1. Functional Polymer Grafted Nanoparticles
for the Modification of HPLC Stationary Phases.
Marcello Iaconob, Ali Alwyb, Damian Connollyb and Brett Paull, Andreas Heisea,b
a: Polymer Research Group, School of Chemical Sciences, Dublin City University.
b: Irish Separation Science Cluster (ISSC), School of Chemical Science,
Dublin City University, Dublin 9, Ireland.
This project is about the preparation of new polymeric materials designed to enhance the performances of HPLC columns. In particular, we aim to synthesise surface modified silica nano-particles
(Si-NPs) to be bound to silica and/or polymeric stationary phase for HPLC columns. We investigate two kinds of surface modified Si-NPs. (1) Si-NPs with an amino-functionalised surface
(hydrophilic) and (2) poly-(tert-butyl acrylate) (PtBA) brush-decorated Si-NPs, which can be subsequently converted into poly(acrylic acid) (PAA) by thermal treatment. Both types of modified
Si-NPs will be linked to a stationary phase in order to explore the selectivity of these new columns in the separation process.
1: The synthesis of the Silica Nano-particles (Si-NPs).
The synthesis of the Si-NPs was performed following the Stöber method1 (diameters range: nm) or, in some cases, the mini-emulsion method2 (diameter range 5-20 nm). The Stöber method (see Figure 1) was selected as a one-step synthesis protocol for the hydrolysis and condensation of tetraethyl ortho-silicate (TEOS) in ethanol/water mixtures under alkaline conditions and under controlled temperature (usually 25° C). Optimising the reaction conditions, it was possible to achieve excellent control of size, narrow size distribution, and smooth spherical morphology of the resulting silica particles.
2.b: The analysis of the silanisation process.
As a complement of our previous work3,4,where it was used a method based on the [2-(4,4-dimethoxytrityl)]butyrate (sSDTB), the amount of free primary amine or Br groups on the decorated surface was deduced by comparison with bare Si-NPs. TGA curves (from 180° to 200°C) and elemental analysis confirmed the presence of APTES and BIDS on the Si-NPs surface with a density of 6 BIDS/nm2 and 15 APTES/nm2.
Figure 1: Reactions in the Stöber method.
The analytical treatment of these Si-NPs is shown in Figures form 2 to 4 .
Figure 6: SEM analysis of bare Si-NPs (left) and APTES decorated Si-NPs (right).
3: ATOM TRANSFER RADICAL POLYMERIZATION (ATRP).
The BIDS decorated Si-NPs will be used as the starting system to perform ATRP. Figure 8 depicts the chemistry of this polymerisation process. The BIDS, chemically bonded on the surface of the Si-NPs, is the actually initiator for this process.
Figure 2: SEM micrograph of the bare Si-NPs,
diameter 115 nm.
Figure 3: Thermogravimetric (TGA) curve for the
Bare Si-NPs, 37°-900° C, 20°C/min
Figure 7: The chemistry of ATRP process.
DLS data: nm +/- 0.4 nm
Polydispersity index: 0.014
Zeta Potential at pH 10.5: - 80 mV
Elemental Analysis: Si:43.65%, O:49.87%
C: 5.19%, H:1.28%
Figure 4: Dynamic Light Scattering (DLS)
results for the bare Si-NPs (blue: differential
Weight % , red: cumulative Weight %).
Figure 8: Target by ATRP.
Using the complex Cu(I)/n,n,n',n',n-pentamethyldiethylenetriamine (PMDETA) as a catalyst and tBMA as a monomer (see Figure 8) in toluene and in oxygen free conditions at 80°C, we were able to perform a preliminary study on the system in solution.: Gel Permeation Chromatography (GPC) confirmed that we can control the polymerisation process and produce Si-NPs with poly(tert-butyl acrylate) (PtBA) brushes with a polydispersity index of 1.4. Thermal treatment of this system at 150°-180º C (or an acidic treatment) removes the tert-butyl protecting groups resulting in free poly(acrylic acid) linear chains on the Si-NPs surface (Si-NPs/PAA). This reactive system will be used to explore new possibilities as separation tool.
2.a: The Silanisation Process.
5: Future Work .
Preparation of 2 different systems:
1. Amino-Coated Si-NPs in the range nm: this will be used in polymeric stationary phase for
HPLC columns.
2. Poly(tert-butyl acrylate) (PtBA) and poly(acrylic acid)(PAA) brush-decorated Si-NPs: these
Systems will be bound to stationary phases for HPLC columns.
6: Acknowledgements.
The author would like to thank Science Foundation Ireland for research funding under the Strategic
Research Cluster programme. A special acknowledgement is due to Dr. Brendan Twamley for SEM
and Dr. Dermot Brougham, Dr. Una Prendergast for DLS measurements. I wish to thank the Dublin
City University Library and Ms Barbara Rosinka for the crucial help.
Figure 5: The silanisation protocol applied to the functionalisation of Si-NPs
Figure 5 Legend: R1: alkoxy-silane. R2: silanols on the Si-NPs surface. n: 1<n<4 (depending on concentration). R: is the group bearing the organic function; in this project, R is or from (3-aminopropyl)triethoxysilane (APTES) or from the 3-Dimethylethoxy silylpropyl-2-bromobutirate (BIDS). Protocol depends on the kind of silane coupling agent used as R group defines the kinetic and the solubility of the sililating system.
General Protocol: The alkoxysilane agent is hydrolysed (for APTES and BIDS in a water/ethanol solution at acidic pH ( )) with formation of highly reactive silanol (step1). The silanols undergo hydrogen bonding (interactions in red) with other silanols (with water elimination) in solution and on the Si-NPs surface, resulting in a network of organosilanes derivatives (steps 2, 3 and 4). A final step (water stripping) is crucial for the formation of chemical bonds between physisorbed derivatives and the treated surface (step5).
7: References.
1: W. Stöber, A. Fink, Journal of Colloid and Interface Science, 26, 62-69, (1968).
2: F. J. Arriagada and K. Osseo-Asare, J. Colloid Interface Sci., 1999, , 210–220.
3: R.P. Gandhiraman,C.Volcke, V. Gubala, C. Doyle, L.Basabe-Desmonts,
C. Dotzler,F. Toney, M. Iacono,R. Nooney,S. Daniels, B. Jamesc and D.Williams
J. Mater. Chem., 2010, 20, 4116–4127 | 4117.
4: C. Volckea, R.P. Gandhiramana, L. Basabe-Desmontsa, M. Iacono, V. Gubala,
F. Cecchet, A.Cafolla, D.E. Williams, Biosensors and Bioelectronics 25 (2010) 1295–1300.