Microgels are cross-linked polymer networks that can respond to environmental change like temperature or pH. When triggered, they collapse or swell in a solvent, preserving their 3D structure. Micron-sized microgels can have plenty of interesting applications in crystallization studies, microlensing or mimicking cells. Microgels with size above 10 µm can be synthesized using microfluidics. However, very low yields and specific equipment requirements lead to high demand on synthesis of microgels via dispersion polymerization approaches. Moreover, the typical size of micro/nanogels synthesized using standard batch polymerization reactions is in nanometer scale. Thus particles ranging from 1 to 10 µm are not easily reachable and means to obtain them need further investigation. For the first time, we have synthesized temperature-responsive poly(N-Vinylcaprolactam) (pVCL) microgels with large diameter (1 -10 µm) via aqueous, surfactant-free precipitation polymerization. The size control was achieved by employing programmed temperature ramp during the nucleation stage of polymerization. Micron-sized poly(N-Isopropylacrylamide) (pNIPAm) microgels have been obtained previously, however known toxicity and suspected cancerogenity of pNIPAm disqualifies the usage of these gels in medical applications. In contrast to pNIPAm, pVCL is non-toxic and biocompatible, making it a great candidate in medical and biomaterial fields. In this work, the influence of various parameters such as monomer, cross-linker and initiator concentration, rate of temperature ramp, start and end temperature as well as dosing of the reagents was investigated. We were able to obtain microgels in different size ranges, depending on parameters altered. To best characterize such big but soft particles, laser diffraction particle sizing technique as well as confocal microscopy were utilized. Consequently this study hopes to give more insight and understanding about the formation mechanism of larger pVCL microgels. For this purpose, in-situ dynamic light scattering measurements as well as in-line reaction calorimetry, where heat flow of the reaction can be monitored, were carried out.

Synthesis of micron-sized poly(N-Vinylcaprolactam) microgels by temperature-ramp polymerization

255th National Meeting (2018)

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