AbstractThe proposition, that low molecular weight polymer fractions in good solvents behave as if they were under ⊖ conditions, has been examined experimentally. Series of monodisperse hydroxy‐terminated polytetrahydrofuran (PTHF), 82 1,4‐polybutadiene (PBD), and 30 1,4‐PBD were prepared, and values ofM̄nobtained by vapor‐pressure osmometry and endgroup analysis. The Mark–Houwink viscosity parametersKand ν were determined in a number of solvents. The general conclusion is that the proposition is invalid for these systems notwithstanding the fact that ν = 0.50 for one of them 82 1,4‐PBD in methyl ethyl ketone (MEK) at 25°C. For this particular case, the following evidence suggests that these are actually ⊖ conditions so that the apparent fulfilment of the proposition is fortuitous. (1) Cloud‐point precipitation yields ⊖ = 26 ± 3°C in MEK. (2) The value ofKis close to that ofK⊖found elsewhere for PBD in a different solvent at a similar temperature. (3) Application of the Kurata‐Stockmayer iterative procedure for estimatingK⊖from data in good and bad solvents yields a reasonably small discrepancy (10) between theK⊖values from data in toluene and MEK at 25°C for this polymer and only a 3 difference in the unperturbed dimensions (〈r02〉/M)1/2derived from them. Measured melting pointsTmof PTHF (M̄n= 1000–13000), plotted as a function of chain lengthZ, viz., 1/Tm= 1/Tm0+ 2R/ZΔHf, yield 43 ± 3°C and 1.6 kcal/submole, respectively, for the limiting melting pointTm0and the heat of fusion ΔHf. The former is in good agreement with the value obtained dilatometrically for high molecular weight polymer, while the latter i
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