The present invention relates to a composition containing a particulate solid, an organic or aqueous medium and a dispersant that may be a reaction product of an organic di or polyepoxide with a primary amine, aminoalcohol, amino acid, hydroxyacid or alcohol containing a fused or non-fused aromatic imide group. The invention further provides compositions for coatings, inks, toners, plastic materials (such as thermoplastics), plasticizers, plastisols, crude grinding and flush.

A biodegradable polyethylene glycol derivative in which a polyethylene glycol chain is linked by an acetal linker capable of accurately controlling the hydrolysis rate under different pH environments in the living body, and whose division rate into a polyethylene glycol chain of low molecular weight in the living body can be accurately controlled. The biodegradable polyethylene glycol derivative is represented by formula (1) or formula (2) as described.

A hydrophilic polymer derivative having a cyclic benzylidene acetal linker represented by the following formula (1):

##STR00001##

wherein R.sup.1 and R.sup.6 are each independently a hydrogen atom or a hydrocarbon group; R.sup.2, R.sup.3, R.sup.4 and R.sup.5 are each independently an electron-withdrawing or electron-donating substituent or a hydrogen atom; X.sup.1 is a chemically reactive functional group; P is a hydrophilic polymer, s is 1 or 2, t is 0 or 1, and s+t is 1 or 2; w is an integer of 1 to 8; and Z.sup.1 and Z.sup.2 are each independently a selected divalent spacer.

The present invention relates to a composition containing a particulate solid, a polar or non-polar organic medium, and a polymer chain having at least one fused aromatic imide pendant group. The invention further provides compositions for coatings, inks, toners, plastic materials (such as thermoplastics), plasticizers, plastisols, crude grinding and flush.