Miscible polymers above room temperature

The order of decreasing viscosity is as follows C q > C12 > C14 > precursor. This order is contrary to that of fully substituted PMAS polymers (7). The decrease in viscosity in this order probably results from the decrease in side-chain miscibility with poly(dimethylsiloxane). Longer side chains, such as Ci4 side chains, are expected to phase-separate and form a more-ordered polymer compared with short side chains (Cio)- However, C12 and Ci4 side chains are not long enough to crystallize above room temperature. 

Polymer pairs miscible at room temperature that appear to have a lower critical solution temperature (LCST) above room temperature. These polymer pairs are also fisted in one of the earlier Tables, usually Table 21.1 or 21.2. 

TABLE 6. POLYMER PAIRS MISCIBLE AT ROOM TEMPERATURE THAT APPEAR TO HAVE A LOWER CRITICAL SOLUTION TEMPERATURE (LCST) ABOVE ROOM TEMPERATURE... 

The above equation also explains why two different polymers are seldom miscible. Both solute and solvent are now polymeric and thus both suffer from the entropy decreases described above. It also explains why it is necessary to heat a mixture in which the solute does not dissolve at room temperature. This increase in T increases the magnitude of the last term in equation (23), and this is the term that generally makes the free energy change negative. 

It follows from Eq. (7.12) that only positive values of y are permitted, whereas it was mentioned above that the criterion for complete solvent-polymer miscibility is yn < 0.5. The conclusion is that the difference in solubility parameters of solvent and polymer must be small. If we assume that Vs 80 cm3/mol = 0.8 x 10-4 m3/mol, then at room temperature, the maximum value of l<5p-<5sl would be 4 (MJ/m3)1/2 = 2 (cal/cm3)1/2. This number, of course, depends strongly on the liquid molar volume. 

The X parameters of a large number of polymer blends exhibit this kind of temperature dependence. An example of this is the SPB(88)/JSPB(78) blend [system 27a], and the temperature dependence of x is shown in Fig. 19.1(a). Increasing temperature in such blends leads to increased miscibility. This behavior is often referred to as upper critical solution temperature (UCST) behavior. A typical phase diagram obtained from such systems is shown in Fig. 19.1(b). The spinodal and binodal curves were calculated for a SPB(88)/JSPB(78) blend with N = 2,000. A 50/ 50 mixture of these polymers is predicted to be two phase at room temperature but single phase at temperatures above 105 °C. The qualitative features of the phase diagrams obtained from all type I blends will be similar to Fig. 19.1(b). Of course the locations of the phase boundaries will depend on A, B, and N. 

Thermal analysis by DSC showed single, composition-dependent TgS at all PCL contents in blends with both PC/TMPC 1 1 and PC/TMPC 7 3 (Fig. 50). Kim and Paul stated that this implied that blends were miscible in all proportions. However, the blends were cloudy at room temperature due primarily to PCL crystallinity and observed TgS were not necessarily representative of the overall composition as amorphous polymer. The cloudiness decreased above Tj of TMPC no liquid-liquid phase separation was observed up to 350 °C, and the systems were totally miscible at high temperatures. 

The system consists of solvent mixture that is biphasic at room temperature and becomes homogeneous when heated (e.g., heptane and 90% DMA/water become miscible in all proportions above 65°C). After completion of the reaction and cooling to room temperature the reaction products are staying in the nonpolar phase and can be isolated by simple phase separation. The polar phase that contains the polymer bound catalyst can be reused in further runs by adding fresh substrate solution in heptane. 

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