SBM triblock terpolymer

Fig. 15 Schematic of the morphological arrangement in PPE/SAN blends compatibilized by SBM triblock terpolymers - nanostructured raspberry morphology (reprinted from [45])...

The aim of this section, therefore, is to correlate systematically the compatibilization of PPE/SAN 60/40 blends by SBM triblock terpolymers with the foaming behavior of the resulting blend. The reduction of the blend phase size, the improved phase adhesion, a potentially higher nucleation activity of the nanostructured interfaces, and the possibility to adjust the glass transitional behavior between PPE and SAN, they all promise to enhance the foam processing of PPE/SAN blends. 

The solubility of carbon dioxide at the selected saturation conditions of 5 MPa and 40°C, is shown in Table 1. Both the uncompatibilized and the compatibilized PPE/SAN blends absorb similarly high amounts of carbon dioxide in the range of 100, mgg-1. However, in contrast to one-phase systems, the solubility data of the overall multiphase blend is not sufficient to describe the system, but the content of carbon dioxide in each blend phases needs to be considered. In the case of PPE/SAN blends compatibilized by the SBM triblock terpolymers, one can distinguish three distinct phases, when neglecting interfacial concentration gradients (idealized case) (1) the PPE phase intimately mixed with the PS block, (2) the SAN phase mixed with the PMMA block, and (3) the PB phase located at the interface between PPE/PS and SAN/PMMA. 

Fig. 17 Effect of compatibilization via SBM triblock terpolymers on the glass transition temperature of PPE/SAN blends, in absence and in presence of carbon dioxide (as predicted by [75] and [76, 77])...

For miscible blend phases, these parameters need to be described as a function of the blend composition. In a first approach to describe the behavior of the present PPE/PS and SAN/PMMA phases, these phases will be regarded as ideal, homogeneously mixed blends. It appears reasonable to assume that the heat capacity, the molar mass of the repeat unit, as well as the weight content of carbon dioxide scale linearly with the weight content of the respective blend phase. Moreover, a constant value of the lattice coordination number for PPE/PS and for SAN/PMMA can be anticipated. Thus, the glass transition temperature of the gas-saturated PPE/SAN/SBM blend can be predicted as a function of the blend composition (Fig. 17). Obviously, both the compatibilization by SBM triblock terpolymers and the plasticizing effect of the absorbed carbon dioxide help to reduce the difference in glass transition temperature between PPE and SAN. 

In summary, compatibilization of PPE/SAN blends via SBM triblock terpolymers allows one to enhance significantly the homogeneity of the foam, while simultaneously reducing the cell size by heterogeneous nucleation activity of the... 

As discussed in the previous sections, the blend morphology as well as the processing window of the individual blend components can be identified as key factors for the foamability of multiphase blend systems [47, 84], As a first step, compatibilization via SBM triblock terpolymers was exploited for controlling the blend morphology on a nanoscale, and for reducing the difference in processing window between PPE and SAN. However, in order to exploit the benefits of all blend phases, the properties of each blend phase and the overall microstructure of the blend need to be controlled. 

Fig. 31 Morphology of (PPE/PS)/SAN/SBM blends following compression-molding (PPE/PS - dark, SAN - bright, PB block of the SBM triblock terpolymers - black)...

A blend of an ABC triblock terpolymer with a BC diblock copolymer is schematically shown in Figure 24. When comparing blends of a lamellar ABC triblock terpolymer with a lamellar AB or lamellar BC diblock copolymer with all block lengths being similar, it was found for the example of a SBM triblock terpolymer and the corresponding diblock copolymers (SB, BM) that blends of SBM with SB macrophase separate while the blends of SBM with BM form common superstmctures. This has heen confirmed by theory. Miscibility can be expected if the interfadal tensions of the diblock copolymers follow the relationship (yABZ/Bc) < 1,... 

SBM) as a compatibilizer. As a result of the particular thermodynamic interaction between the relevant blocks and the blend components, a discontinuous and nanoscale distribution of the elastomer at the interface, the so-called raspberry morphology, is observed (Fig. 15). Similar morphologies have also been observed when using triblock terpolymers with hydrogenated middle blocks (polystyrene-W<9ck-poly(ethylene-C0-butylene)-Wock-poly(methyl methacrylate), SEBM). It is this discontinuous interfacial coverage by the elastomer as compared to a continuous layer which allows one to minimize the loss in modulus and to ensure toughening of the PPE/SAN blend [69],... 

Finally the morphologies of ternary linear block copolymers and heteroarm star terpolymers are compared. Here systems containing I or B are also compared, since these two polymers show rather similar interactions toward the other blocks (see Table 2 for solubility parameters). Figure 22 shows in the left column symmetrically composed SIM heteroarm star terpol5uners (134) and linear BSM and SBM triblock copolymers (76). In the right column corresponding SBV (135) and SIV (144) heteroarm star terpolymers are compared with their linear compositional... 

Triblock terpolymers of styrene, butadiene (or isoprene), and methyl methacrylate with the block sequences SBM or SIM correspond to the set/AC[Pg.10]

Figure 8 Moiphological transitions of polystyrene-Woc -polybutadiene-Woc r-poly(methyl methacrylate) triblock terpolymers (SBM) by hydrogenation into polystyrene-Wock-poly(ethylene-co-butylene)-Woc/r-poly(methyl methacrylate) triblock terpolymers (SEBM) The subscript numbers indicate weight fractions, while superscript numbers indicate the totai moiecular weight in kg mol" . The color code is according to the contrasts obtained by TEM. SBM is stained with OSO4 PS (gray), PB (dark), PMMA (white) SEBM is stained with RUO4 PS (dark), PEB (gray), PMMA (white). Reprinted with permission from Abetz, V. In Encyclopedia of Polymer Science and Technology, 3rd ed. Kroschwitz, J. I., Ed. John Wiley Sons, inc. New York, 2002 Voi. 1, pp 482-523. ...

Changing the block sequence from SBM into BSM leads to triblock terpolymers belonging to the second set of relative... 

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