Crystallization of polycaprolactone with reduced entanglement

Structure of polycaprolactone (PCL) crystallized in a wide concentration range was investigated to correlate entanglement content with the formed structure. Mixed solvent constituted by good solvent chloroform and nonslovent ethanol was used to control the concentration crystallization started (c_onset, weight fraction), which varied from 0.13 to 0.53. Crystallization at higher c_onset was achieved by electrospinning and melt crystallization. The concentration correlates with entanglement number (N) by the scaling law N/N₀ = ϕ^1.3 with ϕ the volume fraction of polymer in solution. In this work, the scaling law was modified as N/N₀ ≈ c_onset ^1.3 as an approximation. Thickness of amorphous region (l_a) and fusion enthalpy (ΔH) were obtained through small angle X-ray scattering (SAXS) and differential scanning calorimetry (DSC). It is found that l_a increases monotonically with c_onset ^1.3 from 4.5 nm to 10.2 nm, and ΔH decreases monotonically from 92 J/g to 50 J/g. The smooth change of l_a and ΔH with c_onset ^1.3 indicates increased entanglement leads to thicker amorphous region and lower crystallinity, which is valid even when the entanglement number is as low as one-tenth of that in melt. Moreover, changes in lamellae thickness (l_c) is also discussed.