Anionic polymerization of caprolactone

Anionic Polymerization of -Caprolactone for Block Copolymer Synthesis... 

Anionic polymerization of -caprolactone has been studied in several laboratories and it was found that considerable amounts of oligomers were found as by-products.— — We have studied the formation of oligomers in the anionic polymerization of 6-capro-lactone by gpc technique.A In view of the very facile intra- and intermolecular transesterification reactions in this system- -, the product distribution seems very interesting to check the validity of the thermodynamic equilibrium. 

In a similar manner, Yoshida and Osagawa [436] synthesized poly(s-caprolactone) with 2,2,6,6-tetramethylpiperdine-l-oxyl (TEMPO) at one end by anionic polymerization of caprolactone using an aluminum tri(4-oxy-TEMPO) initiator. The TEMPO-supported polycaprolactone behaved as a polymeric counter radical for a controlled/ living radical polymerization of styrene to form block copolymers [436]. 

Ito, K., and Yamashita, Y., Propagation and depropagation rates in the anionic polymerization of e-caprolactone cyclic oligomers, Macromolecules. Ij., 68-72, 1978. 

In the anionic polymerization of 6-caprolactone in THF with potassium tert-butoxide, monomer consumption is very fast and monomer could not be detected in any appreciable amount in the equilibrated mixture obtained after several minutes from the initiation. Upon terminating the reaction at 6 seconds after the introduction of the initiator solution, 6% monomer remained unreacted accompanied with polymers (68%) and oligomers (26%). 

The ring-opening polymerization of cyclic monomers can be performed by ionic chain polymerization, as is the case of epoxy monomers. Anionic polymerization of ethylene oxide propylene oxide, and caprolactone can be initiated by alkoxides ... 

Some cyclic oligomers were formed as by-products in the polymerization of e-caprolactone. Yamashita et al. [136] reported that the anionic polymerization of e-caprolactone with f-BuOK in THF results in a living ring-chain... 

Kricheldorf et al. reported an anionic polymerization of y-D,L-butyro-lactone or D,L-lactide with cyclic dibutyltin initiators, such as 2,2-dibutyl-2-stanna-l,3-dioxepane, to give cyclic polymers [ 138-140]. Figure 41 shows the ring expansion polymerization of lactone for synthesizing a cyclic polymer as an example. They also synthesized the cyclic polymer with a living mechanism in the polymerization of e-caprolactone [141]. 

Some heterocycles have both nucleophilic and electrophilic atoms in their molecule. Thus they can be opened and polymerized by the anionic, cationic or coordination mechanisms. Examples are lactams, lactones, and cyclic siloxanes. Investigations of the mechanism of lactam propagation are complicated by the occurence of side reactions. In principle, the mechanism described in Chap. 3 by the schemes (55)—(57) and (71) is accepted. Anionic polymerization of cyclic esters consists, in most cases (see Chap. 4, Sect. 2.2) of repeated reversible attacks on the carbonyl carbon by the anion 0]-. From e-caprolactone, polyester chains grow according to [315]... 

These and related methods allowed us recently to reevaluate the structure of active centers in anionic polymerization of simple, unsubstituted lactones, 5-propiolac-tone. The rationale was put forward in terms of stereo -electronic factors to explain why g-propiolactone propagates on carboxylate and e-caprolactone on alcoholate anions. This is shown in scheme below ... 

Both cationic and anionic polymerizations of e-caprolactone are accompanied by the formation of cycles 4 5) as discussed later in this section. Anionic polymerization leads to living systems whereas side reactions were observed in all cationic processes. 

The anionic polymerization of almost all lactones proceeds by nucleophilic attack at the ring carbonyl group followed by scission of the CO-0 bond, e.g., for caprolactone the initiation and propagation steps can be depicted as... 

Ito K, Hashizuka Y, Yamashita Y. Equilibrium cyclic oligomer formation in the anionic polymerization of e-caprolactone. Macromolecules. 1977 10 821-824. 

The use of water-containing miniemulsions (as described above) is Hmited to particular monomers for anionic polymerization. Since, in many cases, the initiator and active species are sensitive to water, the polymerization caimot be carried out in either water-in-oil or oil-in-water miniemulsions. The anionic polymerization of e-caprolactam in a non-aqueous miniemulsion was first reported in 2005 [103]. As the e-caprolactam monomer is hydrophilic, it was necessary to conduct the polymerization in an inverse miniemulsion. Unfortunately, the molten e-caprolactam-in-oil miniemulsions could not be stabilized efficiently, in contrast to dimethyl sulfoxide (DMSO)-in-oil miniemulsions. Therefore it was necessary to dissolve the e-caprolactam directly in DMSO, to form the dispersed phase. This synthetic strategy, which permitted the production of polyamide-6 nanoparticles, paved the way for a variety of water-sensitive reactions to be performed in miniemulsion nanodroplets, including the creation of hydrophihc polyurethane capsules and particles (see below). Subsequently, poly(e-caprolactone)... 

High-molecular-weight polymers can be produced by the cationic or anionic polymerization of lactones. The cationic polymerization presumably proceeds via an acyl scission, for example, in the polymerization of 8-caprolactone with acetyl perchlorate as initiator ... 

With j8-propiolactone, an acetyl scission has also been discussed. The anionic polymerization of 8-caprolactone probably also occurs by an acyl ring opening ... 

Until about 1975, the major effort in studies of polymerization of cyclic esters was directed toward finding an efficient initiator and/or catalyst leading eventually to the living process. Commercial availability of p-lactones and of s-caprolactone (CL) was one of the reasons that already started extensive research programs on their polymerization at Goodrich in 1948 then at Union Carbide, Dutch Shell, and Japanese companies. Some attempts to elucidate the polymerization mechanisms in these studies were also undertaken, particularly taking into account the ambident structure of cyclic ester monomers. Halfi and later Lenz and co-workers carried out extensive kinetic measurements of the anionic polymerization of p-lactones, but the determined apparent... 

Continuous Media for the Anionic and Pseudoanionic Dispersion Polymerizations of -Caprolactone and Lactides... 

It is worth noting that with respect to transesterification, the anionic polymerizations of s-caprolactone carried out in solution and in dispersion differ significantly. In the anionic... 

Figure 11 Relation between the experimentally determined molecular weight, dispersity (MJMn), and calculated number-average molecular weight (Mn(calcd)) for the pseudoanionic and anionic polymerization of s-caprolactone. Reproduced with permission from Slomkowski, S. Sosnowski, S. Gadzinowski, M. etal. Macromol. Symp. 2000, 150, 259F...

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