Synthesis of Dual-functional Copolymer with Orthogonally Photosensitive Groups Lebo Xu, 1 John Farrell, 1 Raghuraman G. Karunakaran, 1 Apiradee Honglawan, 2 Shu Yang 1,2 1 Department of Material Science and Engineering, University of Pennsylvania, 3231 Walnut Street, Philadelphia, Pennsylvania 19104 2 Department of Chemical and Biomolecular Engineering, University of Pennsylvania, Towne Building, 220 South 33rd Street, Philadelphia, Pennsylvania 19104 Correspondence to: S. Yang (E-mail: shuyang@seas.upenn.edu) Received 6 October 2012; accepted 16 November 2012; published online 18 December 2012 DOI: 10.1002/pola.26490 ABSTRACT: A dual-functional copolymer, poly(4-styrenesulfonyl azide-co-t-butyl-methacrylate), with built-in photoacid labile and photocrosslinkable components was designed and synthesized by radical copolymerization. The mixture of copolymer and photoacid generators was spin coated on aminosilane treated Si wafers and polycarbonate (PC). When exposed to 365 nm UV light, photoacids were generated, which decomposed the acid labile groups, t-butyl- ester, to carboxylic acid in the exposed region, leading to drastic change of wettability from hydrophobic to hydrophilic after devel- oping the film in an aqueous base solution. The patterned polymer film could be subsequently photoimmobilized on the substrate under 254 nm deep UV exposure through CAH insertion via exited azide groups. 1 H-NMR and Fourier transform infrared spectra con- firmed the synthesis of the copolymer, and the photodecomposi- tion and photografting reactions occurred orthogonally at 365 and 254 nm, respectively, without interfering each other. On the pat- terned surfaces, including a hexagonal dot array and a gradient line array, we demonstrated selective wetting in the 365 nm exposed regions. On the gradient line array, we showed an inter- esting ratchet wetting pattern. Finally, we showed that the copoly- mer could be used to modify the wettability of PC while maintaining its high optical quality. V C 2012 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 1215–1222 KEYWORDS: copolymerization; crosslinking; lithography; photo- chemistry; surfaces; thin films INTRODUCTION Grafted polymers are commonly used to modify the surface wettability, (bio)adhesion and responsive- ness to an external stimulus (e.g., pH, temperature, or light) for a wide range of applications, including sensors, tunable wetting, anti-biofouling, directed assembly of nanoparticles, surface patterning, and biomedical devices. Common approaches to immobilize polymers include ‘‘grafting to,’’ ‘‘grafting from,’’ and ‘‘grafting through,’’ 1,2 Although the ‘‘grafting from’’ and ‘‘grafting through’’ can offer higher graft- ing density, the use of solvent and monomer (usually a good solvent for polymer) could lead to swelling and failure of structured polymer substrates. 3 Grafting to’’ approach involves chemical reactions between the substrate and the polymers to be immobilized. However, many substrates are rather inert and require surface pre- treatment, such as oxygen plasma, to activate the surface for further modification. Nevertheless, such treatment may not be desirable for a polymeric substrate. Photochemical reactive groups, such as benzophenone, arylazide groups, aro- matic diazonium derivatives and numerous radical genera- tors, have been used to ‘‘graft to’’ proteins, polypeptides and synthetic polymers on various polymeric substrates, and silanized glass. 4–8 Specifically, there are increasing interests in design and synthesis of functional polymers consisting of azide groups, which can undergo thermolysis (typically 160  C) or photolysis (254 nm UV exposure) to generate transient nitrene radicals. The polymers are then crosslinked through nitrene dimerization or addition to unsaturated species, 9 grafted to an adjacent polymer chain via CAH insertion 5,7 and click chemistry between azides and alkynes. 10 The azide chemistry has been utilized to tune the interfacial interaction for directing block copolymer assemblies, 11–13 to create an array of multifunctional polymers, 10 to stabilize nanoparticles between polymer layers, 14 to control surface wettability, 9,15,16 and to immobilize biomolecules. 17 The reactions do not require the presence of a particular functional group in the polymer chain or on a substrate. More importantly, it will allow us to conduct a grafting reaction in a dry state, there- fore, avoiding potential swelling and damage of a polymeric substrate by an organic solvent or monomers. The photoim- mobilization at 254 nm deep UV (DUV) wavelength offers high spatial resolution and can be conducted at room temper- ature, therefore, is preferred for grafting and crosslinking V C 2012 Wiley Periodicals, Inc. WWW.MATERIALSVIEWS.COM JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2013, 51, 1215–1222 1215 JOURNAL OF POLYMER SCIENCE WWW.POLYMERCHEMISTRY.ORG ARTICLE