ORIGINAL PAPER Characterization of chain dimensions of poly(ε-caprolactone) diols in THF by size-exclusion chromatography coupled with multi-angle light scattering (SEC-MALS) Karla A. Barrera-Rivera & Ricardo Vera-Graziano & Erik López-Sánchez & Antonio Martinez-Richa Received: 30 July 2014 /Accepted: 20 January 2015 /Published online: 3 February 2015 # Springer Science+Business Media Dordrecht 2015 Abstract In this work, we studied the chain dimensions, shape, and thermodynamic characteristics of poly( ε - caprolactone) diols (HO-PCL-OH) in solution. PCL diol sam- ples 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 vis- cometer (DV), and interferometric refractometer IRS detectors offered a proper way to obtain information on thermodynamic characteristics and chain flexibility. The weight-average mo- lecular weights of the PCL diol samples (M w ) ranged from 2, 750 to 13,120 uma. The z-average radius of hydrodynamic volume (<R h 2 > 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 =2.74×10 -3 dL/g and a =0.64) were derived from the plots of [η] w against M w . The overall results clearly suggest that a flexible geometry is present in tetrahydrofuran (THF) solution of PCL at 33 °C. Unlike other PCL systems, PCL diols are more hydrophilic and expected to form associated species. They behave differ- ently 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 [η] 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. Keywords Hydrodynamic radius . Solution properties . PCL diol chain dimensions . Mark–Houwink–Sakurada equation . SEC-MALS Introduction Poli(ε-caprolactone)(PCL) is a biodegradable and biocompat- ible polymer widely used in surgical implants, packaging ma- terials, pharmaceutical formulations, polymer blends, and in applications ranging from controlled-release drug delivery systems to tissue engineering [1–4]. Telechelic poly(ε-caprolactone) diols (HO-PCL-OH) are generally prepared using ring-opening polymerization of ε- caprolactone initiated by diols. They are widely used as pre- cursors of many polymer derivatives, including poly(ester- urethanes), block copolymers, and other advanced architec- tures [4–6]. Some reports have appeared in the literature on the physi- cochemical characterization of diluted PCL solutions [7–11]. PCL has been studied using a number of techniques such as light scattering (LS), osmometry, and viscometry on various solvents at different temperatures [8, 9]. Data reported by the- se authors include characteristic ratio values C ∞ in the range of 4.3 to 5.9. Theoretical calculations, on the other hand, have predicted a value of C ∞ =6 for PCL[10]. Mays et al. reported K. A. Barrera-Rivera : A. Martinez-Richa (*) Departamento de Química, División de Ciencias Naturales y Exactas, Universidad de Guanajuato, Noria Alta S/N, 36050 Guanajuato, Gto, México e-mail: richa@ugto.mx R. Vera-Graziano Instituto de Investigaciones de Materiales, Universidad Nacional Autónoma de México (UNAM), Av. Universidad 3000, CP04510 Ciudad de México, México E. López-Sánchez División de Ciencias e Ingenierías, Universidad de Guanajuato, Campus León, León, Gto, México J Polym Res (2015) 22: 25 DOI 10.1007/s10965-015-0672-z