Comonomer concentrations

Keeping the composition of copolymerization media constant the total comonomer concentration of which is varied. The absorbed dose was kept constant at 0.14 KGy for the AM-AANa and at 0.35 KGy for the AM-DAEA-HCl systems. The results are shown in Figs. 4 and 5, which show the rate of polymerization, Rp, the degree of polymerization, and the intrinsic viscosity increase with increasing monomer concentration. At comonomer concentration >2.1 M/L, DPn decreases with increasing comonomer concentration. From the logarithmic plots, exponents of the comonomer concentration for the AM-AANa system were determined to be [17,54]. 

In addition, the exponent of the comonomer concentration for AM-DAEA-HCl system was also determined to be [22] ... 

Figure 5 Effect of comonomer concentration on copolymerization of acrylamide with EAEA-HCl. O Rp, % = [tj].

Figures 4 and 5 show that the degree of polymerization and the intrinsic viscosity increase with increasing the comonomer concentration. Thus, the increase in the comonomer concentration would increase DP and, consequently [rj] Eq. (2). However, the exponent of the monomer concentration for the degree of polymerization decreases at a high comonomer concentration. The abrupt change in the exponent at comonomer concentration >2.1 M/L (Eq. 9) may be ascribed to polydispersity. This was found by others [34] to be at 2.1 and 2.2 M/L, although it starts theoretically at 2.0 M/L.

The water solubilities of the functional comonomers are reasonably high since they are usually polar compounds. Therefore, the initiation in the water phase may be too rapid when the initiator or the comonomer concentration is high. In such a case, the particle growth stage cannot be suppressed by the diffusion capture mechanism and the solution or dispersion polymerization of the functional comonomer within water phase may accompany the emulsion copolymerization reaction. This leads to the formation of polymeric products in the form of particle, aggregate, or soluble polymer with different compositions and molecular weights. The yield for the incorporation of functional comonomer into the uniform polymeric particles may be low since some of the functional comonomer may polymerize by an undesired mechanism. 

In the organic phase (i.e., monomer + comonomer)-to-water ratio, the polar comonomer concentration in... 

Soapless seeded emulsion copolymerization has been proposed as an alternative method for the preparation of uniform copolymer microspheres in the submicron-size range [115-117]. In this process, a small part of the total monomer-comonomer mixture is added into the water phase to start the copolymerization with a lower monomer phase-water ratio relative to the conventional direct process to prevent the coagulation and monodispersity defects. The functional comonomer concentration in the monomer-comonomer mixture is also kept below 10% (by mole). The water phase including the initiator is kept at the polymerization temperature during and after the addition of initial monomer mixture. The nucleation takes place by the precipitation of copolymer macromolecules, and initially formed copolymer nuclei collide and form larger particles. After particle formation with the initial lower organic phase-water ratio, an oligomer initiated in the continuous phase is... 

Monomers not amenable to direct homopolymerization using a particular reagent can sometimes be copolymcrizcd. For example, NMP often fails with methacrylates (e.g. MMA, BMA), yet copolymerizalions of these monomers with S are possible even when the monomer mix is predominantly composed of the methacrylate monomer,15j This is attributed to the facility of cross propagation and the relatively low steady state concentration of propagating radicals with a terminal MMA (Section 7.4.3.1). MMA can also be copolymerized with S or acrylates at low temperature (60 C).111 Under these conditions, only deactivation of propagating radicals with a terminal MMA unit is reversible, deactivation of chains with a terminal S or acrylate unit is irreversible. Molecular weights should then be controlled by the reactivity ratios and the comonomer concentration rather than by the nitroxide/alkoxyamine concentration. 

A very recent application of the two-dimensional model has been to the crystallization of a random copolymer [171]. The units trying to attach to the growth face are either crystallizable A s or non-crystallizable B s with a Poisson probability based on the comonomer concentration in the melt. This means that the on rate becomes thickness dependent with the effect of a depletion of crystallizable material with increasing thickness. This leads to a maximum lamellar thickness and further to a melting point depression much larger than that obtained by the Flory [172] equilibrium treatment. 

When two or more monomers are polymerized into the same molecular chain they produce a copolymer, The distribution of monomers, in terms of their relative concentrations and placements, is responsible for controlling a copolymer s properties. Figure 5.8 illustrates five possible comonomer distributions for a copolymer comprising equal numbers of two types of monomer. The relative concentrations of the different monomers and the lengths of the various blocks can be varied widely. Relatively small changes in comonomer concentration and placement can result in significant changes in physical and chemical properties. Properties that can be modified include such diverse characteristics as extensibility, elastic recovery, modulus, heat resistance, printability, and solvent resistance. 

Comonomer type Comonomer concentration (mol %) Solution Bulk polymer Tm (°C)... 

The extent of LCB and its distribution depends mainly on the catalyst system and the conditions used in the polymerisation. Polymerisation conditions (monomer and comonomer concentration, type of catalyst, temperature and concentration of transfer agents) are important variables to be taken into account when one is looking at the rheological behaviour of the polymers. By decreasing the ethene concentration and increasing the polymerisation time in the reactor the LCB frequency can be enhanced [59, 81]. The polymers made with these catalysts have a complex branching structure composed of comb and tree structures of different lengths. 

The relative concentrations of the various radical species during copolymerization have been estimated from the intensities of the ESR spectral components. Typical results obtained from the VAc-MA and VAc-FA system are shown in Figure 8, giving the relative radical concentration as a function of comonomer concentration. The addition of small amounts of M2 (molar ratio M2/Mi 0.05) in each case caused a sharp decrease in the concentration of VAc monomer radicals, while the... 

Description A variety of polymers are produced on these large reactors for various applications. The melt index, polymer density and molecular weight distribution are controlled with temperature profile, pressure, initiator and comonomer concentration. Autoclave reactors can give narrow or broad molecular weight distribution depending on the selected reactor conditions, whereas tubular reac-... 

Studies of ethene copolymerization with 1-butene using the Cp2ZrCl2/ MAO catalyst indicated a decrease in the rate of polymerization with increasing comonomer concentration. 

The theoretical derivation of equilibrium comonomer concentrations, of molecular mass distribution in the copolymers, of the mean composition of H-mers as a function of n, and of the placement probability of a certain... 

Samer [104] carried out similar copolymerizations with similar results. An example of his data is given in Fig. 16. Here 2-ethylhexyl acrylate (EHA) was copolymerized with MMA in batch. The miniemulsion polymerizations (two are shown) follow the copolymer equation, while the macroemulsion polymerization gives EHA incorporation that is lower than predicted by the copolymer equation, presumably due to the low concentration of EHA at the locus of polymerization. The dotted hne in Fig. 16 is for a model derived by Samer that accurately predicts the copolymer composition. Samer derived this model by adapting the work of Schuller [149]. Schuller modified the reactivity ratios for the macroemulsion polymerization of water-soluble monomers to take into accoimt that the comonomer concentration at the locus of polymerization is different from the comonomer composition in the reactor due to the water solubilities of the monomers. Samer used the same approach to account for the fact that the comonomer concentration at the locus of polymerization might be different from that of the reactor due to transport limitations of water insoluble comonomers. 

Tf viscosity of polymer solution (Section 3.3) rj function of comonomer concentrations and reactivity ratios (Section 7.6)... 

The random nature of the copolymerization equilibria can be considered a consequence of two concurrent entropically driven equilibria similar to reactions 2 and 3. These copolymerization equilibria, however, would involve the comonomers interacting reversibly with two different chain ends and the reversible transfer of the different comonomer units between chains. Expressed in another way, the equilibria could be written in a manner similar to the Mayo-Lewis model but with rate constants replaced by equilibrium constants, K, K12, K22, and K21, and comonomer concentrations replaced by the total concentrations of the different siloxane units in the system, M and M2, regardless of their locations in the rings or chains. 

Fig. 12. Viscosity Versus Mesogenic Comonomer Concentration of Copolymers of Ethylene Tereph-thalate and p-Hydroxybenzoic Acid (after Jackson and Kuhfuss)...

This can be done, for example, by multiple detection, where the absolute comonomer concentration, Wk, is measured for each analytical fraction after concentration detector calibration according to... 

The knowledge of the response factorsfor each detector, d, and component, k, allows for the absolute measurement of the comonomer concentration (wk) in all detector cells (d) at all elution volumes. 

Fig. 17 shows that the single filament tenacity (Instron) of the precursor may be considered as a suitable, simple indicator for molecular orientation. For a wide variety of precursor compositions, comonomer concentrations and spinning conditions, there is a relatively good linear relationship between sonic modulus and tenacity of the precursor fiber. The identification of the data points is given in Table 11. (Not all of the fibers used for Fig. 17 have been actually transformed to carbon fibers some of the AN/VBr carbon fiber data are taken from Sect. 5.)... 

Table 12. Influence of precursor molecular weight (specific viscosity, r, p) on carbon fiber properties comonomer concentration 4.CM.2% standard screening conditions"...

Obviously, the sum of all comonomer weight fractions is unity. The accurate copolymer concentration and the distribution of the comonomers across the chromatogram can be calculated from the apparent chromatogram and the individual comonomer concentrations [3],... 

Comonomer concentration (ppm) Copolymer density (g mL ) comonomer type used Copolymer melt index (g (10 min) ) comonomer type used ... 

During the manufacture of polyethylene when in situ derived comonomer is incorporated, the increased incorporation efficiency provides a major benefit [27,238,681,682,698-700]. It does not lessen the amount of comonomer in the polymer or the amount actually used during production. However, it does lessen the amount of comonomer in the reactor, and therefore the amount that must be recycled. This lower comonomer concentration in the reactor can affect operations significantly. Because excess comonomer in the diluent enhances polymer swelling, the increased efficiency of the in situ branching process means that lower-density polymers can be made at higher production rates without trouble. It also means that there is less comonomer residue in the polymer to be purged and recycled downstream. If volatile comonomer is left in the... 

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