Peroxide-functional monomer

Organic peroxide-aromatic tertiary amine system is a well-known organic redox system 1]. The typical examples are benzoyl peroxide(BPO)-N,N-dimethylani-line(DMA) and BPO-DMT(N,N-dimethyl-p-toluidine) systems. The binary initiation system has been used in vinyl polymerization in dental acrylic resins and composite resins [2] and in bone cement [3]. Many papers have reported the initiation reaction of these systems for several decades, but the initiation mechanism is still not unified and in controversy [4,5]. Another kind of organic redox system consists of organic hydroperoxide and an aromatic tertiary amine system such as cumene hydroperoxide(CHP)-DMT is used in anaerobic adhesives [6]. Much less attention has been paid to this redox system and its initiation mechanism. A water-soluble peroxide such as persulfate and amine systems have been used in industrial aqueous solution and emulsion polymerization [7-10], yet the initiation mechanism has not been proposed in detail until recently [5]. In order to clarify the structural effect of peroxides and amines including functional monomers containing an amino group, a polymerizable amine, on the redox-initiated polymerization of vinyl monomers and its initiation mechanism, a series of studies have been carried out in our laboratory. 

It is interesting to study the polymerization of functional monomer containing an amino group, so-called polymerizable amine by peroxide initiator, which could be anticipated to cause less pulpal irritation and toxic... 

An alternative to the direct use of peroxides in monomer grafting is to first functionalize the polymer with initiator or transfer agent functionality. 

The introduction of functional groups is suitable to control the chemical and physical properties of the polymer. However, the introduction of functional groups may cause a reaction of the unshared electron pairs of the functional groups with the active catalytic sites. Thus, the active sites of the catalyst are destroyed. In order to overcome this problem, a procedure has been developed, where the functionalized monomers, such as maleic acid, nadic acid or their anhydrides are grafted after the polymerization reaction (4,37). Grafting takes place as a radical reaction, using e.g., dicumyl peroxide. Other attempts use excessive amounts of catalysts. 

Using the same toluene-benzoyl peroxide system Nakatsuka (105) measured polymerization rate and molecular weight as functions of temperature (40° and 58°) and of the concentration of.three retarders p-nitrophenol, 2,4-dinitrophenol and picric acid. Results were consistent with a kinetic scheme postulating (among other things) bimolecular initiation involving peroxide and monomer and spontaneous unimolecular termination of growing polymer chains. 

Peroxidic initiators, like dibenzoyl peroxide, are too reactive with phenolic and aminic moieties and can be applied only exceptionally [50], Inorganic peroxides, like potassium persulfate, were used for emulsion polymerization of functionalized monomers [51]. Phase transfer catalysis may be also applied using persulfate initiation. To circumvent problems with the peroxide initiation, 4,4 -azobis(4-cyanovaleric acid), a water soluble initiator, was successfully used [48]. 

Most functional monomers and cross-linkers contain one or more vinyl functionalities. Polymerization of this type of compound for the preparation of MIPs is traditionally performed as a free-radical polymerization, initiated via either ther-molytic or photolytic homolysis of an initiator. One of the most commonly used free radical initiators for this purpose is 2,2 -azobis (isobutyronitrile) (AIBN). Other examples of free-radical polymerization initiators are phenyl-azo-triphenyl-methane, tert-butyl peroxide (TBP), acetyl peroxide, benzoyl peroxide (BPO), lauroyl peroxide, tert-butyl hydroperoxide and tert-butyl perbenzoate. 

Glycopolymers were recently grafted onto PET fibers by double plasma treatment in order to obtain a surface compatible with biological material. The first step is activation of the PET surface by argon plasma treatment leading to the formation of radicals by scission of the chemical bonds. Then, fibers are exposed to air in order to form (hydro)peroxides functions. The activated fibers are dipped in glycomonomers solutions and dried. A second plasma treatment is applied to polymerize the monomers adsorbed on fibers (43). 

Another example has been presented by Hsuie. Polyethylene films irradiated in the presence of air and stored for a couple of hours have been immersed into an aqueous solution of acrylic or methacrylic acid containing some Fe salt. In this case, the grafting process is initiated by the redox reaction between the peroxide functions and the iron salt. The grafting ratio first increases with time and then reaches a plateau when the peroxide sites have been consumed. It is an increasing function of the irradiation dose and of the monomer concentration. 

This reaction, cataly2ed by uv radiation, peroxides, and some metal catalysts, eg, platinum, led to the production of a broad range of alkyl and functional alkyl trihalosilanes. These alkylsilanes have important commercial value as monomers and are also used in the production of sihcon fluids and resins. Additional information on the chemistry of sihcon hahdes is available (19,21—24). 

The peroxide 179 dissociates in the presence of a monomer giving rise to alkoxyl (CO-) and borinate (BO-) radicals, but the latter are believed to be too stable to initiate polymerization. It should be mentioned that the molecular weight continuously increases throughout the process implying the pseudo-living mechanism for chain growth. After the completion of the process borane residue is completely oxidized into diol <2004MM6260>. Thus, the 8-boraindane molecule not only initiates the polymerization, but also is a precursor to two functionalities in the polymer chain. 

These radical polymerizations may simply be considered as an insertion of monomer molecules into the R-R bond of the initiator leading to the polymer with two initiator fragments. Thus, the end groups of the polymer are controlled by the initiator used. Otsu proposed the name iniferter (im tiator-trans/er agent-terminator) for the initiators with such functions [64]. Many radical initiators, such as peroxides, azo compounds, tetraphenylethane derivatives, and organic sulfur compounds, may be expected to serve as an iniferter, if monomers and polymerization conditions are selected. Some peroxides show relatively high... 

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