Reactive Group Content of the Reacting Polymers

When multifunctional polymers are used in reactive compatibilization (see Alternatives 2 and 3), their reactive group content (RGC) is expected to influence the extent of the interfacial reaction (at constant blend composition) and the molecular architecture of the in situ formed compatibilizer. For instance, there must be a change from a single graft to a multiple-graft comb-like structure, as the RGC of one of the two reactive polymers is increased. This change in the molecular architecture can affect the stability of the compatibilizer at the interface and its physical entanglement with the chains in the phases to be compatibilized. Finally, the RGC of multifunctional preciu ors may also have an effect on the miscibility with the nonfunctional chains in which they are dispersed. 

De Roover studied the effect of the RGC of maleic anhydride (MA) grafted polypropylene (PP-g-MA) on the average size of the PP phases dispersed in nylon 6. The size decreased rapidly with increasing RGC of PP and then levels off. Because the reaction of maleic anhydride with the amine end-groups of nylon 6 was close to completion, a direct relationship between the average size of the dispersed PP phases and the extent of the grafting reaction was proposed by this author [98]. 

The mechanical properties of the polyblends also depend on the architecture of the compatibilizer. A Monsanto patent reported on the influence of the MA content of 

The pair of reactive groups used (NH2/MA vs. carbamate/MA) and the RGC of the reactive SAN chains affected not only the extent of the interfacial reaction, but also the capability of the compatibilizer formed in situ to improve the toughness. 

In the case of SAN bearing primary amine, a unique dependence of the rubber particle diameter (D ) on the SAN reactive groups/anhydride molar ratio was observed, regardless of the RGC of the SAN chains (Fig. 4.14 (top)). This suggests that the particle size was basically controlled by the total amount of reactive groups and by the completeness of the compatibilization reaction for a constant mixing time. In the case of SAN-carb, the same dependence was found, provided that 3.3 more carbamates than amines were added to the polyblend (Fig. 4.14 (top)). This 3.3 coefficient expressed the difference in the intrinsic reactivity of the amine and the carbamate, respectively, towards maleic anhydride. 

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