Stearyl Methacrylate-Based Polymers as Crystal Habit Modifiers for Triacylglycerols

Triacrylglycerols (TAGs) are ubiquitous and naturally occurring fat molecules that can make materials with diverse textural, mechanical, and optical properties. These properties are intimately linked to their complex hierarchical crystal structures, which can be controlled by additives that interfere with crystallization. A series of semicrystalline, bottlebrush-like copolymers have been developed to modify TAG crystallization and influence crystal habit. Synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization, these copolymer additives combine crystalline poly(stearyl methacrylate) with amorphous poly(oleyl methacrylate) in either block or statistical architecture. Upon cooling mixtures of these copolymers with solutions of tristearin (SSS) in triolein (OOO), the polymeric additives affected SSS crystallization at multiple length-scales. Microscopy analysis revealed control over SSS crystal morphology indicative of crystal aggregation, while small and wide-angle X-ray diffraction (SAXD/WAXD) offered insight into the underlying mechanism of action. Analyzing the physical broadening of lamellar peaks suggested that the fraction of amorphous poly(oleyl methacrylate) controls the thickness of primary nanoplatelets, and crystal structures derived from WAXD showed that the less stable alpha- or beta'-polymorphs of SSS are stabilized by block or statistical copolymers, respectively. Exploiting these additives to simultaneously manipulate the packing of TAG molecules within lamellae, the size of primary crystallites, and the aggregation of crystallites could diversify fat material properties and supplement wide-ranging applications.