Polystyrene phase relationships

Fracture Surface Morphology and Phase Relationships of Polystyrene/Poly(methyl Methacrylate) Systems... 

The phase relationships of two-phase polymer systems also have been of considerable interest in recent years. In an important series of papers, Molau and co-workers (19-24) studied systems, which were denoted POO emulsions (polymeric oil-in-oil), prepared by dissolving a given polymer in monomer and then polymerizing the monomer. During polymerizations of this type the composition of the respective phases reverses, and a phase inversion process was proposed to explain this. A similar process has been suggested as the mechanism by which poly-butadiene forms the dispersed phase in the manufacture of high-impact polystyrenes (22,25). Recently, Kruse has pointed out that this phase-inversion point may correspond to that point on a ternary phase diagram at which the reaction line bisects a tie line (26), and we have advanced a similar point of view in our earlier reports (17,18, 27). 

In the previous section we have described the three types of phase behavior observed in the low-molecular-weight PMMA/PS system and reviewed the four types observed in the low-molecular-weight PS/PMMA system. These various phase relationships have been studied in terms of their dependence on the molecular weight (Mn) and weight percent (W) of the initial polymer present. Further, we have presented quantitative data concerning the sizes of the dispersed particles, again correlated to variations in Mn and W. In this section we will discuss the results in terms of the poly (methyl methacrylate )/polystyrene/styrene and poly-styrene/poly( methyl methacrylate)/methyl methacrylate ternary phase diagrams, whichever is appropriate. 

Phase Relationships. The first systematic investigation of the two-phase behavior of polymer/polymer/solvent systems was probably made by Dobry and Boyer-Kawenoki (2) for a variety of polymer pairs, and more recently this work was extended by Kern and Slocombe (3) and Paxton (35) to a number of other systems including several vinyl polymers. Typically, the three-component phase behavior is as shown in Figure 19 for the polystyrene/polybutadiene/benzene system (2), where a one-phase (polystyrene/polybutadiene/benzene) region is separated by a phase boundary from a two-phase (polystyrene-rich/benzene and polybutadiene-rich/benzene) mixture. As with any three-component system of this type, a critical point exists somewhere near the maximum of the phase boundary, and appropriate tie lines give the compositions and amounts of the respective phases in the two-phase region. 

Dobry and Boyer-Kawenoki (1947) investigated the phase relationships existing in ternary systems polymer (l)-polymer (2)-mutual solvent (3). They prepared dilute solutions of polymers in common solvents, and then mixed the two solutions of interest. All of the polymer pairs studied were found to undergo phase separation at only 5-10% polymer concentration. For instance, cellulose acetate and polystyrene were immiscible at 5% concentration in toluene. These investigators concluded that incompatibility of two polymers even highly diluted is the normal situation. 

Recently R. Kuhn etal.( 968a, b Kuhn, 1968) studied the phase relationships of polystyrene-poly(methyl methacrylate) by employing an ingenious dilute solution light-scattering technique. Equations derived from phase separation quantities could be extrapolated to the pure phases, yielding the conclusion that if both polymers had molecular weights less than about... 

MORPHOLOGY AND PHASE RELATIONSHIPS OF LOW-MOLECULAR-WEIGHT POLYSTYRENE IN POLY (METHYL METHACRYLATE) AND METHYL METHACRYLATE/ STYRENE COPOLYMERS... 

Four types of phase behavior characteristic of the PS/P(MMA-S) system have been described and illustrated in some detail in the previous section and further, the average particle sizes have been tabulated as a function of molecular weight and weight percent of PS initially present in the PS/MMA-S mixture and of the composition of the final P(MMA-S) copolymer resulting after polymerization. In the section we will discuss these results in terms of the ternary polystyrene/poly(methyl methacrylate-styrene)/methyl methacrylate-styrene phase diagram, dealing with (1) the four types of phase relationships, (2) particle size, and lastly (3) multiple emulsions or subinclusions within the dispersed phase. 

By combining Eqs. (8.42), (8.49), and (8.60), show that Vi°(52 - 5i) = (l/2)RTj., where T. is the critical temperature for phase separation. For polystyrene with M = 3 X 10, Shultz and Floryf observed T. values of 68 and 84°C, respectively, for cyclohexanone and cyclohexanol. Values of Vi° for these solvents are abut 108 and 106 cm mol", respectively, and 5i values are listed in Table 8.2. Use each of these T. values to form separate estimates of 62 for polystyrene and compare the calculated values with each other and with the value for 62 from Table 8.2. Briefly comment on the agreement or lack thereof for the calculated and accepted 5 s in terms of the assumptions inherent in this method. Criticize or defend the following proposition for systems where use of the above relationship is justified Polymer will be miscible in all proportions in low molecular weight solvents from which they differ in 5 value by about 3 or less. 

As SR decreases, 1 must be decreased too (and thereby also the inlet pressure loss/total pressure ratio is decreased). This is what is really observed when dispersed fillers are added to polymer [182,190,193,194], The rubber phase in heat resistant polystyrene behaves much like a dispersed filler it also diminishes the inlet correction [195]. For polystyrene with different fillers the following relationship was found to be valid [196] ... 

Published refractive index data for the mobile phase, polystyrene, polyacrylonitrile, and the two monomers were used to calculate refractive index detector calibrations for the two homopolymers. The published data were used to determine relationship between refractive index increments of monomer and corresponding homopolymer. Chromatographic refractometer calibrations for the two homopelymers were then calculated from experimentally measured calibration data for the two monomers. 

The compositional and two-phase morphological relationships of "A-B" blocks, the "A-B-A" and starblocks have been studied intensively. It has been demonstrated that there is a substantial difference between random copolymers and block polymers, and this difference is based solely on the architectural arrangement of the monomeric units. One of the most important differences is that one Tg is observed in the random copolymer, which is related to the overall composition of the polymer. The block polymer has been shown to have two Tg s - one for polystyrene and one for the polydiene segment, and that these Tg s are not affected by the composition of the block copolymer. Since we can now synthesize large quantities of these pure block polymers, more detailed physical studies can be carried out. The two Tg s observed in... 

One may attempt to derive the ideal shear strength So of the van der Waals solid normal to the chain axis from the value of the lateral surface free energy, a. This value is well known for common polymers such as PE or polystyrene (PS) (Hoffman et al, 1976) or else can be calculated from the Thomas-Stavely (1952) relationship a = /a Ahf)y, where a is the chain cross-section in the crystalline phase, Ahf is the heat of fusion, and y is a constant equal to 0.12. If one now assumes that a displacement between adjacent molecules by Si within the crystal is sufficient for lattice destruction then the ultimate transverse stress per chain will be given by So = cr/31. The values so obtained are shown in Table 2.1 for various polymers. In some cases (nylon, polyoxymethylene, polyoxyethylene (POE)) the agreement with experiment is fair. In the others, deviations are more evident. In order to understand better the discrepancy between the experimentally observed and the theoretically derived compressive strength one has to consider more thoroughly the micromorphology of polymer solids and the phenomena caused by the applied stress before lattice destruction occurs. 

Measurements [5] in the system of polystyrene/o-xylene droplets in water, in which the viscosity of the organic phase was varied between 0.78 and 1500 mPa s, confirmed the theoretically derived expression (6.21) given above. The following relationship was found ... 

The polystyrene data provide evidence tiiat a cyclic intermediate is involved as part of the chain-breaking mechanism. If one assumes that the kinetics of polymerization and depolymerization are the same, and that solution and gas-phase kinetics are governed by the same molecular factors, then one can apply the relationship ... 

Figure 3.22. Relationship between fatigue crack propagation rate per cycle dajdn and the range of applied stress intensity factor AK for various modifications of polystyrene (Hertzberg et a/., 1973). Note the toughening effect of incorporating a rubbery phase, as in HiPS or ABS, compared to the weakening effect of crosslinking.

Because the solubility and conformation of the chain portions vary independently in dilute solution, the temperature dependence of such systems can be used to examine the various interactions among the components. For example, Girolamo and Urwin (1971) found a sharp maximum in the intrinsic viscosity-temperature relationship of poly(isoprene-h-styrene) dissolved in cyclohexane, a 0-solvent for the polystyrene component at 34 C. (See Figure 4.1.) The authors attribute the anomalous viscosity behavior to a transition that marks the change from the phase-separated form for the polystyrene component to the dissolved, random conformation. 

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