Molecular weight formation

Much has been written about the way in which the polymerization should be conducted. One finds references to dianhydride purification by complexing it with anisole [20, 23] or forming solid ingots of the dianhydride to insure high molecular weight formation just to name a few [24], Although some of this... 

In the Miiller-Calandra model for noncontinuous growth on a porous surface, the limiting condition in a potentiodynamic experiment is the resistance of the solution within the pores. The following parameters rise up for a 0.999 of surface coverage (0) for the growth of a PM (molecular weight) formation ... 

The condensation reaction between the metal salt and the diyne is catalyzed by Cu(I) salts and is usually carried out using amines such as di-ethylamine as solvents under reflux conditions. As in all condensation reactions the important criterion that allows high-molecular-weight formation is the purity of the monomers. Soluble polymers with high-molecular-weights ( 10 ) were isolated using this protocol. 

Of special interest is the behavior of l,l,3,3-tetramethyl-l,3-disilapentene as shown in Table 15. The formation of l,l,3,3-tetramethyl-l,3-disilacyclopentane is attributed to a simple hydrogenation. Apart from unidentified compounds of higher molecular weight, formation of 1,3,5,7-tetrasilaadamantane as well as 2,2,4,4,6,6,8,8-octa-methyl-2,4,6,8-tetrasilabicyclo[3.3.0]oct-l(5)ene should be emphasized. 

Oxidation first produces soluble oxygenated compounds of molecular weights between 500 and 3000 that increase the viscosity of oil then they polymerize, precipitate, and form deposits. Oxidation also causes formation of low molecular weight organic acids which are very corrosive to metals. 

The type of behavior shown by the ethanol-water system reaches an extreme in the case of higher-molecular-weight solutes of the polar-nonpolar type, such as, soaps and detergents [91]. As illustrated in Fig. Ul-9e, the decrease in surface tension now takes place at very low concentrations sometimes showing a point of abrupt change in slope in a y/C plot [92]. The surface tension becomes essentially constant beyond a certain concentration identified with micelle formation (see Section XIII-5). The lines in Fig. III-9e are fits to Eq. III-57. The authors combined this analysis with the Gibbs equation (Section III-SB) to obtain the surface excess of surfactant and an alcohol cosurfactant. 

It is important that the solution of the sodium salt be faintly acid in order that the formation of coloured by-products in the subsequent reaction may be prevented. If the molecular weight of the monobasic acid is known, it is desirable to employ a slight excess of the sodium salt, since excess of the latter is more easily removed than the unchanged reagent. 

Dimerization in concentrated sulfuric acid occurs mainly with those alkenes that form tertiary carbocations In some cases reaction conditions can be developed that favor the formation of higher molecular weight polymers Because these reactions proceed by way of carbocation intermediates the process is referred to as cationic polymerization We made special mention m Section 5 1 of the enormous volume of ethylene and propene production in the petrochemical industry The accompanying box summarizes the principal uses of these alkenes Most of the ethylene is converted to polyethylene, a high molecular weight polymer of ethylene Polyethylene cannot be prepared by cationic polymerization but is the simplest example of a polymer that is produced on a large scale by free radical polymerization... 

Amines have odd numbered molecular weights which helps identify them by mass spectrometry Fragmentation tends to be controlled by the formation of a nitrogen stabilized cation... 

The addition polymerization of a vinyl monomer CH2=CHX involves three distinctly different steps. First, the reactive center must be initiated by a suitable reaction to produce a free radical or an anion or cation reaction site. Next, this reactive entity adds consecutive monomer units to propagate the polymer chain. Finally, the active site is capped off, terminating the polymer formation. If one assumes that the polymer produced is truly a high molecular weight substance, the lack of uniformity at the two ends of the chain—arising in one case from the initiation, and in the other from the termination-can be neglected. Accordingly, the overall reaction can be written... 

It is apparent from Eq. (6.66) that p 1 as v hence those same conditions which favor the formation of a high molecular weight polymer also indicate p values close to unity. 

In any application of a copolymer the rate of formation of the product, its molecular weight, and the uniformity of its composition during manufacture are also important considerations. While the composition of a copolymer depends only on the relative rates of the various propagation steps, the rate of formation and the molecular weight depend on the initiation and termination rates as well. We shall not discuss these points in any detail, but merely indicate that the situation parallels the presentation of these items for homopolymers as given in Chap. 6. The following can be shown ... 

When -xylene is used as the monomer feed in a plasma polymer process, PX may play an important role in the formation of the plasma polymer. The plasma polymer from -xylene closely resembles the Gorham process polymer in the infrared, although its spectmm contains evidence for minor amounts of nonlinear, branched, and cross-linked chains as well. Furthermore, its solubiUty and low softening temperature suggest a material of very low molecular weight (15). 

The first quantitative model, which appeared in 1971, also accounted for possible charge-transfer complex formation (45). Deviation from the terminal model for bulk polymerization was shown to be due to antepenultimate effects (46). Mote recent work with numerical computation and C-nmr spectroscopy data on SAN sequence distributions indicates that the penultimate model is the most appropriate for bulk SAN copolymerization (47,48). A kinetic model for azeotropic SAN copolymerization in toluene has been developed that successfully predicts conversion, rate, and average molecular weight for conversions up to 50% (49). 

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