An Efficient Approach to Surface-Initiated Ring-Opening Metathesis Polymerization of Cyclooctadiene

Abstract

Surface-initiated ring-opening metathesis polymerization of cyclooctadiene (COD), a low ring-strain olefin, is reported for the first time. Polymerization was carried out in the vapor phase, which is advantageous compared to conventional solution methods in terms of minimizing chain transfer by reducing polymer chain mobility at the vapor/solid interface. Attachments of a norbornenylcontaining silane and a Grubbs catalyst to silicon substrates were carried out before samples were exposed to COD vapor. The thickness of grafted 1,4-polybutadiene films was controlled by reaction time and reached ~40 nm after 7 h. The polymer films were further chemically modified to afford a new polymer, head-to-head poly(vinyl alcohol).Polymer thin films have attracted significant interest because of their application in nanopattern fabrication, 1 preparation of "smart" materials, 2 chemical sensing, 3 and separations. 4 Surface grafting methods have been employed to covalently attach polymer films to various inorganic substrates. 5 Among different approaches, surface-initiated ring-opening metathesis polymerization (SiROMP) is an effective method to tether polymer chains to substrates including gold, 6,7 silicon wafers, 8-11 steel, 12 silicon (111), 13 and silica nanoparticles. 14 SiROMP has been used to prepare organic dielectric layers for the construction of field effect transistors; layer thickness has been controlled from less than 100 nm to more than 2 μm. 6 This technique has also been widely used to form a variety of patterned polymer films. 8,11 To the best of our knowledge, the monomers undergoing SiROMP have been limited to norbornene 6,14 and its derivatives; 15 there is no report on SiROMP of low-strain cyclic monomers, such as cis,cis-cycloocta-1,5-diene (COD), due to extensive chain transfer during polymerization.Here we report a versatile approach to SiROMP of this low-strain cyclic monomer in the vapor phase and the subsequent chemical modifications of the grafted polybutadiene (PBd) thin films. Reduced polymer chain mobility at the vapor/solid interface minimizes chain transfer in polymerizations carried out in the vapor phase. The vapor phase also provides an efficient method for new materials synthesis -a new polymer, head-to-head poly(vinyl alcohol) (hh-PVOH) was prepared using oxidation/hydrolysis of the grafted PBd.The 2 nd generation Grubbs catalyst was chosen as the initiator for the SiROMP of COD on silicon wafers due to its high reactivity and tolerance to water, oxygen, and functional groups. As shown in Scheme 1, the catalyst was attached to silicon surfaces through a norbornenyl monolayer which was prepared in the vapor phase from norbornenyltriethoxysilane at 70 °C. The norbornenyl groups have high ring strain and can readily react with the catalyst. Closely E-mail: weichen@mtholyoke.edu. NIH Public Access Author ManuscriptLangmuir. Author manuscript; available in PMC 2008 August 13. NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript packed norbornenyl groups, however...

Ring-opening metathesis polymerization of 8-membered cyclic olefins

“…Lerum et al and Feng et al demonstrated that ROMP of these two monomers was possible by vapor deposition on a previously activated surface. 154,155 The active surface was made by reacting G2 catalyst with a norbornene functionalized silicon surface. The monomer vapor reacted at the surface and the polymerization was followed by measuring the surface thickness.…”

Acute Degradation of Surface-Bound Unsaturated Polyolefins in Common Solvents under Ambient Conditions

“…Our group recently reported the SiROMP of cis , cis -cycloocta-1,5-diene (COD), affording polybutadiene (PBd) films with thicknesses up to ~40 nm 22. The polymerization of low ring-strain monomers such as COD is non-trivial due to the propensity of chain transfer during polymerization.…”

Surface-Initiated Ring-Opening Metathesis Polymerization (SI-ROMP): History, General Features, and Applications in Surface Engineering with Polymer Brushes

“…To confirm a good coverage of the polymer film, one could observe the attenuation of XPS signals from the substrate. For instance, the disappearance of silicon peaks is usually observed after the surface-initiated polymerization on the silica surface [39,86].…”

“…Therefore, the driving force of the polymerization reaction is weaker, and the competitive effect of chain transfer reactions becomes more significant. By using vapor-phase monomers, the rate of chain transfer is minimized due to reduced chain mobility at the vapor-solid interface [86,89], so the polymerization can proceed in the forward direction at a faster rate. Lerum et al reported that the critical strain energy required to render the polymerization reaction thermodynamically feasible using vapor-phase monomers is only 2.2 kcal/mol, while the required strain energy of solution-phase monomers is estimated to be 13.3 kcal/mol [18].…”