Reaction chains quantitative treatment

Cage effects tend to decrease the efficiency of utilization of free radicals produced for the initiation of chain reactions. A quantitative treatment appears in sight but will not be discussed here. 

The quantitative treatment of terpolymerization is more complex than two-component copolymerization though the method is similar. In the copolymerization of three monomers Mi, M2, and M3 there are three different types of growing chain ends aam/Mi, mwM2 , and wwMa. Each of these can react with any of the three monomers of the system, and hence there are nine different chain propagation reactions, as shown below ... 

Regardless of the type of polymerization reaction, quantitative treatments are usually based on the assumption that the reactivity of the functional group at a chain end is independent of the length of the chain, x and y in Equations 8.1a and 8.1Z). Experimentally, this is an excellent assumption for x s greater than five or six. Since most polymers must develop x s on the order of a hundred (or much greater) to be of practical value, this... 

From a practical standpoint, most copolymers are made by free-radical addition polymerization, although step-growth polymerization can also be used. For the sake of simplicity in our discussion, we will focus only on the free-radical meehanism A quantitative treatment of random copolymerization is based on the assumption that the reactivity of a growing chain depends only on its active terminal unit. Therefore, when two monomers, Mj and M2, are copolymerized, there are four possible propagation reactions ... 

Reaction with solvent - The solvent influences the course of cationic reactions not only through its dielectric constant, but also because many substances used as solvents are far from inert in these reactions [22, 23]. Although much more experimental material is required before a full treatment of the subject becomes possible, at least one example, the cationic polymerisation of styrene in toluene, is amenable to quantitative discussion. Experiment shows that polymerisation is rapid and complete, the molecular weight is low and the polymer contains para-substituted rings which are almost certainly tolyl endgroups [22]. Theoretically, a polystyryl carbonium ion can react with toluene in six different ways, only two of which (a.l and b. 1 below) can lead to tolyl endgroups in the first case the tolyl group is at the end of the terminated chain, in the second it is the start of a new chain. The alternative reactions can be represented as follows... 

It is highly unlikely that the reactivities of the various monomers would be such as to yield either block or alternating copolymes. The quantitative dependence of copolymer composition on monomer reactivities has been described [Korshak et al., 1976 Mackey et al., 1978 Russell et al., 1981]. The treatment is the same as that described in Chap. 6 for chain copolymerization (Secs. 6-2 and 6-5). The overall composition of the copolymer obtained in a step polymerization will almost always be the same as the composition of the monomer mixture since these reactions are carried out to essentially 100% conversion (a necessity for obtaining high-molecular-weight polymer). Further, for step copolymerizations of monomer mixtures such as in Eq. 2-192 one often observes the formation of random copolymers. This occurs either because there are no differences in the reactivities of the various monomers or the polymerization proceeds under reaction conditions where there is extensive interchange (Sec. 2-7c). The use of only one diacid or one diamine would produce a variation on the copolymer structure with either R = R" or R = R " [Jackson and Morris, 1988]. 

The reaction protocol was further extended to the concise synthesis of poly-oxamic acid, the unique polyhydroxyamino acid side-chain moiety of the antifungal polyoxin antibiotics (63). Treatment of the template 205 under standard thermal cycloaddition conditions with (5)-glyceraldehyde acetonide led to the formation of a single diastereoisomer 208 in 53% yield. Subsequent template removal released polyoxamic acid 209 in essentially quantitative yield. This represents a matched system, with the mismatched system leading to more complex reaction mixtures (Scheme 3.70). 

E. Therapeutic response Efficacy of Infergen therapy was determined by measurement of serum alanine aminotransferase (ALT) concentrations at the end of therapy (24 weeks) and following 24 weeks of observation after the end of treatment of adults with chronic HCV infection. Serum HCV RNA was also assessed using a quantitative reverse transcriptase polymerase chain reaction (RT-PCR). At the end of 24 weeks of treatment, ALT normalization was observed in 39% of patients on Infergen and in 35% of patients on interferon alfa-2b Intron A). Only 17% of patients in each group... 

The versatile selenenylating agent N-(phenylseleno)phthalimide (NPSP) is an effective carbocyclization mediator, which is capable of effecting acid catalyzed cyclization reactions from open-chain olefins, including the formation of cyclopropanes1. This is demonstrated by the quantitative cyclization of 3-butenyltrimethyltin to (cyclopropyl-methylseleno)benzene upon treatment with 1.1 equivalents of NPSP in CH2C12 at 25 °C under acid (e.g. p-TsOH) catalysis (equation 47). 

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