Synthesis of poly(ester amide)s by the melt polycondensation of semiaromatic polyesters with ethanolamine and their characterization

Semiaromatic poly(ester amide)s (PEAs) were synthesized by the melt polycondensation of ethanolamine (EA) derivatives with dimethyl terephthalate and ethylene glycol in the presence of tetrabutyl titanate as a catalyst, and their crystallization and thermal properties were investigated. The introduction of an amide group into a semiaromatic polyester such as poly(ethylene terephthalate) (PET) produced PEAs (EA-modified PET polymers) with an increase in the melting point. However, these PEAs were found to decompose at a lower temperature than PET on the basis of TGA. Moreover, direct pyrolysis/mass spectrometry measurements suggested that an initial step of the thermal decomposition was a β-CH hydrogen-transfer reaction via asix-member ring transition state at the ester–ethylene–amide unit, at which carbon–oxygen bond scission took place to yield carboxyl and N-vinylamide end groups. Furthermore, molecular orbital calculations using trimer models bis2-4-(methoxycarbonyl)benzoyl]oxy]ethyl]terephthalate, N-2-4-(methoxycarbonyl)benzoyl]oxy]ethyl]-4-2-4-(methoxycarbonyl)benzoyl]oxy]ethyloxycarbonyl]benzamide, and N,N′-bis2-4-(methoxycarbonyl)benzoyl]oxy]ethyl]terephthalamide strongly supported the idea that the β-CH hydrogen-transfer reaction in the thermal decomposition of PEAs might occur more easily at the methylene group next to the amide group in an ester–ethylene–amide unit rather than at the methylene group next to the ester group in an ester–ethylene–ester unit. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2184–2193, 2007