Surface Characterization of Atactic Poly(methyl methacrylate) Aggregates Using Atomic Force Microscopy

Abstract

KEY WORDSAtactic Poly(methyl methacrylate) / Dendritic Aggregates / Solvent / Substrate / Stereoregular poly(methyl methacrylate) (PMMA) recently has been attractive to many researchers. For the mixture of isotactic and syndiotactic poly(methyl methacrylate) (i-PMMA and s-PMMA) leads to formation of a stereocomplex which was revealed a double stranded helical structure in suitable solvents. 1, 2 As for atactic poly(methyl methacrylate), Spevacek et al. and Borchard et al. proved that stereocomplex was able to form in its solution. 3-5 And a stereocomplex was also found in atatic PMMA film from strong complexing solvent acetone. 6,7 In this note, the effects of solvent and substrate on the patterning of a-PMMA aggregates were studied using by atomic force microscopy (AFM). EXPERIMENTALThe average molecular weight of commercial a-PMMA was determined by means of gel permeation chromatography (PL-GP210), M W = 43.3 × 10 4 , M W /M n = 1.34. The tacticities of a-PMMA were determined by 1 H NMR, the proportions of iso, hetero, and syndio triads were 9%, 34%, and 57% respectively. Average segment lengths of mm and rr (monomer unit) of atactic PMMA are 1.53 and 4.35, respectively. The glass transition temperature (T g = 112 • C) was determined by DSC at 10 • C min −1 rate. The solutions of atactic PMMA in acetone and chloroform solvents were prepared with the concentration of 1 g L −1 , and equilibrated for one week at room temperature.Surface topography measurements were performed on a nanoscope III Muti-Mode AFM of Digital Instruments in tapping mode. The images were obtained at room temperature in air. The solutions were spancast onto silicon wafer, mica and glass with the rotating speed of 3000 rpm. Silicon and glass were cleaned by acetone solvent then by hexane solvent prior to the polymer deposition. Fresh mica layer was used.