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Surface Functionalization And Electroless Copper Deposition Of The Fluoropolymer Films

Posted on:2008-10-31Degree:DoctorType:Dissertation
Country:ChinaCandidate:W H SunFull Text:PDF
GTID:1101360215987786Subject:Materials Physics and Chemistry
Abstract/Summary:PDF Full Text Request
In recent years, fluoropolymers, such as poly(tetrafluoroethylene) (PTFE) andpoly(vinylidene fluoride) (PVDF), have received much attention because of itsexcellent physical and chemical properties, such as thermal stability, excellentchemical resistance, low water sorption and low dielectric constant, low dielectricloss and so on. Fluoropolymers have been widely used in space application, protective coatings, microelectronics packaging, and biotechnology (vascularsutures and regeneration templates). Just like the other dielectric polymers, thecharacteristic low surface energy and the resulting poor adhesion to other materialshave created numerous technical challenges. For instance, the adhesion of thepolymers with metals and semiconductors has been a constant challenge to theelectronics and microelectronics packaging industries; the biomedical equipmentscould be polluted easily because of the strong adsorption of proteins and lowbiocompatibility. In this connection, amount of researches have been devoted to thesurface modification of PVDF and PTFE.Firstly, in my thesis, grafting of PMMA brushes on the PVDF surfaces wascarried out via surface-initiated free radical polymerization of MMA. Prior to thesurface initiated polymerization, the PVDF surface was chemically treated withLiOH, NaBH4, and DIBAL-H to obtain hydroxyl functions. The azo initiators wereimmobilized on the surface by esterification of the surface-tethered hydroxyl groupwith 4, 4'-azobis(4-cyanopentanoic acid). Homopolymer brushes of methylmethacrylate (MMA) were prepared by surface-initiated free radical polymerizationfrom the azo functionalized PVDF surface. The chemical composition andtopography of the graft-functionalized PVDF surfaces were characterized by X-rayphotoelectron spectroscopy (XPS), attenuated total reflectance (ATR) FT-IRspectroscopy and atomic force microscopy (AFM). Kinetics study revealed anexponential increase in the graft concentration of polymer brushes with the reactiontime, indicating that the chain growth from the surface was consistence with a chainpolymerization. Water contact angles on PVDF films were reduced by surface grafting of MMA.At the same time, polymer brushes from PTFE surface were was also carried out.Prior to the surface initiated polymerization, the PTFE surface was chemically treatedwith Na/naphtha etchant for hydroxyl functionalization on the surface. Thenaphthalene radical anion causes the breakage of C-F bonds, resulting indefluorination of the PTFE surface. Subsequently exposure of the activated surface toair causes oxygen to be incorporated on the PTFE surfaces, leading to surfaceoxidation and formation of hydroxyl, carbonyl, and carboxyl species. The azoinitiator was immobilized on the PTFE surface by esterification of thesurface-tethered hydroxyl group with 4, 4'-azobis(4-cyanopentanoic acid).Homopolymers brushes of methyl methacrylate (MMA) were prepared by free radicalpolymerization from the azo-functionalized PTFE surface. The chemical compositionand topography of the graft-functionalized PTFE surfaces were characterized byX-ray photoelectron spectroscopy (XPS), attenuated total reflectance (ATR) FT-IRspectroscopy and atomic force microscopy (AFM). Water contact angles on PTFEfilms were reduced by surface grafting of MMA.Then well-defined polymer brushes on PVDF surfaces were successfullysynthesized by surface-initiated living radical polymerizations. Prior to thesurface-initiated RAFT polymerization, the PVDF surface was respectivelysubjected to LiOH, NaBH4, and DIBAL-H solution for obtaining hydroxylfunctions on the surface. The azo species, as used for surface initiator, wasgenerated on the PVDF surface by esterification of the surface-tethered hydroxylspecies and 4, 4'-azobis(4-cyanopentanoic acid). The graft polymerization of MMAand PEGMA was carried out on the azo-functionalized PVDF surface byRAFT-mediated (reversible addition-fragmentationchain transfer) polymerization.Diblock copolymer brushes on PVDF surfaces were subsequently prepared viasurface-initiated RAFT polymerization of second monomer from graftedhomopolymer brushes. Thus, the present work has illustrated that new surfacefunctionalities and molecular architecture arising from well-defined graft chainscan be incorporated onto the inert fluoropolymer films via surface-initiated livingradical polymerizations. Electroless copper deposition was carried out on the PTFE surface by one-stepprocess (Sn-free activation process). For electroless copper deposition with Sn-freeactivation process, grafting of PVP brushes was prepared via surface-initiated freeradical polymerization of 4VP from the PTFE surfaces. Surface modification ofpolytetrafluoroethylene (PTFE) films by exposure to sodium naphthalenide(Na/naphtha) etchant, and esterification of 4, 4'-azobis(4-cyanopentanoic acid)(ACP) with the hydroxyl groups covalently linked to the surface, followed by thesurface-initiated free radical polymerization of 4-vinylpyridine (4VP). The surfaceelemental composition and topography of the poly(4-vinylpyridine) (PVP)graft-functionalized PTFE surfaces (PTFE-g-PVP surfaces) were characterized byX-ray photoelectron spectroscopy (XPS), attenuated total reflectance (ATR) FT-IRspectroscopy and atomic force microscopy (AFM). Water contact angles on thepristine PTFE surface and PTFE-g-PVP surfaces were measured. The PVP brusheson the PTFE surface with well-preserved pyridine groups were was used not onlyas the chemisorption sites for the palladium complexes (without the need for priorsensitization by SnCl2) during the electroless plating of copper, but also anadhesion promotion layer to enhance the adhesion of the electrolessly depositedcopper with the PTFE surfaces. The T-peel adhesion strength of the electrolesslydeposited copper to the PVP grafted PTFE (PTFE-g-PVP) surface could reachabout 7.2 N/cm. This adhesion strength was much higher than that of theelectrolessly deposited copper to the pristine or Na/naphtha-treated PTFE surface.Effects of the graft polymerization time and the activation time in PdCl2 solution onthe T-peel adhesion strength of the electrolessly deposited copper (from the Sn-freeprocess) with the PTFE-g-PVP surface were determined. The strong adhesionbetween the electrolessly deposited copper and the PVP-grafted PTFE surfacecould be attributable to the strong interaction of the pyridine functional groups ofthe PVP chains with palladium and copper, and, to the spatial distribution of thegrafted PVP chains on the PTFE surface and into the metal layer. XPS results suggested that the adhesion failure of the electrolessly deposited copper with thePVP-grafted PTFE surfaces occurred near the PTFE/PVP interface.Electroless plating of copper was also carried out on the PVDF surfacefunctionalized with viologen (1, 1'-disubstituted-4, 4'-bipyridinium salt). The surfacefunctionalization involved a two-step process whereby 4-vinylbenzyl chloride(VBC) was first graft-polymerized, via surface-initiated reversibleaddition-fragmentation chain transfer (RAFT) polymerization, to generate thePVDF-g-PVBC surface. The benzyl chloride groups of the grafted VBC polymer(PVBC) were subsequently derivatized into the viol Surface Functionalization andElectroless Copper Deposition of the Fluoropolymer Films ogen groups(PVDF-g-Viologen). The chemical composition and topography of thegraft-functionalized PVDF surfaces were characterized by X-ray photoelectronspectroscopy (XPS) and atomic force microscopy (AFM), respectively. Pd(â…¡)could be adsorbed onto the PVDF-g-Viologen surface and subsequently reduced toits metal atom under UV irradiation. Electroless plating of copper could be carriedout on the PVDF-g-Viologen surface with the photo-reduced palladium metal.Unfortunately, layer of copper was not continous and uniform. Continuous workshall be done in the following career.At the same time, the hydroxyl coverage on the treated PVDF and PTFE filmswere determined quantitatively by reaction with diphenicanhydrid. This methodhas not been reported yet.
Keywords/Search Tags:Poly(vinylidene fluoride), Poly(tetrafluoroethylene), RAFT, Free radical polymerization, Polymer brushes, Hydrophilicity, Electroless plating, Adhesion
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