Conjugated double bonds during polymer

In the system cyclopentadiene-trichloroacetic acid-benzene the occurrence of ions during polymerization has been shown, but these arise from the protonation of conjugated double bonds in the polymer. However, there is also circumstantial evidence for the participation of carbonium ions in the growth reaction [24]. 

During heating or attack with a base, the polymer undergoes a dehydrofluorination, creating conjugated double bonds that can be involved in a Diels-... 

The thermal degradation of PVC is generally accepted to be a two-step process 893672 871835 830034 755845. The first step (up to 350 °C) mainly involves dehydrochlorination of the polymer (Scheme 6), resulting in the formation of conjugated double bonds that break during the second step (up to 550 C). 

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. 

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