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.     

Mixed films of poly(n-hexyl isocyanate) and poly(vinyl acetate) at the air-water interface

We study interfacial properties of rigid-rod-like poly(n-hexyl isocyanate) (PHIC), flexible poly(vinyl acetate) (PVAc), and mixed films of PHIC and PVAc spread at the air-water interface as a function of the molar fraction of PHIC by surface pressure measurements and fluorescence microscopy. From the plots of the experimental mean area of the mixed polymer films at a constant surface pressure as a function of the molar fraction of PHIC in the mixed films, the binary mixtures of PHIC/PVAc were concluded to be compatible at the air-water interface. This means that the hydrophobic hexyl group of PHIC takes a horizontal orientation to the air-water interface rather than a perpendicular one, leading to PHIC and PVAc having the same interfacial orientation. Compatibility of the binary mixtures of PHIC/PVAc at the air-water interface is also confirmed by their fluorescence microscopic images, since PHIC proves to be inhomogeneous and PVAc is homogeneous with the aid of a fluorescence probe, respectively.     

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.     

AFM studies on LB films of poly(n-hexyl isocyanate), poly(vinyl acetate), and their binary mixtures

LB films of rigid-rod-like poly(n-hexyl isocyanate) (PHIC), flexible poly(vinyl acetate) (PVAc), and binary mixtures of PHIC as well as of PHIC and PVAc transferred on a mica surface from the air-water interface were observed by AFM. The grain structure of three individual PHIC samples in the AFM images changed shape from a rigid rod to a coiled rod with an increase in the molecular weight due to changes in the chain rigidity of PHIC. On the other hand, the AFM image of PVAc was similar to that of a mica surface, indicating that PVAc forms a uniform and homogeneous film. For the binary mixtures of PHIC, the grain structure in the AFM image of the highest molecular weight PHIC was expanded with a similar shape after the addition of the smallest one, whereas it lost its shape after the addition of the middle one. Their peak-to-valley values in the AMF images were similar to those of the individual PHIC samples. For the binary mixtures of PHIC with the highest mass and PVAc, the grain in the AFM image of the PHIC lost its shape after the addition of PVAc and it changed shape from a connected partial lost coil to an extended bundle rod with an increase in the PVAc component.     

Reaction of poly(vinyl chloride) with magnesium and grignard reagents

Reaction of poly(vinyl chloride) with magnesium under various conditions was attempted, but poly(vinyl chloride) did not react with magnesium. The reactions of poly(vinyl chloride) with benzylmagnesium chloride and allylmagnesium chloride as Grignard reagents were carried out in tetrahydrofuran at reflux temperature. It was found that the chlorine atoms in the poly(vinyl chloride) were replaced by benzyl and allyl groups by the coupling reaction, and a small amount of Grignard reagent of poly(vinyl chloride) was formed by the magnesium–halogen exchange reaction. The extent of the substitution increased with increasing reaction time and concentration of the Grignard reagent.     

Molecular properties of conjugates formed by synthetic hydrophilic polymers and sterically hindered phenols

Water-soluble conjugates are prepared via the chemical modification of poly(vinyl alcohol) and poly(ethylene glycol) by antioxidants taken from the family of sterically hindered phenols. The effects of the degree of substitution of conjugates on the dimensions of molecules and their aggregates are studied by viscometry and light scattering in dilute solutions. It is shown that an increase in the amount of antioxidant groups incorporated into the poly(vinyl alcohol) chain leads to a decrease in the dimensions of single conjugate molecules owing to attraction of hydrophobic groups. Poly(ethylene glycol) molecules carrying end groups of sterically hindered phenols form micellar aggregates that are absent in the solution of the initial polymer. The mean number of molecules involved in such an aggregate is 83. It is found that the presence of hydrophobic end groups in poly(ethylene glycol) molecules causes a sharp reduction in the lower critical solution temperature of a solution relative to that of the initial polymer.     

Graft copolymerization of methyl methacrylate to poly(vinyl alcohol) initiated by ferric ion-hydrogen peroxide system

The reaction occurring on treatment of samples of poly(vinyl alcohol) previously oxidized by sodium hypochlorite with ferric ion and hydrogen peroxide was studied. The graft copolymerization taking place on adding methyl methacrylate to the above system was also studied. Early in the reaction there was a period during which hydrogen peroxide was greatly reduced by the poly(vinyl alcohol), and this corresponded with a rapid cleavage reaction of the main chain of the polymer. Moreover, it was found that the reaction was quantitatively proportional to the formation of carbonyl groups in the sample. On the other hand, very few grafts were scarcely formed during this period; they formed by a mild reaction which took place immediately after this period. It seems that this behavior is quite different from that observed with the ceric ion initiating system. It is presumed that the formation of grafts is due to radicals formed by the cleavage of the main chain, and that the structure of the copolymer so formed is something like a block polymer.     

Poly(styrene/pentafluorostyrene)-block-poly(vinyl alcohol/vinylpyrrolidone) amphiphilic block copolymers for kinetic gas hydrate inhibitors: Synthesis,micellization behavior,and methane hydrate kinetic inhibition

Amphiphilic block copolymers of short poly(styrene) (PS) or poly(2,3,4,5,6-pentafluorostyrene) (PPFS) segments with comparatively longer poly(vinyl acetate) or poly(vinylpyrrolidone) (PVP) segments are synthesized using a 2-cyanopropan-2-yl N-methyl-N-(pyridin-4-yl)dithiocarbamate switchable reversible addition–fragmentation chain transfer (RAFT) agent toward application as kinetic gas hydrate inhibitors (KHIs). Polymerization conditions are optimized to provide water-soluble block copolymers by first polymerizing more activated monomers such as S and PFS to form a defined macro chain-transfer agent (linear degree of polymerization with conversion, comparatively low dispersity) followed by chain extensions with less activated monomers VAc or VP by switching to the deprotonated form of the RAFT agent. The critical micelle concentrations of these amphiphilic block copolymers (after VAc unit hydrolysis to vinyl alcohol units) are measured using zeta surface potential measurements to estimate physical behavior once mixed with the hydrates. A PS-poly(vinyl alcohol) block copolymer improved inhibition to 49% compared to the pure methane–water system with no KHIs. This inhibition was further reduced by 27% by substituting the PS with a more hydrophobic PPFS. A block copolymer of PS–PVP exhibited 20% greater inhibition than the PVP homopolymer and substituting PS with a more hydrophobic PPFS resulted in a 35% further decreased in methane KHI. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 2445–2457, 56, 2445–2457     

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%).     

Effects of functional groups on surface pressure-area isotherms of hydrophilic silicone polymers

Organic/inorganic hybrid silicone polymers are increasingly used in cosmetics, inks and paints, and fabric care applications owing to their special Si-O bond characteristics. Because of the presence of organic as well as inorganic groups, they show the properties of both, and the presence of hydrophobic as well as hydrophilic character makes them behave like a hybrid polymer. Though they are widely used, the utilization of hydrophilically modified silicones on a large scale has mainly been empirical due to lack of fundamental knowledge about variation in their properties with systematic change in their structure. The choice of moieties for hydrophilic modification of silicones in most of the earlier works has been nonionic based on ethylene oxide and propylene oxide groups, however, very little is known about their ionic counterparts. The current work focuses on understanding the behavior of functionally grafted silicone polymers with respect to the variation in the hydrophilic part of the grafting chain. Hydrophilically grafted silicone polymers form monolayers at the air-water interface, which are stabilized by interactions of functional groups with water. The present work examined the effects of functional group modifications on the conformational behavior of chains at the interface. It was observed that the shape of the chain depends on the available area at the interface (or surface pressure), and there are conformational changes with an increase in the number of molecules per unit area. While a poly(dimethylsiloxanes) (PDMS) chain may undergo stretched to helix transition as predicted earlier, this may not be the case for hydrophilically grafted chains. On the basis of the shape of the surface pressure-area isotherm and correlation with the scaling theory, a gradation in hydrophilicity of functional groups and hence modified silicone chains at the air-water interface is predicted.     

Relationship between reduction of ceric ion with poly(vinyl alcohol) and graft copolymerization

Various poly(vinyl alcohol) samples were preliminarily subjected to oxidation treatment with sodium hypochlorite, and the reduction of ceric ion and subsequently initiation in the graft copolymerization in the system containing methyl methacrylate were investigated. The reduction behavior of ceric ion could be subdivided into three parts, each of different reaction rate. In the initial stage of the reaction, there was observed rapid cleavage of the backbone chain of poly(vinyl alcohol) with ceric salts. The amount A of cleavage was proportional to the amount of ceric ion reduced at the initial fastest rate for various samples of different extents of oxidation; cleavage of 1 mole required ca. 10 moles of reduction of ceric ion. Higher carbonyl contents of the sample caused increased A. Graft polymerization was carried out in the same system with the addition of the monomer. The amounts of grafted chains produced were determined, and approximately one mole of grafted chains was obtained for per mole of cleavage. The copolymer is concluded to be blocklike in structure. The contribution of the carbonyl groups in poly(vinyl alcohol) sample to the initiation of the polymerization should be emphasized.     

Characterisation by X-ray photoelectron spectroscopy of surface layers of poly(vinyl alcohol) on particles formed by dispersion polymerisation of divinylbenzene

Well-defined dispersions of polydivinylbenzene in methanol and a binary liquid mixture of methanol and water were stabilised by samples of partially hydrolysed poly(vinyl alcohol) (PVOH). Mean particle diameters in the range 0.3–1.0 m were produced in dispersion polymerisations. In order to assess surface coverage by PVOH, alcohol groups in the stabilising surface layer were derivatised with trifluoroacetic anhydride. Characterisation of trifluoroacetate groups by X-ray photoelectron spectroscopy permits the quantitative determination of atomic fluorine. The relative concentrations of surface fluorine are in agreement with expectation based on the degrees of hydrolysis of 35 mol% and 72.5 mol% of the PVOH stabilisers. Treatments based on broadscan and high-resolution spectra permit reasonable estimates of the layer thickness for PVOH chains collapsed onto the surface of dry particles. Calculations of the area occupied per PVOH chain are consistent with estimates for other stabilising chains in hydrocarbon media.     

Long branching in poly(vinyl acetate) and poly(vinyl alcohol). II. Polymerization of vinyl acetate in the presence of crosslinked poly(vinyl alcohol)

It is a common view that poly(vinyl acetate) has many branches at the acetyl side group, but that the corresponding poly(vinyl alcohol) has little branching. In order to study the branching in poly(vinyl acetate) and poly(vinyl alcohol) which is formed by chain transfer to polymer, the polymerization of ¹⁴C-labeled vinyl acetate in the presence of crosslinked poly(vinyl acetate), which was able to be decrosslinked to give soluble polymers, was investigated at 60°C and 0°C. This system made it possible to separate as well as to distinguish the graft polymer from the newly polymerized homopolymer. Furthermore, the degree of grafting onto the acetoxymethyl group and onto the main chain were estimated. It became clear that, in the polymerization of vinyl acetate, chain transfer to the polymer main chain takes place about 2.4 times as frequently at 60°C as that to the acetoxy group and about 4.8 times as frequently at 0°C.     

An efficient approach to surface-initiated ring-opening metathesis polymerization of cyclooctadiene

Surface-initiated ring-opening metathesis polymerization of cyclooctadiene (COD), a low ring-strain olefin, is reported for the first time. Polymerization was carried out in the vapor phase, which is advantageous compared to conventional solution methods in terms of minimizing chain transfer by reducing polymer chain mobility at the vapor/solid interface. Attachments of a norbornenyl-containing silane and a Grubbs catalyst to silicon substrates were carried out before samples were exposed to COD vapor. The thickness of grafted 1,4-polybutadiene films was controlled by reaction time and reached approximately 40 nm after 7 h. The polymer films were further chemically modified to afford a new polymer, head-to-head poly(vinyl alcohol).     

Self-assembly of polystyrene-block-poly(ethylene oxide) copolymers at the air-water interface: is dewetting the genesis of surface aggregate formation?

Block copolymer self-assembly at the air-water interface is commonly regarded as a two-dimensional counterpart of equilibrium block copolymer self-assembly in solution and in the bulk; however, the present analysis of atomic force microscopy (AFM) and isotherm data at different spreading concentrations suggests a nonequilibrium mechanism for the formation of various polystyrene-b-poly(ethylene oxide) (PS-b-PEO) aggregates (spaghetti, dots, rings, and chainlike aggregates) at the air-water interface starting with an initial dewetting of the copolymer spreading solution from the water surface. We show that different spreading concentrations provide kinetic snapshots of various stages of self-assembly at the air-water interface as a result of different degrees of PS chain entanglements in the spreading solution. Two block copolymers are investigated: MW = 141k (11.4 wt % PEO) and MW = 185k (18.9 wt % PEO). Langmuir compression isotherms for the 185k sample deposited from a range of spreading concentrations (0.1-2.0 mg/mL) indicate less dense packing of copolymer chains within aggregate cores formed at lower spreading concentrations due to a competition between the interfacial adsorption of PEO blocks and the kinetic restrictions of PS chain entanglements. From AFM analysis of the transferred Langmuir-Blodgett films, it is clear that PS chain entanglements in the spreading solution also affect the morphological evolution of surface aggregates for both samples, with earlier structures being trapped at higher concentrations. At the highest spreading concentration for the 141k copolymer, the coexistence of long spaghetti aggregates with cellular arrays of holes, along with various transition structures, indicates that various surface aggregates evolve from networks of rims formed as a result of dewetting of the evaporating spreading solution from the water surface.     

Molecular architecture and physicochemical properties of some vinyl alcohol-vinyl acetate copolymers

Two series of vinyl alcohol-vinyl acetate copolymers were prepared by homogeneous and heterogeneous acetylation of the same precursor poly(vinyl alcohol). Their intramolecular monomer distributions were analyzed by IR spectrometry, calorimetry, and differential thermal analysis. The results show a more blocky distribution for the heterogeneously prepared copolymers. The properties of these (co)polymers in dilute aqueous solution were determined by means of viscometry. Whereas the copolymer-solvent interaction parameter of the homogeneously acetylated, random copolymers hardly varied with acetate content, a definite minimum was found for the blocky copolymers at about 7 mole% vinyl acetate. These findings were attributed to the incompatibility of dissimilar sequences, which sharply decreases with decreasing vinyl acetate sequence length. Up to about 17 mole% vinyl acetate content, the solvent quality for the copolymers is at least as good as for poly(vinyl alcohol). In addition, the dilute solution properties of the samples were established in water saturated with 1-butanol. For copolymers with up to about 17 mole% vinyl acetate, at 25°C this mixture is a better solvent than water. The highest increase in solvent quality was found for the homopolymer, whereas the increase diminished with acetate content, irrespective of the intramolecular vinyl acetate distribution. These findings are explained in terms of preferential adsorption of 1-butanol onto the (co)polymer backbone due to hydrophobic interactions and prevention of this process by the bulky acetate groups.     

Dynamic exchange of heterocyclic subunits during halogen substitution in chloroheptamethinecyanine dyes by benzoazolium salts

The chlorine atom present in the exocyclic conjugated bridge incorporated in the polymethine chain of heptamethinecyanine dyes can be easily replaced by a substituted 2-methylbenzoazolium salt. This reaction is promoted by residual water present in the reaction medium. This strategy was applied to the synthesis of a heptamethinecyanine dye possessing a vinyl group in the substituting heterocycle. Surprisingly, the expected monovinyl substituted dye was obtained along with di- and trisubstituted vinyl dyes. Such mixture can be, in principle, incorporated into an organic polymer monolith and used for affinity chromatography. This substitution reaction was investigated varying the nature of the benzoazole moiety of the chloroheptamethinecyanine dye and the substituting 2-methylbenzoazolium salt. A mechanism rationalizing the substitution pattern observed is proposed.     

Effect of the type of hydrogen bonding on the reactivity of hydroxyl groups in the acetalization of poly(vinyl alcohol) with butanal

The parameters of hydrogen bonds formed during acetalization of poly(vinyl alcohol) with butanal are determined via computer-simulation methods. It is shown that alcohol groups involved in the formation of intermolecular hydrogen bonds are the least active in acetalization reactions. The kinetics of the acetalization reactions in 2,4-pentanediol-water-butanal and (vinyl alcohol)-water-butanal systems are studied at various concentrations of alcohols that model a change in the ratio of hydrogen bonds of various types and are realized in the aqueous solutions of poly(vinyl alcohol) and poly(vinyl butyral). The calculated rate constants are in agreement with the computer-simulation-based order of reactivity of alcohol groups involved in hydrogen bonds of various types. It is proposed that the reactivity of residual alcohol groups in a poly(vinyl butyral) macromolecule should increase when a certain conversion of the polymer is attained.     

Design of composite films and ultrathin membranes of interpolymer complexes

The formation of stoichiometric interpolymer complexes (IPCs) between the poly(vinyl ether) of ethyleneglycol and the copolymer of acrylic acid–butyl vinyl ether, between copolymers of vinyl ether of ethyleneglycol–butyl vinyl ether, and the copolymer of acrylic acid–vinylbutyl ether is demonstrated by conductimetric, potentiometric, viscometric and spectroturbidimetric methods in aqueous solution. The swelling/deswelling behavior of composite films derived from the IPC has been studied in water, alcohol and water–alcohol mixtures, depending on various factors. The formation of polyelectrolyte complexes (PECs) between the copolymer of acrylic acid–vinyl butyl ether and poly(vinyl ether of monoethanolamine) on a dimeric interface of water–butanol has been studied by the potentiometric method. The kinetics of PEC formation on a dimeric interface was measured and the activation energy of this process was calculated. Copyright © 2000 John Wiley & Sons, Ltd.     

From linear side-chain functionalized poly(vinyl ether)s to functional macrocycles

This paper deals with the synthesis of functional polymers of controlled chain dimensions and architecture from poly(chloroalky1 vinyl ether)s. The living polymerization of chloroalkyl vinyl ethers initiated by HX/ZnX₂ systems, and the chemical substitution of the pendant chlorines by various organic functions and groups, in order to generate specific polymer properties are first discussed. Also based on the living character of the polymerizations, the preparation of poly(chloroethyl vinyl ether) with monomacrocyclic and plurimacrocyclic architectures as well as their characterization are then reported. Some evidence for specific host–guest interactions between large organic molecules and polymacrocycles is also presented.