# Bitumen and Bitumen Modification: A Review on Latest Advances
## 3 Bitumen Chemical Modifiers
### Maleic Anhydride  
Maleic anhydride (MAH) is an unsaturated cyclic (five atom ring) compound with molecular formula C\({}_{4}\)H\({}_{2}\)O\({}_{3}\). It has been widely used as a bitumen modifier and bitumen-polymer compatibilizer. MAH-bitumen interaction is characterized by complex mechanisms (copolymerization with bitumen molecules [126] or Diels-Alder reactions [195; 196]). Nevertheless, it has been shown that meaningful physical properties change of bitumen are induced by MAH. In this respect [PERSON] et al. [197] studied a bitumen containing different amounts of MAH in terms of dynamic mechanical analysis (DMA), melt viscosity, and softening point. The results have shown that the chemical modification of bitumen with MAH improves the cracking resistance at low temperature and cohesive strength at high temperature.  
Chemical reactions between MAH and bitumens were also investigated by comparing the effects of MAH and the related di-acids and anhydrides such as succinic anhydrides (SAH). The results of FTIR and gas chromatography-mass spectroscopy analysis showed the presence of two acid groups (-COOH) for both MAH and SAH. This leads to the conclusion that the two anhydrides undergo ring opening to give the corresponding di-acid. Moreover, in the case of MAH, the disappearance of the double IR bond signal was noticed. This fact could be explained by its reaction (or coordination) with bitumen molecules [126].  
From another point of view, several studies have shown that the rheological properties of the blends obtained by adding to a bitumen MAH, SAH and different di-acids follow the order: MAH \(>\) SAH \(\sim\) dicarboxylic acids \(>\) monocarboxylic acid.  
These results suggest the hypotheses that the two carboxylic acid groups are able to link two bitumen molecules. The better result obtained by adding MAH to the bitumen was hypothesized to be due to the double bond of MAH that interacts by coordination or other bonding mechanism to the bitumen molecules creating an additional linking. However, a recent study has shown controversial results about the MAH-bitumen reaction. In this respect, new FTIR analysis has shown that the IR band due to the MAH ring was retained during the MAH-bitumen reaction [127]. This observation, leads to the hypotheses that both Diels-Alder and \(\pi\)-\(\pi\) charge-transfer mechanism are involved instead of a ring opening process. The \(\pi\)-\(\pi\) charge-transfer process was possible because of the polynuclear aromatic nature of asphaltenes which act as donors in the charge-transfer processes. However, although the high reactivity of MAH could be used to improve the bitumen properties by promoting its interactions with polymers, this high reactivity raises drawbacks related to its handling and storage. A solution to these problems is achieved by synthesizing a polymer-MAH in advance and then modifying the  
Figure 8: Fluorescence microscopy images showing the morphology of: (**a**) the LDPE and (**b**) GMA-g-LDPE blends (reprinted from [148] with permission of Elsevier).  
bitumen with this modified polymer, namely creating a reactive polymer (see Section 3.3). However, a further purification step is needed to eliminate unreacted MAH monomers, increasing the costs.  
Recently [PERSON] et al. [198], compared storage stability of PmBs prepared using SBS, SEBS, and two commercial SEBS-grafted MAH with different MAH content. SEBS-grafted MAH showed the best storage stability, although it did not improve significantly the rheological behavior of the binder.