Potassium complexes of the acids Ph2C(X)CO2H (X = OH, NH2): ring opening polymerization of ε-caprolactone and δ-valerolactone

The interaction of potassium tert -butoxide with the acids Ph 2 C( X )CO 2 H ( X = OH = benzilic acid = BenzH 2 ; X = NH 2 = 2,2′-diphenylglycine = DpgH 3 ) under mild conditions affords the potassium salts K-BenzH ( 1 ) and K-DpgH 2 ( 2 ) in moderate isolated yield. An improved molecular structure of 1 is reported and is compared versus the molecular structure of 2 . These two complexes have been screened as catalysts for the ring opening polymerization (ROP) of ε-caprolactone (ε-CL) and δ-valerolactone (δ-VL), with and without benzyl alcohol (BnOH) present, in solution and as melts. Results are compared versus the precursor KO t Bu. In the case of ε-CL, results revealed poor to moderate conversion in solution, but much higher conversions when employed as melts. In the case of δ-VL, conversions were higher both in solution and as melts. The resulting polymers exhibited a wide range of molecular weights, with those for PCL < 10,000 Da (highest M n values were noted for 2 as a melt in the presence of BnOH), whilst in general for PVL, the molecular weights were higher (again 2 exhibited the highest M n values ≤14,320 Da). For KO t Bu, the M n values were toward the high end of the observed range, whilst those for the parent acids were at the low end. MALDI-ToF spectra reveal the presence of mostly cyclic polymers and linear polymers with either MeO/H (for 1 ) or BnO/H (for 2 ) end groups. Kinetic profiles indicated the activity order KO t Bu > 2 > 1 for ε-CL and 2 > KO t Bu > 1 for δ-VL, with an induction period (ca. 15 h) observed for 2 in each case. Factors such as sterics, solubility and H-bonding are thought to dictate the kinetic profiles. TGA results indicated that 1 and 2 were stable under the ROP conditions employed herein.