Folding of long multiblock copolymer (PI-b-PS-b-PI)n chains prepared by the self-assembly assisted polypolymerization (SAAP) in cyclohexane

The formation of polymeric micelles made of A-B-A triblock chains in a solvent selectively poor for the middle B-block concentrate and exposes two active end groups so that short triblock chains can be effectively coupled together to form a long (A-B-A)(n) multiblock chain with a controllable block length and sequence. Using this method, we successfully prepared a (PI-b-PS-b-PI)(30) multiblock copolymer, starting from a triblock PI-b-PS-b-PI copolymer (M-n = 4.8 x 10(4) g/mol). The coupling efficiency with and without the self-assembly was compared. The folding of such long multiblock chains (M. = 1.4 x 10(6) g/mol) in a dilute solution (10(-5) g/mL) was studied by a combination of static and dynamic laser light scattering. The results reveal that such long multiblock chains do not collapse into single-chain globule in a dilute solution even when the solution temperature is much lower than the Theta temperature. Instead, each PS block collapses into a small globule stabilized by the two attached PI blocks on the chain backbone to form a string of coils and beads so that the multiblock chain becomes thicker with an extended conformation without interchain or intrachain association, which is completely different for the association of initial triblock PI-b-PS-b-PI chains in a selective solvent, i.e., the formation of polymeric micelles.