Polymer initiator, effect

Once the radicals diffuse out of the solvent cage, reaction with monomer is the most probable reaction in bulk polymerizations, since monomers are the species most likely to be encountered. Reaction with polymer radicals or initiator molecules cannot be ruled out, but these are less important because of the lower concentration of the latter species. In the presence of solvent, reactions between the initiator radical and the solvent may effectively compete with polymer initiation. This depends very much on the specific chemicals involved. For example, carbon tetrachloride is quite reactive toward radicals because of the resonance stabilization of the solvent radical produced [1] ... 

Initia.tors, The initiators most commonly used in emulsion polymerization are water soluble although partially soluble and oil-soluble initiators have also been used (57). Normally only one initiator type is used for a given polymerization. In some cases a finishing initiator is used (58). At high conversion the concentration of monomer in the aqueous phase is very low, leading to much radical—radical termination. An oil-soluble initiator makes its way more readily into the polymer particles, promoting conversion of monomer to polymer more effectively. 

The compound R X is a chain-transfer agent, with X usually H or Cl. The net effect of chain transfer is to kill a growing chain and start a new one in its place, thus shortening the chains. Mercaptan chain-transfer agents ate often used to limit molecular weight, but under appropriate conditions, almost anything in the reaction mass (solvent, dead polymer, initiator) can act as a chain-transfer agent to a certain extent. 

Figure 7. Tubular plug-flow addition polymer reactor effect of the frequency factor (ka) of the initiator on the molecular weight-conversion relationship at constant activation energy (Ea). Each point along the curves represents an optimum initiator feed concentration-reactor jacket temperature combination and their values are all different, (Ea = 32.921 Kcal/mol In ka = 35,000 In sec ...

The di- and monoalkyltin compounds are considered to be effective as stabilizers because they (i) inhibit the onset of the dehydrochlorination reaction by exchanging their anionic groups, X, with the reactive, allylic chlorine atoms in the polymer (ii) react with, and thereby scavenge, the hydrogen chloride that is produced and that would otherwise induce further elimination (jii) produce the compound HX, which may also help to inhibit other undesirable side reactions and iiv) prevent breakdown of the polymer initiated by atmospheric oxidation, i.e., by acting as antioxidants. 

The formation of IBVE-aMeSt block polymers was further supported by results of film-casting experiments (12). These data also show that the starting quasiliving poly(IBVE) dication is sufficiently reactive to initiate effectively subsequent aMeSt polymerization. 

Counterion effects similar to those in ionic chain copolymerizations of alkenes (Secs. 6-4a-2, 6-4b-2) are present. Thus, copolymerizations of cyclopentene and norbomene with rhenium- and ruthenium-based initiators yield copolymers very rich in norbomene, while a more reactive (less discriminating) tungsten-based initiator yields a copolymer with comparable amounts of the two comonomers [Ivin, 1987]. Monomer reactivity ratios are also sensitive to solvent and temperature. Polymer conformational effects on reactivity have been observed in NCA copolymerizations where the particular polymer chain conformation, which is usually solvent-dependent, results in different interactions with each monomer [Imanishi, 1984]. 

Cage Effect in Solid Polymers Migration of Free Valence in Solid Polymers Initiated Polymer Oxidation Diffusion of Dioxygen in Polymer Diffusion Regime of Polymer Oxidation Isomerization of Alkyl and Peroxyl Radicals of Polypropylene... 

Table I shows the results obtained with various bisphenols which are generally considered quite effective as thermal antioxidants. Most of these additives did not retard the discoloration of the polymer. One compound, 4,4 -methylenebis(2,6-di-terf-butylphenol), showed some promise, but it discolored the polymer initially and, therefore, cannot be considered of practical importance.

Another experimental aspect investigated by Stenkamp et al. was the effect of the concentration of the polymer initially dissolved in solution (Figure 2). In general, by decreasing the initial concentration of the polymer, the probability for restabilization to occur decreases. For LiCl and KNO3, a decrease from 60 x 10 3 to 0.6 x 10 3 g/L of the initial concentration of the polymer causes the loss of restabilization. KC1 had a stronger propensity for restabilization and could restabilize the colloidal dispersion for a 0.6 x 10 3 g/L initial polymer concentration, but not for a 0.01 x 10 3 g/L concentration. 

S. Kida, M. Kurata and M. Tamura Diffusion in glassy polymers. I. Effects of initial concentration upon the sorption of organic vapors in polymers. Bull. Chem. Soc. Japan 34, 571 (1961). 

Polymerization is influenced by the physical structure and phase of the monomer and polymer. It proceeds in the monomer, and the chemical configuration of the macromolecules formed depends on whether the monomer is a liquid, vapor, or solid at the moment of polymerization. The influence of structural phenomena is evident in the polymerization of acrylic monomer either as liquids or liquid crystals. Supermolecular structures are formed in solid- and liquid-state reactions during and simultaneously with polymerization. Structural effects can be studied by investigating the nucleation effect of the solid phase of the newly formed polymer as a nucleation reaction by itself and as nuclei for a specific supermolecular structure of a polymer. Structural effects are demonstrated also using macromo-lecular initiators which influence the polymerization kinetics and mechanism. 

In an environment without adequate humidity, the initial effect of heating wood is dehydration. As temperatures approach 55-65 °C for extended periods (2-3 months), hemicellulose and cellulose depolymerization begins (28), Pyrolysis and volatilization of cell wall polymers occur at about 250 °C followed by char formation in the absence of air and combustion in the presence of air. 

Halogen compounds with two reactive carbon-halogen bonds can be bifunctional initiators for metal-catalyzed living radical polymerizations to give telechelic polymers. The effective bifunctional initiators include MI-1 to MI-26 with various spacers between the initiating sites. 

The reason of increased photooxidative stability is not only stabilizing activity of bis-aroilenbenzimidazoles derivatives but also the effect of these compounds on supermolecular structure of polymer matrix. As it is seen from the Table 6 physico - mechanical indexes of polymer do not practically depend on the method of additives introduction. Data of Table 6. agree with data of Table 5. In all cases the greatest degree of conservation of polymer initial properties is registered at the concentration of XLY compound - 1 mass %. 

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