Macrocyclic polyesters

This method exclusively yields macrocyclic polyesters without any competition with linear polymers. Furthermore, the coordination-insertion ROP process can take part in a more global construction set, ultimately leading to the development of new polymeric materials with versatile and original properties. Note that other types of efficient coordination initiators, i.e., rare earth and yttrium alkoxides, are more and more studied in the framework of the controlled ROP of lactones and (di)lactones [126-129]. These polymerizations are usually characterized by very fast kinetics so as one can expect to (co)polymerize monomers known for their poor reactivity with more conventional systems. Those initiators should extend the control that chemists have already got over the structure of aliphatic polyesters and should therefore allow us to reach again new molecular architectures. It is also important to insist on the very promising enzyme-catalyzed ROP of (di)lactones which will more likely pave the way to a new kind of macromolecular control [6,130-132]. 

The use of the step 2 carbene reagent catalyst, l,3-di-l-adamantyl-imidazole-2-ylidene, (I), in preparing macrocyclic polyester oligomers is described by... 

FAB and MALDI-TOF techniques revealed that macrocyclic oligoesters were the main condensation products of catechol or 0,0 -Bistrimethylsilyl catechol (BTSC) with adipoyl chloride, sebaroyl chloride, and sebacoyl chloride, respectively. Macrocyclic polyesters were also obtained when the noncyclic l,3-bis(tributylstannoyl)butane was used as monomer. ... 

It was discovered recently [62] that, when the polymerization of lactide was organocatalyzed with an NHC in the absence of an alcohol, termination would occur via an attack of the terminal alkoxide on the initiating end of the polymer chain, thus reforming the NHC catalyst and generating macrocyclic polyesters (Scheme 31.14, Path B). The cyclic structures of these macromolecules were confirmed with H NMR spectroscopy, mass spectrometry, and comparisons of... 

Puszaszeri depolymerised PET via acid-catalysed hydrolysis, and claimed to recover 98% of available TA [217], GE created macrocyclic polyester oligomers via tin or titanium salt catalysed hydrolysis [218]. Shell used base-catalysed hydrolysis, followed by oxidation of impurities to insoluble products which could then be filtered off prior to isolation of final products [219]. Sirek and Jirousek proposed a process in which PET is crystallised and crushed to a fine powder, hydrolysed with steam, then ammonium hydroxide added. The TA is recovered by acid treatment of the diammonium salt, and EG recovered by distillation of the liquid component of the reaction mix [220]. 

Tin alkoxides have also been preformed and used as ROP initiators. Alkyl-substituted tin(IV) alkoxides are more commonly used than the tin(II) counterparts. Compared with tin monoalkoxide (R sSnOR), tin(IV) dialkoxides (R 2SnOR2) are preferred because of a higher reactivity (42). Cyclic tin(II) alkoxides deserve interest because they form macrocyclic polyesters, which are precursors of telechelics, upon ring opening by acidic hydrolysis or reaction with acid chlorides (Fig. 7). 

In light of the considerable recent Interest in the macrocyclic polyether-polyester antibiotics, Samat and coworkers have prepared a large-ring macrocycle as a model for the... 

Many reports on the polymerization of PET cyclic oligomers, with various results, have appeared. Polymerization in the melt at 275-310 °C has been reported by Goodman and Nesbitt [8], The latter claimed that a linear polyester was formed when the macrocycles are heated with a catalyst, neat, or in 2-methylnaphthalene at 240 °C. They also stated that scrupulously dried material... 

Kricheldorf, H. R., Rabenstein, M., Maskos, M. and Schmidt, M., Macrocycles 15. The role of cyclization in kinetically controlled polycondensations. 1. Polyester synthesis, Macromolecules, 34, 713 (2001). 

Allmendinger M (2004) PhD Thesis. Multi-Site Catalysis - Novel Strategies to Biodegradable Polyesters from Epoxides/CO and Macrocyclic Complexes as Enzyme Models. Universitat Ulm, Ulm... 

A change of architecture is another route that enables diversification of the properties of aliphatic polyesters. This review will focus on star-shaped, graft, macrocyclic, and crosslinked aliphatic polyesters. It must be noted that the ROP of lactones has been combined with several other polymerization mechanisms such as ROP of other heterocyclic monomers, ionic polymerization, ROMP, and radical polymerization. Nevertheless, this review will not cover these examples and will focus on polymers exclusively made up of poly(lactone)s. 

Fig. 39 Synthesis of macrocyclic aliphatic polyester by ring-expansion polymerization initiated by cyclic tin(IV) alkoxides...

The macrocyclic esters hold a special position among the industrially produced lactone fragrance materials. Like the well-known macrocyclic ketones, they have outstanding odor properties as musks. However, the lactones can be prepared more easily than the ketones, for example, by depolymerization of the corresponding linear polyesters. Since replacement of a methylene unit by oxygen affects the odor of these compounds very little, oxalactones with 15-17-membered rings... 

Crystalline macrocyclic polyether complexes may be prepared by several routes,5,381 depending upon the solubilities of the precursors and the products. The polyester and the salt may be dissolved in a small amount of solvent and warmed together the complex can crystallize either on cooling or after evaporation of some of the solvent. It is also possible to warm a suspension of the ligand and the salt to effect solubilization and subsequent crystallization. The reaction can also be carried out by mixing the components in the solid state and heating to melting. 

The occurrence and a limited importance of chain transfer by transacetalization cannot be doubted. We proposed this type of reaction for trioxane polymerization as early as 1959 (6) and assumed that intramolecular transacetalization produces some thermally stable macrocyclic polyoxymethylene (10). We have utilized bimolecular chain transfer by polymers to produce thermally stable block copolymers at temperatures over 100°C. [—e.g., with polyesters, polypropylene oxide, or with polyvinyl butyral)] (12). 

The preparation and use of organotin compounds as re-polymerization agents for linear polyesters and macrocyclic oligomers is provided by Paler [1] and Winckler [2], respectively. 

Celastraceae also elaborate other, more complex, alkaloids, also polyester sesquiterpenes, incorporating a macrocycle derived from an evonic, wilfordic, cassinic or other type pyridine dicarboxylic acid with an additional alkyl chain of the basic eudesmane cycle at C-3 and C-7 (Table III). Celastraceae alkaloids are well-documented for the European and Asian genera, particularly Catha, Celastrus, Euonymus and Trypterigium but are relatively rare among the Latin... 

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