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- Plasma modification (5)
- Functional groups (3)
- Introduction of functional groups (3)
- Peel strength (3)
- Pulsed plasma (3)
- Pulsed plasma polymerization (3)
- Acrylic acid (2)
- Allyl alcohol (2)
- Allylamine (2)
- Aluminium (2)
Functional groups bearing monomers were pulsed plasma polymerised with a degree of retained functional groups of 5591%. The following functional groups could be produced at a maximum of: 30 OH, 18 NH2, and 24 COOH per 100 C atoms. A plasma-initiated radical copolymerisation could also be realised using the functional group bearing monomers as a source of functionalities, olefins as chain-extenders and dienes as chemical cross-linkers. The peel strengths of Al layers on such plasma polymers were correlated to the type and density of functional groups.
The retention of chemical structure and functional groups during pulsed plasma polymerization was used for producing adhesion-promoting plasma polymer layers with high concentrations of exclusively one kind of functional groups, such as OH, NH2, or COOH. The maximum content of functional groups was 31 OH using allyl alcohol, 18 NH2 using allylamine, or 24 COOH per 100 C atoms using acrylic acid. To vary the density of functional groups, chemical co-polymerization with ethylene as 'chain-extending' co-monomer, or butadiene as 'chemical crosslinker' was initiated in the pulsed plasma. The composition of these co-polymers was investigated by XPS and IR spectroscopy. The concentrations of functional groups were measured by derivatizing with fluorine-containing reagents and using XPS. A set of plasma parameters was found to be a good compromise between a high number of functional groups and complete insolubility in water, ethanol or THF,which is needed for further chemical processing. Here, these monotype-functionalized surfaces were used in metal-polymer systems as adhesion-promoting interlayers to examine the influence of type and density of functional groups on adhesion. As expected, COOH- and OH-group-terminated interlayers showed maximum peel strengths to evaporated aluminium layers. The adhesion increased linearly with the number of OH groups to a maximum at about 27 OH per 100 C atoms. Higher concentrations of OH groups did not increase the peel strength further.
Several approaches were investigated to produce monosort functionalized polymer surfaces with a high density and homogeneity of functional groups: (i) Plasma oxidation followed by wet-chemical reduction, (ii) formation of radicals and grafting on of functional group carrying molecules, (iii) plasma bromination followed by (iv) Williamson or Gabriel-like synthesis of spacer molecules, and (v) a pulsed plasma polymerization of functional groups bearing monomers or (vi) their copolymerisation with other comonomers. The formation of hydroxyl (OH), primary amino (NH2), and carboxyl (COOH) groups was studied in detail. The oxygen plasma treatment (i) in a low-pressure non-isothermal glow discharge results in the formation of a wide variety of O functional groups, polymer degradation and crosslinking. Low power densities and short exposure times (0.1 to 2 s) are required to functionalize a surface while preserving the original polymer structure. Carbonate, ester, and aromatic groups are rapidly degraded by an oxygen plasma treatment leading to scissions of polymer backbones and loss in molecular weight. Also the formation of macrocycles and C=C bonds was observed in a region of around 4 nm in depth. The investigated polymers could be classified by their degradation behaviour on exposure to the oxygen plasma.___TAGSTART___BR___TAGEND___ In order to maximize the process selectivity for OH groups, the variety of oxygen functionalities formed by the oxygen plasma was wet-chemically reduced by diborane, vitridetrade (Na complex), and LiAlH4. Typical yields were 9 to 14 OH groups per 100 carbon atoms.___TAGSTART___BR___TAGEND___ Plasma bromination (iii) (40 Br per 100 C atoms) of polymers, followed by grafting of spacer molecules (iv), has been proved to be a highly selective reaction.___TAGSTART___BR___TAGEND___ Another way to produce high densities of monosort functionalities was the pulsed plasma polymerization of functional group bearing monomers such as allylamine, allylalcohol or acrylic acid (v). The retention of chemical structure and functional groups during plasma polymerization was achieved by using low power densities and the pulsed plasma technique. The maximum yields were 30 OH, 18 NH2, and 24 COOH groups per 100 C atoms. To vary the density of functional groups a chemical copolymerization with ''chain-extending'' comonomers such as butadiene and ethylene was initiated in the pulsed plasma (vi). Additionally, the often-observed post-plasma oxidations of such layers initiated by reaction of trapped radicals with oxygen from the air were successfully suppressed by using NO gas as radical quencher.
This new functionalization method consists of the deposition of very thin plasma polymer layers (20 to 100 nm) of functional group bearing monomers in pulsed plasma. With allylalcohol, a maximum of 30 OH groups per 100 C atoms was measured with a selectivity of about 90% and a significant stability at long-time exposure to air. Allylamine was used to produce primary amino groups, with a maximum of 18 NH2 groups per 100 C atoms. Side reactions were observed during the storage in air, such as oxidation of the amino groups. Carboxylic groups could be produced using acrylic acid with a maximum concentration of 24 COOH groups per 100 C atoms. The most prominent side reaction was the decarbonylation/ decarboxylation of the acid group during plasma deposition.___TAGSTART___BR___TAGEND___ The variation of the density of functional groups using the pulsed-plasma polymerization of functional-group-bearing monomers was possible by the chemically-initiated radical copolymerization with either a chain-extending monomer, such as ethylene, or a cross linker, such as butadiene, in plasma. The density of functional groups could be adjusted continuously (0 to 30 OH, 0 to 18 NH2 and 0 to 24 COOH groups per 100 C atoms).___TAGSTART___BR___TAGEND___ The successful application of these densely functionalized polymer surfaces for producing biocompatible surfaces and for use in metalpolymer composites is proposed.
Polyethylene foils, used as greenhouse foils stabilized with various types of sterically hindered amine light stabilizers (HALS), showed an extraordinary prolonged lifetime on exposure to natural or artificial weathering if a gas-phase fluorination under low-pressure conditions was applied. The fluorination was performed using F2/N2 mixtures and provided ca. 50 F/100 C (fluorination degree ap25%). The lifetimes of fluorinated PE foils on exposure to artificial or natural weathering were increased at least by a factor of 2-4 as measured in terms of tensile strength and elongation at break.
Polymers synthesized with plasma techniques are very interesting materials for electronic, optic, and bio compatible applications. Thin films of plasma polymers shows a good adhesion to metals, glass, or other polymers. But the supramolecular structure, the durability, and the chemical and mechanical behavior of these polymers is poorly understood. Therefore dielectric investigations are carried out to study the dynamic behavior of the plasma polymers. As polymer system allyl alcohol/alkene is chosen to get polymers with a defined concentration of hydroxyl groups. The dielectric investigations shows several relaxation processes and a dependency of the dielectric parameters from the ratio of allyl alcohol in the polymer is observed. This results indicated that the alkene monomers were assembled continuous into the polymer matrix.
Monotype functionalizations with different types of functional groups (OH, NH2, COOH) on polypropylene and poly(tetrafluoroethylene) surfaces were synthesized using pulsed plasma-initiated homo- or copolymerization of functional group-carrying monomers. The maximum concentrations of functional groups were 31 OH, 18 NH2 or 24 COOH groups per 100 C atoms using allyl alcohol, allylamine or acrylic acid respectively as the monomer. The measured peel strengths of aluminium deposits increased linearly with the concentration of functional groups. Near the maximum concentration of OH (>27 OH/100 C atoms) or at moderate concentrations of COOH groups (>10 COOH/100 C atoms), constant (maximum) peel strengths were measured due to the mechanical collapse of one component in the composite (cohesive failure). Interface failures in Al-PP composites were found with COOH, NH2 and OH groups and cohesive failures were seen when higher concentrations of COOH groups were applied (>10 COOH/100 C atoms).
Polymer surfaces were modified in low-pressure glow discharge plasmas for introduction of monotype functional groups of different type and density. For this purpose three ways are selected, (i) oxygen plasma treatment followed by wet-chemical reduction of O functional groups to OH groups, (ii) plasma bromination for introducing C - Br groups and (iii) coating by deposition of thin plasma (co-) polymerized layers of functional groups-bearing monomers with OH, NH2, COOH, epoxy etc. functionalities. Subsequently, these groups were used as anchoring points for chemical grafting of spacer molecules, oligomers, prepolymers, fluorescent labels, ionic and nucleic acid residues, employing different chemical routes. The yield in monosort functional groups at polymer surfaces ranged from 1014 (process i), 2040 (process ii) and 1831 groups per 100 C atoms (process iii) as measured by XPS after derivatization. The consumption of functional groups amounted to 4090% of all functionalities present at the surface and depended on the dimensions of grafted molecules. For infinitely variably tuning the number of functional groups process iii was performed as copolymerization of a functional group-carrying comonomer with a non-functionalized (chain-extending) comonomer.