Formation of low molecular weight products

During each photodegradation (in vacuum or air) small amounts of several gaseous and liquid low molecular weight compounds are formed and they can only be detected by chromatographic or mass spectrometry methods (cf. section 10.6). Table 2.1 shows, for example, products formed from polypropylene hydroperoxide photolysis. 

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For catalysts which promote the formation of low molecular weight products, the anion might make the difference, as in the case of the catalyst with C2-bridged diphosphine ligand 23 (Fig. 5), which gives a low molecular weight polymer or MP when the counter-anion is MsO or propanoate, respectively [101]. 

Formation of low molecular weight products from oxidation of N-methylpyrroIe is most successfully achieved with methanol and sodium cyanide as electrolyte. Tire radical-cation is captured by cyanide ion and 2-cyanopyrroles are formed in good yields when a 2-position in the substrate is vacant. In this reaction, a carbon-carbon bond is formed at the site of highest charge density. When both 2- and 5-positions are blocked by a methyl group, the intermediate radical-cation loses a proton to give the benzylic-type radical. Further reaction leads to cyanation on the 2-methyl group as in 61 [200]. 

As in purely thermal degradation, thermal oxidation of rubber is accompanied by formation of low-molecular-weight products in yields too high to be accounted for by random attack on the... 

The radical polymerization behavior of captodative olefins such as acrylonitriles, acrylates, and acrylamides a-substituted by an electron-donating substituent is reviewed, including the initiated and spontaneous radical homo- and copolymerizations and the radical polymerizations in the presence of Lewis acids. The formation of low-molecular weight products under some experimental conditions is also reviewed. The reactivity of these olefins is analyzed in the context of the captodative theory. In spite of the unusual stabilization of the captodative radical, the reactivity pattern of these olefins in polymerization does not differ significantly from the pattern observed for other 1,1-disubstituted olefins. Classical explanations such as steric effects and aggregation of monomers are sufficient to rationalize the observations described in the literature. The spontaneous polymerization of acrylates a-substituted by an ether, a thioether, or an acylamido group can be rationalized by the Bond-Forming Initiation theory. 

RO which form polymers with the formation of low-molecular weight products -polyreactive oligomers. 

The formation of low-molecular weight products of the a-amylase-cat-alyzed starch hydrolysis can be assayed by using a glucoamylase-GOD electrode (Pfeiffer et al., 1980). The sensor is covered by a dialysis membrane with a cutoff of 15 kDa which prevents starch from reaching the enzymes. The cleavage products can easily diffuse into the bienzyme membrane where they are successively degraded to glucose by glu-coamylase. As only the (B-anomer is formed, the sensitivity of the method... 

The rather non-conventional approach to radiation chemistry of polymers leads to conclusions which indicate that the role of multi-ionization spurs in radiation chemistry of polymers cannot be neglected. In spite of low participation of these spurs in radiolysis of low Z materials (ca 20% of total deposited energy), these spurs can explain formation of two basic, different types of crosslinks. Formation of low molecular weight products of radiolysis is also explained, as well as other phenomena. Application of spurs philosophy to polymers is also advantageous in explanation of energy transfer from single ionization spurs and lack of transfer from multi-ionization spurs. 

Low viscosity values of polymers may also be due to the presence of impurities in the dichloride of RMID. The presence of monochloro-derivative of RMID, if any, will terminate the polycondensation process prematurely leading to the formation of low molecular weight products. Although we have purified the dichloroderivative by repeated crystallization, the purity has not yet been checked by chromatographic methods. 

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