Preparation of water‐soluble,syndiotacticity‐rich,low molecular weight poly(vinyl alcohol) microfibrils in high yields with the low‐temperature polymerization of vinyl pivalate in tetrahydrofuran and saponification

To prepare water‐soluble, syndiotacticity‐rich poly(vinyl alcohol) (PVA) microfibrils for various industrial applications, we synthesized syndiotacticity‐rich, low molecular weight PVA by the solution polymerization of vinyl pivalate (VPi) in tetrahydrofuran (THF) at low temperatures with 2,2′‐azobis(2,4‐dimethylvaleronitrile) (ADMVN) as an initiator and successive saponification of poly(vinyl pivalate) (PVPi). Effects of the initiator and monomer concentrations and the polymerization temperature were investigated in terms of the polymerization behaviors and molecular structures of PVPi and the corresponding syndiotacticity‐rich PVA. The polymerization rate of VPi in THF was proportional to the 0.91 power of the ADMVN concentration, indicating the heterogeneous nature of THF polymerization. The low‐temperature solution polymerization of VPi in THF with ADMVN proved to be successful in obtaining water‐soluble PVA with a number‐average degree of polymerization (P_n) of 300–900, a syndiotactic dyad content of 60–63%, and an ultimate conversion of VPi into PVPi of over 75%. Despite the low molecular weight of PVA with P_n = 800, water‐soluble PVA microfibrillar fibers were prepared because of the high level of syndiotacticity. In contrast, for PVA with P_n = 330, shapeless and globular morphologies were observed, indicating that molecular weight has an important role in the in situ fibrillation of syndiotacticity‐rich PVA. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1103–1111, 2002     

Polymerisation anionique du methacrylate de methyle par les organoalcalins—II. Polymerisation en milieu solvant protonique et influence de la temperature sur les tacticites des polymeres

Anionic polymerization of methylmethacrylate, initiated by fluorenyl-alkali metals in amine media, gives syndiotactic polymers.With amines having high dielectric constant (NH₃ and MeA) Li⁺, Na⁺ and K⁺ give approximately the same values of differential enthalpies and entropies of activation for iso- and syndiotactic placements.With primary amines having moderate dielectric constant (5 < ? < 7), influence of the nature of the counter-ion has been observed. The syndiotacticity increases with increasing alkali cation radius.For the same ion pair, the syndiotacticity of the propagation depends on the nature of the primary amine. From the absorption peak shifts detected by u.v. spectroscopy, it has been suggested that the living carbanion is solvated by amines. Because of this solvation, the coordination bond between the carboxy group of the living chain-end and the counter-ion is weakened; the syndiotactic placement is thus favoured.The strength of the solvation phenomenon depends on the steric hindrance of the amine molecule. Differences between the stereoconfiguration propagations have been observed for the bulky cyclohexylamine and the smaller and less rigid n-butylamine and ethylamine. With iso-propylamine, the behaviour of the anionic propagation is intermediate.Finally, with free ions or loose ion pairs, the anionic propagation is not affected by solvation of the living carbanion.     

ESR study on SiO2-supported half-titanocene catalyst for syndiospecific polymerization of styrene

Monocyclopentadienyltitanium trichloride (CpTiCl₃) was directly immobilized on silica surface. The resulting CpTiCl₃/SiO₂-MAO was investigated in view of its suitability for syndiospecific polymerization of styrene using ESR spectroscopy. Polymerization results show that both the syndiotacticity and the activity decrease upon immobilization. A possible explanation is that the active sites may become aspecific after immobilization and part of the immobilized active sites can be leached into the solution in the presence of MAO.     

The Relationship of Reaction Temperature,Tg and Rich‐Syndiotacticity of Poly(alkyl methacrylate)s in Modified Microemulsion Polymerization

Nanoscale poly(alkyl methacrylate)s including poly(methyl methacrylate), poly(ethyl methacrylate), poly(cyclohexyl methacrylate), poly(iso‐butyl methacrylate) and poly(benzyl methacrylate) were prepared by a modified microemulsion polymerization procedure. NMR analysis suggested that these poly(methacrylate)s samples were higher in syndiotactic content, lower in isotactic content and the glass transition temperatures (T_gs) of them were also higher than those reported in the literature. The tacticities of the poly(methacrylate)s, beside the restricted volume effect of nanoparticles during the modified microemulsion polymerization, were mainly influenced by the reaction temperature, the lower the reaction temperature, the higher the syndiotacticity of the products. The syndiotacticity of the product decreased obviously when the polymerization was carried out at a temperature far above the T_g of the resulting polymer. It was also shown that the tacticity of the polymer was affected by the monomer structure, a monomer with the bulkier alkyl side group would liable to result in a polymer with richer syndiotacticity. Possible mechanism of rich‐syndiotacticity was also discussed.     

Effect of syndiotacticity on the aqueous poly(vinyl alcohol) gel 4. X-ray diffraction analysis of gel

Summary The structure of syndiotacticity-rich poly(vinyl alcohol) (PVA)-water gel was investigated by the X-ray diffraction analysis. Diffuse haloes appeared in the gel prepared from lower aqueous solution of PVA (5 wt%) but diffraction pattern became sharper with increasing concentration of PVA. Thed-spacings of gels and films are agreed with each other. The half height width of value of peak position of (101) obtained by photodensitometer decreased with increasing syndiotacticity of PVA. The radius of gyration of gel obtained from theGuinier's plots by the small angle X-ray diffraction increases with increasing syndiotacticity. These results suggest that the syndiotactic sequence length increases with increasing content of syndiotacticity and the crystallites in gel networks become also larger with increasing syndiotacticity. The average size of gel junction is 73–89 Å (s-(diad)% = 49.₄-66.₂).

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Zusammenfassung Es wurden mit Röntgeninterferenzen die Strukturen von einem Polyvinylalkohol-Wasser-Gel mit syndiotaktisch angereichertem Polyvinylalkohol untersucht. Es erscheinen diffuse Halos in dem Gel, das aus niedrigeren wäßrigen Lösungen (5% PVA) präpariert wurde. Doch wurden die Beugungsinterferenzen schärfer mit steigender Konzentration an PVA. Died-Abstände in Gelen und Filmen stimmten miteinander überein. Die Halbwertsbreite der 101-Interferenzen, gemessen mit einem Photodensitometer, nahm mit steigender Syndiotaktizitat des PVA ab. Der Trägheitsradius des Gels aus Guinier-Auftragungen für die Kleinwinkelstreuung nimmt mit steigender Syndiotaktizitat zu. Diese Ergebnisse legen nahe, daß die syndiotaktische Segmentläange mit steigendem Gehalt an Syndiotaktizitat zunimmt und daß die Kristallite in den Gelnetzwerken mit zunehmender Syndiotaktizität gröBer wurden. Die mittlere Größe des Netzwerkabstandes ist 73–89 Å (s-(diad)% = 49.₄-66.₂).

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With 7 figures in 15 details and 3 tables     

Crystal growth in syndiotactic poly(vinyl alcohol) hydrogels

Aqueous solutions of syndiotacticity-rich poly(vinyl alcohol) (s-PVA) form gels easily. The optimum condition of growth of the calcium tartrate crystal formed by diffusing calcium chloride into hydrogels containing tartaric acid was studied with use ofs- PVA of a syndiotacticity of 56 % and a degree of polymerization of 1460. The crystal grew in the gel of the concentrations of 2 % s-PVA and of 0.5 N tartaric acid at pH=4. The relation between the formation of Liesegang rings and shear modulus of a gel was studied by diffusing silver nitrate into gels containing potassium chromate. The distance between rings decreased with increasing shear modulus of a gel in the range from 670 to 7500 dyne/cm². The Liesegang rings were not formed for the shear modulus gel for 280 and 16200 dyne/cm₂.     

Polymerisation radiochimique de l'acide acrylique en solution dans l'alcool isopropylique et le dimethylformamide

The radiation-induced polymerization of acrylic acid in isopropyl alcohol and dimethylformamide solutions was investigated between?196°and40°. Mixtures which form glasses at low temperatures exhibit a maximum in the rate of polymerization at 30° and 50° above the glass transition temperature (T_g). The difference between the most favourable temperature for polymerization and T_g is larger than in systems studied previously. This fact could be due to the presence of H-bonded aggregates.The study of the polymerization of acrylic acid in dimethylformamide solution at 20° led to a correlation between this reaction and the presence of plurimolecular aggregates. The very high polymerization rate and the syndiotacticity of the resulting poly(acrylic acid) confirm the earlier assumption of a favourable orientation for propagation of the molecules of acrylic acid in these aggregates.     

Influence de la tacticite du polychlorure de vinyle sur son comportement physique en fonction de la temperature

Three PVC samples, having syndiotacticity contents between 55 and 68%, have been prepared and characterized by previously described methods. Their thermal behaviour has been studied using three techniques, viz. inverse chromatography. ATD and Rheovibron. The results make clear the influence of tacticity on both the number and the intensity of transitions. These results are accounted for on the basis of a possible influence of TG conformations on the behaviour of the amorphous phase.     

Les fluorations comparees des chloropyrimidines et de la chloro-s-triazine en milieu de fluorure de potassiun solide

The fluorinations of tetrachloropyrimidine, 2,4,6-trichloropyrimidine and trichloro-s-triazine were carried out in sealed tubes with KF in presence of inert gas and then compared. The fluorinated derivatives C₄F_xCl_yN₂ with x + y = 4, 0?x<4 , C₄HF_xCl_yN₂ with x + y = 3, 0?x?3 and C₃F_xCl_yN₃ with x + y = 3, 0?x?3 were obtained. The influence of contact time, temperature and concentration of the ion F^? were investigated and compared; the molar yields were found to be always higher than 50% in our experimental conditions. We compare with the fluorinations of 2, 4 and 4, 6-dichloropyrimidine. It is possible to obtain directly, in good proportions, such fluorinated derivatives as 5-chlorotrifluoropyrimidine, trifluoropyrimidine and others. At high temperature (400°C for 16^h), tetrachloropyrimidine, in presence of KF, gave products of pyrolysis and condensation such as the fluorinated derivatives of C₆Cl₆ and C₅Cl₅N : C₆FCl₅, C₆F₂Cl₄ ··· or C₅FCl₄N, C₅F₂Cl₃N ···     

Effect of stereosequences on crystallinity and properties of zone‐drawn poly(vinyl alcohol) microfibrils

To effectively orient the molecular chains of novel syndiotactic poly(vinyl alcohol) (PVA) microfibrillar fiber (PVA fibril), a high‐temperature zone‐drawing method was adopted. The PVA fibrils were directly prepared from the saponification and in situ fibrillation without a spinning procedure. The maximum draw ratio of the PVA fibril increased with a decrease in the syndiotactic diad (r‐diad) content, indicating that the deformability of PVA molecules was lowered in higher syndiotactic PVA. Degree of crystal orientations up to 0.990 were achieved by stretching the PVA fibril with the r‐diad content of 65.1% and the original degree of crystal orientation of 0.902 at 250 °C close to its crystal melting temperature (T_m). When the same draw ratio was applied to the fibrils, a higher crystal orientation was achieved for the fibrils having higher syndiotacticity. Wide‐angle X‐ray data show that the longitudinal crystal sizes of drawn PVA fibrils were larger in higher syndiotacticities. The degree of crystal orientation, crystallinity, T_m, longitudinal crystal size, and tensile strength of the maximum drawn PVA fibril with a r‐diad content of 65.1% were 0.99, 0.97, 279 °C, 187 Å, and 4.66 N/tex, respectively. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1263–1271, 2001     

Investigation of the intramolecular structure of styrene–ethylmethacrylate copolymers by 1H- and 13C-NMR: Reassignment of 1H-NMR spectra

The compositions and sequence distributions of homogeneous styrene (S)–ethyl methacrylate (E) copolymers, obtained by low conversion solution polymerization have been studied by ¹H- and ¹³C-NMR. A new set of peak triad assignments was proposed for the δ 2.1–4.2 ppm region in the ¹H-NMR spectrum, whereby the reactivity ratios of r_S = 0.59 and r_E = 0.50 were used to establish this new assignment. The EEE and SSS blocks, present in these copolymers, have a high degree of syndiotacticity (σ_EE = 0.23, σ_SS = 0.39), whereas the ESE units are exhibiting a slight tendency toward isotacticity (σ_ES = 0.66).     

Rich‐Syndiotacticity of Poly(cyclohexyl methacrylate) Prepared by Modified Microemulsion Polymerization

Nanoscale poly(cyclohexyl methacrylate) (PCHMA) particles were prepared by a modified microemulsion polymerization procedure. ¹³C‐NMR analysis suggested that such PCHMA samples were higher in syndiotactic content (61–72% rr) and lower in isotactic content (1–3% mm). The glass transition temperatures (T_g's) of the products were also higher than that reported in the literature. The polymer properties, such as particle size, molecular weight, tacticity, and T_g were affected by the reaction conditions. The smaller the particle size, the higher the syndiotacticity, the lower the isotacticity and the greater the molecular weight, then the higher the T_g of the PCHMA samples. Possible mechanism of rich‐syndiotacticity was also discussed.     

Spectrometrie de Masse du Dimethoxy-2,6 Naphtalene et de Certains de ses Derives

The mass spectra of 2,6-dimethoxynaphthalene and 14 of its derivatives are reported. The fragmentation patterns proposed to account for the main peaks observed are frequently based on the presence of the appropriate metastable peaks. The fragmentation is initiated by the cleavage of an O? CH₃ bond. The molecular ion is the most intense ion in each case and it does not appear to directly eliminate a methoxy group or a substituent directly attached to the naphthalene ring. With NO₂ as a substituent the elimination of nitric oxide from the molecular ion has been observed and confirmed by peak matching.     

Preparation of syndiotacticity-rich high molecular weight poly(vinyl alcohol) microfibrillar fiber by photoinitiated bulk polymerization and saponification

Vinyl pivalate (VPi) was polymerized in bulk by ultraviolet-ray initiation at low temperatures using 2,2′-azobis(2,4-dimethylvaleronitrile) (ADMVN) and 2,2'-azobis(isobutyronitrile) (AIBN) as photoinitiators. High molecular weight (HMW) poly(vinyl pivalate) (PVPi), having a number-average degree of polymerization (P_n) of 13,000–28,000, was obtained at conversions below 30% and converted by saponification to a syndiotacticity-rich HMW poly(vinyl alcohol) (PVA) microfibrillar fiber with P_n of 7300–18,300, syndiotactic diad (S-diad) and triad contents of ∼ 64% and ∼ 39%, respectively, and crystal melting temperature (T_m) of ∼ 249°C. ADMVN gave higher P_n than AIBN. On the other hand, conversion was smaller with the former than with the latter, and it was found that the initiation rate of ADMVN was lower than that of AIBN. P_n of PVA was constant while P_n of the precursor PVPi increased with increasing conversion. The syndiotacticity, T_m and thermal stability of PVA obtained from PVPi were much superior to those of PVA derived from poly(vinyl acetate) prepared under the same polymerization conditions. Polymerization of VPi at lower temperatures gave PVA with higher syndiotacticity. © 1997 John Wiley & Sons, Inc.     

Novel Complex Catalyst of η3‐(Pentamethylcyclopentadienyl)dimethylaluminum/Titanium(IV) Butoxide (Cp*AlMe2/Ti(OBu)4) for Syndiotactic Polystyrene

A novel metallocene catalyst was prepared from the reaction of (η³‐pentamethylcyclopentadienyl)dimethylaluminum (Cp*AlMe₂) and titanium(IV) n‐butoxide Ti(OBu)₄. The resulting titanocene Cp*Ti(OBu)₃ was combined with methylaluminoxane (MAO)/tri‐iso‐butylaluminum (TIBA) to carry out the syndiotactic polymerization of styrene. The resulting syndiotactic polystyrene (sPS) possesses high syndiotacticity according to ¹³C NMR. Catalytic activity and the molecular weight of the resulting sPSs were discussed in terms of reaction temperature, concentration of MAO, amounts of scavenger TIBA added, and the hydrogen pressure applied during polymerization.     

Cinetique de polymerisation de monomeres complexes par des acides de Lewis. Etude du systeme methacrylate de methyl-chlorure de zinc-azobisisobutyronitrile

The polymerisation of methyl methacrylate (MMA) initiated by azo-bis-isobutyronitrile (AIBN) in the presence of ZnCl₂ as complexing agent has been investigated. Increase of the polymerisation rate and a minimum in the average polymerisation degree were observed by increasing the ZnCl₂ concentration. By assuming the existence of complexes {AIBN · ZnCl₂} and {MMA · ZnCl₂}, a kinetic scheme is proposed; it is in good agreement with the experimental results and allows calculation of the characteristics of the system.     

Bestimmung der zur Kristallisation notwendigen minimalen Sequenzlänge an Polyvinylchlorid

Zusammenfassung Taktisches Polyvinylchlorid wird als Copolymer aus kristallisierfähigen syndiotaktischen und nichtkristallisierfähigen isotaktischen Sequenzen aufgefaßt. In Anlehnung an dieFlorysche Theorie der Kristallisation von Copolymeren wird aus der Syndiotaxie und dem Kristallinitätsgrad eine untere Grenzlänge der kristallisierten Sequenzen bestimmt. Die Syndiotaxie der Proben war aus Kernresonanz- und UR-Messungen bekannt, der Kristallinitätsgrad wurde röntgenographisch gemessen.Die minimale Sequenzlänge beträgt etwa 12 Monomereinheiten.

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Summary In this paper stereoregular polyvinylchloride is considered as a copolymer of syndiotactic parts being and isotactic parts not being able to crystallize. Following the conception ofFlory's theory of copolymer crystallization a lower limit of the length of crystallized sequences is determined by using syndiotacticity and degree of crystallinity. The syndiotacticity of the samples was known from NMR- and IR-experiments. The degree of crystallinity was measured by x-ray-diffraction.The minimum sequence length is nearly 12 monomer units.

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Vorgetragen am 12. September 1963 auf der Physikertagung 1963 in Hamburg.     

Nouvelle methode de synthese de tetrahydro-2,3,4,5 benzo (b) 1H-azepines substituees en position -2

Treatment of tertiary alcohols and trisubstituted olefins of the tetrahydronaphthalene series with the HN₃H₂SO₄ reagent leads directly and with good yields to a new class of compounds: the 3,4-dihydro 5H benzo (b) azepins substituted on position -2. The latter, on reduction, give the corresponding 2,3,4,5-tetrahydro 1H benzo (b) azepins, most of them being unknown in the literature. This work shows the high regiospecificity of this ring expansion reaction which can be explained by electronic and steric effects.     

La fluoration de l'hexachlorobenzene et de la pentachloropyridine en milieu de fluorure de potassium solide

The fluorinations of hexachlorobenzene and pentachloropyridine were carried out in sealed tubes with KF in presence of inert gas; the fluorinated derivatives C₆F_xCl_y x + y = 6 0?x?6 and C₅F_xCl_yN x + y = 5 0?x?5 are obtained. The influence of contact time, temperature and the concentration of the ion F^? are investigated and compared; the molar yield varied from 45% to 90%. It is possible to get directly and selectively some fluorinated derivatives as C₅Cl₂F₃N. The fluorinations in liquid KFKCl and solid KF are compared.     

杯芳烃钛化合物的合成及用于乙烯和苯乙烯聚合的研究

杯芳烃钛化合物的合成及用于乙烯和苯乙烯聚合的研究李勇郑炎松谢光华（中国科学院化学研究所北京１０００８０）关键词杯芳烃，钛化合物，聚乙烯，间规聚苯乙烯在茂金属／甲基铝氧烷（ＭＡＯ）均相催化体系中，催化剂的结构起着至关重要的作用，配体的空间效应、电...