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  • 1
    Electronic Resource
    Electronic Resource
    Photolytic crosslinking of poly(p-hydroxystyrene) (1992)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 195 (1992), S. 191-204 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Die Photovernetzung von Poly(p-hydroxystyrol) (PPHS) wird durch O2 beachtlich beschleunigt. Dies ergab sich aus der Bestimmung der Molmasse (mit Hilfe der Lichtstreumethode) und des Gelanteils nach kontinuierlicher Bestrahlung bei λinc = 254 nm. Aufgrund von Ergebnissen aus Blitzphotolyseversuchen wird der folgende Reaktionsmechanismus aufgestellt: Die Vernetzung sowohl in An-als auch Abwesenheit von O2 kommt im wesentlichen durch Kombination von Radikalen des Phenoxyltyps zustande. In Abwesenheit von O2 werden Phenoxylradikale ausschließlich durch Spaltung von O—H-Bindungen phenolischer Gruppen, die sich im angeregten Singulettzustand befinden, erzeugt. Triplett-angeregte phenolische Gruppen, die sich auch bilden, desaktivieren nicht durch Spaltung der O—H-Bindungen. Sie reagieren allerdings sehr effektiv, sofern vorhanden, mit O2. Bei dieser Reaktion entstehen HO·2- und zusätzliche Phenoxylradikale. Alle handelsüblichen und die meisten im Labor synthetisierten PPHS-Proben enthalten chemisch gebundene, chinoidartige Verunreinigungen. Durch Versuche mit niedermolekularen Modellverbindungen wurde nachgewiesen, daß triplett-angeregte chinoide Gruppen einerseits mit phenolischen Gruppen unter Bildung von Phenoxylradikalen reagieren und daß sie andererseits unreaktiv sind bezüglich der Abstraktion aliphatischer Wasserstoffatome. Die Bestrahlung von PPHS bei λinc = 254 nm bewirkt die Bildung chinoider Gruppen, die bei dieser Wellenlänge auch stark absorbieren. Die Lichtabsorption dieser Gruppen wird im Laufe der weiteren Bestrahlung zum bestimmenden Faktor hinsichtlich der photochemischen Veränderung des Polymeren.
    Notes: Light-induced crosslinking of poly(p-hydroxystyrene) (PPHS) is significantly enhanced by O2. This was evidenced by molar mass (light scattering measurements) and by gel content determinations which were performed on various polymer samples before and after continuous irradiation at λinc = 254 nm. The following mechanism was elucidated with the aid of flash photolysis studies: Crosslinking in the absence or presence of O2 is mainly due to the combination of phenoxyl type radicals. In the absence of O2 the latter are exclusively formed by O—H bond cleavage of singlet excited phenolic groups. Triplet excited phenolic groups which are also formed do not deactivate via O—H bond cleavage but react very effectively with O2. This reaction leads to the formation of HO2· and additional phenoxyl type radicals. All Commercial and most laboratory-prepared PPHS samples contain chemically bound impurities of quinoid nature. On the basis of results performed with model compounds of low molar mass, it is concluded that triplet excited quinoid groups react effectively with phenolic groups forming phenoxyl type radicals and that they are quite unreactive with respect to the abstraction of alphatic hydrogen atoms. Irradiation of PPHS at λinc = 254 nm causes the formation of quinoid groups which absorb strongly at this wavelength. Light absorption by these groups becomes a determining factor with respect to photochemical alteration in the course of further irradiation.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1992.051950115
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  • 2
    Electronic Resource
    Electronic Resource
    Photoreactions in halogen-containing negative-tone novolac resists (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 214 (1994), S. 197-210 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Elementaranalytische sowie NMR-, IR- und UV-spektroskopische Untersuchungen zeigen, daß die Photolyse von Halogenphenolnovolaken zur Substitution der Halogenatome durch Wasserstoff, der Bildung chinoider Gruppen und intermolekularen Vernetzung führt. Die Geschwindigkeit der Halogeneliminierung hängt von der Art des Halogens ab. Sie steigt in der Reihenfolge F 〈 Cl 〈 Br 〈 I. Die Chloreliminierung aus der 4-Position ist gegenüber der aus der 2- und 3-Position begünstigt. Außerdem verläuft die Abspaltung para-ständiger Chloratome aus Dimeren schneller als aus Trioder Tetrameren. ESR-Messungen bei 77 K sowie die Laserblitzphotolyse bei 296 K deuten auf die intermediäre Bildung von Phenoxyl- und Arylradikalen. Lithographische Tests belegen die hohe UV-Empfindlichkeit von Resisten auf der Basis von Halogenphenolnovolaken. Im Vergleich zu nichthalogenhaltigen Novolakresisten wird eine 6 - 10fache (System: 4-Chlorphenolnovolak/4,4′-Bisazidobiphenyl (5%)) bzw. eine ca. 25fache (System: 4-Chlorphenol-/m-Cresolnovolak/Hexamethoxymethylmelamin (5%)) Steigerung der Empfindlichkeit erreicht. Zur Interpretation wird ein Mechanismus postuliert, demzufolge die durch Halogenabspaltung hervorgerufene Sekundärradikalbildung zu einer zusätzlichen Vernetzung beiträgt. In den melaminhaltigen Resisten katalysiert der gebildete Halogenwasserstoff (Hal· + RH → H-Hal + R·) außerdem die Reaktion der Melaminverbindung mit der Novolakmatrix.
    Notes: The photolysis of halogenophenol novolacs is determined by the substitution of halogens by hydrogen and the formation of quinoid groups and intermolecular crosslinks. This is concluded from elemental analysis, NMR, IR and optical absorption measurements. The rate of halogen release depends on the chemical nature of the halogen. It increases in the order F 〈 Cl 〈 Br 〈 I. Chlorine elimination from 4-position is favored over that from 2- and 3-position. Moreover, dimers release chlorine from 4-position much more readily than trimers and tetramers. ESR measurements at 77 K and flash photolysis studies at 296 K yielded evidence for the intermediate existence of phenoxyl and aryl radicals. Lithographic tests demonstrated the high UV-sensitivity of resist formulations based on halogen-containing novolacs. The increase in sensitivity relative to that of formulations based on nonhalogenated novolacs is 6 to 10fold system: 4-chlorophenol novolac/4,4′-bisazidobiphenyl (5%) and ca. 25fold system: 4-chlorophenol/m-cresol novolac/hexamethoxymethylmelamine (5%). A postulated reactions mechanism concerning the sensitivity increase takes into account that halogen elimination results in the formation of additional radicals that accelerate the rate of crosslinking. Moreover, hydrogen halide generated by hydrogen abstraction of halogen radicals (Hal· + RH → H-Hal + R·) provides for the acid required to catalyze the reaction of the melamine compound with the novolac matrix.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1994.052140117
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  • 3
    Electronic Resource
    Electronic Resource
    OH Radical-induced chemical reactions of polynucleotide complexes (1983)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 184 (1983), S. 165-173 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Poly(A + U), the 1:1 complex of poly(riboadenylic acid), poly A, and poly(ribouridylic acid), poly U, at pH 8 and self-complexed poly A at pH 4 exist as double helices in dilute aqueous solution. These complexes exhibit a similar behavior as native calf thymus DNA upon irradiation with 16 MeV electron pulses. Thus time resolved Rayleight light scattering measurements showed that crosslinking and double strand breakage can be clearly separated, the former proceeding faster than the latter. The extent to which the two processes occur depends on the ionic strength of the solution. At ionic strenghts exceeding 10 -1 mol/l crosslinking is the dominant process indicating that hcrit, the critical length between two single strand breaks for the accomplishment of double strand breaks, is strongly reduced. The investigation of complexes of poly A and Mg2+ ions revealed that the destruction of salt bridges is the rate determining process for the decrease of the light scattering intensity due to mainchain scission. This implies that life-times of salt bridges can be determined.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1983.021840117
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  • 4
    Electronic Resource
    Electronic Resource
    Über den einfluß von fängern auf die hochfeldpolymerisation von α-methylstyrol (1974)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 175 (1974), S. 2687-2703 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Cation scavengers (N(C2H5)3, H2O, cyclopropane) inhibit the polymerization of liquid α-methylstyrene initiated by field emission (FE). Electron scavengers also inhibit the polymerization with efficiencies declining in the series SF6〉N2O〉CO2〉O2. It is assumed that electrons emitted by the high field electrode ionize monomer molecules. Radical cations formed thereby initiate the cationic polymerization. Thus cation scavengers inhibit the growth of kinetic chains, whereas electron scavengers inhibit the initiation reaction.The polymerization initiated by field ionization (FI) is not affected by electron scavengers. However, cation scavengers inhibit this polymerization.Based on the dependence of the specific polymer yield on the N(C2H5)3-concentration it was estimated that in the case of FE only 1 to 10% of the emitted electrons initiate polymerization. In the case of FI up to 100% of the ions generated at the high field electrode start kinetic chains.During all experiments oligomer (degree of polymerization 3 to 4) was formed in a chain reaction. The specific oligomer yield increased with increasing SF6-concentration significantly when the reaction was initiated by FE.
    Notes: Die durch Feldemission (FE) in flüssigem α-Methylstyrol ausgelöste Polymerisation wird durch Kationenfänger (N(C2H5)3, H2O, Cyclopropan) inhibiert. Die Elektronenfänger SF6, N2O, CO2 und O2 inhibieren ebenfalls, wobei die Inhibitorwirksamkeit in der genannten Reihenfolge abnimmt. Dieses Verhalten wird darauf zurückgeführt, daß von der Hochfeldelektrode emittierte Elektronen Monomermolekeln ionisieren; dabei gebildete Radikalkationen starten die kationische Polymerisation. Durch Kationenfänger wird daher die Wachstumsreaktion inhibiert, während Elektronenfänger die Startreaktion inhibieren.Bei der durch Feldionisation (FI) gestarteten Polymerisation sind Elektronenfänger wirkungslos; Kationenfänger inhibieren dagegen.Aufgrund der Abhängigkeit der spezifischen Polymerausbeute von der N(C2H5)3-Konzentration wurde abgeschätzt, daß im Falle der FE nur 1 bis 10% der emittierten Elektronen polymerisationsauslösend wirken. Im Falle der FI starten bis zu 100% der an der Hochfeldelektrode erzeugten Ladungsträger kinetische Ketten.Bei allen Versuchen wurde Oligomeres (Polymerisationsgrad 3 bis 4) durch eine Kettenreaktion gebildet. Die spezifische Oligomerausbeute nahm bei der FE-initiierten Polymerisation mit steigender SF6-Konzentration bemerkenswert zu.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1974.021750914
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  • 5
    Electronic Resource
    Electronic Resource
    On the kinetics of polymer degradation in solution, 9Part 8: cf. 1.. Pulse radiolysis of poly(ethylene oxide) (1980)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 181 (1980), S. 1215-1226 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Poly(ethylene oxide) was irradiated with pulses of 16 MeV electrons (pulse length up to 100 ns) in aqueous and acetonitrile solutions in the absence and presence of oxygen. The change of the light scattering intensity (LSI) after the pulse was monitored. In acetonitrile solution, at a concentration of 2,3 · 10-2 base mol/1, main chain rupture occurred both in the presence and in the absence of O2. In aqueous solutions at [PEO] = 2,3 · 10-2 base mol/1 the LSI increased after the pulse in the absence of O2 (crosslinking) and decreased at [O2] = 1,4. 10-3 mol/1 (main chain scission). The rate of LSI decrease was correlated with a diffusion process in the case of O2 free acetonitrile solution and with a chemical reaction in the cases of O2 saturated aqueous and acetonitrile solutions. In the latter two cases it was found that a bimolecular reaction precedes bond scission in the main chain. It is assumed that peroxyl macroradicals (PO2•) react with each other forming oxyl macroradicals (PO•) which decompose relatively rapidly by main chain scission.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1980.021810606
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  • 6
    Electronic Resource
    Electronic Resource
    Rheological properties of two-dimensional model networksDedicated to Prof. H.-J. Cantow on the occasion of his 65th birthday (1988)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 189 (1988), S. 2395-2408 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: We measured the tensio-active properties of octamethylene dimethacrylate (1), octamethylene diisobutyrate (2) and octamethylene isobutyrate methacrylate (3) at the oil-water interface. The results indicate that these molecules are strongly adsorbed at the boundary between oil and water. The amphiphatic compounds in the monolayer can be polymerized and cross-linked by UV irradiation. The kinetics of surface gelation was studied by measuring the two-dimensional shear modulus as a function of the time of irradiation. A two-dimensional sol-gel transition was observed which is in fairly good agreement with percolation theories. The kinetics of the two-dimensional polymerization can be completely interpreted in terms of a simple reaction scheme. The elasticity of the two-dimensional films depends strongly on the surface concentration of the cross-linking agent. The rheological properties of the polymerized films exhibit typical features of rubber-elastic systems and there exists an interesting analogy to corresponding structures of three-dimensional networks.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1988.021891017
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  • 7
    Electronic Resource
    Electronic Resource
    Phenyl-2,4,6-trimethylbenzoylphosphinates as water-soluble photoinitiators. Generation and reactivity of O=Ṗ(C6H5)(O-) radical anions (1991)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 192 (1991), S. 2307-2315 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Lithium- and magnesium phenyl-2,4,6-trimethylbenzoylphosphinates (TMPPL and TMPPM) are effective water-soluble photoinitiators for the free-radical polymerization of appropriate monomers such as acrylamide (AA) and methacrylamide (MAA) in aqueous solution. They are also capable of initiating the polymerization of other olefinic compounds such as styrene (St), methyl methacrylate (MMA) or acrylonitrile (AN) in water-containing solvent mixtures such as 1:1 water-acetonitrile mixtures. This is due to the fact that TMPPL and TMPPM undergo α-scission with a rather high quantum yield (φ(α) ≈ 0,35) resulting in the formation of 2,4,6-trimethylbenzoyl radicals and O=Ṗ (C6H5)(O-) radical anions. The latter are very reactive toward olefinic monomers. Bimolecular rate constants kR+M/(L/(mol · s)) were determined by flash photolysis at room temperature, e. g. in neat water: 3,8 · 108 (MAA), 2,2 · 108 (AA), and in H2O/CH3CN (1:1, v/v): 1,8 · 107 (St), 1,2 · 108 (MMA), 8,4 · 107 (AN).
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1991.021921010
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  • 8
    Electronic Resource
    Electronic Resource
    Laser flash photolysis of poly(p-vinylbenzophenone) in solution. Intramolecular triplet deactivation processes (1979)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 180 (1979), S. 1487-1495 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Poly(p-vinylbenzophenone) (poly[1-(4-benzoylphenyl)ethylene], PVBP) and p-isopropylbenzophenone (IPB) were irradiated in benzene solution at room temperature with 347, 1 nm laser flashes (duration 25 ns). Triplet-triplet spectra were recorded at the end of the flash. Upon following the decay of the T-T spectra a pronounced polymer effect was found: the decay followed 2nd order kinetics in the case of the polymer and 1st order kinetics in the case of the model compound. The halflife times differ by a factor of about five (τ1/2(PVBP) 〈 τ1/2(IPB)). Whereas τ1/2(IPB) was not influenced, τ1/2(PVBP) decreased with increasing absorbed dose per flash. From the results it is inferred that at relatively high dose rates PVBP triplets decay essentially via intramolecular T-T annihilation and at lower dose rates via intramolecular selfquenching processes. At comparable conditions IPB triplets were essentially deactivated via interactions with solvent molecules.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1979.021800608
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  • 9
    Electronic Resource
    Electronic Resource
    Radiation induced molecular size changes in native and denatured deoxyribonucleic acid under anoxic conditions. A pulse radiolysis study (1982)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 183 (1982), S. 697-709 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Native DNA (M̄w: 5 · 106 and 2 · 107) was irradiated at a concentration of 0,l g/l in Ar- or N2O-saturated solutions. Emphasis was given to reactions induced by OH radicals. The solutions were irradiated with single 16MeV electron pulses (100 ns pulse length) in conjunction with time-resolved Rayleigh light scattering measurements. It turned out that crosslinking and double strand breakage (dsb) can be clearly separated, the former proceeding faster than the latter. The extent to which the two processes - which counteract with respect to changes of the light scattering intensity (LSI) - occur, depends strongly on the ionic strength of the solution. At [NaClO4] 〉 10-1 mol/l crosslinking is the predominant process, which is assumed to be caused by the fact that hcrit, the critical length for the accomplishment of dsb, is strongly reduced. Thus, up to several hundred single strand breaks (ssb) per chain can remian ineffective with respect to the generation of dsb at high ionic strength. Crosslinking can occur both as an inter- and an intramolecular process. As inferred from light scattering measurements singlestranded DNA did not crosslink at a concentration of 0,l g/l and at low ionic strength, but underwent main-chain rupture. The rate of LSI decrease is correlated to the rate of fragment diffusion. The half-life time of the LSI decrease depends on M̄w as τ½ ∝ M̄w,00,6. It was concluded that the lifetime of the species responsible for ssb is shorter than a few ms.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1982.021830319
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  • 10
    Electronic Resource
    Electronic Resource
    Time resolved light scattering measurements on the disentanglement diffusion following the degradation of poly(phenyl vinyl ketone) (1979)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 180 (1979), S. 2371-2378 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Poly(phenyl vinyl ketone) was irradiated in 1,4-dioxane solutions with 25 ns flashes of 347, 1 nm light at various incident intensities. The rate of fragment separation following the very rapid rupture of chemical bonds in the main chains was measured. For this purpose the decrease of the intensity of light scattered by the polymer solution (LSI) was monitored as a function of time after the flash at various scattering angles. It was found that the lifetime of the LSI change τ(LSI) decreased with increasing scattering angle. This is due to the fact that main chain breaks are statistically distributed over all molecules and along the chains thus causing the generation of small and large fragments. The larger fragments which move at smaller speed contribute stronger to the LSI at low scattering angles than the small ones. It was, furthermore, found that τ(LSI) is independent of Zs, the average number of scissions per initial macromolecule, if the fragment size exceeds a critical value which was estimated as being of the order of 103 base units in this case. τ(LSI) decreased with increasing Zs steadily if the average size of fragments was smaller than the critical value. This was evidenced both by measuring τ(LSI) as a function of the initial molecular weight and of the scattering angle. In conclusion: intramolecular interaction is determining disentanglement motions if the chain length exceeds a critical value. At shorter chain lengths pure translational motions become rate determining.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1979.021801011
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