Aqueous solution polymerization

Manufacturing processes have been improved by use of on-line computer control and statistical process control leading to more uniform final products. Production methods now include inverse (water-in-oil) suspension polymerization, inverse emulsion polymerization, and continuous aqueous solution polymerization on moving belts. Conventional azo, peroxy, redox, and gamma-ray initiators are used in batch and continuous processes. Recent patents describe processes for preparing transparent and stable microlatexes by inverse microemulsion polymerization. New methods have also been described for reducing residual acrylamide monomer in finished products. 

Glass-Transition Temperature. The T of PVP is sensitive to residual moisture (75) and unreacted monomer. It is even sensitive to how the polymer was prepared, suggesting that MWD, branching, and cross-linking may play a part (76). Polymers presumably with the same molecular weight prepared by bulk polymerization exhibit lower T s compared to samples prepared by aqueous solution polymerization, lending credence to an example, in this case, of branching caused by chain-transfer to monomer. 

Polyborates and pH Behavior. Whereas bode acid is essentiaHy monomeric ia dilute aqueous solutions, polymeric species may form at concentrations above 0.1 M. The conjugate base of bode acid in aqueous systems is the tetrahydroxyborate [15390-83-7] anion sometimes caHed the metaborate anion, B(OH) 4. This species is also the principal anion in solutions of alkaH metal (1 1) borates such as sodium metaborate,... 

Several articles [7,8] have reported that a persulfate-amine system, particularly persulfate-triethanol amine and persulfate-tetramethylethylenediamine (TMEDA) can be used as redox initiators in aqueous solution polymerization of vinyl monomers. Recently, we studied the effect of various amines on the AAM aqueous solution polymerization and found that not only tertiary amine but also secondary and even primary aliphatic amine and their polyamines can promote the vinyl polymerization as shown in Table 6 [40-42]. 

In the polymerization of acrylic monomers by bulk, suspension, or in organic solution, the most common initiators are diacyl peroxide (e.g., dibenzoyl peroxide supplied as a paste in water) or azo compounds (e.g., 2,2 -azobisisobutyronitrile). For emulsion or aqueous solution polymerizations, sodium persulfate by itself or in combination with bisulfites or a host of other reducing agents may be used. 

In aqueous solutions, polymerization and depolymerization processes are slow under normal conditions. This, in addition to the analytical difficulties in discriminating between different degrees of polymerization,... 

Under steady-state conditions, Equations 5-7 can be reduced to yield the overall rate equation of the APS initiated aqueous solution polymerization of DADMAC [10] ... 

Hydrogen cyanide condenses at 25.6°C to a liquid with a very high dielectric constant (107 at 25°C). Here, as in similar cases, such as water, the high dielectric constant is due to association of intrinsically very polar molecules by hydrogen bonding. Liquid HCN is unstable and can polymerize violently in the absence of stabilizers in aqueous solutions polymerization is induced by ultraviolet light. 

Polycarbobetaines derived from aromatic or heteroaromatic systems are listed in Scheme 3. The vinylimidazolium betaines 13 and 14 were prepared by alkylation of 1-vinyhmidazole with the corresponding bromocarboxylic acid, and aqueous solution polymerization using an azo initiator [29]. Polymers 13b, 15, 16, and 17b were made by the addition of acryUc or propiolic acid to poly(4-vinylpyridine) and poly(N-vinylimidazole). Kinetic measurements revealed a mechanism consisting of two reactions first, addition of two molecules of acid to the polymer second, the formation of an equilibrium between the adduct and the betaine structure [30,31]. 

Once photochemically formed in the early atmosphere via reactions (1), (2), (11), and (12), HhCO, being very water soluble, rained out of the atmosphere. In the early oceans, H2CO accumulated and eventually underwent aqueous solution polymerization reactions leading to the abiotic synthesis of organic molecules of increasing complexity (Pinto et al., 1980). 

In aqueous solution polymerization a water-soluble monomer is polymerized to a water-soluble polymer. For example, polyacryUc acid is produced on a large scale by free radical techniques in this manner [10]. Again, fhe non-flammabiUty and high heat capacity of water are advantageous. Such polymerizations in homogeneous solution can, in some cases, offer better molecular weight control by comparison to polymerization in a multiphase system. 

Protactinium as 231Pa occurs in pitchblende, but even the-richest-ores contain only about 1 part of Pa in 107. The isolation of protactinium from residues in the extraction of uranium from its minerals is difficult, as indeed is the study of protactinium chemistry generally, owing to the" extreme tendency of the compounds to hydrolyze. In aqueous solution, polymeric ionic species and colloidal particles are formed, and these are carried on precipitates and adsorbed on vessels in solutions other than those containing appreciable amounts of mineral acids or complexing agents or ions such as F , the difficulties are almost insuperable. 

Early examples of the precipitation approach include the aqueous solution polymerizations reported by Chaimberg et al. [53] for the graft polymerization of polyvinylpyrrolidone onto silica. The nonporous silica particles were modified with vinyltriethoxysilane in xylene, isolated and dispersed in an aqueous solution of vinylpyrrolidone. The reaction was performed at 70°C and initiated by hydrogen peroxide, after which precipitation on the surface occurred, leading to encapsulation. Nagai et al. [54] in 1989 reported on the aqueous polymerization of the quaternary salt of dimethylaminoethyl methacrylate with lauryl bromide, a surface-active monomer, on silica gel. Although the aim was to polymerize only on the surface, separate latex particles were also formed. 

Interval I Particle Nucleation.—Piirma and Chang have published some very interesting results for the emulsion polymerization of styrene in the presence of an ethylene oxide-fatty alcohol condensate as surfactant. As expected, the rate of polymerization increases with increasing concentration of surfactant, but the unexpected feature is a pronounced increase in the rate of polymerization which always occurs at ca. 40% conversion. This increase is attributed to the nucleation of a new crop of particles following the release into the aqueous phase of surfactant, which was hitherto dissolved in the monomer droplets. It certainly seems to be significant that the pronounced acceleration of the polymerization occurs at approximately the conversion at which the monomer droplets are expected to disappear. Chen and Piirma have proposed that mixed micelles formed by hydrophobic association between surfactant monomer molecules and oligomers formed by aqueous-solution polymerization can provide significant numbers of loci... 

An obvious difference between bulk and aqueous solution polymerization is the higher molecular weight of polymers synthesized in water. In general, it has to be noted that the rate of polymerization is proportional to the square root of the AIBN concentration. Using a viscometric technique for kinetic studies of the polymerization of NVP, Bond and Lee [499] have confirmed the observation of Breitenbach and Schmidt [488,489] that the degree of polymerization of PVP is not influenced significantly by the concentration of initiator or by the reaction temperature. Beside AIBN, dialkylperoxides such as tert-butyl(2,2-dimethylpropanoyl)peroxide [502] or peroxodiphosphate-Ag [503] are employed as initiators for the polymerization of NVP in aqueous or aqueous/alcohol solutions. 

Aqueous Solution Polymerization with Potassium Sulfite. 212... 

During polymerization in acidified aqueous solution, however, partial hydrolysis of the monomer takes place to produce appreciable quantities of acetaldehyde [1]. This is one reason for carrying out aqueous solution polymerizations of this monomer in the presence of a slightly basic buffer. 

As supplied by the manufacturer, monomeric A/-vinylpyrrolidone is normally inhibited with 0.1% flake sodium hydroxide [24]. This inhibitor may be separated by decantation or filtration. An alternative inhibition system involves the use of gaseous ammonia or organic amines. These inhibitors are said not to interfere with the polymerization process and, in fact, may activate it [25]. This activation by ammonia is not entirely surprising. As will be discussed in Section 3B ( Aqueous Solution Polymerization ), aqueous ammonia has been known as an activator in aqueous systems for many years [1]. Certain impurities which have a distinctly inhibitory effect on the polymerization of A-vinylpyrrolidone are y-butyric acid and y-butyrolactone [26]. 

One of the early patents for the polymerization of AT-vinylpyrrolidone discloses sodium (or potassium) sulfite as polymerization initiators. The aqueous solution polymerization process is carried out in neutral or basic media in order to avoid acetaldehyde formation by decomposition of the monomer. In the more usual oxidative initiation, this may also lead to acetic acid generation. In the more generally used procedures, careful buffering of the reaction medium is usual. 

Aqueous Solution Polymerization of A -Vinylpyrrolidone to High Conversions at 50 C [53]... 

Since N-vinylpyrrolidone is soluble in a great variety of solvents, its polymerization need not be confined to aqueous systems. However, interest in aqueous solution polymerization processes has been so overwhelming that few literature references deal with organic solvent systems as an alternative. 

The initiators used in aqueous solution polymerizations of the acrylic acids usually are the water-soluble initiators commonly used in emulsion polymerization, such as persulfate, percarbonate, and perphosphate salts. Monomer-soluble initiators have also been used, usually at sufficiently low concentrations or in the presence of water-soluble solvents to form a homogeneous system. 

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