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First, ∆H po and ∆Spo depend substantially on the monomer and polymer states. For example, thermochemical measurements gave for 16-membered pentadecanolactone in the liquid phase ∆H po = 3 kJmol −1 and ∆Spo = 23Jmol −1 K −1, whereas in the crystalline phase ∆H po = −39 kJmol −1 and ∆Spo = −86 Jmol −1 K −1 [36]. The difference between these sets of parameters is caused by corresponding phase transitions (crystallization/ melting) enthalpies and entropies, although for the melt or solution polymerization analysis the liquid-phase parameters are most likely correct.

G. see Refs [3b, 22, 26, 74]). Cyclic oligomers can be formed in two types of reaction: end-to-end closure and back-biting. 1). 1 General scheme of ring-opening polymerization accompanied by chain transfer to macromolecule with chain rupture. K bb(y ) = [. . −m x − . ][M (y )]eq [. . −m x − y − . 17) where M(y) represents the macrocycle containing y repeating units of …-m-…. 18) Thus, the equilibrium concentration of a given macrocycle should decrease monotonically with increasing ring size. Detailed studies of the equilibrium distribution of cyclic siloxane oligomers provided a very good agreement between the theoretical and experimental values for y > 25; that is, for this range of cyclopolysiloxane sizes the plot of ln[M(y)]eq versus ln y was a straight line with a slope of −5/2 [76].

A method to determine both kp and Ka is possible, however, particularly when the degree of aggregation can be estimated in the manner described above. 38b provides a direct access to both kp and Ka. The power of this analytical approach can be seen by comparing the two figures taken from Ref. 11). Although the degree of aggregation has long been known to equal 3 for polymerizations conducted with diethyl aluminum alkoxide, a decision was taken also to check results when deliberately introducing an incorrect aggregation number of 2.

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