Hydrolysis of poly(ethylene terephtalate). A steric exclusion chromatography study

The hydrolysis of PET (M-w 27 kg mol(-1)) in boiling water has been studied by steric exclusion chromatography. It appears that both the average molar mass and the polydispersity index decrease in a pseudohyperbolic way and tend towards asymptotic values, respectively M-n infinity-->2 kg mol(-1) and I-infinity-->1.50. This behaviour indicates that hydrolysis is homogeneous at dimension scales higher than Lc (lamellae thickness). Hydrolysis occurs in the amorphous phase and at chain folds at the crystal surface, whereas crystals are unaffected due to their impermeability to water. The chain length decreases to tend, thus, towards L-c. Embrittlement is expected to occur when the entanglement network is destroyed in the amorphous phase. Since the corresponding critical chain length L-e and the initial chain length L-0 are such as L-e and L-0 much greater than L-c, it can be considered that in the conversion range of practical interest (e. g. before embrittlement). PET hydrolysis, despite its above quoted peculiarities, can be considered as a random chain scission process in kinetic studies. (C) 1999 Elsevier Science Ltd. All rights reserved.