Web Release Date: February 19,
Folding of Long Multiblock Copolymer (PI-b-PS-b-PI)n Chains Prepared by the Self-Assembly Assisted Polypolymerization (SAAP) in Cyclohexane
and
Department of Chemistry, The Chinese University of Hong Kong, Shatin, N. T., Hong Kong, Institute of Polymer Science, School of Chemistry and Chemical Engineering, Sun Yat-Sen University, Guangzhou, Guangdong, 510275, China, and The Hefei National Laboratory of Physical Science at Microscale, Department of Chemical Physics, University of Science and Technology of China, Hefei, Anhui, 230026, China
Received September 15, 2007
Revised Manuscript Received January 2, 2008
Abstract:
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 (Mn = 4.8 × 104 g/mol). The coupling efficiency with and without the self-assembly was compared. The folding of such long multiblock chains (Mn = 1.4 × 106 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 
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.
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