Blends of poly (e-caprolactone) (PCL)/polylactide (PLA) were prepared by solution-casting method to study their thermal and rheological properties. Differential scanning calorimetry thermographs have shown two separate melting peaks in the blends, which are indicative of immiscible structure at all compositions. Scanning electron microscopy images show droplet morphology of PCL into PLA matrix up to 40 wt% of PCL. Above this concentration, the co-continuous morphology starts to appear, which becomes again droplet morphology for blends with concentration of PCL higher than about 60 wt%. The viscoelastic properties of the various blends were investigated using rotational rheometry. The enhancement of the elastic modulus of blends at small frequencies at which terminal zone behavior is expected, is a signature behavior of immiscible systems due to the presence of interface and contribution to the stress from interfacial tension. Two emulsion models were used to predict the viscoelastic properties of the blends from the corresponding properties of their pure components that led to the determination of the interfacial tension of PCL/PLA in agreement with experimental findings. FIG. 2. SEM images of blends of PLA 3051D/PCL with different compositions (a) 80/20 (b) 70/30 (c) 60/ 40 (d) 50/50 (e) 40/60 (f) 35/65 (g) 30/70 (h) 25/70 (i) 20/80 (j) 15/85.

The dinuclear indium catalyst [(NNO)InCl] 2 (μ-OEt)(μ-Cl), previously reported to be highly active for the living ring-opening polymerization of cyclic esters lactide (LA) and β-butyrolactone (BBL), was used to generate a series of triblock copolymers of poly(lactic acid) (PLA) and poly(hydroxybutyrate) (PHB). Copolymers PLLA−PDLLA−PLLA and PLLA−PDLLA−PDLA, synthesized via sequential monomer addition, showed low molecular weight distributions and excellent correlation between the calculated and experiment molecular weights. Significantly, triblock copolymers of the type PLA−PHB−PLA were also synthesized for the first time through a sequential addition technique. Analysis of polymers after each addition of monomer showed that although only 85% conversion was achieved after addition of BBL, the remaining chain ends were active and addition of more lactide yielded a triblock. Rheological studies of PLLA−PHB−PDLA indicated solid like behavior even well above the temperature at which stereocomplex formation was observed. These elastomeric triblocks exhibited elongations at break 5−10 times greater than those of corresponding PLLA−PDLLA−PLDA triblocks.

A series of pyridonate and amidate supported titanium alkoxides have been isolated. These complexes can be readily prepared in high yield, under mild reaction conditions in only two steps from commercially available (Ti(NMe(2))(4)). We have furnished one of the rare examples of discrete catalysts for random copolymer synthesis.

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Previous studies on polylactide (PLA)/poly(ε-caprolactone) (PCL) biodegradable blends revealed enhanced nucleation of PLA. The mechanism by which this enhancement of nuclei density occurs attracted significant interest. In this study, precursors' transportation from PCL into PLA phase is invoked in order to interpret the experimental findings related to phase separation and crystallization. This mechanism is supported by differential scanning calorimetry (DSC) and polarized optical microscopy (POM). The DSC data revealed that PCL crystallinity within the blends is decreased with PLA content. In addition, POM data showed more nuclei within PLA as the PCL weight fraction is increased. The linear viscoelastic properties of these blends in the vicinity of the phase separation and cold crystallization boundary are examined. It is shown that the combination of POM and rheometry allows determining the phase diagram of the blend and identifying changes occurring due to phase separation and crystallization. Thus, the complete phase diagram of such systems can be fully determined, essential in process design and optimization.