Increasing the hydrophilicity of star-shaped amphiphilic co-networks by using of PEG and dendritic s-PCL cross-linkers

New hyperbranched hydrophobic cross-linkers with peripheral azide groups were synthesized as follows: First, star-shaped polycaprolactones (sPCL) were synthesized by ring-opening polymerization of caprolactone in the presence of pentaerythritol and tin (II) octoate. In the next step, sequential acrylation, Micheal addition, tosylation, and azidation by acryloyl chloride, diethanol amine, tosyl chloride, and sodium azide were respectively exploited to synthesize azide-functionalized hyperbranched star-shaped polycaprolactones which were named sPCL-acrylate-diethanolamine-azide (sPCL-AC-DEA-N-3) and sPCL-acrylate-diethanolamine-acrylate-diethanolamine-azide (sPCL-AC-DEA-AC-N-3). All steps were thoroughly characterized by FT-IR and H-1 NMR spectroscopy. The GPC analysis showed that the molecular weight of sPCL increased after two azide functionalizations. Amphiphilic hydrogels based on sPCL-AC-DEA-N-3 (M-n = 8130 g/mol) and sPCL-AC-DEA-AC-N-3 (M-n = 10112 g/mol) with linear alkyne-terminated polyethylene glycols (PEG) (M-n = 2000, 4000, and 6000 g/mol) were synthesized through click coupling between azide and alkyne groups. In both hydrogels, the swelling ratio increased by increasing the molecular weight of PEG. The obtained results showed that the branching of the cross-linker, significantly affected the swelling ratio of hydrogels. For instance, the swelling ratio of sPCL-AC-DEA-AC-N-3 and PEG-6000 (Q = 900) was higher than sPCL-AC-DEA-N-3 and PEG-6000 (Q = 600). Despite the high cross-linking density of sPCL-AC-DEA-AC-DEA-N-3-based hydrogels, the amount of released theophylline was higher than sPCL-AC-DEA-N-3-based hydrogels, due to the high content of PEG in these hydrogels.