Polymer brushes: surface-immobilized macromolecules

Concepts for the incorporation of inorganic building blocks into organic polymers on a nanoscale

The preparation of a wide variety of unique polymer brush structures can be accomplished by “living” free radical polymerization of vinyl monomers from surface-tethered alkoxyamines or from tethered α-halo esters in the presence of (PPh3)2NiBr2. The use of a “living” free radical process permits the molecular weight and polydispersity of the covalently attached polymer chains to be accurately controlled while also allowing the formation of block copolymers by the sequential growth of monomers from the surface. These block and random copolymer brushes have been used to control surface properties.

Controlled Synthesis of Polymer Brushes by “Living” Free Radical Polymerization Techniques

The preparation of hybrid organic/inorganic nanocomposites comprised of well-defined polymers was reviewed. In particular, synthetic methods using controlled/“living” radical polymerization techniq...

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Synthesis of Nanocomposite Organic/Inorganic Hybrid Materials Using Controlled/“Living” Radical Polymerization

We report on the radical-chain polymerization of styrene using self-assembled monolayers of azo initiators covalently bound to high surface area silica gels. In this process monolayers of poly(styrene) molecules terminally attached to the surface of the inorganic substrate are obtained. As the initiator molecules are immobilized at the surfaces in a one-step reaction, well-reproducible layers can be prepared and the surface concentration of the initiator can be adjusted in a wide range between the limit of detection and full surface coverage. In the subsequent polymerization reactions polymer monolayers with high, controlled graft density can be obtained. The synthesis of the attached layers and the characterization by X-ray photoelectron spectroscopy, diffuse reflectance infrared spectroscopy (DRIFT), and elemental analysis are described. After cleavage of an ester group that connects the polymers to the surface, the molecular weights of the polymers were determined. The results of the study show that th...

Synthesis of Poly(styrene) Monolayers Attached to High Surface Area Silica Gels through Self-Assembled Monolayers of Azo Initiators

Es werden Reaktionen untersucht, durch die oberflachenstandige Silanolgruppen amorpher Siliciumdixide durch Phenyl-, Nitrophenyl- und Aminophenyl- gruppen ersetzt werden. Der kovalente Charakter der Bindung zwischen organischem Molekulrest und der Oberflache des Siliciumdioxids wird IR-spektroskopisch nachgewiesen. Die Nitrophenylgruppen werden quantitativ durch Polarographische Analyse, die Aminophenylgruppen durch UV- spektrometrische Analyse der Phenyl-diazo-naphthol-(2)-Gruppierung bestimmt.



Durch Diazotierung der Aminopphylgruppen und Kupplung der Diazoniumsalze mit H-aktiven Verbindungen werden kovalent an der Oberflache des Silicium-dioxids gebundene Initiatoren des Diazotyps dargestellt. Die Anzahl der kovalent gebundenen Phenyl-diazo-Gruppen wird aus der Menge des Stickstoffs bestimmt, die beim thermischen Zerfall der Gruppierung freigesetzt wird.



Radikalische Polymerisationsreaktionen an der SiO2-Oberflache werden durch kovalent gebundene, beim Zerfall der Phenyl-diazo-Gruppierung entstandene Phenylradikale ausgelost. Durch die Polyreaktionen werden Pfropfprodukte gebildet, die bis zu 80% (bei Polymerisationen in Substanz) bzw. 50% (bei Polymerisationen in Losung) Gewichtsanteile kovalent gebundenen Polymeres enthalten. Durch Adsorption von Homopolymeren an reinem SiO2 bzw. Phenyl-, Nitrophenyl- und Aminophenyl- SiO2 werden nur 0,3-3% Polymeres irreversibel adsorptiv gebunden.



Reactions are studied by which silanol groups on the surface of amorphous silica are substituted by phenyl, nitrophenyl, and aminophenyl groups. The covalent nature of the bonds between the organic molecules and the surface of SiO2 is shown by IR-spectroscopy. The nitrophenyl and aminophenyl groups are determined quantitatively by polarographic analysis and by UV-spectroscopic analysis of the phenyl-diazo-naphthol-(2) group, respectively.



Diazotizing the aminophenyl groups and coupling the diazonium salt with compounds bearing an active hydrogen atom leads to initiators of the diazo type covalently bound to the surface of silica. The measured amount of nitrogen, set free by the thermal decomposition of the diazo group, gives the number of covalently bound phenyldiazo groups.



Radical polymerization reactions on the surface of silica are initiated by covalently bound phenyl radicals originated by decomposition of the phenyl-diazo group. In polymerization reactions graft polymers are formed containing covalently bound polymer material to about 80 wt.-% (bulk polymerization) and 50 wt.-% (poly- merization in solution), respectively. Adsorption of homopolymers on the surface silica or phenylic, nitrophenylic, and aminophenylic silica yields 0,3 to 3% polymer material irreversibly bound.

Polyreaktionen an pigmentoberflächen. III. Mitteilung: Polyreaktionen an SiO2-oberflächen†‡§¶

Chlorsilanmodifizierte Polymere wie Polystyrol und Polymethylmethacrylat mit Chlorsilanendgruppen, reagieren mit oberflachenstandigen Hydroxylgruppen von Siliciumdioxiden unter Ausbildung von Siloxanbindungen und kovalenter Verknupfung der Makromolekulemit der Feststoffoberflache. Die reaktiven Polymeren werden durch Ubertragung bei der radikalischen Polymerisation der Monomeren und durch Abbruch anionisch lebender Polymerer mit Chlorsilanen (Siliciumtetrachlorid, Trichlormethylsilan, Dichlordimethylsilan) dargestellt. Die Menge des an die Siliciumdioxidoberflache kovalent gebundenen Polymeren betragt, abhangig vom Molekulargewicht der Makromolekule, von den Reaktionsparametern Zeit, Temperatur, Losungsmittel, Konzentration an Festkorper und Polymeren sowie von der spezifischen Oberflache der Siliciumdioxide, bis zu 500 mg Polymeres pro Gramm Siliciumdioxid. Durch einfache Adsorption und anschliesende Desorption werden maximal 30 mg Polymeres pro Gramm Siliciumdioxid irreversibel adsorptiv gebunden.



Die mit Polystyrol oder Polymethylmethacrylat modifizierten Siliciumdioxide sind hydrophob und zeigen ein gegenuber unmodifiziertem Siliciumdioxid verandertes Sedimentationsverhalten.



Polymers with chlorosilane endgroups, such as polystyrene and polymethyl methacrylate, react with superficial hydroxyl groups of silicon dioxides by formation of siloxane bonds and covalent binding of the macromolecules to the surface. The active polymers are prepared either by a radical polymerisation of the monomers in presence of chlorosilanes or by a terminating reaction of the anionically living polymers with chlorosilanes (tetrachlorosilane, trichloro methylsilane, dichloro dimethylsilane). The amount of polymer coverage depends on the molecular weight of the macromolecules, on the reaction parameters (time, temperature, solvent, concentration of silicon dioxide and polymers) and on the specific surface of the silicon dioxides. According to varying reaction conditions, the amount of polymer coverage ranges up to 500mg of polymer per gram of silicon dioxide, whereas only 30 mg of polymer per gram of silicon dioxide is bonded irreversibly by adsorption of the polymer from solution and subsequent desorption.



The polymeric modification of the silicon dioxides effects changed properties, such as a hydrophobic character and a different sedimentation behaviour.

Polyreaktionen an Pigmentoberflächen. VII. Mitteilung: Reaktionen von Polymeren mit endständigen Chlorsilangruppen an Siliciumdioxidoberflächen

Durch eine radikalische Polymerisationsreaktion wird Polystyrol kovalent an die Oberflache von Siliciumdioxid gebunden. Die Pfropfreaktion wird ausgelost durch kovalent an der SiO2-Oberflache gebundene Phenylradikale, die durch thermischen Zerfall von Phenyl-diazo-thioathergruppen entstehen. Die Menge des aufgepfropften Polymeren ist abhangig von den Reaktionsparametern Zeit, Temperatur und Konzentration an Monomerem und an initiierenden Diazogruppen. Die Pfropfpolymerisation verlauft in heterogener Phase nach dem fur radikalische Polymerisationen bekannten Zeitgesetz in 1. Ordnung bezuglich Monomerkonzentration und ist beendet, wenn initiierende Radikale infolge von Rekombinationen oder sterischer Hinderung an der SiO2-Oberflache die Polymerisation nicht mehr auslosen konnen.



Der kovalente Charakter der Bindung zwischen Polymerem und Siliciumdioxid wird IR-spektroskopisch und durch Adsorptions-Desorptions-Versuche nachgewiesen. Die durch die radikalische Polyreaktion an der Oberflache gebundene Menge an Polymerem ist um eine bis zwei Grosenordnungen groser als die irreversibel adsorptiv gebundene. Die Struktur der gebundenen Makromolekule kann als solche sich zum Teil durchdringender, elliptoidisch verformter Knauel beschrieben werden.



Polystyrene is covalently bound to the surface of amorphous silica by a radical graft polymerization, which is initiated by phenyl radicals generated by thermal decomposition of covalently bound phenyl-diazo thioether groups. The amount of grafted polymer depends on reaction time, temperature, and concentration of the monomer and the initiating diazo groups. The kinetics of the polymerization reaction obeys a first order in relation to the monomer concentration, up to a conversion of about 70 to 80%. The graft reaction is terminated when initiating radicals are no more available as a result of recombination reactions or sterical hindrance on the silica surface.



The covalent nature of the bond between the macromolecules and the silica surface is shown by means of IR-spectroscopy and by adsorption and desorption experiments. Ten to one hundred times as much polymer can be covalently bound to the silica surface by the radical graft reaction than can be irreversibly adsorbed. The structure of the grafted polymer can be described as mutually-penetrating, ellipsoidally-deformed random coils fixed to the silica surface.

Polyreaktionen an Pigmentoberflächen. VI. Mitteilung: Radikalisch initiierte Polyreaktionen an SiO2-Oberflächen†

Methyl methacrylate (MMA) was copolymerized with acrylamide, N-methylacrylamide, N,N-dimethylacrylamide, 1-vinyl-2-pyrrolidone, 4-vinylpyridine, and 2-dimethylaminomethyl methacrylate in 1,4-dioxane solution at 65°C, using AIBN as initiator, to yield copolymers with comonomer contents between about 5 and 50 mole-%. The monomer reactivity ratios were evaluated. The copolymerizations are in general non-azeotropic and non-ideal. The amine group containing comonomers are preferentially incorporated in relation to MMA, but MMA is preferentially incorporated in relation to the amide group containing comonomers. The average molecular weights of the copolymers, with the exception of the N,N-dimethylacrylamide copolymer, decrease with increasing comonomer concentration, especially in the case of the amine group containing comonomers. The increasing content of amide and amine group containing monomeric units in the copolymers influences the adsorption of the polymers on an iron oxide red pigment, the dispersion stability, as well as the adhesion of the polymer coatings on steel plates and their corrosion protection.

Preparation of amide and amine groups containing copolymers of methyl methacrylate and their performance in solid polymer composites

Die Partikelassoziation von hochdispersem Siliciumdioxid in dem relativ unpolaren Losungsmittel Toluol wird durch kovalent gebundene Polystyrolmolekule, nicht jedoch durch adsorbiertes Polystyrol eingeschrankt. Bei Anwesenheit von n-Butanol wird das Sedimentationsverhalten von Siliciumdioxid mit kovalent gebundenem Polystyrol durch die Polymerschicht, das von Siliciumdioxid mit adsorbiertem Polystyrol durch das coadsorbierte Additiv bestimmt.



The association of particles of high disperse silica in the non polar solvent toluene is restricted by covalently bound polystyrene but not by adsorbed polystyrene. The sedimentation behaviour of the silica in presence of n-butanol is determined by the polymeric layer in the case of silica with covalently bound polystyrene, but by the coadsorbed additive in the case of silica with adsorbed polystyrene.

Richard Laible

Papers

Polyreaktionen an pigmentoberflächen. III. Mitteilung: Polyreaktionen an SiO2-oberflächen†‡§¶

Polyreaktionen an Pigmentoberflächen. VII. Mitteilung: Reaktionen von Polymeren mit endständigen Chlorsilangruppen an Siliciumdioxidoberflächen

Polyreaktionen an Pigmentoberflächen. VI. Mitteilung: Radikalisch initiierte Polyreaktionen an SiO2-Oberflächen†

Preparation of amide and amine groups containing copolymers of methyl methacrylate and their performance in solid polymer composites

Polyreaktionen an pigmentoberflächen VIII. Sedimentationseigenschaften von hochdispersem siliciumdioxid mit kovalent gebundenem polystyrol