Understanding the Crystallization of Random Copolymers beyond Iso(di)morphism and Comonomer Exclusion

In this Perspective, we revisit the classical classification of crystallization behavior in random copolymers, namely isomorphic crystallization, isodimorphism, and comonomer exclusion, and discuss the limitations of these discrete categories. Although these frameworks describe distinct modes of comonomer inclusion or exclusion within crystalline lattices, growing experimental evidence shows that many copolymer systems exhibit composition- and structure-dependent mixed crystallization behaviors that cannot be fully captured by the traditional classifications. We propose that crystallization in random copolymers should instead be understood as a continuum of structural states. Within this continuum, isomorphism, isodimorphism, comonomer exclusion, and mixed crystallization modes represent distinct pathways by which comonomers are accommodated in crystalline lattices, each yielding distinct structural organizations and material properties. This broader perspective reframes crystallization from a passive consequence of molecular structure into an active materials design tool. By tailoring molecular architecture, copolymer composition, and processing conditions, crystallization behavior can be deliberately manipulated to tune thermal, mechanical, optical, barrier, and degradation properties. Advancing toward predictive control of crystallization in random copolymers will require systematic studies that integrate crystallization mechanisms, advanced structural characterization, and functional performance across diverse polymer systems. Such efforts will enable a transition from empirical classification toward a true crystallization-by-design approach, in which targeted crystalline states and morphologies are engineered to achieve tailored material properties and functionalities.