Characterization of chain dimensions of poly(epsilon-caprolactone) diols in THF by size-exclusion chromatography coupled with multi-angle light scattering (SEC-MALS)

In this work, we studied the chain dimensions, shape, and thermodynamic characteristics of poly(epsilon-caprolactone) diols (HO-PCL-OH) in solution. PCL diol samples of different molecular weights and architectures were synthesized using immobilized Yarrowia lipolytica lipase as catalyst. Gel permeation chromatography (GPC) with online right-angle laser-light scattering (RALLS), differential viscometer (DV), and interferometric refractometer IRS detectors offered a proper way to obtain information on thermodynamic characteristics and chain flexibility. The weight-average molecular weights of the PCL diol samples (M-w) ranged from 2, 750 to 13,120 uma. The z-average radius of hydrodynamic volume (z(1/2)) vs. z-average molecular weight curve (M-z) could be satisfactorily fitted to a power-law equation. Mark-Houwink-Sakurada parameters (K=2.74x10(-3) dL/g and a=0.64) were derived from the plots of [eta](w) against M-w. The overall results clearly suggest that a flexible geometry is present in tetrahydrofuran (THF) solution of PCL at 33 degrees C. Unlike other PCL systems, PCL diols are more hydrophilic and expected to form associated species. They behave differently from common hydrophobic polymers and do not strictly conform to thermodynamic relationships generally used in Polymer Science. A more compact geometry is present for M-n lower than 4,000 Da. For higher molecular weights, the chain expands and become more elongated. Plots of ln [eta](w) against ln M-w (MHS equation) and of log R-hz against log M-z suggest that PCL diols behave as flexible chains in a good solvent.