Baroplastic behavior of miscible block copolymer blends

Color, structure, and rheology of a diblock bottlebrush copolymer solution

A structure-property-process relation is established for a diblock bottlebrush copolymer solution, through a combination of rheo-neutron scattering, imaging, and rheological measurements. Polylactic acid-b-polystyrene diblock bottlebrush copolymers were dispersed in toluene with a concentration of 175 mg ml-1, where they self-assembled into a lamellar phase. All measurements were carried out at 5 °C. The solution color, as observed in reflection, is shown to be a function of the shear rate. Under equilibrium and near-equilibrium conditions, the solution has a green color. At low shear rates the solution remains green, while at intermediate rates the solution is cyan. At the highest rates applied the solution is indigo. The lamellar spacing is shown to be a decreasing function of shear rate, partially accounting for the color change. The lamellae are oriented 'face-on' with the wall under quiescence and low shear rates, while a switch to 'edge-on' is observed at the highest shear rates, where the reflected color disappears. The intramolecular distance between bottlebrush polymers does not change with shear rate, although at high shear rates, the bottlebrush polymers are preferentially aligned in the vorticity direction within the lamellae. We therefore form a consistent relation between structure and function, spanning a wide range of length scales and shear rates.

Baroplastics with Robust Mechanical Properties and Reserved Processability through Hydrogen-Bonded Interactions

Conventional polymers are usually processed at a much higher temperature than room temperature, which inevitably leads to huge energy consumption and degradation of the polymers and thus a low recycling ability. Herein, we synthesized a poly( n-butyl acrylate)@polystyrene (PBA@PS) core-shell polymer to prepare a typical baroplastic (processible at room temperature). However, this type of baroplastics always has a low mechanical property. To solve this problem, in this work, we introduced hydrogen bonds into the matrix and successfully reinforced baroplastics for the first time. The hydrogen-bonded interaction was introduced by complexing PBA@PS with poly(acrylic acid) and poly(ethylene oxide). The results show that the reinforced baroplastics possessed notably enhanced mechanical properties and good processability. Their mechanical strength and modulus reached as high as 5.6 (by 73%) and 10 MPa (by 400%), respectively. Moreover, the baroplastics could be remolded many times at room temperature and, at the same time, still showed a higher tensile strength (10.5 MPa, 3.3 times that of the initial PBA@PS, which was never achieved in previous works), which resulted from the reversible hydrogen bonds and reserved orientation of molecular chains. Our work opened a new path to reinforce baroplastics and could widen their applications. Furthermore, not limited to the hydrogen bonds, more sacrificial bonds, such as ionic bonds, host-guest interactions, and metal-ligand coordination bonds, could be used to fabricate high-performance baroplastics.