As emerging atomically ultrathin metal compounds, MXenes show great promise for catalytic and nanoelectronic applications due to their abundant surface terminations and high metallic conductivity. However, the tendency for interlayer adhesion and suffering from environmental disturbances significantly limit their endurance and efficiency. Herein, via conducting first-principles calculations, we explore surface passivation and exfoliation of MXenes via polymers, which have been experimentally proven to promote the performance. Nine kinds of monomers together with a typical MXene, TiCT(T = none, O, F, OH, FO), as prototype composites are explored with respect to the adsorption and charge transfer associated with energetics and chemical redox, respectively. Our work shows that the naked TiCMXene has strong ability to cleave and decompose the monomers. Surface-functionalized TiCF, TiCFO, and TiCOhave a weak binding with monomers through only van der Waals force, whereas TiC(OH)also exhibits strengthened binding for some monomers. Specific functional groups in the monomer, such as the halogen, sulfur, and hydroxyl groups, or a relatively planar aromatic structure, largely contribute to the adsorption. We reveal that the functionalization through polymers would alter the carriers' density via interfacial charge transfer in MXenes. While the naked TiCand TiC(OH)donate electrons to the polymers, TiCF, TiCFO, and TiCOreceive small amounts of electrons transferred from the polymer, highly depending on the types of the monomers. The varying ability for charge transfer and exfoliation energy of different monomers imply great flexibility for designing polymers to exfoliate the MXene and modulate the carrier densities, which are highly desired for altering the conductivity, dielectric properties, and promoting endurance.