Hydrogen bond significance

Most rubbers used in adhesives are not resistant to oxidation. Because the degree of unsaturation present in the polymer backbone of natural rubber, styrene-butadiene rubber, nitrile rubber and polychloroprene rubber, they can easily react with oxygen. Butyl rubber, however, possesses small degree of unsaturation and is quite resistant to oxidation. The effects of oxidation in rubber base adhesives after some years of service life can be assessed using FTIR spectroscopy. The ratio of the intensities of the absorption bands at 1740 cm" (carbonyl group) and at 2900 cm" (carbon-hydrogen bonds) significantly increases when the elastomer has been oxidized [50]. 

For the latter, rate data have been obtained in trifluoroacetic acid-acetic acid media, and the rate versus acidity profiles have been compared to those for compounds (e.g., alkylbenzenes) which do not hydrogen bond significantly. Exchange rates of O- and S-heterocycles relative to alkylbenzenes become progressi vely smaller on going to more acidic media (i.e.,... 

For most polymers, the relationship between the glass transition temperature 7g and T), is 7g = T), -E C where C is a constant that in many dielectric studies is about 50 K [9, 73, 74]. On the basis of the usual uncertainty in C and the above Tq = 285 K, we estimate that Tg for dry annealed chitin is 62 10 °C. This low value for the 7g of a stiff polymer such as a-chitin is slightly surprising, but it is consistent with the low Ig s found in polypeptides (-70 to -50°C) [75-77]. The common denominator between polysaccharides and polypeptides is extensive hydrogen bonding significant thermal dismption of H-bonding and the onset of main chain molecular motions are probably closely related. 

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