Intermolecular chain propagation

Following the findings of Butler et al. [5], that diallyl quaternary ammonium halides form water soluble polymers, the structures of polymers produced via a ring-closing mechanism have been the subject of intensive research. A cyclic structure was elucidated and the mechanism was defined as an alternating intra-intermolecular chain propagation, later termed cyclopolymerization [3]. Based on the general scheme presented in Fig. 6 the chemical structure of PDADMAC is determined by... 

In other words, in the polymer obtained from a solution in which twice the monomer concentration is equal to rc, the structural units are 50 cyclic and 50 °/° unsaturated in the competition between intra- and intermolecular chain propagation there is no winner. 

Difference between intra- and intermolecular chain propagation reactions. 

The hypotheses considered so far share the attempt of explaining the ease of formation of the ring structures in cyclopolymerization taking into account only the relative ability of the double bond pendant from the active chain end, and of the double bonds of an unreacted monomer molecule, to reach the reaction site. No attention is paid to the fact that the intramolecular and intermolecular chain propagation reactions are basically different, in the sense that the former involves an entropy decrease due to the loss of some rotational degrees of freedom at the end of the active chain, whereas the latter involves an entropy decrease... 

Calculation of ASn. The situation is particularly simple (JjB) in the case of the intermolecular chain propagation reactions, generally represented in the following scheme ... 

The radical polymerization of acrylic anhydride(AA) as a typical 1,6-diene has been investigated in detail in terms of cyclopolymerization. Thus, in 1958 Crawshaw and Butler(31) and Jones(32) have independently demonstrated that AA could be polymerized in solution by an alternating intramolecular-intermolecular chain propagation or cyclopolymerization, leading to the formation of saturated, linear polymers consisting exclusively of six-membered ring anhydride structure. Later, Mercier and Smets(33)... 

S(conj) is the decrement of the molar entropy of the monomer due to conjugation effects which are lost in the reaction a is the symmetry number of the monomer molecule and v is the number of optical isomers which can be formed in the reaction. For the intermolecular chain propagation reaction occurring in the free radical polymerization of DPHD the following values must be used ... 

Intermolecular chain transfer reactions may occur between two propagating polymer chains and result in the termination of one of the chains. Alternatively, these reactions take place by an intramolecular reaction by the coiling of a long chain. Intramolecular chain transfer normally results in short branches ... 

The obtained value of a indicates the proximity of the rate constant values of the addition of TBSM to the macroradicals MA and of MA to TBSM This can be explained by a similar influence of intermolecular coordination on chain propagation. The values of pt and p2 indicate that in free-radical copolymerization of TBSM with MA both free and complex-bound monomers are involved in chain propagation with a higher contribution of the latter. 

A molecule of linear alkyl ether possesses a very convenient geometry for intramolecular hydrogen atom abstraction by the peroxyl radical. Therefore, chain propagation is performed by two ways in oxidized ethers intermolecular and intramolecular. As a result, two peroxides as primary intermediates are formed from ether due to oxidation, namely, hydroperoxide and dihydroperoxide [62],... 

Electroreductive one-electron initiation of cyclization was described for the series of E,E-, 1-dibenzoyl-l,6-heptadiene and its derivatives (Roh et al. 2002, Felton and Bauld 2004). In this case, the catalytic effect was also observed (the actual consumption of electricity was substantially less than theoretical). The same bis(enones) can also be cyclized on the action of the sodium salt of chrysene anion-radical in THF, but with no catalytic effect. Optimum yields were obtained only when 70-120 mol% of the initiator was used, relative to a substrate (Yang et al. 2004). The authors suggest that tight ion pairing of the sodium cation with the product anion-radical in THF (which is a somewhat nonpolar solvent) slows down the intermolecular electron transfer to the bis(enone) molecules. Such an electron transfer would be required for chain propagation. 

Let us compare the competition of intermolecular and intramolecular chain propagations in oxidized dibenzyl ether. The rate constant A p(R02 + RH) = 95 L mol-1s-1 (T = 303 K, Table... 

In the oxidation of octan-2-one, undecan-4-one, 1,3-diphenylacetone, and 2-phenylacetophenone, different ratios of intermolecular and intramolecular chain propagation are proposed to lie behind the varying distribution of products, CO2, CO, H2, hydroperoxides, and acids a mechanism involving a-keto hydroperoxides was proposed.227... 

The disproportionation reaction of the free radical chain can generate the monomer as a successive process. There are, however, some other issues regarding the propagation for free radical chain reactions. In addition to the "regular" propagation step, different reactions may occur in a so-called transfer step. In this step, the free radical chain reacts with another molecule and generates a different radical chain and a new polymeric molecule. There are two possible types of transfer reactions. The transfer step can be an intermolecular chain transfer or an intramolecular chain transfer. An example of an intermolecular chain transfer is... 

After the radical formation, intermolecular chain transfer reactions take place. A special case of chain transfer is the propagation reaction (see Section 2.1) of the type ... 

---