Procedures monomer polymerization

The free radical initiators are more suitable for the monomers having electron-withdrawing substituents directed to the ethylene nucleus. The monomers having electron-supplying groups can be polymerized better with the ionic initiators. The water solubility of the monomer is another important consideration. Highly water-soluble (relatively polar) monomers are not suitable for the emulsion polymerization process since most of the monomer polymerizes within the continuous medium, The detailed emulsion polymerization procedures for various monomers, including styrene [59-64], butadiene [61,63,64], vinyl acetate [62,64], vinyl chloride [62,64,65], alkyl acrylates [61-63,65], alkyl methacrylates [62,64], chloroprene [63], and isoprene [61,63] are available in the literature. 

Radical polymerization is the most useful method for a large-scale preparation of various kinds of vinyl polymers. More than 70 % of vinyl polymers (i. e. more than 50 % of all plastics) are produced by the radical polymerization process industrially, because this method has a large number of advantages arising from the characteristics of intermediate free-radicals for vinyl polymer synthesis beyond ionic and coordination polymerizations, e.g., high polymerization and copolymerization reactivities of many varieties of vinyl monomers, especially of the monomers with polar and unprotected functional groups, a simple procedure for polymerizations, excellent reproducibility of the polymerization reaction due to tolerance to impurities, facile prediction of the polymerization reactions from the accumulated data of the elementary reaction mechanisms and of the monomer structure-reactivity relationships, utilization of water as a reaction medium, and so on. 

The beauty of the Szwarc procedure is that the chains can be terminated by hydrolysis, oxidation, carboxylation with COz, and so on, to give polymer with the same kind of groups on each end of the chain. Also, it is possible to form chains in which different monomers are present in blocks. The only requirements are that the different monomers polymerize well by the anion mechanism and contain no groups or impurities that will destroy the active ends. Thus one can start with ethenylbenzene (S), and when the reaction is complete, add methyl 2-methylpropenoate (M) to obtain a block copolymer of the type... 

The procedures described in this unit all utilize a polyacrylamide gel matrix. The gel forms when a dissolved mixture of acrylamide and bisacrylamide cross-linker monomers polymerizes into long chains that are covalently cross-linked. The gel structure is held together... 

Polymerization Procedure. The polymerization apparatus consisted of a simple tube with two constrictions. The THF breakseal was attached between the two constrictions. The catalyst solution was prepared in a serum capped nitrogen purged bottle from weighed amounts of oxonium salt and methylene chloride. This solution was made up so that the final catalyst concentration was 3.25 X 10 3M, and the THF concentration was 7.6M (62.5% v/v THF). This insured a fluid mixture throughout the polymerization. Under these conditions the equilibrium conversion to polymer was 27.5%—i.e., the equilibrium monomer concentration of THF was 5.6M. 

The immunogenicity of some small proteins can be considerably enhanced by polymerization. This is illustrated by the case of cytochrome c polymers prepared with glutaraldehyde. Mammalian cytochromes c are only weakly immunogenic as monomers, and polymerization results in the production of potent immunogens. The procedure for polymerization of cytochrome c follows. 

Ring-Opening Polymerization. Monomer 2 Is phosphlnlte, an analogue of dexophostone according to the reported procedure (20). polymerization of 2 produced white powdery materials of poly(phosphlne oxl e ) whose structure was determined by IR, 31p, 1, and NMR spectroscopy as well as by elemental analysis. The polymerization results are given In Table II (21). 

ATRP allows the synthesis of di-block copolymers by sequential (one-pot) or separated steps (two-pot) methods (26). To synthesize di-block, tri-block, 3-and 4-arm star-block copolymers by the two-pot method, a typical ATRP procedure was performed. First, a homopolymer was synthesized as mentioned above and then this was used as a macroinitiator. In addition to the two-pot procedure, one of the tri-block copolymers (P2 in Table 1) was also synthesized by the one-pot ATRP procedure. Once first monomer polymerized to complete conversion, the second monomer was added to the flask under nitrogen to obtain the block copolymers. In both cases, the samples were taken periodically via a syringe to follow the molecular weight of the polymer by GPC and the conversion of polymerization by GC measurements. 

A historical perspective on the development of hydrophobe-modified, water-soluble polymers is presented. The various synthetic procedures used to obtain different associative thickeners are discussed in terms of the complexities in ionogenic monomer polymerizations. This discussion serves two purposes. The first is to present the peculiarities in anionic and cationic polymer synthesis in contiguity with previous work on water-soluble polymers that related only to their use. The second purpose is to draw parallels between the discontinuities in the classical chain-growth polymerization of nonionic with ionogenic monomers and those that should be expected to occur with hydrophobe-modified monomers, but for which there are insufficient data in associative thickener technology to define properly. 

Procedures. The polymerization of IB was carried out at -40 °C in DCM using the following concentrations [BCl3]=0.103 M, [IB]=0.938 M, [DTBP]=0.003 M. After complete monomer conversion (14 h) DCM and Hex were added to obtain the DCM/Hex (60/40 v/v) solvent mixture and the desired concentrations for capping. The temperature was lowered to -80 C, followed by the addition of TiCU (6.4 x 10 M) and DPE (8.0 x 10" M) both from a stock solution in Hex. Large excess of silyl ketene acetal (silyl ketene acetal/PIB 34) was used in the subsequent fimctionalization. After the desired reaction time, the reaction mixture was quenched with prechilled methanol. The polymers were purified by repeated precipitation from a Hex solution into methanol, followed by drying in vacuum. 

The publication by Chiang et al. [1] led to a huge surge in interest in synthetic metals. In less than a decade, most of the monomer building blocks that we know today had been identified and many procedures for polymeric synthesis had been established. The chemical structures are illustrated in Figure 1.1. (In the nomenclature used in Figure 1.1, polyacetylene would be called polyvinylene. This is because some - common - names derive from the compound that is polymerized, while others, more correctly according to lUPAC conventions, use the monomeric unit in the product polymer.)... 

Along these lines of thinking block copolymers of styrene and 6-[4-(4-methoxyphenyl)phenoxy]hexylmethacrylate (MPPHM) were synthesized by anionic polymerization. Styrene was polymerized first in benzene using 5-BuLi as the initiator. After completion of polymerization the living PSIi chains were end-capped with diphenylethylene and the solvent was changed to THE Anhydrous liCl was introduced to the reactor, and the temperature was lowered to - 40 °C. At that temperature a solution of purified MPPHM in THE was introduced slowly. After complete reaction of the liquid crystalline monomer, polymerization was terminated with methanol . The procedure is outlined schematically in Scheme 9. 

Another example of ionic graft copolymerization is a reaction carried out on pendant olefinic groups using Ziegler-Natta catalysts in a coordinated anionic-type polymerization. The procedure consists of two steps. In the first, diethylaluminum hydride is added across the double bonds. In the second the product is treated with a transition metal halide. This yields an active catalyst for polymerizations of a-olefms. By this method polyethylene and polypropylene can be grafted to butadiene styrene copolymers. Propylene monomer polymerization results in formations of isotactic polymeric branches ... 

Besides seed and feed procedures, batch polymerizations with a free monomer phase are also very popular. In these so-called ab initio polymerizations, water, emulsifier and monomer are charged into the reactor and allowed thermally to equilibrate under gentle stirring. Then, the polymerization is started by adding initiator. The stirrer speed is, compared to suspension polymerization, only of minor importance as both the final particle sizes and particle properties are not governed by the... 

If polymerization is carried out in the gas phase in the presence of heated metal surfaces, then even such unlikely monomers as hexachlorobutadiene can be polymerized to films on the metal surface. In this process, chlorine, among other products, is produced, and the chlorine/carbon ratio rises to 1 2. Therefore, the product cannot contain the same monomeric unit as the monomer. In a procedurally similar polymerization of tetrafluoroethylene, for example, CF3 groups were found in the polymer. 

Polymer separation procedure. The polymerization is stopped by quenching with HCl aqueous solution (5M, 5mL) and then precipitated with MeOH (300 mL). The resulting red precipitate is then filtered into a Soxhlet thimble. Soxhlet extractions are performed with methanol (to remove monomer and salts), hexane (to remove catalyst and oligomers), and chloroform. Yield 0.12g (72%), M = 9300, 1.1. 

Polymerization Procedure. All polymerizations were conducted in one ounce bottles under an argon atmosphere either in bulk or using benzene as a solvent to minimize chain transfer reactions. A typical reaction mixture contained 10 ml benzene that had been distilled from CaH2, copper octanoate (0.1 g, 2.86 x lO mole), pyridine (0.5g), triphenylphosphine (0.3g, 1.14 x 10 mole), triethylamine (O.lg, 1 x 10 mole), monomer (- 5 ml) and aldehyde-functional polydimethylsiloxane (0.4 - 2.34 g, 3.1 x lO" mole of aldehyde groups). After being heated at 70 C for 21 hr., the reaction mixtures were cooled to room temperature, diluted with benzene, and added to methanol to pre-... 

Using the CTC equilibrium constants (table in the appendix to this chapter) it is possible to calculate the true reactivity values for the CTC and for the neutral monomer. Raetzsch and coworkers used this procedure for the cyclopentene-MA and norbornene-MA copolymerizations with acrylonitrile (Table 10.23). The same technique was also used to determine the reactivity constants for several other donor-acceptor-neutral monomer polymerizations (Table 10.23). For the NVP-MA-methyl methacrylate system the true reactivity ratios show the NVP-MA CTC is about 3 000 times the reactivity of NVP and 600 times the reactivity of methyl methacrylate toward the propagating radical ending in methyl methylacrylate.Results of this type support the concept of alternating copolymerization of a CTC with neutral monomer. 

Radical photojK lymerization of vinyl monomers played an important role in the early development of polymerization. One of the first procedures for polymerizing vinyl monomers was the exposure of monomer to sunlight. Blyth and Hoffmaim [5] reported the polymerization of styrene by sunlight more than 150 years ago. 

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