Compatibilization strategies

Note that nearly all commercial polymer blends (the exception is blend of PVDF with PMMA) are immiscible. One tends to study miscibility not to develop single-phase commercial blends, but mainly to design better compatibilizers and compatibilization strategies. 

Of the various compatibilization strategies that have been devised, an increasingly common method is either to add a block, graft, or crosslinked copolymer of the two (or more) separate polymers in the blend, or to form such copolymers through covalent or ionic bond formation in situ during the Reactive Compatibilization step. The first of these processes was described in Chapter 4 of this Handbook, Interphase and Compatibilization by Addition of a Compatibilizer, while the second method is the topic of this Chapter. 

The references in this review are strictly limited to journal articles. Although the majority of Reactive Compatibilization examples are found in industrial research, these are documented mostly in patents. The majority of patents have so few details that often only an educated guess is possible concerning the compatibilization strategy employed. Numerous examples of industrial compatibilization methods have been provided in a recent book based on the patent literature [Utracki, 1998]. 

This chapter attempts to classify the specific copolymer architectures formed by the different chemical reactions that have been described in the open literature for Reactive Compatibilization processes. The emphasis is on illustrating the scope of these particular reactions, and not on presenting every known example of a particular compatibilization strategy. 

Unfunctionalized PPE may be compatibihzed with immiscible PA by addition of functionalized polystyrene capable of forming copolymer with PA (Table 5.16). This is a common compatibilization strategy for PPE blends since both PS itself and functionalized polystyrenes with a relatively low level of functionality are miscible with PPE. The examples below include use of anhydride-, acid-, and epoxide-functionalized polystyrenes, all of which are capable of reacting with nucleophilic end-groups on PA to form a graft copolymer. 

Compatibilization strategy for either addition or reactive blending requires that the copolymer migrates to the interface, thus, on the one hand lowering the thermodynamic immiscibility barrier between the two phases, and, on the other hand, engendering formation of the third phase, the interphase. 

To improve compatibility between phases, the conventional compatibilization strategies have generally been applied, such as the addition of a compatibilizing agent, which can be performed by modification of at least one of the polymers initially present in the blend ... 

The compatibilization strategies comprise (i) addition of a small quantity of cosolvent - a third component, miscible with both phases, (ii) addition of a copolymer whose one part is miscible with one phase and another with another phase, (iii) addition of a large amount of a core-shell copolymer - a compatibilizer-cum-impact modifier, (iv) reactive compounding that leads to modification of at least one macromolecular species that result in the development of local miscibility regions, and (v) addition of a small quantity of nanoparticles which influence blend structure similarly to particle-stabilized water/oil emulsions. 

It is noteworthy that homogeneity at fairly fine level is necessary for optimum performance, but some degree of microheterogeneity is usually desirable to preserve the individual properties of respective polymer components (Hess et al. 1993). Note that nearly aU commercial polymer blends (with the notable exception of the PVDF/PMMA blend) are immiscible. One tends to study miscibility not so much as to develop single-phase commercial blends, but mainly to design better compatibilizers and compatibilization strategies. 

This chapter has not presented every known example of a reactive compatibi-lization strategy, nor has it included every known polymer that has been compatibilized in an immiscible blend with one or more other polymers. However, the compatibilization strategies presented herein illustrate broadly general methods which may be applied to new polymer blends or applied to known polymer blends for a higher return on cost vs. performance ratio. 

The compatibilization strategies have been developed by the polymer blends industry for virtually any pair of immiscible polymers. The material recycling should profit from this waste pool of information. 

An alternative compatibilization strategy is to add one or more low-molecular-weight compounds which can react with both blend components. Typical examples of these are peroxides and/or bifunctional compounds. Although the... 

In earlier compatibilization strategies, the reduction of interfacial tension in a polymer blend was achieved by introducing a copolymer of which the different segments are miscible with different polymer components of the blend. This copolymer is called compatibilizer. Broadly speaking, there are two different ways to introduce the compatibilizer into a polymer blend ... 

The preparation of immiscible polymer blends with or without compatibilization strategies designed to obtain fine dispersions. 

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