decrease as the CPI decreases (i.e., the low CPI values are obtained at the highest cooling rates).…”

Brill Transition in Polyamide 1012 Multiblock Poly(tetramethylene oxide) Copolymers: The Effect of Composition on Hydrogen-Bonding Organization

“…PAs can undergo crystal transition behavior under the applied thermal or elongation fields, such as the reversible transition of PA66 from a triclinic phase to a pseudohexagonal phase upon heating (known as the Brill transition), which was first reported by Brill in 1942. 15 Numerous investigations into Brill transition under external fields have been reported for various PAs, 1,2,16 for example, PA6, 17−19 PA1010, 20 PA1012, 8,21,22 their composites, 23−26 and copolymers. 27−29 As a typical AABB-type even−even long-chain PA (LCPA), the most thermodynamically stable crystal phase in triclinic symmetry of PA1012 is denoted the α-phase, which is featured by the H-bonds all arranged along the a-axis of its unit cell to establish the hydrogen bonding sheets (H-sheets) held together by van der Waals interaction in a well-defined progressive packing along the b-axis.…”

“…It has been demonstrated that T B is highly dependent on the crystallization conditions, 40 which affects the characteristics such as the thickness distribution of lamellae 20 and the H-bond organization. 8 In addition, blending with fillers 24,25,40,41 and chemical modification by inserting the comonomers 29,42−44 in the main chain are two effective ways to control T B . Liu et al found that the T B of PA66 was decreased by blending with silicate and attributed it to the strong interaction between PA66 chains and surfaces of silicate layers.…”