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Preparation of monodisperse polystyrene spheres incorporating polyimide prepolymer by dispersion polymerization in the presence of L ‐ascorbic acid
Author(s) -
Omi Shinzo,
Saito Masato,
Hashimoto Takuzo,
Nagai Masatoshi,
Ma GuangHui
Publication year - 1998
Publication title -
journal of applied polymer science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.575
H-Index - 166
eISSN - 1097-4628
pISSN - 0021-8995
DOI - 10.1002/(sici)1097-4628(19980509)68:6<897::aid-app4>3.0.co;2-c
Subject(s) - polymer chemistry , dispersity , polystyrene , prepolymer , ascorbic acid , polymerization , materials science , polyimide , nucleation , chemical engineering , monomer , chemistry , polymer , organic chemistry , composite material , polyurethane , food science , layer (electronics) , engineering
Addition of a small amount of L ‐ascorbic acid (AA) unexpectedly provided uniform‐sized polystyrene (PS) spheres in an ordinary dispersion polymerization process. PS spheres incorporated with polyimide prepolymer (BANI‐M), designed as possible spacers for liquid crystal displays, were prepared from formulations containing a mixed solvent of isopropanol/2‐methoxyethanol, 2,2′‐azobisisobutyronitrile, and poly‐ N ‐vinylpyrrolidone (PVP) at 343 K. The average particle size decreased by the addition of AA; however, dramatic improvements of monodispersity were observed with various formulations. The best coefficient of variation was 1.37%, compared to 7.03% obtained without the presence of AA. Addition of AA was originally intended to scavenge a trace amount of oxygen remaining in the reactor system, promoting a rapid and short particle nucleation period, and thereby resulting in improved monodispersity. However, there was no difference in the initial reaction rate between the runs with and without AA; no noticeable induction period was observed even without AA provided that an ordinary procedure was employed to eliminate the dissolved oxygen through a nitrogen bubbling, and the nitrogen atmosphere was maintained during the reaction. It was proposed from 1 H‐NMR analysis that the abstraction of hydrogen atom from the PVP chain by the oxidized form of AA promoted the formation of graft copolymer PVP‐PS, which stabilizes precipitating chains in the nucleation period. Approximately 40% of BANI‐M present initially was incorporated in the PS particles, which occupied 4–9% of the weight of polymer particles, well below the target value of 20%. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 897–907, 1998