Copolymerization of Cyclic Carbonates with Lactones

The sequential copolymerizahon of DTC and CL with a variety of initiating systems results in block copolymers, if the conditions are carefully chosen so that transesterification is suppressed, for example, with Mg- and Al-based inihators [12-14]. For these copolymers, only DTC-DTC and CL-CL homodiads were detected in the C NMR spectrum. 

The copolymerization of a mixture of DTC and CL at low temperatures resulted in A-X-B-type copolymers, where A was a PDTC block, B a PCL block, and X a tapered sequence of DTC and CL repeahng units. As a consequence, DTC-CL and CL-DTC heterodiads were observed in the C NMR spectra. The concentration of 

The copolymerization of a mixture of DTC and PVL in toluene as a solvent and with K-naphthaUn as the initiator resulted in an A-B block copolymer, where A was the PDTC block and B the PPVL block [88, 89]. This became evident by C NMR analysis, where only signals corresponding to homodiads were observed. The explanation for this one-pof block copolymer synthesis is based on the large difference in the rate of polymerization of DTC and PVL, combined with the incompatibility of the active species (K-carboxylate does not react with DTC monomer), and with the fact that no transesterification occurs between the ester and carbonate groups. It should be noted that with initiators based on Li, Mg, Al, Zn and Sn, no copolymers were obtained. 

The sequential copolymerization of DTC and LLA [88, 90] revealed different polymer microstructures, depending on the order in which the monomers were added to the initiator. The polymerization of first LLA followed by the addition of 

According to time-dependent H NMR analysis, initially only LLA-LLA diads are formed-that is, at first the LLA is polymerized. However, as time elapsed, triads comprising one DTC and two LLA units were formed, then triads with two DTC and one LLA unit, and finally DTC-lactate-DTC triads and DTC-DTC diads were formed. For a mechanistic proposal, two further experimental observations should be taken into consideration (i) A mixture of hving PLLA and Hving PDTC showed no transesterification, such that after 12 h at 90 °C no mixed diads were observed and (ii) Hving PDTC-block-PLLA and PLLA-stat-DTC showed no changes in microstructure under conditions suited to polymerization. 

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