Abstract
Summary: Analysis was made of the crystallization of the PET blocks in PET/PC copolymers as a function of the block length, varying from $\overline M _{\rm n}$β=β5300 to 17100 gβΒ·βmol^β1^ (X~n PET~β=β28β89, PET monomeric sequences). Analysis was also made of a series of PET homopolymers with the same $\overline M _{\rm n}$ values. The copolymers were found to crystallize at a slower rate, with lower crystallinity and lower crystal perfection, than the homopolymers and secondary crystallization does not take place, unlike with PET homopolymers. However the crystallization mechanism is the same. The plot of the crystallization rate versus X~n PET~ shows that the homopolymers have a maximum crystallization rate at X~n PET~ββ
β50 ($\overline M _{\rm n}$ββ
β10000 gβΒ·βmol^β1^), whereas the crystallization rate for copolymers continuously increases with the increment of X~n PET~ (see Figure). The decrement of the crystallization rate for homopolymers with $\overline M _{\rm n}$ higher than 10000 gβΒ·βmol^β1^ has been interpreted as due to the effect of the high melt viscosity. For copolymers with long PET blocks, instead, a phase separation is likely and improves the PET reptation and fold, causing an increment in crystallization rate. Block size and miscibility between the components are therefore the key parameters in understanding the crystallization process in PET/PC block copolymers.
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