Other Polyhydrocarbons

Poly(para-phenylene)s PPPs and other polyarylenes represent structure-classes of conjugated polyhydrocarbons which are currently under intensive investigation [7]. This, in turn, is the result of important advances that have been made in the chemistry of aromatic compounds in recent years. 

Various other polymers have double bonds in their carbon backbone. Some are polyhydrocarbons such as poly-a-pinene (see Section 6.8), while others are polymers including aromatic cycles in the backbone or possibly heteroatoms. These polymers are typically classified under different groups (see Chapters 8 and 15). 

Polybutadiene, CAS 9003-17-2, is a common synthetic polymer with the formula (-CH2CH=CHCH2-)n- The cis form (CAS 40022-03-5) of the polymer can be obtained by coordination or anionic polymerization. It is used mainly in tires blended with natural rubber and synthetic copolymers. The trans form is less common. 1,4-Polyisoprene in cis form, CAS 9003-31-0, is commonly found in large quantities as natural rubber, but also can be obtained synthetically, for example, using the coordination or anionic polymerization of 2-methyl-1,3-butadiene. Stereoregular synthetic cis-polyisoprene has properties practically identical to natural rubber, but this material is not highly competitive in price with natural rubber, and its industrial production is lower than that of other unsaturated polyhydrocarbons. Synthetic frans-polyisoprene, CAS 104389-31-3, also is known. Pyrolysis and the thermal decomposition of these polymers has been studied frequently [1-18]. Some reports on thermal decomposition products of polybutadiene and polyisoprene reported in literature are summarized in Table 7.1.1 [19]. 

Vulcanization is an industrial process applied to various polymers from the class of unsaturated polyhydrocarbons. The major practical use of vulcanized elastomers is the tire industry. Tires are made from various polymer blends, including natural rubber, typically between 20 and 50%. The other polymers used in various blends that can be vulcanized include copolymers such as poly(styrene-co-1,3-butadiene) or SBR, poly(acrylonitrile-co-1,3-butadiene-co-styrene) or ABS, poly(isobutylene-co-isoprene), poly(ethylene-co-propylene-co-1,4-hexadiene, etc. 

Poly(2-chloro-1,3-butadiene) and other halogenated unsaturated polyhydrocarbons... 

Results for some other halogenated unsaturated polyhydrocarbons were reported in literature. For example, poly(perfluoro-4-chloro-1,6-heptadiene) upon heating between 320° C and 400° C is reported to completely volatilize [12]. Also, reports on chlorinated rubber show that by heating from ambient to 500° C, it generates almost quantitatively HCI, and in the later stages of reaction CH4, C2H4, and H2 [13],... 

Pyrolysis of chlorinated unsaturated polyhydrocarbons is in some respects similar to that of the parent polyhydrocarbon, and in some others similar to halogenated saturated hydrocarbon type polymers. The elimination of the hydrohalogenated acid takes place relatively easily, and the polymers from this class are not resistant to heating. In practice, additives that enhance the resistance to heating frequently are added. Since the elimination of the acid seems to accelerate thermal decomposition, similarly to the case of PVC, metallic oxides that scavenge the acid increase the resistance to heating. The main pyrolysis products of each polymer are not modified by the addition of these additives. 

The simplest polyhydrocarbon, with structural element —CHi—, can be produced by the polymerization of ethylene (CH2=CH2), diazomethane (CH2N2), or a mixture of CO and H2. The polymer produced from diazomethane is called poly(methylene). It is only lightly branched. The polymerization mechanisms has not been established. A carbene mechanism has been discussed for gold as initiator. With boron trifluoride-water as initiator, on the other hand, a regular cationic polymerization with proton addition and subsequent propagation is considered ... 

Some other specialised polyester polyols, like polycarbonate and polycaprolactone, possess superior hydrolytic resistance. Aliphatic polyhydrocarbon polyol such as hydroxyl terminated polybutadiene (HTPB), is advantageous in many respects. These substances are resistant to acidic or basic hydrolysis, possess good adhesion and can be used where low polarity and good electrical insulation are required. 

In this approach, AB2 type or other similar monomers such as AB (x = 4, 6, 8, etc.) monomers are polymerised by a polycondensation reaction. Gelation, a general problem in the polymerisation of multifunctional monomers, is avoided by the use of a dilute solution and the slow addition of monomer(s). Vegetable oil-based hyperbranched polyhydrocarbons, polyethers, polyesters, polyamides, and so on may be prepared by this method. 

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