Polymerization Distinguishing features

The distinguishing features of the polymerization and copolymerization to these interesting monomers have been described in a number of papers48 49 There are, however, no systematic investigations described in the literature to study the laws governing the reaction of AN copolymerization with quartemary salts of substituted vinyl pyridines. 

When precautions are taken to prepare and analyze the chloropolymer under stringently dry conditions, it is possible to study polymerization variables by this GPC technique. Chromatographs of three S2imples of the chloropolymer, prepared by three different polymerization techniques, are shown in Figure 7. The distinguishing feature of these chromatographs is that they show two components of widely different MW s a relatively low MW component and a... 

Before discussing the crystallization results for these elastomers, it is useful to summarize two of the important distinguishing features of the Ba-Mg-Al polymerization system ... 

Anionic polymerization of conjugated dienes and olefins retains its lithium on the chain ends as being active moities and capable of propagating additional monomer. This distinguishing feature has an advantage over other methods of polymerization such as radical, cationic and Ziegler polymerization. Many attempts have been made to prepare block copolymers by the above methods, but they were not successful in preparing the clear characterized block copolymer produced by anionic technique. 

Immiscibility of polymers in the melt is a common phenomenon, typically leading to a two-phase random morphology. If the phase separation occurs by a spinodal decomposition process, it is possible to control the kinetics in a manner that leads to multiphase polymeric materials with a variety of co-continuous structures. Common morphologies of polymer blends include droplet, fiber, lamellar (layered) and co-continuous microstructures. The distinguishing feature of co-continuous morphologies is the mutual interpenetration of the two phases and an image analysis technique using TEM has been described for co-continuous evaluation.25... 

The distinguishing feature of droplet nucleation as opposed to micellar or homogeneous nucleation is the nature of the particle at birth . Droplets, which are nucleated into particles, begin as nearly 100% monomer. Micellar or homogeneous nucleated particles start out with much lower monomer concentrations and eventually swell to around 60% (for MMA) in the presence of monomer droplets. This fundamental difference may lead to large differences between miniemulsion and macroemulsion polymerizations in radical desorption and/or intraparticle termination during Intervals I and II. 

Chain-growth polymerizations have the following distinguishing features ... 

Macroradicals are isolated I rom each other in emulsion polymerizations because they grow in particles, which can accommodate either one or zero radicals at any instant. The distinguishing feature of the kinetics of such reactions is that the polymerization rate and polymer molecular weight are proportional to the number of particles, as distinct from free-radical polymerizations in bulk, solution or suspension. An interesting consequence is that the rate of polymerization will be inversely proportional to the particle size. This holds affixed final polymer content, which is the way such reactions are usually performed. Polymer molecular weight may also be affected by particle size under the same conditions. 

The distinguishing feature of tyrosinase is that it catalyzes the oxidation of monohydric phenols, like tyrosine, to the dihydric form and dihydric phenols, like DOPA and catechol, to the corresponding quinones. The striking biological effects of this enzyme arise from quinones which polymerize to produce the darkening of various plants on injury and melanin in mammals. The relative oxidation rates of several dihydric phenols by tyrosinase are given in Table III. 

Although regarded as a mature and established field, siloxane polymerization has some distinguishing features that are well described in the literature but are often overlooked. These features, as well as some of the more-recent observations and current thinking in this field, are reviewed briefly in this chapter. Two topics not usually included in other reviews, copolymerization and condensation polymerization, are also discussed. 

This chapter will not duplicate the already existing reviews either in their comprehensiveness or special emphasis. Instead the distinguishing features of siloxane polymerization will be highlighted briefly, and perspectives will be given on copolymerization and condensation polymerization. 

One more distinguishing feature of liquid crystalline polymeric systems is a peculiar dependence of the viscosity on the shear stress (r) when the latter is small. Kulichikhin et al. were the first to note that in the range of small shear stresses the... 

One of the most distinguishable features of radical polymerisation is its tolerance to water, relative to the ionic counterparts, however the effective polymerization should be performed conventionally under stringent conditions without protonic or basic impurities to insure effective chain propagation and therefore desired polymer growth without unnecessary inhibition and premature termination. Because of their unique features, suspension, dispersion... 

One distinguishing feature of most synthetic polymers is that they are polydisperse. The entire polymer sample is made up of individual molecules that have a distribution of degrees of polymerization, determined by the particular synthesis method used. If all polymers in a given sample have the same number of monomers, the sampleTs monodisperse. There are many... 

The kinetics of chlorinated hydrocarbon reactions exhibit several distinguishing features when compared to the reactions of analogous hydrocarbons. " First, as a consequence of the weaker C-Cl bond dissociation energies, CHCs decompose at temperatures that are significantly lower than the analogous hydrocarbons. This leads to the early production of Cl radicals, thereby establishing the requisite free radical chain reactions, which destroy the parent CHC and lead to gas phase polymerization, ultimately forming soot. 

Polymerase I plays an essential role in the replication process in E. coli, but it is not responsible for the overall polymerization of the replicating strands. The enzyme that accomplishes this is a less abundant enzyme, polymerase III (pol III). (A DNA polymerase II has also been isolated from E. coli, but it probably plays no role in DNA synthesis.) Pol III catalyzes the same polymerization reaction as pot I but has certain distinguishing features. It is a very complex enzyme and is associated with eight other proteins to form the pol III holoenzyme. (The term holoenzyme refers to an enzyme that contains several different subunits and retains some activity even when one or more subunits is missing.) Pol III is similar to pol I in that it has a requirement for a template and a primer but its substrate specificity is much more limited. For a template pol III cannot act at a nick nor can it unwind a helix and carry out strand displacement. The latter deficiency means that an auxiliary system is needed to unwind the helix ahead of a replication fork. Pol III, like pol I, possesses a 3 5 exonuclease activity, which performs the major editing function in DNA replication. Polymerase III also has a y exonuclease activity, but this activity does not seem to play a role in replication. 

The difference between this principle and the four preceeding ones is that the range of its application is limited to anionic and anionic-coordination polymerization. Only in the anionic propagation mechanism, is the formation of triplet intermediates possible (Scheme 5). This is probably one of the main reasons for the high structure- and stereoregulating ability of anionic and anionic-coordination catalytic systems including Zie r-Natta catalysts and is one of their distinguishing features. 

As noted above, all chain-reaction polymerizations involve essentially the same number of steps. The main distinguishing feature between chain-reaction polymerizations, however, is by the initiation mechanism, which may be a free-radical, ionic (cationic or anionic), or coordinatioa The time between initiation and termination of a given chain is typically from a few tenths of a second to a few seconds. During this time thousands or tens of thousands of monomers add to the growing chain. 

TABLE 2.3 Distinguishing Features of Chain and Step Polymerization Mechanisms ... 

Initiation, as noted above, involves the generation of active species, which can be through free-radical, ionic, or coordination mechanism. This mechanism of chain initiation is the essential distinguishing feature between different polymerization processes. Quite expectedly, therefore, addition polymerization of vinyl... 

There are four principal processes for effecting free-radical polymerization bulk. solutitHL suspoisitxi and emulsion. The first three of these processes produce polytner by homogeneous fiee-radical polymerization and are described briefly in the following sections. The fourth process, of course, is the subject of this book and is a non-homogaieous method of fiee-radical polymerization. The distinguishing features of emulsion polymerization are described in Chapter 2. 

Chain polymerizations are like all chain reactions in that they consist of initiation, propagation, and termination reactions that produce a unique active site at which all polymerization must occur. The distinguishing features of a chain polymerization are that ... 

The buUt-in distinguishing feature of a thermoset polyester, however, is that it is unsatorated. That is, prior to cross-linking, Aere are some R, groups present in which there is a carbon-carbon double bond (C—C bond) contained in the molecular backbone. The mixture for polymerization contains (XXVID plus monomers such as styrene (or other unsaturated non-pofymeric molecules) in liquid form. When catalyst is added and heat is applied the double bonds open and an addition reaction leads to the formation of a highfy cross-linked network, with pofyester chains... 

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