Multiblock copolymers hard domains

The Material of the Example. Poly(ether ester) (PEE) materials are thermoplastic elastomers. Fibers made from this class of multiblock copolymers are commercially available as Sympatex . Axle sleeves for automotive applications or gaskets are traded as Arnitel or Hytrel . Polyether blocks form the soft phase (matrix). The polyester forms the hard domains which provide physical cross-linking of the chains. This nanostructure is the reason for the rubbery nature of the material. 

The size of the hard domains of the multiblock and triblock copolymers is in the range 30-100X and 100-300, respectively. 

The nature of the hard domains differs for the various block copolymers. The amorphous polystyrene blocks in the ABA block copolymers are hard because the glass transition temperature (100°C) is considerably above ambient temperature, i.e., the polystyrene blocks are in the glassy state. However, there is some controversy about the nature of the hard domains in the various multiblock copolymers. The polyurethane blocks in the polyester-polyurethane and polyether-polyurethane copolymers have a glass transition temperature above ambient temperature but also derive their hard behavior from hydrogen-bonding and low levels of crystallinity. The aromatic polyester (usually terephthalate) blocks in the polyether-polyester multiblock copolymer appear to derive their hardness entirely from crystallinity. 

In many phase-separating block copolymers (especially segmented multiblock copolymers such as polyurethanes where the blocks are usually short), lowering the soft block Mn increases the Tg of the soft phase because of the crosslink-like topological constraints imposed by hard phase domains. 

Behl, M., Ridder, U., Feng, Y, Kelch, S., and Lendlein, A. 2009. Shap>e memory capability of binary multiblock copolymer blends with hard and switching domains provided by different components. Soft Matter 5 676-684. 

Sometimes, copolymers with many, but short blocks, are named segmented copolymers (multiblock copolymers). Segmented copolymers contain phase domains of microscopic or smaller size. The domains constituted principally of single types of stmctural unit. Typically, a segmented copolymer comprises hard-and soft-segment phase domains. 

Imai and colleagues reported the synthesis of PDMS and aramid copolymer (PAS) [19,37]. PAS is a multiblock copolymer consisting of hard segment (aramid) and soft segment (PDMS). The aramids are known to have excellent mechanical properties, such as high-thermal stability and a high-elasticity modulus [38]. It was expected that the incorporation of PDMS domains into an aramid matrix would allow the system to exhibit many of the desirable properties of both polymers. However, there has been only a few studies reported on the characteristics of PAS [19]. In this section, we will discuss the synthesis, evaluation of in vitro blood compatibility, and the investigation of the surface composition of PAS from the perspective of a potential biomaterial. 

---