Interfacial tension between polymers copolymers

Table 2.5 Interfacial Tensions between Polymer Melt Pairs Including Compatibilizing Agents. MAH-PP Maleic Anhydride Grafted Polypropylene SEES Hydrogenated Triblock Copolymer of Styrene and Butadiene MAH-g-SEBS Maleic Anhydride Grafted SEES PEMA-Zn Poly(ethylene-co-methacrylic Acid) lonomer Neutralized by Zinc.

Additives can greatly reduce the interfacial tension between polymers and hence modify the mixing process and the properties of the blend. Block and graft copolymers are the most effective interfacial agents and can be added to the blend or formed during the mixing process by reactions between the base polymers. " There are theoretical treatments of the behavior of block copolymers at the polymer/polymer interface but comparable experimental data is scarce. 

The properties of immiscible polymers blends are strongly dependent on the morphology of the blend, with optimal mechanical properties only being obtained at a critical particle size for the dispersed phase. As the size of the dispersed phase is directly proportional to the interfacial tension between the components of the blend, there is much interest in interfacial tension modification. Copolymers, either preformed or formed in situ, can localize at the interface and effectively modify the interfacial tension of polymer blends. The incorporation of PDMS phases is desirable as a method to improve properties such as impact resistance, toughness, tensile strength, elongation at break, thermal stability and lubrication. 

Wagner M, Wolf BA (1993) Effect of block copolymers on the interfacial tension between two immiscible homopolymers. Polymer 34 1460-1464... 

Theories of the interfacial tension were reviewed by Wu [1], who also provided an extensive tabulation of experimental values for amorphous polymer-polymer interfaces [2], including both homopolymers and copolymers, at several temperatures. For example, the interfacial tensions between a number of pairs of homopolymers [2] are listed in Table 7.3. 

A separate compatibiiizing agent included in a blend may be a third material not derived from either of the two immiscible polymers. Representative examples include certain plasticizers, random copolymers, and block copolymers, which may lower the interfacial tension between the two immiscible polymer components. 

An example of adsorption of this kind is the adsorption occurring at the oil-water interface. The driving force for adsorption in this case is the minimization of the interfacial tension between the two interfaces. Typically, random copolymers or block copolymers, in which the monomeric imits are preferentially solvated in either of the two phases, adsorb readily at the interface. In the case of homopolymers, adsorption occurs either if the polymer is soluble in both the phases or if the polymer has functional groups that can reduce the interfacial tension. Thus, both polyCethylene oxide) and poly(methyl methaciylate) readily adsorb at the toluene-water interface. The former is soluble in both the phases while the latter has polar side groups that effectively screen the interactions between toluene and water. However, because of its hydrophobic nature polyst3U ene does not adsorb at the same interface (50). 

Often, even immiscible and/or incompatible polymers are also made compatible by addition of a compatibilizer. Compatibilizers are believed to primarily reside at the polymer/polymer interfaces. The compatibilizer can be presynthesized or formed by in situ polymerization. Often the product engineer can make a judicious choice of compatibilizer resulting in improvement of mechanical properties, sometimes with synergistic effects. The compatibilizer is believed to stitch itself across the polymer/polymer interfaces. The addition of a compatibilizer lowers the interfacial tension between the two immiscible phases. The compatibilizer may sometimes be made of block copolymer composed of two different components. One of the block components may be miscible with polymer A, and the block component may be miscible with polymer B. Even if a polymer A and polymer B are immiscible, such a block copolymer would compatibilize the blend of A and B. 

Ve believe that the ultimate solution to this problem and related problems with other IPN blend combinations lies in the next generation of styrenic block copolymers which will provide chemical groups on the hydrocarbon backbone which will provide specific interactions with complementary groups in a number of polar polymers and will succeed in significantly lowering interfacial tension between the component of the IPN blends. These polymers have been synthesized and are now in the development stage. 

As in the case of emulsion polymerization, particle morphology is ruled by the interplay between thermodynamics and kinetics. Equilibrium morphologies are reached when the internal viscosity of the polymer particle is low. Thus, due to the plasticizing effect of the alkyd resin, equilibrium morphologies are usually reached for alkyd/acrylic systems [96]. The equilibrium morphology is affected by the presence of graft copolymer that reduces the interfacial tension between the polymer phases in the particle. Methods to calculate the equilibrium morphology of multiphase polymer particles are available [43]. 

Anastasiadis et al. [45] investigated the compatibilizing effect of an anionically synthesized model FS-b-FYE diblock copolymer on the interfacial tension between PS and PVE model polymers as a function of the concentration of the copolymer additive. They utilized the pendant drop method [155] to measure the interfacial tension between the immiscible polymer fluids. A sharp decrease in interfacial tension was observed with the addition of small amounts of copolymer (Fig. 24),... 

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