EFFECT OF STANNOUS OCTOATE ON THE COMPOSITION, MOLECULAR-WEIGHT, AND MOLECULAR-WEIGHT DISTRIBUTION OF ETHYLENE GLYCOL-INITIATED POLY(EPSILON-CAPROLACCONE)

Bulk polymerizations of epsilon-caprolactone (CAP) were conducted at 1 20 degrees C, with and without ethylene glycol (EG) as initiator, usin g varying concentrations of stannous octoate (SO) as catalyst. In the presence of EG, GPC showed that molecular weight (MW) was determined b y the [CAP]/[EG] ratio and not by [SO] or the concentration of adventi tious water brought into the reactor via the catalyst. Without EG, MWs were higher but decreased as [SO] was increased; polymerization rates were also lower, and the relationship between MW and conversion sugge sted the participation of both ring-opening and condensation polymeriz ation. Late EG addition at high CAP conversion reduced MW to a level t hat was consistent with the [CAP]/[EG] ratio, regardless of the MW of the initial water-initiated polymerization. To aid in structural analy sis of the polymers by NMR spectroscopy, two model systems were synthe sized using [CAP]:[EG]:[SO] ratios of 0:2:1 and 4:2:1. Additional poly merizations were conducted at 80 degrees C using anhydrous EG as initi ator; three were charged with varying amounts of water (0.5, 1, and 2 moles/mole EG), three with EHA (0.025, 0.05, and 0.1 mole/mole EG), an d one received no additional reagent. Monomer conversion (by H-1 NMR) vs, time curves showed that all three concentrations of water depresse d the rate of polymerization relative to the control; however, the rat e had begun to rise for the highest concentration of water. GPC indica ted lower MW with increasing water, suggesting the rise in rate was ca used by increasing total initiator (EG + H2O). All three concentration s of EHA depressed the rate relative to the control, and again the rat e had begun to rise for the highest concentration. GPC indicated essen tially no effect of EHA concentration on MW. Matrix-assisted laser des orption/ionization time-of-light mass spectroscopy confirmed that poly merizations conducted in the presence of water consisted of two separa te distributions: difunctional chains of higher average MW containing an EG residue, and monofunctional chains of lower average MW containin g a water residue (carboxylic acid end group). The control displayed a small fraction of water-initiated chains, which increased as the amou nt of added water increased. The presence of EHA increased the fractio n of water-initiated chains relative to the control, but the concentra tion of EHA did not affect the fraction of water-initiated chains.