Effects of molecular weight on poly(ω-pentadecalactone) mechanical and thermal properties

A series of poly(ω-pentadecalactone) (PPDL) samples, synthesized by lipase catalysis, were prepared by systematic variation of reaction time and water content. These samples possessed weight-average molecular weights (Mw), determined by multi-angle laser light scattering (MALLS), from 2.5 × 104 to 48.1 × 104. Cold-drawing tensile tests at room temperature of PPDL samples with Mw between 4.5 × 104 and 8.1 × 104 showed a brittle-to-ductile transition. For PPDL with Mw of 8.1 × 104, inter-fibrillar slippage dominates during deformation until fracture. Increasing Mw above 18.9 × 104 resulted in enhanced entanglement network strength and strain-hardening. The high Mw samples also exhibited tough properties with elongation at break about 650% and tensile strength about 60.8 MPa, comparable to linear high density polyethylene (HDPE). Relationships among molecular weight, Youngʹs modulus, stress, strain at yield, melting and crystallization enthalpy (by differential scanning calorimetry, DSC) and crystallinity (from wide-angle X-ray diffraction, WAXD) were correlated for PPDL samples. Similarities and differences of linear HDPE and PPDL molecular weight dependence on their mechanical and thermal properties were also compared.