Block Copolymers

We have characterized mid-block crystallization in low molecular weight triblock copolymers (TBC) with amorphous end-blocks that were synthesized using atom transfer radical polymerization (ATRP) in collaboration with Prof. K. Matyjaszewski (Department of Chemistry, Carnegie Mellon University).

TBC with crystallizable mid-block mole fractions of over 0.5 exhibited crystallinities of around 40%, that was significantly smaller than that of the homopolymer, and a lamellar nanoscale periodicity that was larger than that of the homopolymer. TBC with crystallizable mid-block mole fractions of less than 0.5 exhibited relatively low crystallinities and did not exhibit ordered structures.

Schematic illustration of phase separation and crystallization in a triblock copolymer
Schematic illustration of phase separation and crystallization in a triblock copolymer with poly(styrene-acrylonitrile) end-blocks and a poly(ethylene oxide) mid-block.
Transmission electron micrograph from a triblock copolymer
Transmission electron micrograph from a triblock copolymer with poly(styrene-acrylonitrile) end-blocks and a poly(ethylene oxide) mid-block.