Monomer Conversion Efficiency Research Articles

Substituent effects of accelerator on nitroxide-mediated radical polymerization

The acceleration effect of various agents on the rate of styrene bulk polymerization in 2,2,6,6-tetramethylpiperidinyloxy (TEMPO) mediated polymerization was investigated, including dimethyl malonate (DMM), diethyl methyl malonate (DEMM), diethyl tert-butylmalonate (DEBM), diethyl diethylmalonate (DEDEM), 3-methyl-2,4-pentanedione (MPD), acetyl malononitrile (Ac-MN), and dimethyl malononitrile (DM-MN). Polymerization with the additive proceeded in a living manner, as indicated by keeping a low polydispersity and increasing the molecular weight with the reaction time and conversion. The structure of the styrene polymerization did not change in the presence of these additives. The monomer conversion efficiency was approximately 99% and maintained a relatively narrow polydispersity of 1.29 with the optimal [Ac-MN]/[TEMPO] molar ratios of 4 in 1.5 h. With the accelerator, dipole/dipole interactions led to a weakening of the C-ON bond and an acceleration of the reaction. There is a trend for a higher polymerization rate with more electron-withdrawing substituents.

Mesogen-jacketed liquid crystalline polymers via stable free radical polymerization

Stable free radical polymerization has been used in the controlled synthesis of poly(2,5-bis[(4-butylbenzoyl)oxy]styrene), PBBOS. This “mesogen-jacketed liquid crystalline polymer”, which has mesogenic units attached directly to the backbone in a side-on mode, has been found to exhibit thermotropic liquid crystallinity similar to more conventional main-chain architectures. Stable free radical polymerization of PBBOS consistently produced molecular weight distributions below the theoretical limiting polydispersity of 1.5 calculated for a conventional free radical polymerization process. Surprisingly, a comparison of the synthesis of polystyrene to the polymerization of PBBOS under nearly identical conditions showed that the PBBOS polymerized with a significantly higher reaction rate and monomer conversion efficiency. The nematic phase of these polymers was determined to be stable over the temperature range spanning the polymer glass transition temperature up to the temperature for thermal decomposition. The molecular arrangement of the PBBOS polymers was examined by wide-angle X-ray diffraction and is described here.