Research Article Hybrid polyacrylamide chiral stationary phases for HPLC prepared by surface- initiated photopolymerization Two hybrid polyacrylamide chiral stationary phases (CSPs) for HPLC have been synthe- sized by a new surface-initiated photo-induced radical polymerization approach of enan tiopure N,N 0 -diacryloyl derivatives of (1R,2R)-diaminocyclohexane (CSP1) and (1R,2R)- diphenylethylenediamine (CSP2). This system is based on the activation of mesoporous silica microparticles by chemicallybonded trichloroacetyl groupsand dimanganese decacarbonyl as catalyst. UV irradiation was performed using a lab-made quartz photo- chemical reactor, ad hoc designed for the photo-induced polymerization process on the surface ofmicroparticles. The two phases were evaluated and compared as chromato- graphicsupportsfor the enantioselective HPLC of modelchiral compounds. Their physico-chemical properties and chromatographic performances were also evaluated in comparison with those exhibited by the homologue CSPs obtained by the grafting-from thermal-induced process (CSP3 and CSP4).The new photopolymerization approach yielded higher grafting density than the thermal-induced one, especially in the case of t less reactive monomer (the diacryloyl derivative of (1R,2R)-diphenylethylenediamine), good chromatographic efficiency and a broad application field under normal phase and polar organic mode conditions. Keywords: Chiral polymers / Chiral stationary phases / HPLC / Photopoly- merization DOI 10.1002/jssc.201000355 1 Introduction Investigation on chiral stationary phases (CSPs) based on totallysynthetic,opticallyactivepolymerslinked to a chromatographic matrixiscontinuouslyevolving.Since their introduction in 1980, polyacrylamide and polymeth- acrylamide CSPs were used for the separation of a wide rangeof chiral compounds, including benzodiazepines, barbiturates, and hydantoins [1, 2]. Diverse strategies are indeed available for the grafting of polymersonto the surfaceof ultra-fineparticlesfor non-chromatographic applications [3], based on surface-initiated polymerization (also called grafting-from or g-from approach) from initiators bound to surfaces. Uniform and well permeable polymeric layers are available only if the degree of polymerization and the grafting density are carefully controlled. Such polymeric materials are therefore highly desirable for the preparation of improved polymeric CSPs. We recently reported [4–6] a new hybrid organic/inorganic CSP for HPLC synthesized by the g-from radicalpolymerizationof an enantiopure diacryloyl derivative of trans-1,2-diaminocyclohexane in the presence of mesoporous, azo-activated silica micro-particles. This was the first example ofapplication ofthe g-from approach to the synthesis of a CSP for HPLC applications. However, the thermal grafting process could not be surface- confined only, since concomitant solution polymerization may lead to ungrafted polymer chains [3]. Thus,we moved to study another way to induce polymerization of the above monomer,and focused ourattention on photo-induced polymerization, which has been obtaining much attention in recent years because of its numerous industrial applica- tions [7–9]. The concept of photopolymerization is that the initiators generate free radicals upon light irradiation, and the resultingradicalstartsthe polymerization process. Recently, several photoinitiators in free radical promoted cationic polymerization have successfully been used [10]. In particular,severalvisible light-absorbing systems able to generateoxidableradicalswere reported.For instance, radicals formed by the irradiation of systems containing a xanthene dye and an aromatic amine, were oxidized by a Alessia Ciogli 1 Ilaria D’Acquarica 1 Francesco Gasparrini 1 Carmela Molinaro 1 Romina Rompietti 1 Patrizia Simone 1 Claudio Villani 1 Giovanni Zappia 2 1 Dipartimento di Chimica e Tecnologie del Farmaco, Sapienza Universita ` di Roma, Roma, Italy 2 Istituto di Chimica Farmaceutica, Universita ` di Urbino ‘‘Carlo Bo’’, Urbino, Italy Received May 18, 2010 Revised July 22, 2010 Accepted July 22, 2010 Abbreviations: 3-APSG, 3-aminopropyl silica gel; CSP, chiral stationary phase; DACH, (1R,2R)-diaminocyclohexane; DPEDA, (1R,2R)-diphenylethylenediamine;DRIFT, diffuse reflectance infrared Fourier transform; NP, normal phase; POM, polar organic mode Correspondence: Professor Francesco Gasparrini,Dipartimento di Chimica e Tecnologie del Farmaco, Sapienza Universita ` di Roma, P.le A. Moro 5, 00185 Roma, Italy E-mail: francesco.gasparrini@uniroma1.it Fax: 1390649912780 & 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.jss-journal.com J. Sep. Sci. 2010, 33, 3022–3032 3022