Title

Characterization of pH-Dependent Micellization of Polystyrene-Based Cationic Block Copolymers Prepared by Reversible Addition-Fragmentation Chain Transfer (RAFT) Radical Polymerization

Document Type

Article

Publication Date

5-31-2006

Department

Chemistry and Biochemistry

Abstract

A series of block copolymers composed of a fixed length of an (ar-vinylbenzyl)trimethylammonium chloride (Q) block (the number average degree of polymerization of the Q block, DPn,Q = 57) and varying lengths of an N,N-dimethylvinylbenzylamine (A) block (the number average degrees of polymerization of the A blocks, DPn,A, ranging 11-50) were prepared by reversible addition-fragmentation chain transfer (RAFT) radical polymerization, and their pH-dependent micellization was characterized by potentiometric titration, H-1 NMR spectroscopy, dynamic and static light scattering, and fluorescence techniques as a function of the A block length. At pH < 5.5, the A block is fully protonated, and hence the block copolymers act as a simple polyelectrolyte, dissolving molecularly in acidic water. At pH > 7, the A block becomes deprotonated, and thereby the block copolymers aggregate into a micelle composed of hydrophobic microdomains formed from the deprotonated A blocks. Results of light scattering and fluorescence measurements indicated that the micellization behavior depended strongly on the length of the A block. The number of polymer chains comprising one micelle (i.e. mean aggregation number, N-agg) increased from 3 to 12 as DPn,A increased from 11 to 50 at pH 10.0. In the case of a random copolymer of Q and A with an A/Q molar ratio similar to that of a block copolymer with DPn,A = 50, N-agg similar to 1 (i.e. unimolecular micelle) was confirmed by static light scattering at pH 10.0. (c) 2006 Elsevier Ltd. All fights reserved.

Publication Title

Polymer

Volume

47

Issue

12

First Page

4333

Last Page

4340