Search

Small-angle X-ray scattering (SAXS) was used to obtain solution parameters of a weak polyelectrolyte in water in the absence of any additives, such as neutralizing agents or salt. Poly(acrylic acid) (PAA) was used as a weak polyelectrolyte from which SAXS data were obtained in the dilute region of 1-10 mg cm -3 . An intrinsic viscosity of 15.7 dL g -1 was obtained from a plot of reciprocal reduced viscosities versus the concentration. The application of the SAXS data, that is, the contour length (L = 1.97 x 10 4 A), the persistence length (a* = 58.5 A), and the molecular weight (M = 5.9 x 10 5 Da), to the Yamakawa-Fujii equation suggested that PAA in water at 25 °C could be described as a wormlike chain having a cylindrical body of d = 6 A. An end-to-end distance (r = 1.6 x 10 3 A) was calculated from r = 2a*L - 2(a*) 2 . The nonisotropic expansion factor (α = 2.9) was calculated for PAA expanding from the random coil in dioxane at 30 °C Θ) temperature) to the wormlike chain in water at 25 °C.

Small-angle X-ray scattering (SAXS) has been applied in obtaining the solution parameters (molecular mass M, radius of gyration Rg, radius of gyration of cross-section Rq, mass per unit length Mu, and persistence length a ∗ ) of a poly(acrylic acid) (PAA) sample in dioxane at 25°C. The M and Rg values measured from SAXS were 552 000 Da (daltons) and 292 A, respectively. These values are in reasonable agreement with those obtained from solution viscometry measurements on the same sample of PAA in dioxane at 30°C ( M = 567 000 Da and R g = 227 A ). The Rq and a ∗ values obtained from SAXS were 6.1 A and 14.4 A, respectively. The Mu value measured from SAXS is 27.9 Da A−1, in excellent agreement with the model (theoretical) value of 28.6 Da A−1 calculated from the structure and molecular mass of the monomer unit. The length L (= M/Mu = 19 790 A) obtained from SAXS thus corresponds to the contour length of the molecule and not to the ‘hydrodynamic’ length (i.e. the length the chain assumes in the fluid medium).

Isotactic and atactic poly(4-methyl-1-pentene) powders were degraded in the presence of pure oxygen at temperatures of 145° and 175°C. The functional groups present in the nonvolatile products were identified using infrared spectroscopy. The volatile products that formed were identified by means of a relativly new technique which combines gas chromatography and mass spectroscopy. In this study, seventeen volatile products were detected and identified and their relative abundance estimated. The results obtained could readily be reproduced. Various oxidation mechanisms for these products are postulated.

The kinetics of the acid degradation of Streptococcus salivarius levan was studied by observing changes in the number-average molecular weight, Mn, using end-group analysis. Rate constants for the hydrolysis are presented and a tentative mechanism is forwarded. The data has been analysed according to a statistical model for a polymer with trifunctional branching and it is shown that the hydrolysis of levan proceeds through a mechanism quite different to that reported for the polysaccharide dextran.

Bovine heparin was fractionated according to molecular weight by fractional precipitation utilizing a method described previously. The solution data from sedimentation analysis, intrinsic viscosities and partial specific volumes at pH 2·5 and in 0·5 M NaCl were treated according to the Mandelkern and Flory theory for random coil in calculating the constant β. It was found that the calculated β values for all the fractions were in close agreement with the theoretical value. Based on this observation, the solution data were then treated in light of various hydrodynamic theories for linear polymers to calculate various dimensional and other physical parameters, e.g., ( r 2 ) 1 2 , α (expansion factor), A 2 . In comparing ( r 2 ) 1 2 of a fraction to that calculated from the experimental value of ( s 2 ) 1 2 obtained from low angle X-ray scattering for a comparable molecular weight sample, it was found that heparin in solution with suppressed charges may best be described as approximating the closely related models of Debye and Bueche, Flory and Fox, or Kuhn and Kuhn.

Solution characterization of four samples of high molecular weight linear polystyrene (HMWLPS) in the molecular weight range of 1.61 × 106 to 9.71 × 106 in methyl ethyl ketone (MEK) at 25°C. was assessed from light scattering (LS), viscosity, and small-angle x-ray scattering (SAXS) under five different entrance-slit (E) /counter-slit (Z) combinations of 20/50, 30/75, 60/150, 100/250, and 150/375 μ, using the Kratky camera. The molecular weights and radii of gyration ( 1/2) obtained from SAXS under various slit combinations were then compared to the values obtained from LS. Further, the calculated values of 1/2based on the theoretical relationship between size, entrance-slit and counter slit openings were compared to he experimental values of 1/2 of each sample. Thus establishing the upper limits of size for a given E/Z combination.

All materials are subject to aging, a process of long-term degradation, but not at the same rate or affected in the same manner. The wide variation in susceptibility (or resistance) of polymers to various degradative agents, e.g., oxidative, thermal, mechanical, chemical, biological, depend on their chemical composition and structure. Accordingly, the chemical, physical, and energy considerations inherent in the pure polymer are discussed in relation to degradative stability.

Isotactic poly(1-pentene) was degraded in the presence of pure oxygen at 115°C. The functional groups present in the non-volatile products were identified using infra-red spectroscopy. The volatile products formed were identified by means of a relatively new technique which combines thermal and mass chromatography. In this study, fourteen volatile products were detected and identified and their relative abundance estimated. The results obtained could readily be reproduced. Various oxidation mechanisms for these products are postulated.

The viscosity of heparin was examined in pure glycerol, formamide and in mixtures of the two solvents. This study confirms that the equation η sp c = [η] ∞ [1 + k (c) 1 2 ] , where [η]∞ is the shielded intrinsic viscosity, adequately describes the concentration dependence of the reduced viscosity of the polyelectrolyte, heparin. The [η]∞ linearly increases with the dielectric constant of the solvent.

The kinetics of the thermal oxidation of isotactic poly(1-pentene) was studied in the bulk phase. The experimental data were obtained from the quantitative estimation of carbonyl groups formed in the non-volatile oxidation products using infra-red spectroscopy. Reaction temperature varied from 100° to 115° and oxygen concentrations from 10% to 100% by volume. A general kinetic scheme and mathematical expressions previously reported for the thermal autoxidation of polyolefins satisfactorily explained the experimental results. Activation energies of this polymer for various steps in the kinetic scheme were compared with polypropylene and poly(1-butene).

Small-angle X-ray scattering, SAXS, measurements were obtained from 12-arm near-monodisperse star polystyrenes in methyl ethyl ketone at 25°C. Calculations from the SAXS data yielded information on the molecular weight, Ms, the radius of gyration, Rg, mass per unit length, mu, radius of gyration of the crosssection, Rq, and persistence length, a∗. Values of Ms and Rg from SAXS were in good agreement with values obtained from light scattering. A branching parameter in terms of a∗, s = a∗1a*b where subscripts l and b refer to linear and branch, respectively, is introduced and related in terms of functionability, f, or g, where g = (Rg)b(Rg)l.

The kinetics of the thermal oxidation of isotactic and atactic poly(4-methyl-1-pentene) were studied in the bulk phase using infra-red (i.r.) spectroscopy. The rates of formation of the non-volatile products were assessed from the i.r. bands of the carbonyl groups at different temperatures and various oxygen concentrations. Reaction temperature varied from 120° to 185°C and oxygen concentrations from 10 to 100%, by volume. A general kinetic scheme and mathematical expressions, previously reported for the thermal oxidation of polyolefins, satisfactorily explained the experimental results. Single activation energies for the major oxidation stages in the scheme, were estimated from various Arrhenius plots.

Comb-branched polystyrenes having both fixed backbone length and number of branches but variable branch lengths were prepared anionically. Small angle X-ray scattering of the model polystyrenes from methyl ethyl ketone (MEK) solutions at 25°C was examined and it is shown that the mass per unit length and cross-sectional radius of gyration increase with increasing branch length. A maximum appears in the Kratky plot for the branched polymers. While the linear polymer displays an essentially Gaussian segment distribution in solution, the branched polymers deviate considerably from the behaviour of the linear polymer under the same conditions.

A bovine heparin fraction was examined by sedimentation analysis and intrinsic viscosity measurements as a function of ionic strength in the range of 0·1 to 1·0 M, and at pH 2·5 and 6·0. The following experimental parameters were obtained: M , S 0 20,W , D 0 20,W , V , and [η]. Other physical parameters were calculated based on a random coil model (supported by the theory of Mandelkern and Flory) e.g., ( r 2 ) 1 2 , ( s 2 ) 1 2 . Similar studies were made on a heparin sample as a function of desulphation as resulting from graded mild hydrolysis. Since desulphation is accompanied by decreasing anticoagulant activity of heparin, the latter was correlated with various calculated and measured physical parameters. Significantly ( r 2 ) 1 2 decreases with decreased desulphation and therefore decreased biological activity.

An isotactic polybutene-1 was fractionated, and melting points of several fractions were determined. The fractions were studied by light-scattering and viscosity techniques. The parameters in the Mark-Houwink equation are [η] η 4.73 × 10−5M in heptane at 35°C., [η] = 1.50 × 10−4M in heptane at 60°C., and [η] = 9.49 × 10−5M in decalin at 115°C. The molecular weight range studied was 0.45 × 105 to 0.9 × 106.

The authors had previously reported a general scheme with corresponding kinetic expressions for the uncatalyzed thermal autoxidation of polyolefins, such as atactic polybutene-1 (APB), in the bulk phase. Recently, Bawn and Chaudhri reported that similar kinetic expressions and scheme were also applicable to autoxidation of atactic polypropylene (APP) in solution. These workers did not attempt to correlate their results for the effect of oxidation on the molecular weight of APP as evidenced by intrinsic viscosity. In this paper, we have applied expressions, previously reported for changes in intrinsic viscosity as a function of time during the autoxidation of APB in the bulk phase, to the data provided by Bawn and Chaudhri for the autoxidation of APP in solution. The quantitative evidence obtained indicates that the intrinsic viscosity relationships which were found to be valid for the autoxidation of APB in the bulk phase are also valid for the autoxidation of APP in solution (at polymer concentrations of ca. 1.5M and above).

The autoxidation of a film of isotactic polybutene-1 (IPB) containing a large amount of metallic ash (about 0.2%) was studied by means of infrared spectroscopy. Reaction temperatures were varied from 105 to 120C and oxygen concentrations from 25 to 100% by volume. A reaction scheme previously reported for the autoxidation of atactic polybutene-1 (APB) was utilized for the IPB. Various results obtained for IPB were compared with those previously reported for APB. (Author)

A general scheme previously reported for the autoxidation of polyolefins is further substantiated by results obtained for the uncatalyzed and catalyzed autoxidation of various concentrations of atactic polypropylene (APP) (by admixture with polyisobutylene) under various experimental conditions. Thus, rates of maximum carbonyl formation were measured as a function of APP concentration at 120C, oxygen concentrations ranging from 0.5 - 100% by volume and cobaltic acetylacetonate catalyst concentrations (3 and 17) x 0.0000001 mole/7.5 mg sample. Good agreement was found between experimentally observed and theoretical dependencies of the maximum carbonyl formation rate on APP concentration derived from the combined reaction scheme. (Author)

The kinetics of uncatalyzed autoxidations for polyolefin films, such as atactic and isotactic polypropylene and poly-(butene-1) are reviewed in light of recent work. Reaction temperatures generally varied from 100 to 150°C and oxygen concentrations from 5 to 100% by volume. A general reaction scheme is suggested and kinetic expressions subsequently derived therefrom have been satisfactorily applied to account for experimental results. Linear relationships between a maximum rate and concentration of oxygen for both low and high concentrations were obtained. In the case of the catalyzed autoxidations [Co(III) acetylacetonate] the general reaction scheme was modified to take into account the presence of the catalyst. From this modified scheme, various kinetic expressions relating maximum rate and concentrations of oxygen, polymer and the catalyst were derived. First-order reaction with respect to the concentration of the catalyst was found at low concentrations of the catalyst, and near zero-order at relatively high catalyst concentrations. A correlation between catalytic activities of metal acetylacetonates [Co(III), Mn(III), Cr(III), Fe(III) and Cu(II)] and the oxidation-reduction potentials has been established. Experimental dependencies of maximum carbonyl formation rates as a function of polymer concentration were found to agree well with the theoretical both for catalyzed and uncatalyzed oxidations.

The uncatalyzed, uninhibited thermal oxidation of a film of atactic polybutene-1 was studied by means of infrared spectroscopy. Reaction temperatures varied from 110 to 130°C. and oxygen concentrations from 12.5 to 100% by volume. A reaction scheme previously reported for the oxidation of isotactic polypropylene was utilized for the atactic polybutene-1. It was found that the scheme and the mathematical expressions derived therefrom could satisfactorily explain the experimental results obtained.

Expressions were derived relating changes of intrinsic viscosity to reaction time, based on a scheme previously presented for the uncatalyzed, uninhibited thermal oxidation of polyolefins. A value of the kinetic parameter A may be obtained from these expressions by using an iterative type of procedure and employing data presented by other workers for the oxidation of atactic polybutene-1. This value of A was compared with the corresponding value obtained by the authors from rate of carbonyl formation studies in oxidation of atactic polybutene-1 by means of infrared absorption spectroscopy methods. The good agreement between the values of A obtained from the two different experimental techniques employed lends further support to the validity of the scheme used and the expressions derived therefrom.

Recently the rate constants for the autoxidation of isotactic polypropylene based upon a postulated relatively simple scheme were calculated. Electron spin resonance, volumetric and chemical techniques were employed. This paper demonstrates that similar values of these rate constants could also be calculated from a more general scheme. From this general scheme, expressions were derived which involved the rate constants of interest and other constants which had been previously calculated from experimental data based upon the use of infrared absorption techniques. The values of the calculated rate constants at various temperatures agreed well with those reported earlier where comparison was possible. (Author)

The iron-catalyzed autoxidation of atactic polypropylene has been studied in the solid phase using infrared spectroscopy. The reaction temperature ranged from 110° to 130°C, the ferric acetylacetonate concentration varied from 0.3 × 10−7 to 90.0 × 10−7 mole per 7.5 mg atactic polypropylene, and the oxygen concentration varied from 5 to 100 vol-%. In the region of relatively low catalyst concentrations, the maximum steady rate varied approximately first order in respect to the catalyst concentration and about zero order at relatively high values of the catalyst concentration. Linear relationships between the maximum steady rate and the oxygen concentration, for both low and high concentrations, were obtained. A general scheme and kinetic expressions derived there-from previously reported for the uncatalyzed autoxidation of polyolefins and recently modified to account for cobalt-catalyzed autoxidation of actactic polypropylene has been successfully applied to the experimental results.

A simplified procedure is presented to estimate the two adjustable parameters in a lognormal distribution function. From values of these parameters, the weight distribution function, W(M), as well as various molecular weight averages can be calculated. The method was applied to fractionation data selected at random for several polymers. The agreement between calculated and reported values appears to be good.

A method is described which allows the precise estimation of molecular weight distribution parameters p and A which pertain to free-radical polymerizations. Thus, expressions are developed which allow the estimation of (1 − p) by means of a programmable calculator using molecular weight distribution data derived from GPC. Values of A may subsequently be calculated by means of a plot of one of the expressions given. Values of (1 − p) and A obtained in this paper were checked using theoretical values as well as by a comparison between calculated and observed values. The agreement between calculated and theoretical or experimental values indicates that the method presented for the estimation of (1 − p) and A is both reliable and relatively rapid. Previously reported methods for the estimation of (1 − p) and A have involved curve-fitting trial calculations as well as more precise interpolation procedures. However, the latter are based on single-peak maximum values.

The autoxidation of a film of atactic polypropylene was studied by means of infrared spectroscopy. Reaction temperatures varied from 110 to 135C and oxygen concentrations from 5 to 100% by volume. A general reaction scheme previously reported for the autoxidation of polyolefins was utilized for atactic polypropylene. Various results obtained for this polymer were compared with those previously reported for isotactic polypropylene. (Author)

The autoxidation of a film of atactic polypropylene (APP) in the presence of cobalt salts was studied quantitatively by means of infrared spectroscopy. Reactions were traced as a function of temperature, oxygen concentration and time. Temperatures varied from 100 to 130C and oxygen concentrations from 5 to 100% by volume. A general reaction scheme previously reported by the authors for the uncatalyzed autoxidation of atactic polypropylene was modified to account for the cobalt acetylacetonate-catalyzed autoxidation of APP in the bulk phase.

Experimental data on dilute solutions of poly(hexene-1), obtained from viscosity, osmometry, and light scattering in various solvents, previously reported, were treated and compared with various hydrodynamic theories of linear polymers. It was found that poly(hexene-1) can best be described by the model of Flory-Fox. Furthermore, the data were found to conform to the treatment of Kinsinger and Ballard for nonpolar polymers in the α-olefin series in the unperturbed state.

Utilizing carbonyl formation data previously obtained during the thermal oxidation of unstabilized atactic polypropylene, unstabilized isotactic polypropylene and unstabilized atactic polybutene-1 along with a semi-empirical expression, it was possible to extrapolate and obtain arbitrary induction times at relatively low temperatures. Values of induction times thus obtained were correlated with changes in physical properties, i.e., intrinsic viscosity and the product of ultimate elongation and ultimate tensile strength (a product which is often referred to as the impact index).

Data reported for the autoxidation of poly(ethylene glycol) (PEG) and poly(propylene glycol) (PPG) in solution at relatively long reaction times were analyzed. A relatively simple and a more general kinetic scheme with corresponding rate expressions were used. It was found that the more general scheme gave somewhat more satisfactory agreement between calculated and observed values of several reaction variables. Limitations in the applications of both schemes to PEG and PPG autoxidations are mentioned.

Low molecular weight atactic polypropylene hydroperoxide (APPH), m. (onset) ≈ 80°C, was prepared via oxidation of uninhibited low molecular weight atactic polypropylene (APP). The APPH was thermally decomposed over a temperature range of 115°–125°C in which the APPH was in a neat molten state. The reaction order (n) was found to be close to 2, n = 2.2 ± 0.2, and the activation energy of decomposition (E) was ca. 27 kcal/mole1. In contrast to solid-state decompositions, such values would be anticipated for liquid-phase decompositions due to enhancement of molecule mobility and hydrogen bonding.

The authors previously reported work on the kinetics and mechanism of the uncatalyzed thermal oxidation of isotactic polypropylene. The data, obtained form infrared absorption spectra of the carbonyl region, was utilized in developing the theoretical expressions presented. This paper summarizes this work and presents further evidence which substantiates the derived expressions. The additional evidence is obtained from infrared absorption spectra involving the apparent hydroperoxy region and from measurements on the rate of formation of volatile products. Some recent pertinent literature is also discussed.

This work is a study of some dilute solution properties of polyhexene-1. Results with the following experimental measurements are reported: osmotic pressure, phase equilibrium, viscosity, light scattering, molecular weight, molecular weight distribution, and degree of chain extension. Three good solvents were used, cyclohexane, tetrahydrofuran, and toluene, and one poor solvent, phenetole, in order to obtain theta conditions. The properties of polyhexene-1 are compared with those of other α-olefin polymers reported in the literature.

The kinetics of the thermal oxidation of isotactic poly(4-methyl-1-pentane) were studied in the bulk phase using thermogravimetric analysis (t.g.a.) at temperatures from 155° to 185°C and oxygen concentration from 75 to 100% by volume. The kinetics derived from formation of volatile products using t.g.a. correspond to those from non-volatile carbonyl products obtained from infra-red spectrometry.