Styrene polymerization initiator

In order to test this computer model, we conducted experiments on thermally Initiated styrene polymerization In sealed pressure vessels. We only measured pressures and temperatures In these experiments. We conducted our tests in two phases. 

In conclusion, we have reviewed how our kinetic model did simulate the experiments for the thermally-initiated styrene polymerization. The results of our kinetic model compared closely with some published isothermal experiments on thermally-initiated styrene and on styrene and MMA using initiators. These experiments and other modeling efforts have provided us with useful guidelines in analyzing more complex systems. With such modeling efforts, we can assess the hazards of a polymer reaction system at various tempera-atures and initiator concentrations by knowing certain physical, chemical and kinetic parameters. 

Difunctional initiators such as sodium naphthalene are useful for producing ABA, BABAB, CAB AC, and other symmetric block copolymers more efficiently by using fewer cycles of monomer additions. Difunctional initiators can also be prepared by reacting a diene such as /n-diisoprope ny I benzene or l,3-bis(l-phenylethenyl)benzene with 2 equiv of butyl-lithium. Monomer B is polymerized by a difunctional initiator followed by monomer A. A polymerizes at both ends of the B block to form an ABA triblock. BABAB or CABAC block copolymers are syntehsized by the addition of monomer B or C to the ABA living polymer. The use of a difunctional initiator is the only way to synthesize a MMA-styrene-MMA triblock polymer since MMA carbanion does not initiate styrene polymerization (except by using a coupling reaction—Sec. 5-4c). 

There is yet another general method to prepare random copolymer. As stated earlier, when one uses potassium, rubidium or cesium initiator, styrene polymerizes first, to give a S/B-B type of tapered block polymer. But when one mixes an alkyllithium with a potassium compound such as potassium t-butoxide, quite a different system is obtained. 

Monomers which can be polymerized with aromatic radical anions include styrenes, dienes, epoxides, and cyelosiloxares. Aromatic radical anions which are too stable do not efficiently initiate polymerization of less reactive monomers thus the anthracene radical anion cannot initiate styrene polymerization. 

The case of "living polystyrene and methyl methacrylate is somewhat similar. It was shown, as should be expected, that "living polymethyl methacrylate does not initiate styrene polymerization (70), i. e. methyl-methacrylate is a terminator for the latter polymerization, although its addition to living poly-styrene initiates its polymerization. Hence, one may produce a block polymer by adding methyl methacrylate to "living polystyrene but not vice-versa (9,10). 

Trityl (triphenylmethylium) and tropylium cations are two commercially available carbenium ions. They react with alkenes by either direct addition or by hydride abstraction tropylium ions are usually less reactive than trityl. As shown in Eq. (39), trityl ions initiate styrene polymerization by direct addition. 

In a persulfate initiated styrene polymerization, using sodium lauryl sulfate, (SLS), and Emulphogene BC-840, as the mixed surfactants, Kamath( ) and Wang(2.) found that the rate of polymerization increased rapidly with small increases in the ionic component, SLS. 

The data on initiated styrene polymerization were used in calculations. The reaction system was regarded as quasi-stationary from a hydrodynamic point of view, meaning that the flow velocity profiles instantaneously adjust themselves to variations of viscosity through temperature and conversion. 

The above examples show the complexity of the systems involving radical-anions derived from compounds of higher electron-affinity. It is not surprising, therefore, that benzophenone ketyl and other similar compounds do not initiate styrene polymerization, although they initiate polymerization of acrylonitrile or methyl-methacrylate. On the other hand, the monomeric dianions of benzophenone initiate polymerization of styrene as well as of other monomers, but not of vinyl chloride or acetate. Mechanisms of these initations were not investigated and presumably are complex. 

Over 200 references describing spontaneous, and chemically initiated styrene polymerization chemistry are reviewed with special emphasis on advances taking place in the past decade. The review is limited to chemistry useful for making amorphous high molecular weight polystyrene in solution polymerization processes. Chemical initiators have been categorized into three basic groups as follws 1) anionic 2) mono-radical and 3) diradical. Analytical techniques used for determination of free radical polymerization kinetics and mechanisms are also discussed. 

Over 40 years ago Schulz [103-105] attempted to initiate styrene polymerization with l,l,2,2-tetraphenyl-l,2-dicyanoethane (5). The point of his work was to prove that highly hindered C-C compounds could be used as FR initiators for vinyl polymerization. It was established that Sis consumed relatively quickly at 100 °C in styrene and that the polymer molecular wei t is inversely proportional to initiator concentration. 

Unsymmetrical azo compounds have also been used to initiate styrene polymerization. For example, Otsu et al. [145,14Q studied phenylazotriphenyl-methane as an initiator. They found that both a phenyl and a trityl radical are generated. The phenyl radical initiates polymerization while the trityl radical does not. Instead, the trityl radical acts as a radical trap and efficiently terminates polymerization by primary radical coupling (Scheme 11). As a result of steric crowding between the pendant groups on the polymer chain and the phenyl groups of the trityl moiety, the C-C bond can redissociate at elevated temaperature and add more monomer. This is another example of a living free radical polymerization. 

The cyclic perketal 33 initiates styrene polymerization but with very low efficiency [219]. The molecular weight of the PS produced was no higher than PS prepared at the same rate of polymerization using di-tcrt-butylperoxide. A... 

The ability of butadiene anions to initiate styrene polymerization, and vice versa, is... 

L.H. Garcia-Rubio, N. Ro, and R. D. Patel, Ultraviolet Analysis of Benzoyl Peroxide Initiated Styrene Polymerizations and Copolymerizations I. Macromolecules, (1984), 17, 1998-2005. 

Suspension polymerization processes were developed to solve the heat generation problems that occur in bulk polymerization and the volatile organic recycling problem that oeeurs in the solution processes. In a suspension process, a monomer/water mixmre is stirred to form a suspension of styrene monomer droplets with the aid of suspending agents or surfactants (i.e. surface active agents). When an organie soluble initiator such as a peroxide is added to the suspension, the peroxide diffuses into the monomer droplets and initiates styrene polymerization. 

Because strong Bronsted (proton) acids and Lewis acids can initiate styrene polymerization, other cationically polymerizable monomers can be added to the styrene-based copolymer list. Due to the facile occurrence of chain transfer processes of polymer chains with impurities, cationically prepared polystyrene-based polymers are low molecular weight materials. Nevertheless, low molecular weight polystyrenes still find important applications as additives, as tackifiers for pressure sensitive adhesives, and in hot melt adhesives. However, the market for low molecular weight polystyrene is small. 

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