Dynamics of cyclic poly(methylphenylsiloxane)

Fluorescence spectra of cyclic poly(methylphenylsiloxane)s having 3, 4.4 and 9.0 monomelic units, and of the monochromophoric analog methylphenyldimethoxysilane (MS), were measured as a function of temperature in the range 150 to 320 K. Both the low- and the high-temperature limits were reached in this range. The crossover temperature between both limits was thus determined, as well as the activation energy for excimer formation and the excimer binding enthalpy. From measurements of the lifetime of MS as a function of temperature, the rate constant for excimer formation was also determined, and its relationship with the rate constant for rotation through backbone bonds was discussed.     

Chemical modification of poly(methylphenylsiloxane)

Poly(methylphenylsiloxane) (PMPS) with a narrow molecular weight distribution (MWD) was prepared by anionic polymerization, and ring‐functionalized using procedures optimized to minimize chain degradation. The products were characterized by NMR and IR spectroscopy, and the MWD of the polymers was analyzed by size exclusion chromatography, to monitor polymer degradation and crosslinking during the functionalization reactions. Electrophilic substitution was used to introduce nitro and bromo groups on the phenyl ring of the polymer. Nitration with fuming nitric acid yielded up to 8 mole % substitution with some chain degradation. Bromination was achieved with bromine in the presence of either pyridine or triethylamine. A substitution level of up to 14 mole % and a small increase in the polydispersity index (M_w/M_n) were obtained with triethylamine. Hydroxyethyl functionalities were obtained by lithiation of the brominated PMPS via metal‐halogen exchange, and reaction with ethylene oxide. A polymer with 3 mole % hydroxyethyl functionalities was obtained with moderate chain degradation. A substitution level of 6 mole % could be achieved under different conditions, but with more extensive chain degradation. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 653–664, 1999     

Viscoelastic properties of amorphous polymers 3: low molecular weight poly(methylphenylsiloxane)

By making creep and recoverable creep measurements of a nearly monodisperse low molecular weight poly(methyl phenyl siloxane) sample, we have found on decreasing temperature towardsT _g that there is continuously a change in the viscoelastic spectrum concomitant with a decrease of the steadystate recoverable compliance. This behavior is exactly the same as previously observed in low molecular weight poly(styrene), proving that this spectacular anomaly in the viscoelasticity of low molecular weight polymers is general and deserves an explanation. Photon correlation spectroscopic measurements performed on the same sample have extended the observation of the viscoelastic response to shorter times and the result corroborates the trend of variation established by the creep data.Dedicated to Prof.Dr. E. W. Fischer on his 65th Birthday. Prof.Dr. Fischer is known for his valuable contribution to fosterine, international collaboration of research in polymer science. This work is an example of his contribution because it would not be possible without him bringing us together. One of us (KLN) would like to take this opportunity to thank Prof. Dr. Fischer for his unwaiving support of the 1st (Crete) and the 2nd (Alicante) International Discussion Meeting on Relaxations in Complex Systems     

Hydrodynamic, electrooptical, and conformational properties of fullerene-containing poly(2-vinylpyridines) in solutions

For C₆₀ fullerene-containing poly(2-vinylpyridines) synthesized by anionic polymerization, the molecular mass and hydrodynamic size of macromolecules in solutions have been determined by molecular hydrodynamics (translational diffusion and viscometry) and electrooptics in dilute benzene and THF solutions. Under the same conditions in the molecular mass range (9.8–123) × 10³, the hydrodynamic behavior of linear poly(2-vinylpyridines) and their molecular-mass dependences have been examined and the conformational characteristics of macromolecules have been established. The branching of macromolecules has been characterized by comparing the properties of star-shaped fullerene-containing and linear poly(2-vinylpyridines). With consideration of the hydrodynamic data interpreted within the framework of regular star model, it is inferred that on average three to four linear polymer chains with a molecular mass of (8 ± 3) × 10³ for each chain are attached to a fullerene core of C₆₀ in molecules of fullerene-containing poly(2-vinylpyridines). The specific Kerr constant of fullerene-containing poly(2-vinylpyridines) in dilute benzene solution is ?(14 ± 1) × 10^?12 cm⁵/[g (300 V)²]. As evidenced by the electrooptical data, the incorporation of fullerene into the polymer weakens self-association of macromolecules in solution.     

The bulk viscoelastic properties of poly(styrene-co-sodium styrene-p-carboxylate)

The effect of up to 7.82 mol % ionic groups on the stress relaxation and dynamic mechanical (torsion pendulum) properties of poly(styrene-co-sodium styrene-p-carboxylate) was studied. The results obtained were compared with those reported elsewhere for polymers containing the same ionic groups at a different position on the polystyrene backbone (styrene-sodium methacrylate copolymers) and with polymers containing different ionic groups at the same position (styrene-sodium styrene-p-sulfonate copolymers). The results of these comparisons showed that positioning of ionic groups affects the size of ionic aggregates formed, while their type dictates the strength of the forces within the aggegrates.     

Thermal degradation kinetics of poly(methylphenylsiloxane) containing methacryloyl groups

The kinetics of the thermal degradation of polymethylphenylsiloxane containing methacryloyl groups (PMPS-M) were investigated by thermogravimetric analysis (TGA). Thermal degradation of PMPS-M had two different processes: “unzipping degradation” and “rearrangement degradation”. The corresponding kinetic parameters of the two degradation stages were determined by using Friedman and Flynn-Wall-Ozawa methods, respectively. Coats-Redfern and Phadnis-Deshpande methods were also used to discuss the probable degradation mechanisms of the two different stages. The results showed that the activation energy obtained from Friedman method was in good agreement with the value obtained using Flynn-Wall-Ozawa method. The solid-state decomposition mechanism followed by the first degradation stage of PMPS-M was a decelerated D₄ type (three-dimensional diffusion controlled reaction). However, as for the second degradation stage of PMPS-M, its solid-state decomposition mechanism corresponded to a sigmoidal A₃ type, a nucleation and growth mechanism.     

Dielectric properties of poly(4-methylphenylisocyanate) and poly(4-methoxyphenylisocyanate) in solution

In the range 200 Hz-2 MHz, the dielectric behaviour of two polyarylisocyanates depends on the solvent. In certain solvents, such as toluene, there is only one high frequency absorption for poly(4-methylphenylisocyanate) and it is independent of molecular weight. Its character corresponds to chains having a low kinetic flexibility. In other solvents, this polymer, as well as poly(4-methoxyphenylisocyanate), shows two regions of dielectric absorption. The low frequency relaxation is molecular weight dependent: a polarization due to solvent polymer interactions occurs along the main chain. Despite its solvent-dependence, the total dipole moment of these polyarylisocyanates which behave like coils is much lower than that of polyalkylisocyanates, which are known to be rod-like.     

Characterization and degradation of poly(methylphenylsiloxane)–poly(methyl methacrylate) interpenetrating polymer networks

Poly(methylphenylsiloxane)–poly(methyl methacrylate) interpenetrating polymer networks (PMPS–PMMA IPNs) were prepared by in situ sequential condensation of poly(methylphenylsiloxane) with tetramethyl orthosilicate and polymerization of methyl methacrylate. PMPS–PMMA IPNs were characterized by infrared (IR), differential scanning calorimetry (DSC), and ²⁹Si and ¹³C nuclear magnetic resonance (NMR). The mobility of PMPS segments in IPNs, investigated by proton spin–spin relaxation T₂ measurements, is seriously restricted. The PMPS networks have influence on the average activation energy E_a,av of MMA segments in thermal degradation at initial conversion. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1717–1724, 1999     

Characterization and degradation of the poly(methylphenylsiloxane)–poly(methyl methacrylate) graft copolymer

Poly(methylphenylsiloxane)–poly(methyl methacrylate) graft copolymers (PSXE-g-PMMA) were prepared by condensation reaction of poly(methylphenylsiloxane)-containing epoxy resin (PSXE) with carboxyl-terminated poly(methyl methacrylate) (PMMA), and they were characterized by gel permeation chromatography (GPC), infrared (IR), and ²⁹Si and ¹³C nuclear magnetic resonance (NMR). The microstructure of the PSXE-g-PMMA graft copolymer was investigated by proton spin–spin relaxation T₂ measurements. The thermal stability and apparent activation energy for thermal degradation of these copolymers were studied by thermogravimetry and compared with unmodified PMMA. The incorporation of poly(methylphenylsiloxane) segments in graft copolymers improved thermal stability of PMMA and enhanced the activation energy for thermal degradation of PMMA. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 2521–2530, 1998     

Random-coil dimensions of poly(methylphenylsiloxane) and their dependence on stereochemical structure

Rotational isomeric state theory was used to study the unperturbed dimensions 〈r²〉₀ of poly(methylphenylsiloxane) (PMPS) chains [Si(CH₃)(C₆H₅)? O? ]_x as a function of their stereochemical structure. The required conformational energies were obtained from semi-empirical, interatomic potential energy functions and from known results on poly(dimethylsiloxane). PMPS chains were found to differ from monosubstituted and disubstituted vinyl chains primarily in the larger distance of separation between groups in conformations giving rise to “pentanetype interactions.” In PMPS, the relatively large distance of separation, 3.8 Å, makes such in teractions attractive, particularly in the case of two phenyl groups; in contrast, such interactions are strongly repulsive at the ～2.5 Å separation characterizing vinyl chains. According to the calculated results, PMPS chains are very different from vinyl chains in that increase in isotacticity should cause a significant decrease in 〈r²〉₀ and increase in d ln 〈r²〉₀/dT. Comparison of theory with experimental results in the literature suggests that PMPS polymers which have been studied in this regard must have been significantly syndiotactic in stereochemical structure.     

Synthesis and solution properties of poly(diphenyl itaconate)

Solid diphenyl itaconate monomer was obtained by esterification in the presence of diphosphorus pentoxide and polymerized in bulk with AIBN as initiator. The non-film forming polymer powder was characterized by fractionation, viscosity measurements, light scattering and other techniques. The relation [n] = 3·6 × 10^?3$\text{M}$^0·70_w, obtained for toluene at 25° was extrapolated to θ-conditions by various procedures: the σ-value of 2·60 for unperturbed dimensions indicates a less pronounced influence of phenyl compared with other C₆ hydrocarbon substitutes.     

Synthesis and solution properties of poly(2-methylproline)

The resolution of 2-methylproline and the assignment of absolute configuration to the stereoisomer has been carried out. The L-enantiomer was obtained from the fractional crystallization of the quinine salt of (?)-N-carbobenzoxy-2-methylproline and the D-enantiomer from the collected filtrates. The (?)-2-methylproline was assigned the L-configuration by means of the Clough-Lutz-Jirgensons method. Polymers were obtained in bulk from the N-carboxyanhydrides. Although polymers obtained from different solvents exhibited different solubility properties, subsequent spectral studies indicated that this effect was not due to a large conformational change as in the polyproline case. Spectral evidence suggests that poly(2-methylproline) (P2MP) exists as a polyproline type II helix.     

Synthesis and solution properties of poly(ditoluyl itaconates)

The three o-, m- and p- isomers of ditoluyl itaconate were obtained by esterification of cresols and itaconic acid in the presence of diphosphorous pentoxide, and then polymerized in bulk with AlBN as initiator. The polymers were investigated in dilute solution, including $\text{M}{}_{\mathrm{W}}$ determination and precipitation fractionations, and the results compared with those for poly(diphenyl itaconate). The presence and position of -CH, in the aromatic ring influence the initial rates of polymerization, polymer solubilities in organic solvents and $\text{[η]/}\text{M}{}_{\mathrm{W}}$ relations. Unperturbed dimensions, obtained by extrapolating to τ-conditions, vary slightly with the -CH, group position, due to steric and probably other effects.     

On solution properties of poly(γ-benzyl-L-glutamate)

Summary The refractive index increments,dn/dc, of poly(-benzyl-L-glutamate) in various solvents have been critically examined in respect to their dependence on the refractive index of the solvent. An unusual scatter of data for different solvents and disagreement among the values for the same solvent obtained in different laboratories have been noticed and commented upon. The significance of these findings for the interpretation of light scattering measurements of molecular parameters of this polymer in solution has been discussed.

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Zusammenfassung Der Wertzuwachs des Brechungsindexdn/dc von Poly(-benzyl-L-glutamat) in verschiedenen Lösungsmitteln wird kritisch untersucht mit Rücksicht auf seine Abhängigkeit vom Brechungsindex des Lösungsmittels. Dabei werden eine ungewöhnliche Streuung der Werte für verschiedene Lösungsmittel, und ein Nichtübereinstimmen der Werte für das gleiche Lösungsmittel, die man in verschiedenen Laboratorien gewann, festgestellt und kommentiert. Die Bedeutung der Ergebnisse für die Interpretation der Lichtstreuungs-Messungen von molekularen Parametern dieses Polymeren in Lösung wird diskutiert.

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With 1 figure and 3 tables     

Acid-base properties of poly(1-vinylazoles) in aqueous solution

The interaction of poly(1-vinylimidazole) and poly(1-vinyl-1,2,4-triazole) with HCl and alkalies in aqueous and water-salt solutions was investigated by potentiometric titration, viscosimetry, ¹H and ¹³C NMR, and UV spectroscopy. The effect of the nature and concentration of low-molecular counterions was found. The interaction of poly(1-vinylazoles) with the acid results in the protonation of the azole cycle. The interaction of poly(1-vinylazoles) with alkalies is stipulated by the capability of the pyridine N atom of forming a coordination bond with the metal ion and that of the unsaturated pi-system of the heterocycle of coordinating with the anions.     

Effect of moisture on the bulk properties of salted poly(caproamide)

The glass-transition temperature (T_g) and the elastic modulus of nylon-6 and its mixtures with 4% w/w LiCl and with 2% LiCl+3% LiBr were investigated. In one set of experiments care was taken to avoid absorption of moisture during the measurements. In another set of experiments, samples were exposed to atmospheric humidity for different lengths of time. Both unoriented and oriented specimens were investigated. The presence of 4% LiCl almost doubles the amount of moisture absorbed at equilibrium by nylon-6. The T_g was found to be greatly affected by the moisture content and by salt type. When strict precautions to exclude moisture are taken, the addition of 4% LiCl raises the T_g of nylon-6 by about 25°C. The elastic modulus of oriented samples is increased by the addition of salts provided moisture is completely absent. This beneficial effect is, however, completely eliminated when samples are allowed to equilibrate with atmospheric moisture.     

Dilute solution properties and molecular characterization of poly(butyl methacrylate-co-styrene)

Dilute solution properties of fractionated poly(butyl methacrylate-co-styrene) PBMAS prepared by bulk polymerization, have been investigated by means of light scattering, viscometry, and osmometry. As the composition heterogeneity was narrow, the characterization of the copolymer was effected in a single solvent by light scattering. Infrared and nuclear magnetic resonance spectra were used to determine the composition and sequence distribution of monomer units of the copolymer. The molecular weight dependence of the limiting viscosity number and of the root-mean-square end-to-end distance have been established. The Mark-Houwink relation showed that methylethyl ketone is a good solvent compared with cyclohexane. The validity of various extrapolation procedures that have been proposed to calculate the unperturbed dimensions have been examined. Root-mean-square end-to-end distances have been calculated from the Debye-Bueche and Kirkwood-Riseman methods and compared with the experimental values. The molecular weight dependence of the second virial coefficient agreed well with that calculated from the Orofino-Flory equation. The value of the steric hindrance parameter σ for the copolymer has been found to be 2.27 compared to 2.05 for poly(butyl methacrylate) and 2.22 for polystyrene, which indicates that PBMAS is a stiffer chain in solution than those of the constituent homopolymers.