Continuous Radical Polymerization

HIPS resin with both a high gloss and a high impact strength have been produced using a special in situ polymerization process. A bimodal distribution of the elastomer particles and particular size range and morphology type is maintained (8). 

A continuous bulk polymerization process with three reaction zones in series has been developed. The degree of polymerization increases from the first reactor to the third reactor. Examples of suitable reactors include continuous stirred tank reactors, stirred tower reactors, axially segregated horizontal reactors, and pipe reactors with static mixers. The continuous stirred tank reactor type is advantageous, because it allows for precise independent control of the residence time in a given reactor by adjusting the level in a given reactor. Thus, the residence time of the polymer mixtures can be independently adjusted and optimized in each of the reactors in series (8). 

Styrene monomer and a styrene/butadiene copolymer are fed to the first reaction zone. The polymerization is initiated either thermally or chemically. Many chemical initiators are available such as ferf-butyl peroxybenzoate and ferf-butyl peracetate. Conditions are established to prevent a phase inversion or the formation of discrete rubber particles in the first reaction zone. The conversion in the first reaction zone should be 5-12%. An important function of the first reaction zone is to provide an opportunity for grafting of the styrene monomer to the elastomer (8). 

Redox initiators have been proposed. The initiation system is composed from iron sulfate, dibenzoyl peroxide, and a reductant. Of the latter, hydroxyacetone, 2-hydroxy-2-phenylacetophenone, ascorbic palmitate, and toluene sulfinic acid are among the most economical. The reaction conditions are such that the cyclic oxida- 

Suitable chain transfer agents are ethylbenzene, a-methylstyrene and dodecylmercaptan and most preferred 4-(l-methyl-l-ethylid-ene)-l-methyl-l-cyclohexene, commonly known as terpinolene. 

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Bayer T., Pysall, D., Wachsen, O., Micro mixing effects in continuous radical polymerization, in Ehreeld, W. (Ed.),... 

Radical polymerization, including the question of the dependence of chain termination rate constant on the length of the macroradical chain, the possibility for continuous radical polymerization to be achieved through the complexing and stabilization of free radicals and of catalytic chain transfer in radical polymerization. 

Bayer T, Pysall D, Wachsen O (2000) Micro mixing effects in continuous radical polymerization. In Ehrfeld W (ed) Proceedings 3rd international conference on microreaction technology. Springer, Berlin, pp 165-170... 

One of the key benefits of anionic PS is that it contains much lower levels of residual styrene monomer than free-radical PS (167). This is because free-radical polymerization processes only operate at 60—80% styrene conversion, whereas anionic processes operate at >99% styrene conversion. Removal of unreacted styrene monomer from free-radical PS is accompHshed using continuous devolatilization at high temperature (220—260°C) and vacuum. This process leaves about 200—800 ppm of styrene monomer in the product. Taking the styrene to a lower level requires special devolatilization procedures such as steam stripping (168). 

In conventional radical polymerization, the chain length distribution of propagating species is broad and new short chains are formed continually by initiation. As has been stated above, the population balance means that, termination, most frequently, involves the reaction of a shorter, more mobile, chain with a longer, less mobile, chain. In living radical polymerizations, the chain lengths of most propagating species are similar (i.e. i j) and increase with conversion. Ideally, in ATRP and NMP no new chains are fonned. In practice,... 

The kinetics and mechanism of living radical polymerization have been reviewed by Fischer,21 Fukuda et at.,22 and Goto and Fuktida.23 In conventional radical polymerization, new chains are continually formed through initiation w hile existing chains are destroyed by radical-radical termination. The steady state concentration of propagating radicals is 10"7 M and an individual chain will have a lifetime of only 1-10 s before termination within a total reaction lime that is... 

Many block and graft copolymer syntheses involving transformation reactions have been described. These involve preparation of polymeric species by a mechanism that leaves a terminal functionality that allows polymerization to be continued by another mechanism. Such processes are discussed in Section 7.6.2 for cases where one of the steps involves conventional radical polymerization. In this section, we consider cases where at least one of the steps involves living radical polymerization. Numerous examples of converting a preformed end-functional polymer to a macroinitiator for NMP or ATRP or a macro-RAFT agent have been reported.554 The overall process, when it involves RAFT polymerization, is shown in Scheme 9.60. 

IT Duerksen, J.H., "Free Radical Polymerization of Styrene in Continuous Stirred Tank Reactors", Ph.D. Thesis, McMaster University, Hamilton, Ontario (1968). 

In this short initial communication we wish to describe a general purpose continuous-flow stirred-tank reactor (CSTR) system which incorporates a digital computer for supervisory control purposes and which has been constructed for use with radical and other polymerization processes. The performance of the system has been tested by attempting to control the MWD of the product from free-radically initiated solution polymerizations of methyl methacrylate (MMA) using oscillatory feed-forward control strategies for the reagent feeds. This reaction has been selected for study because of the ease of experimentation which it affords and because the theoretical aspects of the control of MWD in radical polymerizations has attracted much attention in the scientific literature. 

Continuous-flow stirred tank reactors are widely used for free-radical polymerizations. They have two main advantages the solvent or monomer can be boiled to remove the heat of polymerization, and fairly narrow molecular weight and copolymer composition distributions can be achieved. Stirred tanks or... 

Addition of phosphonyl radicals onto alkenes or alkynes has been known since the sixties [14]. Nevertheless, because of the interest in organic synthesis and in the initiation of free radical polymerizations [15], the modes of generation of phosphonyl radicals [16] and their addition rate constants onto alkenes [9,12,17] has continued to be intensively studied over the last decade. Narasaka et al. [18] and Romakhin et al. [19] showed that phosphonyl radicals, generated either in the presence of manganese salts or anodically, add to alkenes with good yields. 

Radical polymerizations have three important reaction steps in common chain initiation, chain propagation, and chain termination. For the termination of chain radicals several mechanisms are possible. Since the lifetime of a radical is usually less than 1 s, radicals are continuously generated and terminated. Each propagating radical can add a finite number of monomers between its initiation and termination. If a divinyl monomer is in the monomer mixture, the reaction kinetics changes drastically. In this case, a dead polymer chain may grow again as a macroradical, when its pendant vinyl groups react with radicals, and the size of the macromolecule increases until it extends over the whole available volume. 

Iwasaki T, Kawano N, Yoshida Y-I (2006) Radical polymerization using micro flow system. Numbering-up of microreactors and continuous operation. Org Proc Res Dev 10 1126-1131... 

Polymer in situ gels, 9 75 Polymerization, 12 188. See also Bulk continuous polymerization Polymers Radical polymerization ABS, 1 419-123 acetaldehyde, 1 103 acetylene, 1 181 acrolein, 1 279 acrylamide, 1 311 acrylic ester monomers, 1 375-386 acrylic esters, 1 342 of acrylonitrile, 11 197-204... 

J. Alvarez, R. Suarez, and A. Sanchez. Nonlinear decoupling control of free radical polymerization continuous stirred tank reactors. Chem. Enq. Sci., 45 3341-3354, 1990. 

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