Unexpected structural properties in the saturation region of the odd-even effects in aliphatic polyethers: Influence of crystallization conditions
Ikusi/ Ireki
Data
2022-01-04Egilea
Flores, Irma
Pérez Camargo, Ricardo Arpad
Gabirondo Amenabar, Elena
Caputo, Maria Rosaria
Liu, Guoming
Wang, Dujin
Sardon Muguruza, Haritz
Macromolecules 55(2) : 584-594 (2022)
Laburpena
A series of aliphatic polyethers with different chain lengths (nCH2= 6 to 12, and 16) is
studied employing differential scanning calorimetry and X-rays scattering. The
calorimetric and structural behavior of samples crystallized from the melt is divided into
the odd-even and saturation regions. In the odd-even region (nCH2 = 6 to 10), the odd
samples (nCH2 = 7, and 9) show enhanced calorimetric properties (e.g., higher transition
temperatures) and faster crystallization kinetics than the even ones (nCH2 = 6, 8 and 10).
The odd samples crystallize in orthorhombic unit cells and the even ones in monoclinic
unit cells. In the saturation region (nCH2 = 11 to 16), the calorimetric properties increase
as nCH2 increases without alternation. However, unexpectedly, the nCH2 = 12 displayed a
mixed structure (monoclinic + orthorhombic) instead of an orthorhombic one. Thus, a
structural saturation effect (i.e., an orthorhombic unit cell) is not reached. This particular
structural feature was investigated under varied thermal histories, induced by different
cooling rates. The samples as synthesized (i.e., crystallized during precipitation from
solution) exhibited a structural saturation effect since both nCH2 = 10 and 12 display an
orthorhombic unit cell. But, the nCH2 = 10 exhibits a monoclinic unit cell, and the nCH2 =
12 a mixed structure when the samples crystallize from the melt at different rates. Only
the nCH2 = 16 crystallizes in an orthorhombic unit cell, independently of the thermal
history. Thus, the complex odd-even effects in these aliphatic polyethers are a function
of the cooling rate from the melt and sample preparation procedures (solution or melt
crystallization).