Cyclohexene oxide polymerization

Several mechanisms for the polymerization of vinyl ether and epoxies have been suggested [20,22,23,25,27,28,33-35]. On irradiation with gamma rays or electrons, pure epoxies polymerize via a cationic mechanism [35]. However, this cationic polymerization is inhibited by just traces of moisture, as shown below for cyclohexene oxide in reaction 5. 

Cationic complexes, such as 55 and 56, catalyze the polymerization of propylene oxide, cyclohexene oxide, and of e-caprolactone with substantially higher activities than neutral zinc complexes. 

The interactions of dimethyl- and diethylzinc with bulky tris(hydroxyphenyl)methanes, Scheme 86, yielded, depending on the reaction conditions, a variety of alkylzinc alkoxides, featuring two-, three-, and four-coordinate zinc centers. These polynuclear compounds (Figure 63 shows the trinuclear ethylzinc derivative 136) are relatively poor catalysts for the co-polymerization of cyclohexene oxide and carbon dioxide.197... 

A chiral ethylzinc aminoalkoxide 147, synthesized by the addition of ZnEt2 to (cyclohexene oxide with C02 in almost quantitative yield and with an ee of 49%. This value is somewhat lower than that obtained by the same authors from the in situ generated monomeric form of the catalyst, which furnished product with an ee of 70%.213... 

In another example, a polymer-supported chromium porphyrin complex was supported on ArgoGel Cl and then employed for the ring-opening polymerization of 1,2-cyclohexene oxide and C02 [95], This complex showed higher activity than a C02-soluble equivalent, and the solid nature of the catalyst meant that recycling of the catalyst was much easier. 

The simplest model compound is cyclohexene oxide III. Monomers IV, V and VII represent different aspects of the ester portion of I, while monomers VII and VIII reflect aspects of both the monomer I and the polymer which is formed by cationic ring-opening polymerization. Monomers IV-VII were prepared using a phase transfer catalyzed epoxidation based on the method of Venturello and D Aloisio (6) and employed previously in this laboratory (7). This method was not effective for the preparation of monomer VIII. In this specific case (equation 4), epoxidation using Oxone (potassium monoperoxysulfate) was employed. 

Carbon dioxide can itself be used as a feedstock as well as a solvent for the synthesis of aliphatic polycarbonates by precipitation polymerization. Propylene oxide [39] and 1,2-cyclohexene oxide [40] can both be polymerized with CO2 using a heterogeneous zinc catalyst (Scheme 10.21). 

Several dyes have been found to sensitize the cationic polymerization of cyclohexene oxide, epichlorohydrin, and 2-chloroethyl vinyl ether initiated by diaryliodonium salts (109,110). Acridinium dyes such as acridine orange and acridine yellow were found to be effective sensitizers. One example of a benzothiazolium dye (setoflavin T) was also reported, but no other class of dye nor any other example of a dye absorbing at longer wavelengths were discovered. Crivello and Lam favored a sensitization mechanism in which direct energy transfer from the dye to the diaryliodonium salt occurred. Pappas (12,106) provided evidence that both energy transfer and electron transfer sensitization were feasible in this system. 

The monomers of styrene oxide, 1,4-cyclohexene oxide, trioxane, and vinyl ether were polymerized at satisfactory rates. However, tetrahydrofuran, e-caprolactone, and cc-methylstyrene could not be polymerized7). 

The evidence in the case of styrene, where both modes of radiation-induced polymerization can be conveniently studied, is quite convincing that reduction of the concentration of water changes the predominating mode of propagation from purely free radical to essentially ionic. Evidence for an ionic propagation initiated by radiation has also been obtained in pure a-methylstyrene (3, 24), isobutylene (12, 32), cyclopenta-diene (5), / -pinene (2), 1,2-cyclohexene oxide (II), isobutyl vinyl ether (6), and nitroethylene (38), although the radical process in these monomers is extremely difficult, if not impossible, to study. 

So far, only a few examples of cationic photopolymerizations using PET corresponding to Scheme 3 have been described [10,13,165]. In the ternary system cyclohexene oxide, 9.10-dicyano anthracene and polynuclear aromatics, the polymerization of the former is initiated by the radical cations of the aromatic hydrocarbons formed via the PET with the dicyano compound. 

Support for direct initiation by PS+ was recently obtained by experiments on the polymerization of cyclohexene oxide using anthracene labelled polytet-rahydofuran as the sensitizer. In this case poly(tetrahydrofuran-b-cyclo-hexeneoxide) is formed [66]. 

Cyclic monomers such as cyclohexene oxide were readily polymerized upon irradiation of the CT complexes of pyridinium salts whereas spontaneous polymerizations were observed upon mixing with strong electron donating monomers such as butyl vinylether and A-vinyl carbazole. These monomers are known to form CT complexes themselves with electron acceptors which may interfere with the rapid polymerization observed. 

UV irradiation of the resulting prepolymers caused a-scission, and benzoyl and polymer bound electron donating radicals are formed in the same manner as described for the low-molar mass analogues. Electron donating polymeric radicals thus formed may conveniently be oxidized to polymeric carboeations to promote cationic polymerization of cyclic ethers. It was demonstrated that irradiation of benzoin terminated polymers in conjuction with pyridinium salts as oxidants in the presence of cyclohexene oxide makes it possible to synthesize block copolymers of monomers with different chemical natures [75] (Scheme 19). 

Free radical promoted cationic polymerization was successfully employed [77] for the preparation of new classes of liquid crystalline (LC) block copolymers comprising a semicrystalline block, poly(cyclohexene oxide), and LC block of different structures ... 

Polymerization of some cationically polymerizable monomers like cyclohexene oxide [49], 3,3-bis(chloromethyl)oxetane [50], or 1,3,5-trioxane [51] may be initiated by irradiation with y-rays both in liquid or solid state. 

Cationic organozinc compounds are expected to be good catalysts for ring opening polymerization reactions of epoxides and lactones because the enhanced Lewis acidity (see Lewis Acids Bases) of the zinc center favors its coordination to the monomer. For example, Walker and coworkers have found that the cationic zinc substituted cyclopentadienyl complex [3,5-Me2C6H3CH2CMe2C5H4Zn(TMEDA)]+ [EtB(C6F5)3] is an active initiator species for the polymerization of cyclohexene oxide and e-caprolactone. ... 

In another example, Yildirim et al. photochemically generated anthracene radical cations in the presence of TEMPO [29]. TEMPO immediately trapped the radical to form the TEMPO-anthracene cation, which was subsequently used to initiate cationic polymerization of cyclohexene oxide (CHOX). The resulting alkoxyamine-functional polycyclohexene oxide was used to macroinitiate styrene polymerization, resulting in the formation of S-6/-CHOX (Scheme 8.9). 

To the first category belongs the photochemical formation of carbenhim ions or protonic acids directly in the polymerization medium this field, discussed in Sect. 3.1 and 3.2 has recently been reviewed by Smets at the lUPAC Macronmlecular Sympo-sium2 ) When cyclohexene oxide is used as a monomer the order of reactivities for iodonium or sulphonium salts, giving photochemically protonic acid, depend on the structure of anion MtX in the following way ... 

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