Influence of the copolymer architecture and composition on the response and mechanical properties of pH‐sensitive fibers

Abstract

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 1208C 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.

pH‐responsive fibers based on acrylonitrile acrylic acid block copolymers: Effect of spinning conditions and postspinning operations on response and mechanical properties

“…The above approach could produce copolymers where the distribution of the comonomer moieties could be controlled to a great extent giving rise to a block type copolymer. The structure and properties of these block type copolymers in comparison to their random counterparts have been reported earlier 14, 15. The quantitative analysis of 13 C NMR proved that there was significant increase in the concentration of segmented acrylonitrile and acrylic acid moieties compared to the random structure using the modified polymerization approach.…”

“…Our recent experiments have shown that the formation of domain morphology was in fact possible and the resultant fiber is stronger than the fibers produced from random copolymers. Also, the acrylic acid domains could provide faster diffusion of water to give larger and rapid swelling and deswelling under suitable pH 14, 15…”

“…The rate of diffusion of water in and out of the fiber is dependent on diffusivity coefficient of the fiber matrix and the path of diffusion. This drastic reduction in the response time as well as the increase in the amount of swelling percentage may be due to two factors: (a) reduction of diameter to a smaller value, i.e., smaller paths of diffusion and lower levels of opposing internal stresses on swelling; (b) the formation of better domains of acrylic acid 14, 15. It appears that since drawing has facilitated the phase segregation and formation of well defined domains, it leads to better diffusivity coefficient of the water through the fiber.…”

“…So far, the stimuli sensitive polymers (SSP) are used in the hydrogel form for diverse applications; however, the potential application of these SSP polymers have not been fully exploited because of their slow response as well as low magnitude of swelling. Therefore, an alternate approach was recently proposed by our group to address some of the abovementioned drawbacks 14, 15. In that approach, a series of pH sensitive copolymers of controlled architecture based on acrylic acid and acrylonitrile were synthesized, in which the solution spun into fine fibers, showed good mechanical properties as well as enhanced pH response without the need of chemical crosslinking.…”

Dendrigraft with citric acid on acrylonitrile/acrylic acid copolymer electrospun fibres

“…The properties of reversible dilation and contraction by changing the state of ionization of polymers have been the subject of pioneering work . Several papers regarding the sensitivity of polyacrylonitrile copolymers have been published recently . These works show that the fibre diameter, spinning conditions and post‐spinning operation, such as heat‐setting temperature, as well as the distribution of monomer moiety, have a significant effect on the pH response of P(AN/AA) copolymer.…”