Oxygen‐barrier properties of polyethylene terephthalate modified with a small amount of aromatic comonomer

Abstract

The oxygen‐barrier properties of amorphous copolyesters based on ethylene terephthalate with 10%, or less, of an acid comonomer were examined. Comonomer units were isophthalate, phthalate, 1,5‐naphthalate, 1,8‐naphthalate, 2,6‐naphthalate, 1,8‐anthracenate, 2,6‐anthracenate, and 2,7‐pyrenate. Even 2.5 mol % comonomer significantly affected the permeability. Linear comonomers decreased the permeability. In contrast, small amounts of a kinked comonomer increased the permeability. However, increasing the amount of kinked comonomer further (gradually) decreased permeability P below that of polyethylene terephthalate. Generally, comonomer affected solubility S less than diffusivity D; therefore, changes in P reflected primarily changes in D. The solubility and diffusivity depended on copolymer composition in accordance with static and dynamic free‐volume concepts of gas permeability in glassy polymers. The solubility correlated with the amount of free volume, as determined by the glass‐transition temperature. This study also explored the relationship of dynamic free volume, which determines D, to thermally accessible segmental motions of the polymer chain. The effect of comonomer on D correlated with the intensity of the gauche component of the subambient γ relaxation. Changes in the fraction of gauche‐glycol conformations resulting from copolymerization were confirmed by Fourier transform infrared spectroscopy. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1900–1910, 2001

Synthesis and characterization of novel ethylene glycol polyesters containing terephthalic and 5-adamantylisophthalic acids

“…Through the incorporation of 5 mol% monomer 2, a 17% increase in oxygen permeability is observed while incorporation of 5 mol% free adamantane results in a 4% reduction in oxygen permeability. In both cases, a 10% increase in oxygen solubility relative to PET homopolymer was observed, consistent with published accounts which correlate permeant solubility with glass transition temperature [17,18]. The diffusivity term, however, appears to dominate the overall permeation trends.…”

“…In the case of copolymer (5 mol% monomer 2, Table 2), diffusivity increases, leading to an overall increase in oxygen permeability. Since diffusivity in PET copolymers is dominated by sub-T g molecular motions (which create dynamic free volume) [17,18], these barrier results suggest that the pendant adamantly groups possess rotational and/or vibrational freedom independent of segmental motion. For comparison, work by Polyakova et al showed an 8% reduction in oxygen permeability with 5 mol% incorporation of isophthalate in PET copolymers [18].…”

“…When the vessel had cooled to ambient temperature, the solid acid was ltered, washed with deionized water and vacuum dried. The product was recrystallized from acetic acid to give white crystals that were rinsed with deionized water and air dried; yield 90%; mp >350 ± C (decomposition); analytical calculated for C 18 …”

“…The hexanes and excess m-xylene were removed in a rotary evaporator. The off-white solid product was recrystallized from hexanes to give white crystals; yield 85%; mp 152-154 ± C; analytical calculated for C 18 …”

Oxygen transport as a solid‐state structure probe for polymeric materials: A review

“…26 S, measured at the test temperature (T test ), is plotted versus the temperature difference from T g , that is, the quantity T g Ϫ T test , for a series of glassy copolymers based on PET. 24,31 In this case, S was measured primarily at T test ϭ 25°C, and the polyesters differed in T g . The right branch of the plot in the temperature region of 20°C Յ T g Ϫ T test Յ 60°C shows a linear decrease in S as T g approaches T test , and this reflects the reduction of the excess-hole free volume.…”