Spiroorthocarbonates

Various methylene derivatives of spiroorthocarbonates and spiroorthocstcrs have been reported to give double ring-opening polymerization e.g. Scheme 4.36). Like the parent monocyclic systems, these monomers can be sluggish to polymerize and reactivity ratios are such that they do not undergo ready copolymerization with acrylic and styrenic monomers. Copolymerizations with VAc have been reported.170 These monomers, like other acetals, show marked acid sensitivity. 

Spiroorthocarbonates and spiroorthoesters are stable toward bases and nucleophiles but easily undergo cationic ROP. Cationic ROP of a spiroorthocarbonate (LXX) proceeds by initial formation of carbocation LXXI in which the carbocation center is stabilized by... 

Spiroorthocarbonates were obtained by coupling of cyclic tin adduct 251, prepared from 1,2-dihydroxymethyl-benzene and dibutyltin oxide, with thiocarbonate 252. Reaction of the resulting orthocarbonate 253 with potassium A/z-butoxide in toluene afforded spiroorthocarbonate 254 (Scheme 77) <2003BKC1371>. 

The polymerization of spiroorthocarbonate 255 and spirotetrathioorthocarbonate 256 has previously been studied. The synthesis of spirotetrathioorthocarbonate 258 was performed by acid-catalyzed transesterification of tetra fr-(methylthio)methane with o-xylenedithiol <1997MM6721> (Scheme 78). 

One of the mechanisms taken into consideration for the polymerisation of propylene carbonate was that this proceeded via orthocarbonate species. The likelihood of such a mechanism might be ascertained by the polymerisation of bispropylene spiroorthocarbonate with diethylzinc as the catalyst at 160 °C, which was found to yield poly(propylene ether-carbonate) [143],... 

The polymerisation of the bispropylene spiroorthocarbonate with zinc-based coordination catalysts probably involves zinc alcoholate propagating species, which is shown schematically as follows ... 

Fairly good confirmation of the postulated mechanism of cyclic carbonate enchainment according to scheme (15) may be the obtaining of poly(oxypro-pylene-co-oxycarbonyloxypropylene) of predominant head-to-tail regioregular-ity from bispropylene spiroorthocarbonate with a zinc-based coordination catalyst [146]. It must be emphasised that the copolymerisation of propylene... 

One of the so far not very numerous group of cyclic monomers able to polymerize and to copolymerize with styrene, methyl methacrylate, etc. under the effect of peroxides is spiroorthocarbonate [307],... 

An alternative method for preparing spiroorthocarbonates entails transesterifying 1,2-acetoxymethyl ethylene with tetraethylortho-carbonate derivatives (1). Similar preparations are discussed (2,3). 

Photoinitiation conditions and methods using spiroorthocarbonates are described (4). 

Methods for preparing orthoesters using lactones (2) or spiroorthocarbonates (3) with boron trifluoride are discussed. 

Sulfur analogs of spiroorthocarbonates, namely spirotetrathiocarbo-nates, also undergo cationic polymerization [212]. A 5-membered monomer gives the mixture of polyethylene sulfide) and ethylene trithiocar-bonate ... 

Rokicki, G. Prog. Aliphatic Cyclic Carbonates and Spiroorthocarbonates bonates as Monomers Polym. Sci. 25, no. 259 (2000). PP 259-342. 

D. Nagai, et al., Non-shrinking networked materials from the cross-linking copolymerization of spiroorthocarbonate with bifunctional oxetane. Macromol. Rapid Commun. 2006, 27(12), 921-925. 

Dimethylene-l,5,7,ll-tetraoxaspiro 5.5 undecane is a spiroorthocarbonate containing two double bonds. It may be prepared starting from cyclopentadiene and acrolein with 40 % yield54). 

Orthocarbonic acid esters s. Spiroorthocarbonic acid esters... 

Density measurements were made to determine the amount of shrinkage of the epoxy matrix during curing and these were compared with epoxy containing 5% dinorbomene-spiroorthocarbonate (DNSOC). If the density of epoxy before cure is 1.154 g/mL and after cure is 1.199 g/mL, calculate the percentage shrinkage. 

Rokicki, G., 2000. Aliphatic cyclic carbonates and spiroorthocarbonates as monomers. Progress in Polymer Science 25, 25259—25342. 

Soga et al proposed the mechanisms in which the polymerization of PC proceeded via spiroorthocarbonate species (2,7-dimethyl-l,4,6,9-tetraoxaspiro[4.4]nonane). To conform this mechanism the authors polymerized the spiroorthocarbonate in the presence of diethylzinc as a catalyst and obtained poly(pro-pylene ether-carbonate) of similar chemical structure. It means that in the first reaction step the monomer decarboxylation takes place. The decarboxylation involves most probably metal carbonate species formation due to the l,3-dioxoIan-2-one ring opening via the alkyl carbon-oxygen bond cleavage. 

When exo-cf die carbon atom of 1 is attacked by oxirane the product with ether-carbonate group 2 is formed (reaction pathway a). On the other hand as a result of oxirane attack on endo-cydic carbon atom of 1 both the ether group 3 and cyclic carbonate are formed (pathway b). The intramolecular reaction between the carbocation and an oxygen atom of linear ether leads to spiroorthocarbonate 4 (pathway c). It was shown that the reaction proceeded partially according to pathway a in the case of using cyclic carbonates bearing phenoxymethyl and chloromethyl substituents, but for other five-membered cyclic carbonates the reaction pathway b dominated. Due to higher stability of the trialkoxycarbenium cation the polymerization rate is slower than that of oxirane homopolymerization. 

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