Copolymers parameter

The theories developed in recent years to predict the micellar characteristics as a function of the block copolymer parameters concern almost exclusively A-B and A-B-A copolymers. Our intention was therefore to verify if the classical theories for A-B diblock copolymer are applicable to our PB-P2VP-PEO copolymers by considering that in aqueous medium such a copolymer has ... 

The scaling parameters for PEO were taken from the literature(Konowalow, 1903), those of P(EO-b-DMS) were calculated with the chemical structure of P(EO-b-DMS) and P(EO-b-DMS) were calculated with the new combine rules for the diblock copolymer parameters. In this paper, the parameters of P(EO-b-DMS) were used for the calculation as the parameters of block copolymer component. 

A better approach is the copolymer SAFT approach of Radosz and co-workers [81-83], in which the copolymer parameters are estimated on the basis of the molecular weight and structure only. For an AB-type copolymer there are three binary interaction parameters, the interaction parameters between A segments and segments of the solvent molecule, the interaction parameter between B segments... 

Fraction p Xylene Temp Yield Mol% Octen Copolym. Parameters ... 

In practice, this relationship is well obeyed. Figure 29 displays results on the cold filter plugging point (X CFPP) for different diblock compositions plotted against the aggregate surface area. These surface areas were obtained from Eq. 59 using the appropriate diblock copolymer parameters. As may be seen, the cold filter plugging point data relates linearly to the surface area from the SANS results. The CFPP results are from the summation of data obtained from four different test fuels. 

This equation relates the composition of the copolymer formed to the instantaneous composition of the feedstock and to the parameters rj and r2 which characterize the specific system. Figure 7.1 shows a plot of Fj versus fj-the mole fractions of component 1 in the copolymer and monomer mixture, respec-tively-for several arbitrary values of the parameters rj and r2. Inspection of Fig. 7.1 brings out the following points ... 

The parameters rj and T2 are the vehicles by which the nature of the reactants enter the copolymer composition equation. We shall call these radical reactivity ratios, although similarly defined ratios also describe copolymerizations that involve ionic intermediates. There are several important things to note about radical reactivity ratios ... 

The reactivity ratios of a copolymerization system are the fundamental parameters in terms of which the system is described. Since the copolymer composition equation relates the compositions of the product and the feedstock, it is clear that values of r can be evaluated from experimental data in which the corresponding compositions are measured. We shall consider this evaluation procedure in Sec. 7.7, where it will be found that this approach is not as free of ambiguity as might be desired. For now we shall simply assume that we know the desired r values for a system in fact, extensive tabulations of such values exist. An especially convenient source of this information is the Polymer Handbook (Ref. 4). Table 7.1 lists some typical r values at 60°C. 

As we have already seen, it is the reactivity ratios of a particular copolymer system that determines both the composition and microstructure of the polymer. Thus it is important to have reliable values for these parameters. At the same time it suggests that experimental studies of composition and microstructure can be used to evaluate the various r s. 

The probabilities of the various dyad, triad, and other sequences that we have examined have all been described by a single probability parameter p. When we used the same kind of statistics for copolymers, we called the situation one of terminal control. We are considering similar statistics here, but the idea that the stereochemistry is controlled by the terminal unit is inappropriate. The active center of the chain end governs the chemistry of the addition, but not the stereochemistry. Neither the terminal unit nor any other repeat unit considered alone has any stereochemistry. Equations (7.62) and (7.63) merely state that an addition must be of one kind or another, but that the rates are not necessarily identical. 

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. 

SAN resins show considerable resistance to solvents and are insoluble in carbon tetrachloride, ethyl alcohol, gasoline, and hydrocarbon solvents. They are swelled by solvents such as ben2ene, ether, and toluene. Polar solvents such as acetone, chloroform, dioxane, methyl ethyl ketone, and pyridine will dissolve SAN (14). The interactions of various solvents and SAN copolymers containing up to 52% acrylonitrile have been studied along with their thermodynamic parameters, ie, the second virial coefficient, free-energy parameter, expansion factor, and intrinsic viscosity (15). 

G-5—G-9 Aromatic Modified Aliphatic Petroleum Resins. Compatibihty with base polymers is an essential aspect of hydrocarbon resins in whatever appHcation they are used. As an example, piperylene—2-methyl-2-butene based resins are substantially inadequate in enhancing the tack of 1,3-butadiene—styrene based random and block copolymers in pressure sensitive adhesive appHcations. The copolymerization of a-methylstyrene with piperylenes effectively enhances the tack properties of styrene—butadiene copolymers and styrene—isoprene copolymers in adhesive appHcations (40,41). Introduction of aromaticity into hydrocarbon resins serves to increase the solubiHty parameter of resins, resulting in improved compatibiHty with base polymers. However, the nature of the aromatic monomer also serves as a handle for molecular weight and softening point control. 

In order to increase the solubiUty parameter of CPD-based resins, vinyl aromatic compounds, as well as other polar monomers, have been copolymerized with CPD. Indene and styrene are two common aromatic streams used to modify cyclodiene-based resins. They may be used as pure monomers or contained in aromatic steam cracked petroleum fractions. Addition of indene at the expense of DCPD in a thermal polymerization has been found to lower the yield and softening point of the resin (55). CompatibiUty of a resin with ethylene—vinyl acetate (EVA) copolymers, which are used in hot melt adhesive appHcations, may be improved by the copolymerization of aromatic monomers with CPD. As with other thermally polymerized CPD-based resins, aromatic modified thermal resins may be hydrogenated. 

Over a period of about 50 years, the science of polymer chemistry has developed a comprehensive means of polymer characterization techniques. In the case of PE, these parameters include the composition, molecular weight, and compositional distribution. The composition of ethylene copolymers is usually measured by C-nmr, H-nmr, or in techniques. 

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. 

Crystallinity and Density. These two parameters, which are closely related, depend mosdy on the amount of a-olefin in the copolymer. Both density and crystallinity of ethylene copolymers are also influenced by their compositional uniformity. Eor example, for LLDPE resias with different a-olefin (1-hexene) content, the density (g/cm ) is as follows ... 

Physical Properties. LLDPE is a sernicrystaUine plastic whose chains contain long blocks of ethylene units that crystallize in the same fashion as paraffin waxes or HDPE. The degree of LLDPE crystallinity depends primarily on the a-olefin content in the copolymer (the branching degree of a resin) and is usually below 40—45%. The principal crystalline form of LLDPE is orthorhombic (the same as in HDPE) the cell parameters of nonbranched PE are a = 0.740 nm, b = 0.493 nm, and c (the direction of polymer chains) = 0.2534 nm. Introduction of branching into PE molecules expands the cell slightly thus a increases to 0.77 nm and b to around 0.50 nm. 

There are many examples known where a random copolymer Al, comprised of monomers 1 and 2, is miscible with a homopolymer B, comprised of monomer 3, even though neither homopolymer 1 or 2 is miscible with homopolymer 3, as illustrated by Table 2. The binary interaction model offers a relatively simple explanation for the increased likelihood of random copolymers forming miscible blends with other polymers. The overall interaction parameter for such blends can be shown (eg, by simplifying eq. 8) to have the form of equation 9 (133—134). 

When more than routine water resistance is required, a copolymer vinyl acetate emulsion can be used. The plasticizing comonomer in the polymer particles increases their intrinsic coalescing ability thus, they can coalesce more readily than homopolymer particles to a film that has a higher resistance to water. This resistance to water does not extend to the organic solvents, however, which are better resisted by homopolymer films. The soft copolymers have lower solubility parameters than homopolymers and are more readily attacked by solvents of low polarity, eg, hydrocarbons. 

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