Polymerization conditions influence

The mechanism of chloroprene polymerization is summarized in Scheme 4.11. Coleman et ai9iM have applied l3C NMR in a detailed investigation of the microstructure of poly(chloroprene) also known as neoprene. They report a substantial dependence of the microstructure on temperature and perhaps on reaction conditions (Table 4.3). The polymer prepared at -150 °C essentially has a homogeneous 1,4-tra/rv-niicrostructure. The polymerization is less specific at higher temperatures. Note that different polymerization conditions were employed as well as different temperatures and the influence of these has not been considered separately. 

Minor (by amount) functionality is introduced into polymers as a consequence of the initiation, termination and chain transfer processes (Chapters 3, 5 and 6 respectively). These groups may either be at the chain ends (as a result of initiation, disproportionation, or chain transfer,) or they may be part of the backbone (as a consequence of termination by combination or the copolymerization of byproducts or impurities). In Section 8.2 wc consider three polymers (PS, PMMA and PVC) and discuss the types of defect structure that may be present, their origin and influence on polymer properties, and the prospects for controlling these properties through appropriate selection of polymerization conditions. 

A wide range of nitroxidcs and derived alkoxyamincs has now been explored for application in NMP. Experimental work and theoretical studies have been carried out to establish structure-property correlations and provide further understanding of the kinetics and mechanism. Important parameters are the value of the activation-deactivation equilibrium constant K and the values of kaa and (Scheme 9.17), the combination disproportionation ratio for the reaction of the nilroxide with Ihe propagating radical (Section 9.3.6.3) and the intrinsic stability of the nitroxide and the alkoxyamine under the polymerization conditions (Section 9.3.6.4). The values of K, k3Cl and ktieact are influenced by several factors.11-1 "7-"9 ... 

Collins S, Gauthier WJ, Corrigan JF, Nicholas NJ (1995) Elastomeric poly(propylene) influence of catalyst structure and polymerization conditions on polymer structure and properties. Macromolecules 28 3771-3778... 

This study examines the effects of the polymerization conditions on the electro-optic performance of PSFLCs, and the influence of the LC ordering on the polymerization behavior of various monomers is discussed. Basic electro-optic proper-... 

Case 1 appears to accurately predict the observed dependence on persulfate concentration. Furthermore, as [Q]+otal approaches [KX], the polymerization rate tends to become independent of quat salt concentration, thus qualitatively explaining the relative insensitivity to [Aliquat 336]. The major problem lies in explaining the observed dependency on [MMA]. There are a number of circumstances in free radical polymerizations under which the order in monomer concentration becomes >1 (18). This may occur, for example, if the rate of initiation is dependent upon monomer concentration. A particular case of this type occurs when the initiator efficiency varies directly with [M], leading to Rp a [M]. Such a situation may exist under our polymerization conditions. In earlier studies on the decomposition of aqueous solutions of potassium persulfate in the presence of 18-crown-6 we showed (19) that the crown entered into redox reactions with persulfate (Scheme 3). Crematy (16) has postulated similar reactions with quat salts. Competition between MMA and the quat salt thus could influence the initiation rate. In addition, increases in solution polarity with increasing [MMA] are expected to exert some, although perhaps minor, effect on Rp. Further studies are obviously necessary to fully understand these polymerization systems. 

Piletsky SA, Piletska EV, Karim K, Freebaim KW, Legge CH, Turner APR Polymer cookery influence of polymerization conditions on the performance of molecularly imprinted polymers. Macromolecules 2002 35 7499-7504. 

In alkyllithium initiated, solution polymerization of dienes, some polymerization conditions affect the configurations more than others. In general, the stereochemistry of polybutadiene and polyisoprene respond to the same variables Thus, solvent has a profound influence on the stereochemistry of polydienes when initiated with alkyllithium. Polymerization of isoprene in nonpolar solvents results largely in cis-unsaturation (70-90 percent) whereas in the case of butadiene, the polymer exhibits about equal amounts of cis- and trans-unsaturation. Aromatic solvents such as toluene tend to increase the 1,2 or 3,4 linkages. Polymers prepared in the presence of active polar compounds such as ethers, tertiary amines or sulfides show increased 1,2 (or 3,4 in the case of isoprene) and trans unsaturation.4. 1P U It appears that the solvent influences the ionic character of the propagating ion pair which in turn determines the stereochemistry. 

Handel and co-workers [11] have investigated the influence of the polymerization conditions on the molecular weight and chemical composition of styrene-butyl acrylate copolymers ... 

Influence of polymerization conditions upon incorporation of flavin-containing polyanion. The amount of polyanion (1) incorporated as dopant in a PPy film during electropolymerization can easily be controlled by changing the ionic strength (low molar mass salt) and/or the pH of the monomer solution. The correlation between the amount of polymer-bound flavin incorporated in the film and the concentration of the added low molar mass salt, sodium-p-toluenesulphonate (NaOTs), at pH=7 is shown... 

Since the partial insolubility of the starch-ceric ammonium nitrate reaction product complicates the interpretation of solubility data, we ran a second series of graft polymerizations using cobalt-60 as an initiator in an attempt to remove this variable (Table II). If combination of PAN macroradicals is occuring during graft polymerization, it should occur during cobalt-60 initiated polymerizations as well as in those initiated by ceric ammonium nitrate. In the first four reactions of Table II, starch was irradiated as a water slurry under graft polymerization conditions, but in the absence of acrylonitrile, to determine the influence of different doses of irradiation on starch solubility. 

Figure 12. Rate of polymerization of propylene at 60° C. as influenced by the ethyl, ethoxy, and chlorine content of the Al compound used as activator for y-TiCh. Catalyst 5 mmole/liter y-TiCh and 15-20 mmole/liter alkylaluminum compound. Polymerization conditions 2 hours at 60°C. at 1 atm.

Pelton and coworkers showed that the size of PNIPAAm microgels decreases by a factor of 10 if sodium dodecyl sulfate (SDS) is used in the polymerization procedure [61]. Lyon s group used SDS for stabilization of PNIPAAm microgels prepared with PEG diacrylates of different PEG chain length [62], To investigate the influence of polymerization conditions on internal structure of PNIPAAm microgels, SDS was used in batch and semibatch polymerization processes [63],... 

Model materials similar to the M41 family can be modeled using lattice MC simulation under the assumption of non silica polymerization conditions. The structures observed are in agreement with experimental evidence with respect to the surfactant/silica ratio, temperature and surfactant architecture. Even when the resulting structures have a strong influence of the lattice constraints, adsorption properties on such materials are in good agreement with experimental observations. Adsorption properties of modeled materials are similar to experimental observations on MCM-41 type materials and show heterogeneity at low pressures. Such behavior is not observed in smooth cylinders. 

Number of C fCp) and their reactivity in a propagation reaction (propagation rate constant kp). Cp data can be used to determine the mole fraction of active metal centers, the localization of active centers on the surface of the solid catalyst, and the role of individual components of the catalytic system in the formation of active centers. Systematic data on the influence of the catalyst composition and polymerization conditions on Cp and the rate constants of individual steps are important for the determination of the composition of the active centers and the elucidation of the mechanism of these steps. Various methods for determining Cp and kp in catalytic polymerizations of olefins have been reported A direct method for the determination of Cp is the radioactive tracer technique. In this method radioactive compounds react with the AC thus introducing radioactivity into the growing polymer chain. The use of radioactive alcohols is the classical example of this technique... 

When using, however, two-component catalysts alcohols also react with inactive metal-polymer (aluminium-polymer) bonds which are formed in the chain transfer reactions with a cocatalyst. It is expedient to use the alcohol method only for catalytic systems and polymerization conditions for which the number of inactive metal-polymer bonds is low. Such a case is the polymerization of 4-methyl-1-pentene on vanadium trichloride activated with various organoaluminium compounds. For this system the influence of catalyst composition and polymerization conditions on Cp and kp was determined by quenching the polymerization with tritiated alcohol. 

More universal is the method of Cp determination using selective tracers such as carbon monoxide and carbon dioxide which interact only with active metal = polymer bondsUsing tagged CO and CO2 as quenching agents systematic data have been accumulated so far on the influence of the composition of catalysts (titanium chlorides with various organometallic compounds) and polymerization conditions on Cp and kp values for the polymerization of ethylene and propylene IS)... 

Ivanchev et al. compared, under the same ethylene polymerization conditions, the performances of some supported systems with those of traditional ones. The authors not only found that the activity of supported systems is determined by the chemical-physical characteristics of the carrier, which influence the number and the propagation constant of the active centres, but also, in agreement with other authors that changes take place, in the elementary polymerization processes, such as to modify the polymer molecular structure. Indeed, as one can observe (Table 6), it is... 

The crospovidone grades are obtained with different specific surface areas, depending on the polymerization conditions, and their particle size. The micronization process has less influence on the specific surface than small modifications of the polymerization conditions. When a normal crospovidone was micronized the specific surface only increased from l m2/g to i.8 m2/g (N2-BET method). The micronized crospovidone of the lowest bulk density available in the market has the highest specific surface of 2.5 to 6 m2/g (Table 118). 

All aspects of syndioselective propagation with ( -symmetric catalysts, the influence of ligand,794,797-807 metal,806,808,809 and counteranion100,104 variations, as well as the influence of the polymerization conditions,805,810 have been studied in detail and reviewed.162,181,209,288,811... 

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