Anionic polymerization of lactones

In anionic polymerizations the initiations result from attacks by bases upon the carbonyl groups  

Common initiators are Li and K alkoxides. In additimi to that, it was reported that phosphazene bases can be used to cany out polymerizations of cyclic esters [92]. Also, commercially available materials, like tert-butoxybis(dimethylamino)methane and tris(dimethylamino)methane yield high molecular weight polylactic acid by ring-opening polymerization with narrow molecular weight distribution  

These steps repeat themselves until the chains are built up. Anionic polymerizations can yield optically active polymers. This was observed in formations of poly(a-methyl, a-ethyl-p-propiolactone) [193] that contains asymmetric carbon atoms. 

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Thus, in the present paper we review the available data, pertinent to the kinetics and mechanism of anionic polymerization of lactones and discuss the recent data of our own, giving eventually an access to the rate constants of propagation on macroions and macroion--pairs. 

As a result. In the anionic polymerization of lactones, low pol3rmer yield, uncontrollable molecular weight, broad distribution, coupling linkage, and cyclic ester oligomers contamination have been frequently encountered O In this paper, a new Improved process was revealed to eliminate such trensesterlflcatlons has been developed. Block copolymers with styrene and butadiene have been prepared and characterized by different techniques. 

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 ... 

J. P., Anionic pol3nnerization of lactones initiated by alkali graphitides. 1 Polymerization of e-caprolactone initiated by KC24, J. Polym. Sci.. Part A Polym. Chem.. 21. 923-936, 1983. 

The polymerization of lactones is initiated by nucleophilic metal alkoxides. It is worth noting that bulky alkoxides are not nucleophilic enough and react as bases. For example, potassium ferf-butoxide deprotonates (3-propionolactone and sCL into new anionic species, which are anionic initiators for the polymerization of lactones [8] (Fig. 4). As a rule, carboxylic salts are less nucleophilic than the corresponding alkoxides and are, in general, not efficient initiators for the polymerization of lactones. Nevertheless, (3-lactones are exceptions because their polymerization can be initiated by carboxylic salts [8]. 

It is worth noting that another transfer reaction to the monomer is reported in the case of the anionic polymerization of (3-lactones, as shown in Fig. 9. This transfer reaction takes place during the polymerization of (3-propionolactone initiated by carboxylates even though molar masses up to 10,000 can be reached, even at room temperature [8]. The situation is even more critical in the case of the polymerization of substituted (3-butyrolactones, as witnessed by a ratio equal to 10, which is the highest number average degree of polymerization that can be reached under these conditions [8]. 

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. 

Successive addition of monomers to the end of macromolecular initiator is the usual technique for the synthesis of tailored blockcopolymers. Anionic polymerization of pivalolactone, a-pyrrolidone— and the NCA of T-methyl-D-glutamate -2 was started from the end group of a prepolymer consisting carboxylate group or acyl lactam group or amino group. Living polymer of C-capro-lactone was expected to be formed by the initiated polymerization from polymer carbanion under kinetic controlled condition. 

Alkoxide-Type Initiators. Using the guide that an appropriate initiator should have approximately the same structure and reactivity as the propagating anionic species (see Table 1), alkoxide, thioalkoxide, carboxylate, and silanolate salts would be expected to be useful initiators for the anionic polymerization of epoxides, thiiranes, lactones, and siloxanes, respectively (106—108). Thus low molecular weight poly(ethylene oxide) can be prepared... 

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]. 

The depolymerization reaction is suppressed in the presence of a more associated alkoxide such as lithium alkoxide. y-Lactones are difficult to polymerize by ROP. However, anionic polymerization of bicyclic bis(y-lactones) [76] can be carried out according to Scheme 8. 

Abstract. This paper reviews ring-opening polymerization of lactones and lactides with different types of initiators and catalysts as well as their use in the synthesis of macromolecules with advanced architecture. The purpose of this paper is to review the latest developments within the coordination-insertion mechanism, and to describe the mechanisms and typical kinetic features. Cationic and anionic ring-opening polymerizations are mentioned only briefly. 

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]... 

Monomers listed above polymerize by the cationic mechanism. For some groups of monomers (lactones, carbonates) anionic or coordinate mechanism also operates and, from a synthetic point of view, this is the preferred method of converting cyclic esters into linear polyesters. The cationic polymerization of lactones, glycolide and it substituted analog, lactide, as well as spiroorthoesters and bicyclic orthoesters has been studied in some detail. 

The kinetic depression is well known in the anionic polymerization of e-capro-lactone, where the formation of the cyclic dimer, trimer and tetramer starts when monomer is almost completely exhausted ... 

The anionic polymerization of A(-benzyloxycarbonyl-L-serine 3-lactone leads to poly(A -acyl-L-serine ester) My, = ca. 40 000), from which poly(L-serine ester hydrochloride) can be obtained by hydrogenation. ... 

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 ... 

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