Order to Order Transition from Cylindrical to Lamellar Microdomain upon Heating for Linear Tetrablock Copolymer
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We investigated the order to order transition (OOT) of polystyrene-block-polyisoprene-block-polystyrene-block-polyisoprene (S1I1S2I2) linear tetrablock copolymer at the symmetric volume fraction of total PS and PI blocks but asymmetry of PI block (τPI = fPI1 /(fPI1+fPI2) = 0.19), in which fPI1 and fPI1 are the volume fractions of PI in the second and forth blocks, respectively). Very interestingly, this block copolymer showed cylindrical to lamellar microdomains transition upon heating. This behaviour is the exactly opposite to commonly observed OOT for linear AB diblock and A1BA2 triblock copolymers with upper critical ordering transition, where lamellar microdomains have been transformed to cylindrical microdomains upon heating. This interesting transition sequence is due to the chain architecture of linear tetrablock copolymer with two PS and two PI blocks.