# Understanding Enhanced Melt Memory in Poly(Octamethylene Carbonate)-Based Random Copolycarbonates with Mixed Isodimorphic/Isomorphic Crystallization

## TL;DR

This study explores how a unique crystallization mode in certain copolymers enhances their melt memory, which is important for polymer material design.

## Contribution

The paper reveals that isomorphic crystallization in specific copolymers leads to significantly enhanced melt memory due to stronger intermolecular interactions.

## Key findings

- Compositions crystallizing in the isomorphic mode show increased melt memory with Domain IIa widths up to 30 °C.
- Stronger intermolecular interactions in the new crystalline phase correlate with higher dielectric constants and enhanced melt memory.
- Copolymer comonomer incorporation critically tunes crystallization behavior and melt memory.

## Abstract

Poly­(hexamethylene
carbonate-ran-octamethylene
carbonate) (PC6/PC8), poly­(heptamethylene carbonate-ran-octamethylene carbonate) (PC7/PC8), and poly­(dodecamethylene-ran-octamethylene carbonate) (PC12/PC8) are the first random
copolymers known to crystallize with a mixed isodimorphic and isomorphic
mode. Here, we investigate for the first time how this dual crystallization
mode affects melt memory. Self-nucleation experiments, combined with
synchrotron X-ray scattering, polarized light microscopy, and dielectric
spectroscopy, show that crystallization in the isodimorphic mode decreases
melt memory as the comonomer content increases, as expected. Conversely,
compositions that crystallize in the isomorphic mode, where a new
crystalline phase forms that is different from the parent components
or their polymorphs, display increased melt memory, with Domain
IIa widthsdirectly related to melt memoryreaching
up to 30 °C, significantly surpassing those in homopolymers.
This heightened melt memory is due to stronger intermolecular interactions
within the new phase, as shown by higher dielectric constants. These
results establish the crucial role of intermolecular interactions
within the crystal lattice in determining enhanced melt memory in
copolymers showing both isodimorphic and isomorphic crystallization,
highlighting the critical role of comonomer incorporation in tuning
crystallization behavior and melt memory.