Free-Radical Polymerization of Styrene

Step 1 Polymerization of styrene usually employs a peroxide as an initiator. The peroxide dissociates on heating to produce two alkoxy radicals. 

Step 2 The free radical produced in step 1 adds to the double bond of styrene. Addition occurs in the direction that produces a benzylic radical. 

Step 4 The radical produced in step 3 reacts with another styrene molecule, and the process repeats over and over to produce a long-chain polymer having phenyl substituents at every other carbon in the chain. 

Willstatter s most important work, for which he won the 1915 Nobel Prize in Chemistry, was directed toward determining the structure of chlorophyll. 

Step 3 The benzylic radical produced in step 2 adds to a molecule of styrene. Again addition occurs in the direction that 

A polymer may be formed by hundreds, thousands, or even tens of thousands of monomeric units. This material can also be present in natural form, for example, cellulose and rubber. The characteristics of these macromolecules depend on the monomer, chain length, and composition of the mixture. The mechanism and kinetics have been presented. We present the free radical polymerization of styrene (solution polymerization) as an example. 

This type of polymerization is quite simple. We used as an example, an experiment from an organic mixture of benzene and styrene with azobisisobutyronitrile (AIBN). AIBN is the reaction initiator, which undergoes a thermal dissociation to form free radicals. 

Problem Determine the conversion of polymerization reaction solution (styrene/ benzene) to different concentrations of initiator ([/] = 0.07 0.03 O.Olmol/L) with styrene concentration [M] = 4 mol/L. Determine also the conversion from three different concentrations of monomer, [M] = 6 3 1 mol/L with [7] = 0.03 mol/L. Use the temperature at 50°C. 

The product is washed with methanol and dried at 60°C for 4h (or longer). The influence of temperature on the density can be neglected. 

Plot a graph X and t and determine the reaction rates for different conditions in the proposed experiment. Use Equation 25.1  

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Section 1117 Polystyrene is a widely used vinyl polymer prepared by the free radical polymerization of styrene... 

There are two problems in the manufacture of PS removal of the heat of polymeriza tion (ca 700 kj /kg (300 Btu/lb)) of styrene polymerized and the simultaneous handling of a partially converted polymer symp with a viscosity of ca 10 mPa(=cP). The latter problem strongly aggravates the former. A wide variety of solutions to these problems have been reported for the four mechanisms described earlier, ie, free radical, anionic, cationic, and Ziegler, several processes can be used. Table 6 summarizes the processes which have been used to implement each mechanism for Hquid-phase systems. Free-radical polymerization of styrenic systems, primarily in solution, is of principal commercial interest. Details of suspension processes, which are declining in importance, are available (208,209), as are descriptions of emulsion processes (210) and summaries of the historical development of styrene polymerization processes (208,211,212). 

Water is extensively used to produce emulsion polymers with a sodium stearate emulsifrer. The emulsion concentration should allow micelles of large surface areas to form. The micelles absorb the monomer molecules activated by an initiator (such as a sulfate ion radical 80 4 ). X-ray and light scattering techniques show that the micelles start to increase in size by absorbing the macromolecules. For example, in the free radical polymerization of styrene, the micelles increased to 250 times their original size. 

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

SINs. Two SIN compositions were studied, one having 10% oil prepolymer and the other 20% oil prepolymer, both dissolved in the styrene-DVB monomer solution. During the synthesis several morphological changes occurred in the mixture. Early in the reaction all components formed a mutual clear solution which was slightly yellow due to the original color of the prepolymer. As the free radical polymerization of styrene began, the polystyrene first produced remained soluble. At a critical concentration, phase separation... 

Benoit D, Grimaldi S, Robin S et al. (2000) Kinetics and mechanism of controlled free-radical polymerization of styrene and n-butyl acrylate in the presence of an acyclic beta-phosphonylated nitroxide. J Am Chem Soc 122 5929-5939... 

Taylor in 1925 demonstrated that hydrogen atoms generated by the mercury sensitized photodecomposition of hydrogen gas add to ethylene to form ethyl radicals, which were proposed to react with H2 to give the observed ethane and another hydrogen atom. Evidence that polymerization could occur by free radical reactions was found by Taylor and Jones in 1930, by the observation that ethyl radicals formed by the gas phase pyrolysis of diethylmercury or tetraethyllead initiated the polymerization of ethylene, and this process was extended to the solution phase by Cramer. The mechanism of equation (37) (with participation by a third body) was presented for the reaction, - which is in accord with current views, and the mechanism of equation (38) was shown for disproportionation. Staudinger in 1932 wrote a mechanism for free radical polymerization of styrene,but just as did Rice and Rice (equation 32), showed the radical attack on the most substituted carbon (anti-Markovnikov attack). The correct orientation was shown by Flory in 1937. In 1935, O.K. Rice and Sickman reported that ethylene polymerization was also induced by methyl radicals generated from thermolysis of azomethane. 

Styrene and its derivatives can be polymerized by all possible propagation mechanisms. Free-radical polymerization, however, is the primary process for industrial production of polystyrene. Free-radical polymerization of styrene can be carried out without chemical initiators simply by heating the monomer.223,224 On heating, isomeric 1-phenyltetralins are formed in the Diels-Alder... 

In connection with the cause of the field influences on the cationic homopolymerization, it is interesting to study how free radical polymerizations are affected by an electric field. Table 1 shows that both the polymer yield and the degree of polymerization were not affected at all by the field, though the intensity was much higher than that applied to cationic systems. The situation was the same for free radical polymerizations of styrene by benzoylperoxide (72), and of methyl methacrylate by benzoylperoxide and azobisisobutyronitiile (77). 

Free radical polymerization of styrene, of acrylate and of methacrylate monomers in solutions at 60° C in the presence of this preformed polymer produced graft copolymers in high efficiency, the chain transfer constants for these mercapto groups with styrene and methyl methacrylate being similar to those found with simple mercaptans (80, 85). 

Singh A, Ma D, Kaplan DL (2000) Enzyme-mediated free radical polymerization of styrene. 

They also tested (10) Case II for the free radical polymerization of styrene (Mi) and methyl methacrylate at 132°C. by the dilution technique. These data are also shown in Table I, where the good agreement between theory and experiment is apparent. The applicability of the theory to different mechanisms of polymerization is a nice verification of the statement that the composition is governed by end-state thermodynamics rather than by mechanism. 

Main-chain poly(styrene rotaxane)s <1997MM337, 1999PLM1823> were obtained by free radical polymerization of styrene in the presence of crown ethers using initiators incorporating bulky blocking groups to prevent dethreading of the macrocyclic components. 

TABLE 2. Effect on the free radical polymerization of styrene in the presence of the free radical regulator, 7,7,9,9- tetramethyl-8-[l-(4-oxlranyhnethoxy-phenyl)-ethoxy]-l,4-dioxa-8-aza-spiro-[4.5]decan. 

Figure 6.2-26 Near-infrared absorbance spectra, recorded during free-radical polymerization of styrene at 40 °C and 2000 bar (the arrows indicate the direction of the absorbance change with the reaction time).

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