The Structure and Properties of Ultra-high density Polymer Brushes

活性自由基聚合（LRP）如原子转移自由基聚合（ATRP）和可逆加成-断裂转移（RAFT）聚合被应用于各种固体（硅片、聚合物膜、二氧化硅或金属纳米颗粒等）。引发位点化学键合在它们的表面上，建立了制备接枝聚合物膜的实验技术（聚合物刷）的不同单体，具有可控的链长和化学结构，表面密度高达0.7链/nm^2。这些接枝膜被认为是一种新的分子组织，在溶胀和干燥状态下，不同于等同的流延膜。例如，通过良溶剂溶胀的高密度膜中的聚合物链垂直于膜表面高度延伸，从而得到完全拉伸链长的80 - 90%的膜厚度。溶胀接枝膜的平板可压缩性不符合标度理论，干（融）膜的平板可压缩性比流延膜大50%左右。在低分子量区（膜厚<50 nm）和高分子量区，干接枝膜的玻璃化转变温度T_g与相应的流延膜有本质的不同。特别是，实验数据表明，聚（甲基丙烯酸甲酯）（PMMA）的高密度接枝膜的Tg是约8 K高于本体PMMA，即使在高分子量的限制，这意味着高密度接枝不仅有效果的薄膜，但也厚膜，因此，以散装的膜。

Living radical polymerizations (LRPs) such as atom transfer radical polymerization (ATRP) and reversible addition-fragmentation transfer (RAFT) polymerization were applied to various solids (silicon wafer, polymer films, silica or metal nano-particles, etc.) with initiating sites chemically bound on their surfaces, establishing experimental techniques to prepare graft polymer films (polymer brushes) of differing monomers with controlled chain length and chemical structure and with a surface density as high as 0.7 chains/nm^2.These graft films were recognizable as a new molecular organization having characteristic properties, in both swollen and dry states, different from those of the equivalent cast films. For example, the polymer chains in the high-density film swollen by a good solvent are highly extended normally to the film surface, thus giving a film thickness of 80 to 90% of the fully stretched chain length. The plate compressibility of the swollen graft film disobeys the scaling theory, and that of the dry (melt) film is about 50% larger than the cast film. Moreover, the glass transition temperature T_g of the dry graft film is essentially different from that of the equivalent cast film in both low-molecular weight (film thickness < 50nm) and high-molecular weight regions. In particular, the experimental data indicate that the Tg of poly(methyl methacrylate) (PMMA) high-density graft films is about 8K higher than that of bulk PMMA even in the limit of high molecular weight, meaning that the high-density grafting has an effect not only to thin films but also to thick films and hence to the bulk of the films.