Rubbers cyclised

In spite of the unsaturation of rubber it is said to be resistant to chemical attack since a few chemical derivatives like chlorinated rubbers, cyclised rubbers and chlorides are formed as protective layers retarding further attack by the chemicals. Properly compounded vulcanizates satisfactorily resist the action of most inorganic acids other than oxidizing acids such as nitric, hydrochloric and sulphuric acids. Rubber linings which are to resist swelling to a lower degree should be "tightly" vulcanized. 

It was found that the amount of chlorine that could be removed (84-87%) was in close agreement to that predicted by Flory on statistical grounds for structure Figure 12.10(a). It is of interest to note that similar statistical calculations are of relevance in the cyclisation of natural rubber and in the formation of the poly(vinyl acetals) and ketals from poly(vinyl alcohol). Since the classical work of Marvel it has been shown by diverse techniques that head-to-tail structures are almost invariably formed in addition polymerisations. 

If natural rubber is treated with proton donors a product is formed which has the same empirical formula. (CjHjj), and is soluble in hydrocarbon solvents but which has a higher density, is inelastic and whose unsaturation is only 51% that of natural rubber. It is believed that intramolecular ring formation occurs to give products containing the segments shown in Figure 30.5. Known as cyclised rubber it may be prepared by treating rubber, on a mill, in solvent or in a latex with materials such as sulphuric acid or stannic chloride. 

Attempts have been made to popularise cyclised rubber as an additive for use in shoe soling compounds but they have not been able to compete with... 

Atmospheres polluted by oxidising agents, e.g. ozone, chlorine, peroxide, etc. whose great destructive power is in direct proportion to the temperature, are also encountered. Sulphuric acid, formed by sulphur dioxide pollution, will accelerate the breakdown of paint, particularly oil-based films. Paint media resistant both to acids, depending on concentration and temperature, and oxidation include those containing bitumen, acrylic resins, chlorinated or cyclised rubber, epoxy and polyurethane/coal tar combinations, phenolic resins and p.v.c. 

Rubber in the form of fine threads produced by vulcanising a thin sheet of rubber compound, winding it on a drum and slitting it to the required size by revolving the drum against a number of sharp, wetted knives which revolve at high speed. Cyclised Rubber... 

Many chemical derivatives of mbber, produced in the course of attempts to elucidate the structure of mbber, became of practical commercial value but have been superseded by the diversity of synthetic polymers. See Cyclised Rubber, Chlorinated Rubber, Rubber Hydrochloride, Rubbone. 

Cyclisation of unsaturated elastomers has been the subject of interesting research. Cyclisation yields hard resinous products which have commercial importance and are designated as cyclised rubber [49, 50]. Cyclisation can be carried out with cationic, radiation induced, photo-induced or by thermal methods. Among all these methods cationic cyclisation has been extensively reported probably because there are less side reactions. The generally accepted mechanism of cyclisation of 1,3 diene elastomers is shown in Scheme 4.3a. 

Chemical modification of rubber such as hydrogenation, chlorination, epoxidation, cyclisation, addition of maleic anhydride, is a popular technique to give a desirable... 

The mass increase of an RB 830 syndiotactic 1,2-BR sample was measured as a function of time at 240°C in an air atmosphere. About thirty minutes were necessary to obtain a mass increase of 0.19 %wt. (0.22 %wt. during the non-isothermal experiment), see Figure 8.5. This sample was cooled and then placed in the DSC. A crystalline phase with a Tm- and Hf-value of respectively 9l°C and 23 J/g was detected the Tg-value of the amorphous phase proved to be -13°C. Hence, the Tg-, Tm- and Hf-values were not influenced at all by the samples heat treatment. Even the strength of the glass-rubber transition effect (0.26 J/g.°C) was not changed. Thus, the detected mass increase effect can not be explained by some cyclisation reaction of the BR. 

Cyclised natural and synthetic rubbers Photoinitiators/stabilisers/preservatives Quinones Anthrones Diphenyls... 

Polychloroprene (CR) has much more chlorine than the chlorobutyl rubber examined by Lawson and good adhesion to untreated CR wonld be expected provided there was no weak layer was on the surface. If such layers exist a suitable solvent treatment or abrasion should result in good adhesion. Cyclisation has been recommended as a pre-treatment [50, 51]. Lawson noted a large uptake of chlorine, nitrogen and oxygen on treatment of polychloroprene with TCICA, indicating addition across the carbon-carbon donble bond. 

Groves and co-workers [a.237] analysed the oil derived from the pyrolysis of natural rubber in a Py-GC at 500 °G. These researchers showed that the major products were the monomer, isoprene, and the dimer dipentene, with other oligomers up to hexamer also being formed in significant concentrations. It was suggested that the isoprene monomer was formed via a depropagating mechanism in the polymer chain, and that dipentene dimer was formed either by intramolecular cyclisation followed by scission, or by monomer recombination via a Diels-Alder reaction. 

It is based on pure crystalline monomers, and kinetic as well as more sensitive statistical tests show that essentially a single random rate process furnishes the intermolecular links, while the small amount of cyclisation can be allowed for to a good approximation. It is therefore of value as a more reliable material than those used previously to test the network theory of the tree-like gel model against measurements of E, and particularly to estimate the controversial front factor in the classical equation of state of rubbers. The plots c and d in figs. 2 and 3 are based on the equations (cf. Dobson and Gordon )... 

Note communicated later It is doubtful that intra-chain cyclisation plays a substantial part in the vulcanisation of rubbers with long primary chains where gelation occurs very early. As explained in the discussion of fig. 1 of GWW, cyclisation immediately after the gel point ceases to be describable in terms of random-flight type models (or equally in terms of the segment distribution function of an individual chain). 

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