A study of the dilation of the unit cell of metallocene isotactic poly(propylenes): The monoclinic form

The lattice parameters of a series of monoclinic metallocene poly(propylenes) of constant molecular weight are measured as a function of defect content, that vary between 0.3 and 2.35 total defects per 100 monomeric units. The parameters are also measured as a function of molecular weight for a fixed defect content and as a function of the crystallization temperature. The b axis is found to increase with decreasing isothermal crystallization temperature whereas only small changes are found for samples rapidly crystallized. The a and c axis showed basically no variation with crystallization temperature. The parameters of the unit cell were essentially constant with varying defect content in the poly(propylene) chain. Lack of observed effect on the dilation of the unit cell by increasing defects is a consequence of the rapid crystallization required to ensure formation of monoclinic crystals. The unit cell parameters increased as a mild function of the molecular weight. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 2511–2521, 1997     

Sol–gel transition of methylcellulose in phosphate buffer saline solutions

The effect of phosphate buffer saline (PBS) on the thermoreversible sol–gel transition of methylcellulose has been systematically investigated with turbidimetric, microcalorimetric, and rheological methods. In the presence of PBS, the cloud points in the sol–gel transition and the clear points in the gel–sol transition shift to lower temperatures with increasing PBS content. This salting-out effect is considered to be due to the competition between salts and methylcellulose for water molecules involved in the formation or destruction of cagelike water structures. The microcalorimetric studies prove that with increasing PBS content, the endothermic peak temperature decreases, whereas the enthalpy and entropy changes of the sol–gel transition increase. The rheological studies show that the addition of PBS favors the sol–gel transition, but the gel strength is almost independent of the PBS content, indicating an effect of adding salt equivalent to that of increasing the temperature. The results obtained from the rheological, microcalorimetric, and turbidimetric measurements are consistent. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1849–1860, 2004     

Cyclodextrin gels which have a temperature responsiveness

β-Cyclodextrin (CD) gels crosslinked by epichlorohydrin (CD-gel) were modified with poly(N-isopropylacrylamide) (PIPA; M_n 4900) chains. The CD residue in the gel associated with 8-anilino-1-naphthalenesulfonic acid (ANS) more strongly than the free PIPA-carrying CD. The van't Hoff plot for complexation of ANS with the gel drifted largely from linear relationship above the coil-globule transition temperature of individual PIPA chains. Furthermore, a relatively more significant temperature effect on the stereoselective adsorption of phenylalanine to the CD gel was observed by the modification with PIPA chains. These results imply that the ability of the CD-gel–PIPA conjugate to form inclusion complex could be skillfully controlled by temperature. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 1535–1541, 1997     

Au@PS纳米颗粒掺杂PDMS/(PVDF-TrFE)复合薄膜的制备及介电-疏水性能

结合乳液聚合和还原法在250 nm的聚苯乙烯(PS)微球表面均匀负载了Au纳米颗粒. 通过溶液共混法, 使Au@PS纳米颗粒与聚二甲基硅氧烷(PDMS)/聚偏氟乙烯-三氟乙烯[P(VDF-TrFE)](质量比为2∶3)均匀混合, 制备出结构致密、 Au@PS均匀分布的微突起的复合薄膜. 研究了不同Au@PS纳米颗粒掺杂量对复合薄膜的结构、 熔融结晶行为和介电疏水特性的影响. 研究发现, Au@PS纳米颗粒的引入阻碍了P(VDF-TrFE)的β相的产生, 但对PDMS/P(VDF-TrFE)复合薄膜的化学健结构没有显著影响; 随着Au@PS纳米颗粒含量的增多, 复合薄膜结晶温度和玻璃化转化温度升高, 熔点略有降低. 由于界面极化和微电容效应协同作用, 掺杂Au@PS复合薄膜的介电常数有显著提升. PS球表面均匀负载的Au纳米颗粒减少了导电网络的构成, 使介电损耗维持在较低值. 掺杂5%(质量分数)Au@PS的复合薄膜介电常数达到22(100 Hz), 分别为纯PDMS和PDMS/P(VDF-TrFE)的8.8倍和3.14倍, 同时具有优异的疏水特性, 接触角达到112.31°.     

Conformation transition of silk fibroin induced by blending chitosan

The conformation of silk fibroin in silk fibroin/chitosan (SF/CS) blend membrane was analyzed by infrared spectrum, X-ray diffractometry, and Raman spectrum. The results demonstrated that the SF could show β-sheet conformation when the SF content in blend membranes was 10% (w/w) and 60–80% (w/w), while the pure SF membrane showed random coil conformation. A mechanism of the conformation transition was suggested in that the SF chain could use the rigid CS chain as a mold plate to stretch itself to form a β-sheet structure according to the strong hydrogen bond between CS and SF. Therefore, a new concept, named “Polymer-Induced Conformation Transition,” was proposed. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 2293–2296, 1997     

Dielectric behavior of P(VDF-TrFE)/PMMA blends

Binary blends of ferroelectric (vinylidene fluoride-trifluorethylene) copolymer [P(VDF-TrFE)] and amorphous poly(methyl-methacrylate) (PMMA) were investigated over the full range of composition, for the copolymer with 50 mol % of trifluorethylene. Dielectric measurements confirmed that the system becomes amorphous when the PMMA contents exceed 40 wt %. The observed dielectric losses could be attributed to the ferroelectric transition of the copolymer and to molecular relaxations, characteristic of the individual polymers. We demonstrate the thermally activated nature of the β-PMMA and β-P(VDF-TrFE) relaxations, with activation energies of 29.3 and 13.5 kcal/mol, respectively. We also demonstrate that the β-P(VDF-TrFE) relaxation cannot be attributed only to the copolymer glass transition and that its origin is not in the crystalline region, based on experimental evidences. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2996–3002, 1999     

Studies on syntheses and properties of novel polyamides containing phosphatidylcholine analogous moieties by interfacial polycondensation

Polyamides (4a-b and 5a-b) were synthesized from interfacial polycondensation of novel diamine containing phosphatidylcholine analogous moiety, hexamethylene diamine with adipoyl chloride, or sebacoyl chloride in the interface of water and carbon tetrachloride at room temperature. The characterizations of synthesized diamine and polyamides were carried out with FT-NMR, or IR spectral method, elemental analysis, and melting point measurements, respectively. These polyamides obtained are insoluble in any normal solvents. From the results of X-ray diffraction analysis and POM observation, it was revealed that the polyamide 4b was prepared with high molecular weight, while polyamide 4a obtained seemed to have low molecular weight. For copolymers 5a and 5b, X-ray reflections from only adipoyl or sebacoyl chloride parts were observed as in crystalline state. In addition, thermal properties were also studied by DSC and transmitted light intensity measurements. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 3065–3074, 1997     

Lamellar thickening of polyethylene under high pressure

Single crystal mat (SCM) samples of polyethylene (PE) were prepared from dilute solution of p-xylen, then they were annealed at pressures of 200 and 500 MPa. Lamellar thickness of the original and annealed SCM samples was measured by small-angle X-ray scattering method. Orientation of the molecular chain in those SCM samples was investigated by wide-angle X-ray diffraction pattern. From these X-ray measurements, annealing temperature dependence of the lamellar thickness, i.e., lamellar thickening, under high pressure was obtained. Melting process of the SCM samples was also investigated at 200 and 500 MPa by high pressure differential thermal analysis. Then correspondence between the lamellar thickening and the melting process was studied. The lamellar thickness increases markedly with approaching to the melting temperature of the orthorhombic crystal even in the high pressure region where the high pressure phase (hexagonal phase) appears. The annealing temperature dependence curve of the lamellar thickness at 200 MPa can be superimposed on the curve at 500 MPa by shifting the curve along the temperature scale by 47 K. Large scale lamellar thickening occurs in the orthorhombic crystal phase in the high pressure region. The formation process of extended-chain crystal is discussed. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys, 35: 535–543, 1997     

Cooperative movements associated with the Curie transition in P(VDF-TrFE) copolymers

The thermal and dielectric behavior of β-PVDF and a series of random P(VDF-TrFE) copolymers with various chemical composition has been investigated in the temperature range of their Curie transition. Dielectric relaxations and phase transitions were characterized by means of differential scanning calorimetry and thermostimulated current spectroscopy. The thermal hysteresis associated with the first order character of the Curie transition decreases as the TrFE content increases, and vanishes for P(VDF-TrFE) 50/50. For the latter, the distribution in lamellar thickness and the dependence of the conformational order in the ferroelectric phase upon thermal history yield an intricate thermal behavior. For the overall investigated polymers, the TSC mode associated with the ferro/para-electric transition is described by a distribution in relaxation times obeying a compensation law. This behavior has been interpreted based on cooperative movements in the ferroelectric phase in the vicinity of the transition temperature. These molecular movements are precursors of the transition. It is valid for β-PVDF, as well as for P(VDF-TrFE) copolymers which for the compensation temperature corresponds to the transition temperature. So, the Curie temperature of PVDF has been found at 170°C, i.e. the melting point. ©1995 John Wiley & Sons, Inc.     

Chromatography of functional polymers: A new approach to the characterization of reactive polymers obtained by chemical modification

High-performance liquid chromatography (HPLC) has been used to complement size-exclusion (gel permeation) chromatography (SEC) for the characterization of functional polymers. Whereas SEC is unable to detect compositional changes, HPLC in an appropriate interacting medium can provide detailed information on compositional changes occurring during chemical modification of a polymer. The method has been demonstrated using a normal-phase column consisting of porous monodisperse 10 μm poly(2,3-dihydroxypropyl methacrylate-co-ethylene dimethacrylate) beads that have a homogeneous coverage of aliphatic hydroxyl groups for the analysis of brominated poly(isobutylene-co-4-methylstyrene). Differences of well below 1 mol % of bromomethylstyrene units are easily detected and quantified. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 1173–1180, 1997     

Observations on the thermoreversible gelation of two-directional arborols in water–methanol mixtures

Reversible gels of two-directional cascade polymers with hydrophilic groups covalently attached by an hydrophobic center chain were studied by light and small-angle X-ray scattering, differential scanning calorimetry, and freeze-fracture transmission electron microscopy. The long, self-assembled fibers interact side-by-side over extended regions to form bundles. A given fiber may participate in several bundles, thus forming a three-dimensional gel network. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 2787–2793, 1997     

Cationic ring-opening copolymerization of seven-membered cyclic sulfite and oxetane in one-shot feeding

Cationic copolymerization of seven-membered cyclic sulfite, 1,3,2-dioxathiepane-2-oxide (1) and oxetane (2) in one-shot feeding was carried out to obtain the corresponding copolymer. When a mixture of equimolar amount of 1 and 2 reacted at 0°C in the presence of methyl trifluoromethanesulfonate (T fOMe) as a cationic initiator, T fOMe and 2 were completely consumed without the consumption of 1. After rising the polymerization temperature up to 25°C, 1 started to be consumed to obtain the corresponding copolymer of 1 and 2. The obtained copolymer showed a unimodal GPC curve, and it afforded a polyether showing a unimodal GPC after alkaline hydrolysis. These results strongly suggested the occurrence of the block copolymerization in one-shot feeding. From the molecular orbital examination, the formation of block copolymerization in one-shot feeding was discussed to be caused by the much larger polymerizability of 2 than that of 1. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 1007–1012, 1997     

The tuning of crystallization behavior of ferroelectric poly(vinylidene fluoride-co-trifluoroethylene)

Poly (vinylidene fluoride-co-trifluoroethylene) [P(VDF-TrFE)] has three crystal forms, including paraelectric α, ferroelectric β, and γ phases. In previous studies, the properties and performances of P(VDF-TrFE) have been the focus of research. However, the formation mechanism and regulation mode of various crystal forms remain unclear. Therefore, it is an important topic for further research to elucidate, summarize, and prospect the polymorphism of P(VDF-TrFE) and regulate the crystal forms. This review systematically summarizes the crystalline structure and phase transition between ferroelectric and paraelectric phase of P(VDF-TrFE) crystals; discusses the influence of annealing, blending and electric field on the crystallinity, selection of polymorphic crystals, and phase transition behavior between them; reviews the effects of annealing, melt-recrystallization, substrate and nanoconfinement on the crystal orientation. Finally, the effects of the crystal structure of P(VDF-TrFE) on its properties are briefly summarized.     

A DSC study of miscibility and phase separation in crystalline polymer blends of phenolphthalein poly(ether ether sulfone) and poly(ethylene oxide)

The miscibility of blends of phenolphthalein poly(ether ether sulfone) (PES-C) and poly(ethylene oxide) (PEO) was established on the basis of the thermal analysis results. Differential scanning calorimetry (DSC) studies showed that the PES-C/PEO blends prepared by casting from N,N-dimethylformamide (DMF) possessed a single, composition-dependent glass transition temperature (T_g), and thus that PES-C and PEO are miscible in the amorphous state at all compositions at lower temperature. At higher temperature, the blends underwent phase separation, and the PES-C/PEO blend system was found to display a lower critical solution temperature (LCST) behavior. The phase separation process in the blends has also been investigated by using DSC. Annealed at high temperatures, the PES-C/PEO blends exhibited significant changes of thermal properties, such as the enthalpy of crystallization and fusion, temperatures of crystallization and melting, depending on blend composition when phase separation occurred. These changes reflect different characteristics of phase structure in the blends, and were taken as probes to determine phase boundary. From both the thermal analysis and optical microscopy, the phase diagram of the blend system was established. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 1383–1392, 1997     

Crystallization behavior and electroactive properties of PVDF,P(VDF-TrFE) and their blend films

PVDF, poly(vinylidene fluoride), as a semi-crystalline polymer, has interesting electroactive properties but usual melt and solution processing techniques result in its thermodynamically favored non-polar α-phase. By comparison, poly(vinylidene fluoride-trifluoroethylene) P(VDF-TrFE), PT for short, directly crystallizes in the polar β-phase under the same conditions as PVDF. In this study, blend thin films comprising PVDF and P(VDF-TrFE) were prepared by solvent casting method. The difference in the crystallization behavior is comprehensively investigated between the polymers: PVDF, P(VDF-TrFE), and the resulting blend films. It is found that replacement of the fluoride atom in TrFE monomer induces a strong steric hindrance that may alter the crystallization process to become more favorable for nucleation of the PVDF β-phase. To figure out the effect of TrFE content on the crystallization behavior and electroactive properties, films with different blend ratios of PVDF and P(VDF-TrFE) were prepared. We found that the PVDF films exhibit higher crystallization activation energy (ΔE) as PT content increases. The atomic force microscopy (AFM) in the piezoresponse force microscopy (PFM) mode illustrated that P5T5 films with equal contents of PVDF and P(VDF-TrFE) induced the highest d₃₃ values.     

Photophysics of carbazole-containing systems. 1. Dilute solution behavior of poly(N-vinyl carbazole) and N-vinyl carbazole/methyl acrylate copolymers

Steady-state and time-resolved fluorescence techniques have been used to study the photophysical behaviors of poly(N-vinyl carbazole), PNVCz and a series of N-vinyl carbazole-methyl acrylate (NVCz-co-MA) copolymers in dilute solution as a function of both NVCz composition and temperature. A kinetic scheme, intended to describe intramolecular excimer formation across the entire NVCz composition range, is proposed. In low aromatic content copolymers, two monomer species (unquenched and quenched monomer) and two excimer species (the sandwich-like excimer and a higher energy excimer) exist. The contribution from monomer emission to the overall fluorescence decreases with increasing NVCz content through increased excimer formation: this is likely to be consequent upon (1) an increase in the number of excimer forming sites, and (2) increasing efficiency of energy transfer from the excited monomers to the excimer forming sites. In the homopolymer, PNVCz, the only emission that can be observed on a nanosecond timescale is excimeric. This fluorescence appears to originate from three excimer species (the sandwich-like excimer, and two higher energy forms). For the homopolymer, the current observations are consistent with the model proposed by Vandendriessche and De Schryver [Polym. Photochem. 7 , 153 (1986)]. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 963–978, 1997     

Investigation of molecular chain orientation change of polymer crystals in phase transitions by friction anisotropy measurement

Direct observation of the molecular orientation change in polymer crystals provides us visible information for understanding their structural phase-transition mechanisms. In this letter, we successfully identified the main-chain orientation of poly(vinylidenefluoride-trifluoroethylene) (P(VDF-TrFE)) crystals over all directions using friction anisotropy measured by lateral-modulation friction force microscopy (LM-FFM). This technique made possible our investigation of molecular orientation changes caused by a ferroelectric phase transition and also a fabrication process for artificial nanometer-scale structures. These results give us visual information that is directly connected to the transition mechanisms.     

Cross‐linking emulsion copolymerization of butyl acrylate with diallyl maleate

The emulsion copolymerization of butyl acrylate (BA) with a trifunctional cross‐linker, diallyl maleate (DAM), was investigated. The effect of the monomer feeding time and the amount of cross‐linker on the microstructural properties (branching, cross‐linking, gel formation, and sol MWD) of the seeded semicontinuous emulsion copolymerization of BA with DAM was investigated. It was found that the gel content was not significantly affected by increasing feeding time, but the level of quaternary carbons (an indication of the branching density) increased. On the other hand, increasing the amount of DAM in the feed composition caused gel content, level of quaternary carbons, and the cross‐linking density to increase. Interestingly, the level of quaternary carbons and the cross‐linking density sharply increased during the cooking period. The molecular weight of the sol decreased as DAM increased in the feed. In addition, the effect of process type, batch versus semibatch, was also considered and important differences in the level of quaternary carbons, cross‐linking, and gel content were found. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4684–4694, 2005     

Synthesis and characterization of optically active polyamides derived from carbohydrate-based monomers

The synthesis of three new stereoregular AB-type polyamides based on D -ribono-1,4-lactone, L -arabinose, and D -xylose has been carried out by the active ester polycondensation method. These polyamides were characterized by elemental analysis, IR and NMR spectroscopies, and powder X-ray diffraction. They displayed optical activity and had a pronounced affinity to water, although they were not soluble in this solvent. The polyamide obtained from D -ribono-1,4-lactone was highly crystalline and yielded films with spherulitic texture. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3645–3653, 1997     

Copolymerization of carbon monoxide and 4-vinylcyclohexene with a palladium catalyst

In this work, carbon monoxide (CO) and 4-vinylcyclohexene (VCH) with [Pd(CH₃CN)₄](BF₄)₂ were copolymerized under various conditions at 60°C. Elemental analysis and infrared, UV, and NMR spectra indicated that copolymers containing a ketone and a cyclic structure of cyclohexyl and norbornane groups are produced. Bidentate nitrogen ligands proved to be more effective at stabilizing catalytic activity than monodentate phosphorus or nitrogen ligands. Also, the bulk substituent on the bidentate ligand led to inactive catalysts. Methanol served as the coinitiator and chain transfer agent. Increasing the concentration of 4-vinylcyclohexene caused the copolymer's CO content to be enhanced. TGA revealed that the copolymer's mass loss starts at 120°C and the maximum peak of decomposition occurs at 450°C. Moreover, X-ray diffraction analysis demonstrated the copolymer to be partially crystalline. Furthermore, reduction of 4-vinylcyclohexene/CO copolymer with LiAlH₄ in THF yields a hydroxyl-containing polymer. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 2759–2768, 1997