| abstract |
The invention relates to a process for preparing an imidized polymer in a mixing or kneading device, by a reaction of a mixture, comprising a polymer, comprising anhydride groups or derivatives thereof and an aromatic polyamine compound, wherein the reaction is carried out in the presence of an acid. With this process an imidized polymer can be obtained with a reduced amount of incomplete reacted anhydride groups with respect to the anhydride groups originally present in the polymer as well as a low amount of free and amid-bound aromatic polyamine. The invention further relates to a solid compound, and in particular a solid multifunctional viscosity modifier comprising a polymer comprising between 0.1 and 10 functional groups per 1000 C-atoms, the functional groups comprising aromatic amine based imide groups, wherein the ratio of imide groups with respect to the functional groups is more than 0.85, preferably more than 0.90 and most preferably more than 0.95 and to a lubricating oil, comprising the multifunctional viscosity modifier according to the invention, wherein the amount of low molecular weight aromatic polyamine in the oil is smaller than 10 ppm. |