One-Step Route to α-Hydroxyl-ω-(carboxylic acid) Polylactones Using Catalysis by Decamolybdate Anion

Asymmetric telechelic α-hydroxyl-ω-(carboxylic acid) poly(ε-caprolactone) (HA-PCL) and α-hydroxyl-ω-(carboxylic acid) poly(δ-valerolactone) (HA-PVL) were synthesized by ring-opening polymerization of ε-caprolactone (CL) and δ-valerolactone (VL), respectively. HA-PCL oligomers were obtained at 150 °C in 2 h using ammonium decamolybdate (NH<INF>4</INF>)<INF>8</INF>[Mo<INF>10</INF>O<INF>34</INF>] as catalyst and water as initiator. A control of the number-average molecular weight (measured by NMR) can be achieved in the range between 212 and 2198 Da, based on the initial monomer/initiator ratio. Number-average molecular weight (M<INF>n</INF>) shows a linear dependence with CL/H<INF>2</INF>O ratio in this range. The nature of hydroxyl and carboxylic acid end groups of HA-PCL and HA-PVL was studied by MALDI-TOF and ¹H and ¹³C NMR. Changes in the chemical shifts observed in the NMR spectra as a function of molecular weight were explained in terms of hydrophobic interactions. Formation of macrocyclic species was studied by MALDI-TOF. It was found that macrocyclic species are favored at longer reaction times. Insertion of alcohols and polycondensation reactions occurring after complete monomer conversion were also studied. Alcohol insertion for this system depends on the nature of alcohol. Polycondensation reactions vary with reaction times and affect the polymer molecular weight in a nonlinear manner. Finally, the α-hydroxyl-ω-(sodium carboxylate) PCL salt (HC-PCL) was prepared from HA-PCL and characterized by FT-IR and solution and solid-state NMR. Important differences between CP-MAS and MAS spectra are observed and discussed in terms of morphology and polarization transfer.