Monovinyl monomer

ARRANGEMENT OF UNITS IN POLYMERS DERIVED FROM MONOVINYL MONOMERS... 

Let us consider first the copolymerization of a divinyl monomer bearing independent vinyls of the same reactivity with a monovinyl monomer the reactivity of which may be different. The vinyl-divinyl copolymerization can be described by the normal copolymerization equation ... 

ATRP was applied to the copolymerization of a monovinyl monomer and a divinyl cross-linker to study the experimental gelation behavior. The fundamental features of ATRP, including fast initiation and reversible deactivation reactions, resulted in a retarded gelation and the formation of a more homogeneous network in the ATRP process compared to gel formation in a conventional radical polymerization. The experimental gel point based on the monomer conversion in the ATRP reaction occurred later than the calculated value based on Flory-Stockmayer s mean-field theory, which was mainly ascribed to intramolecular cyclization reactions. The dependence of the experimental gel points on several parameters was systematically studied, including the ratio of cross-linker to initiator, the concentration of reagents, reactivity of vinyl groups, initiation efficiency of initiators, and polydispersity of primaiy chains. 

Atom transfer radical polymerization (ATRP) was selected as an exemplary CRP technique to systematically study the kinetics and gelation behavior during the concurrent copolymerization of monovinyl monomers and divinyl cross-linkers (Scheme 2). The effect of different parameters on the experimental gelation was studied, including the initial molar ratio of cross-linker to initiator, the concentrations of reagents, the reactivity of vinyl groups present in the cross-linker, the efficiency of initiation, and the polydispersity of primary chains. Experimental gel points based on the conversions of monomer and/or cross-linker at the moment of gelation, were determined and compared with each other in order to understand the influence of each parameter on the experimental gel points. 

In the FRC of vinyl and multivinyl monomers, a drift in the instantaneous copolymer composition throughout the reaction will be undergone due to the different reactivities of the vinyl groups. This compositional drift is caused by the fact that the more reactive monomer will be consumed faster than the less reactive ones. In the simplest instance, assuming equal reactivity of the vinyl groups in mono-and divinyl monomers present in the reaction system, the reactivity of the crosslinker would be twice that of the monovinyl monomer, and therefore, the polymer chain... 

For example, the early monomer mixtures contained crosslinker such as ethylene dimethacrylate and trimethylolpropane trimethacrylate, monovinyl monomers such as butyl methacrylate, and AMPS. The initiator was originally 2,2 -azobisisobutyronitrile. However, the use of aromatic phenone initiators later enabled significant acceleration of the polymerization process such that it was completed in several minutes as opposed to more than 12 h. A large number of various porogenic solvents was also tested. 

Polymeric gels are crosslinked polymers swollen in a liquid. The polymer serves as a matrix to hold the liquid together, while the liquid inside the gel allows free diffusion of some solute molecules. Polymeric gels can be prepared from either monomeric or polymeric precursors dissolved in a solvent. However, the most commonly used method is the free-radical crosslinking copolymerization of a monovinyl monomer with a divinyl monomer (crosslinker) in solution. In the... 

Fig. 4 Formation process of a pore by cryogelation (a) and by freeze-drying (b). Red, green, and gray circles represent monovinyl monomers, divinyl monomers, and polymer repeat units, respectively...

When monovinyl monomers are copolymerized with a divinyl monomer (e.g. styrene with divinylbenzene) in the presence of diluents (good solvents, poor solvents, or polymers), microsyneresis usually occurs when the critical concentrations of the divinyl monomer and diluent are surpassed. Preceding sections give an answer to why phase separation usually prefers to take the form of microsyneresis and not that of macrosyneresis. 

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