Polymerization irradiation

Among the various radiation-induced modifications, the EB-processing of polymers has gained special importance as it requires less energy, is simple, fast, and versatile in application. The overall properties of EB-irradiated polymeric materials are also improved compared to those induced by other ionizing radiation. 

Wavelength used in irradiation (oligomerization)/nm Wavelength used in irradiation (polymerization)/nm 4>... 

There are numerous examples of solid state polymerizations. Here we will briefly describe examples based on addition polymers. Generally, the crystalline monomer is irradiated with electrons or some form of high-energy radiation, such as gamma or x-rays. Since many monomers are solids only below room temperature, it is customary to begin irradiation at lower temperatures with the temperature raised only after initial polymerization occurs. (Some reactions are carried to completion at the lower temperature.) After polymerization, the monomer is removed. Table 6.10 contains a list of some of the common monomers that undergo solid-state irradiation polymerization. 

Monomers That Undergo Solid-State Irradiation Polymerization... 

Later, Tieke reported the UV- and y-irradiation polymerization of butadiene derivatives crystallized in perovskite-type layer structures [21,22]. He reported the solid-state polymerization of butadienes containing aminomethyl groups as pendant substituents that form layered perovskite halide salts to yield erythro-diisotactic 1,4-trans polymers. Interestingly, Tieke and his coworker determined the crystal structure of the polymerized compounds of some derivatives by X-ray diffraction [23,24]. From comparative X-ray studies of monomeric and polymeric crystals, a contraction of the lattice constant parallel to the polymer chain direction by approximately 8% is evident. Both the carboxylic acid and aminomethyl substituent groups are in an isotactic arrangement, resulting in diisotactic polymer chains. He also referred to the y-radiation polymerization of molecular crystals of the sorbic acid derivatives with a long alkyl chain as the N-substituent [25]. More recently, Schlitter and Beck reported the solid-state polymerization of lithium sorbate [26]. However, the details of topochemical polymerization of 1,3-diene monomers were not revealed until very recently. 

In order to study the correlation between the anion radicals and radiation-induced polymerization, the latter was examined by irradiating the glass containing nitroethylene and warming it. Post-irradiation polymerization is found to occur, giving polynitroethylene when the glass is warmed to 133° 143° K, where, according to the ESR study, the anion radicals disappear. 

I, 3-diene polymerization. Monomer molecules are included in chiral channels in the matrix crystals, and the polymerization takes place in chiral environment. The y-ray irradiation polymerization of trans- 1,3-pentadiene included in 13 gives an optically active isotactic polymer with a trans-structure. The polymerization of (Z)-2-methyl-1,3-butadiene using 15 as a matrix leads to a polymer having an optical purity of the main-chain chiral centers of 36% [47]. 

Starting from monomers Monomers in bulk or in solution are irradiated. Polymerization takes place as the first stage of reaction. The polymer chains are then cross-linked. It is frequent practice to add bifunctional monomers to increase the efficiency of cross-linking. Typically, this procedure is used for synthesis of wall-to-wall hydrogels or microspheres. For biomedical use of the formed gels, all non-reacted monomers and residues have to be extracted. 

Since the photolysis of the salt is reversible, the formation of the proton is scavenged by the ylide to form the starting photoinitiator when irradiation ceases [43]. During irradiation, polymerization takes place via protonation of a monomer followed by sequential monomer addition. Notably, a termination via addition of a ylide to the growing cationic chain end is feasible. The overall polymerization process is summarized in Scheme 11.13. 

Another remarkable fact about ionic polymerization in general, in contrast to other polymerization techniques, is that in the absence of adventitious terminators, ionic polymerization will go on after irradiation has ceased, and will often continue until most of the monomer has been exhausted. Although such post-irradiative polymerization may be an advantage in UV curing, it is undesirable in imaging applications where it limits resolution and degrades feature sharpness. ... 

In the y irradiated polymerization-reduction technique (Co radiation), the polymer samples were immersed in silver nitrate and in 2-propanol solution until the complete reduction of Ag ions. 

R.L. Leung, PL. Fan, W.M. Johnston, Post-irradiation polymerization of visible light-activated composite resin, J. Dent. Res. 62 (1983) 363-365. 

Various indications suggest that high-energy irradiation polymerizations are started at crystal defects. If a crystal is scratched, the polymer chains will start to grow at this point. In addition, the points where polymerizations begin are randomly distributed. Because of the density difference between polymer and monomer, polymerizations in monomer crystals lead to the buildup of stresses which produce further crystal defects. New polymerizations can be started at these new defects sites. Electron microscope pictures show a number of craters caused by polymerizations, which, after a further polymerization time, become surrounded by satellite craters. 

In the majority of cases, high-energy-irradiation polymerization appears to proceed free radically (see Section 21.2). According to esr measurements, the start reaction appears to involve a disproportionation,... 

Similarly, Lan et al. [7] developed a one-step microfluidic method for fabricating nanoparticle-coated patchy particles. A coaxial microfluidic device was employed to produce Janus droplets composed of curable phase and non-curable phase. The results showed that nanoparticles were dispersed either in the continuous fluid or the non-curable phase fluid. The nanoparticles (30 nm or 300-500 nm) were adsorbed onto the interface between these phases, and the curable phase was solidified by UV-irradiated polymerization. Thus, the patchy microparticles asymmetrically coated by nanoparticles were synthesized. They also employed Si02, TS-1, and fluorescent polystyrene nanoparticles as the coating materials to demonstrate the validity of the method. The microfluidic approach exhibited excellent controllability in morphology, monodispersity, and size for the nanocomposites. The morphology of the particles could be controlled from less than a hemisphere to a sphere by adjusting the flow rate ratio of the two dispersed phases. The method can be applied to other nanoparticles with specific surface properties. 

Asymmetric synthesis polymerization of 1,3-dienes with solid matrices has been reported." This was first attained by using optically active (R)-(-)-trans-anti-trans-flnti-trans-perhydrotriphenylene (256) matrix for y-ray irradiation polymerization of trans-1,3-pentadiene to afford isotactic poly-trans-254. °° Deoxyapocholic ° ° and apocholic acids (257 and 258) are also effective as optically active matrices. Matrix polymerization tended to result in higher optical purity. The highest value of optical purity so far reported is 36% for the polymerization of (Z)-2-methyl-1,3-butadiene with 258 as a matrix. 

To date core-shell nanomaterials based on PANI have been synthesized using PS, titanium oxide, gold, and vanadium oxide as seeds [275-283]. Various ways to nanometer-size PANI core-shell materials have been continuously developed, including ultrasonic irradiation polymerization, oxidative polymerization and electrochemical polymerization. 

The polymerization of compound 106a was studied more in detail. A y-ray dose of 30 Mrad is sufficient to nearly cause a complete conversion to polymer. However, the reactivity strongly depends on the morphology of the crystals and a txrnsiderable amount of polymer is formed due to a post-irradiative polymerization This is in contrast to the photoreaction in layer perovskites From X-ray powder patterns of 106a a layer structure with a head-head-tail-tail orientation of the monomers is evident This packing is different from the structure... 

Keywords Microwave irradiation Polymerization Polymer cnre Composite Polymer matrices... 

When the stationary concentration in the radical polymerization of vinyl compounds is larger than 10 M, ESR measurement of growing radicals does not require use of the special cavities described in Sect. 7.2. Infact, Kamachi etal. were able to observe, even at room temperature, a well-resolved 5-line spectrum in BPO-initiated, UV-irradiated polymerization of TPMA by use of the commercially available TE j... 

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