Benzoylperoxide, radical initiator

Yin et al. [73,74] prepared new microgel star amphiphiles and stndied the compression behavior at the air-water interface. Particles were prepared in a two-step process. First, the gel core was synthesized by copolymerization of styrene and divinylbenzene in diox-ane using benzoylperoxide as initiator. Microgel particles 20 run in diameter were obtained. Second, the gel core was grafted with acrylic or methacryUc acid by free radical polymerization, resulting in amphiphilic polymer particles. These particles were spread from a dimethylformamide/chloroform (1 4) solution at the air-water interface. tt-A cnrves indicated low compressibility above lOmNm and collapse pressnres larger than 40 mNm With increase of the hydrophilic component, the molecnlar area of the polymer and the collapse pressure increased. 

The use of reverse ATRP enlarges the scope of substrate polymers for controlled polymerizations even further because the required radical initiators can in many cases be provided more easily than ATRP initiators on surfaces of inert polymers. For example, poly(vinylidene fluoride) microfiltration membranes were irradiated with UV light and then exposed to air to create hydro(peroxide) species [11]. These were then used to initiate the reverse ATRP of methyl methacrylate in the presence of copper(I) chloride, 2,2 -bipyridine, and benzoylperoxide (Figure 3.5). Similar reaction schemes are applicable to (hydro)perox-ide patterns created directly on polymer surfaces using the lithographic methods discussed in Chapter 2. 

Whether a monomer can be polymerized free-radically also depends in certain cases on the initiator. Azobisisobutyronitrile, for example, polymerizes 5-vinyl mercaptals CH2=CH—S—CH2—S—R to products of high molecular weight, whereas no polymer is formed at all under the same conditions with benzoyl peroxide. Here, in fact, the result is an induced decomposition of the benzoylperoxide by the ——CH2—S— group to form an (unstable) ester CH2=CH—S—CH(OCOC6H5)—S—R and benzoic acid. 

The propagating radical of dialkyl itaconate in the homogeneous polymerization was foimd by Sato et al. to be stable enough to be observed by ESR even above 60 °C. Fig. 62 a displays the 5-line spectra obtained when dimethyl 2,2 -azobis-isobutyrate, benzoylperoxide, and di-tert-butylperoxide were used as initiators. On the other hand, the polymerization of DBI initiated with azonitriles such as 2,2 -azobisisobutyronitrile, 2,2 -azobis(2,4-dimethylvaleronitrile), and cyclohexanecarbo-... 

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