Influence of vinylidenefluoride on the physical ageing of poly(chlorotrifluoroethylene)

The influence of vinylidenefluoride (3% composition) on the physical ageing of poly(chlorotrifluoroethylene) at 70 °C has been investigated using the positron annihilation lifetime technique. Both the ortho-positronium (o-Ps) pick-off lifetime and its intensity show a systematic variation with ageing time. The o-Ps intensity exhibits non-exponential character which can be fitted with two additive exponential decay curves and the free volume is found to exhibit the Doolittle type of free volume relaxation. The relaxation times were evaluated from the structural relaxation function and the non-exponentiality parameter was estimated using the Kohlrausch-Williams-Watts (KWW) function, which indicates the deviation from exponential relaxation. Based on the relaxation times, the activation energies calculated seems to label the different kinetic units/irregularity in the chain backbone of PCTFE structure participating in the relaxation process. Physical ageing seems to yield close packing of polymer chains.     

Photochemical behavior of poly(ethylacryloylacetate) and poly(acryloylacetone) films

Films of poly(ethylacryloylacetate) (PEAA) and poly(acryloylacetone) (PAA) were subjected to UV irradiation (λ = 254 nm) at room temperature. The photoinduced structure transfer from cis-enol onto a diketo forms has been investigated. The structure transfer caused by UV light was found to be slower than for the corresponding process in solution. The spectral investigations (UV, IR) showed reversible process of photoketonization. The results were analyzed in terms of the model for the participation of the trans-enol form in the process of the ketonization. Based on the results obtained, some general conclusions were made about the organization of the units in the polymer chain. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3683–3688, 1997     

Molecular modeling of polymers. 10. Characterization of conformational transitions of poly(acrylic acid) and poly(methacrylic acid) using dyad structures

The conformational profiles of nearest side-chain neighbors, methylene-dyad structures, of poly(acrylic acid), PAA, and poly(methacrylic acid), PMA, were determined as a function of tacticity, extent of ionization, and presence of counterion. The dominant backbone conformer states are quite similar for both isotactic and syndiotactic diads in a common charge state. Thus, the overall dimensional properties of isotactic syndiotactic and atactic chains of PAA or PMA, based upon dyad interactions, are predicted to be alike for a given charge state. Significant deviations from precise t, g⁺, and g^? states are found for the dyad minimum energy conformations. The rod-to-coil and coil-to-rod transitions observed in PAA and PMA, respectively, as a function of increasing counterion concentration can be explained, to a large extent, by the conformational profiles of the corresponding dyad model structures. © 1994 John Wiley & Sons, Inc.     

Solid-state 19F MAS NMR study on the conformation and molecular mobility of poly(chlorotrifluoroethylene)

The temperature dependence of molecular mobility and conformational changes of poly(chlorotrifluoro- ethylene) (PCTFE) have been investigated by solid-state (19)F magic angle spinning (MAS) NMR spectroscopy. The pulse techniques of dipolar-filter and T(1rho)-filter allow selective observation of the amorphous and crystalline domains, respectively. The temperature dependence of T(1rho) (F) revealed that the segmental motion in the amorphous domain becomes vigorous above ca 80 degrees C, which is well above the glass transition (T(g)) temperature (52 degrees C) and more close to the beta-relaxation temperature (95 degrees C). On the other hand, vigorous molecular motions in the crystalline domain occur above 120 degrees C, which is much below the melting temperature (212 degrees C). This indicates that the polymer chains in the PCTFE crystallites are more mobile than those of typical semicrystalline fluoropolymers like poly(vinylidene fluoride) (PVDF), which can be associated with structural imperfections in the crystallites. In addition, the density functional theory (DFT) calculations of (19)F magnetic shielding suggest that the high-frequency shifts observed for the crystalline signals above 80 degrees C can be ascribed to the conformational change around meso diads toward more twisted and/or helical conformations in the main chain.     

Recovery as a measure of oriented crystalline structure in poly(ether ester)s based on poly(ethylene oxide) and poly(ethylene terephthalate) used as shape memory polymers

Poly(ether ester)s consisting of poly(ethylene oxide) and poly(ethylene terephthalate) segments, EOET copolymers, could be used as shape memory polymers (SMP). Crystalline structural characters of the copolymers during the memory process were investigated by dynamic mechanical analysis, differential scanning calorimeter, wide-angle X-ray diffraction, polarizing microscopy, and recovery measurements. PEO crystals in stretched EOET copolymer preferentially oriented along fiber axis or stretch direction. During stretching, the structure of the copolymer undertake a transformation from spherulite to fiber, resulting in a crystalline morphology similar to shish-kebab, and recovery properties of stretched EOET samples were dependent on as-described crystalline structural characters that can be influenced by draw ratio. Driving forces for contraction come from the oriented chains, and only oriented or extended chains can be contributive to the recovery of deformation; these extended chains involve both crystalline and amorphous segments. The recovery process in shape memory behavior was noticed to be deorientation of oriented chains due to thermodynamic entropy effect, and was divided into three stages. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 101–112, 1999     

From poly(dialkylstannane)s to poly(diarylstannane)s: comparison of synthesis methods and resulting polymers

The efficiency and applicability of three different methods to synthesize polystannanes with different side chains are described. By means of dehydrogenative coupling utilizing the transition metal catalyst RhCl(PPh₃)₃ (Wilkinson's catalyst), n‐Bu₂SnH₂ reached the highest molar masses. Dehydrogenetive coupling in the presence of tetramethylethylenediamine could be best employed for (4‐n‐BuPh)₂SnH₂. Wurtz coupling using sodium in liquid ammonia was best suited for Ph₂SnCl₂. Next to the above‐mentioned educts, n‐Bu(Ph)SnX₂ (X = H or Cl (as appropriate for the particular route) was used for polymerization resulting in one of so far rare example of asymmetric polystannanes with high molecular masses. Copyright © 2011 John Wiley & Sons, Ltd.     

Structural features of crystallized poly(ethylene terephthalate) polymers

Polyethylene terephthalate (PET) is a widely used polymeric material. In this work, the microstructural features before and after the solid‐state polymerization (SSP) of several DuPont PET products were investigated by low‐voltage scanning electron microscopy (LV‐SEM) and atomic force microscopy (AFM). The microstructural features on the cross section of various PET samples included crystallites, voids, boundaries, defects, and amorphous phases. The SEM images revealed layered and stepped structural features at the micron and 10‐micron scales that are highly crystallized at the near‐edge region of the cross section for both linear and branched PET samples after the SSP process. The AFM images demonstrate that the degree of crystallization for the linear and branched PET samples increases gradually from the central area to the edge on the cross section. The linear crystallized PET has a higher degree of orientation than the branched crystallized PET in the 10‐micron to micron scales, but their crystalline structures have no significant differences in the submicron to nanometer scales. The PET crystallization process occurs when the molecular chains in the amorphous phase are aligned and folded to form straight molecular chains at the nanometer scale, and small crystallites are formed. The crystallites aggregate and align together into a polygon rod‐like‐shaped crystallites at the submicron scale. Finally, large crystallites at the micron size are formed that appear on the edge area of the cross section. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 40: 245–254, 2002     

Electrochemical behavior of high-molecular-weight poly(ferrocenylsilane) films in aqueous electrolyte solutions

The electrochemical behavior of high-molecular-weight poly(ferrocenyldimethylsilane) films and poly(ferrocenylmethylphenylsilane) films, which contained about 2.8 × 10⁻⁶ mol cm⁻² ferrocene sites in eight kinds of aqueous electrolyte solutions, was investigated with cyclic voltammetry (CV). In some aqueous electrolyte solutions, the CV peak currents diminished gradually with an increase in the scanning times, whereas in other aqueous electrolyte solutions, stable and repeated cyclic voltammograms were obtained. The polymer films were poor-solvent-swollen in aqueous electrolyte solutions, and this resulted in a high resistivity of mass transfer and a slow rate of electrode reaction; therefore; quasireversible or irreversible CV processes were obtained. The kinetic parameters of the film-electrode processes, such as the surface transfer coefficient, the apparent diffusion coefficient, and the standard rate constant for electron transfer, for the two films in aqueous LiClO₄ solutions were measured, and the electrode process mechanism of the films was examined. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2245–2253, 2004     

Polar phase formation in poly(vinylidene fluoride) induced by melt annealing

It is still a challenge to obtain polar phase of poly(vinylidene fluoride) from melt crystallization at normal conditions. This study demonstrates that polar β‐ and γ phases can be produced through melting re‐crystallization of α phase, provided that moderate memory effects in the melt is achieved by annealing. Otherwise, it is inevitable to re‐crystallize into α phase without any trace of polar phase. Small fragments, generated from the disintegration of long TGTG′ sequences, most likely adopt trans conformation in the melt before approaching random coils, thus responsible for the formation of polar phase upon cooling. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Radiation effects on the thermal degradation of poly(vinyl chloride) and poly(vinyl alcohol)

Radiation effects on the formation of conjugated double bonds in the thermal degradation of poly(vinyl chloride) (PVC) and poly(vinyl alcohol) (PVA) were investigated. Thin films of PVC and PVA were either irradiated with γ-rays at ambient temperature (pre-irradiation) and then subjected to thermal treatment, or irradiated at elevated temperatures (in situ irradiation). An extensive enhancement of the thermal degradation was observed for the pre-irradiation of the PVC films, which was more effective than the effect of the in situ irradiation at the same absorption dose. For the PVA degradation, however, the effect of the in situ irradiation was larger than that of the pre-irradiation. The results were explained and related mechanisms were discussed based on radiation-induced chemical reactions and their individual contributions to the thermal degradation behaviors of the two polymers. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 3089–3095, 1998     

Fully-biodegradable poly(3-hydroxybutyrate)/poly(vinyl alcohol) blend films with compositional gradient

Fully-biodegradable bacterial poly(3-hydroxybutyrate) (PHB)/chemosynthetic poly(vinyl alcohol) (PVA) blend films with compositional gradient from one surface to the other surface of the films were prepared by a dissolution-diffusion technique. Three kinds of PVA samples, high- and low-molecular weight atactic PVA and highly syndiotactic PVA (s-PVA), were used in order to investigate the effects of molecular weight and tactic structure on the generation of compositional gradient. The solution of PHB in 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP), which is also a good solvent for PVA, was cast on the PVA film and then the solvent HFIP was evaporated. By selecting the optimum volume of solvent and the evaporation rate, the PHB/PVA blend film with compositional gradient was obtained. The formation of compositional gradient was confirmed by FT-IR microscopy and ATR-FT-IR analysis. The 50%/50% PHB/s-PVA blend film with a nearly ideal compositional gradient, that is, the composition of PHB (or PVA) in the film changing gradually from 100% at one surface to 0% at the other surface of the film was obtained by casting PHB/HFIP solution on to the s-PVA film. Positional dependence of the absorbance of C==O and OH stretching bands along the film thickness direction for the PHB/S-PVA cast films.     

Greatly Enhanced Energy Density and Patterned Films Induced by Photo Cross‐Linking of Poly(vinylidene fluoride‐chlorotrifluoroethylene)

Greatly enhanced energy density in poly(vinylidene fluoride‐chlorotrifluoroethylene) [P(VDF‐CTFE)] is realized through interface effects induced by a photo cross‐linking method. Being different from nanocomposites with lowered dielectric strength, the cross‐linked P(VDF‐CTFE)s possess a high breakdown field as well as remarkably elevated polarization, both of which contribute to the enhanced energy density as high as 22.5 J · cm⁻³. Moreover, patterned thin films with various shapes and sizes are fabricated by photolithography, which sheds new light on the integration of PVDF‐based electroactive polymers into organic microelectronic devices such as flexible pyroelectric/piezoelectric sensor arrays or non‐volatile ferroelectric memory devices.

     

Aging and cold crystallization of melt‐extruded poly(trimethylene terephthalate) films

We analyzed the thermal crystallization, glass‐transition behavior, and mechanical properties of melt‐extruded poly(trimethylene terephthalate) (PTT) films to investigate their physical aging and annealing effects. The physical aging and annealing of PTT films had an influence on the glass‐transition temperature, recrystallization behavior, and mechanical properties. When samples were aged at an ambient temperature, the crystallization temperature decreased largely within 5 h, the heat of crystallization increased, and the breaking stress and breaking elongation increased. The glass‐transition temperature of annealed samples, which was obtained from differential scanning calorimetry and dynamic mechanical measurements, increased with increasing annealing temperature below 80 °C but decreased above that temperature. In addition, the glass‐transition temperature and modulus of annealed samples were largely affected by the annealing time; in particular, they increased sharply within 1 h on annealing at 50 °C. Consequently, the change in the glass‐transition temperature on annealing was ascribed to the fact that the molecular constraint due to recrystallization and the mobility of rigid amorphous PTT chains competed with each other, being dependent on the annealing temperature. The mechanical properties of aged samples were closely related to their cold‐crystallization behavior. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1920–1927, 2001     

A thermoreversible conformational change in two poly(zwitterions) evidenced by thermally stimulated depolarization currents

A thermally induced conformational change of zwitterionic groups of two polymers has been observed by thermally stimulated depolarization currents. Different dipole moments of the two conformations is a prerequisite. The appearance of peaks of opposite sign confirms the process. Giant dielectric constants can be obtained at room temperature using high-temperature poling and rapid cooling.     

Glass transition and miscibility in blends of two semicrystalline polymers: Poly(aryl ether ketone) and poly(ether ether ketone)

Binary melt‐blended mixtures of two aryl ether ketone polymers (i.e., a new poly(aryl ether ketone) (code name PK99) and poly(ether ether ketone) (PEEK), have been studied. Polymer miscibility in glassy amorphous (or melt) domains has been demonstrated for the binary blend comprising of two aryl‐ether‐ketone‐type semicrystalline polymers. Composition‐dependent, single T_g was observed within full composition range in the PK99/PEEK blends, and the narrow T_g breadth also suggests that the scale of mixing was fine and uniform. To better resolve any possible overlapping T_g's, physical aging was imposed on a comparison set of blend samples for the purpose of improving detectability of overlapped multiple transitions if existing. The result still showed one single T_g. The relative sharp T_g and lack of cloud point transition suggest that the scale of molecular intermixing is good. Phase homogeneity was further confirmed using optical and scanning electron microscopy. The X‐ray diffractograms suggest that isomorphism does not exist in the PK99/PEEK blends and that the crystal forms of the respective polymers remain distinct and unchanged by the miscibility in the amorphous region. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1485–1494, 1999     

Water soluble poly(ethylene oxide) functionalized norbornene polymers

The synthesis of three different poly(ethylene oxide) macromonomers with a norbornene and oxanorbornene end group is presented. The macromonomers were polymerized to comb‐polymers by ring‐opening metathesis polymerization (ROMP) using Grubbs' Catalyst G3 to produce water soluble polymers with polydispersities between 1.04 and 1.30 and molecular weights between 14,000 and 50,000 g/mol. Characterization by static and dynamic light scattering reveals that the comb‐polymers with norbornene backbone are molecularly disperse in aqueous solution, while the oxanorbornene‐backbone polymers form small water‐soluble aggregates. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2640–2648, 2008     

Subglass-transition-temperature annealing of poly(ethylene terephthalate) studied by FTIR

Using FTIR spectroscopy we have examined conformational changes in the quenched and slowly cooled amorphous PET films during physical aging process. It was observed that the amount of trans conformers for quenched sample decreased upon sub-T_g annealing. For the slowly cooled sample that corresponds to a state closer to equilibrium, the amount of trans conformers hardly decreased, but increased gradually during sub-T_g annealing process. The conformational populations of these two samples tend to be identical with annealing time. These results demonstrate that sub-T_g annealing will lead to closer interchain packing and result in the formation of new cohesional entanglements along the chains. In situ FTIR studies on the conformational changes of these samples were also carried out during heating up of the sample through the glass transition region. The results showed that incremental changes of the amount of trans conformers in Samples Q and SC were gradual, while an abrupt change of trans conformers occurred in the sub-T_g annealed samples. These results were in agreement with the formation of the interchain cohesional entanglement due to sub-T_g annealing. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 783–788, 1998     

Degradation of poly(N-vinylcarbazole) by annealing under iodine pressure

After room temperature doping of poly(N-vinylcarbazole) by iodine, the powders are annealed at different temperatures (370, 470, and 570 K) for 24 h under vacuum or under iodine pressure. The obtained powders were studied by infrared absorption, x-ray photoelectron spectroscopy, x-ray diffraction, and nuclear magnetic resonance. Annealing of pure PVK powder increases the crystallization quality of the sample. Annealing with iodine induces progressive polymer degradation. At 570 K under iodine pressure the PVK is totally destroyed. The aromatic rings and the C(SINGLEBOND)N bonds have disappeared. NH₄I crystallites have formed, embeded in a degraded, cross-linked polymer matrix. © 1996 John Wiley & Sons, Inc.     

Segmented block copolymers of poly(ethylene glycol) and poly(ethylene terephthalate)

A new series of segmented copolymers were synthesized from poly(ethylene terephthalate) (PET) oligomers and poly(ethylene glycol) (PEG) by a two‐step solution polymerization reaction. PET oligomers were obtained by glycolysis depolymerization. Structural features were defined by infrared and nuclear magnetic resonance (NMR) spectroscopy. The copolymer composition was calculated via ¹H NMR spectroscopy. The content of soft PEG segments was higher than that of hard PET segments. A single glass‐transition temperature was detected for all the synthesized segmented copolymers. This observation was found to be independent of the initial PET‐to‐PEG molar ratio. The molar masses of the copolymers were determined by gel permeation chromatography (GPC). © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4448–4457, 2004     

Amphiphilic comb-shaped polymers from poly(ethylene glycol) macromonomers

Comb-shaped amphiphilic graft copolymers composed of hydrophobic backbones and hydrophilic side chains were prepared by radical copolymerization of poly(ethylene glycol) monomethacrylate macromonomers, and methacrylate and acrylate comonomers in toluene. The copolymerizations were very sensitive to the reaction conditions, and insoluble cross-linked gels were easily formed. The yields of soluble copolymers were affected by the initiator concentration, the macromonomer concentration, and the choice of chain transfer agents and comonomers. Solubilities of the copolymers in water or methanol were found to depend on the sizes and the numbers of the PEG side chains. The copolymers showed surface activity with CMC:s in the order of 0.1–1.5 g/L and surface tensions of 36–56 dyn/cm. When tested as emulsifiers most of the copolymers gave oil-in-water type emulsions at room temperature. Polymers carrying MPEG 2000 side chains were crystalline with melting points of 38–44°C, while those based on PEG 400 and 1000 were mostly amorphous with glass transition temperatures between -55 and -60°C. © 1992 John Wiley & Sons, Inc.