Alternating polymerization

An alternative polymerization process utilizes a slurry of calcium chloride in NMP as the polymerization medium. The solubiHty of calcium chloride is only 6% at 20°C however, the salt continues to dissolve as conversion of monomers to polymer proceeds and calcium chloride/polyamide complexes are formed. Polymer molecular weight is further increased by the addition of /V, /V- dim ethyl a n i1 in e as an acid acceptor. This solvent system produces fiber-forming polymer of molecular weights comparable to that formed in HMPA/NMP. 

Strong evidence for the radical cation-radical cation coupling mechanism shown in Scheme 1 has been obtained from double-step chronoam-perometry studies.66,67 However, an alternative polymerization mechanism, involving the coupling of radical cations with unoxidized molecules, has been claimed by a number of authors.55,68,69 Some of the... 

Consider alternative polymerization processes in solid state, inducing the polymerization reaction of N3P3CI6 thermally [40-42],photochemically [61, 67,68],y-radiolytically [66,210], using X-rays [74,75,90] or electron irra-... 

Intercalation This occurs when the polymer is intercalated in the dispersed material. This phenomenon results in alternated polymeric chains within the nanometric material. 

Isomeric polymers can also be obtained from a single monomer if there is more than one polymerization route. The head-to-head placement that can occur in the polymerization of a vinyl monomer is isomeric with the normal head-to-tail placement (see structures III and IV in Sec. 3-2a). Isomerization during carbocation polymerization is another instance whereby isomeric structures can be formed (Sec. 5-2b). Monomers with two polymerizable groups can yield isomeric polymers if one or the other of the two alternate polymerization routes is favored. Examples of this type of isomerism are the 1,2- and 1,4-polymers from 1,3-dienes (Secs. 3-14f and 8-10), the separate polymerizations of the alkene and carbonyl double bonds in ketene and acrolein (Sec. 5-7a), and the synthesis of linear or cyclized polymers from non-conjugated dienes (Sec. 6-6b). The different examples of constitutional isomerism are important to note from the practical viewpoint, since the isomeric polymers usually differ considerably in their properties. 

An alternative polymerization mechanism and polymer architecture has been proposed by Kirchhoff [1, 2, 3], Tan and Arnold [77], By this mechanism, polybenzocyclobutenes which do not contain reactive sites of unsaturation are proposed to polymerize by the 1,4 addition of the o-quinodimethane intermediates to give a substantially linear poly(o-xylylene) structure. Since the monomers all contain at least two benzocyclobutene units the net result of this reaction will to a first approximation be a ladder type polymer as shown in Fig. 17. The formation of a true ladder polymer however would require that all... 

Among the alternative polymerization schemes, the approach involving acyl imidazolides is quite unique. Although, imidazolides are generally sufficiently... 

The last terms in Equation 18 express the fact that new reactive chain end —(Mi) .i — M. is formed by the reversible alternating polymerization step... 

Thus, Equation 27 is in this case a possible distribution function. It is of the type of the Schulz-Flory (25) distribution function. The expressions p and chain termination). The validity of the Schulz-Flory distribution function in this example of a polymerization with reversible propagation steps is evident. This type of distribution is always present if the distribution of the chain lengths... 

We are at present beginning to investigate in more detail, as an alternative, polymeric materials as possible CW agent coatings for the optical waveguide system. Among their advantages over dyes, are... 

Size enlargement of fine particles in liquid suspension can be accomplished in a number of ways. Electrolytes can be added to a suspension to cause a reduction in zeta potential and allow colliding particles to cohere. Examples include the use of trivalent aluminum and iron ions to flocculate the particles responsible for the turbidity of many water supplies and the flocculation of metallurgical slimes by pH adjustment to the isoelectric point. Alternatively, polymeric flocculants can be added to suspensions to bridge between the particles. A wide range of such polymeric agents [1] is available today to aid the removal of fine particles from water. 

Polymerizations of vinyl ethers initiated by HI/I2 in hexane are zero order in monomer, but first order in monomer in more polar solvents. Several groups [177-179] have proposed that this zero-order dependence is due to monomer complexing with iodine. Alternatively, polymerization will be zero order in monomer if ionization is the rate-determining step, followed by faster addition of monomer to carbenium ions [180]. In this case, the concentration of monomer will not affect the polymerization rate. 

There are now alternative polymeric film-forming materials that achieve low e values without the need for fluorine substitution, e.g. crosslinked... 

While all of these results are far from providing commercial products, they highlight the possibilities for alternative polymerization chemistries in miniemulsions. 

Several alternative polymerization media have been proposed for reducing the amount of unstable end groups in poly(tetrafluoroethylene). These include chlorofluorocarbons, which are detrimental to the environment, perfluoro-carbons, hydrofluorocarbons, and perfluoroalkyl sulfide acids, which are all expensive. Supercritical carbon dioxide has been identified as a viable alternative to aqueous and fluorocarbon reaction media [31]. Further more, mixing... 

Although Gorham process is the most popular method of parylene polymerization, there are reports of at least two other polymerization schemes for parylenes. Figure 3 shows the different polymerization schemes used for CVP of parylene thin films. However, in this paper, only the Gorham process will be discussed, the details of alternate polymerization schemes can be found elsewhere. ... 

Two general strategies are possible for the synthesis of star-shaped copolymers The arm-first method is based on the reaction of living chains with plurifunctional electrophiles carrying at least three reacting groups alternatively, polymerization can be initiated by a multifunctional initiator according to the core-first method. 

Synthetic polymers can be prepared to contain chirality as is the case for cellulose and other natural polymers. Chirality can be introduced into the monomer before polymerization to yield the chiral polymer. Alternatively polymerization of an achiral monomer in the presence of some chiral catalyst yields the chiral polymer. Polymethacrylates exhibiting chirality due to single-handed helicity have been prepared via polymerization in the presence of a chiral catalyst. These materials are used in liquid chromatography primarily under low-pressure conditions and have shown good resolution for compounds capable of hydrogen-bond formation. 

Alternative polymerization methods, such as suspension polymerization, dispersion polymerization, and microbead production, have been shown to produce spherical particles of a determined size however, their use is limited. Finally, the production of monohthic polymeric imprinted materials is a straightforward method of producing MIP rods inside a stainless steel or a PEEK column however, this method still needs to provide further evidence of enhanced selectivity and molecular recognition. 

LUMO, namely the Z-substituted olefin (383)—and so on, as the polymerization proceeds. This explanation for alternating polymerization avoids the vague terms, such as "polar factors , which have often been used in the past. 

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