Crystallization Kinetics and Morphology of PLLA--PCL Diblock Copolymers

2 Crystallization Kinetics and Morphology of PLLA-6-PCL Diblock Copolymers 

Poly(L-lactide)- -poly(e-caprolactone) (PLLA-fe-PCL) diblock copolymers were synthesized by controlled/ living sequential block copolymerization as initiated by aluminum trialkoxides in toluene solution. These procedures were reported in detail previously [50,98]. Table 11.6 lists the molecular weight characterization data obtained by size exclusion chromatography (SEC) and by NMR. The diblock nomenclature we have used denotes the PLEA block as L and the PCL block as C, the subscripts indicate the approximate composition in wt% and the superscripts the approximate number average molecular weight of the entire block copolymer in kg/mol. 

PLLA-fe-PCL linear diblock copolymers were found to be either melt miscible or weakly segregated in the melt. This means that upon cooling the material will be able to form spherulites (see details in Refs [50,51,66,95]). 

TABLE 11.6 Molecular Characteristics of PLLA-fr-PCL Block Copolymers and Homopolymers 

Similar effects have been reported for miscible block copolymers such as polyethylene- -poly(ethylene-a/t-propylene) where a stronger dilution effect induced by amorphous poly(ethylene-6i/t-propylene) chains cause the need for much higher supercoolings in order to crystallize the PE block chains but at compositions close to 50 wt% [77, 111]. 

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