Secondary macromolecular substitution

One of the important aspects of poly(organophosphazenes) over other polymers lies on the ease of control of final properties by either introducing additional functionalities during macromolecular substitution reactions or secondary modification of side groups on the backbone. Thus, properties can be finely tuned with respect to different applications. Examples of biodegradable ther-mogelling poly(organophosphazenes) with additional functionality are shown in Table 4. 

In conclusion, the macromolecular properties of polymers and their interactions with cell surfaces result in a specific pharmacokinetic behaviour of polymers. The routes of parenteral administration are far from being equivalent, e.g. the intraperi-toneal application often used cannot substitute the intravenous administration. Molecular parameters of the polymer circulating in the coitral compartment are changed in time not necessarily by a direct biological modification of the polymer but as a consequence of a selective processing of different fractions. The intracellular accumulation in secondary lysosomes is the only proven mode of persistence of a soluble polymer in tissues. Variations in the chemical structure of the polymer may result in a different pattern of polymer distribution in the body as a consequence of a different rate of cellular accumulation. 

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