Facile synthesis of eight-membered cyclic(ester-amide)s and their organocatalytic ring-opening polymerizations

Abstract

Five eight-membered cyclic(ester-amide)s (M1–M5) were synthesized from phthalic anhydride and β-amino alcohols by sequential nucleophilic addition and intramolecular esterification. The organocatalytic ring-opening polymerization (ROP) of these monomers with 1,5,7-triazabicyclo[4.4.0]-dec-5-ene (TBD) and 1,8-diazabicyclo[5.4.0]undecane-7-ene (DBU)/thiourea (TU) as the catalysts was investigated, and they could all be polymerized in a controlled manner under optimized conditions, affording well-defined poly(ester-amide)s (PEAs) (P1–P5) with tailored molar masses and narrow dispersities. The structures of these PEAs were characterized, confirming that the main-chain tertiary amide bonds existed as a mixture of cis/trans isomers. These PEAs are amorphous materials with high thermal stability (T_d,5%: 260–301 °C) and side chain-dependent glass transition temperatures (T_gs) (62–138 °C). Polymer P1 contains both a rigid benzene ring and a pyrrole ring in the backbone, being a PEA with the highest T_d,5% (301 °C) and T_g (138 °C). The TBD-catalyzed copolymerization of M1 and rac-LA could generate a series of random copolymers with tunable and enhanced T_gs (52–96 °C) with increasing incorporation ratio of M1 (0–51 mol%). Finally, These PEAs could be selectively and completely converted into their corresponding monomer precursors in alkaline aqueous solutions.