Development of high amine content microgels and systems for use in enzyme responsive materials

This thesis presents a study of the preparation and characterisation of microgels (MGs) and microgel-based systems which contain a high proportion of primaryamine groups. This is carried out with the aim of being used as the precursor materials for the development of an enzyme responsive system. The particle preparations discussed in this thesis begin with a particle dispersion prepared by a polymer-polymer interaction between partially oxidised dextran (Dexox) and poly(allylamine)(PA) or poly(vinylamine) (PVAM). The particle dispersions did show good tunability of properties by altering certain variables, such as extent of oxidation which resulted in the largest  -potential change with pH. However, these particles were not viable for further work as the largest swelling ratio by volume, Q value measured was only around 1.25, not sufficient for a pH responsive property swelling change (e.g. fluid-to-gel transition or drug delivery). MG particles were prepared using a non-aqueous dispersion polymerisation of Nvinylformamide (NVF), glycidylmethacrylate (GMA) and a crosslinker, 2-(Nvinylformamido)ethyl ether (NVEE). The PNVFx-GMAy-NVEEz particles were then hydrolysed to expose the primary amine groups in the resulting PVAMx-GMAy-BEVAMEz core-shell MGs. The shell, made up of GMA and NVF prevented hydrolysis taking place on the inside of the MGs, resulting in a PVAM rich shell. These hydrolysed MGs were cationic at low pH and were shown to have polyampholyte behaviour, caused by hydrolysis of some of the GMA groups. The inclusion of the NVEE crosslinker led to increased integration of the GMA and NVF into one homogenous phase in the shell and prevented hydrolytic fragmentation. The final system studied here concerns the macroscopic gel formation between the amine-rich MGs, poly(vinylamine-co-bis(ethyl vinylamine)ether) (PVAMBEVAME)and Dexox. These mixed dispersion gels were prepared and characterised. The MGs were externally crosslinked with the Dexox in order to form an elastically effective network. This was done by forming imine bonds by reaction between the primary amine groups present on the MGs and the aldehyde groups of the Dexox. These networks displayed high storage modulus (G’) and yield strains(*) of up to 140% and the G’ values for the MG-Dexox gels increased with mass ratio (MR) of Dexox to MG. The yield strains determined from rheology remained high (~125%) with increased MR. As the imine bonds formed were not reduced, they became unstable at low pH. This was exploited in order to investigate pH-triggered gel disruption of the network. This work demonstrates that new MG/aldehyde mixtures form ductile and versatile colloidal gels and our new method provides a route to increasing ductility of hydrogels containing MG particles. This research has led to the formation of amine rich MGs, as well as an injectable gel system. These materials are well placed to be developed for enzyme responsive materials in the future.