Ring-closing depolymerization of poly(epsilon-caprolactone) in toluene
solution with catalytic amounts of Bu(2)Sn(OMe)(2) results in a mixtu
re of cyclic oligomers, the equilibrium concentration of which corresp
onds to the concentration predicted according to the Jacobson-Stockmay
er theory. epsilon-Caprolactone, however, is absent from this reaction
mixture. When poly(epsilon-caprolactone) is depolymerized in the melt
at 260 degrees C in the presence of a catalyst, beside epsilon-caprol
actone its cyclic dimer and trimer are distilled off. The composition
is dependent on the catalyst used, e.g., Bu(2)Sn(OMe)(2) produces 95,4
wt.-% of epsilon-caprolactone and 3,7 wt.-% its dimer while with Ti(O
iPr)(4)(iPr: isopropyl) 51,4 wt.-% epsilon-caprolactone and 49,6 wt.-%
of its dimer are obtained. Block copolymers containing poly(epsilon-c
aprolactone) result in a similar product distribution, however, the se
cond block may influence the rate of decomposition. The activation ene
rgy of the catalysed (0,5 mol-% Bu(2)Sn(OMe)(2)) and uncatalysed ring-
closing depolymerization were determined to be 63 kJ/mol and 87 kJ/mol
, respectively.