Polymerization conditions monomer concentration

Figure 3. Effect of EtsA l i-BusA l molar ratio on microstructure. Polymerization conditions monomer concentration, 11 wt % in hexane catalyst concentration, 7.5 X 10 5 mol/L molar ratio Nd(vers), Et3Al2Cls AIRS, 1 1 30 polymerization time, 2 h and 60°C.

The patent and open literature were searched for examples of dye sensitized photopolymerization in which a common monomer (acrylamide), and one of several common dyes (thionine, T methylene blue, MB or rose bengal, RB) were used in combination with a stated concentration of an activator. The polymerization conditions (monomer concentration, light intensity absorbed, and extent conversion) were stated in each case chosen for inclusion. The relative photospeed of the system was calculated based on several corrections to the raw data. We here define the relative photospeed of a composition as the inverse of the exposure time t needed to effect some fixed percentage of monomer conversion. 

Following these previous results, we investigated in this study the influence of the polymerization conditions(monomer concentration and polymerization temperature) on the structure of poly(divinyl formal). 

Polymerization conditions monomer concentration, lOg/lOOmL hexane Nd/Bd 0.3 micromol/g third component, PhCH Cl Cl/Nd(mole ratio), 3.5 cocatalyst, Al(i-C4Hg)3 ... 

Optimum polymerization conditions monomer concentration 22%, reaction time 3.3 h and reaction temperature 42°C for the specified catalyst system Maiti, M Srivastava, V K Shewale, S Jasra, R V Chavda, A Modi, S, Chem. Eng. Sci., 107,256-65, 2014. 

The physicochemical characterization of a colloidal carrier is necessary because important characteristics, such as particle size, hydrophobicity, and surface charge, determine the biodistribution after administration [129-132]. Preparation conditions, such as the pH of the polymerization medium, monomer concentration, and surfactant concentration, can influence the physicochemical characteristics of the particles [60, 62, 64]. It is, therefore, essential to perform a comprehensive physicochemical characterization of nanoparticles, which has been reviewed by Magenheim and Benita [133]. 

We tried to optimize the polycoupling conditions by varying such parameters as polymerization time, monomer concentration and monomer addition mode, in an effort to control the polymer formation and to render the polymers soluble and processable. The optimization worked well and our A2 + B3 approach offered ready access to a soluble hb-PAE containing luminescent anthracene and fluorene chromophores (Scheme 5) [27]. Similarly, soluble azo-functionalized polymers hb-P13 and hb-P15 were obtained from the palladium-catalyzed polycoupling of triiodoarenes (12 and 14) with a di-ethynylazobenzene (11) [28]. 

The idea of particle inhomogeneity was supported experimentally by Williams [149], However, his representation of growth is more complicated. In phase II, the monomer concentration in the particle decreases with conversion, while the rate remains constant. The particle has a core with a relatively high polymer content surrounded by a monomer-rich layer (see Fig. 16). Polymerization occurs at the polymer—monomer interface. Under these conditions, monomer concentration at the interface remains constant, even when its amount in the particle decreases. Napper presented the idea of an exactly opposite composition of the monomer—polymer particle [150], The core should be enriched in monomer and surrounded by a layer with a higher polymer content. Van den Hul and van der Hoff found most growing ends of macromolecules at the particle surface [151], which supports Napper s model. 

The relative concentration of EO THF crowns formed is usually in the range of 8-2Q% of the linear polyether glycol. Variables influencing macrocyclic concentration and composition are polymerization conditions, monomer ratio, and catalyst. 

That is, in terms of reaction rates, the molecular weight of polyolefins is given by the ratio between the overall rate of propagation (Rp) and the sum of all rates of chain release (Rr) reactions this means that the molecular weight is dependent on the type of catalyst and the kinetics of the process, that is, the polymerization conditions (polymerization temperature, monomer concentration, catalyst/cocatalyst ratio). Hence, understanding the details of the mechanisms of chain release reactions is the key to molecular weight control in metallocene-catalyzed olefin polymerization. Here, chain release reactions (usually referred to as termination or transfer reactions) are all those steps that cause release of the polymer chain from the active catalyst, with the formation of a new initiating species (see section... 

Mechanical synthesis by cold mastication of rubber and monomers depends on the reaction condition (monomer concentration, temperature, solvent concentration, atmosphere, presence of transfer agents, radical acceptors, atmosphere and/or catalyst) and on the physical and chemical properties of the rubbers, the monomers, and the product interpolymers. Rubber composition can influence reaction even more than the presence of oxygen [86, 95]. A critical factor is the shear stress developed in the system rather than instrumentally defined shear rates. The degree of reaction of polymer and consequently also the concentration of free macroradicals depends on stress. As a consequence, the influence of the above parameters may be connected to their influence on the viscosity of the reaction medium since an increase in viscosity causes an increase in stress at constant shear rate. Temperature may increase during polymerization. This is compensated by... 

Depending on the final polymerization conditions, an equilibrium concentration of monomers (ca 8%) and short-chain oligomers (ca 2%) remains (72). Prior to fiber spinning, most of the residual monomer is removed. In the conventional process, the molten polymer is extmded as a strand, solidified, cut into chip, washed to remove residual monomer, and dried. In some newer continuous processes, the excess monomer is removed from the molten polymer by vacuum stripping. 

Kinetics. Details of the kinetics of polymerization of THF have been reviewed (6,148). There are five main conclusions. (/) Macroions are the principal propagating species in all systems. (2) With stable complex anions, such as PF , SbF , and AsF , the polymerization is living under normal polymerization conditions. When initia tion is fast, kinetics of polymerizations in bulk can be closely approximated by equation 2, where/ is the specific rate constant of propagation /is time [I q is the initiator concentration at t = 0 and [M q, [M and [M are the monomer concentrations at t = 0, at equiHbrium, and at time /, respectively. 

PTHF does not behave ideally in solution and the equiHbrium monomer concentration varies with both solvent and temperature. Kinetics of THF polymerizations fit equation 2, provided that the equiHbrium monomer concentration is deterrnined for the conditions used. 

Primary radical termination is also of demonstrable significance when very high rates of initiation or very low monomer concentrations are employed. It should be noted that these conditions pertain in all polymerizations at high conversion and in starved feed processes. Some syntheses of telechelics are based on this process (Section 7.5.1). Reversible primary radical termination by combination with a persistent radical is the desired pathway in many forms of living radical polymerization (Section 9.3). 

Sulfate radical anion may be converted to the hydroxyl radical in aqueous solution. Evidence for this pathway under polymerization conditions is the formation of a proportion of hydroxy end groups in some polymerizations. However, the hydrolysis of sulfate radical anion at neutral pi I is slow (k— 107 M"1 s 1) compared with the rale of reaction with most monomers (Ar=l08-109 M 1 s 1, Table 3.7)440 under typical reaction conditions. Thus, hydrolysis should only be competitive with addition when the monomer concentration is very low. The formation of hydroxy end groups in polymerizations initiated by sulfate radical anion can also be accounted for by the hydration of an intermediate radical cation or by the hydrolysis of an initially formed sulfate adduct either during the polymerization or subsequently. 

Cationic polymerization of cyclic acetals generally involves equilibrium between monomer and polymer. The equilibrium nature of the cationic polymerization of 2 was ascertained by depolymerization experiments Methylene chloride solutions of the polymer ([P]0 = 1.76 and 1.71 base-mol/1) containing a catalytic amount of boron trifluoride etherate were allowed to stand for several days at 0 °C to give 2 which was in equilibrium with its polymer. The equilibrium concentrations ([M]e = 0.47 and 0.46 mol/1) were in excellent agreement with that found in the polymerization experiments under the same conditions. The thermodynamic parameters for the polymerization of 1 were evaluated from the temperature dependence of the equilibrium monomer concentrations between -20 and 30 °C. 

In summary, then, polymerization of ATP-actin under conditions of sonication displays two characteristic deviations from the simple law described by equation (4), which is only valid for reversible polymerization. These are (a) overshoot polymerization kinetics, and (b) the steady-state amount of polymer formed decreases, or the steady-state monomer concentration increases, with the number of filaments. These two features are the direct consequence of ATP hydrolysis accompanying the polymerization of ATP-actin, as will be explained now. 

We emphasize that the conditions subscripted with a zero (time, initiator and monomer concentration) are not the beginning of a reaction, but rather some point well advanced in the polymerization process when the remaining amount of monomer is small in absolute terms but large compared to the desired end state of the polymerization (Mg M ). The amount of initiator Ig is to be achieved by addition to any present immediately before time zero, and the final monomer concentration, M, is set by production specifications. We do not set any predetennined bounds on upper and lower temperature limits. In practice the upper limit will be detennined by either reaction variables (depropagation and initiator depletion) or by process variables (heat exchange), while the lower temperature limit will be determined by process variables (solubility, heat exchange). We do not here consider the process variables to be constraints. 

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