Dynamic covalent bond exchange at block copolymer junctions impact self-assembly kinetics

Methods to accelerate the self-assembly kinetics are needed for the widespread use of block copolymers at an industrial level. Here, vinylogous urethane bonds were incorporated at the junction of PDMS-PEO block copolymer and the effects of conserved dynamic bonds were investigated through the addition of excess nucleophiles (amine groups) and salt to facilitate bond exchange. Ordering kinetics were studied using the time-dependent X-ray scattering at two annealing temperatures. Excess homopolymer with amine groups has a greater impact on ordering kinetics compared to the addition of catalyst at 70 °C where bond exchange is slow, and a trade-off between chain diffusion and bond exchange control can be observed as distinct regimes. At 120 °C, both chain diffusion and bond exchange are facilitated significantly reducing the time required for assembly. Even as VU bond exchange is accelerated, chain diffusion still contributes more to the overall ordering process. Pure PEO and PDMS vitrimers were also investigated with shear rheology and a large difference in relaxation times between PEO and PDMS vitrimers is observed attributed to the distribution of the salt catalyst. Both bond exchange and diffusion contribute to the self-assembly of BCPs leading to a complex ordering process.