Kinetics of Sn(Oct)2-catalyzed ring opening polymerization of ε-caprolactone
To evaluate the effects of different alcohols (primary, secondary, and two different tertiary alcohols) as initiators on the structure of polycaprolactone (PCL) in ring-opening polymerization (ROP), four experiments were conducted in toluene with tin(II) 2-ethylhexanoate (Sn(Oct) 2 ) as the catalyst. The kinetics of ε -caprolactone ( ε -CL) ROP at different temperatures and monomer concentrations were studied with n -butanol as the initiator and Sn(Oct) 2 as the catalyst. The kinetic plot of ln(M 0 /M t ) vs. time ( t ) seems a linear, which indicates that the propagation rate is in the first order with respect to monomer concentration. When the reaction temperature increased, the reaction rate and the final relative maximum monomer conversions also increased. The molecular weight of PCL initially increased and then decreased as monomer conversion increased. This behavior can be attributed to the high viscosity of the system, which affected monomer diffusion and polymer chain propagation. In addition, prolonging reaction time caused inter-/intramolecular transesterification. However, when monomer concentration decreased, the reaction rate decreased. The actual activation energy of Sn(Oct) 2 -catalyzed ROP of ε -CL in toluene was -75 kJ/mol.
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