High-Barrier Poly(hydroxy amide ethers):  Effect of Polymer Structure on Oxygen Transmission Rates. 3

The synthesis of a series of new high-barrier poly(hydroxy amide ethers) is described. The polymers are formed by the reactions of aromatic diglycidyl ethers, with N,N‘-bis(3-hydroxyphenyl)adipamide, HOC₆H₄NHCO(CH₂)₄CONHC₆H₄OH, at 140−160 °C in propylene glycol monophenyl ether solvent using ethyltriphenylphosphonium acetate as initiator. Poly(hydroxy amide ethers) of general structure [−CH₂CH(OH)CH₂OArOCH₂CH(OH)CH₂OC₆H₄NHCO(CH₂)₄CONHC₆H₄O−]_n are readily prepared in high molecular weight. The mainly amorphous thermoplastics have glass transition temperatures (T_g) of 78−146 °C and oxygen transmission rates (O₂TR) that range from 0.2 to 1.8 cc·mil/(100 in.·atm·day) (barrier units or BU) at 23 °C and 45−90% relative humidity. It was determined that barrier properties improve (i.e., O₂TR decreases) as the aromatic core unit, Ar, becomes less bulky or more polar. For example, the poly(hydroxy amide ether) in which Ar is the aromatic unit based on 2,2-bis(4-hydroxyphenyl)-1,1,1,3,3,3-hexafluoropropane has an O₂TR of 1.8 BU, while the poly(hydroxy amide ethers) in which Ar is based on the more compact 2,6-dihydroxynaphthylene or more polar 1,1-bis(4-hydroxyphenyl)acetamide units have lower O₂TR of 0.2 BU. In one instance, an amorphous poly(hydroxy amide ether) was induced to crystallize, yielding a semicrystalline polymer with significantly lower O₂TR. The derivative in which Ar is the 4,4‘-biphenylene unit (O₂TR = 0.3 BU, T_g = 110 °C) was annealed at 160 °C to yield a crystalline material with significant improvement in oxygen barrier (O₂TR = 0.06 BU, T_g = 117 °C, T_m = 195 °C). Other effects that polymer structure has on O₂TR and T_g are discussed.