Copolyesteramides—IV. Anionic copolymers of ε-caprolactam with ε-caprolactone. Molecular and chain structure

Abstract The chain structures of copolyesteramides formed by anionic ring-opening copolymerisation of e -caprolactam with e -caprolactone have been investigated. The copolymers are shown to possess random multiblock structures with chains composed of O(CH 2 ) 5 CO[NH(CH 2 ) 5 CO] n groups (having relatively small values of n ) intercalated with sequences of O(CH 2 ) 5 CO groups. The distributions of structural units in the chains are significantly affected by reaction time and by the method of introducing lactone into the copolymerising system. A mechanism is proposed to explain the formation of the multiblock structures. The nature of an additional absorbance in the NH-stretching region of the i.r. spectra of the copolyesteramides has been investigated with the aid of model compounds and attributed to hydrogen-bonding between amide and ester groups in the amorphous regions of the copolymers. This bonding may be the cause of the anomalous mechanical properties found at high ester contents.