1,4-Polybutadiene reactions, degradation

Degradation of polyolefins such as polyethylene, polypropylene, polybutylene, and polybutadiene promoted by metals and other oxidants occurs via an oxidation and a photo-oxidative mechanism, the two being difficult to separate in environmental degradation. The general mechanism common to all these reactions is that shown in equation 9. The reactant radical may be produced by any suitable mechanism from the interaction of air or oxygen with polyolefins (42) to form peroxides, which are subsequentiy decomposed by ultraviolet radiation. These reaction intermediates abstract more hydrogen atoms from the polymer backbone, which is ultimately converted into a polymer with ketone functionahties and degraded by the Norrish mechanisms (eq. 

Here PNO2 partial pressure of nitrogen dioxide in pascals (1 Pa = 0.000145 psi), and the activation energy is 3870 kJ/mol. Other saturated polymers are less susceptible to attack by NO2 than most unsaturated polymers such as synthetic rubbers (polyiso-prene, polybutadiene, and butyl rubber). The presence of oxygen also tends to accelerate degradation by NO2. The reaction of sulfur dioxide with saturated polymers is complex, but appears to be activated by ultraviolet radiation. 

Like ldpe, polybutadienes are resistant to most nonoxidizing acids, alkalis, and salts. However, because they are unsaturated, the polyalkadienes are attacked by hydrochloric, hydrobromic, and hydrofluoric acids, as well as by hydrogen and chlorine. The reaction products, which are thermoplastic, have been used as commercial nonelastomcric plastics. NR and other diene elastomers are also attacked by peroxides and ozone. In the absence of an tioxidants and carbon black filler, these unsaturated elastomers are degraded in the sunlight. 

A substantial amount of work has been done on the ozone degradation of polymers. For Instance, mechanical properties and adhesion have been shown to degrade sharply during ozone exposure (1-4). Polystyrene (PS) and polybutadiene (PBD) show very different sensitivities to ozone exposure. Since reaction with a gas would occur first at the surface, we planned to study the reactivity of the PBD as affected by copolymerization with styrene. In particular it was of Interest to know if random and block copolymers of styrene would show different surface sensitivities because of changes in surface distribution of the groups. For the same group concentration, block structures should segregate PS better. 

Following Ashby s first observation (7) of chemiluminescence from the oxidative degradation of polymers, a number of papers have appeared dealing with oxidative chemiluminescence from a variety of polymers (8-16). In this chapter we continue the 1,4-polyisoprene work with a study of the low-temperature chemiluminescence emitted in the autoxidation of three additional elastomers, cis-1,4-polybutadiene, amorphous 1,2-polybutadiene, and fmns-polypentenamer. We also report the chemiluminescence obtained from singlet-oxygenated samples of cis-1,4-polybutadiene and trans-polypentenamer, as well as rate data for singlet oxygen reactions with the 1,4-polyisoprene, 1,4-polybutadiene, and model compounds in solution. 

When czj-1,4-polybutadiene is added to a solution of cyclododecene that has been polymerized using WCl6/Et3Al2Cl3 as catalyst, a block copolymer is obtained, but at the same time the polybutadiene chains undergo considerable intramolecular degradation. The amount of degradation can be reduced to acceptable levels by careful control of the reaction conditions. However, the technological properties of such block copolymers are not superior to those of blends (Streck 1982). 

Degradation of Unsaturated Polymers by Metathesis 16.3.5 Polybutadienes modified by partial addition reactions... 

Fig. 16.5 Degradation of partially (25%) cyclopropanated di-1,4-polybutadiene by metathesis with troni-oct-4-ene. GC of a reaction mixture in the early stages of reaction. n, m above the peaks correspond to the number of Mj and M2 units, respectively, in Q(Mi/2) (Mi) (M2)m(M /2)Q (see text). S = internal standard, tetradecane (Hummel 1984).

Cyclooctadienyl substituents at the methylene groups in c/s-1,4-polybutadiene can be introduced by the radical-induced reaction with cycloocta-1,5-diene. Metathesis degradation of the product with tra 5-oct-4-ene shows that the substitution reaction is accompanied by double-bond shift reactions (Hummel 1990a). 

Two reactions can occur during wear oxidative degradation as a result of frictional heating in the contact zone and mechanochemical degradation initiated by shear-induced rupture of chemical bonds. Present evidence favors the latter process. For example, in the absence of oxygen, the wear of cis-polyisoprene changes to resemble that of c/x-polybutadiene, whereas the wear of poly(ethylene-co-propylene) is unaltered (Gent and Pulford, 1983). These results are in accord with the response of these materials to free radical reactions. 

Functionalization vs. Degradation of Polybutadiene in the Reaction with Vinyltrialkoxysilanes Catalyzed by Ruthenium Complexes... 

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