E-Caprolactone polymerization

The living nature of PCL obtained in the presence of Zn(OAl-(OPri)2)2 has been used to prepare both di- and triblock copolymers of e-caprolactone and lactic acid (42,43). Treatment of the initial living PCL with dilactide afforded a PCL-PLA diblock with M /Mn = 1.12, with each block length determined by the proportions of the reactants, i.e., the ratio of [monomer]/[Zn]. While the living diblock copolymer continued to initiate dilactide polymerization, it failed to initiate e-caprolactone polymerization. To obtain a PCL-PLA-PCL triblock, it was necessary to treat the living PCL-PLA-OAIR2 intermediate with ethylene oxide, then activate the hydroxy-terminated PCL-PLA-(OCH2CH2)nOH with a modified Teyssie catalyst (Fig. 5). 

Initiation of stannous octoate-catalyzed copolymerization of e-caprolactone with glycerol was used to prepare a series of trifunctional hydroxy-end blocked oligomers, which were then treated with hexane-1,6-diisocyanate to form elastomeric polyesterurethanes with different crosslink densities (49). Initiation of e-caprolactone polymerization with a hydroxypropyl-terminated polydimethylsiloxane in the presence of dibutyl tin dilaurate has been used to prepare a polyester-siloxane block copolymer (Fig. 4) (50). 

Stevels WM, Ankone MJK, Dijkstra PJ, Feijen J (1996) Kinetics and mechanism of e-caprolactone polymerization using yttrium alkoxides as initiators. Macromolecules 29 8296-8303... 

Palard I, Soum A, Guillaume SM (2005) Rare earth metal tris(borohydride) complexes as initiators for e-caprolactone polymerization general features and IR investigations of the process. Macromolecules 36 54—60... 

Propagation according to scheme (168a) is typical of carbocation initiators both modes were observed with acylium (RC+=0) initiators. During chain growth from y -propiolactone, the concentracion of acylium ions decreases until oxonium ions become the active centres. In e-caprolactone polymerization, both types of centre continue to operate. 

Zhou, S.L., Wang, S.W., Yang, G.S. et al. (2007) Synthesis, stractrrre, and diverse catalytic activities of [ethylenebis(indenyl)]lanthanide(III) amides on N-H and C-H addition to carbodumides and e-caprolactone polymerization. Organometallics, 26, 3755. 

Figure 4 First-order Rate Plots of e-Caprolactone Polymerization ([M] = 1 [Initiator] = 0.5 x 10 )...

Another class of aluminium compounds used in e-caprolactone polymerization are aluminium porphyrins. In two studies the use of (5,10,15,20-tetraphenylporphinato)-aluminium alkoxides (TPPAIOR) was evaluated Living polymerization of e-caprolactone and 5-valerolactone could be achieved. It was established that a major improvement in polymerization rate was obtained if an inert Lewis acid was added, e.g. TPPAICP . The polymerization proceeds then by the mechanism shown in Eq. 9-10. 

Again, tri(alkoxide)s are more active than alkyl aluminium alkoxides. Even at the elevated temperatures used the propagation rate constants for L-lactide polymerization are low compared to e-caprolactone polymerization... 

Stevels, W.M., Ankone, M.J.K., Dijkstra, P.J., and Feijen, J., 1996, Kinetics and Mechanism of e-Caprolactone Polymerization Using Yttrium Alkoxides as Initiators, Macromolecules, 29 8296... 

Figure 7.19 Best screw configurations for e-caprolactone polymerization [173].

Dobrzynski, P., 2007. Mechanism of e-caprolactone polymerization and s-caprolactone/ trimethylene carbonate copolymerization carried out with Zr(Acac)4. Polymer 48, 2263-2279. 

Figure 5. First order kinetics plot of dbmOH, dbm(OH)2 and dbm e-caprolactone polymerizations.

Pofycaprolactone (PCL) has been thoroughly examined as a biodegradable medium and as a matrix in controlled drug-release systems. PCL is predominantly produced in the e-caprolactone polymerization process [32-35]. Tokiwa and Suzuki [36] studied the hydrolysis process and PCL biodegradation by fungi and showed that polycaprolactone can be broken down enzymatically. 

Shen, Y., Shen, Z., Shen, J., Zhang, Y. and Yao, K. (1996) Characteristics of mechanism of e-caprolactone polymerization with rare earth halide system. Macromolecules, 29, 3441-6. 

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