Linear polymers from conjugated

Linear polymers from conjugated dienes readily undergo oxidation in air, in some cases even at room temperature (14). The allylic carbon... 

Isomeric polymers can also be obtained from a single monomer if there is more than one polymerization route. The head-to-head placement that can occur in the polymerization of a vinyl monomer is isomeric with the normal head-to-tail placement (see structures III and IV in Sec. 3-2a). Isomerization during carbocation polymerization is another instance whereby isomeric structures can be formed (Sec. 5-2b). Monomers with two polymerizable groups can yield isomeric polymers if one or the other of the two alternate polymerization routes is favored. Examples of this type of isomerism are the 1,2- and 1,4-polymers from 1,3-dienes (Secs. 3-14f and 8-10), the separate polymerizations of the alkene and carbonyl double bonds in ketene and acrolein (Sec. 5-7a), and the synthesis of linear or cyclized polymers from non-conjugated dienes (Sec. 6-6b). The different examples of constitutional isomerism are important to note from the practical viewpoint, since the isomeric polymers usually differ considerably in their properties. 

By comparing the photochemical behavior of conjugated diolefinic monomers in the crystalline state and in solution, a crystal matrix effect on four-center type photopolymerization has been revealed. It has been concluded that high molecular weigth linear polymers are produced photochemically from these monomers only by way of a crystal-lattice controlled mechanism. 

From the above spectral data, the polymer structure is believed to be a linearly cyclized form as described in Scheme 20. Also, it has been known that the resulting cyclized polymers with conjugated double bonds have both five- and six-membered ring structures with a certain ratio, which should depend on the polymerization conditions, monomer structures, and the kinds of catalysts used. ieo... 

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