Spiro orthocarbonate polymerization

Sulfur-containing spiro orthocarbonates, cationic polymerization of, 23 729 Sulfur-cured EPDM, 21 8041. See also Ethylene- propylene-diene monomer (EPDM) rubber Sulfur deposits... 

This reaction is thermodynamically controlled, because the polymer containing 1,3-dioxolane rings converts itself to a polyether when allowed to stand at room temperature for several days or heated at 80 °C for a few hours in the presence of an acid catalyst. Similar double ring-opening polymerizations were observed for 2,6,7-trioxabicyclo[2.2.2]octane and its derivatives [86, 87] and for spiro orthoesters and spiro orthocarbonates as well (see Sects. 6 and 7). 

Takata et al. [99] found for two spiro orthocarbonates (119 and 121) having l,4,6,9-tetraoxaspiro[6.6]tridecane skeletons different cationic ring-opening polymerization behavior Irrespective of solvent, initiator, and temperature (from room temperature to 150°C), 119 gave polycarbonate (120), whereas 121 gave poly (ether-carbonate) (122). 

Cationic polymerization of spiro orthocarbonates leading to a poly (ether-carbonate) alternating copolymer proceeds via the trialkoxycarbenium ion as a possible propagating species. Since this type of carbenium ion was found to be quite stable, [100] the growing chain end is expected to remain living after the completion of the polymerization. [101]... 

Cationic polymerization of norbomene spiro orthocarbonate (125) differs from that of other spiro orthocarbonates in that it gives a structurally complicated polymer. [102] When polymerized with boron trifluoride etherate at 100 °C in chlorobenzene for 24 h, the 1H NMR of a polymer of 125 showed very reduced olefinic proton signals (22% of the original monomer). The monomer was... 

Scheme 20 [103] shows that the polymerization of 131 proceeds via a stable tris(alkylthio)carbenium ion 135. This species can be attacked in three different ways by the second monomer, producing 134, 133, and 132 via paths a, a, and b, respectively. Kinetically, path a should dominate over the others. Path a is one of the possible pathways, but presumably it is of minor importance. Although the conversion of 134 to 132 cannot be ruled out, 132 is more likely to be formed via path b, as is the case with six-membered spiro orthocarbonates. At high... 

In contrast, radical polymerization of 2,3-benzo-7-methylene-l,4,6,9-tetraoxa-spiro[4.4]nona-2-ene (138) gave only a vinyl polymer (139) with no occurrence of ring-opening isomerization, even in the solution polymerization at 165 °C. [105] It appears that the propagating radical having a spiro orthocarbonate structure is too stable to liberate the corresponding carbonyl compound, phenylene carbonate. 

Figure 15. Radical ring-opening polymerization of spiro orthocarbonate derivatives bearing an exo-methylene group at a- (a) and P-position (b) of the...

Scheme 13 Photoinitiated radical ring-opening polymerization of spiro orthocarbonate 45.

In a program to develop monomers that expand on polymerization, we had prepared a series of spiro orthoesters, spiro orthocarbonates, trioxabicyclooctanes, and ketal lactones that could be polymerized with ring-opening by ionic catalysts to give either no change in volume or slight expansion... 

The review will be limited to atom- and bond-bridged bicyclic monomers. The important work of Bailey on the polymerization of spiro bicyclo orthoesters and spiro bicyclic orthocarbonates has been adequately described elsewhere 0 1 60 3. The outstanding and systematic body of work by Schu-erch2 3> and others on the ring opening polymerization of bicyclic acetals derived from carbohydrate precursors will also not be covered here. 

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