Abstract
Gelatin was immobilized selectively on the amide groups-modified bottom of a trench array of a photoresist template with 2 μm resolution by the ethyl(dimethylaminopropyl) carbodiimide/N-hydroxysuccinimide reaction. The gelatin-immobilized line array was brominated to generate a macroinitiator for atom transfer radical polymerization. Poly(methacrylic acid) (PMAA) brushes were grafted from the macroinitiator layer as line arrays of one-dimensional diffraction gratings (DGs) for various grafting polymerization times. A laser beam system was employed to analyze the optical feature with a characteristic diffraction effect of the PMAA DGs at a 45° incident angle along the transverse magnetic and transverse electric polarization. The growth of the PMAA brush lines increased both their heights and widths, leading to a change in the reflective diffraction intensity. The PMAA brushes under various grafting polymerization times were cleaved from the substrate by digestion of gelatin with trypsin, and their molecular weights were obtained by gel permeation chromatography. The change degree of the diffraction intensity varied linearly with the molecular weight of the PMAA brushes over a wide range, from 135 to 1475 kDa, with high correlation coefficients. Molecular weight determination of polymer brushes using the reflective diffraction intensity provides a simple method to monitor their growth in real time without polymer brush cleavage.
Highlights
The widths of the gelatin lines matched the trench peaks disappeared in the diffraction gratings (DGs)-g-PMAA16 spectrum
The results suggest that the growth of the Poly(methacrylic acid) (PMAA) brushes contributed to the height increase and to the side extension in the trench bottom regions because of the collapse of the polymer brushes
PMAA brushes were grafted from a brominated gelatin line array under various grafting polymerization times as DGs via ATRP
Summary
P-toluenesulfonic acid was employed to cleave the covalent graft bonds of polymer brushes grafted from silicon surfaces initiated by an acid-labile linker These approaches can only be applied to HF-dissolvable substrates and HF-insensitive grafts. SI poly(methacrylic acid) (PMAA) is grafted from the brominated gelatin backbones on the silicon surfaces by ATRP as a line array of diffraction gratings (DGs) [23,24]. The change in the diffraction intensity of the PMAA DGs with the grafting polymerization time is used as an indicator to establish the correlation with the molecular weight of the PMAA, obtained by digesting the gelatin backbone with trypsin. Polymers grafted on the surface are stripped from the substrate to measure the exact molecular weight This strategy offers a convenient approach for monitoring the growth of polymer brushes in real time without destructed cleavage. The exact molecular weight of the polymer grafted on the surface is not well-known, the molecular weight measured by our method is expected to be proportional to that molecular weight measured in the bulk solution
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