The synthesis of thermoresponsive graft copolymers based on a carboxymethylcellulose (CMC) backbone is reported. Thermal responsive properties are introduced by grafting the CMC sample with amino-terminated poly(N-isopropylacrylamide) (PNIPAM) side chains of a relatively low molecular weight. Turbidity measurements in dilute copolymer solutions showed that, due to the hydrophilic CMC backbone, macroscopic phase separation by increasing temperature above the lower critical solution temperature (LCST) of PNIPAM is not allowed for pH ≥ 3. Pyrene fluorescence probing studies in aqueous solutions revealed the formation of hydrophobic microdomains above the LCST of PNIPAM. In semidilute solution these microdomains interconnect the polymer chains, leading to the thermally induced formation of a physical network. The macroscopic result is the observation in semidilute solutions of a pronounced thermally induced viscosity enhancement. This thermothickening phenomenon is almost irrespective of pH, and it remains very important even at pH values as low as 3.

Summary: A technique to cover microelectromechanical systems (MEMS), such as micromechanical cantilever (MC) sensors, with a covalently bound brush layer has been developed. The polymer layer was grown using a “grafting‐from” synthesis of polymer brushes under mild conditions, by surface‐initiated atom transfer radical polymerization. Atomic force microscopy (AFM) and ellipsometry have revealed a uniform thickness of about 12 nm from which a grafting density of polymer brushes of 0.19 chains · nm−2 was estimated. The coating with polymer brushes can be realized on a selected surface. It was shown that a single‐sided brush layer swells reversibly in toluene, resulting in a bending of the micromechanical cantilever.Schematic representation of the PMMA brush synthesis on the MC surface, by surface‐initiated ATRP.magnified imageSchematic representation of the PMMA brush synthesis on the MC surface, by surface‐initiated ATRP.

Polymer brush coatings are well-known for their ability to tailor surface properties in a wide range of applications from colloid stabilization to medicine. In most cases, the brushes are used in solution. Consequently, efforts were expended to experimentally investigate or theoretically predict the swelling behavior of the brushes in solvents of different qualities. Here, we show that the micromechanical cantilever (MC) sensor technique is a tool to perform time-resolved physicochemical investigations of thin layers such as polymer brushes. Complementary to scattering techniques, which measure the thickness, the MC sensor technique provides information about changes in the internal pressure of the brushes during a swelling and deswelling process. We show that the kinetics of both swelling and deswelling are dependent on solvent quality. Comparing the measured data with its thickness evolution, which was calculated based on the Flory-Huggins theory, we found that only the first 10% of the thickness increase of the polymer brush results in a significant pressure increase inside the polymer brush layer.

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Micromechanical cantilever arrays coated with polymer brushes are an alternative to traditional chemical sensors. A critical parameter for the sensor sensitivity is the coating quality, and small changes in the coating uniformity generate a different behavior of the sensors. Microfocus grazing incidence small-angle x-ray scattering proved to be a sensitive tool to characterize coating quality, enabling a structural and chemical coating analysis.

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Summary: The hydrogen bonding‐interpolymer association of hydroxypropyl cellulose (HPC) with maleic acid‐styrene (MAc‐S) copolymer has been investigated in dilute aqueous solution by viscometry, turbidimetry and potentiometry. At a mixing ratio between MAc‐S and HPC of 10:90, the solution exhibits a phase separation upon heating, while for other mixing ratio no phase separation could be detected. The stability of the interpolymer complex (IPC) increases as the temperature rises. The stoichiometry of the IPC, in mole units, was estimated as being MAc‐S:HPC = 5:2. The thermodynamic functions (enthalpy and entropy) of the complexation process have been determined.