LAUSR

Molecular weight is a crucial characteristic of polymers which has a great influence on various polymer properties. Controlling molecular weight is a key aim in polymer research. Traditionally, chemical synthesis as a “bottom‐up” approach is the most common method to tune polymer molecular weight. Alternatively, breaking polymer chains by mechanical forces (e.g., ultrasound, ball‐mill grinding, and flow) is another pathway to adjust the molecular weight distribution. Herein, a new “top‐down” approach employing ultramicrotome to cut the polymer chains to manipulate the polymer molecular weight is reported. By controlling the slice thickness and polymer swelling conditions, and the initial high molecular weight polymer chains can be cropped into fragment chains with designed molecular weight in a well‐defined way. This work presents a new strategy to manipulate polymer molecular weight and will also provide a unique platform for further study of polymer mechanochemistry.