摘要:

AbstractDextrans with mass‐average molar masses 8.104g/mol ⩽M̄w⩽ 108g/mol have been studied in water by means of static and dynamic light scattering at different temperatures. Static light scattering (SLS) yields the z‐average mean‐square radius of gyration, 〈S2〉zand the second virial coefficientA2. It is found that the dependences of 〈S2〉 z1/3andA2on the mass‐average molar mass,M̄w, can be well described by the power laws 〈S2〉 z1/3=KS·M̄ w svandA2=KA·M̄ w Av. The exponentvsis independent of the temperatureT, whilevAdecreases asTis raised. Dynamic light scattering (DLS) yields the apparent diffusion coefficient,Dapp(q,c), and the hydrodynamic radius,Rh, whereqis the wave vector andcthe polymer concentration. For smallq, a plot ofDapp(q, c) versusq2· 〈S2〉zgives a straight line. The intercept$ D_{\rm z} (c) = \mathop {\lim }\limits_{q \to 0} D_{{\rm app}} (q,c) $represents the centre‐of‐mass translational diffusion coefficient. Its dependence on the concentration,c, can be well simulated by the relation\documentclass{article}\pagestyle{empty}\begin{document}$ D_{\rm z} (c) = D_{{\rm z,}0} \left[ {1 + k_{{\rm D},2} \cdot c} \right] $\end{document}. HerekD, 2is the second hydrodynamic virial coefficient andDz,0the z‐average of the translational diffusion coefficient at infinite dilution. The analysis of thekD,2‐data shows that dextran molecules behave rather as interpenetrable than as non‐interpenetrable spheres. The densityp= (3M̄w)/(NA· 4 πR h3) proves to be a measure for the degree of penetration;pdecreases with increasingM̄w, ind

ISSN:0025-116X    

DOI:10.1002/macp.1993.021941101

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractThe synthesis of 2‐perfluorohexylethyl α‐acetoxyacrylate (b) H2CC(OAc)CO2C2H4C6F13(1) was performed in two steps starting from pyruvic acid and 2‐perfluorohexylethanol (3,3,4,4,5,5,6,6,7,7,8,8,8‐tridecafluoro‐1‐octanol) with an overall yield of about 50%. Esterification of pyruvic acid with the adequate fluorinated alcohol was followed by enol acetylation to give monomer1. Homopolymerization and copolymerization of1are easily carried out. From the kinetic study of the homopolymerization and copolymerization of1with styrene, the numerical values of the ratio square of the rate constant of propagation over the rate constant of terminationk P2/ktand of the copolymerization reactivity ratiosr1andr2of the two monomers

ISSN:0025-116X    

DOI:10.1002/macp.1993.021941102

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractA conductometric method is developed for the study of the ternary solutions in tetrahydrofuran of bis(polystyryl)magnesium (PStMgPSt) containing various proportionsrof magnesium bromide. The concentration of bis(polystyryl)magnesium varies from 10−4to 2.10−3mol.dm−3, the ratiorfrom O to 17,4 and the temperature from +20°C down to −60°C. The addition of MgBr2provokes the replacement of the ion pairs PStMgPSt by PStMgBr, the dismutation constant being at 20°CKdism= 42 ± 2 with a molar enthalpy of − 5 ± 2 kJ.mol−1. The dismutation is chiefly ruled by a conjugated steric effect that lowers the stability of PStMgPSt. In this concentration range, aggregation of styryl ion pairs is negligible. Moreover for a givenrthe degree of dissociation of the polymer is independent of its concentration. This is due to the complete predominance in this concentration range of the triple anions Mg(PSt) 3−, MgBr(PSt) 3−and MgBr2PSt−, approximately in the proportions of the ion pairsfpp,fbpandfbbas calculated from the dismutation constant. The triple anions MgBr 3−are still completely negligible, as are also the triple cations. The single cations MgPSt+and MgBr+are approximately in the proportionfpp.Kdism/fbp, the latter are ones

ISSN:0025-116X    

DOI:10.1002/macp.1993.021941103

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractPoly(N‐tert‐butylaziridine) (poly(TBA)) with hydroxy, amino, HOC(O)CHCHC(O)and P(O)(OCH3)2end‐groups were synthesized via termination reactions of living poly(TBA) with appropriate nucleophiles. 2‐Aminoethanol, sodium 2‐aminoethylate, maleic anhydride and dimethyl phosphonate were used. The functionally terminated oligomers were of uniform size and with a

ISSN:0025-116X    

DOI:10.1002/macp.1993.021941104

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractLangmuir‐Blodgett films from a polymer with triphenylene moieties in the side groups deposited on a quartz substratum with aluminium and gold electrodes show a dark conductivity in the plane of the Langmuir‐Blodgett film. This dark conductivity is increased using gold electrodes as compared with aluminium electrodes. It depends in a superlinear way upon the applied electric field and is not enhanced by oxygen. The dark conductivity can be enhanced by doping the Langmuir‐Blodgett films with iodine but it is not influenced by doping the Langmuir‐Blodgett films with 2,4,7‐trinitro‐9‐fluorenone. Upon excitation in the absorption band of the triphenylene moiety an in‐plane photocurrent, which is enhanced by oxygen, could be observed. Also the photocurrent is enhanced by using gold electrodes. Doping the Langmuir‐Blodgett films with iodine or 2,4,7‐trinitro‐9‐fluorenone quenches the photocurrent. Up to 10 W/m2the photocurrent depends linearly upon the intensit

ISSN:0025-116X    

DOI:10.1002/macp.1993.021941105

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractThe synthesis of novel telechelic monodispersed diols produced from the radical monoaddition of an excess of 10‐undecenol with novel α, ω‐dithiols, initiated by peroxides, is presented. The telechelic dithiols employed were prepared from nonconjugated dienes and a commercially available dithiol, or by esterification of adipic acid with 2‐mercaptoethanol. From these dithiols, the diols were selectively obtained in high yields. Such α, ω‐dihydroxylated compounds were characterized by both1H and13C NMR spectroscopy. The diol which exhibits the ester functions shows excellent solubility in common organic solvents contrarily to the other ones. The physical properties (Tg,Tmand decomposition temperatures) of these diols were compared and it is noted that the thermostability of these monodispersed telechelic diols is much better than those of the polydispersed commercially available ones such as poly(ethylene glycol)s or poly(tetramethyle

ISSN:0025-116X    

DOI:10.1002/macp.1993.021941106

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractThe rate of polymerization was described as a function of the monomer concentration of 36 monomer/solvent systems in terms of the reactant‐solvent complex (RSC) model. One‐, two‐and three‐parameter optimization procedures were used to fit the rate function to experimental data. Fitting increments were the complex equilibrium constantKand the relative monomer reactivity parameterr11. Irrespective of the optimization procedure,Kandr11, were found to correlate with the monomer exponentnand to beK= 0 andr11, = 1 atn= 1. In these cases the RSC model reduces to the classical rate model. Despite the weak character of the monomer (radical)/solvent complexation, this interaction should not be neglected in rate modelling. The RSC model is a convenient tool to describe the chain propagation sep

ISSN:0025-116X    

DOI:10.1002/macp.1993.021941107

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractA theoretical approach to network formation by cyclotrimerization is presented which allows a full description of all network characteristics. Its application to trimerization of bisphenol‐A dicyanateSystematic IUPAC name: 4,4′‐isopropylidenebis(1,4‐phenylene) dicyanate.shows full agreement between theoretical predictions and experimental data. Cyanate analysis was accomplished by means of Fourier transform infrared spectroscopy and a photometric method. The experimental gel point (at conversion 50,4%) was in close agreement with theoretical pred

ISSN:0025-116X    

DOI:10.1002/macp.1993.021941108

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractIn this paper the mechanism of the thermo‐and photo‐oxidation ofcatena‐poly[bis(4‐benzylphenoxy)‐λ5‐phosphazene] films at short and long wavelengths has been followed under accelerated conditions using FTIR and UV‐visible spectroscopic techniques. The decrease of the band at 1453 cm−1and the simultaneous appearance of new bands at 3400 and 3481 cm−1, due to free and bonded hydroperoxides, show that the primary hydroperoxidation in this polymer occurs at CH2 groups belonging to benzylic moietics. According to our previous paper, the bands observed in the carbonyl region at 1657, 1704 and 1725 cm−1during photo‐oxidation have been assigned to the formation of benzophenone, benzaldehyde and benzoic acids (dimmers), respectively. The formation rate of benzophenone groups increases during irradiation at long wavelengths (λ>400 nm). Under thermo‐oxidative condition (90°C), the benzophenone groups are the main oxidation products derived from hydroperoxide decomposition. In addition, the photooxidation of a film pre‐thermo‐oxidized for 500 h shows clearly that the benzophenone groups can generate aldehydes, benzoic acids and peracids. Crosslinking takes place in high yields by hydrogen abstraction occurring at both benzylic and secondary alcohol units. The regeneration of benzophenone groups has been ev

ISSN:0025-116X    

DOI:10.1002/macp.1993.021941109

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractNovel polyimides containing 2,7‐diphenoxynaphthalene moieties were prepared from 4,4′‐(2,7‐naphthylenedioxy)dianiline (DAPON) and various aromatic tetracarboxylic dianhydrides via a two‐stage procedure that includes ring‐opening polyaddition in a polar solvent such asN,N‐dimethylacetamide to give poly(amic acid)s, followed by cyclodehydration to polyimides. The poly(amic acid)s exhibit inherent viscosities between 0,63 and 1,94 dL/g depending on the tetracarboxylic dianhydrides used. Except for the polyimide4d, obtained from 3,4 : 3′,4′‐benzophenonetetracarboxylic dianhydride (2d), all polymides from yellow, flexible, and tough films upon casting from the poly(amic acid) solutions. Polyimide4ederived from 4,4′‐sulfonyldiphthalic anhydride (2e) exhibits better solubility than the other polymides. The polyimides synthesized from and2dare semicrystalline polymers, whereas the other polyimides are amorphous due to their X‐ray diffractograms. Tensile strength and elongation of the DAPON‐based polyimide films from 86–107 MPa and 6–25% respectively. These polyimides have glass transition temperature223and285°C. Thermal analyses indicated that these polymers are fairly stable, and the 10% weight loss temperatures were recorded in the ranges 568–581

ISSN:0025-116X    

DOI:10.1002/macp.1993.021941110

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY