Aliphatic AB(2) functional polyesters were conveniently prepared by the ring opening polymerization of epsilon-caprolactone and L-lactide in the presence of the AB(2) functional initiator 2,2-bis(hydroxymethyl)propionic acid (bis-MPA) and Sn(Oct)(2) as the catalyst. In L-lactide polymerization, both bis-MPA hydroxyl groups initiated the polymerization reaction, but for epsilon-caprolactone polymerization this depended on the monomer to initiator to catalyst ratio. Initiation at two hydroxyl groups occurred at high monomer to initiator (M/I) ratio and at high Sn(Oct)(2) to monomer ratio. The melting temperatures of the AB(2)-functional PLLA and PCL polymers were comparable to linear polymers with a (DP) over bar equal to the (DP) over bar per arm in the polymer.
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