Initiated Processes

Cationically Initiated Processes.—In 1976 the 4th International Symposium on Cationic Polymerization focused attention on many aspects of this field of study including cationically initiated copolymerization reactions and the proceedings have been published in full.  

In general one might expect cationic copolymerizations to conform to the same general pattern as that observed in the statistically random free-radically initiated copolymerizations. Ham has presented the thesis that the reactivity of monomers in cationic copolymerizations is correlatable with Alfrey-Price e 

Many papers relate to the cationic polymerization of acrolein but the unambiguous estimation of this has not been made. Copolymerization of acrolein with styrene initiated by BFjOEt at - 78 °C produces a copolymer, which by n.m.r. analysis contains a large proportion of acrolein incorporated into the copolymer through aldehyde addition (92%). Kinetic equations have been proposed to describe the cationic copolymerization of 1,3-dioxolane with formaldehyde.  

Co-ordination Processes.— The general field of co-ordination polymerization has been reviewed. Hirai examines the relationship between the structure and reactivity of metal complexes in co-ordination polymerization and Yamamoto and Yamamoto give particular attention to transition-metal alkyls and hydrides as catalysts. Oligomerization is the main concern of Reichert.  

The measured values of the reactivity ratios for copolymerization reactions involving olefins (particularly those with four or more carbon atoms) where polymerization has been initiated by co-ordination catalysts has been examined by Kissin. In general there is a tendency for block formation to take place and the distribution of monomer units in the copolymers is in general accord with 

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Solvent Preparation. The most critical aspect of the solvent is that it must be dry (less than 0.02 wt % of H2O) and free of O2. If the H2O content is above 0.02 wt %, then the reaction of Mg and RX does not initiate, except for an extremely reactive RX species, such as benzyl bromide. Although adventitious O2 does not retard the initiation process, the O2 reacts with the Grignard reagent to form a RMg02X species. Furthermore, upon hydrolysis, the oxidized Grignard reagent forms a ROH species that may cause purification problems. 

One characteristic of chain reactions is that frequentiy some initiating process is required. In hydrocarbon oxidations radicals must be introduced and to be self-sustained, some source of radicals must be produced in a chain-branching step. Moreover, new radicals must be suppHed at a rate sufficient to replace those lost by chain termination. In hydrocarbon oxidation, this usually involves the hydroperoxide cycle (eqs. 1—5). 

Other nonpolymeric radical-initiated processes include oxidation, autoxidation of hydrocarbons, chlorination, bromination, and other additions to double bonds. The same types of initiators are generally used for initiating polymerization and nonpolymerization reactions. Radical reactions are extensively discussed in the chemical Hterature (3—15). 

Two secondary propagating reactions often accompany the initial peroxide decomposition radical-induced decompositions and -scission reactions. Both reactions affect the reactivity and efficiency of the initiation process. Peroxydicarbonates and hydroperoxides are particularly susceptible to radical-induced decompositions. In radical-induced decomposition, a radical in the system reacts with undecomposed peroxide, eg ... 

With transition-metal activators, the initiation process is postulated as ... 

Moist iodine vapor rapidly corrodes metals, including most stainless steels. The initial process is the formation of corrosion centers where small amounts of metal iodide are formed which deHquesce, and the corrosion then takes place electrochemically (41,42). Only titanium and molybdenum steels are unattacked by iodine (42,43). The corrosion of molten iodine has also been studied. 

Contraction of muscle follows an increase of Ca " in the muscle cell as a result of nerve stimulation. This initiates processes which cause the proteins myosin and actin to be drawn together making the cell shorter and thicker. The return of the Ca " to its storage site, the sarcoplasmic reticulum, by an active pump mechanism allows the contracted muscle to relax (27). Calcium ion, also a factor in the release of acetylcholine on stimulation of nerve cells, influences the permeabiUty of cell membranes activates enzymes, such as adenosine triphosphatase (ATPase), Hpase, and some proteolytic enzymes and facihtates intestinal absorption of vitamin B 2 [68-19-9] (28). 

Metabolic Functions. The formation of phosphate esters is the essential initial process in carbohydrate metaboHsm (see Carbohydrates). The glycolytic, ie, anaerobic or Embden-Meyerhof pathway comprises a series of nine such esters. The phosphogluconate pathway, starting with glucose, comprises a succession of 12 phosphate esters. 

A protonic acid derived from a suitable or desired anion would seem to be an ideal initiator, especially if the desired end product is a poly(tetramethylene oxide) glycol. There are, however, a number of drawbacks. The protonated THF, ie, the secondary oxonium ion, is less reactive than the propagating tertiary oxonium ion. This results in a slow initiation process. Also, in the case of several of the readily available acids, eg, CF SO H, FSO H, HCIO4, and H2SO4, there is an ion—ester equiUbrium with the counterion, which further reduces the concentration of the much more reactive ionic species. The reaction is illustrated for CF SO counterion as follows ... 

Ha.logena.tion, Chlorine can be added to sulfolane by a uv-initiated process to give 3-chlorosulfolane [3844-04-0] 3,4-dichlorosulfolane... 

This synthesis method can be utilised by any alkene or alkyne, but steric hindrance on internal double bonds can cause these reactions to be quite slow. Conjugated dienes and aromatic alkenes are not suited for the ultraviolet light-initiated process. The use of other free-radical initiators is required in free-radical-initiated reactions involving these species. 

Chlorine atoms obtained from the dissociation of chlorine molecules by thermal, photochemical, or chemically initiated processes react with a methane molecule to form hydrogen chloride and a methyl-free radical. The methyl radical reacts with an undissociated chlorine molecule to give methyl chloride and a new chlorine radical necessary to continue the reaction. Other more highly chlorinated products are formed in a similar manner. Chain terrnination may proceed by way of several of the examples cited in equations 6, 7, and 8. The initial radical-producing catalytic process is inhibited by oxygen to an extent that only a few ppm of oxygen can drastically decrease the reaction rate. In some commercial processes, small amounts of air are dehberately added to inhibit chlorination beyond the monochloro stage. 

Chemical Exposure Index (CEI) Chemical Exposure Index, 1994). The CEI provides a method of rating the relative potential of acute health hazard to people from possible chemical release incidents. It may be used for conducting the initial process hazard analysis and it establishes the degree of mrther analysis needed. The CEI also may be used as part of the site review process. 

For new facilities, the initial process hazard analysis (PHA) has been performed and recommendations have been resolved. ... 

To meet sales specifications, gas produced at the wellheads must be free of water and hydrocarbon liquids. Twin turboexpanders are a key component in this process, providing dewpoint control with optimal efficiency. Initial processing takes place at the wellhead platforms, where methanol is injected to inhibit hydrate formation. A corrosion inhibitor is also added to prevent gas from damaging downstream equipment. 

When considering the possibility of using internal combustion drivers, evaluate process requirements and costs. If a low-cost, gaseous fuel is available, gas engines and gas turbines may surpass other drivers in economical installation and operation. In the initial process design stage, a method of establishing the cost of purchase, installation, and operation for drivers is needed. 

An initial process hazard analysis (PrHA) is performed on the processes, appropriate to the complexity to identify, evaluate and control the hazards, Employers determine the pr conducting process hazard analyses based on a rationale which includes such consider extent of the ss hazards, number of potentially affected employees, age of the pro ... 

The employer establishes a system to promptly address the team s results, timely resolve recommendations, schedule completion, and communicate the activities to affected personnel, livery five years after the completion of the initial process hazard analysis, it is equivalently updated and revalidated. Employers retain the required process hazards analyses for the life of the nmei-v -.. 

The initial process for molecular conversion was thermal reforming (late 1920s). Thermal reforming at 950 - 1050 F and 600 psi produced gasolines of 70 to 80 octane and heavy naphthas less than 40 octane. Products were olefins, diolefins, and aromatic compounds that were unstable in storage and tended to form heavy polymers and gums, which caused combustion problems. 

Initial process safety management implementation usually focuses on your own production operations. However, there are a variety of related activities that teneht from similar approaches to safety. 

The quantum yield of the initiation process (<, ) is quite low 8 x 10, indicating the great stability of the chelate ring toward photolysis. However, the quantum yield of photodecomposition 4>d) under similar condition is 2 X 10, which is higher than It is clear, therefore, that not every molecule of Mn(acac)3 that is decomposed initiates polymerization apparently, ex-... 

Pitting corrosion always remains a worthy subject for study, particularly with reference to mechanism, and the problem conveniently divides into aspects of initiation and growth. For 6061 alloy in synthetic seawater, given sufficient time, pit initiation and growth will occur at potentials at or slightly above the repassivition potential . In an electrochemical study, it was found that chloride ions attack the passive layer as a chemical reaction partner so that the initiation process becomes one of cooperative chemical and electrochemical effects . 

It can be seen that for non-zero and positive values of p that Kobs < Ka (i.e., the potency of the overall process will be greater than the potency for the initial process). 

All of these initiation processes have one feature in common in each of them a stable X—M bond is formed on one end of a bifunctional monomeric unit, while a reactive center is created on the other end. Hence, as the addition of further monomeric units proceeds a polymeric species growing on one end only is produced, the other end being blocked by the stable X—M bond. 

Alkali metals are obvious examples of electron donors, and indeed polymerization of butadiene or styrene initiated by metallic sodium results from an electron transfer initiation process. This reaction has been, and is still, being studied by many investigators, notably by Ziegler55 and by Russian workers.1 In Ziegler s notation the initiation is represented by the equation... 

The red solution of polystyryl carbanions can be kept for days without change in color or viscosity. No changes are observed on addition of further amounts of naphthalene to the red solution. These observations raise some questions. An electron transfer, say for example, between naphthalene" and phenathrene, is a reversible process and it leads eventually to an equilibrium between naphthalene , naphthalene, phenathrene-, and phenanthrene. Is the reaction involving styrene irreversible Now, the initial process of electron transfer from naphthalene to styrene that produces... 

Yoshida, H. and Hayashi, K. Initiation Process of Radiation-induced Ionic Polymerization as Studied by Electron Spin Resonance. Vol. 6, pp. 401—420. 

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