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Chemical vapor deposition (CVD) polymerization utilizes the delivery of vapor-phase monomers to form chemically well-defined polymeric films directly on the surface of a substrate. CVD polymers are desirable as conformal surface modification layers exhibiting strong retention of organic functional groups, and, in some cases, are responsive to external stimuli. Traditional wet-chemical chain- and step-growth mechanisms guide the development of new heterogeneous CVD polymerization techniques. Commonality with inorganic CVD methods facilitates the fabrication of hybrid devices. CVD polymers bridge microfabrication technology with chemical, biological, and nanoparticle systems and assembly. Robust interfaces can be achieved through covalent grafting enabling high-resolution (60 nm) patterning, even on flexible substrates. Utilizing only low-energy input to drive selective chemistry, modest vacuum, and room-temperature substrates, CVD polymerization is compatible with thermally sensitive substrates, such as paper, textiles, and plastics. CVD methods are particularly valuable for insoluble and infusible films, including fluoropolymers, electrically conductive polymers, and controllably crosslinked networks and for the potential to reduce environmental, health, and safety impacts associated with solvents. Quantitative models aid the development of large-area and roll-to-roll CVD polymer reactors. Relevant background, fundamental principles, and selected applications are reviewed.

Abstract: Chemical vapor deposition (CVD) is an attractive technique for the fabrication of high‐quality polymer thin films. The scheme used to initiate polymer chain growth is fundamental to controlling polymer thin film chemistry. A new initiation scheme for polymer CVD utilizing cationic initiation with a strong Lewis acid, TiCl4, in combination with a hydrogen donor, H2O, is presented. This coinitiation scheme results in polystyrene deposition rates of 139 nm min−1, relative to just 34 nm min−1 when TiCl4 is used alone. Characterization by Fourier transform infrared spectroscopy shows that the polymer structures of polystyrene films prepared by conventional solution‐based techniques and cationic CVD are similar. Synthesis of cross‐linked polymer thin films is also demonstrated by depositing poly(divinylbenzene) and showing its insolubility in a range of solvents. The practical utility of these poly(divinylbenzene) films as corrosion resistant coatings is demonstrated. In 1 n HCl, 200 nm thick films on stainless steel increase the polarization resistance by a factor of 44 relative to bare, untreated stainless steel. [ABSTRACT FROM AUTHOR]

Abstract: The ability of initiated chemical vapor deposition to finely tune crosslinking densities in copolymer thin films has been used to develop a functional, reactive hydrogel system. The system consists of poly[maleic anhydride-co-dimethyl acrylamide-co-di(ethylene glycol) divinyl ether] films covalently attached to silicon substrates using the coupling agent 3-aminopropylethoxydimethylsilane. The swelling of the films in water is pH-dependent, with a maximum swelling ratio of 11 at pH=8. The hydrogel was also functionalized with 0.1 M cysteamine solutions in 2-propanol for 30 min to convert 97% of the anhydride functional groups to carboxylic acid and amide functionalities, confirmed by XPS and Fourier transform infrared spectroscopy. The functionalization yielded free thiol groups at the surface, which were used to attach CdSe/ZnS core-shell semiconductor nanoparticles to the hydrogels. [Copyright &y& Elsevier]

Abstract: A new “click chemistry” active functional polymer film was directly obtained from a commercially available monomer of propargyl acrylate (PA) via easy, one-step process of initiated chemical vapor deposition (iCVD). Fourier transform infrared (FTIR) spectra confirmed that significant amount of the click-active acetylene functional group was retained after the iCVD process. The degree of crosslinking could be controlled by intentionally adding crosslinker, such as ethylene glycol diacrylate (EGDA) that was polymerized with PA to form click-active, completely insoluble copolymer. The formed iCVD polymers could also be grafted on various inorganic substrates with silane coupling agents. These crosslinking and grafting techniques give iCVD polymers chemical and mechanical stability, which allows iCVD polymers applicable to various click chemistry without any modification of reaction conditions. Pre-patterned iCVD polymer could be obtained via photolithography and an azido-functionalized dye molecule was also successfully attached on iCVD polymer via click chemistry. Moreover, pPA film demonstrated sensitivity to e-beam irradiation, which enabled clickable substrates having nanometer scale patterns without requiring the use of an additional e-beam resist. Direct e-beam exposure of this multifunctional iCVD layer, a 200 nm pattern, and QD particles were selectively conjugated on the substrates via click chemistry. Thus, iCVD pPA has shown dual functionality as of “clickable” e-beam sensitive material. [Copyright &y& Elsevier]

Abstract: Initiated chemical vapor deposition (iCVD) is used for the first time to deposit a non-acrylic carbon-based polymer, polyvinylpyrrolidone (PVP). PVP is known for its hydrophilicity and biocompatibility, and its thin films have found many applications in the biomedical community, one of which is as antibiofouling surfaces. From vapors of 1-vinyl-2-pyrrolidone (VP) and tert-butyl peroxide (TBPO), iCVD produces PVP thin films that are spectroscopically identical to bulk PVP without using any solvents. iCVD works by selectively fragmenting gaseous TBPO with heat to create radicals for initiation of polymerization. This selectivity ensures that the monomer VP does not disintegrate to form species that do not conform to the structure of PVP. Fourier-transform infrared (FTIR), nuclear magnetic resonance, and X-ray photoelectron spectroscopy (XPS) show full retention of the hydrophilic pyrrolidone functional group. Number-average molecular weights range between 6570 and 10,200g/mol. The addition of ethylene glycol diacrylate (EGDA) vapor to the reaction mixture creates a cross-linked copolymer between VP and EGDA. Films with different degrees of cross-linking can be made depending on the partial pressures of the species. Methods for quantifying the relative incorporation of VP and EGDA using FTIR and XPS are introduced. The film with the lowest degree of cross-linking has a wetting angle of 11°, affirming its high hydrophilicity and iCVD''s ability to retain functionality. [Copyright &y& Elsevier]