The liquid component of hybrid ionomer cements usually contains a water solution of:
The liquid component of hybrid ionomer cements usually contains a water solution of polyacrylic acid, HEMA, and polyacrylic acid modified with methacrylate. 
The powder component contains fluoroaluminosilicate glass particles of a conventional GIC plus initiators, such as camphorquinone, for light curing and/or chemical curing. The acid-base reaction begins upon mixing and continues after polymerization at a much slower rate than for conventional GICs, because less water is present and the reaction is much slower in the solid phase than in the liquid phase.
Ref: Phillip’s Science of Dental Materials ed 12 pg 326
HEMA
Polyacrylic acid
Polyacrylic acid modified with methacrylate
All of the above