9-Phenyl-2,4,8,10-tetraoxaspiro[5,5] undecanone (PTO) was synthesized from pentaerythritol via the acid-catalyzed acetal formation reaction with benzaldehyde and subsequent ring closure with ethyl chloroformate. The cyclic carbonate monomer was subsequently polymerized by ring-opening polymerization (ROP) initiated from 1,4-butanediol (1,4-BDO) using the 1-(3,5-bis( trifluoromethyl) phenyl)-3-cyclohexylthiourea and 1,8-diazabicyclo[ 5.4.0] undec-7-ene dual organocatalytic system. It was found that the organocatalyst allowed for the synthesis of well-defined polymers with minimal adverse side reactions and low dispersities. This system was then employed in the ROP of PTO initiated from an alpha, omega-dihydroxy poly(caprolactone) (PCL) macroinitiator, with varying molecular weights, to yield a series of A-B-A block copolymers. These materials were characterized by H-1 NMR spectroscopy, gel permeation chromatography, differential scanning calorimetry, thermogravimetric analysis and tensile analysis. It was found that the chain extension from PCL with poly(PTO) (PPTO) blocks yielded a thermoplastic material with superior tensile properties (elongation and Young's modulus) to that of the PCL homopolymer. Furthermore, it was noted that the addition of PPTO could be employed to alter the crystallization properties (crystallization temperature (T-c), and percentage crystallization) of the central PCL block. (c) 2014 Wiley Periodicals, Inc.