Polyblends preparation

Methods. Polyblend samples were prepared by solution casting from tetrahydrofuran (THF), or chloroform or by injection molding using a Mini-Max Molder by Custom Scientific Instruments. Specific experimental details are given elsewhere (9,10,11). 

Polyblends were prepared by dissolving both polymers in benzene, followed either by precipitating with hexane, or by freeze drying. The concentration of the solutions was about 2g./dl. The resulting powder was then dried under vacuum at 40°-50°C. 

Evidently, the homogeneous complex phase is an equilibrium property for copolymers. Any effects resulting from the history of specimen preparation (cf., photomicrographs and dashed lines in Figures 9 and 10) are eliminated by annealing. In contrast, for polyblends the compatible phase is a metastable state. 

Elastomeric graft copolymers of methyl methacrylate upon diene and acrylic rubbers were prepared by R. G. Bauer and co-workers. These elastomers are compatible with rigid methyl methacrylate-styrene copolymers of identical refractive index, yielding transparent polyblends. 

Using these techniques to prepare the resin and rubber components of polyblends, transparent impact polymer blends can be obtained which exhibit mechanical properties comparable with ABS materials. Like ABS, they have a fairly flat modulus curve, which varies gradually over a wide temperature range (Figure 4). Impact properties are outstanding for these transparent impact polymers even at temperatures as low as —40°C. 

Preparation of Electron-micrographs. The polystyrene-rubber polyblend sample was etched by solvent according to the technique developed by Traylor. A double replica technique was used to prepare the sample. The first replica was methylcellulose, the second platinum and carbon, 800 A. thick. 

Cellulose is an old polymer with new industrial applications. The derivatization of cellulose has opened up tremendous production and marketing possibilities for the adhesives industry. Various important adhesives have been derived from cellulose ethers. The structure and molecular size of cellulose and their influence on swelling and solubility are important considerations in the preparation of cellulose derivatives for adhesive applications. Modern cellulosic adhesives derived from grafted copolymers and polyblends are also proving very useful. 

Copolymerization techniques offer the opportunity to control polymer structure and hence the degree of mixing of the components. The multiphase physical characteristics of polyblends are also observed in graft, block, and heterogeneous copolymers (4, 5). Materials suitable for broad temperature range viiBration damping have been prepared from polyblends (4, 6, 7), graft copolymers (2, 8), and IPN s. 

Heat-resistant [218] soft foams were prepared from the blends of hdPE with E-P random copolymers. The azodicarbanamide acts as a thermal antioxidant and the crosslinking of the blend was increased by electron beam radiations and foamed at 225 °C with 2320% expansion. A blend of 35 wt.% PE-PP (8 92), 15 wt.% E-P block copolymers, and 50 wt.% EPDM showed accelerated weathering resitance [219] 1000 h probably due to crosslinking between constituents of the block copolymer, polyblend and EPDM. The effect of filler and thermodynamic compatibility on kaolin-filled PE-PP blend was studied by Lipatov and coworkers [220]. The thermodynamic interaction parameter (%) decreased and thermodynamic stability increased by filler addition, the degree of crystallinity decreased with increasing thermodynamic compatibility of the components due to sharp decrease in the phase separation rate during cooling. 

On a cost-benefit basis, it is interesting to outline that the best mechanical performances of the PE-PS polyblends can be reached using a minimum amount (ca. 2wt%) of an appropriate diblock copolymer (19). Furthermore, not only reproducible samples can be prepared under processing conditions, but an apparent equilibrium of phase morphology and mechanical properties is obtained within half to a few minutes depending on the melt viscosity of the blend and especially the microstructure of the diblock copolymer. 

Following a brief review of the development of dynamic membranes and an overview of the current state of the art, Spencer (10) discusses dynamic polyblend membranes. In particular, he looks at the Influence that polymer selection and membrane preparation procedures have on membrane performance. Dynamic membranes composed of a poly(acrylic acid)/basic polyamine blend deposited on a ZOSS (hydrous zirconium oxide on stainless steel) ultrafiltration membrane are discussed. Their hyperfiltration or reverse osmosis properties are compared to the more traditional ZOPA (zirconium oxide plus poly(acrylic acid)) membrane. 

Additional types of hyperfiltration membranes produced by CARRE, Inc. Include polyblend membranes prepared by the deposition of pairs of polymers that form miscible blends ( 5). High rejection of molecular solute species in the molecular weight range above about 80 is obtainable with these dynamic polyblend membranes. 

Preparation of iPS-b-iPP-iPS-iPP Polyblends. The blends of iPS-fo-iPP, iPS, and iPP were prepared by completely dissolving all polymers and an antioxidant into o-dichlorobenzene at 165 °C, and using a 1 1 mixture of acetone and methanol as a precipitant. After being thoroughly washed and dried under vacuum at 60 °C for 20 h, the precipitated powders were compression-molded at 300 °C into sheets or plates suitable for cutting specimens for mechanical testing and morphologic study. 

The question then arose what would be the nature of the polyblend which could be prepared if the acrylic monomers were polymerized in the... 

Inasmuch as the emulsifying effect was studied semiquantitatively by a given film technique, the boundaries between areas may not be as sharp as in Figure 5. Area size may depend on polyblend type and on the technique used for blending the different polymers. Although study of the emulsifying effect of block copolymers in the PS-PI and PS-PMM systems has led qualitatively to similar conclusions, the areas defined in Figure 5 cannot be superimposed exactly for these two systems. With the film technique, which seems to be the most reproducible, a shift of the different boundaries can also be observed when various solvents are used for film preparation, especially preferential solvents for either polymer (10). 

The location of the copolymer was studied as a function of the characteristics of the polymers in the blend (e.g., homopolymer molecular weights and copolymer molecular weight and composition) which are related to the a and P of Equations 1 and 2. For a given PS-PI-Cop system, it was found that the location of Cop is practically independent of the amounts of PS, PI, and Cop in the polyblend. Therefore for such a system, two types of blends were generally prepared one rich in PS with PS forming the continuous phase (Blend 1), and one rich in PI with a continuous PI phase (Blend 2). The different fluorescence possibilities are listed in Table IV. If blue fluorescence is observed in the continuous PS phase of Blend 1, it can be inferred that Cop is soluble in PS and in fact the dispersed PS phase of Blend 2 (PI continuous phase) is also fluorescent. 

Block and graft copolymers (incompatible copolymers) — For block or graft copolymers in which the component monomers are incompatible, phase separation will occur. Depending on a number of factors — for example, the method of preparation — one phase will be dispersed in a continuous matrix of the other. In this case, two separate glass transition values will be observed, each corresponding to the Tg of the homopolymer. Figure 4.6 shows this behavior for polyblends of polystyrene (100) and 30/70 butadiene-styrene copolymer (0). 

The first commercial blend of two dissimilar polymers was Noryl, a miscible polyblend of poly(phenylene oxide) and polystyrene, introduced by General Electric in the 1960s. Since that time a large number of different blends have been introduced. A number of technologies have been devised to prepare polyblends these are summarized in Table 4.34. For economic reasons, however, mechanical blending predominates. 

Figure 2.8. Stress-relaxation data for a PVAc/PMMA 50/50 polyblend. The PMMA portion was prepared from a lightly crosslinked latex to suppress flow at high temperatures. Numbers at right are temperatures in °C. (Takayanagi et ai, 1963.)...

In the polyblends considered previously in Section 3.1, domain dimensions and fine structure were controlled by preparation techniques, such as by applying shearing forces during mixing, grafting reactions, etc. Most of... 

These systems, whose phase characteristics resemble those of the polyblends discussed in Chapter 3, can be prepared by first blending the molten polymers together until the minor component is dispersed in the form of droplets that are small in comparison to the fiber diameter desired (Allied Chemical Corp., n.d. Buckley and Phillips, 1969 Hayes, 1969 Mumford and Nevin, 1967 Papero et a/.,1967). The material is then melt-spun and drawn in order to orient both constituents and cause the dispersed phase to form elongated cylinders or fibrils. For satisfactory dispersion, the viscosities of both components must be comparable (for a discussion of rheological effects in molten polymer blends, see Section 9.6). An important biconstituent system is based on a combination of nylon 6 with a linear polyester poly(ethylene terephthalate), with nylon 6 as the continuous phase (Buckley and Phillips, 1969). As shown in Figure 9.5, fibrils of polyester... 

Flory and Ronca[126,127] predicted that asymmetric molecules with aspect ratios higher than 6.417 can act as a mesogett and mesogens with different aspect ratios also form liquid crystals. According to the theoretical predictions, an anisotropic solittion of single phase composed of polymeric mesogens with different aspect ratios is prepared, which was experimentally verified[128,129]. The theoretical predictions further suggest that miscible mesomorphic polyblends may be prepared. Takayanaki et a/.[56,130] exantined the phase transition of... 

Therefore, to minimize the effect of phase separation, the as-prepared polyblend solution is poured into an excess amount of nonsolvent such as methanol to obtain a quenched bulk powder of polymer blend. The obtained polymer blends could be molded into the desired shape by hot-pressing at 180°C for 5 min. Figure 8.43 shows the electrical conductivity of the molded blend as a function of PPy-DBSA weight fi-action [68]. The electrical conductivities of PPy-DBSA/PMMA blend exhibit a percolation threshold level at about 40%. Nevertheless, the PPy-DBSA/PMMA blends exhibit conductivities ranging from 10 to 10 S/cm with 2% PPy-DBSA, which satisfy the electrical conductivity required for static dissipative (10 to S/cm) or antistatic applications (10 to 10 S/cm). 

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