Lewis Gregory T, Cohen Yoram
Department of Chemical and Biomolecular Engineering, University of California, Los Angeles, CA 90095-1592, USA.
Langmuir. 2008 Nov 18;24(22):13102-12. doi: 10.1021/la8014173. Epub 2008 Oct 21.
Polymer layer growth by free radical graft polymerization (FRGP) and controlled nitroxide-mediated graft polymerization (NMGP) of polystyrene was achieved by atmospheric pressure hydrogen plasma surface activation of silicon. Kinetic polystyrene layer growth by atmospheric pressure plasma-induced FRGP (APPI-FRGP) exhibited a maximum surface-grafted layer thickness (125 A after 20 h) at an initial monomer concentration of [M] 0 = 2.62 M at 85 degrees C. Increasing both the reaction temperature ( T = 100 degrees C) and initial monomer concentration ([M] 0 = 4.36 M) led to an increased initial film growth rate but a reduced polymer layer thickness, due to uncontrolled thermal initiation and polymer grafting from solution. Controlled atmospheric pressure plasma-induced NMGP (APPI-NMGP), using 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO), exhibited a linear increase in grafted polystyrene layer growth with time due to controlled surface graft polymerization as well as reduced uncontrolled solution polymerization and polymer grafting, resulting in a polymer layer thickness of 285 A after 60 h at [TEMPO] = 10 mM, [M] 0 = 4.36 M, and T = 120 degrees C. Atomic force microscopy (AFM) surface analysis demonstrated that polystyrene-grafted surfaces created by APPI-NMGP exhibited a high surface density of spatially homogeneous polymer features with a low root-mean-square (RMS) surface roughness ( R rms = 0.36 nm), similar to that of the native silicon surface ( R rms = 0.21 nm). In contrast, polymer films created by APPI-FRGP at [M] 0 = 2.62 M demonstrated an increase in polymer film surface roughness observed at reaction temperatures of 85 degrees C ( R rms = 0.55 nm) and 100 degrees C ( R rms = 1.70 nm). The present study concluded that the current approach to APPI controlled radical polymerization may be used to achieve a grafted polymer layer with a lower surface roughness and a higher fractional coverage of surface-grafted polymers compared to both conventional FRGP and APPI-FRGP.
通过硅的大气压氢等离子体表面活化，实现了聚苯乙烯的自由基接枝聚合（FRGP）和可控的氮氧介导接枝聚合（NMGP）来生长聚合物层。在85℃下，当初始单体浓度[M]0 = 2.62 M时，大气压等离子体诱导的FRGP（APPI-FRGP）动力学聚苯乙烯层生长在20小时后显示出最大表面接枝层厚度（125 Å）。提高反应温度（T = 100℃）和初始单体浓度（[M]0 = 4.36 M）会导致初始膜生长速率增加，但聚合物层厚度减小，这是由于不受控制的热引发以及从溶液中进行的聚合物接枝。使用2,2,6,6-四甲基-1-哌啶氧基（TEMPO）的可控大气压等离子体诱导的NMGP（APPI-NMGP），由于可控的表面接枝聚合以及减少的不受控制的溶液聚合和聚合物接枝，接枝聚苯乙烯层生长随时间呈线性增加，在[TEMPO] = 10 mM、[M]0 = 4.36 M和T = 120℃下60小时后聚合物层厚度达到285 Å。原子力显微镜（AFM）表面分析表明，由APPI-NMGP产生的聚苯乙烯接枝表面呈现出空间均匀的聚合物特征的高表面密度，均方根（RMS）表面粗糙度较低（Rrms = 0.36 nm），类似于天然硅表面（Rrms = 0.21 nm）。相比之下，在[M]0 = 2.62 M时由APPI-FRGP产生的聚合物膜在85℃（Rrms = 0.55 nm）和100℃（Rrms = 1.70 nm）的反应温度下显示出聚合物膜表面粗糙度增加。本研究得出结论，与传统的FRGP和APPI-FRGP相比，当前这种APPI可控自由基聚合方法可用于获得具有更低表面粗糙度和更高表面接枝聚合物分数覆盖率的接枝聚合物层。
