2D Confined Crystallization of Precisely Synthesized POSS-Containing Homopolymers Beyond Chain Folding Model

This study investigates the influence of chain length on the crystalline structure and thermodynamic behavior of side-chain polyhedral oligomeric silsesquioxane (POSS)-containing homopolymers. A series of precisely synthesized POSS-containing polymers with exact chain lengths was prepared using precision chemistry. Comprehensive characterization revealed that the covalent attachment of crystalline POSS cages to the polymer backbone confined their crystallization to a 2D lattice, fundamentally distinct from the chain-folding mechanism of conventional polymers. Polarized optical microscopy confirmed the absence of birefringence during crystallization, consistent with this constrained geometry. Differential scanning calorimetry demonstrated that the melting temperature systematically increased with longer chain lengths, attributed to reduced configurational entropy in the molten state, but remained invariant with isothermal crystallization temperature for each sample. Crystal structure analysis confirmed identical interlamellar spacing and crystalline packing across different chain lengths, supporting a model where POSS cages form crystalline bilayers sandwiching the incompatible polyester backbone layer. These findings provide robust experimental validation for the 2D lattice crystallization model in POSS-containing polymers and establish precise molecular design as a key strategy for tailoring the hierarchical organization and thermal properties of hybrid nanocomposites.