Controlled chain-folded crystals

Context : Polymer crystals consist of thin lamellae wherein the polymer chains pack more or less perpendicularly to the basal faces. Upon emergence from the crystal, the chains fold back to the crystal, or cross an amorphous interlayer to connect a neighbouring crystal. Important mechanical properties are directly dependent on the details of the conformations of the chains in the amorphous interlayer between neighbouring crystals. It is therefore crucial to control the configuration of this interlayer, but this is very rarely done.

Our contribution : We have succeeded in forcing polyester chains to fold at specific locations along the chains, by introducing sequences that prevent crystallization at regular intervals in the chain. This required synthesizing sequenced multiblock copolymers of very-precisely defined chemical architecture. The information stored in the chain sequence is decyphered during the crystallization process, resulting in the formation of materials with crystals all having the same thickness, and displaying a series of unusual properties. This work was reported in Nature Materials, and resulted from a close and frutiful collaboration with Jacques Penelle, then at UMass (Amherst).