Polymerization in the presence of water

Polymers are also used as sutures. Fighters and other athletes have used poly(alpha-cyanoacrylates), super glues, to quickly stop blood flow in surface cuts. Today, super glue is also used for, in place of or along with, more traditional polymeric suture threads for selected surface wounds, internal surgery, and retinal and corneal surgery. The alpha-cyanoacrylate polymers (structure 19.22) undergo anionic polymerization in the presence of water. More about sutures is explained in Section 19.6. 

In most cases, di- and trifunctional reagents will polymerize in the presence of water forming linear (for difunctional) and branched alkoxysilanes (for trifunctional modihers). Trace amounts of water are always present on the surface of polar silica. 

Although the possibility of carrying out catalytic polymerizations in the presence of water had been known since the 1960s, significant advances in catalytic polymerizations in aqueous systems have only been achieved over the past decade. Today, (1) various different types of transition metal-catalyzed polymerizations can be carried out efficiently in aqueous systems. (2) A variety of polymers, ranging from hydrocarbons to water-soluble polymers, and a scope of polymer architectures are accessible. (3) Polymerization can be carried out in a controlled fashion. 

Vinyl acetate homopolymers are simply-made adhesive bases manufactured by addition polymerization in the presence of water and stabilizers. They are made commercially by the batch reactor process or by the Loop reactor continuous process. External plasticizers such as dibutyl phthalate are often added to confer flexibility and to lower the temperature at which they form a film on drying. Higher-quality products may be made by the copolymerization of ethylene with vinyl acetate to form an EVA. This involves the safe handling of ethylene gas under high pressure, and the plant required is more complex and considerably more costly. The Loop process has considerable attraction in the field of pressure polymerization. 

The simplest monomers to polymerize anionicaUy are probably alkylcyanoacry-lates, as they are highly reactive and can be polymerized in the presence of water. Moreover, the polymers produced have been shown capable of traversing... 

Surely, five- and six-membered lactams are much more reactive in the anionically initiated mechanism (Section 4.14.7.1), where a nucleophilic attack on the laaam ring is implied, as compared to the polymerization in the presence of water or acids, involving an electrophilic attack and proceeding at a significantly lower rate. 

The fourth and most interesting of the polymerization techniques we shall consider is called emulsion polymerization. It is important to distinguish between suspension and emulsion polymerization, since there is a superficial resemblance between the two and their terminology has potential for confusion A suspension of oil drops in water is called an emulsion. Water-insoluble monomers are used in the emulsion process also, and the polymerization is carried out in the presence of water however, the following significant differences also exist ... 

The boric and sulfuric acids are recycled to a HBF solution by reaction with CaF2. As a strong acid, fluoroboric acid is frequently used as an acid catalyst, eg, in synthesizing mixed polyol esters (29). This process provides an inexpensive route to confectioner s hard-butter compositions which are substitutes for cocoa butter in chocolate candies (see Chocolate and cocoa). Epichlorohydrin is polymerized in the presence of HBF for eventual conversion to polyglycidyl ethers (30) (see Chlorohydrins). A more concentrated solution, 61—71% HBF, catalyzes the addition of CO and water to olefins under pressure to form neo acids (31) (see Carboxylic acids). 

Friedel-Crafts (Lewis) acids have been shown to be much more effective in the initiation of cationic polymerization when in the presence of a cocatalyst such as water, alkyl haUdes, and protic acids. Virtually all feedstocks used in the synthesis of hydrocarbon resins contain at least traces of water, which serves as a cocatalyst. The accepted mechanism for the activation of boron trifluoride in the presence of water is shown in equation 1 (10). Other Lewis acids are activated by similar mechanisms. In a more general sense, water may be replaced by any appropriate electron-donating species (eg, ether, alcohol, alkyl haUde) to generate a cationic intermediate and a Lewis acid complex counterion. 

Propiophenone. Propiophenone [93-55-0] (ethyl phenyl ketone) is a colorless Hquid with a flowery odor. It can be prepared by the Friedel-Crafts reaction of benzene and propionyl chloride in the presence of aluminum chloride (346), or by the catalytic reaction of benzoic acid and propionic acid in the presence of water (347). Propiophenone is commercially available (348), and is sold in Japan at 2700 Y/kg (349). It is used in the production of ephedrine, as a fragrance enhancer, and as a polymerization sensitizer. 

At the same time, however, considerable research was being done, especially in Germany, on a novel process called emulsion polymerization, in which the monomer was polymerized as an emulsion in the presence of water and soap. This seemed advantageous since the product appeared as a latex, just like natural mbber, leading to low viscosity even at high soHds content, while the presence of the water assured better temperature control. The final result, based mainly on work at the LG. Farbenindustrie (IGF) (10), was the development of a butadiene—styrene copolymer prepared by emulsion polymerization, the foremnner of the present-day leading synthetic mbber, SBR. 

The above data were obtained on a polymeric bonded phase and not a brush phase. The so-called brush phases are made from monochloro-sxlants, (or other active group) and, thus, the derivative takes the form of chains attached to the silica surface [2]. The bulk phases are synthesized from polyfunctional silanes in the presence of water and, thus, are cross linked and form a rigid polymeric structure covering the silica surface. These two types of phases behave very differently at low concentrations of moderator. 

Possible impurities of the tertiary amine include primary and secondary amines. The presence of aniline slows the reaction, while the presence of A-methylaniline actually accelerates the polymerization [51]. As the secondary amine may be formed during polymerization (especially in the presence of water) reaction kinetics may be complicated. 

Chemical Reactivity - Reactivity with Water No reaction Reactivity with Common Materials No reactions Stability During Transport Stable Neutralizing Agentsfor Acids and Caustics Not pertinent Polymerization Polymerizes in the presence of acids and caustics Inhibitor of Polymerization Not pertinent. 

A macroporous polystyrene-divinylbenzene copolymer is produced by a suspension polymerization of a mixture of monomers in the presence of water as a precipitant. This is substantially immiscible with the monomer mixture but is solubilized with a monomer mixture by micelle-forming mechanisms in the presence of the surfactant sodium bis(2-ethylhexylsulfosuccinate) (22). The porosity of percentage void volume of macroporous resin particles is related to percentage weight of the composite (50% precipitant, 50% solvent) in the monomer mixture. 

The steady-state polymerization in the presence of Cr (it-CsHb) was first order with respect to the monomer concentration (125) the effective activation energy was 4.7 0.5 kcal/mole. When the concentration of Crfir-CaHs was varied, first a linear rise of the polymerization rate occurred with an increase of tris-ir-allylchromium concentration to the upper limit then the rate does not depend on Crfx-CaHs concentration (126). The value of the upper limit of the polymerization rate increased with an increase in the water content of the solvent used. 

With stannous octoate-promoted polymerization, the metal species is believed to function as the catalyst and water (added or endogenous), or alcohol, serves as the initiator (Fig. 2). This mechanism is supported by recent kinetic studies of PCL polymerization in the presence of triphenyltin acetate (46). After an induction period, polymerization is zero order with respect to monomer and near first... 

As described above, the enzymatic polymerization of phenols was often carried out in a mixture of a water-miscible organic solvent and a buffer. By adding 2,6-di-0-methyl-(3-cyclodextrin (DM-(3-CD), the enzymatic polymerization of water-insoluble m-substituted phenols proceeded in buffer. The water-soluble complex of the monomer and DM-(3-CD was formed and was polymerized by HRP to give a soluble polymer. In the case of phenol, the polymerization took place in the presence of 2,6-di-O-methyl-a-cyclodextrin (DM-a-CD) in a buffer. Only a catalytic amount of DM-a-CD was necessary to induce the polymerization efficiently. Coniferyl alcohol was oxidatively polymerized in the presence of a-CD in an aqueous solution. ... 

The concept of extractive reaction, which was conceived over 40 years ago, has connections with acid hydrolysis of pentosans in an aqueous medium to give furfural, which readily polymerizes in the presence of an acid. The use of a water-immiscible solvent, such as tetralin allows the labile furfural to be extracted and thus prevents polymerization, increases the yield, and improves the recovery procedures. In the recent past an interesting and useful method has been suggested by Rivalier et al. (1995) for acid-catalysed dehydration of hexoses to 5-hydroxy methyl furfural. Here, a new solid-liquid-liquid extractor reactor has been suggested with zeolites in protonic form like H-Y-faujasite, H-mordenite, H-beta, and H-ZSM-5, in suspension in the aqueous phase and with simultaneous extraction of the intermediate product with a solvent, like methyl Aobutyl ketone, circulating countercurrently. 

Polyethylene terephthalate also has the tendency, because it is produced by a condensation polymerization process, to depolymerize under high pressure and temperatures in the presence of water. Although this is usually a negative attribute, it can be utilized to regenerate pure monomers which can be repolymerized to make fresh polymer. This avoids the issues experienced by reprocessing resins, as the new resin has not experienced a previous heat history. A major drawback to this process is the requirement that the monomers used in polymerization processes must be highly pure, Unfortunately, this process is extremely costly and not performed on a commercial scale. 

When ethylene is reacted at 573 K in the presence of water in static conditions, oligomerization and conjunct polymerization give rise to paraffinic, olefinic and aromatic products (8). Nevertheless, the distribution of the aliphatics and aromatics is quite different from that of the steam-cracking products. In the former a great variety of products is formed they include propane, n-butane, isobutane and isopentane as aliphatics, and toluene, xylenes and ethylbenzene as aromatics (Figure 6B). 

We have repeatedly reported that a coexistense of water is indispensable for the uncatalyzed polymerization. Also in the present cases of PVPA and PSS-Na, the polymerization of MMA proceeded only in the presence of water, as shown in Fig. 1. 

HTE liquid polymers were synthesized by cationic ring-opening polymerization of epichlorohydrin (ECH) in the presence of water or ethylene glycol (EG) as a modifier (1). Cyclic oligomers were removed by extraction. After extraction, the liquid polymers were essentially free from cyclic oligomers as determined by gel permeation chromatography (GPC) (Figure 1). 

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