bluuebunny/crossref_metadata_2025 huggingface dataset:
Polyurethane cationomers with pendant trialkylammonium groups: Effects of ion content, alkyl group, and neutralizing anion
Authors: Goddard R. J. , Cooper S. L.
Published: April 2003

Diphenylmethane‐4,4′‐diisocyanate based polyether polyurethane cationomers were synthesized using 3‐trialkylammonium‐(1,2‐propanediol)iodide (TAPI) as the chain extender. The ionic content was varied by substituting up to 100% of 3‐dialkylamino‐1,2‐propanediol (DAP) for TAPI. Cationomers with bromine and chlorine ions were prepared from the iodine‐based polymer via ion exchange. The morphology and properties of the cationomers were studied as a function of alkyl group, ion content, and anion type using small‐angle x‐ray scattering, tensile testing, dynamic mechanical thermal analysis, and differential scanning calorimetry. The bulky side groups of DAP and TAPI prevented crystallization in the hard domains, and consequently little or no phase separation was evident in the unionized materials. Polyurethanes with cationic functionality showed dramatic improvements in phase separation and tensile properties. Results suggest tht while ionic interactions are the primary driving force for phase separation, they produce a morphology not typical of ionomers, but rather akin to that of a conventional polyurethane with semicrystalline hard segments. © 1994 John Wiley & Sons, Inc.
NMR analysis of distribution of chain lengths between crosslinks of polymer networks
Authors: Sandakov G. I. , Smirnov L. P. , Sosikov A. I. , Summanen K. T. , Volkova N. N.
Published: April 2003

A novel technique for the analysis of the distribution of chain lengths between crosslink junctions of polymer networks is proposed. The technique is based on the relation between the high‐temperature nuclear magnetic resonance free‐induction decay and the network structure. The distribution functions are determined for a number of networks. In particular, the evolution of structure of a thermally degrading network is studied. © 1994 John Wiley & Sons, Inc.
Influence of intrachain hydrogen bonding on the cyclization of a polystyrene chain
Authors: Farinha J. P. S. , Martinho J. M. G. , Xu H. , Winnik M. A. , Quirk R. P.
Published: April 2003

Cyclization of a polystyrene chain (Mn = 10,600; Mw/Mn = 1.09) both ends labeled with 4‐(1‐pyrenyl)butanoamide groups was studied in cyclohexane between 25 and 95°C. The amide groups (peptide bonds) at both ends can form an intrachain hydrogen bond between the amide hydrogen at one chain end and the carbonyl oxygen at the other. The presence of two sets of conformers, random coils, and chains cyclized through hydrogen bonding, complicates the data analysis. The pyrene excimer kinetics of this polymer is well described by a model composed of two monomers (hydrogen bonded and nonbonded chains) and one excimer, in equilibrium. The cyclization rate constant for hydrogen‐bonded chains is larger than the one for nonhydrogen‐bonded chains. The pyrene excimer binding energy (ca. 1.6 kcal/mol) is lower than the published value for nonhydrogen‐bonded chains (∼ 9 kcal/mol), suggesting that intrachain hydrogen bonding hinders the stabilization of the excimer. © 1994 John Wiley & Sons, Inc.
Sulfone‐Containing polymers as high barrier materials
Authors: Zhang Tianhong , Litt Morton H. , Rogers Charles E.
Published: April 2003

Three types of sulfone‐containing polymers, poly(carbonate‐sulfone)s, poly(ester‐sulfone)s, and poly(urethane‐sulfone)s, were characterized as high barrier materials. They were made by condensing sulfone‐containing diol, 1,3‐bis(3‐hydroxypropylsulfonyl)propane (Diol‐333), or 1,4‐bis(3‐hydroxypropylsulfonyl)butane (Diol‐343), with diphenyl carbonate, diphenyl esters, and diisocyanates, respectively. The incorporation of polar sulfone groups into polymer backbones increases the glass transition temperature of polymers in all cases; however, the increment is different with different functional linkages. The increments in polycarbonates and polyesters are higher than that in polyurethanes. This is because the interactions between carbonate or ester groups are much weaker than the interactions between sulfone groups, whereas the hydrogen bonding between urethane groups is comparable with the polar interaction between sulfone groups. The polymers were coated on 50‐μm‐thick Kapton films by solution casting and their permeabilities toward carbon dioxide were measured at 25°C using the ASTM D1434 volumetric method. The sulfone‐containing polymers have carbon dioxide permeability coefficients at least 50 times smaller than the corresponding polymers without sulfone groups. The carbon dioxide barrier properties of sulfone‐containing polymers are comparable with ethylene/vinyl alcohol copolymers (EVAL), which are commercial high barrier polymers. An isomer effect on polymer permeability was observed in the aromatic‐aliphatic poly(ester‐sulfone) series. The permeability coefficients of the aromatic‐aliphatic poly(ester‐sulfone)s decrease from terephthalate to isophthalate to phthalate, corresponding to the increase of chain flexibility above the Tg. These results support the hypothesis that high chain flexibility in the rubbery state and a glass transition temperature above room temperature are two key factors that promote low permeability. © 1994 John Wiley & Sons, Inc.
The effect of counterions on the chain conformation of polyelectrolytes, as assessed by extensibility in elongational flow: The influence of multiple valency
Authors: Narh K. A. , Keller A.
Published: April 2003

An elongational flow technique was used to determine the effect of counterions on the chain conformation of polyelectrolyte molecules in solution, by means of the extensibility of the chains in the flow field. It is demonstrated that adding excess cations of seven low molecular weight salts, NaCl, CaCl2, BaCl2, SrCl2, MgCl2, AlCl3, and SnCl4, to a very dilute solution of fully sulphonated polystyrene (NaPSS) reduces the extensibility of the chains, that is, the facility by which a chain can be extended to varying degrees, an effect associated with chain contractions. In the case of multivalent counterions, these contractions, which with monovalent counterions are primarily due to screening of charges by excess counterions, are greatly enhanced, which we attribute to the formation of intramolecular ionic bridges. When, in the case of multivalent counterions, the polymer concentration is increased, in inversion of the effect, namely increase in chain extensibility on addition of ions, is observed. We attribute this latter effect to the ionic bridges becoming increasingly intermolecular, leading to effectively large molecules, and eventually to a gel. All these effects were accentuated with increase in valency. They could also be accompanied by precipitation which were of two kinds: one due to formation of insoluble ionic associations and a second attributable to enhanced hydrophobic interaction within the contracted chain itself. © 1994 John Wiley & Sons, Inc.
Miscibility of tetramethyl‐hexafluoro copolycarbonates with styrene‐methyl methacrylate copolymers
Authors: Takakuwa K. , Gupta S. , Paul D. R.
Published: April 2003

The compositions for which blends of copolycarbonates of tetramethyl bisphenol‐A and hexafluoro bisphenol‐A (TMPC‐HFPC) with styrene‐methyl methacrylate copolymers (SMMA) are miscible were determined experimentally. These copolymer compsition boundaries were compared to predictions based on the Flory‐Huggins theory combined with the binary interaction model. The theoretical predictions employed interaction energies from the literature for the TMPC/PS, PS/PMMA, and TMPC/PMMA pairs, and values for the TMPC/HFPC, HFPC/PS, and HFPC/PMMA pairs were established or verified using independent experiments. The recommended set of interaction energies predicts that miscibility occurs in two separate regions of copolymer compositions. These predictions agree well with the experimental observations. The theoretical requirements for a single, continuous miscible region versus two disjointed miscible regions when the two limiting homopolymer pairs exhibit miscibility, that is, TMPC‐PS and HFPC‐PMMA in this example, are described. © 1994 John Wiley & Sons, Inc.
Dynamic scattering properties of branched polymers in the high‐wave vector region
Authors: Benoît H. , Benmouna M. , Borsali R. , Rinaudo M.
Published: April 2003

An analysis of dynamic scattering behavior of branched polymers in the high‐wave vector region is presented. In particular the first cumulant of the dynamic structure factor Ω(q) is examined. This quantity is calculated using the standard formula which defines Ω(q) within a proportionality constant as a ratio of the generalized mobility M(q) and the static structure factor S(q), where q is the amplitude of the scattering wave vector. The latter quantity has already been calculated by Benoît et al. who obtained a general formula for a branched polymer with an arbitrary architecture. Here, this calculation is extended to the mobility M(q) including hydrodynamic interaction with the angular pre‐averaged Oseen tensor. This result may be useful in the cases where the measurement of the first cumulant by quasi‐elastic scattering techniques can be made to complete the information obtained by the absolute intensity measurements. © 1994 John Wiley & Sons, Inc.
Phase equilibrium and mutual diffusion in the poly(sulfone)–dimethylsulfoxide system
Authors: Mikhailov Yu. M. , Ganina L. V. , Ye. Chalykh A.
Published: April 2003

Phase equilibrium and mutual diffusion in the poly(sulfone) (PSF)–dimethylsulfoxide (DMSO) system have been studied at temperatures from 20 to 110°C over a wide solution composition range. The phase diagram for this system has been obtained and the effect of water on boundary concentrations has been studied. It is shown that the presence of water in DMSO has a considerable effect on the binodal curve. Thus, increasing the water content up to 1.3% by weight results in the displacement of the upper critical solution temperature by 30°C and the widening of the two‐phase region. The kinetic regularities in mutual dissolution of components have been investigated. The concentration dependencies of the mutual diffusion coefficients in the systems studied are presented. The effect of moisture in DMSO on the mutual diffusion coefficients appears near the phase transition in the system. © 1994 John Wiley & Sons, Inc.
Estimation of interaction energies by the critical molecular weight method: 2. Blends with polysulfones
Authors: Callaghan T. A. , Paul D. R.
Published: April 2003

The interaction energies between PS, Pα‐MS, and PMMA, as well as acrylonitrile and maleic anhydride units, with a series of polysulfones were quantitatively determined from oligomer/oligomer, oligomer/homopolymer, and homopolymer/copolymer blends. Interaction energies were calculated from the Flory‐Huggins theory and the Sanchez‐Lacombe equation of state theory using experimental cloud points or miscibility boundaries. Alkyl addition to the phenyl rings of polysulfone is favorable for miscibility with polystyrene whereas halogenation of the bisphenol connector unit favors miscibility with poly(methyl methacrylate). Interaction energies are quantitatively ranked and described qualitatively in terms of changes in the electronic charge distribution of the polymer repeat units as calculated by SYBYL software. © 1994 John Wiley & Sons, Inc.
Optical properties of cholesteric (2‐hydroxypropyl) cellulose (HPC) esters
Authors: Rusig I. , Godinho M. H. , Varichon L. , Sixou P. , Dedier J. , Filliatre C. , Martins A. F.
Published: April 2003

Acetoxypropylcellulose (APC) and propionic, n‐butyric, isobutyric, valeric, isovaleric, hexanionic, and heptanionic acid esters of hydroxypropylcellulose (HPC) (respectively PPC, BPC, iBPC, VPC, iVPC, HexPc, and HepPc) were prepared and characterized by differential scanning calorimetry, chromatography, polarizing microscopy, chemical methods, and spectroscopy. All these esters form thermotropic cholesteric liquid crystalline phases. The glass (Tg) and clearing (Tc) transition temperatures were determined. The stability interval of the mesophases appears to be greater in the case of longer‐linear side chains. The mesophases of APC, PPC, iBPC, VPC, and iVPC exhibit reflection bands in the visible region, at wavelengths that depend on temperature, moisture content, size and number of substituents, and degree of polymerization (
\[
\overline {{\rm DP}}
\]
). The pitch of the cholesteric helical structure increases with side chain length and with increasing temperature. At room temperature, a fingerprint‐like pattern can be observed for HepPc. No reversal in the sense of the pitch with temperature variations was observed. The pitch of BPC increases with moisture content and with decreasing values of the degree of esterification (
\[
\overline {{\rm DE}}
\]
) and
\[
\overline {{\rm DP}}
\]
. A theory for cholesteric mesophases composed of helical rod‐like species and a model of elastic bend chain have been compared to the experimentally observed changes in the pitch with temperature and with the length of the side chain substituents (for iBPC, iVPC, BPC, PPC, and APC) and
\[
\overline {{\rm DE}}
\]
and
\[
\overline {{\rm DP}}
\]
(for BPC). © 1994 John Wiley & Sons, Inc.
Molecular weight dependence of diblock copolymer segregation at a polymer/polymer interface
Authors: Dai Kevin H. , Kramer Edward J.
Published: April 2003

Utilizing forward recoil spectrometry (FRES), we have determined the segregation isotherm which describes the interfacial excess zi* of diblock copolymers of poly (d8‐styrene‐b‐2‐vinylpyridine) (dPS‐PVP) at the interface between the homopolymers PS and PVP as a function of ϕ∞, the volume fraction of diblock copolymer remaining in the host homopolymer. All the samples were analyzed after annealing at temperatures and times sufficient to achieve equilibrium segregation. The effect of the degree of polymerization of both the diblock copolymers and the host homopolymers on the segregation isotherm is investigated. When the degree of polymerization of the homopolymer is much larger than that of the diblock copolymer, the normalized interfacial excess (zi*/Rg), where Rg is the radius of gyration of an isolated block copolymer chain, is a universal function of that portion of the block copolymer chemical potential due to chain stretching. The existence of such a universal function is predicted by theory and its form is in good agreement with self‐consistent mean field calculations. Using these results, one can predict important aspects of the block copolymer segregation (e.g., the saturation interfacial excess) without recourse to the time‐consuming numerical calculations. © 1994 John Wiley & Sons, Inc.
Solution characterization of poly(isobornyl methacrylate) in tetrahydrofuran
Authors: Zhang X. Q. , Wang C. H.
Published: April 2003

Thermodynamic and hydrodynamic properties of dilute solutions of poly (isobornyl methacrylate) (PIMA) in tetrahydrofuran (THF) were characterized by using viscosity, static, and dynamic light scattering measurements. PIMA samples with different molecular weight were obtained by fractional precipitation of PIMA solution. Chain dimension parameters (Rg and RH), together with second virial coefficient A2 and intrinsic viscosity [η], were used to calculate various solution parameters characterizing polymer chains in polymer solutions. The experimental results are compared with calculation, indicating that PIMA behaves as a flexible coil in THF. © 1994 John Wiley & Sons, Inc.
On the glass transition temperature of styrene‐n‐butyl methacrylate copolymers in dependence on chemical composition, molecular weight, and mixtures
Authors: Schellenberg J. , Vogel J.
Published: April 2003

For statistic copolymers of styrene and n‐butyl methacrylate, the relation between the glass transition temperature and the chemical composition or molecular weight of the copolymers has been determined. Further, the dependence of the glass transition temperature on the composition of binary and ternary blends from statistical poly (styrene‐co‐n‐butyl methacrylates) of a nearly equal chemical composition but a very different molecular weight has been studied. Among several equations considered for the correlation between glass transition temperature and composition of the mentioned copolymers with relatively low molecular weights, the Gordon/Taylor and Couchman equations gave the best agreement with the experimental results. For the glass transition temperature of poly(styrene‐co‐n‐butyl methacrylate) with an n‐butyl methacrylate content of about 30 wt % in dependence on the molecular weight, the Kanig‐Ueberreiter and Fox‐Flory equations proved to be useful for the examined molecular weight range. The glass transition temperatures of the polymer blends have been studied for a low/high‐molecular component system, a system of two low‐molecular components, as well as for systems with a third component. The glass transition temperatures of the mixtures frequently exceeded those of their individual components. © 1994 John Wiley & Sons, Inc.
Influence of heat treatment conditions on the porosity changes of sulfonated styrene/divinylbenzene copolymers
Authors: Kolarz Bożena N. , Wojaczyńska Maria , Kaczmarczyk Jan , Siemieniewska Teresa , Tomków Kazimierz
Published: April 2003

Sulfonic cation exchangers with two ion exchange group concentrations (0.5 and 2.4 mmol/g, samples A and B, respectively) were obtained by sulfonation of a porous styrene (S) and divinylbenzene (DVB) copolymer with chlorosulfonic acid. Strong thermal decomposition of the sulfonated copolymer A, accompanied by significant changes in its porous structure, starts at ca. 400°C. The char has no sulfonic groups. After heat treatment at 400°C in steam, a sorbent was obtained (yield 65%) that shows higher phenol sorption than the untreated sample when related to the bed volume. The chlorosulfonic derivatives of the initial copolymer were less thermally resistant than the sulfonic ones obtained by hydrolysis. Pyrolysis of the cation exchanger B, in its H+ and Ca2+ forms, was carried out at 900°C (yield of both chars close to 30%). By subsequent steam activation at 800°C to a 50% burn‐off of the char, sorbents with well‐developed, but distinctly different, porous structures were obtained. The activated char from the sulfonated copolymer in its hydrogen form was highly microporous and indicated an effective surface area of 1180 m2/g. However, because of a low contribution of mesopores, its ability to adsorb phenol from the liquid phase was not very high. The activated char from the calcium‐doped copolymer, indicating a smaller surface area (580 m2/g) but characterized by a well‐developed mesoporosity, was a better sorbent for phenol. © 1994 John Wiley & Sons, Inc.
FTIR investigation of cross‐linking and isomerization reactions of acetylene‐terminated polyimide and polyisoimide oligomers
Authors: Huang W. X. , Wunder S. L.
Published: April 2003

The interrelationship between the cross‐linking and isoimide‐imide isomerization reactions of oligomeric isoimides and imides was investigated using FTIR spectroscopy. It was found that cross‐linking of the acetylene units of Thermid IP‐600 retarded the local rearrangement of the isoimide to imide conversion of Thermid IP‐600 compared with an aniline‐terminated analog, decreasing the rate constant by a factor of about 2. The increased flexibility of both the isoimide (Thermid IP‐600) and imide (Thermid FA‐700) oligomers increased the cross‐linking rate of the acetylene end groups by a factor of 4 and 2, respectively, over that of the more rigid imide oligomer (MC‐600). With increasing conversion of the isoimide to imide linkages in Thermid IP‐600, the kinetic parameters, Eα and in A, for the cross‐linking reaction of this oligomer became the same as those for the oligomeric imide, Thermid MC‐600. © 1994 John Wiley & Sons, Inc.
High density polyethylene/hydrogenated oligo(cyclopentadiene) blends: Phase structure, thermal and mechanical properties
Authors: Cimmino S. , Di Pace E. , Martuscelli E. , Mendes L. C. , Silvestre C.
Published: April 2003

The article discusses the influence of an oligomeric resin, hydrogenated oligo (cyclopentadiene) (HOCP), on the morphology and properties of its blends with high density polyethylene (HDPE). HDPE/HOCP blends after solidification contain three phases: the crystalline phase of HDPE and two amorphous phases, one rich in amorphous HDPE and the other in HOCP. DSC thermograms and the loss modulus behaviors show that the γ transition is influenced by HOCP molecules and, in addition to the αc transition of HDPE, there is another transition that is attributed to the HOCP‐rich phase. The hypothesis of the two amorphous phases is confirmed by the optical microscopy observations performed on isothermally crystallized blend films. © 1994 John Wiley & Sons, Inc.
A synopsis of empirical gel fraction analytical methods: Application of the Wanxi equation to polyethylenes irradiated in vacuo and in the presence of acetylene
Authors: Jones Richard A.
Published: April 2003

Gel fraction data from linear low‐density polyethylene (LLDPE) films and high‐modulus polyethylene (HMPE) fibers, which had previously failed to give reasonable results when treated with Charlesby‐Pinner and Saito‐Kang‐Dole theory, have been fitted to a modified form of the Wanxi equation. The fitting yields parameters that compare very well with literature values derived by the Wanxi equation, confirming that fracture and cross‐linking densities are proportional to a power function (β) of the radiation dose. Extrapolated G(S) values have been obtained from LLDPE using the fit parameters and UV‐Vis spectroscopy data. A brief synopsis of the empirical analytical methods available for gel fraction analysis is given. © 1994 John Wiley & Sons, Inc.
Structural changes and chain orientational behavior during tensile deformation of segmented polyurethanes
Authors: Lee H. S. , Hsu S. L.
Published: April 2003

Structural changes and segmental orientation behavior of polyurethane have been studied during uniaxial deformation. The orientation function change of the two (free and hydrogen bonded CO stretching peaks) peaks during a full cycle of deformation has been observed to be distinctively different. Even though the hydrogen‐bonded CO peaks showed hysteresis behavior, the free CO peaks exhibited quite elastic behavior. It was thus concluded that the orientation behavior of free and hydrogen‐bonded CO stretching peak represents the deformation characteristics of soft and hard domains, respectively. The orientation behavior at different temperatures also has been studied. Temperature has a significant effect on the orientation behavior of the soft domain, whereas it has negligible effect on the hard domain orientation. It was also demonstrated that the structural change due to the deformation could be analyzed by infrared spectroscopy. Some of the hydrogen‐bonded carbonyl groups have been observed to be transferred to the free carbonyl groups, indicating that a small amount of the hard segments in the hard domain have been pulled out into the soft matrix upon deformation. The orientational relaxation also has been studied as a function of time. The segmental relaxation of the hard segments appears to be quite characteristic depending on the nature of the domain in which they reside. © 1994 John Wiley & Sons, Inc.
Deformation mechanisms in nylon 6/ABS blends
Authors: Majumdar B. , Keskkula H. , Paul D. R.
Published: April 2003

The deformation mechanisms during fracture of a Nylon 6/ABS blend compatibilized with an imidized acrylic polymer were compared to those of an uncompatibilized blend. A postmortem examination of deformed zones in samples loaded to failure in a double‐notch four‐point‐bend geometry was made using transmission electron microscopy (TEM). For the compatibilized blend, cavitation of the rubber particles followed by massive shear yielding of the polyamide matrix was concluded to be the sequence of events leading to toughness; while, for the brittle uncompatibilized blend, the evidence indicated that a lack of adhesion at the Nylon‐ABS interface prevented the rubber particles from cavitating and the subsequent plastic deformation of the polyamide matrix. © 1994 John Wiley & Sons, Inc.
Phase considerations in digital image analysis of polarized‐light images
Authors: Moneva I. T.
Published: April 2003

The phase statistics in digital imaging (DIA) is considered for the case when Fourier transformation is performed over images obtained in polarized light. An additional phase shift associated with “directionality” of scatterers is shown significant for the true simulation of nonisotropic scattering. The proof is based on analysis is particular of DIA simulated patterns and optical Fourier transforms of spherulitic particles, the latter transforms being obtained by optical modelling of spherulitic polarized light scattering. The constraints on the phase shift in the simulation process have been established. The phase analysis additionally implies that the nonisotropic scattering might be considered as a new special case of the apodization technique, with a number of potential applications. © 1994 John Wiley & Sons, Inc.
Elastic constant anisotropy, core structure of wedge disclinations and optical texture of main‐chain P‐4‐BCMU liquid crystals
Authors: Wang Wei , Hashimoto Takeji , Lieser Günter , Wegner Gerhard
Published: April 2003

The elastic constant anisotropy and the core structure of wedge disclinations with strengths s = ±½ of lyotropic liquid crystals of a soluble polydiacetylene, P‐4‐BCMU (Mw = 5.15 × 105, Mn = 2.16 × 105, and Mw/Mn = 2.4), in chloroform was studied. The Frank elastic constant anisotropy defined by ε = (k11 − k33)/(k11 + k33) for this polymer was determined by three different methods. The results show that the value of ε for this polymer is 0.5 (±0.05) in solid state and/or in liquid crystal state, indicating that the splay constant k11 is three time higher than the bend constant k33. This result further implies that splay is unfavorable in the liquid as it requires greater energy than bend. In the area adjacent to the core of a singularity the value of ε increases with decreasing distance to the core, indicating increasing anisotropy of the elastic constants toward the core. The influence of the elastic constant anisotropy on the optical texture of the LC polymer when viewed by polarizing light microscope is studied. © 1994 John Wiley & Sons, Inc.
Direct signal analysis applied to the determination of the relaxation parameters from TSDC spectra of polymers
Authors: Aldana M. , Laredo E. , Bello A. , Suarez N.
Published: April 2003

A new method to evaluate the thermally stimulated depolarization current curves based on the direct signal analysis is first applied here to the fitting of computer‐generated curves to test its validity and accuracy. The method consists in finding the N elementary curves that best fit the experimental spectrum. The adjustment of the τ0 values associated with each energy bin is also included in the fitting. The results are presented for a monoenergetic peak and a peak generated with a Gaussian broadened energy distribution both with a single τ0. Good agreement is also found when a random noise of width σ0 ≤ 0.01 Jmax is added to the data to simulate experimental errors. Experimental complex curves corresponding to the γ and β overlapping relaxations in DGEBA‐EDA epoxy resin system are separated into their fine structure components. The complex band corresponding to water dipoles physisorbed in different sites of the microporosity of bituminous coal is analyzed and different processes are identified. The results are compared to those performed on cleaned peaks. Finally, the TSDC peak corresponding to the glass transition temperature in bisphenol‐A polycarbonate is analyzed and could only be fitted by using a Vogel‐Fulcher expression for the temperature dependence of the relaxation times. © 1994 John Wiley & Sons, Inc.
Application of proton multiple‐quantum NMR to the study of dynamics in bulk chloral polycarbonate
Authors: Roy Ajoy K. , Gleason Karen K.
Published: April 2003

Proton multiple quantum (MQ) nuclear magnetic resonance (NMR) is applied for the first time to probe chain dynamics in the polycarbonate of 1,1‐dichloro‐2,2‐bis(4‐hydroxyphenyl)ethylene (chloral) over a temperature range of 195–280 K. Since chloral polycarbonate contains only one essentially indistinguishable proton, any dynamical information is associated with the phenylene group motion, the dominant sub‐Tg motion. First, the fractional multiple quantum (fMQ) signal which can be refocused at a fixed MQ preparation time decreases with increase in temperature from 195 to 200 K, associated with the onset of the phenylene π flips. Since π flips do not modulate dipolar couplings between phenylene protons at positions 2 and 3 on the same ring, this decrease in fMQ can be attributed to modulation of the remaining couplings on the time scale of the MQ experiment. Next, over the range 200–240 K, the fMQ maintains a reduced, nonfluctuating value. This suggests a broad distribution of correlation times exists for the π flips, since at any one temperature in this intermediate range, only a small portion of the phenylene groups undergo motion at the precise kHz frequency required to refocus the MQ signal. The increase in the signal strength as the temperature rises above 240 K is due to the majority of π flips occurring in the fast motional limit. These observations are in agreement with previous single quantum proton NMR studies on phenylene group rotation in choral polycarbonate. Furthermore these fMQ measurements show several similarities to those for PTFE (poly(tetrafluoroethylene)), measured by 19F MQ‐NMR. One notable difference is that in as‐polymerized PTFE at intermediate temperatures (200–220 K) rapid oscillations of fMQ were noted as the temperature was changed by a few degrees. Such behavior is not observed in the chloral polycarbonate. © 1994 John Wiley & Sons, Inc.
Carbon‐13 NMR measurments of polybutadiene local dynamics in dilute solution: Further evidence for non‐Kramers' behavior
Authors: Zhu Wei , Gisser Daniel J. , Ediger M. D.
Published: April 2003

The local segmental dynamics of cis‐polybutadiene in dilute solutions have been investigated using natural abundance 13C NMR spectroscopy. The time integral of the CH orientation autocorrelation function 〈σ〉 is extracted from T1 measurements in five solvents covering a viscosity range of two decades. The hydrodynamic Kramers' equation, which is generally assumed to be appropriate for local polymer dynamics in dilute solution, cannot describe these results. 〈σ〉 is found to depend upon the solvent viscosity η raised to the 0.33 power whether η is varied by changing the temperature or the solvent. This apparent power law behavior has been observed for other polymers in dilute solution and can be rationalized if the solvent is viewed as viscoelastic. This view is supported by experimental results which show that local polymer dynamics can occur as much as an order of magnitude faster than solvent reorientation. Trends for a mixed microstructure polybutadiene are similar to those of cis‐polybutadiene. © 1994 John Wiley & Sons, Inc.
Molecular level study of the crystallization of a thermoplastic polyimide by infrared spectroscopy
Authors: Ishida H. , Huang M. T.
Published: April 2003

The crystallization process of the thermoplastic polyimide derived from 3,3′,4,4′‐benzophenonetetracarboxylic dianhydride (BTDA) and 2,2‐dimethyl‐1,3,‐(4‐aminophenoxy) propane (DMDA) is studied at the molecular level by utilizing infrared spectroscopy's sensitivity to local molecular environment. Assignments of the unique spectral features appearing upon crystallization are made with additional verification from crystalline model imide compounds. A direct comparison of an annealed polyimide film studied by both infrared spectroscopy and x‐ray diffraction shows fairly close agreement in the amount of crystallinity obtained. The unique crystalline infrared spectral features provide insight into the molecular mechanism involved with the crystallization process. Spectral shifts occurring upon crystallization reflect intramolecular rotations toward increased coplanarity as well as intermolecular chain packing of certain molecular groups at specific sites of the chain backbone. The site specific information is then used to study the relative kinetic behavior of the intramolecular and intermolecular effects occurring during crystallization. © 1994 John Wiley & Sons, Inc.
Blends of metal acetates and polyurethanes containing pyridine groups II. SAXS and EXAFS studies
Authors: Grady B. P. , O'Connell E. M. , Yang C. Z. , Cooper S. L.
Published: April 2003

Polyurethanes containing pendant pyridine units were blended with various metal acetates and studied by small‐angle x‐ray scattering (SAXS) and extended x‐ray absorption fine structure spectroscopy (EXAFS) to better understand the microscopic effect of blending on these materials. An earlier investigation found a dramatic enhancement in mechanical properties after blending, which suggests at least two pyridine units were coordinating to a single cation. This coordination would enable the cation to act as a cross‐linking site, which could then cause the observed changes in mechanical properties. To determine the effect of complexation on the microphase‐separated domain structure, small‐angle x‐ray scattering patterns were collected. Neutralization with a metal acetate increased the scattered intensity, which can be explained by an increase in electron density contrast but may also have been due to an improvement in phase separation. The distance between lamellar domains was basically unaffected by the addition of metal acetate, with the exception of nickel acetate. In this instance the distance decreased, which was caused by an improvement of packing inside the hard segments. EXAFS at the nickel and zinc edges indicated that the same qualitative changes occurred in the local environments around both cations after blending versus the unblended acetates. The magnitude of the first shell peak in the radial structure function (RSF) increased significantly upon blending, a result that is difficult to rationalize. The higher shell peaks exhibited significant changes in position and magnitude upon blending, which indicates substantial local rearrangement around the metal cation These fundamental changes in the EXAFS spectra may have been due to complexation between the cation and the pyridine group, but the results were not conclusive. © 1994 John Wiley & Sons, Inc.
Sorption and transport of water in nylon‐6 films
Authors: Hernandez Ruben J. , Gavara Rafael
Published: April 2003

Sorption and transport properties of water through films of Nylon‐6 were obtained at 5, 23, and 40°C. Commercially available films were used and a Cahn electrobalance was employed for measuring the water uptake by the polymer samples. Values of the water sorption isotherms are accurately described by the Langmuir/Flory‐Huggins dual‐mode sorption model. At water activity values below 0.15, the volume fraction of water described by the Langmuir portion of the model was greater than the Flory‐Huggins population. Solubility and diffusion coefficients of water, as well as the diffusion activation energy and enthalpy of dissolution of water for Nylon‐6, were determined from the sorption experiments. Values obtained support the hypothesis of a bimodal water sorption mode, and the formation of water clusters. © 1994 John Wiley & Sons, Inc.
Hopping conduction in “pure” polypropylene
Authors: Okoniewski A. , Perlman M. M.
Published: April 2003

A recently developed theory of steady‐state conduction in high‐density polyethylene is applied to “pure” polypropylene (PP) in the temperature range 50–93°C. Morphological changes occur in PP, including a disordered‐amorphous to monoclinic‐amorphous transition between 50 and 80°C, where, with increasing temperature T, free volume increases, and decreases with decreasing amorphous fraction. The latter competing processes lead to large increases in hopping site separation, λ, in the transition region, followed either by saturation or a maximum in λ vs. T. We speculate that segmental and/or main chain molecular motions lower apparent activation energies, are “pinned“ by applied field, and impeded by dangling bonds in regions surrounding the surfaces of crystallites. Our analysis is semi‐quantitative only, because the latter mechanisms have not been adequately quantified, and the relative contributions of each are unknown. Measurements were carried out on heated and cooled disordered‐amorphous, and 106°C, 17‐h annealed, 43% crystalline samples. Hopping distances, obtained from measured current vs. applied field characteristics, ranged from 1.2 to 5.2 nm. Apparent activation energies up to 1.80 eV were obtained from In (I/T) vs. (1/T) plots. Remarkable plateaus in the temperature range of the transition were observed in these plots, implying some carrier conduction with near zero activation energy. Possible explanations for the latter, and the electronic nature of the carriers are given. X‐ray and density flotation measurements enabled crystallinity determinations. © 1994 John Wiley & Sons, Inc.
Thermophysical properties of azomethine ether main‐chain liquid crystalline polymers at pressures to 200 MPa
Authors: Fakhreddine Youssef A. , Zoller Paul
Published: April 2003

This article reports on an experimental investigation of the equation of state and the transition behavior of main‐chain thermotropic liquid crystalline polymers over a wide temperature range, and at pressures to 200 MPa. The materials studied were a series of azomethine ether polymers. A varying number n (= 4, 7, 8, 9, 10 and 11) of methylene spacer units in the backbone provided systematic variation of the structure.

Experimental techniques used included high‐pressure dilatometry (PVT measurements) to 200 MPa, high‐pressure differential thermal analysis, also to 200 MPa, and conventional (atmospheric‐pressure) differential scanning calorimetry (DSC).

The equation of state of the materials can be well represented by the Tait equation in distinct regions, separated by a glass transition, Tg(P), a first‐order transition to a nematic state, Tk‐n(P), and a first‐order transition to an isotropic melt state Tc(P). The atmospheric pressure values of Tk‐n and Tc decreased with increasing number of spacer units and showed a clear odd‐even effect. Tg and Tk‐n both increased with pressure. The pressure dependence of Tc could not be observed due to the onset of degradation in the same temperature region. On isobaric cooling at 3°C/min, the crystallization from the nematic state occurred a few tens of degrees below Tk‐n. This supercooling was independent of pressure for some materials, while for others it increased with increasing pressure. The values of the enthalpy and entropy associated with the first‐order transition into the nematic state were lower than those of typical isotropic polymers at their melting transitions. The transition enthalpy did not have any systematic variation with increasing number of spacer units. Values of the transition enthalpy calculated from the Ciapeyron equation did not always agree with the values measured by DSC. This may be due to the two‐phase nature of the low‐temperature state. At the transition to the isotropic state, the transition enthalpy at P = 0 decreased with n and showed an odd‐even effect. © 1994 John Wiley & Sons, Inc.
Structure and dynamics of concentration fluctuations in a polymer blend solution under shear flow
Authors: Lai Janet , Fuller Gerald G.
Published: April 2003

The technique of small‐angle light scattering (SALS) has been employed to investigate the time‐dependent behavior of a single‐phase, semidilute solution of polystyrene and polybutadiene in dioctyl phthalate under shear flow. Concentration fluctuations in the polymer blend solution are found to grow with time in the direction of flow, and their orientation angles evolve from 45° from the flow direction toward 0°, with the steady‐state value being dependent on shear rate. SALS patterns are simulated using a modified Cahn‐Hilliard‐Cook model, with an additional collective restoring force to account for polymer elasticity. Predictions from this modified model for the orientation angles of the concentration fluctuations are in excellent agreement with the experimental results. Our model also predicts that the quiescent structure factor has a Gaussian form and that the steady‐state orientation of the scattering patterns is dependent on shear rate. These predictions are also in good agreement with our experimental observations. © 1994 John Wiley & Sons, Inc.
Effect of polymerization catalysts on the microstructure of P(LLA‐co‐εCL)
Authors: Choi Eui‐Jun , Park Jung‐Ki , Chang Ho‐Nam
Published: April 2003

The copolymerization of L,L‐lactide and ε‐caprolactone was carried out using antimony trioxide and stannous octoate as catalysts. The effect of polymerization catalysts on the physical and the chemical microstructures of this copolymer was investigated by 13C NMR and DSC analysis. Antimony trioxide causes more random sequence distribution within the copolymer chain due to its higher transesterification characteristic than stannous octoate. The copolymer samples made with the antimony trioxide catalyst seem to have more amorphous phase structure, than those prepared using stannous octoate which are semicrystalline for the entire compositional range due to blocky copolymer sequences. © 1994 John Wiley & Sons, Inc.
Impedance spectroscopy of reactive polymers. 1
Authors: Bellucci Francesco , Valentino Maio , Monetta Tullio , Nicodemo Luigi , Kenny Jose , Nicolais Luigi , Mijovic Jovan
Published: April 2003

Dielectric measurements were utilized to follow the advancement of cure in an epoxy/amine formulation. In contrast to earlier studies, complex impedance was measured during cure and used to calculate ionic resistivity. By using complex impedance were able to separate according to their frequency dependence the contributions to overall polarization from electrode blocking layers, migrating charges, and dipole relaxations. At any stage of cure, there is a unique frequency at which ionic resistivity can be singularly measured. Our approach does not involve trial‐and‐error frequency search and is conducive to the development of phenomenological models based on equivalent circuits. Excellent agreement was reported between the calculated values of normalized degree of cure obtained by dielectric and calorimetric measurements. © 1994 John Wiley & Sons, Inc.
Orientation and relaxation in uniaxially stretched styrene‐co‐methyl methacrylate random copolymers
Authors: Oultache A. K. , Jasse B. , Monnerie L.
Published: April 2003

Orientation and relaxation behavior in uniaxially stretched styrene‐co‐methyl methacrylate random copolymers was investigated. When compared at a reference temperature T = Tg + constant, orientation of methyl methacrylate units (MMA) decreases while styrene units orientation increases with a decrease in the styrene percentage. This behavior can be related to intermolecular interactions between MMA units and to the stiffness of styrene‐MMA units, which do not undergo conformational changes upon stretching. Both monomer units relax the same in a given copolymer and chain relaxation increases when the styrene percentage increases. Orientation relaxation of styrene and MMA units can be reduced to two general relaxation master curves whatever the blend composition, when the results are compared at same monomeric friction coefficient. © 1994 John Wiley & Sons, Inc.
On the plasticization of poly(2,6‐dimethyl phenylene oxide) by CO2
Authors: Handa Y. Paul , Lampron Steeve , O'neill Mark L.
Published: April 2003

Change in the glass transition temperature, Tg, of poly(2,6‐dimethyl phenylene oxide), PPO, due to the dissolved CO2 has been measured as a function of the gas pressure, p, using a high‐pressure DSC cell. At 61.2 atm, the highest pressure studied, Tg is depressed by 31.6°C. The depression in Tg is found to be linear with pressure, with dTg/dp of −0.5°C atm−1. The experimental results are in fair agreement with those calculated from a quasilattice solid‐solution model for polymer‐diluent systems. The present results, however, differ markedly from a recent investigation on PPO‐CO2 system which reported a depression in Tg of 226°C at 60 atm and a dTg/dp of −3.8°C atm−. © 1994 John Wiley & Sons, Inc.
Crystallization of poly(aryl ether ketone ketone) copolymers containing terephthalate/isophthalate moieties
Authors: Hsiao Benjamin S. , Gardner Kenncorwin H. , Cheng Stephen Z. D.
Published: April 2003

In a previous study, we have investigated the structure, crystallization, and morphology of poly(aryl ether ketone ketone), PEKK, copolymers prepared from diphenyl ether (DPE), terephthalic acid (T), and isophthalic acid (I) with T/I ratios from 100/0 to 50/50. These materials were considered as having ‐DPE‐T‐DPE‐T‐ (TT) and/or ‐DPE‐T‐DPE‐I‐ (TI) “phthalate diads.” In this work, we continue the study of this copolymer series with six different T/I ratios (40/60, 30/70, 20/80, 15/85, 10/90, and 0/100), which are viewed as having TI and/or ‐DPE‐I‐DPE‐I‐ (II) “diads.” The I moieties (1,3‐linked isomers) were always found to be incorporated in the crystals and acted as “entropy or symmetry” defects that effectively decreased the equilibrium melting temperature Tmo and the rate of crystallization. However, the retardation of crystallization in PEKK 0/100 (the homopolymer with pure II diads) was significantly less than expected, which was attributed to the segregation of I moieties between the chains leading to a reduction of total entropy in the unit cells. The evidence of segmental segregation in PEKK 0/100 was seen in x‐ray diffraction patterns, where several extra reflections were seen that could only be indexed by the published unit cell modified with a larger c‐axis dimension (3.048 nm, corresponding to the length of six phenyl residues or 1.524 nm, the length of three phenyl residues). The composition of 15/85 was found to have the lowest value of Tmo and the slowest crystallization rate. Upon heating, the “II” crystals (T/I from 30/70 to 0/100) exhibited the conventional double‐melting behavior rather than the triple‐melting behavior as in the “TI” crystals (50/50 to 40/60). No indication of the second polymorph form 2 was found in “II” crystals. © 1994 John Wiley & Sons, Inc.
In situ monitoring of free‐radical polymerization by fluorescence quenching of fluorene and reactive derivatives
Authors: Miller Keith E. , Burch Eric L. , Lewis Frederick D. , Torkelson John M.
Published: April 2003

A new approach for monitoring in situ the progress of an addition polymerization has been developed based on the fluorescence quenching of fluorene. Fluorene is quenched by the enone functionality on acrylates and methacrylates, but is not quenched after the carbon‐carbon double bond in this group is broken by incorporation into the polymer backbone. Ethyl (2‐fluorenyl)methacrylate was used as a self‐quenching comonomer during the 2,2'‐pazo bis(2‐methylpropionitrile)‐initiated free‐radical copolymerization of methyl methacrylate at 60°C. The fluorescence intensity increases by 60% up to the onset of the gel effect (defined as the sudden increase in the temperature profile). The system shows sensitivity well into the glassy state, with fluorescence increasing more than two orders of magnitude from the beginning of the reaction. This sensitivity is compared with that of two free‐volume‐dependent probes, 1,3‐bis(1‐pyrene)propane and dimethylaminobenzylidenemalononitrile, and to fluorene. The temperature profile of the test‐tube‐scale reaction was used as an internal reference for characterizing the sensitivity of the probes with respect to the gel effect region. © 1994 John Wiley & Sons, Inc.