Free radical polymers

These act similarly to the phenol anti-oxidants the N-H group in the amine reacts with the polymer free radical R to give a stabilised nitrogen radical and RH. 

Figure 2.19 Addition polymer free radical formation, initiation of the monomer, and propagation...

Peroxy free radical Polymer Dead polymer Free radical (15.8)... 

Degradation of Polymers Free-radical Polymerisation Non-radical Polymerisation... 

The tendency to foul tubes could best be eliminated by eliminating salts, wax, particulates, corrosion products, polymers, free radicals, and all the myriad of other factors that contribute to fouling. Possibly— but not likely. 

Alternatively, one might investigate the reaction between polymer free radicals and monomer vapor. Chains of polymer molecules, kept in a monomer atmosphere, are ruptured by a suitable photochemical technique, thus producing the respective polymer radicals. These undergo polymerization and consume monomer, if its vapor pressure exceeds the... 

Some of the different chemistry of DNA as compared to its low-molecular-weight model compounds is due to the fact that DNA is a polymer, and some aspects of polymer free-radical chemistry are dealt with in a separate chapter. The special properties of dsDNA allow hole and electron transfer to trapping sites. This is an area that attracts very strong attention at present, and the level of understanding is already very high. 

In peroxyl-free-radical chemistry, H02702 " elimination reactions play a major role (Chap. 8.4). In polymer free-radical chemistry, these reactions are of special interest, because they lead to a conversion of slowly diffusing polymer-derived radicals into the readily diffusing HCV/CV radicals. The H02 /02 "-elimina-tion typically proceeds from an a-hydroxyalkylperoxyl radical [reaction (22)]. In poly(vinyl alcohol), for example, such an structural element is formed by H-abstraction and subsequent 02 addition [reactions (18) and (19)]. The same structural element may also be formed during the bimolecular decay of peroxyl radicals which carry an H-atom in [3-position [reactions (20) and (21)]. 

Volume 14 Volume 14A Volume 15 Section 5. POLYMERISATION REACTIONS (3 Volumes) Degradation of Polymers Free-radical Polymerisation Non-radical Polymerisation... 

Therefore, in essence the problem is not the oxidizability as such, but the synergistic action of factors like electromagnetic radiation and thermal energy on the oxidation. By the action of these factors on the polymer free radicals are formed, which together with oxygen initiate a chain reaction. Hence most oxidation reactions are of an autocatalytic nature. 

One of the issues that concern liquid feedstock cracking operations is a higher rate of fouling. This is not only a consequence of heavier coke forming precursors, but also as a consequence of long lived free radicals which act as agents for the formation of a polymer (often referred to as pop-corn polymer) in the primary fractionator and downstream units. For instance, free radicals based on styrene or indene have sufficiently long half-lives to pass from the pyrolysis section into the primary fractionator. These can concentrate in this unit and produce polymer (free radical polymerisation) when sufficient amounts of suitable olefins are present, in particular styrene itself and di-olefins such as cyclo-pentadiene or butadiene. 

Tobita H (2004) Scale-free power-law distribution of emulsion-polymerized nonlinear polymers Free-radical polymerization with chain transfer to polymer. Macromolecules... 

ESR signals of dangling bonds are broad single-line signals without hyperstructure [3] as depicted in Figure 6.1, whereas the polymer free radicals have hyperstructures that are characteristic of the polymer structure as depicted in Figure 6.2 for synthetic polymers and Figure 6.3 for natural polymers, which were... 

TMS deposition on PE showed only substrate signals with no detectable TMS signal (Fig. 6.12b). The absence of the TMS signal in this system could be due to the fast reaction of TMS radicals with the surface radicals generated from PE. The more likely explanation is that the number of free radicals in the plasma polymer layer is too small in comparison with the free radicals created in the bulk of the substrate, PE. What we see in Figure 6.13 is the decay of PE polymer free radicals, which were created by the luminous gas of TMS. With substantial decay of the PE free radicals, TMS dangling bonds, which decay much slower, became discernible. 

EX SITU ESTIMATION OF DANGLING BONDS AND POLYMER FREE RADICALS... 

It is tempting to use such relatively simple wet chemical methods to determine the amount of free radical on plasma polymers and on polymers treated with glow discharge. However, these methods have serious limitations when applied to the dangling bonds in plasma polymers or polymer free radicals in polymers treated with glow discharge. The most serious limitation is the accessibility of the chemical to the free radicals to be analyzed. Another serious limitation is the specificity of chemical reactions. 

The dangling bonds and polymer free radicals (on the surface of glow discharge treated polymer) capture molecular O2 or H2O, producing hydroxyl and carbonyl groups as schematically shown ... 

The main effect of exposure to a luminous gas phase is the detachment of small molecules such as H2, CO, CO2, and so forth, depending on the nature of gas used, which leaves free radical (unpaired electron) sites on the polymer chains (polymer free radicals described in Chapter 6). The weight loss rate greatly depends on how... 

Recently it has been found (2 ) that tetrahydrofurane (THF) retained by poly(vinyl chloride) (PVC) in amounts of 2 to 6 may influence the photodegradation of polymers. Free radicals which are formed during the photolysis of THF in PVC matrix are capable of abstracting hydrogen and forming macroradicals. If the effects of solvent traces are ignored a false interpretation of observed phenomena may result. 

The concept of controlled hydrolytic stability based on substituted phospha-zenes can be extended to organic polymers. Free radical polymerization of acrylic acid in aqueous solution in presence of 39 yields a degradable hydrogel with imidazolyl groups as controlling sites with respect to the hydrolytic stability. ... 

Termination can also occur by the reaction of polymer free radicals with primary initiator radicals (called primary termination) or free-radical scavenging species, especially oxygen. Activation energies for propagation and termination for some typical monomers are listed in Table 2. 

Both evidence of the browning caused by the high-intensity absorption of conjugated chromophoric groups and upward shifts in the ultraviolet-visible spectral baselines indicate that higher hydroquinone concentrations produce more polymers. Free radical coupling is probably involved in the polymerization since the existence of free radicals is correlated to hydroquinone concentration. The ultraviolet-visible absorption profiles of these polymers formed in the systems that are not sterilized (Kung and McBride, 1988) appear to be similar to those of phenol-derived polymers in the systems free... 

If these free radicals are produced in sufficient number and are stable enough to produce a high enough concentration, they may be detected and their concentration measured by an ESR spectrometer. In a great many polymers, free radicals are either very unstable, (they may be annihilated through reaction with other radicals and/or Impurities), or are produced in numbers too small for detection by currently available Instruments. There are, however,... 

Monomer/unsaturated Growing polymer Cured polymer polymer (free radical)... 

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