Oligomers oxiranes

It is often the case that chemists involved or familiar with ethylene oxide (oxiran) chemistry refer to these cyclic oligomers as EO-4, EO-6 and EO-7 respectively. Such designations are informal if not colloquial but, like any name, are useful if they correctly convey an idea. The difficulty with these informalities, indeed with the crown nomenclature system is that it cannot adequately deal with complicated structures or even isomers of simple ones. 

Step-growth polymerization. Epoxy resins were prepared from nadlc methyl anhydride and Epon 828. This blfunctlonal oxirane also supplies reactive hydrogen sites. The major component is at 1=0, minor components include oligomers with 1=1,2,3. Their concentrations rapidly diminish as degree of polymerization Increases. 

The anionic polymerization of 2-furyl oxirane 4a (17) proceeds smoothly and can be made to yield oligomers bearing a hydroxyl group at each end ... 

Another approach to the formation of the oxirane groups is the peroxidation of a carbon-carbon double bond. Various types of oligomers fall into this category epoxidized oils, epoxidized rubbers, and cycloaliphatic... 

According to Entelis the formation of cyclic oligomers in the polymerization of oxiranes initiated by borontrifluoride would be an intramolecular reaction between the chain ends of the zwitter ion produced in such polymerizations ... 

Cationic polymerization of the unsubstituted oxirane (ethylene oxide) leads to the mixture of relatively low molecular weight (M < 103) linear polymer and up to >90% of cyclic oligomers, predominantly cyclic dimer (1,4-dioxane) 191,102]. The same behavior was observed for polymerization of substituted oxiranes, propylene oxide [103], epichlorohydrin [104], and other oxiranes having one or more substituents in the ring, although the distribution of cyclic fraction varied, depending on the structure of monomer. 

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]. 

Substituted oxiranes as monomers, oligomers, and polymers 90MI28, 90MI33, 90UK738. 

A polyadduct formed from aniline, phenothiazine, oxirane and 2,3-epoxypropane [145] was proposed as a component for the synthesis of a light stable PUR. A polyadduct of 4,4 -isopropylidenebisphenol with 2-hydroxy-4-(2,3-epoxypropyl)-benzophenone [131], polymeric HALS 115 formed from bis(2,3-epoxypropyl)ani-line and 4-amino-2,2,6,6-tetramethylpiperidine [146] or a brominated oligomer 116 used in combination with antimony trioxide as FR for PET [147] are other examples of polyaddition stabilizers. 

In another series of papers, published by Yamashita a.o. and describing macrocyclization in the cationic polymerization of oxiranes, much more complicated mixture of cyclic products was observed. Besides typical macrocyclic polyethers ° cyclic oligomers having acetal structure were found. These products can be fom d, according to Yam hita, as a result of back-biting to the rearranged growing species ... 

Cyclooligomerization of substituted oxiranes has been found to be highly stereo-specific Cis-2,3-dimethyloxirane gave only one dioxolane-type dimer namely 2,cis-4,trans-5-trimethyl-2-ethyl-l,3-dioxolane isomer (plus other cyclic- and linear oligomers) ... 

In139) the researchers studied the nonisothermal kinetics of polyaddition reactions of oxiranes to aromatic amines up to high conversion levels, as well as the kinetic laws governing the curing of epoxide oligomers by diamines under the conditions of a propagating reaction front. 

The mechanism for the gas-phase reaction of trans-2,3-dideuterioethene oxide with HBr and HCl has been shown to involve anti ring-opening, with the formation of e fhro-R(CHD)2 0H (R = Cl or Br). The reaction of ethene oxide with HF followed a somewhat different course, affording only 5% of fluorohydrin together with (126) (37%) and oligomers and polymers. A possible mechanism for this reaction is shown (see Scheme 8) in which two moles of oxiran react with HF to give intermediate (125), which is open to polymerization with other oxiran molecules or to ring-expansion, with the subsequent formation of dioxane (126). 

It is difficult at present to recommend a general method for the synthesis of a given cyclic oligomer from an oxirane. The template technique of Dale seems to provide background for a general approach 20). It follows also from the data analysed in this section that the presence of hydroxyl containing compounds has to be avoided. 

Cationic Oligomerization of Oxiranes Leading to Linear Oligomers. Activated Monomer Mechanism... 

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