title: Effect of Low-Concentration Polymers on Crystal Growth in Molecular Glasses: A Controlling Role for Polymer Segmental Mobility Relative to Host Dynamics.
abstract: Low-concentration polymers can strongly influence crystal growth in small-molecule glasses, a phenomenon important for improving physical stability against crystallization. We measured the velocity of crystal growth in two molecular glasses, nifedipine (NIF) and o-terphenyl (OTP), each doped with four or five different polymers. For each polymer, the concentration was fixed at 1 wt % and a wide range of molecular weights was tested. We find that a polymer additive can strongly alter the rate of crystal growth, from a 10-fold reduction to a 10-fold increase. For a given polymer, increasing molecular weight slows down crystal growth and the effect saturates around DP = 100, where DP is the degree of polymerization. For all the systems studied, the polymer effect on crystal growth rate forms a master curve in the variable (Tg,polymer- Tg,host)/Tcryst, where Tgis the glass transition temperature and Tcrystis the crystallization temperature. These results support the view that a polymer's effect on crystal growth is controlled by its segmental mobility relative to the host-molecule dynamics. In the proposed model, crystal growth rejects impurities and creates local polymer-rich regions, which must be traversed by host molecules to sustain crystal growth at rates determined by polymer segmental mobility. Our results do not support the view that host-polymer hydrogen bonding plays a controlling role in crystal growth inhibition.
authors.forename: Chengbin
authors.identifier: 0000-0002-0759-0942
authors.initials: C
authors.lastname: Huang
authors.forename: C Travis
authors.initials: CT
authors.lastname: Powell
authors.forename: Ye
authors.initials: Y
authors.lastname: Sun
authors.affiliation: State Key Laboratory of Natural Medicines, Jiangsu Key Laboratory of Drug Discovery for Metabolic Diseases, Department of Pharmaceutics, College of Pharmacy, China Pharmaceutical University , Nanjing 210009, China.
authors.forename: Ting
authors.initials: T
authors.lastname: Cai
authors.forename: Lian
authors.initials: L
authors.lastname: Yu