Real time rheological study of first network effects on the in situ polymerized semi-interpenetrating hydrogels

The in situ polymerization of monomers to form a second network within a preexisting network (first network) is a facile and effective strategy to fabricate semi-interpenetrating (semi-IPN) hydrogels with enhanced mechanical strength; while to comprehend the effects of the first polymer network on the polymerization process of the second network is still a challenging project. This paper introduces a simple method of employing dynamic rheological measurement loops to monitor the real time progress of the in situ polymerized acrylamide (AAm) in a chitosan (CS) solution towards the formation of a semi-IPN hydrogel. To identify the effects of the preexisting network on the polymerization gelation process, the concept Effective Conversion Ratio (ECR) is introduced to evaluate the first network effects on the requirement for the polymerized conversion ratio of the second network to form a critical gel. The rheological properties before gel point, at gel point, and at post-gel stage are discussed via the obtained real time data, respectively. The experimental results have proved the suitability of utilizing dynamic rheology to obtain the real time details of the semi-IPN gel fabrication process.