There is a growing interest in polymers designed for biomedical application.Such biomedical polymers are, in general, complex polymer systems with covalent linkage of various chemical structures to achieve the multi-functionalities.For example, polymers as an effective gene delivery have to meet a series of requirements for the extracellular and intracellular transport of the DNA vector.First of all, the polymers have to be positively charged under physiological conditions to compact the DNA into small particles, called polyplexes.Secondly, the polyplexes have to be able to target the specific cells, and facilitate endosomal escape and localizing into the nucleus as well as vector unpacking.Thirdly, the polymers should be non-toxic, non-immunogenic and preferably biodegradable.However, since the synthetic method is not perfect, variations in the chemical structure of polymers occur unavoidably, which can have dramatic effects on the properties of the polymers.To establish relationships between molecular structure and material performance of polymers, we need to obtain information on the average molecular structure, as well as on the underlying distributions, which require separation techniques.