Abstract
Abstract The poly(N-isopropylacrylamide) copolymers with the enhanced hydrophilicity were synthesized by free radical polymerization from a mixture of the monomers N-isopropylacrylamide (NIPAAm), N-vinyl pyrrolidone (NVP), hydroxypropyl methacrylate (HPM) and 3-trimethoxysilypropyl methacrylate (TMSPM) at different feeding ratios. The attenuated total reflectance-Fourier transform infrared spectrometry (ATR-FTIR), nuclear magnetic resonance (1H-NMR) and gel permeation chromatography (GPC) were applied to characterize the resultant copolymers. The lower critical solution temperature (LCST) of the copolymers was determined via dynamic light scattering (DLS). By alternating the molar ratios of NIPAAm and NVP, the copolymers were synthesized to have their own distinctive LCST from 25°C to 40°C. Regardless of the starting feed ratio used, the final copolymers had the similar monomeric ratio as planned. The copolymer films were then formed on platinum wafers by drop coating and thermal annealing owing to 3-trimethoxysilyl crosslinking and reacting with hydroxyl groups. The surface wettability and morphology of the specimens were observed using contact angle measurements and scanning electron microscopy (SEM), respectively. The results demonstrated that with the increase of the NVP content, the film surface became more hydrophilic. The surface microstructure of the thermoresponsive films varied depending on the copolymer composition and ambient temperature. The experimental results indicated that the addition of NVP not only increased the LCST of copolymers but also improved the hydrophilicity of the products derived from the copolymers. This ability to elevate the LCST of the polymers provides excellent flexibility in tailoring transitions for specific uses, like controlled drug release and nondestructive cell harvest.
Highlights
Thermoresponsive systems have attracted considerable interests for their ability to change the swelling behaviors and network structures dramatically in response to temperature stimuli, which have potential applications in biomedical and biochemical fields such as drug delivery, protein separation and cell detachment [1,2,3]
PNTHV copolymers were synthesized by free radical polymerization with NIPAAm, hydroxypropyl methacrylate (HPM), trimethoxysilypropyl methacrylate (TMSPM), and N-vinyl pyrrolidone (NVP) under the moderate reaction conditions (60°C, ordinary pressure)
HPM was available for adjusting film hydrophilicity [20], the higher hydrophobicity of TMSPM led to the lower critical solution temperature (LCST) of the copolymers bearing NIPAAm, HPM and TMSPM reaching 25°C
Summary
Thermoresponsive systems have attracted considerable interests for their ability to change the swelling behaviors and network structures dramatically in response to temperature stimuli, which have potential applications in biomedical and biochemical fields such as drug delivery, protein separation and cell detachment [1,2,3]. PNIPAAm in aqueous solutions exhibit a lower critical solution temperature (LCST) in the vicinity of 32°C [4,5]. LCST, PNIPAAm is extremely soluble in water, whereas it becomes hydrophobic and readily precipitates from the aqueous solution when the temperature is above its LCST. It is widely believed that the thermoresponsive behavior of PNIPAAm in aqueous solutions is closely correlated with the destabilization of hydrogen bonds between water molecules and amide linkages with the increase of temperature, probably caused by the presence of hydrophobic isopropyl groups [6]. If PNIPAAm is used as smart substrates of cell culture, it is required to increase the LCST to somewhat lower than physiological temperature, which can
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