Deepak V D, Asha S K
Speciality Polymers, Chemical Sciences & Technology Division, Regional Research Laboratory, Thiruvananthapuram 695019, India.
J Phys Chem B. 2006 Nov 2;110(43):21450-9. doi: 10.1021/jp063469a.
Here we report, for the first time, a novel molecular design for three-dimensional honeycomb structures through a self-organization of hydrogen-bonded bulky anchoring group in a methacrylic polymer backbone. The polymerizable monomer design includes a methacrylic double bond linked to various hydrophobic anchoring units such as ethane, n-decane, tricyclodecane (TCD), and adamantane via a hydrogen-bonded cycloaliphatic urethane linkage. The structures of the polymers were confirmed by nuclear magnetic resonance (NMR) and the molecular weights of the polymer were determined by gel permeation chromatography (GPC). The methacrylate polymers having tricyclodecane and adamantane bulky anchoring groups self-organized to produce three-dimensional honeycomb patterns in tetrahydrofuran-water solvent mixture at ambient conditions, whereas its linear analogues (ethane, n-decane) failed to produce any micropattern. The scanning electron microscopy (SEM) analysis of the above-prepared polymer films revealed that the structure of the polymer played a major role in the formation of the honeycomb patterns. The solution Fourier transform infrared (FTIR) measurements confirmed that the bulky tricyclodecane and adamantane polymers have strong hydrogen-bonding interaction compared to that of their linear analogues, which is the driving force for the micropatterns. Transmission electron microscopy (TEM) and atomic force microscopy (AFM) analysis of the bulky polymers revealed that the polymers exist as vesicles or micelles in the solution, which leads to the formation of the honeycomb pattern. The honeycomb pattern formation in the bulky polymer systems suggests that two cooperative factors such as hydrogen-bonding interaction and hydrophobicity of bulky anchoring units are necessary to induce three-dimensional honeycomb structures. To investigate the effect of molecular weights and its distribution on the self-organization process, both benzoyl peroxide (BPO) initiated free radical and atom transfer radical polymerization (ATRP) techniques were employed for the polymerization. Micropores formed irrespective of differences in molecular weight and polydispersity index (PDI); however, the pore size distribution was influenced by both molecular weights and PDI. Low molecular weight samples afforded polydisperse pores with the ATRP samples with more narrow PDI producing pores with large dimensions. The approach has also been investigated for polystyrene-bulky methacrylic copolymer, and the results revealed that uniform honeycomb patterns were produced for copolymers having more than 50 mol % incorporation of bulky units.
在此，我们首次报道了一种通过甲基丙烯酸聚合物主链中氢键连接的大体积锚定基团的自组装来设计三维蜂窝结构的新分子方法。可聚合单体的设计包括一个通过氢键连接的脂环族聚氨酯键与各种疏水锚定单元（如乙烷、正癸烷、三环癸烷（TCD）和金刚烷）相连的甲基丙烯酸双键。聚合物的结构通过核磁共振（NMR）得以确认，聚合物的分子量通过凝胶渗透色谱法（GPC）测定。具有三环癸烷和金刚烷大体积锚定基团的甲基丙烯酸酯聚合物在环境条件下于四氢呋喃 - 水溶剂混合物中自组装形成三维蜂窝图案，而其线性类似物（乙烷、正癸烷）则无法产生任何微图案。对上述制备的聚合物薄膜进行扫描电子显微镜（SEM）分析表明，聚合物的结构在蜂窝图案的形成中起主要作用。溶液傅里叶变换红外光谱（FTIR）测量证实，与线性类似物相比，大体积的三环癸烷和金刚烷聚合物具有更强的氢键相互作用，这是微图案形成的驱动力。对大体积聚合物进行透射电子显微镜（TEM）和原子力显微镜（AFM）分析表明，聚合物在溶液中以囊泡或胶束形式存在，这导致了蜂窝图案的形成。大体积聚合物体系中蜂窝图案的形成表明，诸如氢键相互作用和大体积锚定单元的疏水性这两个协同因素对于诱导三维蜂窝结构是必要的。为了研究分子量及其分布对自组装过程的影响，采用了过氧化苯甲酰（BPO）引发的自由基聚合和原子转移自由基聚合（ATRP）技术进行聚合反应。无论分子量和多分散指数（PDI）存在差异，都会形成微孔；然而，孔径分布受分子量和PDI两者的影响。低分子量样品产生多分散的孔，而具有较窄PDI的ATRP样品产生尺寸较大的孔。该方法也已针对聚苯乙烯 - 大体积甲基丙烯酸共聚物进行了研究，结果表明，对于大体积单元掺入量超过50摩尔％的共聚物，会产生均匀的蜂窝图案。
