In short, a Schlenk tube equipped with a magnetic stirrer was charged sequentially with catalyst (MBTO, 2 equiv), initiator (diethylene glycol, 1 equiv), and CL in n-octane followed pumping vacuum and high pure dry nitrogen in turn for three times [15, 16].
When monobutyltin oxide (MBTO) was employed as catalyst and reflexed in n-octane at 150[degrees]C for 8 hours under nitrogen, an off-white polymer (PGL) was precipitated from the solution.
In this work, the d-GL was successfully catalyzed by MBTO into polymer without hydroxyl protection and deprotection and copolymerization with CL through one-pot-two-step process.
At first, MBTO formed active species with initiator; then the active species ring-opening d-GL in the chain propagation step and dormant chain were formed by isolating MBTO segment in the chain growing process.
This PGL was operated under the condition of MBTO as catalyst and diethylene glycol as initiator in n-octane, 160[degrees]C, 4h ((a) DMSO-[d.sub.6]; (b) [D.sub.2]O).
Caption: Scheme 2: Proposed mechanism for the ROP of d-GL using diethylene glycol as initiator and MBTO as catalyst.
An apparent activation energy for formation of BHBS with using MBTO as a catalyst is 136KJ/mol, whereas the value of uncatalized reaction is slightly higher (149KJ/mol).
Figure 10 shows the correlation between extent of reaction and time at various concentration of MBTO and DBTO as a catalyst in the direct-esterification.
We investigated the rate of reaction on direct-esterification of SA and BD both in the presence of MBTO as a catalyst and in the absence of catalyst.
In the effect of the concentration of MBTO and DBTO catalyst, the reactivity of the MBTO catalyst is higher than that of the DBTO.