On the structure of biocompatible, thermoresponsive poly(ethylene glycol) microgels

- Poly(ethylene glycol) based microgel particles with tunable VPTT were synthesized.
- Microgel network consists of dense core and fuzzy shell in the swollen state.
- Size of dense core increases with rising comonomer content.
- Two correlation lengths of the liquid-like network fluctuations in the swollen state.
- Spherical nanophases are formed during the collapse.

The aim of the present study is the preparation and characterization of microgel particles which are, contrary to other microgels, thermoresponsive as well as biocompatible. Hence, monodisperse p-MeO2MA-co-OEGMA microgel particles were synthesized by precipitation polymerization. Swelling/deswelling behavior and the structure of poly(ethylene glycol) (PEG) based microgel particles were investigated. A combination of dynamic light scattering (DLS) and small angle neutron scattering (SANS) was used. Particle size and the volume phase transition temperature (VPTT) are adjustable by changing the amount of comonomer. SANS measurements indicate an inhomogeneous structure of the PEG microgels in the swollen state. At temperatures above the VPTT a compact structure was observed. An increase of the comonomer content leads to a densely packed core and a fuzzy shell in the swollen state. Additionally, nanodomains inside the polymer network were observed in the temperature range around the volume phase transition (VPT). Due to this heterogeneous structure in the swollen state two correlation lengths of the network fluctuations were observed.

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