Chain effective

The molecular weight of a polymer can be controlled through the use of a chain-transfer agent, as well as by initiator concentration and type, monomer concentration, and solvent type and temperature. Chlorinated aUphatic compounds and thiols are particularly effective chain-transfer agents used for regulating the molecular weight of acryUc polymers (94). Chain-transfer constants (C at 60°C) for some typical agents for poly(methyl acrylate) are as follows (87) ... 

Telomerization. Polymerization of DAP is accelerated by telogens such as CBr, which are more effective chain-transfer agents than the monomer itself (65) gelation is delayed. The telomers are more readily cured in uv than DAP prepolymers. In telomerizations with CCl with peroxide initiator, at a DAP/CCl ratio of 20, the polymer recovered at low conversion has a DP of 12 (66). 

The condensation reaction is promoted by certain polar solvents and of the many which have been tested dimethyl sulphoxide appears to be the most effective. As usual with linear condensation polymers molecular equivalence and near-absence of monofunctional material is necessary to ensure a high molecular weight. Moisture and alcohols can also have a devastating effect on the molecular weight. In the case of water it is believed that 4-chlorophenyl 4-hydroxyphenyl sulphone is formed which functions as an effective chain terminator. Gross contamination with air is also believed to reduce the maximum attainable molecular weight as well as causing intense discolouration. 

Another approach to safer stabilization is to use a biological antioxidant such as vitamin E (a-tocopherol is the active form of vitamin E, AO-9, Table la). It is essentially a hindered phenol which acts as an effective chain breaking donor antioxidant, donating a hydrogen to ROO to yield a very stable tocopheroxyl radical, a-Tocopherol is a very effective melt stabilizer in polyolefins that offers high protection to the polymer at very low concentration [41], (Table 2). 

When the chain undergoes extension, the stretching fields increases the number of trans isomers in the chain and, hence, decreases the effective chain flexibility which is related to by the equation (see Eq. (11))... 

The kinetics and mechanism of vacuum decomposition of AgMn04 at 378—393 K [466] are believed to differ from the behaviour of KMn04 in that the effective chain branching coefficient diminishes with time and this leads (Chap 3, Sect. 3.2) to the modified form of the Prout—Tompkins equation... 

Individual climate controls do not function in isolation from one another rather, many factors link together in complex cause-effect chains (Figure 2). Factor interactions may involve feedback loops that at one extreme amplify... 

We can determine a sample s crosslink density from the degree to which it swells when immersed in a suitable solvent. We use this method to calculate the average molecular weight of the effective chains , that is, those chain segments terminated at each end by a crosslink. We can only apply this analysis to samples that contain no soluble material. 

We immerse a weighed sample of a crosslinked polymer in a suitable solvent and allow it to swell for up to 24 hours. We calculate the molecular weight of effective chains from Eq. 5.7. 

Mc - Molecular weight of effective chains pp = Density of polymer (g/cm3)... 

USEtox calculates characterization factors for human toxicity and freshwater ecotoxicity. Assessing the toxicological effects of a chemical emitted into the environment implies a cause-effect chain that links emissions to impacts through three steps environmental fate, exposure, and effects. Linking these steps, a systematic framework for toxic impacts modeling based on matrix algebra was developed to some extent within the OMNIITOX project [10]. USEtox covers two spatial scales, the continental and the global scales. 

So, these reactions cannot lead to effective chain termination in oxidized alcohol. The decomposition of tetroxides depends on pH and apparently proceeds homolytically as well as heterolytically in an aqueous solution. The values of the rate constants (s 1) of tetroxide decomposition at room temperature in water at different pH values are given below [38,39],... 

The former possibility previously described could be refuted by the spin-trap-ping experiments and the living radical polymerization of St with 46. Therefore, 13 was added to the polymerization system to conserve the active site of the inifer-ter. It was expected to reproduce the iniferter site due to the formation of DC radicals which can function as primary radical terminators and/or the effective chain transfer ability of 13. It was pointed out that the DC radical generated from 13 had high selectivity for monomers, i.e., 13 acted as an initiator for the polymerization of St, but did not as an initiator for the polymerization of MA, VAc, and AN [72,175,177]. 

It is evident that by far the most effective chain breaking reaction is that involving the chain breaking agent X, the concentration of which is proportional to that of the monohydrate. 

In polymerizations catalysed by a metal halide and some others one of the most effective chain-breaking agents is a species, the concentration of which is proportional to the water concentration (see e.g., references 36, 37, 39, 69, 110, 125) but in most cases we know neither the exact nature of this species nor the type of reaction. 

Type (C). DP falling to Minimum, Constant Value. In this case (Figure 6) there is present in the system a reagent, G (at a concentration g), which itself may or may not be a chain-breaker but forms a (more effective) chain-breaking reagent (complex) H with F, whilst F itself is not a chain-breaker (case 4 of Table 1). 

This evidence indicates that the principal chain-breakers in these solutions are free ions and that the 1 1 complexes which are formed are much less ionised and are much less effective chain-breakers than the compounds (probably 2 1 and 1 2 complexes) which are prevalent on either side of the neutralisation point. This matter is discussed further in Example 5 below. The authors concluded from their results that the propagating species is also a free ion rather than an ion-pair. However, whilst this may be true, it does not follow from this evidence, since the cation in an ion-pair may well be able to react with a free anion. 

The crosslink density of a polymer network determines the number of elastically effective chains. Some of the chains are tied to a network and... 

Another highly effect chain extender is trimellitic anhydride (TMA) which gives rise to branching of the PET structure. Note that the multifunctional epoxies (see Table 14.2) react quickly with the terminal carboxylic acid groups of PET but can also react with the film former and the silane coupling agent on glass fibre reinforcements. 

Aromatic carboxylic dianhydride chain extenders (e.g. PMDA) are a low-cost way of converting recycled PET flakes into high-IV crystalline pellets that can be used in high-value applications (e.g. bottles, strapping, foam, engineering alloys/compounds, etc.) (see Figure 14.2). PMDA is an effective chain extension additive for thermoplastic polyesters such as PET and PBT. It is suitable for the following applications ... 

During this reaction, some caprolactam is also liberated. The reaction is largely completed within the processing time (typically 3-5 min). The increase in intrinsic viscosity of PET can be adjusted by the amount of CBC. In practice, about 0.5 wt% of CBC is typically used. CBC is commercially available under the trade-name ALLINCO (DSM, Geleen, The Netherlands). ALLINCO is one of the most effective chain extender systems available for PET [21, 22], CBC is often used in combination with PBO for an enhanced chain extension effect. Typically, the relative viscosity of PET is increased from 1.6 to 2.0 with a stoichiometric amount of CBC + PBO (ca. 1.2 wt%) in a single-screw extruder at 300 °C. 

The second explosion limit must be explained by gas-phase production and destruction of radicals. This limit is found to be independent of vessel diameter. For it to exist, the most effective chain branching reaction (3.17) must be overridden by another reaction step. When a system at a fixed temperature moves from a lower to higher pressure, the system goes from an explosive to a steady reaction condition, so the reaction step that overrides the chain branching step must be more pressure-sensitive. This reasoning leads one to propose a third-order reaction in which the species involved are in large concentration [2], The accepted reaction that satisfies these prerequisites is... 

Since the diethyl ketene acetal (XII) appears to be a moderately effective chain transfer agent as well as a comonomer, a search... 

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