DOI: 10.1021/cg9006185
Phase Behavior and Polymorphism of Organic Crystals Confined within Nanoscale Chambers
2009, Vol. 9 4766–4777
Jeong-Myeong Ha,† Benjamin D. Hamilton,† Marc A. Hillmyer,† and Michael D. Ward*,‡ †
Department of Chemical Engineering and Materials Science and Department of Chemistry, University of Minnesota, 421 Washington Avenue SE, Minneapolis, Minnesota 55455, and ‡Molecular Design Institute, Department of Chemistry, New York University, 100 Washington Square East, New York, New York 10003-6688 Received June 6, 2009; Revised Manuscript Received July 13, 2009
ABSTRACT: Controlling polymorphism, the ability of a compound to adopt more than one solid-state structure, often relies on empirical manipulations of conditions such as solvent, temperature, and mode of crystallization. Despite a growing interest in nanocrystalline formulations, however, the influence of crystal size on polymorph formation and stability is largely unexplored. Nanocrystals of pimelic acid, HO2C(CH2)n-2CO2H (n = 7), glutaric acid (n = 5), suberic acid (n = 8), and coumarin (1,2-benzopyrone) in nanometer-scale pores of controlled pore glass (CPG) beads and hexagonally ordered cylindrical pores of poly(cyclohexylethylene) (p-PCHE) monoliths exhibit size-dependent polymorphism and thermotropic behavior because of the physical constraints imposed by the dimensions of the pores. Pimelic acid, suberic acid, and coumarin also exhibit heretofore unknown polymorphs, denoted δ-pimelic acid, β-suberic acid, and β-coumarin, in CPG with pore sizes
