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(O n C 4 H 9 ) 2 ), tin(ii) n -hexoxide (Sn(O n C 6 H 13 ) 2 ), and tin(ii) n -octoxide (Sn(O n C 8 H 17 ) 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 (SnOct 2 / n ROH) 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(O n C 4 H 9 ) 2 > Sn(Oct) 2 / n C 4 H 9 OH > Sn(Oct) 2 ≅ liquid Sn(O n C 6 H 13 ) 2 > Sn(Oct) 2 / n C 6 H 13 OH ≅ liquid Sn(O n C 8 H 17 ) 2 > Sn(Oct) 2 / n C 8 H 17 OH. 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(O n C 4 H 9 ) 2 as the initiator, thereby showing it to be the most efficient initiator in the ROP of l-lactide.