Nuclear magnetic resonance studies on microstructure of ethylene copolymers. VI. Carbon-13 spectra of ethylene–vinyl acetate copolymers

The 22.6-MHz Fourier-transform noise-decoupled ¹³C (carbon-13) NMR spectra of several ethylene–vinyl acetate (E–VA) copolymers were obtained. We found that triad information on monomer placement can be deduced from carbonyl resonances, triad and pentad information can be deduced from methine carbon resonances, and triad information is available from the methylene carbon resonances. The random comonomer distributions in E–VA polymerizations were demonstrated up to pentad placements. In addition, the use of model-compound data in the analysis of copolymer spectra was shown.     

Reactivity differences between isolated and vicinal vinyl acetate functions in high pressure ethylene/vinyl acetate copolymers

Three ethylene/vinyl acetate copolymers (3.5, 12.0 and 18.8 mol% VA; average melt index 8.5 g/10 min) were transformed into ethylene/vinyl alcohol copolymers and ethylene/vinyl alcohol/vinyl acetate terpolymers by homogeneous saponification. The reaction rate increased with mol% VA. This feature originated in the reactivity differences beteen vicinal and isolated VA functions. Simultaneous steric and polarity effects caused the reaction rate differences. ¹H-NMR, i.r., dielectric measurements and additional saponification reactions confirmed the difference of reactivity.     

Structure and property relationships in ethylene–vinyl acetate copolymers

The effects of vinyl acetate content on crystallinity of ethylene–vinyl acetate (E/VA) copolymers were investigated by x-ray diffraction and differential thermal analysis (DTA). The values of these parameters obtained from DTA were found to agree quantitatively with data calculated from x-ray, probability equations, and copolymer theory. The melting points of the crystalline copolymers, and the molar amounts of vinyl acetate to produce a completely amorphous rubber corresponds exactly to that predicted by the Flory theory. The random character expected in E/VA copolymers is thereby confirmed. The physical properties of E/VA copolymers of all ranges of compositions and crystallinity were determined. Depending directly upon vinyl acetate content, the copolymers changed progressively from highly crystalline polyethylene to semicrystalline polyethylene, a completely amorphous rubber, a soft plastic with a glass transition near room temperature. Properties which were correlated with copolymer composition include: crystallinity, melting point, density, modulus, tensile strength, glass transition, and solubility. Finally, the effect on crystallinity and physical properties of replacing the acetoxy group in E/VA with the smaller, highly polar hydroxyl group (ethylene—vinyl alcohol copolymer) was also investigated.     

The effects of overall composition and monomer sequence distribution on the infrared carbonyl stretching frequencies of ethylene–vinylacetate and styrene–vinylacetate copolymers

The vinyl acetate centered triad fractions of some free radically prepared ethylene–vinyl acetate and styrene–vinyl acetate copolymers have been determined from the patterns of vinyl acetate methine carbon peaks in their ¹³C nuclear magnetic resonance (NMR) spectra. The positions and shapes of the carbonyl bands in the infrared (IR) absorption spectra of the copolymers recorded in chloroform are shown to depend on the compositions of the copolymers and on the proportions of the various vinyl acetate centered triads. Infrared absorption measurements may thus be used in part to characterize the monomer sequence distributions of these copolymers.     

Grafting of polycaprolactone onto poly(ethylene‐co‐vinyl alcohol) and application to polyethylene‐based bioerodable blends

Poly(ethylene‐co‐vinyl acetate) (EVA) powders containing 10 and 20 wt % of vinyl acetate (VAc) units was saponified in ethanol/KOH solution in a heterogeneous manner. Intermolecular interaction between vinyl alcohol(VOH) units in the produced poly(ethylene‐co‐vinyl alcohol) (EVOH) promoted the crystallization of intervening segments composed of ethylene units. Ring opening polymerization of caprolactone (CL) in the presence of EVOH gave EVOH‐g‐PCL graft copolymers with relatively short chain branches. Even though the graft copolymerization was carried out in a homogeneous solution, all the VOH units were not equally reactive for the PCL grafting. And the unreacted VOH units decreased very slowly with the graft copolymerization time. EVOH‐g‐PCL decreased the domain size of the dispersed phase in low density polyethylene (PE)/biodegradable master batch (MB) blends, and thus increased their tensile properties significantly. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2561–2569, 2002     

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.     

Multidimensional chromatographic techniques for hydrophilic copolymers II. Analysis of poly(ethylene glycol)-poly(vinyl acetate) graft copolymers

A large variety of hydrophilic copolymers is applied in different fields of chemical industry including bio, pharma and pharmaceutical applications. For example, poly(ethylene glycol)-poly(vinyl alcohol) graft copolymers that are used as tablet coatings are responsible for the controlled release of the active compounds. These copolymers are produced by grafting of vinyl acetate onto polyethylene glycol (PEG) and subsequent hydrolysis of the poly(ethylene glycol)-poly(vinyl acetate) graft copolymers. The poly(ethylene glycol)-poly(vinyl acetate) copolymers are distributed with regard to molar mass and chemical composition. In addition, they frequently contain the homopolymers polyethylene glycol and polyvinyl acetate. The comprehensive analysis of such complex systems requires hyphenated analytical techniques, including two-dimensional liquid chromatography and combined LC and nuclear magnetic resonance spectroscopy. The development and application of these techniques are discussed in the present paper.     

Block copolymers derived from azobiscyanopentanoic acid. X. Synthesis of silicone–vinyl block copolymers via polysiloxane(azobiscyanopentanamide)s

The synthesis of silicone–vinyl block copolymers has been studied by the use of poly(azo-containing siloxaneamide)s (abbreviated as PASAs), i.e., polysiloxane (azobiscyanopentanamide)s as macroazoinitiators. PASAs with number-average molecular weight of 12000–31000 and with siloxane chain lengths of 250–9800 were prepared by the condensation of azobiscyanopentanoyl chloride and α,ω-bis(3-aminopropyldimethyl)polysiloxanes in equimolar feeds. Several kinds of silicone–vinyl block copolymers were synthesized by radical polymerization of vinyl monomers such as methyl methacrylate, styrene, and vinyl acetate, in the presence of PASA in homogeneous media. The block copolymers with siloxane contents up to 30 mol % were then characterized on the basis of infrared absorption, proton NMR spectra, and gel permeation chromatography.     

Alternating ethylene–alkyl acrylate copolymers. II. Polymer properties

Properties such as viscosity correlations and spectral data of alternating ethylene–ethyl acrylate copolymers are described. The proton and ¹³C-NMR spectra show that there is a considerable amount of tacticity in these polymers. Although the alternating configuration predominates, there is also some random structure present. Terpolymers were prepared with cure-site monomers, such as 2-chloroethyl acrylate. The terpolymers were compounded with carbon black and cured to give vulcanizates with excellent properties. The cured products are resistant to oil, water, heat, and oxidation. They also have good low temperature properties (stiffening temperature ?31°C, brittleness temperature ?50°C), tensile properties (tensile strength 17.2 MPa, elongation at break 250%) and compression sets (25% at 150°C for 70 hr).     

Solution properties of ethylene-vinyl acetate copolymers

High-pressure ethylene–vinyl acetate copolymers of four different chemical compositions(9%, 15%, 45%, and 70% VA) were characterized to determine molecular weight and distribution. The four samples were fractionated by solvent–nonsolvent precipitation methods. Light-scattering, osmometry, and viscosity measurements were made on these fractionated copolymers to determine weight-average molecular weight \documentclass{article}\pagestyle{empty}\begin{document}$ \overline {M_w } $\end{document}, number-average molecular weight \documentclass{article}\pagestyle{empty}\begin{document}$ \overline {M_n } $\end{document}, molecular size in solution, and interaction constants. Dilute solution viscosity was measured on the fractions to determine intrinsic viscosity and Huggins' constant k′. Viscosity–molecular weight equations were established for the four copolymer compositions. The log intrinsic viscosity versus log molecular weight diagrams were analyzed and the average length of branches calculated. The composition of the polymer fractions, determined by C and H combustion analysis, was found not to vary significantly with molecular weight. The uniformly random character of the E/VA copolymers was thereby confirmed. The density of the fractions was determined by density-gradient column method. Chain sequence distribution of monomer units for the four copolymers was calculated by using IBM 704 computations involving the actual monomer reactivity ratios. Long sequences of either ethylene or vinyl acetate are improbable, except at the extremes of copolymer composition.     

Permeation of water through polar and nonpolar polymers and copolymers: Determination of the concentration‐dependent diffusion coefficient

The diffusion and permeation properties of liquid water through different polar and nonpolar polymers and copolymers were studied with a highly sensitive permeameter. The transient permeation fluxes through the polar polymer films could be fitted well only with an exponential equation for the diffusivity concentration dependence; this empirical exponential equation represented the diffusion plasticization effect of water on the materials. For the hydrophobic polyolefins, this exponential equation was no longer valid, and another form of the equation was empirically found to account for the reduction of the water diffusivity with the extent of the permeation. Such a negative plasticization effect might be attributed to the formation of water clusters in the polyolefins. The values of the diffusion coefficient of water in the dry polar polymers were smaller than those in dry polyolefins, but the opposite behavior was found for the permeability because it was much more favorable for water sorption in the polar polymers than in the hydrophobic polyolefins. For the ethylene–vinylacetate copolymers, the plasticization effect of water on its own diffusion was negative for the sample with a low vinyl acetate (VA) content; it became nil at 19 wt % VA and positive at higher VA contents. This increase in the extent of the water sorption with the increase in the VA content led to a steady increase in the water permeability in the poly(ethylene‐co‐vinylacetate) copolymers. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1998–2008, 2000     

Discrimination of ethylene/vinyl acetate copolymers with different composition and prediction of the content of vinyl acetate in the copolymers and their melting points by near-infrared spectroscopy and chemometrics

Near-infrared (NIR) diffuse reflectance spectra have been measured by use of a rotating drawer for pellets of 12 kinds of ethylene/vinyl acetate (EVA) copolymers with vinyl acetate (VA, the comonomer) varying in the 7–44 wt % range. They are unambiguously discriminated from one another by a score plot of the principal component analysis (PCA) Factor 1 and 2, based upon the NIR spectra pretreated by multiplicative scatter correction (MSC). Principal component (PC) weight loadings for Factor 1 show that the discrimination relies largely upon bands due to the overtone and combination modes arising from the VA unit. We have found one “outlier” in the score plot and elucidated its spectral characteristics based upon PC weight loadings for Factor 2. Partial least-squares (PLS) regression has been applied to propose calibration models which predict the VA content in EVA. The models have been prepared for three kinds of pretreatment, the first derivative, the second derivative, and MSC; and four kinds of wavelength regions. The NIR spectra in the 1100–2200 nm region after the MSC treatment has given the best correlation coefficient and standard error of prediction (SEP) of 0.998 and 0.70%, respectively. The calibration models, prepared by NIR diffuse reflectance spectroscopy for the pellet samples, are compared with previously reported models by NIR transmission spectroscopy for the flowing molten samples, and with those by Raman spectroscopy for the pellet samples. PLS regression has also allowed us to predict melting points of the copolymers with the correlation coefficient and SEP of 0.997 and 0.78°C, respectively. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1529–1537, 1998     

The effect of residual acetate groups on the structure and properties of vinyl alcohol–ethylene copolymers

Vinyl alcohol–ethylene (VAE) copolymers, commercially manufactured by hydrolysis of the corresponding vinyl acetate–ethylene copolymers, can contain small amounts of unhydrolyzed vinyl acetate. This article shows the influence of these residual groups on the structure of the resulting copolymers, studied by nuclear magnetic resonance and wide‐angle X‐ray scattering. Thermal and mechanical properties of these materials were investigated by differential scanning calorimetry, thermogravimetry, drawing behavior, birefringence measurements, and dynamic mechanical analysis. The structure of the copolymers is considerably affected by the volume of the residual acetate groups, bigger than that of the hydroxyl ones, which hinders the crystallization process. In relation to the thermal and mechanical properties, the temperature and enthalpy of melting as well as the Young's modulus and yield stress, decrease as vinyl acetate molar fraction increases. Moreover, the α and β relaxations are shifted to lower temperatures as residual content in the copolymer is raised. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 573–583, 2000     

The thermal degradation of copolymers of vinyl acetate with methyl methacrylate and other monomers

The thermal degradation of copolymers of vinyl acetate with methyl methacrylate, styrene and ethylene has been investigated using thermal volatilization analysis and thermogravimetry, together with analysis of volatile and involatile degradation products. All three copolymer systems show some of the features characteristic of the homopolymers of the monomers concerned. There is evidence, however, for an intramolecular lactonization process in VA—MMA copolymers, involving reaction of adjacent VA and MMA units with elimination of methyl acetate. This reaction occurs less readily than the analogous process in vinyl chloride—MMA copolymers. Mechanisms of the various degradation reactions are discussed.     

High‐molecular‐weight symmetrical multiblock copolymers: Synthesis by RAFT polymerization and characterization

High‐molecular‐weight (MW) symmetrical multiblock copolymers, based on the hydrophobic monomers styrene (Sty) and methyl methacrylate (MMA), and the more polar monomer, 2‐vinyl pyridine (2VPy), were prepared using stepwise reversible addition‐fragmentation chain transfer polymerization. All copolymers shared a common poly(ethylene glycol) (PEG) midblock, introduced as a bifunctional macromolecular chain transfer agent. In total, five ABA triblock copolymers, five ABCBA pentablock terpolymers, and two ABCDCBA heptablock quaterpolymers (comprising four different monomer types) were synthesized. The MWs of the multiblock polymers were determined using gel permeation chromatography (GPC) and proton nuclear magnetic resonance (¹H NMR) spectroscopy, with the latter values being closer to the theoretically expected, whereas GPC MW distributions were relatively narrow, broadening with the number of blocks. The compositions of the synthesized polymers, as determined by ¹H NMR spectroscopy, were also close to the expected values. Finally, films cast from chloroform solutions of the pentablock terpolymers P2VPy‐b‐PSty‐b‐PEG‐b‐PSty‐b‐P2VPy, PSty‐b‐PMMA‐b‐PEG‐b‐PMMA‐b‐PSty, and P2VPy‐b‐PMMA‐b‐PEG‐b‐PMMA‐b‐P2VPy examined using transmission electron microscopy exhibited PSty and PMMA cylinders (first two) and lamellae (third terpolymer). © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4957–4965     

Block copolymers of poly(ethylene oxide) and poly(vinyl alcohol) synthesized by the RAFT methodology

A methodology for the synthesis of well‐defined poly(ethylene oxide)‐block‐poly(vinyl alcohol) (PEO‐b‐PVA) and PVA‐b‐PEO‐b‐PVA polymers was reported. Novel xanthate end‐functionalized PEOs were synthesized by a series of end‐group transformations. They were then used to mediate the reversible addition–fragmentation chain transfer polymerization of vinyl acetate to obtain well‐defined poly(ethylene oxide)‐b‐poly(vinyl acetate) (PEO‐b‐PVAc) and PVAc‐b‐PEO‐b‐PVAc. When these block copolymers were directly hydrolyzed in methanol solution of sodium hydroxide, polymers with brown color were obtained, which was due to the formation of conjugated unsaturated aldehyde structures. To circumvent these side reactions, the xanthate groups were removed by adding a primary amine before hydrolysis and the products thus obtained were white powders. The polymers were characterized by gel permeation chromatography, ¹H NMR spectroscopy and FT‐IR. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1901–1910, 2009     

Ethylene copolymers with Fischer-Tropsch olefins

The properties of ethylene copolymers, terpolymers and multipolymers prepared with even and uneven carbon number linear and branched α-olefins were compared. The most likely microstructures of ethylene/linear α-olefin copolymers was assigned by considering co-unit bulkiness, average crystallizable sequence lengths and thermal properties. The higher α-olefins were found to be more effective at decreasing density, but peak melting temperatures were higher. In terpolymers where lower α-olefins such as 1-butene and 1-pentene were used as comonomers, density was decreased more than the mathematical average expected from the ratio of comonomers in the terpolymers. Peak melting temperatures were also lower. Based on NMR evidence and the microstructures of the different copolymers the rationale for this occurrence could be ascribed to decreased clustering for these terpolymers. Branched α-olefins produced ethylene co- and terpolymers with significantly decreased densities as compared to the linear α-olefins. Impact strength of these polymers was also substantially higher, even at low comonomer content. Thermal evidence indicates that the microstructure of the co- and terpolymers containing branched α-olefins are very similar to that of the copolymers prepared with linear α-olefins of the same carbon number.     

Thermal properties of copolymers of 2‐Acrylamido‐2‐methylpropanesulphonic acid with some vinyl monomers

2‐Acrylamido‐2‐methylpropanesulphonic acid (AMPS) was copolymerized with both acrylic acid (AA) and vinyl acetate (VA) at different compositions. The thermal behaviors of the resulted copolymers, PAMPS, PAA and PVA were studied using thermogravimetric analyses. In all cases of homopolymers and copolymers, there are two degradation stages. The observed enhancement of the thermal properties of the copolymers compared with that of PAMPS are attributed to intramolecular cyclization reactions and ring formations. The apparent activation energies of the decomposition were determined and correlated to the sequence of the thermal stabilities of the various polymers.     

13C-NMR study of chlorinated ethylene–vinyl acetate copolymers

¹³C-NMR has been used to analyze the microstructures of a series of experimental chlorinated ethylene–vinyl acetate copolymers (15–56% CI). Previously established line assignments for EVA copolymers and substituent effect parameters for chlorine have enabled us to tentatively assign partial structures up to five carbon atoms in length. The ¹³C-NMR analyses of a commercial vinyl chloride–vinyl acetate copolymer, a commercial vinyl chloride–vinyl acetate–ethylene terpolymer, and a commercial chlorinated polyethylene support the structural assignments. Data obtained for the experimental resins indicate that the acetate groups influence the way in which chlorine is added to the polymer chain. furthermore, the data indicate the acetate groups undergo little, if any, chlorination.     

Thermal degradation of vinyl alcohol/vinyl acetate copolymers. III. Study of the reaction products

The thermal decomposition of vinyl alcohol/vinyl acetate copolymers have been studied at p = 10⁻²–10⁻⁴ Torr and T = 0–600°C. The decomposition products (solids, liquids, and gases) have been characterized by infrared (IR) and ultraviolet (UV) spectroscopy, gas chromatography, vapor pressure osmometry, and elemental analysis. It has been ascertained on the basis of the obtained data that the decomposition mechanism of the vinyl alcohol/vinyl acetate copolymers depends on the chemical composition and sequence distribution of comonomers.