A series of copolymers based on acrylonitrile (AN) and acrylic acid (AA) with varying architecture and composition were synthesized using free radical polymerization. The distribution of monomers in the copolymer chains could be successfully controlled by regulating the addition of more reactive monomer (AA). Copolymers having nearly random distribution of comonomer moieties to block type distribution with different composition (10-50 mol % AA) were synthesized to investigate the effect of polymer architecture and composition on pH response and mechanical properties of resultant structures. These copolymers were solution spun from dimethylformamide-water system, drawn in coagulation bath, and annealed at 120 degrees C for 2 h to make pH-sensitive fibers which were structurally stable without the need of chemical crosslinking. The fibers from block copolymers showed significantly better tensile strength (34.3 MPa), higher retractive forces (0.26 MPa), and enhanced pH response (swelling 3890%) in comparison with fibers from random copolymer (13.55 MPa, 0.058 MPa, and 1723%, respectively). The tensile strength and retractive forces could be further improved to a value of 72 MPa and 0.36 MPa, respectively, by changing the composition of the block copolymer while retaining the swelling percentage similar to the random copolymer mentioned above. It is proposed that on processing to fibers, the block copolymers could form a segregated domain structure with separate domains of AA and AN, where AN domains were responsible for high structural integrity by providing connectivity among polymer chains, while AA domains showed improved response to changing pH of the environment. (c) 2007 Wiley Periodicals, Inc.