Effects of molecular architecture on the rheological and physical properties of polycaprolactone

The molecular modification of polycaprolactone (PCL) is of great importance for producing optimum physical properties for a given application. Linear polycaprolactone (L-PCL) and 4-arm star polycaprolactone (4-PCL) with similar molecular weights were prepared, and their rheological, thermal, and morphological properties were investigated in relation to their molecular architecture. In dilute solutions, L-PCL exhibited a higher intrinsic viscosity than 4-PCL. In the molten state, the former displayed a higher viscosity and greater temperature dependence of molecular relaxation time than the latter. DSC thermograms showed that molecular architecture had little effect on the melting/crystallization temperature and crystallinity. Thermogravimetric analysis indicated that the introduction of a branched structure deteriorated the thermal stability of PCL, which might be associated with the increased number of hydroxyl end groups in the polymer chains. In isothermal crystallization under shear at two different temperatures, 4-PCL exhibited longer crystallization times than L-PCL. A more notable difference in dynamic crystallization behavior caused by the chemical architecture was observed at 40°C than at 45°C. Examination with a wide angle X-ray diffractometer revealed that shear and temperature applied during isothermal crystallization, as well as chemical architecture, had little effect on the crystal structure.