Polymerization occurring simultaneously with

Fairly recently, another method for obtaining polymer materials with uniaxial orientation has been developed. It is the directed polymerization i.e. the synthesis of polymers under conditions at which the material attains instanteneously the oriented structure. The formation of crystals from the macromolecules in an extended conformation occurs in those polymerizing systems simultaneously with polymerization22. ... 

These facts are different demonstrations of the same event degradation reactions occur simultaneously with electropolymerization.49-59 These reactions had also been called overoxidation in the literature. The concept is well established in polymer science and consists of those reactions between the pristine polymer and the ambient that promote a deterioration of the original polymeric properties. The electrochemical consequence of a strong degradation is a passivation of the film through a decrease in the electrical conductivity that allows a lower current flow at the same potential than the pristine and nondegraded polymer film did. Passivation is also a well-established concept in the electrochemistry of oxide films or electropainting. 

Cement hydration and epoxy polymerization occur simultaneously to form a structure that is similar to the latex-modified cementitious system. Epoxy systems develop high strength, adhesion and have low permeability, good water resistance and chemical resistance. A major advantage of this system is that it can be cured under moist or wet conditions. According to a recent study, the epoxy-modified mortars can be made without the hardeners with superior properties to those obtained with conventional epoxy mortars [89, 90]. 

The F/C ratio model accounts for the fact that for carbon-containing gases etching and polymerization occur simultaneously. The process that dominates depends upon etch gas stoichiometry, reactive-gas additions, amount of material to be etched, and electrode potential and upon how these factors affect the F/C ratio. For instance, as described in Figure 8, the F/ C ratio of the etchant gas determines whether etching or polymerization is favored. If the primary etchant species for silicon (F atoms) is consumed either by a loading effect or by reaction with hydrogen to form HF, the F/... 

The polymerization of a-olefins, promoted by homogeneous Ziegler-Natta catalysts based on bis(cyclopentadienyl)titanium(IV) or analogous zirconium compounds and aluminum alkyls, occurs simultaneously with a series of other reactions that greatly complicate the kinetic interpretation of the polymerization process (see Scheme 3). 

Petrov and Shchekin (297) showed that below the cracking temperature (250-316°C.) cyclohexene undergoes over silica-alumina hydrogen disproportionation and dimerization. Identical results were obtained from 1-methyl-l-cyclopentene. Ring expansion of lower alkylated cyclopentanes occurs simultaneously with polymerization. However, no bicyclic compounds with similar rings were formed. 

It should be noted that VIII gives neither polymer nor oligomer under the conditions described, and the yield is smaller with VII than with VI. Moreover, the percentage composition of the polymers does not correspond to that of the monomers about one atom of chlorine per molecule of monomer is lost when polymerization occurs. The polymer does not possess the characteristics of the cyclopropanes. It therefore appears that opening of the cyclopropane ring, dehydrochlorination, and polymerization occur simultaneously. 

Only about 10% of /er/.-ROLi molecules yield polymer chains. The remaining alkoxide, coordinated to the growth centres, forms a protective envelope. It suppresses the basicity of the centres and thus limits their ability to react with the ester group of the monomer. When the reaction conditions are selected so that almost no tert-ROLi is left for the formation of the protective envelope, propagation occurs simultaneously with termination. Polymerization ceases prior to the consumption of all monomer and a strongly branched polymer results. 

Polymerization proceeds predominantly with ionic species, because they are more than 1000 times more reactive than esters k k "", in which k "" is the rate of covalent propagation). Rapid isomerization allows simultaneous growth on all ains. Typically, during the polymerization of THF, polydis-persities (M /M J are >1.5, because depropagation occurs simultaneously with chain growth. The equilibrium monomer concentration, [M]g, at room temperature is around 5 mol/L. Thus, the initial concentration of THF under these conditions should exceed 50 vol %. 

The use of rf cold plasmas to cause polymerization of monomers on such non-conducting substrates as glasses (6) and other polymeric substances (7) is not new. However, the chemistry involved in rf cold plasmas is complicated, and within the reactor, depolymerizations of substrates and of newly formed polymers occur simultaneously with polymerization reactions. Clark (8) has reported on such phenomena, and it is known that the relative rates of polymerization to depolymerization vary within the reactor. 

The polymerization rate for an anionic polymerization where termination occurs simultaneously with propagation follows in a manner similar to free-radical polymerizations. An example is the potassium amide initiated polymerization in liquid ammonia. This is one of the few anionic systems in which all active centers behave kinetically as free ions. In this system, initiation involves dissociation followed by addition of amide ion to monomer ... 

In bound-ion-radical mechanism for ethylene polymerization, initiation can be either through a chemisorbed ethylene molecule (Fig. 9.9) or a chemisorbed hydrogen atom. With ethylene as initiator, polymerization occurs simultaneously at two sites, each associated originally with the ends of the double bond in the ethylene molecule adsorbed on an active dual site. With hydrogen as initiator, polymer growth occurs only at one site. In either case, an organometallic bond is formed. 

Olefins are then formed either by polymerization or by sp insertion of the carbene species into methanol or dimethylether. The latter occurs simultaneously with the a-elimination, since the presence of two free carbenes is unlikely, given their high reactivity. 

Polymerization may occur simultaneously with devolatilization. This is the case for condensation polymerizations such as that for PET and in free-radical polymerizations such as that for styrene. For the condensation polymers, high molecular weights are achieved only at very high conversions so that the polymerization occurring during devolatilization is obviously desirable. It typically gives low molecular weights in free-radical polymerizations and is typically undesirable. 

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