Department of Fibre and Polymer Technology, School of Chemical Science and Engineering, KTH Royal Institute of Technology, Teknikringen 56-58, SE-100 44 Stockholm, Sweden.
Biomacromolecules. 2013 Jan 14;14(1):64-74. doi: 10.1021/bm3013132. Epub 2012 Oct 24.
In the present study, the two grafting techniques grafting-from - by activators regenerated by electron transfer atom transfer radical polymerization (ARGET ATRP) - and grafting-to - by copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) - were systematically compared, employing cellulose as a substrate. In order to obtain a meaningful comparison, it is crucial that the graft lengths of the polymers that are grafted from and to the substrates are essentially identical. Herein, this was achieved by utilizing the free polymer formed in parallel to the grafting-from reaction as the polymer for the grafting-to reaction. Four graft lengths were investigated, and the molar masses of the four free polymers (21 ≤ M(n) ≤ 100 kDa; 1.07 ≤ Đ(M) ≤ 1.26), i.e. the polymers subsequently employed in the grafting-to reaction, were shown to be in the same range as the molar masses of the polymers grafted from the surface (23 ≤ M(n) ≤ 87 kDa; 1.08 ≤ Đ(M) ≤ 1.31). The molecular weights of the chains grafted from the surface were established after cleavage from the cellulose substrates via size exclusion chromatography (SEC). High-resolution Fourier transform infrared microscopy (FT-IRM) was employed as an efficient tool to study the spatial distribution of the polymer content on the grafted substrates. In addition, the functionalized substrates were analyzed by X-ray photoelectron spectroscopy (XPS), contact angle (CA) measurements, and field-emission scanning electron microscopy (FE-SEM). For cellulose substrates modified via the grafting-from approach, the content of polymer on the surfaces increased with increasing graft length, confirming the possibility to tailor not only the length of the polymer grafts but also the polymeric content on the surface. In comparison, for the grafting-to reaction, the grafted content could not be controlled by varying the length of the preformed polymer: the polymer content was essentially the same for the four graft lengths. Consequently, the obtained results, when employing cellulose as a substrate and under these conditions, suggest that the grafting-from approach is superior to the grafting-to technique with respect to controlling the distribution of the polymeric content on the surface.
在本研究中，我们系统地比较了两种接枝技术：由电子转移原子转移自由基聚合（ARGET ATRP）引发的接枝-从（grafting-from - by activators regenerated by electron transfer atom transfer radical polymerization (ARGET ATRP)）和铜（I）催化的叠氮-炔环加成（CuAAC）引发的接枝-至（grafting-to - by copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC)），以纤维素为底物。为了进行有意义的比较，至关重要的是，从底物接枝的聚合物和接枝至底物的聚合物的接枝长度基本相同。在这里，通过利用与接枝-从反应平行形成的游离聚合物作为接枝-至反应的聚合物，实现了这一点。研究了四种接枝长度，四种游离聚合物的摩尔质量（21 ≤ M(n) ≤ 100 kDa；1.07 ≤ Đ(M) ≤ 1.26），即随后用于接枝-至反应的聚合物，与从表面接枝的聚合物的摩尔质量（23 ≤ M(n) ≤ 87 kDa；1.08 ≤ Đ(M) ≤ 1.31）处于相同范围。通过尺寸排阻色谱（SEC）从纤维素底物上裂解后，确定了从表面接枝的链的分子量。高分辨率傅里叶变换红外显微镜（FT-IRM）被用作研究接枝底物上聚合物含量空间分布的有效工具。此外，通过 X 射线光电子能谱（XPS）、接触角（CA）测量和场发射扫描电子显微镜（FE-SEM）分析功能化的底物。对于通过接枝-从方法修饰的纤维素底物，表面上聚合物的含量随着接枝长度的增加而增加，这证实了不仅可以控制聚合物接枝的长度，还可以控制表面上的聚合物含量。相比之下，对于接枝-至反应，通过改变预形成聚合物的长度不能控制接枝的含量：对于四种接枝长度，接枝的含量基本相同。因此，当以纤维素为底物并在这些条件下使用时，所得结果表明，与接枝-至技术相比，接枝-从方法在控制表面上聚合物含量的分布方面具有优势。
