The present invention relates to new biocompatible polymer derivatives including peptide spacers of formula (I) and their methods of preparation. The present invention also relates to the conjugates formed by covalent or non-covalent bonding and their methods of preparation. These biocompatible polymers with peptide spacers providing regions of hydrophobicity and positive charge can enhance their interaction with cell membrane to increase the cell trafficking, endosomal disruption, the circulation half-life in blood, and the stability of conjugated therapeutic drug.