Polymer solvent methods

Polymer-Solvent Method Refs. Potymer-Solvent Method Refs. 

Air-blown asphalts, more resistant to weather and changes ia temperature than the types mentioned previously are produced by batch and continuous methods. Air-blown asphalts, of diverse viscosities and flow properties with added fillers, polymers, solvents, and ia water emulsions, provide products for many appHcations ia the roofing industry. 

Tseng et al. [164] suecessfully used UNIFAC to optimize polymer-solvent interactions in three-solvent systems, determining polymer activity as a function of the solvent eomposition. The composition yielding the minimum in polymer aetivity was taken as the eriterion for optimum interaetion, and it eompared well with experimental measurements of dissolution rate and solution clarity. Better agreement was obtained using UNIFAC than using solubility parameter methods. 

Theta temperature (Flory temperature or ideal temperature) is the temperature at which, for a given polymer-solvent pair, the polymer exists in its unperturbed dimensions. The theta temperature, , can be determined by colligative property measurements, by determining the second virial coefficient. At theta temperature the second virial coefficient becomes zero. More rapid methods use turbidity and cloud point temperature measurements. In this method, the linearity of the reciprocal cloud point temperature (l/Tcp) against the logarithm of the polymer volume fraction (( )) is observed. Extrapolation to log ( ) = 0 gives the reciprocal theta temperature (Guner and Kara 1998). 

Values obtained for and a for a number of polymer-solvent pairs are given in Table XXX. It will be observed that the exponent a varies with both the polymer and the solvent. It does not fall below 0.50 in any case and seldom exceeds about 0.80. Once K and a have been established for a given polymer series in a given solvent at a specified temperature, molecular weights may be computed from intrinsic viscosities of subsequent samples without recourse to a more laborious absolute method. 

Reciprocals of the critical temperatures, i.e., the maxima in curves such as those in Fig. 121, are plotted in Fig. 122 against the function l/x +l/2x, which is very nearly 1/x when x is large. The upper line represents polystyrene in cyclohexane and the lower one polyisobutylene in diisobutyl ketone. Both are accurately linear within experimental error. This is typical of polymer-solvent systems exhibiting limited miscibility. The intercepts represent 0. Values obtained in this manner agree within experimental error (<1°) with those derived from osmotic measurements, taking 0 to be the temperature at which A2 is zero (see Chap. XII). Precipitation measurements carried out on a series of fractions offer a relatively simple method for accurate determination of this critical temperature, which occupies an important role in the treatment of various polymer solution properties. 

There are three methods for synthesizing polymers melt state compounding, in situ polymerization and solvent methods [185-187,177]. 

Solvent methods are similar to in situ polymerizations. During the first stage, the nanomaterial is dispersed in a solvent. In some cases a surfactant can be used as a bridge between the nanomaterials and the matrix (Fig. 4.9). This reaction occurs in a liquid or gel form in the presence of a solvent such as toluene, chloroform, acetonitrile, water, acetone, etc. The solution of modified nanoparticles is then added to a polymeric solution under agitation (at room or elevated temperatures) in order to ensure a homogeneous dispersion of the nanomaterials in the matrix. Finally, the polymer composite... 

Size exclusion chromatography (SEC) polymer elution profiles yield information regarding the molecular size distributions of polydisperse macromolecules. Polymer molecular weight distribution (MWD) represents an intrinsic property which provides direct correlation with many end-use physical properties and a universal criterion for polymer characterization (1). In order to convert elution profiles or chromatograms into MWD information proper calibration methods are required. SEC molecular weight calibration techniques represent experimental approaches for transformation of polymer elution profiles into MWD information and are dependent upon instrumentation, columns, and the polymer/solvent system under study. 

SEC calibration methods can be generally categorized into techniques which employ a series of narrow MWD standards and those which employ one (or more) broad MWD standards (2). Calibration techniques which utilize polydisperse, broad MWD standards have been found to be particularly useful when narrow MWD standards are not available or universal calibration methodology is impractical as for example with most water-soluble polymers or polymer/solvent/temperature combinations for which appropriate Mark-Houwlnk constants are not known or readily available. 

One of the most common techniques for determining x parameters for polymer-solvent systems is the vapor pressure method.(10) In this approach, the uncrosslinked polymer is exposed to solvent vapor of known pressure, p. The polymer absorbs solvent until equilibrium is established, x is related to p and V2, the volume fraction of polymer at equilibrium, by the Flory-Huggins equation (ll)... 

Samples were either prepared by direct addition of polymer to solvent (Method I) or by a careful method to reduce dust (Method II) In Method II, PBLG was added from a stock solution in distilled DMF via a 0 2ym filter (Millipore type FG) into preweighed cells that had been exhaustively rinsed with nearly dust-free water from a Millipore 4 stage purifier and dried Under vacuum, the samples were either concentrated or evaporated to dryness, depending respectively on whether a PBLG/DMF or PBLG/toluene sample was desired For... 

As a medium strength liquid (Table 16.1), THF is commonly used also in the coupled methods of polymer HPLC. It promotes desorption of medium polar polymers such as poly(acrylate)s and poly(methacrylate)s including poly(methyl methacrylate) from the nonmodified silica gel. Other strong(er) solvents widely used in the coupled polymer HPLC methods are acetonitrile that exhibits high UV transparency, and dimethyl formamide. The latter solvent readily decomposes into amine and formic acid and its strength may differ from batch to batch. 

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