Structure and properties of naphthalene-containing polyesters .2. Miscibility studies of poly(ethylene naphthalene-2,6-dicarboxylate) with poly(butylene terephthalate) by C-13 CP/MAS NMR and DSC

The miscibility of poly(ethylene naphthalene 2,6-dicarboxylate) (PEN) with poly(butylene terephthalate) (PBT) has been studied by C-13 CP/MAS NMR complemented with DSC measurements. The blends were prepared by a solution precipitation method. The DSC examination shows that the T-g of the blends is between the T-g of the two homopolymers. The crystalline enthalpy of PEN decreases continuously when the amount of PEN decreases. The T-m and Delta H-m of PBT were lowered continuously as the PEN ratio was increased, while that of PEN was lowered as the PBT ratios were increased. These results imply that PEN is compatible with PBT. T-H(1) rho values for the blend 50 PEN/50 PBT and pure components have been measured. Since single-component NMR relaxation behavior was observed, miscibility was demonstrated for the blend. Intermolecular cross polarization from the protons in PBT to carbons in deuterated PEN was examined by measuring the full decoupling, no decoupling, and delayed decoupling C-13 CP/MAS spectra of the blends of deuterated PEN with different compositions of PBT. The results from such independent measures of effective mixing of chains within the deuterated PEN and PBT blends lead to the conclusion that the PEN/PBT blends with weight ratios 80/20, 50/50, and 20/80 are miscible in the molecular level.