Specific retention volume, polymer blends

IGC was used to determine the thermodynamic miscibility behavior of several polymer blends polystyrene-poly(n-butyl methacrylate), poly(vinylidene fluoride)-poly(methyl methacrylate), and polystyrene-poly(2,6-dimethyl-1,4-phenylene oxide) blends. Specific retention volumes were measured for a variety of probes in pure and mixed stationary phases of the molten polymers, and Flory-Huggins interaction parameters were calculated. A generally consistent and realistic measure of the polymer-polymer interaction can be obtained with this technique. 

Figure 3.6 Variation of retention with the composition of the stationary phase in GLC. Stationary phase styrene-butadiene polymer blends and copolymers, the butadiene fraction is plotted on the horizontal axis, (a) Specific retention volumes for three n-alkanes and benzene. V is proportional to the capacity factor, (b) the retention index for benzene. The solid line is calculated from the straight lines in figure 3.6a. The circles (polymer blends) and triangles (copolymers) represent experimental data. Figure taken from ref. [310], Reprinted with permission.

The usefulness of inverse gas chromatography for determining polymer-small molecule interactions is well established (1,2). This method provides a fast and convenient way of obtaining thermodynamic data for concentrated polymer systems. However, this technique can also be used to measure polymer-polymer interaction parameters via a ternary solution approach Q). Measurements of specific retention volumes of two binary (volatile probe-polymer) and one ternary (volatile probe-polymer blend) system are sufficient to calculate xp3 > the Flory-Huggins interaction parameter, which is a measure of the thermodynamic... 

The procedure for IGC involves coating the stationary inert support material with the polymers and the blends and measuring the retention time according to GC protocols. The retention time is a function of the activity of the probe and can be used to qualitatively assess interactions in the polymer blend by employing probes such as hydrogen bonding, polar or non-polar probes. The key experimental parameter, V°, is the specific retention volume and is determined from ... 

A series of pure low molar mass solutes with different polarities, such as alkanes, acetates, alcohols, formic acid, dimethyl amine and water were injected into the chromatographic colunm that contains the polymer blend. Their interaction with the stationary phase will reveal the effect of the chemical nature of the injected solutes on their miscibility with the blend. Several chromatographic quantities, illustrated in Equation 1 are precisely measured directly from the IGC experiment. These quantities will yield the specific retention volume. Kg". Kg" is the key term in the calculation of thermodynamic parameters and is commonly used to describe the chromatographic elution behavior of solutes. It is defined as ... 

The portion of a composition having a particular MW range and a particular SLCBI may be expressed in terms of wt% calculated from the SEC measurements. Its value should be 100 wt% at zero retention volume and zero after the polymer composition has fully eluted. For various applications, the SLCBI should be determined for a specific MW, e.g., M , = 100 or 300 kg moP. An example of the SLCBI plot is presented in Fig. 18.9. Here PE-1 represents the most common behavior. Its blends with PE-2 are expected to be advantageous with good transparency and mechanical performance resulting from strong interactions between phases. 

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