Reaction of poly(vinyl alcohol) with formaldehyde and polymer stereoregularity. Model compounds

The reaction of stereoisomers of pentane-2, 4-diol and heptane-2, 4, 6-triol with formaldehyde was investigated as a model for the formalization reaction of poly(vinyl alcohol) in order to determine effect of the stereochemical configuration of the polyol molecules on the reaction. The isotactic (meso) diol portion reacted with formaldehyde to give cis-formal several times faster than did the syndiotactic (dl) diol portion to give trans-formal at 30–80°C. In the reaction of heterotactic (meso-dl) triol which provides both the isotactic and syndiotactic diol portions in a molecule, the proportion of trans-formal in the total formal decreased as the reaction proceeded. This shows that the formation of cis-formal is also favored thermodynamically to a greater extent, and hence the intramolecular migration of trans-formal to cis-formal did occur during the reaction. The rates of hydrolysis of formals of the diols were compared with those of the triols in order to see the effect of a hydroxyl group adjacent to the formal ring on the reaction. No appreciable rate difference was observed between the dimer and trimer models both in cis- and trans- formals. Therefore it was deduced from these results that the increase of the rate of hydrolysis of poly(vinyl formal) with the increase of hydroxyl groups along the polymer chain is a characteristic of macromolecules that is not observed in the low molecular weight models.     

Graft Polymerization of Vinyl Monomers Onto Carbon Black by Use of the Redox System Consisting of Ceric Ions and Carbon Black Carrying Alcoholic Hydroxyl Groups

The radical graft polymerization of vinyl monomers onto carbon black initiated by a redox system consisting of ceric ion and carbon black having alcoholic hydroxyl groups was investigated. The introduction of alcoholic hydroxyl groups onto the carbon black surface was achieved by the reaction of carbon black with alcoholic hydroxyl radicals, formed by the reaction of alcohol with benzoyl peroxide. The rate of the polymerization of acrylamide (AAm) initiated by the redox system was found to increase in the following order of hydroxyl groups: 1-hydroxyoctyl < 1-hydroxypropyl < 1-hydroxyethyl < hydroxymethyl < 1-hydroxy-1-methylethyl. In the redox polymerization, poly-AAm was effectively grafted onto carbon black by propagation of the polymer from the radical formed by the reaction of ceric ions with the alcoholic hydroxy groups. The percentage of grafting increased with increasing conversion. By use of this redox system, poly(acrylic acid), polyacrylonitrile, and poly(N-vinyl-2-pyrrolidone) could be grafted onto carbon black, but poly(methyl methacrylate) and polystyrene could not be so grafted. The graft polymerization of AAm by use of a redox system consisting of ceric ion and PVA-grafted carbon black was also investigated.     

The Structure of Water-Swollen Poly(Vinyl Alcohol) and the Swelling Mechanism

The swelling mechanism of poly(vinyl alcohol) (PVA) in a wide range of the equilibrium swelling index, of 7–153% (with H₂O) and of 12-297% (with D₂O), was investigated by IR, Raman, and broad-band NMR spectroscopy. Analysis of the spectral data obtained confirmed the presence of hydration water (bonded with polymer-free hydroxyl groups) and condensation water (not having been bonded with polymer hydroxyl groups) in poly(vinyl alcohol) swollen samples at low (～7%) and high (>23%) equilibrium swelling indexes, respectively. Moreover, it revealed the intra- and inter-molecular hydrogen bonds breaking in the polymer swollen to higher extent (equilibrium swelling index > 85%).     

Studies of reactions with polymers. V. The reaction mechanism and resultant structure of PVA with PAN in DMSO without any catalyst

The reaction of polyacrylonitrile with poly(vinyl alcohol) in dimethyl sulfoxide without any catalyst was studied, and it showed that the adjacent nitrile groups on polyacrylonitrile could be linked up to form conjugated carbon-nitrogen sequence by the presence of poly(vinyl alcohol). However, no such reaction occurred when poly(vinyl alcohol) was replaced by i-propanol or poly(vinyl alcohol) graft copolymers. The structure of the resulting polymers were proposed by means of IR, UV, ¹H, and ¹³C-NMR spectroscopies. On the basis of the results, the effect of polymer feed and polymerization condition on this reaction were discussed. The compositions were determined by elemental analysis. The viscosity and thermal analysis of the products were also determined. At feed weight ratios of poly(vinyl alcohol) to polyacrylonitrile above one-half, gels were obtained.     

Novel method for preparation of photocrosslinkable poly(vinyl alcohol)

A convenient procedure to prepare photosensitive poly(vinyl alcohol) by acetalization with 1-methyl-4-(p-formylstyryl)pyridinium methosulfate in heterogeneous condition is described. The reaction of fully saponified poly(vinyl alcohol) was carried out in suspension in acidic aqueous solution, while partially saponified poly(vinyl alcohol) was acetalized in acidic aqueous organic solvent. The photosensitive poly(vinyl alcohol) thus prepared was purified by filtration and successive washing out with methanol. The effect of the preparative condition on the electronic absorption spectra of the styrylpyridinium group attached to poly(vinyl alcohol) is discussed.     

Vibrational spectra and assignments of 2-phenylethanol and 2-phenoxyethanol

The structural stability of 2-phenyl- and 2-phenoxyethanols were investigated at the DFT-B3LYP/6-311G**, MP2 and MP4(SDQ) levels of theory. From the calculations at the three levels of theory 2-phenylethanol and 2-phenoxyethanol were predicted to exist predominantly in non-planar gauche conformations. For 2-phenylethanol the lowest energy Gg1 structure was predicted to be stabilized by an interaction between the hydroxyl H atom and the phenyl ring. For 2-phenoxyethanol the Ggg1 structure was predicted to be strongly stabilized by dipolar interactions between the hydroxyl H atom and the phenoxy O atom of the alcohol. For both alcohols the planar trans structure with minimum steric interactions between the CH₂ groups was predicted to be significantly higher in energy than the ground state gauche structure of the alcohols. The dipolar interactions are reported to play more important role than steric ones in stabilizing the molecules. The vibrational frequencies of each of the two alcohols in its lowest energy gauche structure were computed at the B3LYP level and tentative vibrational assignments were made for their normal modes on the basis of the calculated and experimental data.     

Crosslinking of hyaluronic acid with glutaraldehyde

Hyaluronic acid (HA) was chemically crosslinked with glutaraldehyde (GA) to produce water-insoluble films having low water contents when brought into contact with water. The crosslinking reaction was performed using uncrosslinked HA films in acetone–water mixtures. This method could produce water-insoluble HA films with water contents as low as 60 wt % when subjected to swelling with phosphate-buffered saline of pH 7.4 at 37°C. This 60 wt % water content was lower than any values for HA ever reported. There was an optimal HCl concentration around 0.01N for the HA crosslinking with GA in acetone—water mixtures. To get information on the crosslinking mechanism, alginic acid, which possesses hydroxyl and carboxyl groups in one molecule, similar to HA, and poly(vinyl alcohol) (PVA) and amylopectin, which possess only hydroxyl groups, were subjected to crosslinking with GA. PVA and amylopectin were also found to become water-insoluble after reaction with GA. On the basis of the infrared spectra of these crosslinked films, it was concluded that intermolecular formation of hemiacetal bonds with GA between the hydroxyl groups belonging to different HA molecules led to crosslinking. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 3553–3559, 1997     

Synthesis of optically active polynucleotide analogs with poly(vinyl alcohol)s as backbones and adenine and 5-bromouracil derivatives as pendants

The optically active polynucleotide analogs were prepared by grafting nucleic acid base derivatives onto poly(vinyl alcohol). The (R)-ethyl 2-(5-bromouracil-1-yl)propanoate was obtained either by reaction of 5-bromouracil sodium salt with (S)-ethyl 2-[(methylsulfonyl)oxy]propanoate or reaction of 5-bromouracil with (S)-ethyl lactate in the presence of triphenyl phosphine and diethyl azodicarboxylate. Subsequent hydrolysis of the ester is aqueous acid provided the optically pure (R)-bromouracilypropanoic acid. The monomer model compounds were prepared by an esterification reaction of the pendant groups with 3-pentyl alcohol in the presence of dicyclohexylcarbodiimide and a catalytic amount of 4-pyrrolidinopyridine. Poly(vinyl alcohol) underwent reaction with the (R)-bromouracilylpropanoic acid or the (R)-adeninylpropanoic acid in the presence of dicyclohexylcarbodiimide and a catalytic amount of 4-pyrrolidinopyridine. The resulting polymers were optically active and percents grafting were almost quantitative.     

Fluorine-containing poly(vinyl alcohol): A helix or a random coil

Substitution of several mole per cent of the hydroxyl groups of poly(vinyl alcohol) by fluorine results in marked changes in polymer properties. These fluoro poly(vinyl alcohols) (PVAF) form thermally reversible gels in water at low polymer concentrations. In solution, a helical conformation or a random coil containing helical sequences is more in accord with the experimental observations than the random coil structure of poly(vinyl alcohol). This helical hypothesis is supported by high heats of crosslinking of the aqueous thermally reversible gels, the difficult solubility of PVAF in H₂O, the insolubility of the PVAF–iodine complex under conditions where the PVA–iodine complex remains soluble, the temperature-independent high value for the Huggins k ′ slope constant, the greater stability of the PVAF–iodine complex, the shear dependence of the solution viscosity and our inability to form thermally reversible gels by the introduction of fluorine into other water-soluble polymers which are capable of hydrogen bond formation. Infrared dichroism and deuteration measurements do not differentiate between PVA and PVAF. If this conclusion is correct, PVAF is the first vinyl polymer of which we are aware that maintains a helical conformation in solution.     

Pervaporation of alcohol-toluene mixtures through polymer blend membranes of poly(acrylic acid) and poly(vinyl alcohol)

Homogeneous membranes were prepared by blending poly(acrylic acid) with poly(vinyl alcohol). These blend membranes were evaluated for the selective separation of alcohols from toluene by pervaporation. The flux and selectivity of the membranes were determined both as a function of the blend composition and of the feed mixture composition. The results showed that a polymer blending method could be very useful to develop new membranes with improved permselectivity. The pervaporation properties could be optimized by adjusting the blend composition. All the blend membranes tested showed a decrease in flux with increasing poly(vinyl alcohol) content for both methanol—toluene and ethanol—toluene liquid mixtures. The alcohols permeated preferentially through all tested blend membranes, and the selectivity values increased with increasing poly(vinyl alcohol) content. The pervaporation characteristics of the blend membranes were also strongly influenced by the feed mixture composition. The fluxes increased exponentially with increasing alcohol concentration in the feed mixtures, whereas the selectivities decreased for both liquid mixtures.     

聚乙烯醇非均相法环氧乙烷衍生化反应的研究

 采用聚乙烯醇与环氧乙烷非均相加合反应合成了不同环氧乙烷结合量的羟乙基化聚乙烯醇（ＨＥＰＶＡ）．在通过１３Ｃ－ＮＭＲ和ＩＲ对产物进行表征的基础上，讨论了反应与ＰＶＡ空间立构性及结晶性间的关系，证明了ＨＥＰＶＡ中聚氧乙烯链的存在，且其含量增长速率随反应深度的增加而增大．     

聚甲基乙烯基酮的不对称还原反应

聚甲基乙烯基酮的不对称还原反应李弘姚金水何炳林（吸附与分离功能高分子材料国家重点实验室南开大学高分子化学研究所天津３０００７１）关键词对称硅氢化，聚甲基乙烯基酮，手性噻唑烷，铑近年来手性过渡金属络合物催化的前手性酮和烯的不对称硅氢化反应已在国际上受...     

A Method for Esterification Reaction Rate Prediction of Aliphatic Monocarboxylic Acids with Primary Alcohols in 1,4‐Dioxane Based on Two Parametrical Taft Equation

Esterification reaction rates of aliphatic monocarboxylic acids with primary alcohols in 1,4‐dioxane as inert solvent were investigated. Acids were esterified with 1‐propanol and alcohols with acetic acid as model reactants at a constant temperature of 60°C, at a fixed ionic strength and pH in a batch reactor with a constant volume. For evaluation of reaction rates, an exact kinetic equation for the equilibrium reaction was applied. Under these conditions and for low reactants, concentrations reaction rate depends only on the structure of reactants and, therefore, can be predicted by a correlation equation with two Taft coefficients (inductive and steric effects). From these equations, it is possible to estimate the esterification reaction rate constant for other acid‐alcohol pairs. This methodology may also be suitable for other kinetic systems measured under comparable experimental conditions.     

Statistical Chain Dimensions of Poly (vinyl acetal)-Type Molecules

Acetalization of poly(vinyl alcohol) molecules results in acetal ring formation between two successive hydroxyl groups. This will dominate the chain stiffness of poly(vinyl acetal) in different ways, depending on the stereospecificity of poly(vinyl alcohol) used as the starting material. The present paper first deals with calculations of statistical dimensions of hypothetical poly(vinyl acetal) chains with a 100% degree of substitution and different stereospecificities (isotacticity and syndiotacticity). The calculations are essentially identical with those made by Wall and Markovitz, but recent stereochemical knowledges of the acetal ring and poly(vinyl alcohol) are taken into account. The results show that the chain dimension of poly-(vinyl acetal) chain derived from isotactic poly(vinyl alcohol) is much larger than that of poly(vinyl acetal) derived from the syndiotactic one. The treatment used above is extended to more realistic chains that have any degree of stereoregularity and of substitution. As has been anticipated intuitively, it is ascertained that the chain dimensions increase with increase in the degree of substitution for each stereospecificity.     

Acetalization of poly(vinyl alcohol) by a fatty aldehyde in water medium: Model study,kinetics, and structure analysis

Acid catalyzed poly(vinyl alcohol) (PVA) acetalization was investigated in aqueous medium at 80 °C for a PVA concentration of 8 wt %. The reactant, 10‐undecenal, was composed of a long alkyl chain with a vinyl end group, and the functionalization reaction was studied in heterogeneous media for low reactant concentrations (from 0.33 to 2.0 mol % compared with PVA hydroxyl groups concentration). First, the reaction was scrutinized with pentane‐2,4‐diol, as a model compound of PVA. Besides the expected reaction, the oxidation of the aldehyde into 10‐undecenoic acid in the presence of water was evidenced. This carboxylic acid appeared unreactive toward esterification of pentane‐2,4‐diol and PVA in water. Characterization of acetal stereochemical structure formed on the PVA backbone was performed by NMR spectroscopy in accordance to the model approach. A protocol based on ¹H NMR analysis was developed to quantify grafted aldehyde, residual aldehyde, and created carboxylic acid through direct sampling of the reaction medium. Conversions and reaction rate constants were calculated for pH ranging from 1 to 3. Finally, the acetalization yield was found to be enhanced at low pH and, in such conditions, the oxidation reaction contribution was limited. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 661–671     

Polymers containing fluorinated ketone groups. II. NMR studies of the reaction of methylbenzyl trifluoromethyl ketones with alcohols in carbon tetrachloride

Prior to the study of poly(o- and p-vinylbenzyl trifluoromethyl ketone) (PVTFK) polymers and their reaction with alcohols, the reactions of some simple model compounds with alcohols were investigated. The reaction of fluorinated ketones toward alcohols was determined by proton nuclear magnetic resonance (NMR) spectroscopy. Two fluorinated ketones–p-methylbenzyl trifluoromethyl ketone (p-MTFK) and o-methylbenzyl trifluoromethyl ketone (o-MTFK)–were prepared. Studies of the reaction of p-MTFK and o-MTFK to various alcohols based on NMR produced equilibrium constants (1M in CCl₄) at 31°C that ranged from 0.1 to 6.0. The equilibrium constants for p-MTFK with alcohols were larger than those for o-MTFK. In addition, the equilibrium constants for primary alcohols were larger than those for secondary and tertiary alcohols. Steric effects in this reaction could explain the lowered equilibrium constants for o-MTFK and the secondary and tertiary alcohols.     

Réactivité du polychloroformiate de vinyle et cinétique de relargage in vitro des molécules greffées

The chemical modification of poly(vinyl chloroformate) with amines (diethylamine, N-methylbenzamine, morpholine and piperidine), alcohols (sec. butyl alcohol and benzyl alcohol) and phenol has been investigated. We have found convenient conditions in order to obtain soluble modified polymers with nearly quantitative substitution; these modified polymers has been used as model molecules for biologically active compounds; kinetics in vitro of cleavage have shown that the rates of hydrolysis in stomacal medium are twice those in intestinal medium. These rates of cleavage are very low (0.1 at 1% in 24 hr) and allow use of poly(vinyl chloroformate) as a support for biologically active compounds during prolonged treatment.     

聚乙烯醇非均相法环氧乙烷衍生化反应的研究

采用聚乙烯醇与环氧乙烷非均相加合反应合成了不同环氧乙烷结合量的羟乙基化聚乙烯醇（ＨＥＰＶＡ）．在通过１３Ｃ－ＮＭＲ和ＩＲ对产物进行表征的基础上，讨论了反应与ＰＶＡ空间立构性及结晶性间的关系，证明了ＨＥＰＶＡ中聚氧乙烯链的存在，且其含量增长速率随反应深度的增加而增大．     

Chiral Phosphoric Acid Dual‐Function Catalysis: Asymmetric Allylation with α‐Vinyl Allylboron Reagents

We report a dual function asymmetric catalysis by a chiral phosphoric acid catalyst that controls both enantioselective addition of an achiral α‐vinyl allylboronate to aldehydes and pseudo‐axial orientation of the α‐vinyl group in the transition state. The reaction produces dienyl homoallylic alcohols with high Z‐selectivities and enantioselectivities. Computational studies revealed that minimization of steric interactions between the alkyl groups of the diol on boron and the chiral phosphoric acid catalyst influence the orientation of α‐vinyl substituent of the allylboronate reagent to occupy a pseudo‐axial position in the transition state.     

Dynamic structure of poly(vinyl pyrrolidone)/ethyl alcohol mixtures studied by time domain reflectometry

Dielectric studies of poly(vinyl pyrrolidone)/ethyl alcohol (PVP–E) binary mixtures with concentration variations were carried out in the frequency range of 10 MHz to 10 GHz by time domain reflectometry at 15, 25, 35, and 45 °C. One relaxation process, corresponding to ethyl alcohol molecules in the poly(vinyl pyrrolidone) (PVP) matrix, was observed in this frequency range for all the mixtures. The static dielectric constant of the PVP–E mixtures decreased linearly with an increase in the weight fraction of PVP. The observed anomalous increase in the value of the relaxation time (τ) of these mixtures was interpreted by the consideration of the variation in the local structure of self‐associated ethyl alcohol molecules and also the PVP behavior as a geometric constraint for the rotational motion of ethyl alcohol molecules. Furthermore, the τ values of these mixtures were independent of the viscosity. The energy parameters for the dielectric relaxation process (the free energy, enthalpy, and entropy of activation for the dipolar orientation) were determined to confirm the transient behavior of the heterogeneous species due to the breaking and re‐forming of hydrogen bonds with the internal rotation of ? OH groups in the ordered structure of the PVP–E mixtures. On the basis of the evaluated dielectric parameters, the formation of supermolecular structure in the PVP–E mixtures in dynamic equilibrium was sketched and examined by the consideration of the hydrogen bonding between the terminal hydroxyl groups of self‐associated ethyl alcohol flexible chains and the carbonyl groups of monomer units of PVP coiled chains. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1134–1143, 2005