Polymeric Acids and Anhydrides

These are an interesting class of surface modifiers, now finding significant commercial uses and capable of being used as dispersants and coupling agents with a wide range of filler types. With these products, the unsaturated acid, or pre-cursor such as anhydride, is pre-reacted onto a suitable polymer backbone. Two main classes of product are available, one with a saturated hydrocarbon backbone, the other with an unsaturated one. 

The use of such materials was prompted by the need to find coupling agents for calcium carbonate, as silanes were largely ineffective with this filler. Simple unsaturated acids also appeared to have little effect, but Hutchinson and Birchall found unsaturated polymeric acids to be excellent treatments for precipitated calcium carbonate [39]. The concept was developed and extended by Evans and co-workers [40, 41]. 

Sufficiently high levels of acid can be introduced to allow water soluble products to be produced, and so this type of additive can be used either pre-coated onto a filler, or added separately during compounding. The relative merits of the two processes have been discussed earlier. 

The effectiveness of an MPBD type additive when pre-coated onto precipitated calcium carbonate is demonstrated in Table 4.5. This compares uncoated, fatty acid coated, and MPBD coated fillers in a crosslinked ethylene-propylene-diene terpolymer (EPDM) elastomer and clearly shows the benefits arising from the use of the latter coating. 

Property Untreated filler Fatty acid coated MPBD coated 

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