An insight into the monomeric isomerism in the polymerization of glycidol with B(C6F5)3: A DFT study of the initiation, propagation and cyclization steps

The polymerization of glycidol (Gly) using tris-(pentafluorophenyl)borane [B(C 6 F 5 ) 3 ] leads to the formation of water-soluble polymer structures with a cyclic core and hydroxyl-terminated branches. The polymerization mechanism is complex, as it involves competitive reactions between B(C 6 F 5 ) 3 and both the epoxide and hydroxyl groups of Gly, with two possible propagation mechanisms: the active chain end mechanism (ACEM) and the activated monomer mechanism (AMM). Additionally, polymerization occurs through a ring-expansion polymerization mechanism that allows the formation of cycles. There are many structural parameters that cannot be experimentally determined in this reaction and which can be advantageously addressed by quantum calculations. These are the probability of formation of isomeric structures L 1,3 and L 1,4 , which is clearly linked to whether ACEM or AMM operates, but also whether the monomer attack to the active center occurs on the α- or β-carbon of the epoxide ring. This study focuses on the quantum calculations and energetics of the initiation of Gly with B(C 6 F 5 ) 3 , first propagation step and termination by cyclization. The results indicate that the thermodynamic stability and kinetic barriers of the products resulting from α- and β-attacks on the epoxide ring, and from the ACEM and AMM mechanisms are similar during the first propagation step. These similar reaction probabilities would result in an L 1,3 :L 1,4 ratio of 3:1. However, the higher thermodynamic stability of cycles containing a larger number of L 1,4 units qualitatively explains why the L 1,3 :L 1,4 ratio is experimentally reduced to unity (1:1). • DFT based full characterization of the polymerization of glycidol to form cyclic polymers using B(C 6 F 5 ) 3 as catalyst. • Initiation can occur via epoxide or hydroxyl groups, with a slight preference for OH initiation. • ACEM and AMM propagation via α/β attack show comparable kinetic and thermodynamic profiles. • DFT rationalizes the experimentally observed 50:50 L 1,3 /L 1,4 isomer ratio in cyclic polyglycidol. • New structural data, not available from experiments, are provided by simulations.