step in dynamic crystallization where a continuous solvent flow is maintained
through the column during the cooling process; see Fig. 2.44b. The polymer
components that reach their crystallization temperatures will segregate and anchor
on the support while other components in solution move along until they reach their
crystallization temperatures. The physical separation of the polymer components is
achieved with regard to crystallizability within the column in the crystallization
cycle. The key to improving separation during the crystallization step is the flow
rate. After the completion of crystallization, the solvent flow is stopped and
dissolution of the polymer components is achieved by heating the column to higher
Fig. 2.44 Separation diagram by crystallizability. TREF (a), dynamic crystallization (b), CEF (c)
(reprinted from [114] with permission of Wiley-VCH).
Fig. 2.45 Separation of two metallocene-type resins of very similar densities by TREF and CEF,
cooling rate 2
C/min, CEF crystallization flow 0.4 mL/min, elution flow 1 mL/min (reprinted
from [9] with permission of Springer Science + Business Media)
66
2 Crystallization-Based Fractionation Techniques