bluuebunny/crossref_metadata_2025 huggingface dataset:
Helical poly(L‐alanine) in trifluoroacetic acid
Authors: Kricheldorf Hans R.
Published: April 2003

In contrast to previous reports of other authors different 1H NMR chemical shifts were found for poly(L‐alanine) and poly(D,L‐alanine) in pure trifluoroacetic acid. The 13C and 15N NMR signals of poly(L‐alanine) are likewise different from those of poly(D,L‐alanine), and they are also different from the signals of the L‐alanine blocks in random copolypeptides such as (Ala/Gly)n, (Ala/Leu)n, (Ala/Val)n, and (Ala/Phe)n. It is concluded that poly(L‐alanine) is helical in trifluoroacetic acid (TFA); however, the optical purity, and thus, the helix stability is dependent on the reaction conditions used for the polymerization of L‐alanine‐NCA. The base initiated polymerization of L‐alanine‐NCA can cause substantial racemization in contrast to the primary amine‐initiated NCA polymerization. Sulfonic acids were found to be better solvents for polypeptides than trifluoroacetic acid, and their addition to TFA solutions of L‐alanine containing polypeptides exerts a strong influence on the chemical shifts and on the optical rotation. However, no clear experimental evidence was found for the helix‐coil transition of poly(L‐alanine) in TFA/sulfonic acid.
Oligomer‐oligomer incompatibility, 2. Oligo(dimethylsiloxane)/oligo(propylene glycol)
Authors: Wolf B. A. , Blaum G.
Published: April 2003

The demixing behavior of 20 representatives of the system oligo(dimethylsiloxane)/oligo(propylene glycol) (ODMS/OPG)

The prefix “oligo” has been chosen for all products, since the addition or removal of a few monomeric units changes the physical properties considerably (cf. Tab. I), even in the case of the highest molecular weight sample.

is investigated at pressures up to 1 500 bar. The degrees of oligomerization range from 2 to 5 for the first and from 1 to 57, 6 for the second component. The experimental results are compared with those for the previously studied system oligoisobutene/oligo(propylene glycol) (OIB/OPG). In both cases the observed upper critical temperatures Tc increase with the number of monomeric units of the less polar component, whereas they run through a minimum when the number of monomeric units of the glycol is raised. For the present system the Tc values are found to be considerably higher than that of OIB/OPG and the optimum compatibility can normally be observed already between 1 and 7 propylene glycol units as against 50 in the case of OIB/OPG. In the low pressure region Tc of ODMS/OPG is decreased by pressure for all representatives of this system, while enhanced incompatibility has been found with OIB/OPG. For ODMS/OPG the special features of the critical lines are determined by the chain length of OPG, for OIB/OPG by that of OIB. For ODMS/OPG the initial reduction of Tc by pressure is most pronounced with the highest molecular weight oligo(propylene glycol), for which it amounts up to 0,3 K/bar; with increasing pressure and decreasing chain length the effects become smaller. For the lowest molecular weight sample of OPG the critical lines show a vertex at 700–1000 bar. In any case the two systems under consideration behave in an increasingly similar manner as the pressure is raised. The theoretical evaluation and discussion of the above results is performed by analogy with that of the first paper in this series.
Mechanismus der photopolymerisation des styrols, 4. Zur rolle der photo‐(4π + 2π)‐addukte als kettenüberträger und zur kinetik der photopolymerisation in gegenwart überlagerter, thermischer prozesse
Authors: Kauffmann Harald Friedrich
Published: April 2003

The photopolymerization of styrene was investigated at 25°C, by following the variations in the rate of polymerization and the degree of polymerization with the light intensity, JM, at different wavelengths of the exciting light (λe = 313 nm, λe = 335 nm). The corresponding data were analyzed in terms of the formalism between the rate RP and the viscosity average degree of polymerization Pη. The kinetic evaluation shows that at least at small fractions of the absorbed light and at short duration of the irradiation the stabilization of the growing chain radicals will occur predominantly by bimolecular termination processes and not by chain transfer. This must be attributed to the fact that among the four theoretically possible isomeric photo‐(4π + 2π)‐intermediates (I) 1‐phenyl‐1,2,3,8a‐tetrahydronaphthalene (diastereomers 1a and 1b) and 2‐phenyl‐1,2,3,8a‐tetrahydronaphthalene (diastereomers 1′a and 1′b) the photostationary concentration [1a]∞ of the most reactive chain transfer agent 1a is—as a result of its very small quantum yield of formation (φ1a ≪ φ1b + φ1′a + φ1′b)—extremely low and contributes only a few percent to the total photo‐steady‐state concentration of I. At higher temperatures (T > 25°C) and at small fractions of the absorbed light JM/Jo (λe = 335 nm), the rate of photopolymerization RP is controlled by the contributions of two independent routes of initiation: (1) the rate R, which accounts for the photo‐free radical formation of the photo‐intermediates I, and 2 the rate R, which is derived from the photoinduced free radical generation of the thermally produced Diels‐Alder adducts 1a and 1b. As a further aspect of this analysis the results give strong evidence that the endo adduct 1a, when electronically excited, enters into a very efficient radical forming process, contrary to the other isomers 1b, 1′b, and 1′a, which seem to be mainly deactivated by their individual retro‐Diels‐Alder decompositions and will not enter into free radical formation to any noticeable extent: φS1a ≫ (φS1b + φS1′b + φS1′a) An explanation of the very different stereodynamic behaviour is given.
Synthesis of aromatic polyamides from reactive N, N′‐isophthaloyldi(thiolactam)s and aromatic diamines under mild conditions
Authors: Ueda Mitsuru , Aoyama Shigeto , Imai Yoshio
Published: April 2003

Solution condensation polymerization of new reactive diamides, N, N′‐isophthaloyldipyrrolidine‐2‐thione (1a) and N, N′‐isophthaloyldiperhydroazepine‐2‐thione (1b), with aromatic diamines 2 in 1‐methyl‐2‐pyrrolidone at room temperature or above leads to polyamides 3 with moderate molecular weights. The ease of aminolysis of these diamides is discussed in relation to the good leaving nature of the thiolactam moieties and an intramolecular general base catalysis. The condensation polymerization is strongly catalyzed by 1‐hydroxybenzotriazole giving aromatic polyamides with higher inherent viscosities up to 0,9 dl.g−1.
Hydroxyl‐modified epoxy resins: Some technical and analytical aspects
Authors: Dobinson B. , Green G. E. , Hinton I. G. , Hope P. , Martin R. J. , Stark B. P. , Waterhouse J. S. , Young E. W.
Published: April 2003

The modification of epoxy resins by reactions involving their hydroxyl groups is described. For example, reactions with enol ethers, acrylonitrile, ethyl acetoacetate and certain other carboxylic esters, or triethyl orthoformate, gave products which had reduced reactivities towards various hardeners, and which therefore gave lower peak temperatures on cure and/or longer usable lives. Suitable modification of epoxy resins with various other reagents(certain acid anhydrides, epichlorohydrin, or N‐hydroxymethylacrylamide) introduces additional useful functional groups. The uses of a diisocyanate and of α‐naphthyl isocyanate to modify epoxy resins or their mixtures prior to GPC analysis are also mentioned.
Versuche zur modifizierung von poly(9,10‐anthrylen)
Authors: Hinterhofer Otto
Published: April 2003

Attempts were made to obtain fusible or soluble derivatives of poly(9,10‐anthrylene) by incorporation of intermediate links in 9‐ and 10‐position, i.e., by preparing a polyester and a polyanhydride of 9,10‐anthracenedicarboxylic acid as well as a polycarbonate of 9,10‐anthrahydroquinone. The results showed that the preparation of the polyester is very difficult and that its thermal resistance is very low (m.p. 140°C, decomposition). The polyanhydride could be obtained in good yields, but it is insoluble and decomposes at the melting point. The polycarbonate could easily be prepared, but it decomposes in a strongly exothermic reaction at 185°C and forms anthraquinone.
Helix‐coil transition in polypeptides having linear alkyl side‐chain and ester group, and some conformational aspects observed by 13C NMR
Authors: Suzuki Yasuyuki , Inoue Yoshio , Chûjô Riichirô
Published: April 2003

13C NMR has been used to study the helix‐coil transition induced in polypeptides by trifluoroacetic acid. An attempt is made to separate the influences of conformational change and direct solvent interaction. For poly(γ‐methyl‐L‐glutamate), interactions between trifluoroacetic acid and the ester group of the side chain occur in the helical region. Poly(L‐norvaline) and poly(L‐norleucine) are in the form of “partially distorted helical conformation”. Conformational change and the interaction between trifluoroacetic acid and the peptide group which accompany the helix‐coil transition, affect the chemical shift difference up to Cδ or Cβ of poly(L‐norvaline) and poly(L‐norleucine), On the contrary, in the case of polyglutamates and polyaspartate, these effects are minor for the carbons in the ester portion. The chemical shift differences of these polypeptides can be well interpreted qualitatively by the results for some butyrates, poly(L‐norvaline), and poly(L‐norleucine).
Induced 13C shifts by coil‐supporting solvents observed in oligopeptides as model compounds of polypeptides
Authors: Suzuki Yasuyuki , Inoue Yoshio , Chûjô Riichirô
Published: April 2003

The origin of the chemical shift differences of carbons in polypeptides which accompany the helix‐coil transition has been investigated by using oligopeptides, benzyloxycarbonyl‐γ‐ethyl‐L‐glutamyl‐diethyl‐L‐glutamate and benzyloxycarbonyl‐di‐(γ‐ethyl‐L‐glutamyl)‐diethyl‐L‐glutamate, as models of the backbone of polypeptides. Structures of aggregates in deuterated chloroform were proposed for these oligopeptides on the basis of concentration dependence and temperature dependence of the chemical shifts of protons and carbons, and spin‐lattice relaxation times. Antiparallel and/or parallel “in‐register” structures for extended forms and “out‐of‐register” network of extended forms are coexisting in deuterated chloroform solution for these oligopeptides. From the shift for the carbons of the oligopeptides induced by organic acids, it was in ferred that down‐field shifts are induced at α and amide carbons in polypeptides by organic acids. By comparing the induced shift of the carbons in the peptides with the chemical shift differences of the carbons in polypeptides which accompany the helix‐coil transitions, it was found that the conformational changes play a predominant role in the origin of the chemical shift differences of the carbons in polypeptides which accompany the helix‐coil transitions, it was found that the conformational changes play a predominnant role in the orgin of the chemical shift differences of amide, α, β, and γ carbons in polypeptides.
The copolymerization of methacrylaldehyde with hydrophilic monomers
Authors: Schauer Jan , Houska Milan , Kálal Jaroslav
Published: April 2003

Copolymers of methacrylaldehyde with hydrophilic monomers — 2‐hydroxyethyl methacrylate, 5‐hydroxy‐3‐oxapentyl methacrylate, 8‐hydroxy‐3,6‐dioxaoctyl methacrylate, N‐ethylmethacrylamide, N,N‐diethylacrylamide, and N,N‐diethylmethacrylamide — were prepared by solution polymerization in N,N‐dimethylformamide initiated with 2,2′‐azodiisobutyronitrile. In the copolymer of methacrylaldehyde (1) with 2‐hydroxyethyl methacrylate (2) (r1 = 0,77, r2 = 0,36) and in the copolymer of methacrylaldehyde with N,N‐diethylacrylamide (r1 = 3,79, r2 = 0,14) the content of CHO groups corresponds to that ot methacrylaldehyde units in the triads comonomer — methacrylaldehyde — comonomer; in the copolymer of methacrylaldehyde with N‐ethylmethacrylamide (r1 = 4,07, r2 = 0,14) both comonomers react with each other and the content of CHO groups is very low, while in the copolymer of methacrylaldehyde with 5‐hydroxy‐3‐oxapentyl methacrylate (r1 = 1,48, r2 = 0,34) the majority of methacrylaldehyde units contain an unreacted CHO group.
Radiation‐induced, solid‐state polymerization of derivatives of methacrylic acid, 10. Polymerizability of barium methacrylate anhydrate
Authors: O'Donnell James H. , Pomery Peter J. , Sothman Robert D.
Published: April 2003

Whereas the radiation‐induced polymerization of crystalline barium methacrylate monohydrate has been well established there have been conflicting reports concerning barium methacrylate anhydrate. We have now shown that the yields of high molecular weight polymer are negligible if adequate precautions are taken to prevent polymerization occurring during the separation of polymer from residual monomer. However, monomer losses of up to 80% have been observed by titration of CC bonds with bromine and confirmed by decreases in the appropriate infrared absorptions. X‐ray diffraction studies showed that the crystalline lattice was largely destroyed during the reaction. ESR spectra indicate that initial trapped radicals are converted into propagating radicals with a different conformation than has been reported for the monohydrate.
15N NMR spectroscopy, 22. Influence of shift reagents and paramagnetic ions on the spectra of peptides and polyamides
Authors: Kricheldorf Hans R. , Hull William E.
Published: April 2003

The influence of Eu(dpm)3 and Dy(fod)3 on the 15N NMR spectra of Z‐Gly‐Leu‐Leu‐OMe or Z‐Ala‐Leu‐Leu‐OMe was investigated; however, solvent effects were found to be more useful than shift reagents to improve the spectroscopic structure analysis of peptides. Furthermore, the influence of manganese and copper ions on the Nuclear Overhauser Effect and on the line width of benzyloxycarbonylglycine, polysarcosine, polyglycine and poly(β‐alanine) was investigated in various solvents. The nature of the solvent was found to have a strong influence on the relaxation efficiency of the paramagnetic ions. Manganese ions can be used to shorten the pulse interval without risk of line broadening, when the measurements are carried out under the conditions of “inverse‐gated‐decoupling”.
Functional monomers and polymers, 62. Synthesis of polypeptides from dipeptide 4‐acyl‐2‐nitrophenyl esters
Authors: Hanabusa Kenji , Kondo Koichi , Takemoto Kiichi
Published: April 2003

A series of active glycylglycine 4‐acyl‐2‐nitrophenyl esters having different chain length of the acyl groups (that is, 4‐acetyl‐, 4‐hexanoyl‐, and 4‐dodecanoyl‐2‐nitrophenyl esters) was prepared, and their polycondensation was studied in various solvents at 30°C. In general, the yield of the polycondensates was high in nonpolar solvents, while the reaction in polar solvents was accompanied by formation of the cyclodimeric product. D,L‐Alanyl‐D,L‐alanine, glycyl‐D,L‐alanine and D,L‐alanylglycine 4‐dodecanoyl‐2‐nitrophenyl esters were also prepared and their polycondensation was tried.
Propriétés viscoélastiques de la poly(α,α‐diéthyl‐β‐propiolactone)
Authors: Noah Joseph , Prud'homme Robert E.
Published: April 2003

The viscoelastic properties of poly(α,α‐diethyl‐β‐propiolactone) were investigated in the linear range using stress relaxation and dynamic mechanical methods. Using Ferry's reduction method, a horizontal shift factor was determined at each temperature, that satisfactorily agreed with the WLF equation in the transition zone. No vertical shift was required to superimpose different relaxation curves. The apparent activation energy was temperature dependent and passed through a maximum near Tg whose value is (311 ± 2)K. The relaxation spectrum has been calculated according to the first method of approximation of Schwarzl and Staverman. It consists of a high intensity plateau at shorter times, a wedge type portion with a slope of −0,15 and a low intensity plateau at longer times. Dynamical mechanical measurements revealed a β relaxation peak at 333 K and yielded the evidence of a γ peak around 120 K.
Molecular size and gel formation in branched poly(methyl methacrylate) copolymers
Authors: Whitney Robert S. , Burchard Walter
Published: April 2003

Branched copolymers of methyl methacrylate with ethylene dimethacrylate or pentaerythritol tetramethacrylate with high weight average molecular weights Mw were prepared by free radical polymerization. The double bond conversion of these polymers (β) was measured dilatometrically and the gel point (βc) was located by extrapolation of bulk viscosity measurements. The polymers were studied by light‐scattering, 1H NMR and viscometry. Hence it was possible to investigate the relationship between the molecular weight Mw and the reduced conversion quantity (1 − β/βc)−1 and also the molecular weight dependence of the z‐average mean square radius of gyration 〈S2〉z. Considerable deviations from the classical Stockmayer theory but also from percolation theory were observed. 1H NMR showed a relative small extent of ring formation (10 to 24%) and a reduced apparent reactivity of the pendant double bonds, while the delay in the gel formation appeared to be caused by a much higher ring formation (80 to 90%). This apparent inconsistency is explained by a size‐dependent ring formation, where the extent of ring formation is increased with the molecular dimensions; simultaneously, the pendant double bonds become progressively less accessible to cross‐linking by growing radicals. The molecular weight dependence of 〈S2〉z is found to be in agreement with this heterogeneous reaction model.
Haupt‐ und seitenkettenkristallinität bei isotaktischen poly(1‐alkylethylen)en, 3. Änderung der ordnungszustände bei den höheren homologen
Authors: Trafara Gundolf
Published: April 2003

The higher homologues for isotactic (it) poly(1‐alkylethylene)s (from it‐poly(1‐dodecylethylene) to it‐poly(1‐eicosylethylene)) show three polymorphic modifications. The modification of highest order crystallizes in an orthorhombic structure (modification I). This modification is formed during melt crystallization at a cooling rate ϕ < 2,5 K·s−1. The main‐chain conformation is a quaternary helix. The side‐chains are tilted 130,6° against the axes of the helices and crystallize like orthorhombic polyethylene. The DSC‐curves of these homologues in modification I show the endotherm of melting and an endotherm at a temperature, about 25 K to 30 K below the melting temperature. The endotherm at the lower temperature is caused by atactic material in the samples, by only partially ordered crystallites in isotactic material, and by the change of conformation of some CH2‐groups of the side‐chains near the main chain.
Nature et consequence des interactions se développant lors de la mise en contact de polyéthylène avec des produits mouillants et non mouillants, 1. cas des produits mouillants apolaires (alcanes) et polaires (alcools)
Authors: Escoubes Marcelle , Berticat Philippe , Chabert Bernard , Soulier Jean‐Pierre
Published: April 2003

The nature of interactions between polyethylene and a wetting solute was analyzed to know if the interface can be characterized by the expression of the sticking work or if other phenomena than adhesion and wetting must be taken into account. In this way, the sorption isotherms, the molar interaction heats and the cinetic characters of the sorption gave informations about the possible importance of a diffusion of the solvent. Two types of systems were investigated: polyethylene/alkanes and polyethylene/alcohols. The formation of almost homogeneous solutions or, on the contrary, of aggregates is discussed.
Polymer‐solvent interactions: Dextrans in water and DMSO
Authors: Basedow Arno Max , Ebert Klaus Heinrich , Feigenbutz Willi
Published: April 2003

Enthalpies of solution, dilution and mixing of several dextran fractions with different molecular weights (MW) and low MW carbohydrates were determined in water and dimethyl sulfoxide at 25°C. The enthalpies of solution of dextran increase in the oligomer range up to a MW of about 1000; for higher MWs the enthalpies of solution are almost constant. The enthalpies of dilution decrease strongly with increasing MW and remain constant for MWs higher than 2 000. The interaction parameter was found to depend on the concentration of the solute in both solvents. From the experimental results it can be concluded that dimethyl sulfoxide is a better solvent for glucose and dextran than water. In dilute solutions glucose interacts considerably more strongly with the solvent than dextran. The conformational properties of dextran are similar in both solvents; for MWs above 2 000 the degree of solvation is found to be independent from the MW.
Solvent effect on the asymmetric induction copolymerization of styrene with maleic anhydride in the presence of lecithin
Authors: Doiuchi Tohru , Minoura Yuji
Published: April 2003

The asymmetric induction radical copolymerization of styrene (St) with maleic anhydride (MAn) was studied in various solvents with different dielectric constants in the presence of lecithin as a chiral surfactant. The observed specific rotation of the resulting alternating copolymer decreased with an increase in the dielectric constant of the solvent used. It was concluded that the asymmetric induction depends mainly upon the incorporation of MAn within the reversed lecithin micelles.
Hypochromism of polyhalogenvinylcarbazoles
Authors: Pielichowski Jan , Obrzut Jan
Published: April 2003

Spectrophotometric studies in the UV region were carried out for a series of chlorine and bromine derivatives of N‐ethylcarbazole and poly(N‐vinylcarbazole). All the examined polymers, in the whole spectral range, exhibit considerably less absorptivity than their low molecular models, i.e. ethylcarbazoles. Absorption bands of the polymers are shifted, in comparison to the respective absorption bands of halogenethylcarbazoles, towards shorter wavelenghts. Halogen substituents in the carbazole ring reduce the transfer energy π → π*. This bathochromic effect is especially observable for low‐energy bands 1La and 1Lb, and it was noticed that the bromine substituent exerts more influence than the chlorine substituent.
Aqueous polymerization of methyl methacrylate using quinoline‐sulfur dioxide complex and tetrahydrofuran‐sulfur dioxide complex as initiators
Authors: Ghosh Premamoy , Chakraborty Soumen , Biswas Samir
Published: April 2003

Aqueous polymerization of MMA was kinetically studied using separately two complexes of sulfur dioxide as initiators, namely, quinoline‐sulfur dioxide (Q‐SO2) complex and tetrahydrofuran‐sulfur dioxide (THF‐SO2) complex. In each case the initiator exponent was 0,5 and the monomer exponent was 1,5. Kinetic data, inhibitory effect of hydroquinone, and incorporation of sulfoxy end groups in the polymers indicate a radical mechanism of polymerization with first order dependence on monomer for the rate of initiation while termination appears to take place bimolecularly.
Nuclear magnetic resonance studies on polymer carbanions, 1. Living polystyrene and its model compounds
Authors: Matsuzaki Kei , Shinohara Yoshinao , Kanai Taiichi
Published: April 2003

1H and 13C NMR investigations were carried out on polystyryl carbanions and model compounds for the active chain end of living polystyrene, changing counter cation (Li, K, and Cs), solvent, and temperature. The structure of the model compounds with K and Cs as counter cation was planar with sp2‐hybridized α‐carbon, which indicates strongly hindered rotation of the phenyl ring. For the model compound with lithium as counter cation, the phenyl ring rotation was hindered at lower temperatures. The 13C1H coupling constants of the compound indicated less sp2 character of α‐carbon. The differences in the chemical shifts of the two ortho or meta carbons depended on the type of counter cation, suggesting an interaction between counter cation and phenyl ring. Quantum chemical calculations on the structure of the model compounds were carried out and the results were compared with the excess charge distributions calculated from 13C NMR chemical shifts.
15N NMR spectroscopy, 25. Terpolymerization of glycine‐NCA, leucine‐NCA, and valine‐NCA
Authors: Hull William E. , Kricheldorf Hans R.
Published: April 2003

The copolymerization of Leu‐NCA and Val‐NAC was achieved in solution by initiation with benzylamine, diethylamine, triethylamine, pyridine or by simple heating of the pure monomers to 120°C. Under similar conditions the terpolymerization of Gly‐NCA, Leu‐NCA and Val‐NCA was carried out. 400 MHz 1H NMR spectra and natural abundance 36,48 MHz 15N NMR spectra of the resulting copolypeptides were measured in trifluoroacetic acid. The various kinds of peptide groups of these copolypeptides show individual 15N NMR signals because of strong neighboring residue effects. The quantitative evaluation of NMR spectra allows one to calculate the average length of the homogeneous blocks and the copolymerization parameters. The terpolymerization of Gly‐NCA, Leu‐NCA and Val‐NCA was found to behave like a superposition of the corresponding binary copolymerizations. The primary amine‐initiated terpolymerization of Gly‐NCA, Val‐NCA and γ‐methyl Glu‐NCA, was also investigated.
Haloaldehyde polymers, 15. Stabilization of polychloral by posttreatment
Authors: Corley L. Steven , Vogl Otto
Published: April 2003

Polychloral prepared by anionic polymerization has primarily alkoxide endgroups as the living terminal ends. The initial endgroups depend on the type of nucleophile used for the initiation. Alkoxide‐terminated polychloral degrades to monomer on heating to slightly above 100°C or on extraction with methanol or acetone. Programmed DTG shows a degradation rate maximum (MDT) near 150°C. Terminations of the polymer endgroups were observed when the polymer was allowed to stand for long periods of time before workup. The type and amount of stabilization depends on the cation and residual monomer. With HCI the alkoxide ends can be protonated to give hydroxyl terminated polychloral, which is stable to extraction and has an MDT of 220°C. Acylation or alkylation as posttreatments could not be shown to produce the expected acyl‐ or alkyl endcapped polychloral, but posttreatment with acetyl chloride produced partially stable polymer (one MDT higher than 300°C) without detectable acetyl endgroups. The most effective posttreatment is with PCl5/CCl4 which gives highly stabilized polychloral with an MDT near 350°C. The treatment was only effective in thin sections of polymer and appeared to have introduced a chlorine endgroup.
Thermal degradation of polyurethanes investigated by direct pyrolysis in the mass spectrometer
Authors: Ballistreri Alberto , Foti Salvatore , Maravigna Pietro , Montaudo Giorgio , Scamporrino Emilio
Published: April 2003

Direct pyrolysis in the mass spectrometer yielded evidence on the mechanisms of thermal decomposition of N‐monosubstituted and N‐disubstituted polyurethanes. Our results indicate that N‐monosubstituted polyurethanes undergo quantitatively a depolycondensation process, producing diisocyanate and diol. In contrast, disubstituted polyurethanes decompose to give selectively secondary amine, olefine and CO2.
Biomimetic approach to the design of a pyridoxal enzyme model, 1. Hydrophilic polyacrylamide gel with stereochemically defined arrangement of salicylaldehyde and lysine fragments
Authors: Belokon' Yuri N. , Tararov Vitali I. , Savel'eva Tatiana F. , Belikov Vasili M.
Published: April 2003

A polymeric gel in which salicylaldehyde and lysine moieties are capable of forming an “internal” aldimine at pH > 6,0 has been prepared by copolymerization of Nα‐5‐methacryloylaminosalicylidene‐Nε‐methacryloyl‐(S)‐lysinatocopper (II) (1a) with acrylamide and N,N'‐methylenebisacrylamide in water with subsequent removal of the copper ions by 0,1 M HCl or the disodium salt of EDTA. The equilibrium formation constants of the “internal” aldimine are ca. 30 times (at pH 7,1) and ca. 100 times (at pH 9,2) higher than the equilibrium constants of the model reaction of Schiff base formation from 5‐isobutyrylaminosalicylaldehyde (2) and Nt‐isobutyryl‐(S)‐lysine (3). The α‐amino group of the lysine residue in the gel acts as a nucleophilic catalyst in the reaction of the salicylaldehyde moiety of the gel with semicarbazide. The reaction proceeds 5,3 times faster in the gel than in a model polymeric system which does not contain lysine moieties.
Synthesis and physico‐chemical properties of poly[4‐(1,1,3,3‐tetramethylbutyl)phenyl methacrylate]
Authors: Ojeda Tomas , Radic Deodato , Gargallo Ligia , Boys Daphne
Published: April 2003

Poly[4‐(1,1,3,3‐tetramethylbutyl)phenyl methacrylate] (1a) was synthesized and its physicochemical properties were determined in the condensed phase and in dilute solution. The polymerization of 4‐(1,1,3,3‐tetramethylbutyl)phenyl methacrylate was carried out by radical mechanism in solution with 2,2′‐azoisobutyronitrile as initiator. Several samples were characterized by their intrinsic viscosity, by osmometric measurements, differential scanning calorimetry, and X‐ray diffraction. The viscometric behaviour of fractions of 1a was studied in good solvents and theta solvents, and the conformational parameters were calculated. Polymer 1a presents an unusual high rigidity in the chain. X‐Ray diffraction of this polymer indicates a one‐dimensional ordering of a mesomorphic type.
Haloaldehyde polymers, 18. Rate of copolymerization of chloral with isocyanates
Authors: Kubisa P. , Teshirogi T. , Hatada K. , Corley L. S. , Vogl O.
Published: April 2003

Cryotachensic copolymerization of chloral with various aliphatic and aromatic isocyanates, initiated by lithium tert‐butoxide and triphenylphosphine at 0°C, was followed by 1H NMR spectroscopy. Information on the mobility of comonomers and solvent molecules in the polymerization mixture was obtained by measuring the line width of the signals. Relative rates of incorporation of chloral and isocyanates into the copolymer were determined, indicating that the copolymer was not uniform in structure and that the content of isocyanate units increased significantly in the final stages of copolymerization.
Redox polymerisation, 6. Kinetics of the polymerisation of acrylonitrile initiated by the systems glycerol‐Mn(III) and allyl alcohol‐Mn(III) in aqueous sulfuric acid
Authors: Jayakrishnan Athipettah , Mahadevan Venkatanarayana
Published: April 2003

Polymerisation of acrylonitrile initiated by the redox systems glycerol‐Mn(III) and allyl alcohol‐Mn(III) is investigated in the temperature range 25–45°C in aqueous sulfuric acid/acetic acid and aqueous sulfuric acid, respectively. Oxidation of both glycerol and allyl alcohol proceeds through an intermediate complex. Decomposition of the complex is reversible with glycerol, whereas with allyl alcohol it is irreversible. Addition of Mn(II) retards both oxidation and polymerisation in the former system, while with the latter oxidation in the absence of monomer is unaffected, although polymerisation rates are retarded. Mutual termination predominates with the system glycerol‐Mn(III), whereas primary radical termination accounts for the kinetics of polymerisation with the system Mn(III)‐allyl alcohol. Rate and equilibrium parameters are evaluated and their significance is discussed.
Lineare polybenzyle, 6. Polymerisation von α‐methylbenzylchlorid
Authors: Skura Josef , Lenz Robert W.
Published: April 2003

α‐Methylbenzylchloride (1) was polymerized in ethyl chloride and in 1‐nitropropane at various temperatures with AlCl3 as catalyst, mainly at −115 and at 0°C. The polymers obtained were crystalline or amorphous, depending on the reaction conditions. The reactions were complete within seconds. The tacticity of the polymers was determined by 1H and 13C NMR‐spectroscopy. Polymers prepared at low temperatures in ethyl chloride showed isotactic sequences; in 1‐nitropropane at 0°C atactic configuration. A reaction mechanism for the formation of the isotactic polymer is proposed on the basis of GPC‐data. DSC‐data are reported and discussed.
Aromatic spiro polymers
Authors: Niume Kazuma , Kurosawa Shigeru , Toda Fujio , Uno Keikichi , Iwakura Yoshio
Published: April 2003

Aromatic spiro polymers, polyoxoindoline‐spiro‐benzimidazolines 9a–c, were prepared by the solution polycondensation reaction of biisatyls with aromatic tetramines in polar organic solvents. The spiro polymers were found to exhibit good solubility in polar organic solvents, such as N,N‐dimethylacetamide and hexamethylphosphoramide, in contrast to the insolubility of the corresponding polyindoloquinoxalines in these solvents. The improvement of the solubility was discussed mainly in terms of the hydrogen bonding and packing in polymer molecules. The spiro polymers slowly rearranged at high temperatures to give polyindoloquinoxalines with high thermal stability.
Synthesis and photochemical behavior of polynuclear dithiolato‐metal‐dye complexes
Authors: Kaneko Masao , Yamada Akira
Published: April 2003

Polynuclear dithiolato‐metal‐dye complexes were prepared and their photochemical behaviors were studied. The dimercapto ligands used were maleonitriledithiol (MNT) and toluene‐3,4‐dithiol (TDT); metal ions were copper, manganese and nickel; and dyes were thionine (TH), tolusafranine (SAF) and methylene blue (MB). From IR spectra, elemental analyses and magnetic measurements they were found to be polynuclear complexes having bis(dithiolato)‐metal structure incorporating the dyes as cations. The complexes showed almost the same visible spectra as the free dyes. The molar absorption coefficients of the maximum absorption were in most cases larger than in the free dye. The dithiolato‐metal complex affected remarkably the photochemical reactivity of the dye incorporated in it. The rates of the photochemical reduction of the TH complexes (Cu‐MNT‐TH, Mn‐MNT‐TH and Cu‐TDT‐TH) in hexamethylphosphortriamide were higher than the free TH, while those of the SAF complexes (Cu‐MNT‐SAF and Mn‐MNT‐SAF) and MB complexes (Cu‐MNT‐MB and Ni‐MNT‐MB) were much lower than the free SAF and MB, respectively.
Immobilisierung von polymergebundenen oligodesoxyribocytidylsäuren an DEAE‐cellulose
Authors: Schott Herbert , Watzlawick Hildegard
Published: April 2003

N‐Anisoyl‐deoxyribocytidine‐5′‐phosphate is chemically polycondensed. From the polycondensate, oligomers containing four or more monomeric units are isolated chromatographically and subsequently linked to a soluble polyvinylalcohol. After cleavage of the nucleobaseprotecting groups, the unreacted oligodesoxyribocytidylic acids are separated from polyvinylalcohol bound oligomers through ultrafiltration. DEAE‐Cellulose is subsequently coated with this polymer‐bound oligodeoxyribocytidylic acids. The now obtained PVAL‐p(dC)n‐DEAE‐Cellulose acts as a specific sorbent in template‐chromatography.
Kuhn‐Mark‐Houwink‐Sakurada‐Beziehung für poly(ϵ‐caprolactam)
Authors: Müller Herbert , Neuray Dieter , Horbach Alfred
Published: April 2003

The Kuhn‐Mark‐Houwink‐Sakurada relationship for poly(ϵ‐caprolactam), (polyamide 6), is established, based on the absolute determination of the weight‐average molecular weight by light scattering. It is obtained ([η] in cm3.g−1):

The unperturbed dimensions of this polymer in both solvents are also determined by using the Stockmayer‐Fixman method.
The use of graft copolymers as enzyme supports, 3. The Immobilization of proteins and enzymes on poly(fluorostyrene) and poly(nitrofluorostyrene) — nylon graft copolymers
Authors: Abdel‐Hay Fouad , Beddows Clifford G. , Guthrie James T.
Published: April 2003

The radiation induced, graft copolymerization of m‐ and p‐fluorostyrene onto nylon was successfully achieved. Grafting was followed by nitration of the fluorostyrene groups in the copolymer to provide substrates which were active to the coupling of various enzymes and proteins. Bovine serum albumin, ovalbumin, pepsin, β‐galactosidase, and alkaline phosphatase proteins all coupled very efficiently but the activities of the coupled enzymes were relatively low.
Structural Study on styrene/ε‐caprolactone block copolymers in absence and in presence of a solvent of the polystyrene block
Authors: Herman Jean‐Jacques , Jérome Robert , Teyssié Philippe , Gervais Monique , Gallot Bernard
Published: April 2003

The lamellar crystalline structure of styrene/ε‐caprolactone block copolymers (SCL) of different compositions and molecular weights is studied by X‐ray diffraction and differential scanning calorimetry. The studies were performed in the absence and in the presence of diethyl phthalate, a preferential solvent of the amorphous polystyrene block. The influence of the molecular characteristics of the copolymer and of the solvent concentration on the parameters of the lamellar structure and especially on the number of folds and on the crystallinity of the crystallizable poly(ε‐caprolactone), (PCL), chains is established. It is shown that copolymers SCL can be divided in three categories depending upon their composition.
Copolymères du chlorure de vinylidène avec l'acrylonitrile, le chlorure de vinyle et le méthacrylate de méthyle, 2. Fusion — utilisation d'un modèle de simulation
Authors: Dumont Bernard , Berticat Philippe , Guillot Jean
Published: April 2003

The melting point depression in vinylidene chloride copolymers, when introducing an increasing number of units B = vinyl chloride, acrylonitrile or methyl methacrylate is studied in this paper. A Monte‐Carlo simulation model of chains growing and crystallization is applied and allows to know the proportion Xc of defects in the crystalline phase. An equation given by Sanchez is then applied, and the excess energy ε of the defect created by the incorporation of a B unit in the crystalline vinylidene chloride lattice is calculated.
Étude de l'état solide des copolymères du chlorure de vinylidène avec le chlorure de vinyle, l'acrylonitrile et le méthacrylate de méthyle, 1. Structure des copolymères, modélisation mathématique en relation avec la structure chimique des chaînes
Authors: Douillard Alain , Dumont Bernard , Guillot Jean
Published: April 2003

The properties of a random copolymer are not only determined by composition, but also by the repartition of the monomeric units along the chain. In order to explain the properties of such a copolymer it is necessary to know the sequence distribution or microstructure, each sequence by itself showing structural characteristics: length, relative position, etc. It is thus necessary to conduct a precise synthesis process, and to know the kinetic parameters of the polymerization reaction. Knowledge of the kinetic invariants and monomer feed composition gives access to the theoretical sequence distribution. By different physicochemical methods (NMR, IR and UV spectroscopy), the results obtained by calculation are confirmed. Specifically the effect of microstructure and composition on the properties of some vinylidene chloride (VDC) copolymers with acrylonitrile (AN), vinyl chloride (VC) and methyl methacrylate (MMA) is studied. VDC leads to a very cristalline polymer, whereas PVC generally shows very poor cristallinity, and PAN shows particular structural characteristics. VDC copolymers can easily crystallize when they are rich in VDC. Generally the polymers are semi‐crystalline with an amorphous phase. A theoretical model accounting for the lamellar structure and crystallinity of VDC copolymers is described. It utilizes the microstructural data, obtained by a kinetic study and some simple hypotheses, among them the possibility for molecules to slide along each other. This sliding brings together the material which is crystallizable in determined areas. It is thus possible to explain the presence of crystallinity peaks, or at least of paracrystallinity, up to a relatively high amount of comonomer MMA, AN and especially VC in the diffractograms of VDC copolymers with MMA, AN and VC. The paracrystalline domains are defined as areas which can present some degree of order at great distance, with a relatively high amount of comonomer defects.
Polymers based on p‐aminophenol, 2. Poly(oxycarbonylimino‐1,4‐phenylene) and related polyurethanes
Authors: Kurita Keisuke , Matsuda Shoko , Iwakura Yoshio
Published: April 2003

The simplest AB‐type aromatic polyurethane, poly(oxycarbonylimino‐1,4‐phenylene) (1), was successfully synthesized by pyrolysis of phenyl N‐p‐hydroxyphenylcarbamate. The resulting polyurethane was colorless and soluble in some organic polar solvents. It was also confirmed to undergo “apparent sublimation” by first thermal dissociation to p‐hydroxyphenyl isocyanate and subsequent repolymerization to the polyurethane on a cool surface. Three other polyurethanes with related structures were prepared by solution addition polymerization to compare the unique properties. The most remarkable difference was observed in thermal behavior. The polyurethane 1 was found to dissociate much more readily at elevated temperatures than a similar AABB‐type polyurethane derived from hydroquinone and p‐phenylene diisocyanate.
Changes of molecular weights of thermally exposed polymers
Authors: Hudec Pavel , Laita Zdeněk , Peroutka Oldřich
Published: April 2003

Theoretical relations between the change of molecular weights of thermally exposed polymers with arbitrary initial distribution and time have been derived. These relations were used to correlate the changes of molecular weights of thermally exposed polypropylene.
Polymer retention mechanisms in GPC on active gels, 3. Poly(dimethylsiloxane) and poly(methyl methacrylate)
Authors: Figueruelo Juan E. , Soria Vicente , Campos Agustín
Published: April 2003

Elution curves on spherosil gels in pure and mixed eluents of poly(dimethylsiloxane), PDMS, and poly(methyl methacrylate), PMMA, as well as those of polystyrene, PS, just for comparison, have been determined. In a general way, PDMS elution volumers fit to those of PS, whereas PMMA elution curves shift to higher retention volumes. The differences in retention volumes between the different polymeric solutes have been interpreted in terms of differences in polymer‐gel and polymer‐solvent interactions. Hydrogen‐bonding seems to be the main contribution to solute‐substrate interactions.
Determination of the stereoisomers distribution in 1,4‐polybutadiene chains: A general restatement of the question
Authors: Walckiers Emmanuel , Julémont Michel
Published: April 2003

After a definition of the bases of statistical computations allowing the description of the cis and trans stereoisomers distribution along the 1,4‐polybutadiene chains, the relationships between the distribution statistics and the mechanism of propagation are deduced. The parameters necessary and sufficient to describe the stereoisomer proportions and distribution are also established, as well as the parameters related to the determination of the most probable propagation mechanism. Analysis of typical samples are proposed to illustrate the method. Finally, a way is settled for computing the mean length of stereosequences.
Determination of rate constants of initiation and propagation in the cationic polymerization of α‐methylstyrene with CF3SO3H and H2SO4
Authors: Takarabe Kunihide , Kunitake Toyoki
Published: April 2003

The polymerization of α‐methylstyrene with CF3SO3H and H2SO4 as initiators was studied at 30°C in dichloroethane by the stopped‐flow/rapid‐scan spectroscopic technique. The propagating cation shows λmax at 336–340 nm. The initiation process and the early stage of propagation were analyzed kinetically on the basis of the cation formation and monomer consumption by taking into account the equilibrium monomer concentration. The rate of initiation with CF3SO3H was found to be proportional to the concentrations of CF3SO3H and monomer, but the initiation with H2SO4 is not proportional to the H2SO4 concentration. The rate constant of initiation was estimated to be (2 ± 1)·103 1.mol−1.s−1 with CF3SO3H, and similar values were found with H2SO4. The rate constant of propagation is 3.104 1.mol−1.s−1 with CF3SO3H as initiator and 106 − 107 1.mol−1.s−1 with H2SO4 as initiator. These kp values are close to that obtained previously in the radiation polymerization. Finally, λmax values of the propagating cation, obtained by the stopped‐flow technique, were collected.
Cosolvents of PMMA
Authors: Fernández‐Piérola Inés , Horta Arturo
Published: April 2003

Several cosolvent mixtures for PMMA are reported. Their cosolvency has been confirmed by studying phase separation temperatures as a function of solvent composition. The results show that they are very powerful cosolvents. Acetonitrile forms such cosolvent mixtures with compounds containing different chemical groups (ester, ketone, alcohol, chloroalkane). The mixtures of acetonitrile with alcohols are nonsymmetrical with respect to the solubility parameter value of PMMA. They cannot be explained by simple δ theory. The mixture of formamide with ethanol is also nonsymmetrical and constitutes a true cosolvent pair for PMMA. The associating tendency of the polymer in the single solvent, plus the somewhat ordered structure of the pure liquids, are invoked to suggest that cosolvency is attained by breaking such order and association (in addition to the existence of unfavourable interactions between the cosolvents).
Living anionic stereospecific polymerization of 2‐vinylpyridine, 2. Kinetics of polymerization and nature of active centres
Authors: Soum Alain , Fontanille Michel
Published: April 2003

The kinetic study of the propagation reaction and the viscosity measurements on solutions of active centres indicate that the living stereospecific polymerization of 2‐vinylpyridine initiated by organomagnesium compounds in hydrocarbon solvents, proceeds through unsymmetrical non‐aggregated ion pairs. Cryoscopic measurements on a model compound of the active centres, indicate the lack of aggregation which is attributed to the complexation of the magnesium cation by the last and the penultimate pyridine ring of the living polymer chain.
Polymers containing enzymatically degradable bonds, 2. Poly[N‐(2‐hydroxypropyl)methacrylamide] chains connected by oligopeptide sequences cleavable by chymotrypsin
Authors: Rejmanová Pavla , Obereigner Blahoslav , Kopeček Jindřich
Published: April 2003

Copolymers of N‐(2‐hydroxypropyl)methacrylamide (1) with p‐nitrophenyl esters of N‐methacryloylated oligopeptides (2–16) were prepared. These copolymers were crosslinked below the gel point by diamines (17–27). The crosslinks connecting poly[N‐(2‐hydroxypropyl)methacrylamide] chains contained an oligopeptidic sequence of 2–4 amino acids, cleavable by α‐chymotrypsin: ‐Gly‐X‐Y‐ (X… Gly, Ala, β‐Ala, Val, Leu, Ile, Phe, D‐Phe; Y… Phe, Tyr), ‐Gly‐Gly‐Phe‐Y‐; ‐U‐Gly‐Val‐Phe‐ (U… Ala, Gly); ‐Gly‐Phe‐W‐ (W… Ala, Gly, D‐Phe); ‐Gly‐Phe‐Ala‐U‐. The changes in the distribution of molecular weights of the studied copolymers, after incubation with α‐chymotrypsin, allowed us to estimate the amount of degradable crosslinks and to determine the relationship between the structure and cleavability. The results are interpreted from the viewpoint of the contribution of subsite (S‐P) interactions to the degradability of the studied polymers.
Polymeric drugs by direct copolymerization: Polymer of β‐adrenergic antagonist alprenolol and its binding to receptors and antibodies
Authors: Pitha Josef , Zjawiony Jordan , Lefkowitz Robert J. , Caron Marc G.
Published: April 2003

Alprenolol (1‐(o‐allylphenoxy)‐3‐isopropylamino‐2‐propanol), a drug which is used in the management of cardiovascular diseases, was copolymerized with acrylamide. The incorporation of alprenolol into the copolymer decreased its potency for binding to beta‐adrenergic receptors located on membranes of frog erythrocytes a thousand times. However, this incorporation decreased the potency of alprenolol for binding to antibodies specific for catecholamines and alprenolol‐related drugs only about three times. The incorporation of the drug into the polymer apparently results in steric strains preventing the approach of the drug residues to sterically constrained receptor binding sites, but allowing its approach to the accessible antibody binding sites. Copolymerization with acrylamide was used to prepare the polymer bound form of another drug which contains an allyl group, an alpha‐adrenergic antagonist, azapetine (6‐allyl‐6,7‐dihydro‐5H‐dibenz[c,e]azepine).