Unbranched Chain Reactions in Solids and in Viscous Media: Nontraditional Methods and Analysis

A. M. KAPLAN1 and N. I. CHEKUNAEV2

:N.N. Semenov’s Institute of Chemical Physics, Russian Academy of Sciences, Russian Federation, E-mail: This email address is being protected from spam bots, you need Javascript enabled to view it

2Kosygin Street 4, Moscow 119991, Russian Federation

DEFINITION

On the example of the radiation-induced post-polymerization reaction of crystalline acrylonitrile (AN), it was first discovered the effect of continuation of the chain reaction after its termination at a specific temperature Tv This effect was not consistent with traditional views. The continuation of such reaction was obseived at the temperature Tl + 15K. This effect was called the phenomenon of "congealing” and “reanimation” of polymer chains in the solid state (phenomenon). Later, this phenomenon was obseived repeatedly in the study of solid-phase polymerization of other monomers and unbranched chain reactions in solids (UChSR).

An original kinetic model was proposed, which could explain the marked phenomenon and other nontrivial kinetic features of UChSR.

In 1975, an unconventional method of implementing an effective radiation- induced radical post-polymerization was proposed - the method consisted in slowly heating of an y-irradiated at 77K monomer without any additives from the temperature T = T - (10 15)K to Г = 300K. T is the glass transition

temperature of the studied monomer. It was shown that the proposed method provided the conditions for the continued growth of the polymer chains in the absence of their termination. Thus, on the example of post-polymerization of butyl methacrylate (BMA) was first discovered living radical polymerization (LRP) at temperatures T> T to produce polymers with improved properties.

HISTORICAL ORIGIN AND SCIENTIFIC DEVELOPMENT

The introduction in the chemical science of the authors’ concept has been dictated by the necessity of an explanation of polymer chains “congealing” and “reanimation” during the AN post-polymerization (PP) (Kaplan Anatoly, 1996).

Kinetics of post-radiation polymerization of AN at T= 143K and T = 156K

FIGURE 42.1 Kinetics of post-radiation polymerization of AN at T= 143K and T = 156K. The points (•) mark the polymer yield (q) in AN specimens placed into thermostat with T = 156K after holding the specimens during 20 h at T= 143K.

On a proposal by Kaplan Anatoly an original experiment was carried out: з'-irradiated at 77K AN sample was initially kept at T = 143K for 20 hours, which is enough time to reach the limit of the polymer yield (q = 3.0 ± 0.4%). Then, after a fast transfer of the AN sample from the thermostat with Tl = 143K into thermostat with T2 = 156K researchers continued the process observation. Polymerization at T = 156K was resumed (see dark points (•) in Figure 42.1). In this process, there was an increase of the polymer yield up to the new limit (q = 5.0 ± 0.4%). According to traditional views reaching the limit yield of AN PP (q = 3.0 ± 0.4%) at 143K should be considered as a result of the doom of polymerization active centers. But without the active centers, the chain polymerization is not possible (see Gimblett, 1970).

Several approaches to the qualitative explanation of the mentioned phenomenon are discussed in Chapter 23.

The most clear explanation of the phenomenon and others non-trivia! kinetic particularities (NTKP) of unbranched chain reactions in solids and viscous media on the quantitative level was given in 2008. This became possible taking into account the formation offriable zones (FZs) near nanodefects with an excess of free volume in solids. It was shown that only in FZs the steric hindrances to the chemical interaction of CAC with neighboring particles reagents are removed.

Proper accounting of the concentration evolution of mentioned FZs in the studied systems allowed to explain the nontrivial kinetic features of UChSR on the example of the solid phase polymerization (SP) of different monomers (Kaplan & Chekunaev, 2012).

 
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