Effect on polymerization rate

High pressure can have appreciable effects on polymerization rates and polymer molecular weights. Increased pressure usually results in increased polymerization rates and molecular weights. Figure 3-17 shows these effects for the radiation-initiated polymerization of styrene [Moore et al., 1977]. 

Diffusion-Controlled Free Radical Polymerization - Effect on Polymerization Rate and Molecular Properties of PVC , Abstracts - Third International Symposium on PVC, Case Western Reserve University, Cleveland, August 10-15 (1980). 

Figure 4. (top) Effect on polymerization rate of solutions at 60° C. (bottom) Adsorption isotherms at 20° C on PVAc latex. 

In their work, Dow researchers tested five soluble organic acids (acetic, benzoic, pyruvic, and phenylphosphonic acids, in addition to CSA) having a variety of acid strengths (Figure 7.8) [14]. The effects on polymerization rate and Mw (140 °C/2h) were not significant for the weaker acids (pATa> 2). CSA, the strongest acid available that did not initiate cationic polymerization, had the most impact on the results and was selected as the catalyst for further study. 

Since chain transfer stops growing chain, it always results in a lower molecular weight than would occur in its absence. The effect of chain transfer on the rate of polymerization varies, however, and depends on the relative rates of the transfer [Eq. (6.135)] and reinitiation [Eq. (6.136)] compared to that of the normal propagation reaction [Eq. (6.6d)]. Several possible situations that may be encountered are sumniarized in Table 6.8. These are all instances of chain transfer, but they are usually given different names, as shown, depending on the net effects on polymerization rate and molecular weight. 

Process name Characteristics Effect on polymerization rate Effect on Polymer molecular weight... 

Neglecting initiator mass, [SJbenzene == (830g — 200g)/(78 g mol" ) = 8.08 molL. Assuming that chain transfer has no effect on polymerization rate, Eq. (6.33) can be used. Using relevant data and p = 0.5, this equation gives... 

This assumption is valid for transfer to most species, and can be verified by examining whether addition of the transfer agent has an effect on polymerization rate. 

While PTC has become a powerful tool for the synthetic organic chemist, it has also had tremendous Impact in the field of polymer science. Numerous examples of polymer modification and functionalization reactions employing phase transfer catalysts have been described. Even more striking, however, has been the role of PTC in actual anionic polymerization reactions, where dramatic effects on polymerization rates, yields, and microstructure can be attributed to the catalyst. Condensation poly merizations have also been facilitated in the presence of phase transfer catalysts. Only recently we reported the first examples of phase transfer initiated free radical polymerization.The present article will detail the features of phase transfer free radical polymerizations and will also describe some of the characteristics of the polymers formed. 

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