Triblock Copolymer Systems

The substantial work on polystyrene/polybutadiene and polystyrene/ polyisoprene blends and diblock and triblock copolymer systems has lead to a general understanding of the nature of phase separation in regular block copolymer systems (5,6). The additional complexities of multiblocks with variable block length as well as possible hard- and/or soft-phase crystallinity makes the morphological characterization of polyurethane systems a challenge. 

Kloxin, C. J. and Zanten, J.H. van, High pressure phase diagram of an aqueous PEO-PPO-PEO triblock copolymer system via probe diffusion measurements, Macromolecules, 43, 2084, 2010,... 

Figure 1 Schematic representation of the pH-induced volume change in polyacid and polybase triblock copolymer systems.

Our qualitative understanding of the phase behavior of linear nonfrustrated ABC triblock copolymers is rapidly expanding. This is far less the case for the frustrated systems where the set of possible candidate stractures is much larger. An exhaustive quahlication for the frill parameter space of linear ABC triblock copolymer systems is still elusive. 

Bailey, T.S., Pham, H.D., and Bates, F.S. (2001) Morphological behavior bridging the sytrrmetric AB and ABC states in the poly(styrene-6-isoprene-6-ethylene oxide) triblock copolymer system. Macromolecules, 34,6994-7008. 

Figure 24.9 Schematic depiction of possible structures and processes occurring in an ABA triblock copolymer system in a selective solvent for B and under irradiation. The processes denoted by gray arrows should be avoided for macrocycle formation. On the right are some structural details for the pompons of P (CEMA-r-TFAEMA). The TFAEMA units should segregate preferentially on the surface. (Reprinted with permission from J. Hu, R. Zheng, J. Wang et al, Macrocycles from the photochemical coupling of preassociated terminal blocks of copolymers, Macromolecules, 42, 13, 4638 645, 2009. 2009 American Chemical Society.)...

PMAA as a middle block was used. A similar morphology was observed, as reported in the previous triblock copolymer system. Both the systems shown change in aggregation number with varying pH and ionic strength [99]. 

---