Kinetic Study of D,L-Lactide and Glycolide Homopolymerizations by Differential Scanning Calorimetry

Efficiency of liquid tin(ii) n-alkoxide initiators in the ring-opening polymerization of l-lactide: kinetic studies by non-isothermal differential scanning calorimetry

Novel soluble liquid tin(ii) n-butoxide (Sn(OnC₄H₉)₂), tin(ii) n-hexoxide (Sn(OnC₆H₁₃)₂), and tin(ii) n-octoxide (Sn(OnC₈H₁₇)₂) initiators were synthesized for use as coordination–insertion initiators in the bulk ring-opening polymerization (ROP) of l-lactide (LLA). In order to compare their efficiencies with the more commonly used tin(ii) 2-ethylhexanoate (stannous octoate, Sn(Oct)₂) and conventional tin(ii) octoate/n-alcohol (SnOct₂/nROH) initiating systems, kinetic parameters derived from monomer conversion data were obtained from non-isothermal differential scanning calorimetry (DSC). In this work, the three non-isothermal DSC kinetic approaches including dynamic (Kissinger, Flynn–Wall, and Ozawa); isoconversional (Friedman, Kissinger–Akahira–Sunose (KAS) and Ozawa–Flynn–Wall (OFW)); and Borchardt and Daniels (B/D) methods of data analysis were compared. The kinetic results showed that, under the same conditions, the rate of polymerization for the 7 initiators/initiating systems was in the order of liquid Sn(OnC₄H₉)₂ > Sn(Oct)₂/nC₄H₉OH > Sn(Oct)₂ ≅ liquid Sn(OnC₆H₁₃)₂ > Sn(Oct)₂/nC₆H₁₃OH ≅ liquid Sn(OnC₈H₁₇)₂ > Sn(Oct)₂/nC₈H₁₇OH. The lowest activation energies (E_a = 52, 59, and 56 kJ mol⁻¹ for the Kissinger, Flynn–Wall, and Ozawa dynamic methods; E_a = 53–60, 55–58, and 60–62 kJ mol⁻¹ for the Friedman, KAS, and OFW isoconversional methods; and E_a = 76–84 kJ mol⁻¹ for the B/D) were found in the polymerizations using the novel liquid Sn(OnC₄H₉)₂ as the initiator, thereby showing it to be the most efficient initiator in the ROP of l-lactide.

The efficiency of homogeneous liquid tin(ii) n-alkoxide initiators in the ROP of l-lactide was reported in this work by non-isothermal DSC kinetic approaches.