Poly(vinyl alcohol) modification with n-alkyl chloroformates

This work deals with the modification reaction of poly(vinyl alcohol) with n-alkyl chloroformates using pyridine as catalyst. The structure of the modified polymers was determined by means of IR, ¹H and ¹³C-NMR spectroscopy as well as by chemical analysis. Vinyl alcohol-vinyl n-alkyl carbonate copolymers were obtained. The presence of cyclic carbonates has not been observed. It has been found a linear dependence of reaction rate on polymer, n-alkyl chloroformates, and pyridine concentrations, respectively. The activation energy found was of 15.4 kcal/mol. The water absorbed in the copolymers made it reasonable to conclude that the hydrophilic character of the copolymers decreased progressively when either the carbonate groups content or the side chain length increased. Water insoluble alcohol-vinyl n-alkyl carbonate copolymers were hydrolyzed in an alkaline medium. They were found to recover their solubility in water after a certain hydrolysis extent was reached.     

Packing mode and conformational transition of alkyl side chains in N-alkylated poly(p-benzamide) comb-like polymer

A series of rigid-rod poly(p-benzamide) polymers (PBA) with different length of flexible alkyl side chains, denoted as PBA(n)Cs, have been prepared by N-alkylation method. The alkyl side chain lengths varied from decyl (n=10) to octadecyl (n=18), with an interval of two carbon atoms. The packing mode and conformational transition of the alkyl side chains of the prepared PBA derivatives were characterized by wide-angle X-ray diffraction (WAXD), differential scanning calorimertry (DSC), and Fourier transform infrared spectroscopy (FTIR). WAXD results revealed that the derivatives form layered structure in which the distance between the backbones depends on the length of alkyl side chains. DSC studies indicated that melting transition temperature of PBA(n)Cs increases accordingly with increasing the alkyl chain length of the substituents. Meanwhile, DSC results proved that as the carbon atom number of the side group exceeds 14, alkyl side chains in PBA(n)Cs tend to crystallize FTIR spectroscopic investigation showed that the all-trans zigzag conformation is the most stable state for the alkyl side chain in PBA18C comb-like polymer. Temperature variation caused the reversible transition between trans and gauche conformational states of the side octadecyl group, and in turn made the molecular chain packing mode of PBA18C comb-like polymer undergo an reversible transformation from ordered packing to disordered packing.     

Electrosynthesis and spectroelectrochemical characterization of poly(3,4-dimethoxy-thiophene), poly(3,4-dipropyloxythiophene) and poly(3,4-dioctyloxythiophene) films

Poly(3,4-dialkoxythiophene) films with different length of alkyl chain (1,3 and 8 carbon atoms) were obtained on Pt and ITO electrodes from the monomer solutions in acetonitrile by cyclic voltammetry (CV). The properties of the resulting films were studied by electrochemical methods, UV-Vis, FTIR and NMR spectra. The CVs were correlated with differential cyclic voltabsorptograms (DCVA) recorded at the absorption maxima to explain the shape of the voltammograms of the polymers studied, dependent on the alkyl-chain length in alkoxy group. The presence of the zones of different crystallinity in the polymer film was postulated. Significant influence of the type of the solvent on asymmetry of the cyclic voltammograms for the polymer doping-undoping has been discussed in terms of the solvent interaction with radical cation (polaron) delocalized on the alkoxy side groups. The polaron delocalization was proved by ¹H-NMR spectra. Appearance of infrared activated vibrations (IRAVs) in the range 1500-600 cm⁻¹ and a characteristic electronic band at 3300 cm⁻¹ at the polarization potential +0.25 V versus Ag/Ag⁺ and their gradual changes upon further polymer oxidation were interpreted in terms of evolution of different charge carriers in lightly and heavily doped polymer.     

The critical organic modifier aliphatic tail length for the formation of poly(methyl methacrylate)-montmorillonite nanocomposites

In this article, we report the influence of organic modifier structure (alkyl chain length C8-C20, single vs ditallow) and thereby, the effect of hydrophobicity on the structure, thermal and mechanical properties of poly(methyl methacrylate) (PMMA)-clay hybrids. Melt processed PMMA-clay hybrids were characterized using wide-angle X-ray diffraction, transmission electron microscopy, and differential scanning calorimetry. The organoclays having an alkyl chain length of more than 12 CH₂ groups resulted in the formation of nanocomposites. The glass transition temperature (T_g) of PMMA increased in the presence of clay. The mean-field lattice model was used to predict the free energy for nanocomposite formation, which showed a reasonable match with the experimental results and provided a general guideline for the proper selection of polymer and organoclay (ie, organic modifier) to obtain nanocomposite. Tensile modulus showed maximum improvement of 58% for the nanocomposites compared to 9% improvement for the composites. Tensile modulus increased with increases in the alkyl chain length of the organic modifier and clay loading. The level of improvement for the tensile properties of nanocomposites prepared from primary and secondary ammonium-modified clay is the same as that obtained with the commercial organoclays.     

Surface properties for poly(perfluoroalkylethyl methacrylate)/poly(n-alkyl methacrylate)s mixtures

A poly(perfluoroalkylethyl methacrylate) and a series of poly(n-alkyl methacrylate)s such as poly(methyl methacrylate), poly(ethyl methacrylate), and poly(n-butyl methacrylate) were prepared and used to investigate the surface properties of polymer mixtures containing a fluorinated homopolymer and a nonfluorinated homopolymer and the effect of the side-chain length of poly(n-alkyl methacrylate) on the surface free energy for the polymer mixtures. Contact angles were measured for the surfaces of polymer mixtures by varying the concentration of poly(perfluoroalkylethyl methacrylate). From the contact angle data, it can be inferred that most of the poly(perfluoroalkylethyl methacrylate) added to poly(n-alkyl methacrylate)s is located in the outermost layer of polymer-mixture surface. Surface free energies for the outermost surfaces of polymer mixtures were calculated from the contact angle data using Owen and Wendt's equation. The decrease in the surface free energy for the polymer mixture with the poly(perfluoroalkylethyl methacrylate) addition is more pronounced as the side-chain length of poly(n-alkyl methacrylate) decreases. Due to the steric effect of the side chain of poly(n-alkyl methacrylate), the arrangement of the perfluoroalkylethyl group of poly(perfluoroalkylethyl methacrylate) to the air side is considerably hindered. The ESCA analysis of atomic compositions of the surface for the polymer mixture verified that poly(perfluoroalkylethyl methacrylate) is preferentially arranged and concentrates at the polymer mixture–air interface. The results of functional group compositions obtained by ESCA showed that the functional group composition of  CF₃ for the outermost layer has a more important effect on the surface free energy than that of  CF₂ and confirmed the hindrance of the arrangement of perfluoroalkylethyl group to the air side by the side chain of poly(n-alkyl methacrylate). © 1994 John Wiley & Sons, Inc.     

Permeability of water vapor and carbon dioxide gas through poly(n-alkyl L-glutamate)

To elucidate the permeation mechanism in polypeptide membranes, permeation of water vapor and carbon dioxide gas through a series of poly(n-alkyl L -glutamate) (polymers of methyl, ethyl, propyl, butyl, amyl, hexyl, and octyl glutamate) were studied. It was confirmed that diffusion of small molecular substances in polypeptides takes place through the side chain region between helices. The diffusion coefficient of carbon dioxide gas increases with increase in side chain length. As for water vapor, the diffusion coefficient is highest with poly(n-butyl glutamate), and the clustering effect of water may contribute to the diffusion coefficient with increase in the hydrophobic nature of the polymer.     

Dynamic mechanical analysis of barium ferrite magnetic tapes with aramid and poly(ethylene naphthalate) substrates

Frequency‐ and temperature‐dependent viscoelastic characteristics of advanced materials used for high‐capacity digital magnetic tapes were analyzed using a custom ultra‐low frequency dynamic mechanical analyzer (ULDMA). The magnetic tapes studied both use barium ferrite (BaFe) magnetic particles. One tape uses an aromatic poly(amide) or aramid substrate, and the other tape uses a poly(ethylene naphthalate) or PEN substrate. ULDMA studies were performed for both types of tape materials using samples cut from reels and the substrates after the front and back coats were removed. Two‐hour experiments were performed at 25, 30, 50, and 70°C temperatures, and four test frequencies were used at each temperature: 0.006, 0.010, 0.033, and 0.065 Hz. Properties determined were the peak strain‐based elastic modulus, E, and the storage modulus, E′, loss modulus, E″, loss tangent, tan(δ), complex modulus, E*, and complex loss, E″/E*, expressed as a percentage. When compared with the PEN tape and substrate materials, the peak elastic modulus, storage modulus, and complex modulus were higher for the aramid materials. Substrates for each material exhibited higher elastic, storage, and complex moduli compared with their respective tapes. Through the complex loss percentage, comparisons were made between the aramid and PEN materials related to their viscoelastic characteristics. Finally, the influence of frequency was shown to have increasing relevance at higher temperatures, with the PEN tape and substrate exhibiting an increase in complex loss modulus in the 50°C range because of the β* secondary transition. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41478.     

Fabrication and properties of composites from BST and polypropylene-graft-poly(styrene-stat-divinylbenzene)

In this work, ceramic–polymer composites were fabricated from barium strontium titanate powder (BST) and polypropylene-graft-poly(styrene-stat-divinylbenzene) (ER) using a twin-screw extruder. The compounding process was characterized by rheological measurements. The effects of volume loading of BST on dielectric and mechanical properties were investigated. The dielectric properties were measured as a function of frequency and BST loading. For example, the relative permittivity and loss tangent (tan δ) of the BST–ER composites at 1 GHz were gradually increased from 2.4 and 0.0001 to 28.5 and 0.0085, respectively, as the loading was increased from 0 to 50.5 vol.%. Stearic acid (StA) was used as a surface-modifier of the BST. With an approximate surface coverage of 83%, an improvement in processability and a slight increase of the permittivity was observed, while tan δ remained low. The excellent dielectric characteristics of these composites, with high permittivity and low tan δ, make them attractive novel electronic materials for high frequency applications.     

Comparative study on the phase transitions in PZT-based ceramics by mechanical and dielectric analyses

This paper investigated the low-frequency mechanical properties of ferroelectric ceramics (PZT-5H and PZT-8) and anti-ferroelectric ceramics ((Pb_0.97?xBa_xLa_0.02)(Zr_0.50Ti_0.10Sn_0.40)O₃, x = 0.08, 0.09, 0.10, 0.11) by a dynamic mechanical analyzer (DMA). The dynamic mechanical analysis was performed from ?100 to 400 °C in temperature and 0.1–4 Hz in frequency. The dielectric properties were also measured as a comparison. The results showed an obvious turning point (T_m) where tan δ reached its maximum and the modulus began to increase for all the samples. tan δ revealed an relaxation region in the ferroelectric ceramics and no corresponding region in the anti-ferroelectric ceramics, which may be originated from the domain walls’ motion in the ceramic. The tan δ started to decrease to nearly zero around the tetragonal to cubic phase transition temperature (T_c) for all of the tested samples.     

Low temperature internal friction in some poly(α-olefins)

1 Hz internal friction experiments have been carried out using a torsion pendulum. The temperature range was between 4 and 100K. The existence of a very low temperature δ peak has been studied in poly(α-olefins)

where n = 0–3. Polyethylenes have been studied in the same way. Evidence has been given for the existence of a low temperature peak coming from the presence of nitrogen or air. After purification we obtained $\text{ΔW}\text{W}$ against temperature curves without a δ peak for polyethylene and polypropylene samples. Evidence has been given for the existence of such δ peaks in polypentene and polyhexene. A possible mechanism involving the rotation of the alkyl group is proposed.     

Modification of gel-drawn poly(vinyl alcohol) fibers with formaldehyde

Poly(vinyl alcohol) fibers which were drawn from dried gels were chemically treated with formaldehyde to induce crosslinking in the amorphous phase. The room temperature storage modulus decreased early in the treatment, to an almost constant value of 50–60% of the initial modulus of the fiber. This behavior was independent of the concentration of formaldehyde used. The modulus at low temperature was also reduced, and no T_g peak could be seen in heavily treated fibers. The modulus above the original T_g, 70°C, was much less affected. The crystallinity determined by DSC fell by one third as the room temperature modulus decreased, and X-ray diffraction indicated a reduction in the crystal length along the chain direction at the same time. Thus, under the conditions of treatment used, the loss of properties due to destruction of crystals outweighs the stiffening and reduced water sensitivity of the crosslinked amorphous phase.     

Dynamic mechanical analysis of fibre‐reinforced plastic composites based on carboxyl terminated poly(ethylene glycol) adipate modified epoxy and E glass fibre

Fibre reinforced plastic (FRP) composites prepared from E glass woven fabrics as reinforcing agent and carboxyl terminated poly(ethylene glycol) adipate (CTPEGA) modified epoxy as a matrix, were subjected to dynamic mechanical thermal analysis at a fixed frequency of 5 Hz. The volume fraction of glass was about 0.45. The concentration of CTPEGA in the matrix was varied gradually from 0 to 40 phr (phr stands for parts per hundred parts of resin), to investigate the effect of CTPEGA concentration on the dynamic properties of the composites. It was found that the tan δ peak temperature and storage modulus gradually decrease with incorporation of CTPEGA. However, the tan δ peak value increases up to 20 phr of CTPEGA concentration and decreases thereafter. The same trend was obtained in the case of impact strength. © 2000 Society of Chemical Industry     

Structure and properties of hydrophobic cationic poly(vinyl alcohol)

A new class of derivatives of poly(vinyl alcohol) (PVA) was prepared through hydrophobic cationic modification. The structure and composition of PVA grafted with glycidyl‐N‐alkyl‐N,N‐dimethyl‐ammonium chloride (DA) (PVA‐ graft ‐DA) was confirmed with Fourier transform infrared spectral analysis and ¹H NMR spectral analysis. The stress‐strain curves of PVA‐ graft ‐DA samples all exhibited an elastic deformation stress plateau, and strain hardening behavior can be observed, indicating the transition of PVA from brittle fracture to ductile fracture. Compared with virgin PVA, the relaxation peak (T_g) of PVA‐ graft ‐DA shifted to a lower temperature. With increasing alkyl chain length and grafting ratio of DA, T_g decreased, and PVA‐ graft ‐DA exhibited a gradually decreasing storage modulus over the whole temperature range of testing due to the relatively weak intermolecular hydrogen bonding and increasing flexibility of molecular chains by introduction of long alkyl chains. PVA crystallites were not affected by grafting with DA, while the crystallization temperature and crystallinity of PVA were improved and the grain size decreased. On grafting with DA, the fracture surface of PVA changed from a smooth surface to regularly distanced striations, displaying much obvious character of tough fracture, indicating that appropriate intermolecular association of the hydrophobic groups facilitated the formation of physical entanglement of molecular chains to strengthen and toughen the PVA matrix. PVA‐ graft ‐DA showed a significant decreasing surface tension with polymer concentration, while the surface tension of PVA‐ graft ‐DA12 dropped most dramatically and declined with increasing grafting ratio of DA12, indicating improvement of the surface activity of PVA by introduction of hydrophobic alkyl chains and hydrophilic cationic groups. Copyright © 2011 Society of Chemical Industry     

Dynamic mechanical properties of polyimide/poly(silsesquioxane)‐like hybrid films

Polyimide/poly(silsesquioxane)‐like (PI/PSSQ‐like) films have three‐dimensional structure with linear PI blocks and a crosslinked PSSQ‐like structure. They have higher thermal stability and char yields than pure PI from 4,4′‐diaminodiphenyl ether and 3, 3′‐oxydiphthalic anhydride (ODPA). In a series of X‐PIS [PI modified with p‐aminophenyltrimethoxysilane (APTS), where X is the molecular weight of each PI block] hybrid films, decreasing the PI block chain length enhances the storage modulus, tensile modulus, and glass‐transition temperature (T_g) but reduces the α‐relaxation damping peak intensity, density, and elongation. The change in the former three properties may be caused by an increase in the crosslinking density and rigidity of the network structure. The changes in the next two properties are caused by an increase in the free volume or the PI interblock separation and decreases in the interblock PI chain interaction. The change in the last property (i.e., a decrease in elongation) is related to the increase in the rigidity of the network structure. The activation energy of the α transition depends on the chain length of the PI block. A maximum value is reached at the chain length of 10,000 because of two different factors: crosslinking density and free volume. In a series of X‐PIS‐y‐PTS [X‐PIS modified with phenyltrimethoxysilane (PTS), where y is the weight‐ratio percentage of PTS to APTS–polyamic acid] films with a constant PI block length, the storage modulus, tensile modulus, T_g, density, and α‐relaxation damping peak intensity decrease with the PTS content. This could be because of the increase of the PSSQ‐like domain size with the PTS content, which leads to the introduction of more free volume or interblock separation and to a decrease in the interblock chain interaction force. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2500–2516, 2001     

Effect of branched alkyl groups on physical properties in poly(ethylene-co-branched alkyl methacrylate)s

Summary Poly(ethylene-co-5.4 mol% n-alkyl/branched alkyl methacrylate)s (PEM) were prepared by a dehydrogenchloride reaction of poly(ethylene-co-5.4 mol% alkyl methacrylic chloride) with the corresponding alkyl alcohol to investigate effect of branching structure and length of alkyl ester on a few physical properties of PEM [glass transition temperature (T_g), degree of crystallinity in polyethylene region (X_c) and dielectric molecular motion], where the alkyl groups used here are n-propyl, n-butyl, n-hexyl, n-decyl, 2-ethylhexyl, 3,5,5-trimethylhexyl and 2-(1,3,3-trimethylbutyl)-5,7,7-trimethyloctyl. In the n-alkyl methacrylate copolymers, T_g and X_c were almost unchanged with the presence of alkyl ester, but T_g increased and X_c decreased in the highly branched alkyl methacrylate copolymers even at the low methacrylate content of 5.4 mol%.     

Structural,thermal, dielectric and ac conductivity properties of lithium fluoro-borate optical glasses

Transparent and stable glasses in the chemical composition of Li₂O–LiF–B₂O₃–MO (M = Zn and Cd) have been prepared by a conventional melt quenching method. For these glasses, absorption spectra, structural (XRD, FT-IR, and Raman spectra), thermal (TG–DTA and DSC), dielectric (?′, ?″, tan δ), ac conductivity (σ_ac), and electric modulus (M′ and M″) have been investigated. Amorphous nature of these glasses has been confirmed from their XRD profiles. The LFB glasses with the presence of ZnO or CdO an extended UV-transmission ability has been achieved. The measured FT-IR and Raman spectra have exhibited the vibrational bands of B–O from [BO₃] and [BO₄] units and Li–O. The dielectric properties (tan δ, dielectric constant (?′), dielectric loss (?″)), electrical modulus and electrical conductivity (σ_ac) of these glasses have also been studied from 100 Hz to 1 MHz at the room temperature. Based on the trends noticed in the ac conductivities, the present glasses could be found useful as battery cathode materials.     

Molecular dynamics of chiral semi-crystalline poly(R)-(3-hydroxyalkanoates)

The inversion-recovery cross-polarization (IRCP) sequence used for measuring cross-relaxation time (T_CH) is modified to obtain signals that show exponential or spin-lock (SL) decay to zero. The new sequence may, therefore, be analogously abbreviated as SLCP. Poly(R)-(3-hydroxybutyrate-co-3-hydroxyhexanoate) {P(HB-HHx) (85:15)} is found to be more mobile than poly(R)-(3-hydroxybutyrate) {PHB} in the crystalline regions. The molecular-level evidence by solid state nuclear magnetic resonance (NMR) that the P(HB-HHx) chain is more flexible than PHB is echoed by the dynamic frequency sweep measurements of the biopolymer melts, which show that the PHB melt has an unusual rheological response with the dynamic loss moduli dominating the storage moduli at all frequencies. This is most likely to be caused by the local anisotropic melt structures due to the long persistence length of PHB in the melt. Upon cooling the PHB melt to the solid state, such high levels of anisotropy may be frozen into the solid causing lower chain mobility, and hence giving rise to lower toughness. The incorporation of longer side chain unit to the main chain gives rise to a dynamic rheological response in P(HB-HHx) similar to that of an isotropic melt. This is believed to be due to the enhanced chain flexibility, and hence reduced persistence length. This further allows P(HB-HHx) to be processed into a more uniform isotropic morphology, and hence with improved mechanical toughness.     

Dynamic mechanical properties and correlation with dynamic fragility of sisal reinforced composites

In this study, the reinforcement effect in sisal/polyester composites containing distinct reinforcement content was studied ranging from fragile to strong classification. The results indicate that the reduced storage modulus changes steadily, and the loss modulus and the tan δ peak are broader for composites containing more fiber (dynamically strong composites). As more fiber was incorporated in the resin, lower peak height for the tan delta curve was obtained, which may be indicative of lower energy dissipation due to a greater relative amount of interface. Also, the use of reduced dynamic mechanical curves (similar to dynamic fragility) is an alternative to facilitate the study of the material behavior. POLYM. COMPOS., 36:161–166, 2015. © 2014 Society of Plastics Engineers     

Photocuring and thermomechanical properties of multifunctional amide acrylate compositions derived from castor oil

The photopolymerization of multifunctional acrylate monomers synthesized from castor oil was investigated by photo-DSC. These studies revealed that the extent of photopolymerization depended on the double bond concentration and a greater degree of crosslinking occurred in monomer mixtures with higher difunctional content. The monomer mixtures displayed significantly higher maximum rate of polymerization (R_p^max) and shorter time to reach peak maximum than the pure monomers. DMTA studies of films showed good storage modulus and broad tan δ transitions indicating heterogeneity in the crosslinked networks. The films displayed sub-T_g transitions in the loss modulus curves were possibly due to the side chain motions of the monomer acrylates which increased with increasing triacrylate concentration. Glass transition temperature (T_g) of these networks depended on composition and shifted to higher values with increasing amount of triacrylate.     

Surface characterization and study of Langmuir films of poly(4‐vinylpyridine) quaternized with n‐alkylbromide

The surface behaviour of poly(4‐vinylpyridine)s (P4VP) quaternized with four different alkyl chains (pentyl, hexyl, octyl and decy bromide) were studied. Surface pressure–area isotherms (π–A) at the air–water interface were determined. Depending on the length of the side‐chains, the π–A isotherms show a plateau region. An extensive plateau is observed for n > 6. The plateau pressures are similar for n = 8 and n = 10. The monolayers are stable and exhibit hysteresis phenomena. Brewster angle microscopy (BAM) is used to monitor the monolayer topography of the polymer on water subphase. To obtain information about the surface energy (SE) and the degree of hydrophobicity of these systems, we have estimated the critical surface tension, γ_c, and the dispersion force and polar contributions to SE, γ_D and γ_P, respectively, by measurements of the contact angle (CA) of water and bromobenzene on the polymer surface. The results obtained are depend on the length of the alkyl lateral chain of the functionalized polymers. © 2001 Society of Chemical Industry