Thermosensitivity studies of hyperbranched dendrimers and branched polymer with terminal N-isopropylamide

Abstract

Thermoresponsive polymers, such as poly(N-isopropylacrylamide) (PNIPAM) and poly(amidoamine) dendrimers generation 5 (PAMAM, G5), have been both studied and developed for use in a variety of biomedical applications, in part because of their unqiue solution behavior. Despite this, there are a few studies on the thermosensitivity of poly(amidoamine) dendrimers in aqueous solution of different ionic strengths. Furthermore, it is not demonstrated how the stoichiometric (1:1) conjugation of a macromolecule to a dendrimer alters its thermoresponsive behavior. Motivated by these knowledge gaps, we synthesized a series of polymer based on N-isopropylamide with various carbon spacer lengths and conjugated to both G5 dendritic and branched polymers to evaluate their altered thermosensitivity in phosphate buffer saline (PBS) of different ionic strengths. Additionally, we synthesized mono substituted G5-(N3)1 followed by stoichiometric (1:1) dendrimer-poly(ethylene glycol) conjugatation in high purity and quantitative yield. Thermoresponsive behavior of this conjugate was much different from a modified dendrimer despite having the same peripheral functional groups. Moreover, dendrimer-poly(ethylene glycol) conjugate showed no unusual phase transition behavior in PBS unlike the modified dendrimers with similar peripheral functional groups. Additionally, we synthesized N-isosopropylamide terminated poly(allylamine) (PAH) that consists of higher nitrogen and longer side chain than prototype PNIPAM, yet both showed similar transition temperature (Tt) in water.