Deuterium substitution effect thermodynamics

In the early years (prior to 1980), the effect of deuterium substitution on polymer blend thermodynamics was assumed to be negligible. In a pioneering publication, Buckingham and Hentschel [43] estimated x between protonated and deuterated polymers that are otherwise identical (isotopic blends) to be about 10 . They thus came to the surprising conclusion that isotopic blends should be phase separated at modest molecular weights (V IO ). Elegant experimental proof for this effect was provided by Bates and CO workers [44]. 

Prolonged treatment with a strong base e.g. potassium tert-butoxide in tert-butanol) has the effect of permitting equilibration of the end anions, so that the A > -enolate becomes the main product under thermodynamic control. This is apparent in the methylation of the enolate anion at C(4) (see p. 168). Under acidic conditions equilibration proceeds much more rapidly, and acid catalysed substitution via enols occurs almost entirely at C(6) the transient intervention of a small proportion of the A -enol under acidic conditions was detected only by short-term deuterium-exchange experiments [no]. 

Isotope effects on equilibrium constants can be understood on the basis of statistical thermodynamics (Stihnel Schowen, 1991). If the hydrogen is substituted by deuterium, the overall equilibria are... 

As pointed out in Section 7.3.1, SANS studies of deuterium-labeled polymers were initially based on the assumption [8] that the molecular configurations and interactions are independent of deuteration, or alternatively that the Flory-Huggins interaction parameter for labeled and unlabeled segments of the same species, /hd. is zero. However, it was subsequently discovered that isotopic substitution can influence polymer thermodynamics, in that deuterated and protonated polyethylenes exhibit melting temperatures differing by 6 °C, so their mixtures can segregate in the solid state (see Section 7.5.2), due to differential-crystallization effects [103]. Also, the... 

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