The ring-opening-metathesis polymerization (ROMP) of strained cyclic olefins has been studied extensively, [1,2] especially since Grubbs' catalyst 1 [3] and the more recently introduced "second-generation" Grubbs' catalyst 2, [4] both of which are tolerant of many functional groups, became commercially available. The ROMP of strained cyclic olefins is mainly enthalpy-driven.A relatively new type of ring-opening polymerization (ROP) exploits the well-known equilibria between cyclic oligomers and polymers [5][6][7][8][9][10] (Scheme 1). At high dilutions the equilibria lie heavily in favor of the cyclic oligomers, whereas at high concentrations they lie heavily in favor of the polymers. Thus, if one or more cyclic oligomers are taken neat as starting materials, and equilibrium is established, polymer synthesis results. The cyclic oligomers used as the feedstock are generally not strained, so the enthalpy change on polymerization is minimal. This type of polymerization is, therefore, mainly entropically driven, and so the process can be abbreviated ED-ROP. As a neat mixture the cyclic oligomers have relatively little translational entropy and the rings occupy limited conformations; conformational flexibility increases greatly upon conversion into polymers. Since ED-ROP is an equilibration process the polydispersity of the polymer is expected to have a value of 2.0. ED-ROP has been investigated for various types of macrocyclic oligomers, [11,12] but not for macrocyclic olefins.Examples in which large, unstrained macrocycles (> 13 ring atoms) have been subjected to ROMP are rare, [2,[13][14][15] and there only appear to be two examples in which the polymer has been formed in high yield, isolated, and characterized. The first was the ROMP of the 14-membered cyclic ether 3 in the presence of the catalyst 1. This gave a polymer with M n 65 900 (M n = number-average molar mass).[2] The second example was the ROMP of ambrettolide, an unsaturated macrolide with 17 ring atoms.[13] A neat sample of this compound was polymerized in the presence of a catalyst prepared from tungsten hexachloride and tetramethyltin to give a polymer in 95 % yield with M n 95 000. Herein we show that when appropriate reaction conditions are used, unstrained macrocyclic olefins with up to 84, and possibly even more, ring atoms readily undergo entropically driven ROMP (ED-ROMP). Given that Grubbs and co-workers have recently reported an efficient method for the synthesis of very large macrocyclic olefins, [16] and that olefin-containing polymers are easily hydrogenated in the presence of decomposed metathesis catalysts, [17,18] ED-ROMP of large macrocyclic olefins is of more than theoretical interest.In the present work the monomers 4, 5, and 6, which have 21-, 28-, and 38-membered rings, respectively, were prepared by ring-closing metathesis (RCM). [2,[19][20][21] The monomer 4 had been synthesized previously by RCM in 70 % yield.[20] In a similar procedure, the a,w-diolefinic ester 7 and Grubbs' catalyst 1 (3 mol %) were slowly added over 24 h to ...

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We report the cyclo‐depolymerization of poly(propylene terephthalate) to give a mixture of cyclic oligomers in 94% yield, the characterization of the mixture by 1H‐NMR spectroscopy, matrix assisted laser desorption ionization time of flight mass spectrometry and gel permeation chromatography. The major cyclic oligomer in the mixture was shown to be the cyclic dimer. It was isolated and its X‐ray crystal structure determined. Some entropically‐driven ring‐opening polymerizations of the cyclic oligomers were carried out. So too were some copolymerizations using mixtures of the cyclic oligomers and those derived similarly from poly(ethylene terephthalate) and poly(butylene terephthalate). 13C‐NMR spectroscopic analysis showed that the copolymers were random. Copyright © 2003 John Wiley & Sons, Ltd.

Copolyesters were synthesized in a high throughput (HT) manner and in high yield on ca. a 90 mg scale using entropically driven ring-opening polymerizations (ED-ROPs). This synthetic approach is a valuable addition to the HT polymer synthesis arsenal in that it allows condensation-type polymers with relatively large repeat units, such as those in poly(ethylene terephthalate) and poly(butylene terephthalate), to be obtained easily. The synthetic procedure involved taking mixtures of the appropriate macrocyclic oligoesters and heating them together under neat conditions at 250-300 degrees C for 2 h in the presence of 0.1 mol % of di- n-butyltin oxide or tetra- n-butylammonium tetrafluoroborate. In most cases Mw values were >25,000 and, as expected for ED-ROPs, the polydispersity indices were close to 2.0. Higher molecular weights could be obtained by using longer reaction times, but this might lead to product decomposition. The method worked well for esters formally derived from aliphatic or aromatic acids and alcohols, but less well for esters derived from phenols. Attempts were also made to synthesize copolymers by mixing together the two homopolymers and heating with a catalyst. These reactions were successful in a few instances, but generally, they were not. This is probably because the homopolymers did not mix well. An aluminum reaction block with 36 wells lined with Teflon cups, that fitted snugly in a cylindrical Buchi oven, was the most successful method for carrying out syntheses in an HT manner.

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