Cyclophosphazene microgels with adjustable number of crosslinks and deformability by precipitation polycondensation of mono- and bifunctional amines with hexachlorocyclotriphosphazene

Abstract

Starting from hexachlorocyclotriphosphazene (HCCTP), hexamethylenediamine (HMDA) and 2-dimethylaminoethylamine (DMEN) novel amino-functional cyclomatrix-type poly(organophosphazene) microgels with tunable amount of cross-links were synthesized via precipitation polycondensation in acetonitrile. The synthesis is carried out as a facile one-pot approach in which the microgels' cross-linking density is directly adjusted through the concentration of DMEN acting as reactive diluent. In addition, the influence of different concentrations of DMEN on the cross-linking density of poly(HCCTP-HMDA-DMEN) microgels is investigated through corresponding changes of the microgels' size, degree of swelling, form factor and deformability. To this end, microgels prepared with different ratios of DMEN are thoroughly characterized by means of FTIR spectroscopy, dynamic light scattering (DLS), static light scattering (SLS) and microscopy (FESEM and AFM). The obtained microgels are uniform in size and exhibit high degrees of swelling in water. Our study clearly shows that the microgels' cross-linking density gradually decreases with an increasing concentration of the reactive diluent DMEN. This direct correlation is particularly verified via side-view FESEM micrographs and AFM cross-section profiles, which both reveal an increasing deformability of the microgels with the concentration of DMEN. Results from DLS and SLS measurements support these findings as they reveal an increase of the microgels’ size and degree of swelling, while the form factor (ρ = Rg/Rh) shows a gradual decrease with increasing DMEN concentration. To our knowledge, this study demonstrates for the first time a facile one pot approach for the synthesis of a new class of cyclomatrix-type poly(organophosphazene) microgels with tunable crosslink density providing a functional colloidal toolbox for different applications. © 2001 Elsevier Science. All rights reserved.