Compatibilization Using Low Molecular Weight Reactive Additives

The fundamentals and practice of compatibilizing polymer blends using polymeric additives, has been amply discussed in several earlier chapters of this volume. Here we describe a relatively new technique for reactive compatibilization, which involves the addition of low molecular weight components. Using many two component systems we review how some of these components show the ability to form copolymers of the two starting polymer constituents during melt processing. 

The effectiveness of these components can be enhanced by co-catalysts, coreactants or surface active fluids. While the precise chemistry is not always clear, noticeable improvements in morphology and mechanical properties are reported. Some of the cases described are early examples of what may be a new approach to reactive blend compatibilization. 

Most polymers are immiscible with each other. When two or more immiscible polymers are melt blended, without any planned compatibilization process, the components of the blend form different phases, which are separated from each other in the final product. This phase separation is due to the high surface tension between the immiscible polymer components in the interface region. The compatibilization of an immiscible polymer blend relies on the reduction of this interfacial tension. Normally, a blend that has been compatibilized can still be phase separated, but with a finer, stabilized dispersion of minor phase in the matrix. Improvement in mechanical properties of compatibilized blends are often observed due to a better adhesion between different phases and/or a better stress distribution in the solid state morphology when the material is under stress. 

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 latter process mentioned above is called in situ reactive compatibilization and is the major focus of this volume. 

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Compatibilization Using Low Molecular Weight Reactive Additives... 

Einally, a direct, reactive compatibilization by addition of an active, low molecular weight coupler can be used to upgrade and compatibilize mixtures of engineering resins. The process may be expensive (the required tapered block copolymers are usually dear), thus used only in specific cases. 

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