Initiators free radical polymerization using

High pressure (60—350 MPa) free-radical polymerization using oxygen, peroxide, or other strong oxidizers as initiators at temperatures of up to 350°C to produce low density polyethylene (LDPE), a highly branched polymer, with densities from 0.91 to 0.94 g/cm. ... 

Of these, the most commonly used in letterpress printing is photo-initiated free-radical polymerization of acrylates. 

Figure 104 Free radical polymerization using benzoyl initiator...

Organic peroxides are used to initiate free-radical polymerization of ethylene, butadiene, styrene, vinyl chloride, vinyl acetate, and methyl methacrylate. They are also used to cure unsaturated polyesters, occasionally to cross-link thermoplastics such as polyethylene and polyacrylates, and increasingly for grafting and compatibiliza-tion of polymer blends. A variety of organic peroxides offer useful reactivity over a temperature range from 0 to 130°C or more, for different polymers and different processes. 

Recently an aromatic capillary monolithic acrylate material was prepared via a thermally initiated free radical polymerization in the confines of 200-pm inner diameter fused silica capillaries. The material proved to be very robust and was applied to IPC of oligodeoxynucleotides with good reproducibility [21]. Similarly a derivatized poly[(trimethylsilyl-4-methylstyrene)-co-bis(4-vinylbenzyl)dimethylsi-lane] capillary monolith was used for the same purpose [22],... 

Azo functions are well known to initiate free radical polymerization and have been used previously in polymeric initiators [6]. However, triazene functions are only rarely used in free radical polymerization [7], and not much is known about their thermal decomposition mechanism. The comparison of the thermal characterisitics of two model compounds, 3 and 4 (see Fig. 3), for AMP and TMP has shown that the azo fimction is much more thermally labile than the triazene group. The maximum of decomposition in bulk for 3 is at 135 °C and for 4 at 270 °C. Decomposition of 3 and 4 in DMSO solution at 80 °C followed by UV spectroscopy led to complete decomposition of 3 after 600 min whereas only about 5 % of the triazene functions are destroyed at this time. 

Oxidation-reduction reactions can also be used to initiate free-radical polymerizations. Such initiators include a metallic ion that can undergo a one-electron transfer ... 

The effect of pulsed discharge on plasma polymerization may be viewed as the analogue of the rotating sector in photoinitiated free-radical chain growth polymerization. The ratio r of off time I2 to on time li, r = (t2/h), is expected to influence the polymerization rate depending on the relative time scale of I2 to the lifetime of free radicals in free-radical addition polymerization of a monomer. This method was used to estimate the lifetime of free radicals in conventional photon-initiated free radical polymerization. 

Figure 2.4 Key organic peroxides used to initiate free radical polymerization of ethylene.

Use of air has been largely supplanted by organic peroxides (see section 2.3). Organic peroxides are injected at several points in the autoclave and initiates free radical polymerization by chemistry discussed in Chapter 2. Reactor residence... 

It must also be noted here that not all photoinitiators initiate free-radical polymerization, for example, the use of onium salts as photoinitiators is based on their ability to initiate cationic polymerization processes. 

In the early 1980s, Moad et al initially attempted to control free-radical polymerization using stable free radicals such as nitroxides. Following developmental work by Georges et al. at Xerox, the approach has led to the realization of a diverse range of polymer architectures that were previously unobtainable using traditional anionic or cationic polymerization techniques. 

All measurements were performed using toluene as solvent unless otherwise stated. Poly (VBuPBD) was prepared by thermally initiated free radical polymerization in benzene solution at 70 C, the mixture being thoroughly degassed and sealed in glass ampules under high vacuum. Purification of the resultant... 

Polymers were prepared by AIBN-initiated free-radical polymerization in degassed toluene at 6O C. With the exception of poly(4-aceto-l-naphthyl methacrylate), the polymers precipitated on formation. Polymers were purified by reprecipitation from CHCl 3 into methanol. Copolymer compositions were determined by UV spectroscopy using the extinction coefficients of the corresponding homopolymers and of 2,4-di aceto-l-naphthyl methacrylate monomer as references. Tables I and II list the properties of the homopolymers and copolymers used in the present study. 

Free Radical Polymerization Using Enzymatic Initiators... 

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