Poly(ethylene naphthalate) and Poly(ethylene-2,6-naphthalenedicarboxylate -co-ethylene terephthalate) containing 90 to 50 mole\% dimethyl-2,6-naphthaenedicarboxylate (DMN)/acid were synthesized by polycondensation reaction of dimethyl terephthalate, DMN and ethylene glycol.
Melt blends of poly(ethylene terephthalate) and poly(ethylene naphthalate) homopolymer and melt blends of poly(ethylene terephthalate) and poly(ethylene terephthalate-co-ethylene naphthalate) containing 10~50 mole% DMN/acid were prepared by dry blending with different blend ratio. Injection molding machine was used to prepare melt blended sample for NMR, DMTA, DSC and haziness analysis, and single screw extruder for rheological property analysis.
Transesterification, miscibility and rheological property of blends of PEN homopolymer with PET, and PEN/PET copolymer with PET have been studied by thermal analyzer, dynamic mechanical thermal analyzer, NMR and capillary rheometer. The data was compared against those of with melt polymerized copolymer containing equal mole% DMN/acid.
Tg curves of the blend of PEN homopolymer with PET and the blend of PEN/PET copolymer with PET were increased with increased DMN contents. No splitted Tg curves were observed in samples prepared by injection molding, but DMTA curves of the blends showed two separated Tg's when samples were prepared with single screw extruder and when melt retention time was very short.
NMR spectroscopy was used to detect the amount of transesterification in the melt blend of PEN and PET.
Transparency of PEN/PET melt blend was observed in the UV-visible spectrometer. When PEN contents were less than 10 mole%/acid, transparency decreased as the amount of PEN mole ratio increase. But when more than 10 mole% of PEN was used, transparency of the blends increased as PEN mole ratio approaches up to 50 mole%.
Shear rate vs. shear viscosity of PEN and PET with different molecular weight were measured. PEN showed about 7 times higher melt viscosity than PET at 280℃ when samples with the same I.V.(0.6 ㎗/g) were compared.
