Synthesis and characterization of poly (ε-caprolactam-co-lactide) polyesteramides using Brønsted acid or Brønsted base organocatalyst

Abstract

Polyesteramides (PEAs) are considered intriguing materials due to the combination of the favorable degradable capacity of aliphatic polyesters given by the hydrolizable ester groups and the desirable thermal and mechanical behavior of polyamides given by the amide groups. Between polyamides and polyester families, poly(ε-caprolactam) and poly(l-lactide) stand out due to their commercial value and outstanding properties. Nevertheless, to date these two monomers have not been co-polymerized due to their different reactivities. In this work, we report for the first time, up to our knowledge, the synthesis of poly(ε-caprolactam-co-l-lactide) copolymers with different compositions. Two different catalysts: (a) Brønsted acid ionic liquid 1-(4-sulfobutyl)-3-methylimidazolium hydrogen sulfate (BAIL) and (b) Brønsted base P4-t-Bu have been explored. In the presence of Brønsted acid the l-lactide reactivity is higher than the ε-caprolactam while in the presence of Brønsted base the opposite behavior is observed. Using Kelen-Tudos method the monomer reactivity ratios are calculated and obtained as rCLa=0.39 and rLA=1.6 and rCLa=2.2 and rLA=0.1 using BAIL and P4-t-Bu, respectively. These differences in the monomer reactivity ratios give us the possibility to create copolymers with different chain microstructure depending on the employed catalyst between 2 and 9kDa. Thus, using P4-t-Bu random copolymers can be obtained at high l-lactide concentration and blocky character copolymers at high ε-caprolactam concentration. Meanwhile, using BAIL catalyst random like copolymers are obtained at high ε-caprolactam contents and blocky character at high l-lactide contents.