摘要:

AbstractTheoretical analysis of resonant microwave absorption of cloned linear DNA in aqueous solution is given. To this end we calculate the absorption of electromagnetic waves by an ensemble of linear harmonic chains modelling DNA molecules in solution. The absorption depends crucially on the boundary conditions for the DNA molecules. To obtain proper boundary conditions the solvent is considered as a non‐Newtonian fluid of the second order in this frequency range. Calculated values of the resonant absorption coefficient are in agreement with recently found experimental dat

ISSN:0025-116X    

DOI:10.1002/macp.1991.021921001

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractIn order to elucidate some of the parameters controlling the transfer of compressed monomolecular layers of preformed poly(octadecyl methacrylate)s (PODMA) onto substrates by the so‐called Langmuir‐Blodgett technique, an investigation was undertaken of PODMA's of different tacticity and different molecular weights. For the preparation of multilayered structures it was necessary to decrease the interaction between the side chains. This could be accomplished by introducing side chain inhomogeneities especially in the form of comonomers with shorter alkyl side chains. The transferability of a monolayer could be correlated with features in the pressure‐area diagrams, as there is a liquid‐analogous state formed when shorter alkyl chains are introduced; moreover a partial “melting” with lowering of the collaps pressure of the layer is seen. It appeared that with isotactic PODMA regular Y‐type transferY‐Type transfer: During one dipping and withdrawing cycle, two layers are transferred. Z‐Type transfer: Only during withdrawing one layer is transferred.took place, whereas with the atactic polymers at the beginning a Z‐type transfer occurred, gradually changing into a Y‐type transfer. Applying the concept of decreasing interaction of the side chains it was possible to prepare multilayers of isotacti

ISSN:0025-116X    

DOI:10.1002/macp.1991.021921002

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractLangmuir‐Blodgett (LB) mono‐ and multilayers of preformed atactic and isotactic poly(octadecyl methacrylate)s were studied on gold surfaces and silicon wafers. The average orientation of the carbonyl bond of the ester group was found to be about 50° with respect to the normal to the substrate, and the side chains were concluded to be oriented perpendicular to the substrate. Furthermore, the degree of side chain orientation increased on going from a single monolayer to a multilayer. This is explained by an interdigitation of the side chains during or after the transfer process. A peculiar transfer behavior of the atactic samples is discussed in terms of the effect of disorder of the first layer on the transfer process. On heating multilayers of the polymers, melting of the crystalline domains formed by the side chains was observed at temperatures of about 35°C to 40°C. However, the layer structure appeared to be stable up to 100°C. The oriented structure was completely recovered after cooling down to room temp

ISSN:0025-116X    

DOI:10.1002/macp.1991.021921003

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractThe polymerization ofN‐(2,6‐dimethylphenyl)itaconimide(1)with azoisobutyronitrile(2)was studied in tetrahydrofuran (THF) kinetically and spectroscopically with the electron spin resonance (ESR) method. The polymerization rate (Rp) at 50°C is given by the equation:Rp=K[2]0,5·[1]2,1. The overall activation energy of the polymerization was calculated to be 91 kJ/mol. The number‐average molecular weight of poly(1)was in the range of 3500–6500. From an ESR study, the polymerization system was found to involve ESR‐observable propagating polymer radicals of1under the actual polymerization conditions. Using the polymer radical concentration, the rate constants of propagation (kp) and termination (kt) were determined at 50°C.kp(24–27 L · mol−1· s−1) is almost independent of monomer concentration. On the other hand,kt(3,8 · 104–2,0 · 105L · mol−1· s−1) increases with decreasing monomer concentration, which seems mainly responsible for the high dependence ofRpon monomer concentration. Thermogravimetric results showed that thermal degradation of poly(1)occurs rapidly at temperatures higher than 360°C and the residue at 500°C was 12% of the initial polymer. For the copolymerization of1(M1) with styrene (M2) at 50°C in THF the following copolymerization parameters were found;r1= 0

ISSN:0025-116X    

DOI:10.1002/macp.1991.021921004

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractSynthesis and characterization of a series of copolysiloxanes containing crown ether andtrans‐1,3‐dioxane based mesogens are presented. The phase behaviour of the copolymers was studied using differential scanning calorimetry and optical polarizing microscopy and compared with the phase behaviour of the corresponding copolysiloxane‐containing crown ether and biphenyl‐based mesogens. Two copolysiloxanes containingtrans‐2‐(benzo‐[15]crown‐5)‐5‐(ω‐alkan‐1‐yloxy)‐1,3‐dioxane side groups present no liquid‐crystalline behaviour. The other four copolysiloxanes exhibit a nematic mesophase and undergo side‐chain crystallization at low temperature. Two of the four copolysiloxanes which contain atrans‐1,3‐dioxane‐2,5‐diyl group in the mesogenic unit present lower isotropization temperatures and narrower mesophase ranges than the other two. This result reveals that replacing a phenyl ring in the mesogenic unit of a liquid‐crystalline polymer by atrans‐1,3‐dioxane ring will decrease the thermal stab

ISSN:0025-116X    

DOI:10.1002/macp.1991.021921005

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractNeedle‐like crystals (whiskers) of poly(4‐hydroxybenzoate) were prepared by thermal condensation of 4‐acetoxybenzoic acid in Marlotherm‐S® at 300, 350 and 400°C. In addition to the temperature, also reaction time and concentration were varied. Wide‐angle X‐ray scattering powder patterns show that the “300°C whiskers” contain nearly equimolar fractions of orthorhombic modifications I and II, “350°C whiskers” and “400°C whiskers” only consist of modification I. Differential scanning calorimetry measurements revealed a phase transition at 325, 346 and 359°C for the “300°C”, “350°C” and “400°C whiskers”, respectively. Electron microscopy shows that with increasing conversion the thickness of the whiskers passes through a maximum. The previously proposed whisker growth model along a central screw was not confirme

ISSN:0025-116X    

DOI:10.1002/macp.1991.021921006

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractThe oligomers formed in the beginning of the emulsion polymerization of vinyl acetate were characterized by surface tension measurements, analysis of molecular weight distribution and light scattering. The results indicate that primary particle formation in the emulsion polymerization of vinyl acetate is due to an oligomeric micellization. Additionally, these oligomers are strongly adsorbed onto highly dispersed silica particles in the aqueous phase. This effect leads to a disaggregation of the filler particles during the beginning of the emulsion polymerization.

ISSN:0025-116X    

DOI:10.1002/macp.1991.021921007

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractPolystyrene‐block‐poly(p‐phenylene) block copolymers were prepared from polystyrene‐block‐poly(1,3‐cyclohexadiene) (PS‐PCHD) precursors. The PS‐PCHD copolymers were initiated bysec‐butyllithium in benzene. The aromatization of poly(1,3‐cyclohexadiene) sequences was carried out by dehydrogenation with substituted quinones. Secondary reactions occur during this reaction leading to defects in the poly(p‐phenylene) (PPP) sequences which limit the mean length of conjugated blocks at about 11–12 phenylene units. The defects result from the addition of hydroquinone ether groups to the chain. The influence of experimental conditions (nature of quinone, additives, temperature) on the aromatization yield and defect content is studied. The reaction withp‐chloranilSystem. name: tetrachloro‐p‐benzoquinone.at 130°C gives the best results. The formation of aggregates during this reaction is observed and explains the final slow kinetics. The purified copolymers are partly aggregated into micelles with a PPP core. For a given polystyrene sequence the fraction of aggregated chains and the size of PPP core increases with the length of PPP sequences. Improvements of PPP blocks are expected by a better cont

ISSN:0025-116X    

DOI:10.1002/macp.1991.021921008

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractPermeation and separation characteristics for aqueous alcoholic solutions through a modified silicone rubber membrane containing poly(propylene glycol) in the polymer chain were studied by both pervaporation and evapomeation. Both the permeation rates in pervaporation and evapomeation increase, and the selectivity for ethanol in pervaporation does not change but that in evapomeation increases with an increase in the permeation temperature. When the temperature in the membrane surroundings was kept constant and the temperature of the aqueous ethanol solution was varied, or vice versa, it was found that the permeation rate and the permselectivity for ethanol are significantly influenced by the temperature in each permeation condition. The selectivity for alcohols through the modified silicone rubber membrane in the evapomeation method with control of the temperature difference decreases in the order methanol>ethanol>1‐propano

ISSN:0025-116X    

DOI:10.1002/macp.1991.021921009

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractLithium‐ 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 constantskR+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

ISSN:0025-116X    

DOI:10.1002/macp.1991.021921010

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY