Quantitatively unravel the effect of chain length heterogeneity on polymer crystallization using discrete oligo l-lactide

Abstract

As one of the most fundamental features of synthetic polymer, molecular weight distribution profoundly influences the structures and properties. In this work, chain length heterogeneity was precisely regulated by a reconstruction approach using a library of discrete oligol-lactide (oLLA). Crystallization of a series of binary blends were systemically investigated. At a specific crystallization temperature, each fraction experiences varied degrees of supercooling, leading to non-uniform nucleation and growth kinetics. Both oLLA fractions co-crystallize homogeneously when chain length heterogeneity is not significant, while partial segregation occurs when the difference is sufficiently large. The co-crystals consisting of non-uniform chains are metastable, which rearrange into a homo-crystal of longer chains by excluding the shorter components upon heating. This work highlights the profound contribution of chain length heterogeneity on crystallization, which not only provides insights into the importance of molecular weight distribution, but also bridges the intrinsic gap between discrete and disperse polymers.