Solution viscosity – molar mass relationships for poly(butylene succinate) and discussion on molar mass analysis

Poly(butylene succinate) (PBS) is currently developing due to its biodegradability and the similarity of its mechanical properties to those of polyolefins. Relationships between the number average molar mass,(M) over bar (n), and solution viscosity such as [eta] and eta(red) were derived for this aliphatic polyester. (M) over bar (n) values were determined by end-group analysis and size exclusion chromatography (SEC). Mark-Houwink-Sakurada (MHS) parameters were proposed in two solvents and for the different molar masses and viscosity measurement methods. As an example, the MHS equations were respectively, [eta] = 6.4 10(-4).M-n (0.67) in chloroform and [eta] = 7.1.10(-4).(M) over bar (-0.69)(n) in 50/ 50 wt% 1,2-dichlorobenzene/ phenol at 25 degrees C for molar masses measured by SEC in hexafluoro isopropanol (HFIP) with poly(methyl methacrylate) (PMMA) standards. Empirical relationships were also suggested to derive (M) over bar (n)directly from reduced viscosity, eta(red), which is much easier to determine than intrinsic viscosity. With these data, the number average molar mass of PBS can be conveniently estimated from a single viscosity measurement. In addition, it was shown that PBS contains 1-2 wt% of cyclic oligomers produced during esterification and that molar masses determined by taking this fraction into account or not were significantly different, especially for long chains.