ORIGINAL PAPER Synthesis, characterization and physiochemical investigation of chitosan-based multi-responsive Copolymeric hydrogels Abbas Khan 1 & Muhammad Sajjad 1 & Ewaz Khan 1 & Hazizan Md. Akil 2 & Luqman A. Shah 3 & Zahoor H. Farooqi 4 Received: 1 July 2017 /Accepted: 18 September 2017 # Springer Science+Business Media B.V. 2017 Abstract This paper describes the synthesis and physicochem- ical characterization of Poly(N-isopropylacrylamide)-Chitosan- Poly(Acrylic acid) [PNIPAAm-CS-PAA] based polymeric microgels. Three different samples of multi-responsive (PNIPAAM-CS-PA) microgels were synthesized using various amounts of N N - Methylene bis-acrylamide (MBA) and Acrylic acid (AA) by free radical emulsion polymerization. The redox initiator Ammonium per sulfate (APS) was used to initiate the reactions while MBA was used as a crosslinking agent. The purified polymeric microgels were then characterized using UV-Visible spectroscopy, Fourier transform infrared spec- troscopy (FT-IR), Laser light scattering (LLS), Ostwald viscom- etry, dynamic Rheology and swelling/de-swelling measure- ments. From the spectroscopic result it was observed that all the reactions have been completed and the resultant microgels were successfully synthesized. The influence of various param- eters such as, chemical composition and some external stimuli like temperature and pH on the physicochemical behavior of polymeric microgels was investigated through visual stability test, laser light scattering, viscometry and rheological measure- ment. The LLS analysis was performed to deduce the size, in the terms of hydrodynamic radius (R h ), of the microgel samples in aqueous media at different pH and temperature. From LLS analysis the microgels were found to be stable at all pH values above the pKa values (4.2) of AA in temperature ranges from 20 °C to 50 °C. With rising in temperature and pH causes aggregation of particles and decrease in stability of microgels due to the decrease in hydrophobicity. From the Rheological measurements, various physiochemical properties such as, elas- ticity, viscosity, shear stress, storage modulus, loss modulus, phase angle and complex viscosity of the microgels were gath- ered. The Ostowald viscometry was used to measure the flow viscosity of microgels at different pH and temperatures. The present observations reflect that the prepared samples are multi-responsive and their physicochemical behavior can be tuned very easily by changing their composition and/or varying the external stimuli. Keywords Emulsion polymerization . Chitosan . pH-responsive . Temperature-responsive . Physicochemical properties . Rheology . Viscosity . Light scattering Introduction Polymeric microgels have received considerable attention in the drug-release system because of their ability to deliver drugs to the therapeutic targets at appropriate times and doses. Because of their small particle size, they could pass through the capillary vessels and avoid rapid clearance by phagocytes. Hence, their duration in blood stream is greatly prolonged. In addition, they could penetrate cells by transcytosis and/or overcome biological barriers to arrive at target organs. Furthermore, by using materials with biodegradability or en- vironmental sensitivity to the pH, ion, chemicals, glucose and/ or temperature, they could exhibit controlled-release * Abbas Khan abbas053@gmail.com 1 Department of Chemistry, Abdul Wali Khan University Mardan, Mardan 23200, Pakistan 2 School of Materials and Mineral Resources Engineering, Universiti Sains Malaysia, Engineering Campus, 14300 Nibong Tebal, Penang, Malaysia 3 National Center of Excellence in Physical Chemistry, University of Peshawar, Peshawar, Pakistan 4 Institute of Chemistry, University of the Punjab, New Campus, Lahore, Pakistan J Polym Res (2017) 24:170 DOI 10.1007/s10965-017-1332-2