Preparation and thermal behavior of poly-p-phenylene diacrylic acid dimethyl ester

The photopolymerization behavior of p-phenylene diacrylic acid dimethyl ester (p-PDA Me) crystal and the thermal behavior of the resultant poly-p-PDA Me were investigated. From the kinetic study of polymerization at various temperatures a topochemical process via a stepwise mechanism was observed. Continuous change from monomer to polymer crystals was demonstrated by x-ray diffraction pattern and DSC analysis. Crystallinity of the reacting phase was maintained at an extremely high degree during the polymerization process in support of monomer crystal lattice control. Thermal study on as-polymerized poly-p-PDA Me crystal confirmed that the thermal reaction was a polymer crystal lattice-controlled depolymerization, which was followed by miscellaneous processes that involved vaporization, sublimation, and deterioration of the oligomeric or monomeric units of p-PDA Me. Thermal stability was dependent on the molecular weight. All the results are compared with those of four-center-type photopolymerization in the crystalline state.     

Small-angle x-ray scattering from poly(tetramethyl-p-silphenylene) siloxane (TMPS) fractions

Small-angle x-ray scattering studies were made on bulk-crystallized samples and annealed oriented films of TMPS. The temperature dependence of the small-angle scattering was determined over a range of annealing conditions. The effect of sample molecular weight on the small-angle peaks was also studied. The peak intensity, measured at room temperature after annealing, was strongly dependent on the annealing conditions. The position of the peak gradually moved to smaller angles (larger d spacings) as the annealing temperature was raised. Surface free energies were deduced from the melting point dependence of the crystallite size. This surface energy was found to increase with molecular weight in accord with values deduced for spherulite growth rate-temperature dependence.     

Small-angle x-ray and neutron scattering studies of amorphous polymer blends

Dilute mixtures of poly(ε-caprolactone) (PCL) in poly(vinyl chloride) (PVC), poly(p-iodostyrene) (PpIS) in polystyrene, and deuterated polystyrene (d-PS) in protonated poly(o-chlorostyrene) (PoCIS) were investigated by means of small-angle x-ray scattering and small-angle neutron scattering. The radii of gyration of PCL in PVC and of d-PS in PoCIS were found to be expanded over the θ values by 50 and 30%, respectively. Values of the second virial coefficient were positive although errors prevented definitive evaluation of the interaction parameter. PpIS was found to aggregate, with both the radius of gyration and molecular weight increasing with concentration. Concentrated mixtures of PCL and PVC were also investigated by using the Debye–Bueche correlation function analysis. Correlation distances indicated good mixing throughout the entire composition range.     

Synthesis of a well-defined polybromostyrene by living radical polymerization with a nitroxyl radical

Radical polymerization of p-bromostyrene was investigated with benzoyl peroxide (BPO) as an initiator in the presence of 4-methoxy-2,2,6,6-tetramethylpiperidine-1-oxyl (MTEMPO). The polymerization was performed in bulk for 3.5 h at 95°C and then continued for another 48 h at 125°C to afford the corresponding polybromostyrene with a narrow molecular weight distribution in high yield. ¹H NMR study revealed that the polymer obtained had BPO and MTEMPO moieties at its head and tail, respectively. It was confirmed that the polymerization proceeded in accordance with living mechanism, because the molecular weight linearly increased with an increase of the conversion, and it was directly proportional to the reciprocal of the initial concentration of BPO. Furthermore, the polystyrene obtained in the present study could quantitatively act as the initiator for the polymerization of p-bromostyrene in the living radical manner to afford the corresponding block copolymer, and vice versa. © 1996 John Wiley & Sons, Inc.     

A comparison of thermoreactive water-soluble poly-N,N-diethylacrylamide prepared by anionic and by group transfer polymerization

Several batches of poly-N,N-diethylacrylamide were synthesized by anionic and by group transfer polymerization (GTP). A radical poly-N,N-diethylacrylamide prepared from the same monomer was also included in the comparison. According to matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) both types of living polymerization resulted in narrow molecular weight distributions with M_w/M_n values below 1.5. Average molecular weights (M_n) between 888 and 4678 g/mol were calculated in these cases. The radical polymer had an average molecular weight (M_n) of approximately 130,000 g/mol. The dry anionic and GTP polymers were investigated by differential scanning calorimetry (DSC) and x-ray diffraction spectrometry. Evidence for partial crystallinity in the solid state was found. The conformation of all polymers was examined by high resolution (600 MHz) NMR. According to these measurements, 75% of the ? CHR? groups of the anionic poly-N,N-diethylacrylamide were located in an isotactic triade. The remaining 25% had heterotactic structure, while no indication for the presence of syndiotactic protons was found. Poly-N,N-diethylacrylamide prepared by GTP, on the other hand, had mainly syndiotactic structure. The aqueous solutions of the polymers showed phase separation upon heating. Whereas the lower critical solution temperature (LCST) was approximately 30°C in the case of the poly-N,N-diethylacrylamide prepared by GTP and by radical polymerization, uncommonly high LCSTs of more than 40°C were observed for the anionic poly-N,N-diethylacrylamide. © 1994 John Wiley & Sons, Inc.     

Investigations of a series of PPDI-based polyurethane block copolymers. I. General morphology

The morphology of a series of segmented polyurethane block copolymers is characterized by x-ray scattering, differential scanning calorimetry (DSC), density measurements, and tensile studies. The materials contain hard segments formed from paraphenylene diisocyanate (PPDI) and flexible segments formed from poly(oxytetramethylene) (POTM) ranging in molecular weight from 650 to 2000. Four different molecular weight compositions were investigated, with the weight fraction of the hard segment (w_h) ranging from 0.14 to 0.33. The microphase structure has been examined using small-angle x-ray scattering, and the microphase transition zone thickness is estimated to be on the order of 1 nm. Oriented samples have been characterized with wide-angle x-ray scattering, and the flexible segment is shown to undergo stress-induced crystallization. DSC thermograms show flexible segment melting in the compositions containing the highest two molecular weights of the flexible segments. The hard segment thermal transitions were complex with a broad melting peak that varied with weight fraction and with a high temperature transition attributed to regions with hard segment lengths longer than the bulk of the hard segment component. There is an increase in tensile strength and initial modulus and decrease in elongation with increasing w_h. Density data suggest the existence of a multiphase system.     

Light-scattering studies of phase-demixing of polystyrene/poly(o-chlorostyrene) blends

The phase separation of blends of polystyrene and poly(o-chlorostyrene) has been studied by observing the changing small-angle light-scattering profile with time. As a blend is heated to a temperature at which it undergoes phase separation, a light-scattering maximum is observed which grows in intensity and moves to smaller angles with time. This maximum is associated with a characteristic spacing which increases at a rate which becomes greater at higher temperature or with lower molecular weight. This spacing varies with a power of time as might be expected for domain growth occurring by a viscous flow mechanism. The integrated scattering intensity (invariant) is found to increase initially with time and then remain constant, as is characteristic of phase separation followed by phase ripening.     

Inverse gas chromatography of lignocellulosic fibers coated with a thermosetting polymer: Use of peak maximum and conder and young methods

The Conder and Young (CY) and the peak maximum (PM) methods were used to estimate the retention time of n-alkane probes on chemithermomechanical pulp (CTMP) wood fibers treated with a low molecular weight grade phenol-formaldehyde resin (PFR). Thermodynamic functions (ΔH_a^o, ΔG_a^o, and ΔS_a^o) and the London dispersive component of the surface energy were derived from these retention times. Treated wood fibers show a high energy surface due to the presence of the thermoset resin on their surface. Values of ΔH_a^o obtained from the CY method were higher than those obtained with the PM method at relatively high temperatures and with relatively low molecular weight alkanes. The results from the two methods were identical at low temperature (293 K) and with the relatively high molecular weight alkane n-undecane.     

Structural studies of radiation-crosslinked poly(ethylene oxide)

The structure and thermal behavior of freeze-dried gels of radiation-crosslinked high molecular weight poly(ethylene oxide) (PEO) were investigated by optical and electron microscopy, wide-angle x-ray scattering (WAXS), DTA, TGA, and thermomechanical analysis. The gels are highly porous with thin crystalline walls. Small spherulite and hedrite structures are observed on the walls. A model for gel formation in solution is suggested. A statistically homogenous chemical network is formed as a result of intrachain and interchain crosslinking. Simultaneous grafting of macromolecular fragments formed by chain scission also occurs. On increasing the irradiation dose from 1 to 15 Mrad, the degree of crystallinity determined by x-ray diffraction and the total intensity of diffraction gradually decrease. The temperature and enthalpy of melting diminish steeply up to 5 Mrad, fall only slightly from 5 to 8 Mrad, and do not change from 8 to 15 Mrad. By comparing the x-ray and DTA crystallinity values, this is shown to be due not only to reduced crystallinity at higher network density but also to Tree energy changes of entropic origin in crystalline and amorphous regions. Radiation chemical yields, G(-units), for these dose ranges are 100, 38, and 0, respectively. Thermomechanical analysis was used to determine the elastic modulus of compression as a function of the dose absorbed, and the average molecular weight of network chains was estimated. decreases with doses up to 10 Mrad and does not change with further irradiation.     

The effect of molecular weight on the topography of thin films of blends of poly(4-bromostyrene) and polystyrene

Blends of polystyrene and poly(4-bromostyrene) phase-separate during spin-casting onto silicon wafers to give a thin film with islands of poly(4-bromostyrene) in a sea of polystyrene. Variation of the molecular weights of the blend components shows that the poly- (4-bromostyrene) and polystyrene influence the film structure in different ways. For poly(4-bromostyrene) of a given molecular weight, the ratio of the observed feature height to the overall film thickness remained constant as the film thickness increased. Moreover, the mean height of the topographical features was independent of the polystyrene but decreased with the molecular weight of the brominated polymer. It is concluded that the substrate–poly(4-bromostyrene) interaction dominates the formation of topography and consequently, though the islands are poly(4-bromostyrene), the mean height of the topographical features is greater the lower the molecular weight of the brominated polymer. The polystyrene has a secondary role, altering the thermodynamics or viscosity of the blend, thereby controlling the number of islands formed: the higher the molecular weight of the polystyrene the greater the number of islands. Received: 2 December 1999 Accepted: 7 April 2000     

The morphology of ultradrawn polyethylene. I. Nitric acid etching plus gel permeation chromatography

Transparent strands of high-density polyethylene of unusually high c-axis orientation have been produced by a solid-state extrusion, involving pressure, temperature, and deformation, in an Instron capillary rheometer. Measured values for tensile modulus are higher than previously reported for any polyolefin. Previous modulus and electron microscopic data are consistent with a strand morphology comprised (≤20%) of of extended chain crystals. The remainder resembles an oriented fibrillar morphology such as found in highly drawn polyethylene. In the present study, fuming nitric acid etching of the ultraoriented strands, in combination with gel permeation chromatography (GPC), has provided incisive structural information. The strands exhibit ≥3X the resistance to acid degradation shown by conventionally drawn polyethylene. GPC molecular weight distributions (MWD) of etched samples show a single broad peak with a prominent high molecular weight tail. The crystal size, represented by the MWD, is in agreement with the crystal long period determined by small-angle x-ray scattering. The absence of multiple peaks in the etched MWD's is evidence of limited chain folding. The extended chain content, determined from the etched MWD's, is a strong function of strand formation temperature and is in agreement with the fraction of extended chains calculated from modulus measurements.     

Time-resolved structural studies in fiber processing

Time-resolved and off-line synchrotron wide-angle and small-angle x-ray scattering (WAXS and SAXS) was used to study the structure formation in poly-p-phenylenebenzobisoxazole (PBO) fibers during various stages of spinning, coagulation, and heating processes. WAXS data could be explained in terms of liquid-crystalline structures of varying degrees of order. A structure model is proposed that is in accordance with the observed SAXS four-point pattern.     

Electrochemical Properties of Poly-o-Phenylenediamine Films in Solutions with Variable Concentration of Hydronium Ions

Electrochemical behavior of poly-o-phenylenediamine (PoPhD) films in lithium perchlorate and perchloric acid solutions of different pH and constant ionic strength is studied using cyclic voltammetry, low-amplitude chronoamperometry, chronopotentiometry, and faradaic-impedance spectroscopy. The experimental results point to the diffusion–migration kinetics of charge transfer processes in redox-active PoPhD films and show that two such processes occur during oxidation–reduction of PoPhD. The processes are separated most fully at low concentrations of hydronium ions. Effect of the electrode potential and electrolyte composition on these processes is examined. Different methods yield similar results and permit their more reliable interpretation.     

Molecular weight distribution of poly-N-vinylcarbazole obtained in catalytic solid-state polymerization

The molecular weight distribution of poly-N-vinylcarbazole (PVCar) obtained in solid-state polymerization with various catalysts or γ-rays was measured by gel-permeation chromatography, in order to determine the mechanism of the solid-state polymerization. In addition, the molecular weight distribution of PVCar obtained in the solution polymerization by the cationic catalyst was also measured. The molecular weight distribution of PVCar obtained in the catalytic solid-state polymerization was broad and had three peaks, independent of the nature of catalysts, radical and cationic. A large amount of low molecular weight oligomer (probably dimer or trimer) was formed in the catalytic solid-state polymerization of VCar. The molecular weight distribution of PVCar obtained in the cationic solution polymerization showed only one sharp peak. On the other hand, the molecular weight of PVCar obtained in the radiation-induced solid-state polymerization was larger than that obtained in the catalytic solid-state polymerization, and dimer or trimer was not formed. The molecular weight distribution of PVCar obtained was composed of one sharp peak in the high molecular weight region, and a broad peak in the low molecular weight region, and was extremely different from that of PVCar obtained in the catalytic solid-state polymerization.     

The drawing behavior of linear polyethylene. I. Rate of drawing as a function of polymer molecular weight and initial thermal treatment

The drawing behavior of a series of linear polyethylene homopolymers with weight-average molecular weight (M?_w) ranging from 67,800 to ～3,500,000 and variable distribution (M?_w/M?_n = 5.1?20.9) has been studied. Sheets were prepared by two distinct routes: either by quenching the molten polymer into cold water or by slow cooling below the crystallization temperature (～120°C) followed by quenching into cold water. When the samples (2 cm long) were drawn in air at 75°C using a crosshead speed of 10 cm/min it was found that for low M?_w polymers the initial thermal treatment has a dramatic effect on the rate at which the local deformation proceeds in the necked region. At high M?_w such effects are negligible. An important result was that comparatively high draw ratios (λ > 17) and correspondingly high Young's moduli could be obtained for a polymer with M?_w as high as 312,000. It is shown how some of the structural features of the initial materials (mainly studied by optical microscopy, small-angle x-ray scattering and low-frequency laser Raman spectroscopy) can be interpreted in terms of the molecular weight and molecular weight distribution of the polymers. Although crystallization and morphology can be important at low M?_w, it suggested that the concept of a molecular network which embraces both crystalline and noncrystalline material is more helpful in understanding the drawing behavior over the whole range of molecular weights.     

Dielectric studies on some mesogenic,non-mesogenic and organic molecules

Two important molecular parameters, namely, the dielectric relaxation time τ and electric dipole moment are highly useful in having insight into the molecular structure, size, shape, apart from the inter- and intra-molecular forces, etc. With these in view dielectric measurements in benzene at room temperature on the pure samples of o-ethyl phenol, 2-n-butylphenol, 4-n-butylphenol, 2,6-dimethoxyphenol and 3,4-difluorophenol were carried out at a frequency of 9.98 GHz by employing concentration variation method. Similar measurements, on a single weight fraction of each of them at 9.98 GHz and also at 8.74 GHz are carried out. Measurements on a single weight fraction in benzene of each of the liquid crystal samples, namely, EPCP.car (Butyl-p-(p-ethoxy phenoxy corbonyl)-phenyl carbonate), PPPB (p-pentylphenyl-p-propyl benzonate), EPAP.Hp (p-(p-ethoxyphenyl azo) phenyl heptenate) and EPAP. Und (p-(p-ethoxyphenyl azo) phenyl undecylenate were also carried out at the said two frequencies. Using the obtained values of ε′, ε′′ relaxation time and dipole moment were determined using different methods. The obtained results are compared with earlier results wherever available.     

Chemical synthesis of poly-o-phenylidenediamine-silicomolybdic acid composite and its electrochemical and spectral properties

A new method for chemical production of composites based on poly-o-phenylidenediamine (PPD) by oxidizing o-phenylidenediamine (OPD) with silicomolybdic acid (SiMo) in neutral and acidic media is developed. Electrochemical and spectroelectrochemical studies reveal the presence of small deviations in the properties of composites synthesized. Cyclic voltammetry studies show that the composites are active and exhibit sufficiently high electrochemical stability. The presence of SiMo anions in the PPD matrix is confirmed by electrochemical and spectral studies in combination with x-ray microanalysis of composites. The ratio between the number of phenylazine polymeric links and heteropolyanions is found.     

Chromatographic Analysis of Structural Elements of Molecular Polyimide Brushes with Polymethacrylate Side Chains

The method of thin-layer chromatography under critical conditions was used for the analysis of the functional and structural inhomogeneities of polymethylmethacrylate and poly-tert-butylmethacrylate side chains cleaved from molecular polyimide brushes. Acetic acid–containing mobile phases are suggested, allowing a gradual transition from adsorption to exclusion chromatographic regime to be observed upon variation of the mobile phase composition for both cleaved side chains and “reference” polymethylmethacrylate and poly-tert-butylmethacrylate linear polymers. The presence of a few kinds of cleaved side chains having one terminal carboxylic group and differing in the nature of the other terminal group is revealed.     

Osmotic compressibility in dilute polystyrene‐cyclohexane and polystyrene‐methylcyclohexane solutions: Correlation of polystyrene virial coefficients with solvent quality

Osmotic compressibilities were determined as a function of temperature for solutions of polystyrene in cyclohexane and methylcyclohexane by static light scattering, the measurements extending well below the theta temperature, T = θ. Virial coefficients extracted from the data are compared with literature values obtained by light scattering, membrane osmometry, and phase equilibrium measurements, and successfully correlated over wide ranges of molecular weight, temperature, and solvent quality. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 184–196, 2001     

Crystal structure of poly-p-xylylene. I. The α form

The molecular conformation and the crystal structure of α-form poly-p-xylylene has been determined by x-ray diffraction. The polymer has a monoclinic unit cell with a = 5.92, b = 10.64, c (fiber axis) = 6.55 Å, and β = 134.7°. Two chains pass through the unit cell, and the space groups is C2/m. The packing fraction is 0.705. One monomer unit makes up the fiber identity period and the internal rotation angles are 0° and 90° for the ? CH₂? CH₂? and ? CH₂? ?? bonds, respectively. All benzene rings are in parallel orientation, perpendicular to the ac plane.