2- oxetane

A large number of substituted 1,3-epoxides as well as the parent oxetane (oxacyclobutane, trimethylene oxide, 1,3-epoxypropane) have been prepared and polymerized. Likewise a wide variety of substances have been used to initiate their polymerizations. Much of this work has been extensively reviewed previously [1, 3, 7] and the interested reader is referred to these earlier reviews. Here we confine ourselves to reporting representative major kinetic studies. In this section the organization is by monomer. 

Rose [50] carried out one of the earliest, really thorough investigations of the kinetics of polymerization of a cyclic ether polymerization. He studied oxetane polymerizations initiated by BF3. Rose was aware from the work of Farthing and Reynolds [51] that polymerization does not occur when BF3 comes into contact with pure, dry monomer. However, simultaneous addition of water, ethanol or hydroxy terminated polymer is sufficient to initiate polymerization. Since Rose [50] observed polymerization in his sytem, he assumed that it was not completely dry and discussed his results assuming water is a co-catalyst. As the concentration of water increased, the rate of polymerization at first increased. The rate 

Rose [50] derived kinetic equations to fit this mechanism and the experimental data. When the concentration of added water was below 0.1 of the BF3 concentration, the kinetics were expressed by 

Rose also derived heats of polymerization. The values he obtained were 20.0 kcalmole for polymerization in methyl chloride solution at —20°C and 19.3 kcalmole for polymerization in a mixture of ethyl chloride and methyl chloride at —9°C. It is at once a bit unfortunate that this elegant piece of work was carried out as early as 1956 before catalysts leading to less complicated kinetics were discovered, and a tribute to Rose s careful work that he was able to sort out the many complications involved. No other detailed kinetic study of the polymerization of oxetane was made until many years later. In 1971 Saegusa et al. [52], reported a kinetic study of the polymerization of oxacyclobutane initiated by a BF3—THF complex. 

There are two general methods, one direct and the other indirect, by which the concentration of growing ends can be determined [8]. In the direct method, certain physical properties of the system, such as conductivity or UV or NMR spectra, are measured during the polymerization. In the indirect method, the polymerization is quenched with a reagent that combines with the growing chain ends, and gives a product which can be conveniently measured after purification. 

This results in a compromise between bond angle strain and Pitzer strain, which minimizes the total strain energy. The activation energy of the ring inversion amounts to 0.181 kJ mopi, which is less than the energy of the molecular vibration. Consequentely, the process occurs so fast that the molecule should be regarded as planar. 

Oxetanes react like oxiranes with ring-opening at a slower rate and under forcing conditions. Two reactions are of general importance  

Hydrogen halides react with oxetanes to give 3-halo alcohols. The acid-catalyzed hydrolysis yields 1,3-diols. 

Lewis acids, e.g. boron trifluoride, can add to a nonbonding electron pair of the 0-atom. Thus, in di-chloromethane as solvent, a cyclooligomerization is induced. The main product is the cyclotrimer 1,5,9-trioxacyclododecane [1]  

The Chemistry of Heterocycles, Second Edition. By Theophil Eicher and Siegfried Hauptmann Copyright 2003 Wiley-VCH Verlag GmbH Co. KGaA ISBN 3-527-30720-6 

In the first step 4,4 -bis(3,3-dimethyIoxetan-2-yI)-diphenyI ether is synthesized by the Friedel-Crafts reaction of 3-chIoro-2,2-dimeth-ylpropionylchloride with diphenyl ether to get 4,4 -bis(3-chIoro-3,3-dimethyIpropionyI)-diphenyI ether. This is reduced with sodium boron hydride to yield 4,4 -bis(3-chloro-3,3-dimethyI-l-hydroxy-propyI)-diphenyI ether. Finally the end product is obtained in an alkaline process. 

Examples of the photoly ticaUy acid generating agents are arylsulf-onium derivatives, diazonium salts, or triazine type initiators (37). 

In addition, the photocurable compositions contain radically polymerizable monomers, such as various acrylics (38). Thus, the photopolymerization initiator will decompose in radicals. 

It is also possible to obtain a radical-cation pol5Hnerizable hybrid curable ink by using a radical pol5nnerization monomer and an initiator in combination (37). 

Besides oxetanes, oxirane compounds have also been proposed as curable moieties (39). Examples of epoxidized vegetable oils having an unsaturated bond are olive oil, safflower oil, sunflower oil, soybean oil, and linseed oil. 

The Chemistry of Heterocycles Structure, Reactions, Synthesis, and Applications, 

Third Edition. Edited by Theophil Eicher, Siegfried Hauptmann, and Andreas Speicher. 

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The reaction of alkenyl mercurials with alkenes forms 7r-allylpalladium intermediates by the rearrangement of Pd via the elimination of H—Pd—Cl and its reverse readdition. Further transformations such as trapping with nucleophiles or elimination form conjugated dienes[379]. The 7r-allylpalladium intermediate 418 formed from 3-butenoic acid reacts intramolecularly with carboxylic acid to yield the 7-vinyl-7-laCtone 4I9[380], The /i,7-titisaturated amide 421 is obtained by the reaction of 4-vinyl-2-azetidinone (420) with an organomercur-ial. Similarly homoallylic alcohols are obtained from vinylic oxetanes[381]. 

See also Tetrahydromran. [POLYETTiERS - TETRAHYDROFURAN AND OXETANE POLYTffiRS] (Vol 19)... 

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