Comonomer composition parameters

Use of Average Comonomer Composition Parameters Benoit provided a useful alteruative representation of in terms of mass weighted moments of the copolymer composition distribution. Generalizing his method to N comonomers, F. is expressed as ... 

Table 22-2. Monomeric Unit A Sequence Distribution in Initially Produced Copolymers for Different Copolymerization Parameters, r, and an Initial Comonomer Composition of I l...

Acrylamide copolymerizes with many vinyl comonomers readily. The copolymerization parameters ia the Alfrey-Price scheme are Q = 0.23 and e = 0.54 (74). The effect of temperature on reactivity ratios is small (75). Solvents can produce apparent reactivity ratio differences ia copolymerizations of acrylamide with polar monomers (76). Copolymers obtained from acrylamide and weak acids such as acryUc acid have compositions that are sensitive to polymerization pH. Reactivity ratios for acrylamide and many comonomers can be found ia reference 77. Reactivity ratios of acrylamide with commercially important cationic monomers are given ia Table 3. 

The compositional distribution of ethylene copolymers represents relative contributions of macromolecules with different comonomer contents to a given resin. Compositional distributions of PE resins, however, are measured either by temperature-rising elution fractionation (tref) or, semiquantitatively, by differential scanning calorimetry (dsc). Table 2 shows some correlations between the commercially used PE characterization parameters and the stmctural properties of ethylene polymers used in polymer chemistry. 

The final properties depend not only on unstaturated polyester structure but also on a number of other parameters, such as the nature and proportion of unsaturated comonomer, the nature of the initiator, and the experimental conditions of the crosslinking reaction. Moreover, since polyester resins are mainly used as matrices for composite materials, the nature and amount of inorganic fillers and of reinforcing fibers are also of considerable importance. These aspects have been discussed in many reviews and book chapters and are beyond the scope of this chapter.7-9... 

In the case of proteins or nucleic acids we do not have two, but several comonomers furthermore we are not dealing with the simple case of radical polymerization, but with the more complex polycondensation. Very little is known about the kinetics of the copolymerization of polycondensates - for example analysis of ta and re has not been done systematically for amino acids. However, a few general points can still be made on the basis of the general principles of copolymerization. One has been already mentioned that the initial composition of amino acids in the prebiotic soup may not correspond to the amino-acid composition in the chain. Thus, the fact that one given amino acid has a very small frequency of occurrence in protein chains may not necessarily mean that this amino acid was not present under prebiotic conditions the low frequency in the chains can simply be the result of the kinetics of polycondensation. Conversely, the presence of preferred residues or short sequences in protein chains might be due to the interplay of kinetic parameters, and have little to do with the initial biological constraints. 

Given the preceding mechanistic discussion, one would not expect the reactivity ratios to represent true kinetic parameters. Indeed, the reactivity ratios are sensitive to monomer and simple electrolyte concentrations, comonomer feed compositions, temperature and whether the reaction was carried out in aqueous solutions or a heterophase system. Clearly the data from the various groups are partly inconsistent, but still some general conclusions regard DADMAC/AAM copolymerization, listed in Table 6, are reasonable. 

The relationship between flexibility and copolymer composition was explored by measuring Tg and Tgp for a series of copolymers consisting of styrene or methyl methacrylate paired with several "softer" comonomers. An example of the kind of results obtained is illustrated in Figure 11 with the methyl methacrylate/ ethyl acrylate pair. Included in this plot is a ductility, or toughness, parameter, q, defined by Wu as,... 

Today, the majority of all polymeric materials is produced using the free-radical polymerization technique [11-17]. Unfortunately, however, in conventional free-radical copolymerization, control of the incorporation of monomer species into a copolymer chain is practically impossible. Furthermore, in this process, the propagating macroradicals usually attach monomeric units in a random way, governed by the relative reactivities of polymerizing comonomers. This lack of control confines the versatility of the free-radical process, because the microscopic polymer properties, such as chemical composition distribution and tacticity are key parameters that determine the macroscopic behavior of the resultant product. 

Based on the pioneering work of Molau [64], it is evident that phase separation can occur in blends of two or more copolymers produced from the same monomers when the composition difference between the blend components exceeds some critical value. The mean field theory for random copolymer-copolymers blends has been applied to ES-ES blends differing in styrene content to determine the miscibility behavior of blends [65,66]. On the basis of the solubility parameter difference between PS and PE, it was predicted that the critical comonomer difference in styrene content at which phase separation occurs is about 10 wt% S for ESI with molecular weight around 105. DMS plots for ES73 and ES66 copolymers and their 1 1 blend are presented in Figure 26.8. 

The varieties of copolymers that can be prepared with styrene have greatly expanded the use of the monomer. Dramatic improvements or modifications of physical properties can be achieved by choosing the right comonomer. The dynamic mechanical properties of these copolymers are strongly influenced by the characteristics of the comonomer, the copolymer composition and the miscibility parameter of the constituents parts to function as separable identities. 

The lipophilicity of PSA polymers, which is markedly affected by chemical composition, may influence drug solubility (Table 5). In general, acrylic copolymers have medium lipophilicity compared with other PSA polymers, and have the most excellent drug solubility. A suitable lipophilicity of copolymers can be obtained by changing the compositional content of comonomers. The lipophilicity of acrylic copolymers can be roughly estimated by the theoretical calculation of the hydrophobic parameters of copolymers according to the hydrophobic fragments of each comonomer, or the calculation of the octanol-water partition coefficients (log PC). ... 

Since only four copolymer compositions were studied and particularly since the maximum trimethyl comonomer content available was only 20%, it is difficult to precisely determine the three binary interaction parameters, suggested by the "copolymer model", Equations 1 and 2, from the observed variation of B with trimethyl comonomer content in the PEC, Figure 8. It is none the less interesting, however, to qualitatively assess the... 

The reological properties of investigated solutions have been studied. It has been shown that such compositions have non-Newtonian flow mode, structural nature of flow becomes more expressed with decrease of temperature and increase of solution concentration. It has been shown that viscosity of the composition may be varied in wide range (1.6 - 500 mPa s). It makes possible to apply different production techniques. Influence of dimethacrylic comonomer concentration on dynamic viscosity and flow activation parameters of compositions has been analyzed. 

The reliable synthesis of a copolymer with a desired composition requires the knowledge of relative reactivities of both comonomers, i.e. the values of reactivity ratios rt, and r2, and the system has to conform to the simple Scheme (15-1). The reactivity ratios can then be obtained from the copolymer composition (Equation (15-2)) or from the micrpstructure of the chains. Agreement between the values calculated in these two ways indicates that the simple four parameter Scheme (15-1) can be applied. 

The lattice parameters vary continuously with composition of the blend and the cocrystaUization process is ascribed to the closeness of the crystaUization rate of both species The tendency to cocrystaUize increases with increasing HDPE concentration ° P(E)q43(K)q5. is a random copolymer composed of phenyl ether and phenyl ketone units p Copolymer of styrene and p-methyl styrene containing 30 mol% of the latter comonomer... 

Tip 12 Copolymerization, reactivity ratios, and estimation of reactivity ratios. In a binary copolymerization of monomers and M2, reactivity ratios r and r2 are important parameters for calculating polymerization rate, copolymer composition, and comonomer sequence length indicators (see Chapter 6 for basic equations and further information). 

The relative hydrophilicity of the comonomers used in the synthesis of composite latexes has been considered to be the main polymoization parameter which influences particle morphology [48,51]. In the literature, the surface polarity of a latex particle has often been erroneously related to the bulk polymer polarity [6,45]. The most important propaty of an interface is its interfacial tension, which depends on the molecular interactions between the boundary polymer phase which is swollen with the second-stage monomer. The outermost layer of a latex particle is different from its interior (core), being enriched with p lar groups of different origins (e.g., S04 . OH, COOH, CN) which are better solvated by water, and thus tend to concentrate near the wato phase. 

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