Polymers containing conjugated double bonds

A different subclass of unsaturated hydrocarbon type polymers is formed by polyacetylenes. This type of polymer contains conjugated double bonds in a linear structure, and due to their special electrical properties they have been the subjects of numerous studies including some on thermal stability. 

Crosslinking of alkyds containing conjugated double bonds results in more carbon-carbon bonds in the crosslinks than in the alkyds containing unconjugated double bonds. The crosslinking mechanism involves the formation and decomposition of cyclic peroxides, to yield radicals that initiate crosslinking by 1,4-polymerization of the polymer molecules. 

M. G. Matveeva, and A. E. Kalmenson Polymers with conjugated double bonds. IV. Polymers containing heteroatoms in the conjugated chain. Vysokomol. Soed. 1, 1647 (1959) [2, 96 (1962)]. 

A number of molecules with two conjugated double bonds, such as 1,3-butadiene or 2-methyl-1,3-butadiene (isoprene), can undergo a 1-4 polymerization with the migration of the doubie bond in the 2 position. The resulting polymer contains isolated double bonds, but their presence leads to the possibility of having cis- and trans- forms, as shown below ... 

Polyacetylene contains conjugated double bonds in a linear structure [51-54], which leads to special electrical conductivity properties. For this reason, polyacetylene and some other related polymers have applications in the optical and electronic industries. Pojyacetylene synthesized at relatively low temperature seems to have a cis-conformation, with two possible cis- forms indicated as c/s-transoid, and frans-cisoid, as shown below ... 

Sulfur dioxide does not homopolymerize, but on reaction with olefins it yields copolymers.Terminal olefins react more readily than those with an internal double bond. The presence of various substituents affects the rate of polymerization. Conjugated dienes copolymerize with sulfur dioxide to give linear polymers containing residual double bonds. 

K.-Y. Hsu, T.-C. Chang, and C.-H. Li, Studies on thermotropic liquid-crystalline polymers Part X. Synthesis and properties of crossUnkable aromatic copoly(ester)s containing conjugated double bonds. Journal of Polymer Science Part A Polymer Chemistry, 31, 971 (1993). 

Several decades ago, only two natural oils (tung oil and oiticica) were known to contain conjugated double bonds. Oils that contain these bonds rapidly form a polymer fihn ( drying ) if a thin layer is exposed to air mng oil was widely used in the paint and varnish industry. An increasing demand for such oils and limited availability encouraged efforts to produce drying oils from nonconjugated oils. 

For this aim, first condition is that the polymer to consist in an alternation of simple and double bonds in chain, i.e., to contain conjugate double bonds. The simplest candidate is polyacetylenes. Figure 3.44 (Putz, 2006). 

Of the plethora of systems containing conjugated double bonds, poly(acetylene)s, poly(heterocycle)s, and poly(aminoaromatic) compounds are undoubtedly the most popular both in regard to their electrical conductivity and their stability and ease of preparation. Poly(acetylene), poly(pyrrole), and poly(aniline) are the most intensively studied polymers. 

In rigid and soft PUR foams, mainly tertiary amines are used as catalysts. They may in part remain in the foams after polyaddition and are capable, e.g., in contact with a PC film, of migrating into the film, thus causing a red discoloration of the PVC. The mechanism of this discoloration proceeds by what is called a Baylys-Hillmann reaction. The tertiary amine first acts as a catalyst for HCl elimination from the PVC chain and subsequently adsorbs to the polymer chain that already contains conjugated double bonds at this point [686]. 

Cesca, S., Priola, A. and Bruzzone, M. Synthesis and Modification of Polymers Containing a System of Conjugated Double Bonds. Vol. 32, pp. 1—67. 

Polyacetylenes are the most important class of synthetic polymers containing conjugated carbon-carbon double bonds. Some optically active monomers have been used with the following conclusions. Polymers of 1-alkynes having a branched side-chain assume in solution a helical conformation. A chiral side-chain induces a predominant screw sense in these helices. In particular, for alkyl branching, it has been shown that (S) monomers lead to a left-handed screw sense. 

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