<i>trans-</i> and <i>cis-</i>DACH-Based Bifunctional Squaramides Catalyzed Ring-Opening Polymerizations of Asymmetric Substituted Glycolides

A broad scope of the library squaramide organocatalysts was prepared starting from two geometric isomers (trans- and cis-(1,2-diaminocyclohexane) (DACH)) with various numbers −CH2– linkages between core aromatic group, different electron-withdrawing −CF3 groups on ring, sizes cyclic tertiary amines piperidine to pyrrolidine DACH ring. Then, ring-opening polymerizations asymmetrically substituted glycolides (ASGs) such as isobutyl glycolide (IBG), methyl (IBMG), ethyl (IBEG) were achieved bifunctional at ambient temperature (20 °C) in dichloromethane (DCM) or 1,2-dichloroethane (DCE) 50 °C. Predictable molecular weights poly(substituted glycolide) (PSG) homopolymers accordance monomer/initiator ratios, high conversions up 100%, narrow polydispersity (PDI) values low 1.04, yields 93% acquired. IBG, IBMG, IBEG monomers showed much better polymerization activity presence trans-DACH-based catalysts when compared cis-DACH-based derivatives. It revealed that change chemical shifts NHCH2 NHCy amine peaks trans catalyst 4.6 2.2 times higher than cis upon addition monomer according 1H NMR titration analyses, which proves interacts catalyst, probably due proximity trans-organocatalyst monomer, thus opening ring more easily. The relative reactivities within three toward are closely related sterically crowded alkyl substituents monomers. For instance, IBG having less led faster IBMG Thus, all 19–25 very efficient 20 On other hand, existence steric group made selectivity important their polymerizations. most effective trans- cis- both found be 22 34 no acidity, respectively. One asymmetric centers leading structural chains (H–H, T–T, H–T segments) PIBG, PIBMG, PIBEG analyzed depth by single-frequency decoupled NMR.