Polystyrene phases

It is worth noting that occasionally high Tg compatible additives are incorporated into the polystyrene phase, when the PSA requires higher temperature performance. These additives are usually based on poly-a-methylstyrene. 

A new process to develop interface vulcanization is grafting of selective accelerators onto a polymer chain, which in the subsequent process of vulcanization acts as an effective cure accelerator for the second polymer component in the blend. Beniska et al. [6] prepared SERFS blends where the polystyrene phase was grafted with the accelerator for curing SBR. Improved hardness, tensile strength, and abrasion resistance were obtained. Blends containing modified polystyrene and rw-1,4-polybutadiene showed similar characteristics as SBS triblock copolymers. 

There is a limit in composition, at about 15% elastomer content, at which stirring alone can no longer induce the polystyrene phase to be continuous, and the quality of the mechanical properties of the materials change drastically. 

It can be seen from Table I that the oil phase viscosity increases at a much slower rate than the polystyrene phase due to its lower reactivity at 80°C. Also, the volume of the polystyrene-rich phase is increasing at the expense of the oil-rich phase as styrene and polystyrene migrate to the polystyrene-rich phase. 

After polymerization was complete, transmission electron microscopy was carried out on thin sections of the 10/90 and 20/80 compositions. Confirming the optical micrographs, the polystyrene phase was continuous for the fully reacted product. As illustrated in Figure 5 for the 10/90 system, the oil phase (stained dark) contains a considerable amount of occluded polystyrene. For the 20/80 system, data not shown, dual phase continuity was found. The polystyrene phase was relatively pure, but the oil-rich phase had much occluded... 

The SIN s from castor oil and the other oils were tough materials, either reinforced elastomers or impact resistant plastics depending on their composition and whether phase inversion had occurred. Impact strengths in the range of 40-60 J/m were obtained. The glass transitions of the rubber phase of the SIN s tended to be a little higher than those shown in Table IV. The polystyrene phase... 

Figure 20. Model of two consecutive growth stages for the polystyrene phase. (1) Early stages microgels of increasing size. (2) Intermediate to final stages Domains become wormlike cylinders and then interconnected cylinders that exhibit dualphase continuity 41).

A system with clearly defined disperse (A) and continuous (B) component phases is afforded by copolymers of styrene (A) grafted onto a polydimethyl siloxane matrix (B)101 Lack of appreciable interaction between the components was indicated by gas solubility and Tg measurements. The permeability coefficient of propane and other paraffins over a composition range vA = 0 — 0.55 followed the trend described by Eqs. (30)—(33) (with PA = 0, in view of the fact that the polystyrene phase is practically impermeable). Of particular relevance to the present discussion is the close agreement with the Bruggeman, and definite deviation from the Bottcher, equations at higher vA (cf. Fig. 11). Corresponding block copolymer membranes with vA = 0.34 also fitted into this pattern, except in one case where the structure was found to be lamellar and P was considerably lower. 

Shen and Kaelble (29) found the same linear dependence in the region —60° and 60°C but state that below —50°C and above 80°C the temperature dependence of Kraton 101 could be described by the WLF equation with cx = 16.14, C2 = 56, and Tr — — 97°C below —50°C, and Tr — 60°C above 80°C. They ascribe the temperature dependence below —50 °C to the pure polybutadiene phase and that above 80 °C to the pure polystyrene phase. They then assume that at temperatures between —50° and 80°C the molecular mechanisms for stress relaxation are being contributed by an interfacial phase visualized as a series of spherical shells enclosing each of the pure polystyrene domains and characterized... 

In an investigation of the birefringence and stress relaxation of Kraton 101 cast from solution in toluene and in methyl ethyl ketone, Wilkes and Stein (33) considered the relaxation modulus to be a weighted average of the moduli of the pure polybutadiene and polystyrene phases. Ferry and co-workers, in their investigations of time-temperature superposition in polymethacrylates with relatively long side chains, found the com-... 

As shown in Figures 5 and 7 the nature of the solvent does not appear to have any effect on T0 within experimental error. However, the solvent can have a profound influence on the morphology of cast block copolymer specimens. Thus, instead of the continuous polybutadiene phase normally observed, a continuous polystyrene phase appears to exist in Kraton 101 films cast from solution in MEK/THF mixtures (2). Methyl ethyl ketone has a solubility parameter of 9.3, only slightly higher than that of the solvents used in our work. It is clear from the data presented here that our films must have had continuous polybutadiene phases. 

Two other aspects of the behavior of these block polymers are noteworthy. The first is demonstrated in Figure 11 by the curve for the 40% styrene polymers. These exhibit an unusual yield point at very low strain, after which they show a typical curve for an elastomer. This yield point occurs only during the first draw and is not reproduced unless the sample is remolded or reheated. This behavior has been ascribed to the presence of a continuous polystyrene phase at such high styrene levels, and this has actually been observed by electron microscopy (I, 6). The interdomain contacts are, of course, disrupted on the first extension and cannot reform unless the material is reheated. 

Mechanical tests indicate that these blends do not behave like conventional blends and suggest that the polystyrene phase is continuous in the substrate. The moduli of the blends as a function of blend composition is plotted in Figure 10.6. The Voigt and Reuss models are provided for comparison (Nielsen, 1978) These are the theoretical upper and lower bounds, respectively, on composite modulus behavior our data follows the Voigt model, suggesting that both the polystyrene and polyethylene phases are continuous. In most conventional composites of polystyrene and HDPE, the moduli fall below the Voigt prediction indicating that the phases are discontinuous and dispersed (Barentsen and Heikens, 1973 Wycisk et al., 1990). 

Figures 3A, 3B, and 3C show the ultra-thin cross-sections of OsOi+-stained two-stage (styrene//styrene-butadiene) latex particles at the stage ratio of 20/80, whose S/B ratios in the second stage are 70/30 (LS-7), 90/10 (LS-8), and 95/5 (LS-9), respectively. It can be seen from the micrographs that the size of polystyrene phase domains decreases with decreasing butadiene level in the second-stage S-B copolymers and becomes so small at the S/B ratio...

Block Size and Glass-Transition Temperatures of the Polystyrene Phase in Different Block Copolymers Containing Styrene Blocks as the Hard Phase... 

When applying this method according to micrograms one can calculate volume fraction of HIPS rubber phase Vf in per centage Intermediate surface of rubber and polystyrene phases Sy in mm2/mm3 Mean cord spheres C which is proportioned to diameter of rubber peirticles C in / - Mean free distance among the particles MPD in yu., ... 

V/hile analysing the composition of phases of the full separation of the emulsion it was fo xnd that the experimentally found concentrations of polymers in these solutions differ from those calculated for the case when each polymer is present in one phase only. It can be supposed that due to the partial compatibility in both emulsion phases there are both polymers present, but the "rubber" phase is a polybutadiene solution with the admixture of small quantity of PS, and the "polystyrene" phase represents a polystyrene solution with the admixture of PB, On the basis that in model emulsions of equal compositions the voliirae of rubber phase increases as the molecular weight of polystyrene decreases, and My of homopolystyrene in the polystyrene phase increases (table IIlJ we can draw a conclusion that low-molecular fractions of polystyrene migrate into the rubber phase. 

---