Polybutadienes with ozone

The reaction of ozone with olefinic compounds is very rapid. Substiments on the double bond, which donate electrons, increase the rate of reaction, while electron-withdrawing substituents slow the reaction down. Thus, the rate of reaction with ozone decreases as follows polyisoprene > polybutadiene > polychloroprene [48]. The effect of substiments on the double bond is clearly demonstrated in Tables 15.2 and 15.3. Rubbers that contain only pendant double bonds such as EPDM do not cleave since the double bond is not in the polymer backbone. 

Only recently first reports appeared describing the potential of the nanostructured thin block copolymer films for lithographic etching. A thin film of polystyrene-block-polybutadiene with a hexagonal cylindrical morphology where the poly-(butadiene) cylinders were oriented perpendicular to the substrate was deposited on a silicon wafer and selectively decomposed by treatment with ozone or converted with osmium tetroxide. By a subsequent reactive ion etching process the pattern could be inscribed into the surface of the silicon wafer yielding small holes or islands with a lattice constant of 27 nm and hole/island sizes of 13 nm [305,312]. 

It is proposed that this is due to attack of carbonyl oxides, in their biradical form, on the rubber double bonds. Typical diene rubbers (polyisoprene and polybutadiene) have rate constants several orders of magnitude greater than polymers having a saturated backbone (polyolefins). Other unsaturated elastomers having high reaction rates with ozone include styrene-butadiene (SBR) and acrylonitrile-butadiene (NBR) rubbers. As an example, Polychloroprene (CR) is less reactive than other diene rubbers, and it is therefore inherently more resistant to attack by ozone. 

Acid, acid chlorides, and hydroxy-functionalized telechelics have been described (418). The reaction of polybutadiene with controlled amoimts of ozone can be used to prepare hydroxy-terminated telechelic polybutadienes (419). The oxidative cleavage of copolymers of isobutylene with dienes has been studied... 

Polybutadienes with various microstructures crosslink rapidly below their decomposition temperature, which affects the subsequent breakdown behaviour." Oxidation of c/s-1,4-polybutadiene at 90—180 °C gave primarily epoxides as products with smaller quantities of alcohols, peroxides, and carbonyl-containing, structures. "C n.m.r. was used to determine the structure of the oxidized products. The oxidation of cis- 1,4-polybutadiene by molecular oxygen, singlet oxygen, atomic oxygen, and ozone has also been studied." All the forms of oxygen interact by a... 

The ozonization method has been extended to the most varied polymer/monomer systems, such as polybutadiene-03 with acrylamide, methyl methacrylate or styrene, cellulose-03 with styrene or acrylonitrile (127), starch-03 with styrene (126). In this last case the formation of some homopolystyrene as side-product has been mentionned by the authors. The starch-styrene graft copolymers are claimed to be good emulsifiers for water-oil suspensions. 

As a result of its saturated polymer backbone, EPDM is more resistant to oxygen, ozone, UV and heat than the low-cost commodity polydiene rubbers, such as natural rubber (NR), polybutadiene rubber (BR) and styrene-butadiene rubber (SBR). Therefore, the main use of EPD(M) is in outdoor applications, such as automotive sealing systems, window seals and roof sheeting, and in under-the-hood applications, such as coolant hoses. The main drawback of EPDM is its poor resistance to swelling in apolar fluids such as oil, making it inferior to high-performance elastomers, such as fluoro, acrylate and silicone elastomers in that respect. Over the last decade thermoplastic vulcanisates, produced via dynamic vulcanisation of blends of polypropylene (PP) and EPDM, have been commercialised, combining thermoplastic processability with rubber elasticity [8, 9]. 

In other work. Fog and Rietz used a polybutadiene-coated TSM resonator to detect ozone in workplace environments [137]. Ozone reacts irreversibly with unsaturated hydrocarbons to form ozonides, which typically react further with moisture to give ketones and hydrogen peroxide. They reported stable operation at a concentration of 20 ppb for up to 4 hours, with a 10% decrease in sensitivity during a 15-minute exposure to 100 ppb of ozone. 

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. 

It is claimed that styrene/butadiene diblock polymers bring about an improvement in the hardness, strength, and processability of polybutadiene elastomers (27), as well as an improvement in the ozone resistance of neoprene rubber (28). Styrene diblock polymers have also been made with isoprene, a-methyIstyrene, methyl methacrylate, vinylpyridine, and a-olefins. Block copolymers of ethylene, propylene, and other a-olefins with each other have been made as well. Heteroatom block copolymers based on styrene or other hydrocarbons and alkylene oxides, phenylene oxides, lactones, amides, imides, sulfides, or slloxanes have been prepared. 

In the spectra of the ozonized polybutadienes the appearance of bands at 1,111 and 1,735 cm, which are characteristic for ozonide and aldehyde groups, respectively, is observed [22, 31], It was found that the integral intensity of ozonide peak in the l,4-cz5-polybutadiene Emulsion Butadiene Rubber (E-BR) spectrum is greater and that of the aldehyde is considerably smaller in comparison with the respective peaks in the Diene 35 NFA (BR) spectrum at one and the same ozone conversion degree of the double bonds. The differences in the aldehyde yields indicate that, according to IR-analysis, the degradation efficiency of the BR solutions is greater. 

FIGURE 10.5 Selection of protons with characteristic signals in the H-250 MHz NMR spectra of partially ozonized polybutadiene macromolecules. 

Polymers can be divided into two main classes on the basis of their reactivity to NO [1]. Saturated polymers such as polyethylene (PE) and polypropylene (PP) belong to the first group, but Nylon 66 does not. The second group covers elastomers. Butyl rubber (BR) undergoes scissions of the main chain, and polybutadiene is extensively cross-linked under the action of NO. These elastomers have approximately the same reactivity to NO as to ozone. All films exposed to NO become yellow, and their infrared (IR) spectra show that nitro groups enter into macromolecules. In polyvinylchloride in the presence of NO, a decrease in the amount of chlorine, along with the appearance of nitro and nitrite groups, are observed from IR spectra. 

The basic route of the reaction - the formation of normal ozonides does not lead directly to a decrease in the molecular mass of the elastomer macromolecules, because the respective 1,2,4-trioxolanes are relatively stable at ambient temperature (by analogy with Scheme 1 of polyisoprenes, see it below) [31, 32]. The most favorable conditions for ozone degradation emerge when the cage interaction (Scheme 1, reaction 3) does not proceed. Therefore, the higher ozonide yield the lower the intensity of ozone degradation of the polybutadienes and vice versa. As it was already determined the ozonide yields for the, A-cis- and 1,2-monomer units are... 

It is now well-recognized that the cross-linking site does not have to be at or adjacent to main chain carbon-carbon double bonds such as is common with natural rubber, SBR, NBR, polybutadiene and butyl rubber. Such bonds may have the disadvantage that they provide a weak link susceptible, for example, to attack by oxygen and ozone. One development is to build the double bond into a ring structure within the chain so that on rupture the effect is less catastrophic—a practice used with ethylene-propylene terpolymers. 

In the paper the interaction of the syndiotactic 1,2-polybutadiene and the reagents of different chemical nature as ozone, peroxy compounds, halogens, carbenes, aromatic amines and maleic anhydride are considered. Various polymer products with a set complex of properties is possible to obtain on the syndiotactic 1,2-polybutadiene basis varying the nature of the modifying agent, a functionalization degree of the polymer and synthesis conditions. 

The influence of polymers and additives on the service life of non-tread tyre components is discussed on the basis of results obtained from studies of inner liner, belt and sidewall compounds. The effects of the bromine content of bromobutyl rubbers on the performance of inner hners, and of sulphenamide accelerators on the adhesion of NR belt compounds to brass coated steel cords were investigated. The mechanical properties and ageing and ozone resistance of black sidewall compounds consisting of NR blends with neodymium catalysed polybutadiene protected with different antioxidants and antiozonants were also evaluated. 5 refs. 

A review is made of the literature describing the surface discolouration of black tyre sidewalls caused by exposure to ozone and formulation studies undertaken to overcome this problem. Methods examined include the use of nonstaining antiozonants and blending inherently ozone resistant rubbers such as EPDM, halobutyl rubbers and brominated isobutylene-paramethylstyrene copolymers with NR and/or polybutadiene. 67 refs. 

The most outstanding property of butyl rubber is its very low air permeabdity, which has led to its extensive use in tire inner tubes and liners. A major disadvantage is its lack of compatibility with SBR, polybutadiene, and natural rubber. An ozone resistant copolymer of isobutylene and cyclopentadiene has also been marketed. 

Other oxygen species are also reactive with double bonds. Detailed sp ctroscopical studies show hat all oxygen species, i.e. singlet ( O2) and molecular oxygen ( atomic oxygen (0) and ozone (0 ) react with cis-l,4-polybutadiene forming different... 

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