Cationic polymerization of lactones

Shibasiki Y, Sanada H, Yokoi M, Sanda F, Endo T (2000) Activated monomer cationic polymerization of lactones and the application to well-defined block copolymer synthesis with seven-membered cyclic carbonate. Macromolecules 33 4316-4320... 

Cationic polymerization of lactones is achieved with the range of initiators used for cyclic ethers (Sec. 7-2b) [Hofman et al., 1987a,b Kricheldorf and Sumbel, 1988a,b Kricheldorf et al., 1986, 1987a,b Kubisa, 1996 Penczek and Slomkowski, 1989a,b]. Initiation was formerly thought to involve attack of a positive species on the endocyclic oxygen to form an... 

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. 

Cationic polymerization of cyclic carbonates, e.g., ethylene carbonate resembles cationic polymerization of lactones. The postulated polymerization scheme is shown by Eq. (153) (for initiation with CF3SO3CH3) [201,202] ... 

Recently, a series of works have been published on the cationic po merization of lactones (e.g. p-propiolactone and e-caprolactone ) and various ionic ecies have been reported together with elaborate kinetic treatments and some electrochemical measurements. In our opnion the chemical structure of the growing species in the cationic polymerization of lactones has not yet firmly been established (see also Ref. 190) and, therefore, a more detailed discussion of the% interesting and important systems must wait until these structures are known. 

Cationic polymerization of lactones can be initiated by a wide variety of protonic and Lewis acids, and by oxonium and carbenium salts. 

The cationic polymerization of lactones is not yet sufficiently well understood. The structure of the active centers is not known with certainty and the direction of the opening of the lactone ring (O-alkyl (a) vs. O-acyl (b)) has been established only recently for a few representative monomers 16,17) ... 

Describe cationic polymerization of lactones, showing the initiation and propagation processes. 

Cationic polymerizations of lactones has been carried out with the help of alkylating agents, acylating agents, Lewis acids, and protonic acids. Various reaction schemes were proposed to explain the... 

Bourissou et al. reported recently controlled cationic polymerization of lactones using a combination of triflic acid with a protonic reagent as the initiators [90]. The reaction was carried out in CH2CI2. Results indicated that the process is controlled is a linear relationship between the molecular... 

Jonte, J.M., Dunsing, R., Kricheldorf, H.R., 1985. Polylactones. 4. Cationic polymerization of lactones by means of alkylsulfonates. Journal of Macromolecular Science Part A Chemistry A22 (4), 495-514. 

Cationic polymerization of lactones has been demonstrated to involve active centres which are ionic triplets. ... 

Shibasaki Y, Sanada H, Hokoi M, Sanda F, and Endo T (2000), Activated Monomer Cationic Polymerization of Lactones and the apphcation to Well-Defined Block Copol5Tner Synthesis with seven-membered cychc carbonates , Macromolecules, 33, 4316 320. 

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]. 

Cationic ROP of lactones has been known for a long time but is not very popular due to its poor control of the molecular parameters. In 1984, Penczek and coworkers reported the cationic polymerization of sCL and p-propionolactone... 

Nomura N, Taira A, Tomioka T, Okada M (2000) A catalytic approach for cationic living polymerization Sc(OTf)3-catalyzed ring-opening polymerization of lactones. Macromolecules 33 1497-1499... 

Epoxides readily undergo anionic copolymerization with lactones and cyclic anhydrides because the propagating centers are similar—alkoxide and carboxylate [Aida et al., 1985 Cherdron and Ohse, 1966 Inoue and Aida, 1989 Luston and Vass, 1984]. Most of the polymerizations show alternating behavior, with the formation of polyester, but the mechanism for alternation is unclear. There are few reports of cationic copolymerizations of lactones and cyclic ethers other than the copolymerizations of [5-propiolactone with tetrahydrofuran and... 

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. 

As discussed already for cationic polymerization of oxiranes, cycliza-tion can be eliminated if polymerization is performed under the conditions at which the activated monomer mechanism operates. This approach was used for cationic polymerization of e-caprolactone and other higher lactones [191]. Thus, in the polymerization of e-caprolactone in the presence of ethylene glycol (EG) and (C2Hs)30 +, PF6- catalyst, linear increase of molecular weight with conversion was observed up to M 3000 and polymers with DP = [M]o/[EG]0 and relatively narrow molecular weight distribution (MJM 1.3) were obtained. No cyclic oligomers were detected in reaction products. Similar results were obtained for polymerization of 5-valerolactone and j8-butyrolactone. Kinetic studies of the AM polymerization of lactones have been reported [192]. 

Copolymerization of N-alkylazlrldlnes with g-proplolactone. g-proplolactone (PL) reacts with tertiary amines to form the corresponding zwltterlon (7 ). If an N-substltuted azlrldlne Is used, a zwltterlon containing an azlrldlnlum Ion and a carboxylate Ion Is formed. This zwltterlon can Initiate a cationic polymerization of the azlrldlne or an anionic polymerization of the lactone or undergo a coupling reaction with another (monomeric or polymeric) zwltterlon. 

Polymerization of pPL with a variety of initiators is a terminationless process. Lyudvig a.o. have mostly contributed to our present knowledge of the influence of reaction variables on the rates of polymerization 24 27). They obtained quantitative yields in the polymerization of lactones using bulky complex counterions, like SbClf1. Thus, the decomposition of these anions, leading to transfer and termination in the polymerization of cyclic ethers and acetals, does not lead to side reactions in the polymerization of lactones. This can be ascribed to reversible reactions between acyl halides plus Lewis acids and the acylium cation 28) ... 

The ring opening polymerization of lactones, lactides, and glycolides to polyesters can be carried out by both anionic and cationic means using a variety of initiators similar to those used for cyclic ethers. However, cationic polymerization is... 

Because of strong transfer reactions, the free radical polymerization of lactones only produces polymers of low molar masses even though the yields are high. High molar masses are achieved by cationic or anionic polymerizations. Both types of polymerization presumably involve an acyl scission, as for example, with 6-caprolactone ... 

On the other hand, syntheses of block copolymers based on cyclic esters (lactones) rather than cyclic ethers by a combination of controlled polymerization and AM polymerization techniques have been reported several times. The first example of cationic polymerization of cyclic esters such as CL in the presence of hydroxyl compounds and (Et)sO PFg" was... 

Polymerization of lactones can be carried out by three mechanisms, namely, cationic, anionic, and coordinated one. Often, the mechanism by which a specific lactone polymerizes depends upon the size of the ring. 

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 ... 

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