Multifunctional vinyl monomers

Low-molecular weight polymers + Vinyl monomers + Multifunctional vinyl monomers... 

The most common and most versatile technique for the production of synthetic hydrogels is the free radical (chain) copolymerization of monofunctional and multifunctional vinyl monomers. Gels can also be created by the step (e.g., con-... 

Radical polymerization is induced by photoinitiators, cleaverage type, and hydrogen abstraction type. The merits of radical polymerization are its higher cure rate and availability of a variety of materials. Most acrylate and methacrylate monomers are applied for radical polymerization. Figure 4.7 shows typical polymerization of a monomer. Mono-, bi-, and multifunctional vinyl monomers are used for polymerization. Figure 4.8 shows typical initiators for photopolymerization. Benzophenone is a hydrogen abstract type initiator. 2,2-Diethoxy-l,2-diphenylethane-l-one is a cleavage type initiator. 

There is a wide range of morphologies and compositions of polymeric microspheres. Core-shell microbeads can be created by sequentially polymerizing vinyl monomers, typically methacrylates and styrene. Each layer may consist of a homopolymer or a copolymer in the copolymers multifunctional vinyl monomers (e.g., diacrylates and divinylbenzene) may be used to create a cross-linked material. An optional final step can be grafting of functional groups to the surface in order to enhance compatibility to the surrounding medium. 

Radiation sensitizers are multifunctional vinyl monomers (MFA) that are highly reactive towards free radicals. Since all common MFAs contain terminal unsaturation, it can be expected that addition/polymerization is the principal mechanism by which they react in the polymer compound. These additives are used mainly to accelerate the radiation-induced crosslinking in the polymers. The addition of MFA to the polymer formulations suppresses the chain scission reactions and allows more crosslinking to occur. 

Olefin isomerization can be catalyzed by a number of catalysts such as molybdenum hexacarbonyl [13939-06-5] Mo(CO)g. This compound has also been found to catalyze the photopolymerization of vinyl monomers, the cyclization of olefins, the epoxidation of alkenes and peroxo species, the conversion of isocyanates to carbodiimides, etc. Rhodium carbonylhydrotris(triphenylphosphine) [17185-29-4] RhH(CO)(P(CgH )2)3, is a multifunctional catalyst which accelerates the isomerization and hydroformylation of alkenes. 

Some of the multifunctional crosslinking monomers used in emulsion polymerization include pentaerythritol tetraacrylate and trimethylolpropane triacrylate (high boiling, low viscosity, fast cure system for vinyl acrylic latex paints) [34]. 

In this linkages are covalent bonds. They are influenced by the chemical linkages and functional groups present in the gel networks. Hydrophilic polymers and hydrophilic-hydrophobic copolymers are examples of chemically crosslinked gels obtained by the polymerization of vinyl monomers in fhe presence of multifunctional crosslinkers. These crosslinkers are the crosslinking points within and between the polymeric chains allowing modification of the entire physicochemical properties of the gel systems... 

An idealized formulation guideline showing possible interactions of single vinyl unsaturated monomers, multifunctional vinyl cross-linking molecules and polymeric materials is represented by Pig. 5. 

Monte Carlo vinyl monomer in the presence of a multifunctional initiator at equal rate [93]... 

In the free-radical polymerization of vinylic monomers, gel is formed if the following conditions are fulfilled (1) a mechanism leading to LCBs is operative, for example chain transfer to polymer, and (2) a mechanism that links polymer chains is also operative, for example termination by combination or propagation to pendent double bonds. Obviously, if multifunctional monomers are homopolymerized or copolymerized with vinylic monomers, gel is also formed. In this case, the predominant reaction linking polymer chains and leading to polymeric networks is the propagation to pendent double bonds of the multifunctional monomers. 

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