Polymerization Leading (polymerization + leading)

Distribution by Scientific Domains


Selected Abstracts


Direct Observation of , -Chloro- p -quinodimethane as the Real Monomer in the Gilch Polymerization Leading to Poly(p -phenylene vinylene)s

MACROMOLECULAR RAPID COMMUNICATIONS, Issue 2 2007
Jens Wiesecke
Abstract It is the general consensus that in Gilch polymerizations the 1,4-bis(chloromethylene)benzene starting material first changes into p -quinodimethane intermediates which then act as the real monomers. However, direct observation of these intermediates has not been possible so far. This is because usually the p -quinodimethane auto-initiates its rapid radical polymerization instantaneously, keeping its concentration extremely low throughout the whole process. Here it is shown that, when the reaction is carried out at very low temperatures, the formation of p -quinodimethane still proceeds but chain growth is suppressed. Hence, the concentration of the active monomer reaches a level sufficient for NMR analysis. [source]


Open-tubular capillary columns with a porous layer of monolithic polymer for highly efficient and fast separations in electrochromatography

ELECTROPHORESIS, Issue 21 2006
Sebastiaan Eeltink
Abstract Open-tubular columns for CEC separations having inner-wall coated with a thin layer of porous monolithic polymer have been studied. A two-step process including (i),UV-initiated polymerization leading to a layer of porous poly(butyl methacrylate- co -ethylene dimethacrylate), and (ii),UV-initiated grafting of ionizable monomers appear to be well suited for the preparation of these columns. The thickness of the porous polymer layer is controlled by the percentage of monomers in the polymerization mixture and/or length of the irradiation time. The layer thickness significantly affects retention, efficiency, and resolution in open-tubular CEC. Under optimized conditions, column efficiencies up to 400,000 plates/m can be achieved. Use of higher temperature and application of pressure enables a significant acceleration of the open-tubular CEC separations. [source]


Crosslinking polymerization leading to interpenetrating polymer network formation.

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 21 2003

Abstract As part of our continuing studies concerned with the elucidation of the crosslinking polymerization mechanism leading to interpenetrating polymer network (IPN) formation, in which IPNs consist of both polymethacrylates and polyurethane (PU) networks, this article explores the polyaddition crosslinking reactions of multifunctional poly(methyl methacrylate- co -2-methacryloyloxyethyl isocyanate) [poly(MMA- co -MOI)] [MMA/MOI = 90/10] with various diols leading to PU network formation. Thus, the equimolar polyaddition crosslinking reactions of poly(MMA- co -MOI) with ethylene glycol (EG), 1,6-hexane diol, and 1,10-decane diol (DD) were carried out in N -methyl pyrrolidone at a 0.25 mol/L isocyanate group concentration at 80 °C. The second-order rate constants decreased from EG to DD. The deviation of the actual gel point from the theoretical one was smaller from EG to DD. The intrinsic viscosity of resulting prepolymer demonstrated almost no variation with progressing polymerization for the EG system, whereas it gradually increased with conversion for the DD system. Close to the gel point conversion it increased rather drastically for both systems. The swelling ratio of resulting gel was higher from EG to DD. These are discussed mechanistically in terms of the significant occurrence of intramolecular cyclization and intramolecular crosslinking reactions leading to shrinkage of the molecular size. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3243,3248, 2003 [source]


Crosslinking polymerization leading to interpenetrating polymer network formation.

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 4 2003

Abstract At the start of our research program concerned with the elucidation of the crosslinking polymerization mechanism leading to interpenetrating polymer network (IPN) formation, in which IPNs consist of both polymethacrylates and polyurethane (PU) networks, this article deals with the polyaddition crosslinking reaction leading to PU network formation. Therefore, 2-methacryloyloxyethyl isocyanate (MOI) was radically copolymerized with methyl methacrylate (MMA) in the presence of CBr4 as a chain-transfer agent. The resulting poly(MMA- co -MOI)s, having pendant isocyanate (NCO) groups as novel multifunctional polyisocyanates, were used for polyaddition crosslinking reactions with ethylene glycol as a typical diol. The second-order rate constants depended on both the functionality of poly(MMA- co -MOI) and the NCO group concentration. The actual gel points were compared with the theoretical ones calculated according to Macosko's equation; the deviation of the actual gel point from the theoretical value became more remarkable for a greater functionality of poly(MMA- co -MOI) and at a lower NCO group concentration or at a lower poly(MMA- co -MOI) concentration. These are discussed mechanistically, with consideration given to the significance of intramolecular cyclization and intramolecular crosslinking reactions leading to the shrinkage of the molecular size of the prepolymer, along with the data of the intrinsic viscosities of resulting prepolymers and the swelling ratios of resulting gels. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 606,615, 2003 [source]


The Effect of Persistent TEMPO Radicals on the Gilch Polymerization

MACROMOLECULAR RAPID COMMUNICATIONS, Issue 1 2007
Jens Wiesecke
Abstract The mechanism of the Gilch polymerization leading to poly(p -phenylene vinylenes) is still a matter of controversial discussion. Similar to some other research groups, we strongly favor a basically radical process. Moreover, we believe it is initiated by spontaneously formed diradicals. Here, we describe further experimental evidence which clearly supports the assumed initiation step: it is shown how the polymerization process is affected quantitatively when different amounts of 2,2,6,6-tetramethylpiperidine- N -oxyl (TEMPO) are added as a scavenger. In full agreement with our expectations, the chain growth is either retarded or completely prevented, depending on the respective molar ratio of monomer and scavenger. [source]