ABC Triblock Linear and Star Shaped Terpolymers

The synthesis and characterization of polystyrene-6-poly(ethylene oxide)-6-poly(e-caprolactone) triblock terpolymers in a linear or star shaped fashion is very interesting because they combine in the same molecule a glassy amorphous block, polystyrene a biocompatible crystalhzable poly(ethylene oxide) block, and a crystalUzable poly(e-caprolactone) block, which is biodegradable and exhibits miscibility with a variety of polymers. 

Floudas et al. [22, 23] carried out the characterization of star shaped PS, PEO and PCL based triblock terpolymers by means of WAXS, SAXS, DSC, POM, Atomic Force Microscopy (AFM) and rheological measurements. 

S4 EOgg Cgo . SAXS experiments showed that all samples are miscible in the melt, and that the crystallization process produces microphase segregation, indicating that the star architecture induces a reduction of the Tqdt in comparison to this transition in sequential copolymers. The miscibility was also favoured by the low molecular weight of the PS block in the stars (i.e., 4.7 Kg/mol). 

In Fig. 13.17 the evolution of the SAXS invariant is shown simultaneously, the intensity of WAXS signals due to the PEO monocUnic and PCL orthorhombic structures can be appreciated, together with the intensity of a signal that arise from an overlapping of the reflections of both blocks for the Sg copolymer. At 39°C it is possible to observe the beginning of 

Isothermal crystallizations performed by Floudas et al. [22,23] between 39° C and 43° C allowed them to conclude that the crystallization of the PEO and PCL blocks only occurs when the two star branches have similar lengths. On the other hand, when one of the branches has three times the length of the other, the crystallization of the shorter block is impeded. Nevertheless, it would be interesting to expand the temperature range in which the crystallization is studied, since other authors have reported crystallization of these blocks at higher supercoolings. 

---