Copolyesteramides—II. Anionic copolymers of ε-caprolactam with ε-caprolactone. Preparation and general properties

The N-sodiocaprolactam-catalysed anionic polymerisation of ε-caprolactam is activated by ε-caprolactone which itself acts as a comonomer, yielding copolyesteramides. At lower temperatures and lower catalyst concentrations, copolymerisation of the lactone is favoured over that of lactam; higher temperatures, higher catalyst concentrations and longer reaction times cause a more equal incorporation of the two comonomers giving products with molecular weights in the order of 10⁴ and with NH(CH₂)₅CO and O(CH₂)₅CO unit contents approximating to those in the reactant feeds. The T_g's of the products lie between those of the homopolymer extremes but the T_m vs composition relationship displays a shallow eutectic minimum at ca 20% NH(CH₂)₅CO group content and, for given NH(CH₂)₅CO group contents, is sensitive to changes in the technique of copolymerisation. Alternatingly-sequenced NH(CH₂)₅CO/O(CH₂)₅CO copolymers prepared by polycondensation also differ from anionic copolymers of similar sub-unit stoichiometry. The property differences imply differences of chain-sequential order and hence complexity in the mechanism of the anionic copolymerisation.