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Monomer species

Recently, the above mentioned model reaction has been extended to polycondensation reactions for synthesis of polyethers and polysulfides [7,81]. In recent reports crown ether catalysts have mostly been used in the reaction of a bifunctional nucleophile with a bifunctional electrophile, as well as in the monomer species carrying both types of functional groups [7]. Table 5 describes the syntheses of aromatic polyethers by the nucleophilic displacement polymerization using PTC. [Pg.42]

Reactions between one monomer species with two different functional groups. One functional group of one molecule reacts with the other functional group of the second molecule. For example, polymerization of an amino acid starts with condensation of two monomer molecules ... [Pg.313]

Limit Concentration of Monomers in Solution In the calcic environment considered, the CMC values of surfactants are low. For example, sulfonate and Genapol solutions reach their CMC at 30 ppm (Table II). The surfactant solutions injected in practice at concentration of about one or several percent are thus generally used well above their CMC. Under such conditions, the predominant fraction of each surfactant is the micellar form whose composition (xj) is practically equal to the initial proportion of products (i.e. alpha 1 for sulfonate). At this concentration level of products, very small proportions of monomer species coexist, the limit concentrations of which are respectively ... [Pg.278]

In acidic aqueous solution, protonation reactions of tetracyanodioxotech-netate(V) give a complicated equilibration, leading to formation of [TcO(OHXCN)4]- and [TcO(H2OXCN)4] . At pH values less than 1, these monomer species are fairly stable, while at pH 2-5, [Tc203(CN)8]4 is formed rapidly. This complicated feature is seen in a plot of /cobsd against pH (Fig. 4). When thiocyanate ion is added to this system at pH 1, it replaces a water molecule or hydroxy group in the coordination site. [Pg.266]

The presence of Ga—C rr-bonds in many dimeric precursor complexes was found to affect the quality of the resultant films and the film growth rate in many cases films obtained from dimers were found to contain significant levels of carbon. Monomer species have also been investigated. [Pg.1039]

As earlier noted, PET has no dye attachment sites for chemically active dyes. It is possible to add ionic dyeability by forming copolymers of PET with monomer species that possess active sites, for example, on a pendant side chain. The most common of these has been the incorporation of a sodium salt of a dicarboxylic acid, e.g. of 5-sulfoisophthalic acid (Figure 12.14). The acidic sulfo group allows the attachment of cationic dye molecules. If both the modified and the unmodified fibers are put into a dye bath containing a mixture of disperse and cat dyes, they will emerge with two different colors. This is useful in the creation of specialty fabrics, e.g. when two different dye types are woven into fabrics with a predetermined pattern. The multicolored pattern emerges upon dyeing. [Pg.425]

It has been reported that molecularly non-homogeneous surfactants are able to enhance the solubility of very hydrophobic chemicals, e. g., DDT, at surfactant concentrations well below the CMC. This is attributed to the successive micellization of the heterogeneous monomer species [271, 273, 274,276,278]. Examination of the solubility enhancement with different types of commercial surfactants reveals that molecularly homogeneous surfactants show relatively insignificant (but linear) solubility enhancement below CMC. Molecularly non-homogeneous surfactants, on the other hand, show a much greater solubility enhancement at concentrations below the CMC. [Pg.146]

Polymers containing radicals. A related problem arises from the way in which an in situ EPR cell is constructed. Many monomers polymerize via a radical mechanism and, although set and hard, the polymer may still contain traces of paramagnetic radical monomer species. For this reason, EPR cells tend to be constructed from silica and inorganic adhesives and cements. [Pg.273]

PBS (Figure 30) is an alternating copolymer of sulfur dioxide and 1-butene. It undergoes efficient main chain scission upon exposure to electron beam radiation to produce, as major scission products, sulfur dioxide and the olefin monomer. Exposure results first in scission of the main chain carbon-sulfur bond, followed by depolymerization of the radical (and cationic) fragments to an extent that is temperature dependent and results in evolution of the volatile monomers species. The mechanism of the radiochemical degradation of polyolefin sulfones has been the subject of detailed studies by O Donnell et. al. (.41). [Pg.127]

Note Copolymers that are obtained by copolymerization of two monomer species are sometimes termed bipolymers, those obtained from three monomers terpolymers, those obtained from four monomers quaterpolymers, etc. [Pg.13]

Whereas subscripts placed immediately after the formula of the monomeric unit or the block designate the degree of polymerization or repetition, mass and mole fractions and molar masses - which in most cases are average quantities - may be expressed by placing corresponding figures after the complete name or symbol of the copolymer. The order of citation is the same as for the monomer species in the name or symbol of the copolymer. Unknown quantities can be designated by a, b, etc. [Pg.380]

Most polymerisation reactions can be assigned to two catagories usually described as addition and condensation polymerisation (sometimes called chain reaction polymerisation and step reaction polymerisation , respectively). In both types of reaction, some form of initiator or catalyst is usually required. The tranformation which occurs in the addition polymerisation of a single monomer species can be represented as... [Pg.131]

Several boundary combinations of reactivity ratios are illustrated in Figure 4. For the case in which neither active center shows any preference for any monomer species, i.e., r = = 1, copolymer composition is deter-... [Pg.517]

In a plasma polymerization process, the growth of low molecular weight monomer species to a high molecular weight plasma polymer network takes place. In a chemical sense, plasma polymerization is different from conventional polymerizations, such as radical or ionic. The term radical polymerization means that propagating reactions of monomers are initiated by radical species. Ionic polymerization means that chemical reactions are propagated by ionic species in the polymerization step. Plasma polymerization involves an energy source to... [Pg.172]

In all these condensation processes there are a number of monomer species, related to one another by acid-base equilibria, that can combine to give the observed product. Thus, all binary combinations of [Cr(OH2)6]3+, [Cr(OH)(OH2)5]2+, [Cr(OH)2(OH2)4]+, and [Cr(OH)3 (OH2)3]° need to be considered (75) when forming the hydroxo-bridged dimer. Even though some of the lower-charged species are only present at low concentrations, the reactivity increases with deprotonation. In fact, the oligomerization processes (monomer - dimer dimer —> tetra-mer) are dominated by six reaction pathways (Table II), and each deprotonation step affords a rate enhancement. [Pg.361]

The acceptors in untagged PS and P2VN are the EFS, which have essentially the same absorption spectrum as the monomer species (see Sect. 2.1 and 2.4). Thus, the value of Ro for transfer from monomer to an EFS is the same or slightly larger than Ro for migration from monomer to monomer. However, the overlap of the monomer fluorescence and absorption spectra is small, so that Ro = 6.47 A for isopropylbenzene/isopropylbenzene and Ro = 11.75 A for 2-methylnaphthalene/2-... [Pg.78]

The monomer species, M, has been described by Kraus (31) as an ion pair. Although he did not elaborate on its possible structure, one may assume that he pictured this species as two ammoniated ions held together by electrostatic forces. Douthit and Dye (12) pointed out that such a picture is consistent with the absorption spectra of sodium-ammonia solutions. Becker, Lindquist, and Alder (2) proposed an expanded metal model in which an electron was assumed to circulate in an expanded orbital on the protons of the coordinated ammonia molecules of an M + ion. The latter model is difficult to reconcile with optical, volumetric, and NMR data (16). [Pg.35]

The Pseudo-Phase Model Consider a process in which surfactant is added to water that is acting as a solvent. Initially the surfactant dissolves as monomer species, either as molecules for a non-ionic surfactant or as monomeric ions for an ionic surfactant. When the concentration of surfactant reaches the CMC, a micelle separates from solution. In the pseudo-phase model,20 the assumption is made that this micelle is a separate pure phase that is in equilibrium with the dissolved monomeric surfactant. To maintain equilibrium, continued addition of surfactant causes the micellar phase to grow, with the concentration of the monomer staying constant at the CMC value. This relationship is shown in Figure 18.14 in which we plot m, the stoichiometric molality,y against mj, the molality of the monomer in the solution. Below the CMC, m = m2, while above the CMC, m2 = CMC and the fraction a of the surfactant present as monomer... [Pg.343]

Figure 1. Energy-level diagram for excimer formation. Symbols represent hv, absorbed photon k emissive rate from the monomer species k, bimolecular rate coefficient for formation of the pyrene excimer k, unimolecular rate coefficient for dissociation of the excimer and k, emissive rate from the excimer species. Note no ground-state association is indicated. Figure 1. Energy-level diagram for excimer formation. Symbols represent hv, absorbed photon k emissive rate from the monomer species k, bimolecular rate coefficient for formation of the pyrene excimer k, unimolecular rate coefficient for dissociation of the excimer and k, emissive rate from the excimer species. Note no ground-state association is indicated.

See other pages where Monomer species is mentioned: [Pg.1703]    [Pg.645]    [Pg.532]    [Pg.209]    [Pg.321]    [Pg.6]    [Pg.10]    [Pg.194]    [Pg.288]    [Pg.191]    [Pg.34]    [Pg.9]    [Pg.38]    [Pg.133]    [Pg.65]    [Pg.95]    [Pg.917]    [Pg.131]    [Pg.265]    [Pg.279]    [Pg.145]    [Pg.517]    [Pg.517]    [Pg.189]    [Pg.67]    [Pg.66]    [Pg.78]    [Pg.114]    [Pg.8]    [Pg.109]    [Pg.76]   
See also in sourсe #XX -- [ Pg.29 ]

See also in sourсe #XX -- [ Pg.213 ]




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Active species-heterocyclic monomer addition

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Monomer-micelle equilibrium species

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