Lactones cyclic, polymerization

In contrast to the fact that cyclic acetals can be polymerized only by cationic initiators, lactones undergo polymerization both cationically and anionically, and therefore a wide variety of initiators including coordinated catalysts can be used. In this section, the polymerization of bicyclic lactones is described, although only a limited number of papers on this subject have been published. 

Lactones (cyclic esters) undergo anionic and cationic polymerization to form polyesters (Eq. 7-75) [Duda and Penczek, 2001 Johns et al., 1984 Kubisa, 1996 Lundberg and Cox, 1969 Young et al., 1977]. The reactivity of different lactones generally follows the pattern for other cyclic monomers, except that the 5-membered lactone (y-butyrolactone) does... 

The first group of high molecular weight polyesters were produced by the direct ring-opening polymerization (ROP) of lactones (cyclic esters) synthesized from 1,3-propanediol. 

Thus, we first discuss thermodynamics, paying attention to features that are important for polymer synthesis (e.g., dependence of equilibrium monomer concentration on polymerization variables) then we describe kinetics and thermodynamics of macrocyclization, trying to combine these two related problems, usually discussed separately. In particular we present the new theory of kinetic enhancement and kinetic reduction in macrocyclics. Thereafter, we describe the polymerization of several groups of monomers, namely cyclic ethers (oxiranes, oxetanes, oxolanes, acetals, and bicyclic compounds) lactones, cyclic sulfides, cyclic amines, lactams, cyclic iminoethers, siloxanes, and cyclic phosphorus-containing compounds, in this order. We attempted to treat the chapters uniformly we discuss practical methods of synthesis of the corresponding polymers (monomer syntheses and polymer properties are added), and conditions of reaching systems state and reasons of deviations. However, for various groups of monomers the quality of the available information differ so much, that this attempt of uniformity can not be fulfilled. 

Some lactones can polymerize in the presence of compounds like alcohols, amines, and carboxylic acids without additional catalysts. The reactions, however, are slow and yield only low molecular weight polymers Exceptions are polymerizations of pivalolactone in the presence of cyclic amines that yield high molecular weight polyesters at high conversion. The initiating steps result from formations of adducts, amine-pivalate betaines ... 

Many heterocyclic compounds can be polymerized by ring opening under certain conditions with ionic initiators, to produce linear macromolecules. Amongst these are cyclic ethers, cyclic sulfides, cyclic acetals, cyclic esters (lactones), cyclic... 

Random polymers are the statistical arrangement of comonomer in their backbone. Numerous monomers have been used to copolymerize with LA, such as lactones, cyclic carbonates, hydroxyl acid, amino acid, and so on, to improve the flexibility, thermal stability, degradability, biocompatibility, hydrophilicity, functionality, etc. The most widely used technique to synthesize random copolymers of PLA is controlled/ living ring-opening polymerization. 

Two molecules of lactic acid can be dehydrated to lactide, a cyclic lactone. Then, polymerized to lactide to either heterotactic or syndiotac-tic polylactide, which is also called PLA. Lactic acid can be produced from chemical or biotechnological methods. Chemical synthesis can be based on the hydrolysis of lactonitrile by strong acids, or by base-catalyzed degradation of sugars, oxidation of propylene glycol, or by chemical reactions of acetaldehyde, carbon monoxide, and water at elevated temperatures (Mussatto et al. 2008). 

Lactones can polymerize with cyclic ethers such as epoxides, tetrahydrofuran, oxetans and trloxane as well as Imines. The copolymerization of lactones with epoxides, for example, should lead to the formation of copolymers containing ether and ester links in the chain. 

Ring opening polymerization of lactones (cyclic esters) is another interesting technique to derive polyesters. For instance, lactones are reacted with polyols (as an initiator) to derive a linear polyester (polylactone) by ring opening polymerization as shown in Figure 2.13. One interesting aspect of this technique is that the functionality of the final polymer is the same as that of the initiator polyol. 

The first real trial of asymmetric polymerization of unsaturated cyclic monomers was reported by Shuerch et al [195]. Cyclic olefins (4,5-dihydro-2-methylfuran, indene, 1-methyl cyclopentene and a-angelica lactone) were polymerized using complexes of BF3 with asymmetric Lewis bases like 1-a-methylbenzyl alcohol, tosyl-1-valine or camphor. 

Figure 1.2 illustrates the characteristic changes in standard thermodynamic parameters with increasing size of cyclic monomer, as shown by the example of lactones bulk polymerization. Similar dependencies were also observed for other monomers, though with only slight changes in the position of the local minima or maxima on the thermodynamic parameter-ring size dependencies [21, 22, 26]. 

The synthesis of five-, six-, and seven-membered cyclic esters or timides uses intramolecular condensations under the same reaction condifions as described for intermolecular reactions. Yields are generally excellent. An example from the colchicine synthesis of E.E. van Ta-melen (1961) is given below. The synthesis of macrocyclic lactones (macrolides) and lactams (n > 8), however, which are of considerable biochemical and pharmacological interest, poses additional problems because of competing intermolecular polymerization reactions (see p. 246ff.). Inconveniently high dilution, which would be necessary to circumvent this side-... 

Less important methods are the self condensation of w-hydroxy acid and the ring opening of lactones and cyclic esters. In self condensation of w-hydroxy acids, cyclization might compete seriously with linear polymerization, especially when the hydroxyl group is in a position to give five or six membered lactones. 

Various cyclic esters have been subjected to hpase-catalyzed ring-opening polymerization. Lipase catalyzed the ring-opening polymerization of 4- to 17-membered non-substituted lactones.In 1993, it was first demonstrated that medium-size lactones, 8-valerolactone (8-VL, six-membered) and e-caprolactone (e-CL, seven-membered), were polymerized by lipases derived from Candida cylindracea, Burkholderia cepacia (lipase BC), Pseudomonas fluorescens (lipase PF), and porcine pancreas (PPL). °... 

This polymeric lipid can first be polymerized by free radical initiator in organic solutions before making the vesicles. The proton NMR spectrum of the polymerized lipid shows that vinyl protons of the cyclic acrylate between 85.00 ppm and 86.00 ppm disappeared from the spectrum, compared with that of monomeric lipid. Also in the IR spectrum (Figure 6) the absorption peak at 1670 cm"1 for the cyclic acrylate carbon carbon double bond disappeared as the result of polymerization. The carbonyl absorptions of the esters at 1740 cm 1 and the lactone at 1805 cm"1 still remain in the spectrum. 

Polyester syntheses have been achieved by enzymatic ring-opening polymerization of lactide and lactones with various ring-sizes. Here, we focus not only on these cyclic esters but also other cyclic monomers for lipase-catalyzed ringopening polymerizations. Figure 8 summarizes cyclic monomers for providing polyesters via lipase catalysis. 

The high level of interest in the ring-opening polymerization (ROP) of cyclic esters (lactones) stems from the biocompatibility and biodegradability of their polymers. Resorbable aliphatic... 

The most widely studied aluminum-based initiator for the ROP of lactones is Al(0 Pr)3, (246), which has been used to initiate the living polymerization of a variety of cyclic esters including CL 747-749 LA 750,751 GA 752 . 745 and cyclic anhydrides.753 754 Polymerizations initiated by... 

The lanthanocene systems have been extended to cover a range of monomers including LA,890 cyclic carbonates891 and even MMA.454 Block copolymers of MMA and lactones, with Mw/Mn = 1.11-1.23, may be prepared but only if the vinyl monomer is polymerized first. The... 

In the presence of catalytic amounts of sodium methoxide, dimethylketene /3-lactone dimer is polymerized at moderate temperature to a polyester.3 At higher temperatures (above 100°), disproportionation to the cyclic trimer, hexamethyl-1.3,5-cyclohexanetrione, takes place.9 Addition of a stoichiometric amount of sodium methoxide to the lactone dimer generates the sodium enolate of methyl 2,2,4-trimethyl-3-oxovalerate. This reaction provides a convenient entry into certain ester anion chemistry that formerly required the use of a strong base like tritylsodium.10... 

Studies on the cationic polymerization of cyclic ethers, cyclic formals, lactones and other heterocyclic compounds have proliferated so greatly in the last few years that a detailed review of the evidence concerning participation of oxonium and analogous ions in these reactions cannot be given here. Suffice it to say that there is firm evidence for a few, and circumstantial evidence for many such systems, that the reactive species are indeed ions and there appears to be no evidence to the contrary. A few systems will be discussed in sub-sections 3.2 and 4.4. 

On the other hand, in cyclic ethers (alkene oxides, oxetans, tetrahydrofuran) and formals the reaction site is a carbon-oxygen bond, the oxygen atom is the most basic point, and, hence, cationic polymerization is possible. The same considerations apply to the polymerization of lactones Cherdron, Ohse and Korte showed that with very pure monomers polyesters of high molecular weight could be obtained with various cationic catalysts and syncatalysts, and proposed a very reasonable mechanism involving acyl fission of the ring [89]. 

Activity in the field was, however, expanding. For example, in 1927 Drew and Haworth (65) obtaind a crystalline polymeric powder by the action of hydrogen chloride on the lactone of 2,3,4-trimethyl-l-arabonic acid. Citing the increase in melting point and molecular weight, and loss of specific optical rotation, they ascribed a cyclic, high polymer structure to this polyester. 

---