Nanostructures from POSS-Grafted Block Copolymer Precursors
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Nanostructures from POSS-Grafted Block Copolymer Precursors Seung B. Chuna and Patrick T. Mathera,b,* a Polymer Program, bChemical Engineering Department, University of Connecticut, Storrs, CT 06269, U.S.A. ABSTRACT A new method to prepare novel nanocomposites has been studied in which a polyhedral oligomeric silsesquioxane (POSS) monomer is grafted to a polyisopreneblock-polystyrene copolymer to yield an inorganic-organic hybrid copolymer (POSS-gPI-block-PS). PS-block-PI copolymers (SI) were synthesized via anionic polymerization in tetrahydrofuran (THF) as solvent. The polyisoprene block of the SI diblock copolymers in this study featured a very high vinyl group fraction (65 mole % of 3,4addition and 35 mole % of 1,2-addition) available to react with hydride-substituted POSS (isobutyldimethyl silane-POSS) to form a grafted block copolymer. Due to the immiscibility between POSS-grafted PI block and PS block, the grafted block copolymer developed a microdomain structure. The volume fraction of PS block in the grafted block copolymer was varied in the range of 0.45 to 0.37 in order to yield cylindrical PS microdomains in the matrix of POSS-grafted PI. After exposure to an oxygen plasma, it is expected that preferential erosion of the grafted block copolymer will occur for the organic potion (PS microdomains) thus leaving a well-defined nanoporous surface structure for nonlithographic functionalization of coated substrates. INTRODUCTION Block copolymers consist of two or more different polymer blocks that are covalently bonded. Immiscibility between blocks gives rise to microphase separation where the microdomains have the dimension on the scale 10-100 nm. The shape of microdomains that form depends upon the volume fraction and the Flory-Huggins interaction parameter (χ) whereas their size is a function of the molecular weight of each block. Very recently, several reports have appeared that focus on surface patterning using block copolymer self-assembly behavior. [1-3] For example, polystyrene-bpolyethylene (SE) diblock copolymers and polypropylene-b-polyethylene-bpolypropylene (PEP) triblock copolymers were utilized to form a well-ordered surface pattern on a benzoic acid surface. [1,2] Also, polystyrene-b-polymethylmethacrylate (PS-b-PMMA) diblock copolymers have been ordered on self-assembled monolayers surfaces exposed to an intense and patterned x-ray flux. [3] Our present goal is to obtain organic/inorganic hybrid block copolymers and to prepare thin coatings that have wellordered surface patterns. Such surface-patterned thin films will enable numerous practical applications after selective oxygen plasma etching of organic microdomains or matrix, especially patterned sensors from silicon substrates. Previously we have studied nanostructures formed from polyhedral oligomeric silsesquioxane polynorbornene (POSS-PN) block copolymers as another example of a hybrid organic/inorganic block copolymer.[4] In particular, POSS-polynorbornene-bKK10.8.1
polynorbornene (POSS-PN-b-PN) block copolymers were synthesized via r
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