Solution properties of poly(methyl methacrylate) in methyl methacrylate, 1. Viscosities from the dilute to the concentrated solution regime

The viscosities of samples of poly(methyl methacrylate), PMMA, with narrow molecular weight distributions and with molecular weights in the range 1,75·10⁴ < M?_w < 1,60.10⁶ were measured in methyl methacrylate, MMA, as solvent at 20, 40, and 60°C in the dilute and in the semi-dilute concentration regime. By extrapolation to zero polymer concentration the limiting viscosity numbers and therefrom the Mark-Houwink-Kuhn-Sakurada parameters for PMMA in MMA were obtained. In addition, unperturbed dimensions were determined from dilute solution viscosity data. Together with some published results for more concentrated solutions of PMMA in MMA the viscosities of the semi-dilute systems were analysed in terms of scaling theories. It was found that irrespective of temperature, polymer concentration, and molecular weight all data could be quite well fitted by a single master curve when the relative viscosity η/η₀ was plotted as a function of the product of the intrinsic viscosity and mass concentration [η]·c. No sharp transitions between different concentration regimes were observed, however, and the scaling law exponents for the entangled solution are significantly higher than predicted by theory.     

Possibilities and limits of photon correlation spectroscopy in determining polymer molecular weight distributions

The effect of concentration and polydispersity on the collective diffusion coefficient D_c, evaluated using Photon Correlation Spectroscopy (PCS), has been investigated on poly(methyl methacrylate) (PMMA) in acetone solutions. The concentration dependence of the collective diffusion coefficient follows a linear regression law, the slope being fairly independent of polydispersity, molecular weight and temperature. The diffusion coefficient at infinite dilution D₀ obeys the scaling law D₀ = AM_w^–ν in the range from M_w = 10 000 to M_w = 800 000; the value of the scaling exponent, ν = 0.57, proves the good solvent quality of acetone. The inversion of the scattered intensity autocorrelation data by the regularization method CONTIN allowed the evaluation of the molecular weight distribution function of the polymeric samples. Although this algorithm gives valuable information on average quantities or on the width of the distribution, it has limited resolution power; therefore a comparison with the results obtained by Size Exclusion Chromatography (SEC) was carried out for a set of samples having monomodal and bimodal distribution functions.     

2H NMR study of solvent and solute mobility in polymer solution,gel and glass states

²H spin relaxation times, T₁ and T₂ and solid echo line shapes were investigated in 2-propanol (2-POH) solutions of poly(butyl methacrylate) (PBMA) in a wide concentration and temperature range, covering the solution, gel and glass states. From the results in deuterated 2-POH-d₆ we found that the polymer influence upon solvent mobility is largely suppressed in the gel and glass states in contrast to normal polymer solutions where below the glass transition an increasing amount of solvent slows down with decreasing temperature. From ²H NMR of deuterated butyl side groups in the PBMA-d₉/2-POH system we found that the side group motion is anisotropic and largely independent of solvent concentration in the gel and glass states which confirms that polymer-polymer interaction via side group interpenetration should be considered as the main cause for gel formation in this system.     

Osmotic coefficients of aqueous polyelectrolyte solutions at low concentrations, 3. Dependence on macroion molecular weight

Eight sodium salts of polystyrenesulfonic acid (poly[1-(sulfophenyl)ethylene]) of different molecular weights were prepared similarly and purified in the same way. Their aqueous solutions were thus chemically equivalent, and differed only in their molecular weights, which were determined viscosimetrically. The osmotic coefficients (Φ) of the acid and its sodium, thallium, calcium and cadmium salt solutions were measured by a membrane osmometer for counterion molalities m_c = 10^?2 to 5·10^?4mol/kg, at 25°C. In the same concentration range, the activity coefficients of hydrogen counterions (γ_H) of acid solutions were calculated from electromotive force measurements and the osmotic coefficients of the acid solutions were determined by the cryoscopic method for two different molecular weights. The values obtained are presented graphically as functions of the measured average molecular weight for m_c = 10^?3 and 10^?2 mol/kg and are in good mutual agreement within experimental error. This agreement of results could be assumed to verify experimentally that the colligative properties of polystyrene-sulfonate polyelectrolytes at low concentrations are dependent on the molecular weight of the polyion. The obtained results together with some literature data, allow us to evaluate very approximately the activity coefficients of monovalent counterions (γ_c) for m_c = 10^?2 mol/kg as a function of the degree of polymerization (n) of linear oligoions or polyions, for values of n up to 10⁴.     

Carbon-13 relaxation study of crosslinked gels of poly(methyl methacrylate)

The motion of covalently crosslinked gels of poly(methyl methacrylate) (PMMA) swollen by benzene-d₆ was studied by means of ¹³C NMR spectroscopy. The dependence of the segmental motion of PMMA on stereosequence was not affected by the presence of the covalently crosslinked part in the chain; isotactic sequence was more mobile than syndiotactic sequence. The spin-lattice relaxation times, T₁'s, for all the ¹³C nuclei of PMMA swollen with benzene (benzene content, 90 wt.-%, 0,01 mole-% of crosslinking) were considerably longer than those observed for the linear PMMA (benzene content, 75 wt.-%). Moreover, all the T₁ values decreased with increasing of the degree of crosslinking, regardless of the crosslinking agent and reached to the values of T₁ observed for uncrosslinked PMMA or to slightly larger values when the content of crosslinking agent was 1 mole-%. However, the nuclear Overhauser enhancement data were essentially independent of the degree of crosslinking within experimental error.     

Internal mobility of PMMA in concentrated CDCl3 solutions, 1. 1H NMR spectra

Measurements of the second moment and analysis of the derivative shape of ¹H NMR spectra of PMMA have shown that in CDCl₃ solutions containing 60% (w/w) or more of polymer, the internal mobility of PMMA is similar to the mobility of the pure polymer. The main chain is rigid on the NMR scale, and only CH₃ groups are mobile. The motion of CH₂ groups, representing the segmental mobility of the backbone chain, becomes appreciable on the NMR scale at concentreations of 60–50%, depending on the temperature. Measurements of ¹H MAR-NMR spectra of solutions containing 30% or more of polymer indicate spatial anisotropy of internal motions of PMMA. This spatial anisotropy is probably due to intermolecular interactions of ester groups, similarly as in the gels of the PMMA stereocomplex.     

Zur unverträglichkeit von polymergemischen. III. Lichtstreuungsmessungen an hochmolekularen polystyrolen in polymethylmethacrylat/benzol

Polystyrenes of high molecular weight were investigated by means of light scattering in the isorefractive polymer/solvent mixture polymethylmethacrylate/benzene. It was found, that the second osmotic virial coefficient, A₂, was strongly dependent on the molecular weight and the concentration of polymethylmethacrylate (PMMA) but neglegibly on the molecular-weight of polystyrenes (PS) or on the temperature between 20 and 60°C. A plot of A₂/A vs. c_PMMA/c_Θ revealed that all points fall on a common line for all molecular weights of PS and PMMA. Herein A means the second osmotic virial coefficient of PS in pure benzene, c_PMMA the concentration of PMMA, and c_Θ the concentration of PMMA at the Θ-point (A₂ + 0). This result could be theoretically interpreted in terms of the STOCKMAYER light scattering theory for multicomponent systems. The radii of gyration of PS in PMMA/benzene decrease with increasing concentration of PMMA. Furthermore, these radii increase slightly with increasing molecular weight of PMMA at the Θ-point. The coil dimensions, however, are generally bigger than those found in binary Θ-systems. For the measured radii of gyration of PS in PMMA/benzene a common line for all molecular weights of PS and PMMA could be found by normalizing with respect to both the radii of gyration and the concentration of PMMA.     

13C NMR relaxation studies of poly(vinyl alcohol) and its derivatives

Spin-lattice relaxation times (T₁) have been measured by ¹³C NMR for poly(vinyl alcohol), poly(vinyl benzoate), poly(vinyl cinnamate) and poly(vinyl acetate) in dimethyl sulfoxide as a function of temperature and concentration. As expected, T₁ increases with increasing temperature and decreases with increasing polymer concentration. The influence of the microstructure (tacticity) of the polymers on the relaxation times is negligible. T₁ for the methine carbon of the polymer main chain is observed to serve as a measure of the rigidity and/or mobility of the chain. Assuming isotropic motion of the polymer chains, the activation energies for the protonated carbons were determined using the calculated correlation times.     

Mechanischer Scherabbau von Polymeren in Lösung mittels turbulenter Strömung, 2. Die Abhängigkeit der Abbaugeschwindigkeit von der Polymergesamtkonzentration in guten Lösungsmitteln

Mechanical shear degradation of poly(decyl methacrylate), (viscosity average molecular weight in tetrahydrofuran M?_η = 1,3·10⁶, M?_w/M?_n = 5) in the thermodynamically good solvent tetrahydrofuran has been studied in turbulent flow through a capillary as a function of polymer concentration in the range from 0,22 to 8,9 g/100 cm³. Due to turbulent flow conditions the shear stress, shear rate and shear energy proved to be the same for all concentrations and remained constant during degradation, giving a general insight into mechanism of degradation. The rate of degradation has been followed using molecular weight distribution curves obtained by gel permeation chromatography. The reaction was found to be of first order. Rate constants determined for molecular weights from 3,2–9,5·10⁶ decreased with increasing concentration following a law of the type k_i = (K + b·c)^?1, K and b being constants for each molecular weight. Hydrodynamic volumes of polymer molecules have been calculated according to models of Rudin as function of molecular weight and concentration. It can be shown that rate constants of degradation and calculated hydrodynamic volumes are proportional for the whole range of molecular weight and concentrations up to 3,6 g/100 cm³. There is also a rather good proportionality between these rate constants and the volumes of polymer coils predicted by de Gennes. This result is an additional confirmation of the concept that hydrodynamic volume governs shear degradation of polymer solutions. Additional experiments show that this type of concentration dependence is also to be found for other polymers in other solvents.     

Lösungseigenschaften von polymethylmethacrylat und polystyrol aus Röntgenkleinwinkelmessungen

Light scattering investigations of solutions of polymethylmethacrylat (PMMA) and polystyrene (PST) are extended to low molecular weights by small-angle X-ray scattering. In a medium range of molecular weights (M = 10³ to 3·10⁴) the radius of gyration is proportional to M^0.5 even in good solvents. For M < 3·10⁴ the radii of gyration of PMMA found in the good solvent acetone are equal to those in the used Θ-solvent within the limits of error. In the case of PST in toluene this is not valid. From the relations α⁵ - α³ ～ z and α³ - 1 ～ z graphical methods were derived for the determination of r²₀/M from measurements in goods solvents by extrapolation to M = 0. For these extrapolation procedures it is necessary to perform measurements in the range between M = 10⁴ and M = 10⁵. The dependence of the second osmotic virial coefficient on the molecular weight in the low molecular range can be interpreted by Monte Carlo calculations on model compounds.     

Phase Separation in Poly(N,N‐diethylacrylamide)/D2O Solutions and Physical Gels as Studied by 1H NMR Spectroscopy

The structural‐dynamic changes during temperature‐induced phase separation in poly(N,N‐diethylacrylamide) (PDEAAm)/D₂O solutions and physical gels in a broad range of concentrations (c = 0.5–50 wt.‐%) were studied by conventional high‐resolution and MAS ¹H NMR spectra. In the whole concentration range, irrespective of whether the studied system is a solution (c < 5 wt.‐%) or physical gel (c > 5 wt.‐%), the phase transition is manifested by line broadening (linewidth ≈ 3.6 kHz) of a major part of PDEAAm units, evidently due to the formation of compact globular‐like structures. ¹H MAS NMR spectra have shown that this broadening is not due to near‐static dipolar interactions. The respective motion is effectively isotropic with correlation time ≈ 1 μs, probably corresponding to Brownian tumbling of the whole globular particles. The thermotropic phase transition, as revealed by NMR, is not discontinuous, but ≈  6 K broad (302–308 K). Above the LCST transition, the fraction p* of PDEAAm segments in globular‐like structures is between ≈   0.94–1.0, independent of the polymer concentration. At temperatures below the LCST a certain preaggregation of PDEAAm is indicated by smaller line broadening (linewidths ≈ 100 Hz) in the ¹H NMR spectra.     

Non-newtonian flow behaviour of poly(decyl methacrylate) solutions

The viscosity of solutions of poly(decyl methacrylate)s, PDMA, in 1-pentanol (thermodynamically poor solvent) and in toluence or isooctane (good solvents) was measured up to shear rates of 3 · 10⁴s^?1 by means of rotational viscosimeters. The observed pronounced shear thinning is for all solutions well described by the theory of Graessley, with the extension, introduced by Ito. Two parameters, resulting from the evaluation of the flow curves on the basis of the above theory, are discussed: τ₀, a characteristic relaxation time of the polymer chain, is found to be in the range of ms. η_fric, a frictional parameter, independent of shear rate, amounts upto 50% of the zero-shear viscosity for the measured solutions. Both, τ₀ and η_fric, increase with decreasing solvent quality, increasing molecular weight, and increasing concentration, in accord with theory. A comparatively sharp downward bend, separating two power-law regimes, shows up with moderately concentrated solutions, as the shear rate exceeds about 10³ to 10⁴ s^?1. This transition is tentatively interpreted as an orientation of the long side chains of PDMA.     

Continuous fractionation and solution properties of PVC, 6. Pressure dependence of the viscosity — influence of molecular weight and composition

Viscosities were measured as a function of pressure and temperature with solutions of PVC 75 000 in cyclohexanone (CHO) and polymer contents ranging from 0,6 to 12 wt.-%, by means of a Searle-type (≥3 wt.-%) and a rolling-ball viscometer (<3 wt.-%). Furthermore, the influence of molecular weight was determined with solutions of 8 wt.-% of PVC 20 000, PVC 37 000 and PVC 100 000. (The numbers in the codes of the PVC specimens are their approximate molecular weights.) For all concentrations and molecular weights, the viscosity increases in a more or less exponential manner with increasing pressure. The ratio f₁₀₀₀ of the viscosity of the solution at 1 000 and 1 bar can be varied by the change of the polymer content from 2,5 (the value of the pure solvent, index s) to 3,5 (12 wt.-% PVC 75 000) at t = 25°C and from 2,23 to 2,94 at t = 80°C. An increase of the molecular weight of the polymer raises f₁₀₀₀ in a similar manner as the polymer concentration. Using the reduced variables V^≠/V^≠ (ratio of the volumes of activation of the solution and the pure solvent) and c? (product of the polymer concentration and the intrinsic viscosity), all results obtained by variation of T, c and M_w can be represented by a master curve. This means that it is possible to calculate the pressure dependence of a given polymer solution of arbitrary polymer concentration from a mere measurement of the intrinsic viscosity at normal pressure. Criteria are presented which allow a forecast concerning the occurrence of minima in the concentration dependence of the energy of activation of the viscous flow E^≠ and V^≠.     

Bulk polymerization of styrene and methyl methacrylate using tetraphenylbisphosphine as an initiator

In this study a controlled polymerization of styrene (S) and methyl methacrylate (MMA) with tetraphenylbisphosphine (TPhBP) as the initiator in bulk was carried out, using UV light as the energy source. The yield of polymerization was up to 15% for PS and up to 62% for PMMA. TPhBP is decomposed to form ∗︁PPh₂ radicals, or is oxidized to form bisphosphine oxide. Only non-oxidized TPhBP initiates the photo-polymerization. For S and MMA an insignificant portion of photo- and thermal-polymerization was detected. In the presence of oxygen the phosphine end-groups of the polymer are oxidized to —PO(Ph)₂ groups. The molecular weights of PMMA were determined from ¹H NMR spectra and the molecular weights of PMMA and PS were determined by gel permeation chromatography (GPC) measurements. With increasing concentration of the initiator the molecular weight decreases and at a high concentration of the initiator the molecular weight decreases with conversion. The polydispersity decreases with increasing concentration of TPhBP. Termination occurs by combination of primary radicals ∗︁PPh₂, by combination of macroradicals, and by chain transfer to the initiator. Because of different types of termination the ratio between the tail —CH₂P(Ph)₂ and the head —C(CH₃,COOCH₃)P(Ph)₂ groups is about 4 to 1, and decreases with increasing concentration of the initiator.     

Synthesis and nonlinear optical properties of aromatic esters with an electron donor and an electron acceptor end group

We synthesized a series of aromatic esters having an electron donating and an electron accepting end group as a new class of nonlinear optical (NLO) active chromophores ( ArESn D‐A , n = 2,3, D = MeO (as reference), MeS and Me₂N, A = CN). Second‐order NLO properties for poled polymer films consisting of poly(methyl methacrylate) ( PMMA ) doped with 10 wt.‐% ArESn D‐A ( ArESn D‐A/PMMA ) were investigated. The UV/vis spectra of these polymer films have cutoff wavelengths (λ_co) of about 350 ˜ 370 nm, which are much shorter than in the case of p‐nitroaniline (pNA) (λ_co = 473 nm) which is a typical strong donor‐acceptor (D‐π‐A) molecule. In addition, some of these polymer films exhibit higher second‐order nonlinear coefficients (d₃₃) than a PMMA film doped with 10 wt.‐% pNA ( pNA/PMMA ) (2.8×10^–9 esu). Namely, ArES3 Me₂N‐CN (d₃₃ = 5.6×10^–9 esu, 10 wt.‐% in PMMA) and ArES2 Me₂N‐CN (3.8×10^–9 esu, 10 wt.‐% in PMMA) showed excellent second‐order NLO activity as well as transparency in the visible region (λ_co: 362 nm for ArES3 Me₂N‐CN and 366 nm for ArES2 Me₂N‐CN , respectively).     

Synthesis and nonlinear optical properties of end-group modified aromatic esters as chained chromophores

We synthesized aromatic ester derivatives with some electron accepting groups at molecular ends as new class of nonlinear optical (NLO) active chromophores (ArESn-X , n = 2, 3, X = CN, CF₃, NO₂, DCV). Some second-order NLO properties for poled polymer films consisting of poly(methyl methacrylate) (PMMA) doped with 10 wt.-% ArESn-X (ArESn-X/PMMA) were investigated. UV/vis spectra of these polymer films have cutoff wavelengths (λ_co) of about 300∼380 nm, which are much shorter than in the case of p-nitroaniline (pNA) (λ_co = ca. 450 nm) as a typical strong donor-acceptor (D-A) molecule. In addition, some of these polymer films exhibited larger second-order nonlinear coefficient (d₃₃) values than PMMA film doped with 10 wt.-% pNA (pNA/PMMA) (2.8 × 10⁻⁹ esu). Namely, ArES3-CN (d₃₃ = 3.1 × 10⁻⁹ esu, 10 wt.-% in PMMA), ArES3-NO₂ (3.0 × 10⁻⁹ esu, 10 wt.-% in PMMA) and ArES2-DCV (4.0 × 10⁻⁹ esu, 10 wt.-% in PMMA) showed not only excellent second-order NLO activity but also excellent transparency in the visible region (λ_co = 304 nm (ArES3-CN) , 340 nm (ArES3-NO₂) and 370 nm (ArES2-DCV) , respectively). Consequently, these compounds are believed to be promising chromophores for second-order nonlinear optics.     

Spinodal decomposition induced by cross-linking reaction in a binary polymer mixture

Phase separation of a binary polymer mixture of poly{styrene-co-[p-2,2,2-trifluoro-1-hydroxy-1-trifluoromethylethyl-α-methylstyrene]} (PS(OH)) and poly[(methyl methacrylate)-co-(glycidyl methacrylate)] (PMMA(G)) upon cross-linking reaction was studied using time-resolved light scattering (TRLS) and optical microscopy. The blends of PS(OH)/PMMA(G), in which PMMA(G) containing 1.4 mol-% epoxy groups can be selectively cross-linked with the multifunctional agent 4,4′-methylenebis(o-chloroaniline) (MOCA) and PS(OH) contains 1.8 mol-% of the strongly proton-donating group  C(CF₃)₂OH, exhibit a lower critical solution temperature (LCST). The cross-linking reaction was carried out for two compositions of PS(OH)/PMMA(G)/MOCA, 50/50/0.7 and 40/60/0.8 (w/w/w), at various temperatures located in the one-phase region between the coexistence curve and the glass transition temperature of the blends. TRLS investigation shows that the phase separation takes place via spinodal decomposition (SD) induced by the increase in the molecular weight of PMMA(G) during the cross-linking reaction. A modulated phase structure with the characteristic features of periodicity and dual connectivity of the phases was developed in this case. The dynamics of SD were investigated in terms of changes of the peak scattering vector q_m(t) as a function of time. They are dependent on the reaction temperature and composition. A scaling relation q_m(t) ∝︁ t^−af(x) describing the behavior of the evolution of phase separation upon reaction was supported by the experiments.     

Kinetics of the anionic polymerization of tert-butyl methacrylate in tetrahydrofuran

The anionic polymerization of tert-butyl methacrylate (TBMA) in tetrahydrofuran, using Na⁺ and Cs⁺ as counterions proceeds without side reactions even at room temperature. The resulting molecular weight distributions are nearly monodisperse (M _w/M _n ? 1,01). The rate constants for the propagation of ion pairs were measured in the range from + 15 to ?100°C. The Arrhenius plots are linear, but different for the two counterions, resulting in the following numerical values for the frequency exponent A and the activation energy E_a:

• A = 8,5 and E_a = 7,2 kcal/mol = 30 kJ/mol for Na⁺;
• A = 9,5 and E_a = 5,6 kcal/mol = 23 kJ/mol for Cs⁺.

The difference between the counterions, which is in contrast to the polymerization of methyl methacrylate (MMA), as well as the lower rate constants are not due to the steric factor of the tert-butyl group but to its positive inductive effect which influences the structure of the propagating macroion pair by decreasing its reactivity. The relative reactivities of the PMMA and PTBMA ion pairs towards MMA and TBMA are estimated.     

Spontaneous polymerization of amphiphilic vinyl monomers, 1. Spontaneous polymerization of sodium dodecyl 2-hydroxy-3-methacryloypropyl phosphate

Sodium dodecyl 2-hydroxy-3-methacryloyloxypropyl phosphate as an amphiphilic vinyl monomer was found to polymerize spontaneously without initiator in water. The polymerization takes place at a monomer concentration higher than the critical micelle concentration via a free-radical mechanism, and complete conversion is achieved even at a very low initial monomer concentration (3 mmol/L) and a rather low temperature (35°C). In benzene, capable of forming inverse micelles, the polymerization also occurs spontaneously. In methanol, which gives an isotropic solution, the spontaneous polymerization proceeds only at high concentration (near 300 mmol/L). The ¹H spin-spin relaxation time (T^*₂) of the monomer changes discontinuously in a range of monomer concentration from 250 to 300 mmol/L in CD₃OD, suggesting that some kind of monomer mutual interaction takes place in methanol too. Thus, it can be concluded that the micellar aggregation monomer molecules triggers the polymerization.     

Estimation of chain molecular dimension of poly(2-methylpent-1-ene sulfone) at critical polymer contents by dielectric measurements

Dielectric measurements were made in the frequency range from 30 Hz to 3 MHz for a series of the solutions of poly(2-methylpent-1-ene sulfone) (PMPS) having two different molecular weights in benzene at 30°C. The unperturbed chain molecular dimension was estimated from dielectric relaxation time at the critical polymer contents, C_cr. This value of the unperturbed dimension was much higher than that from the intrinsic viscosity measurement. The dielectric motion at C_cr involves simultaneous co-operative reorientations of about three spheres. The number of the spheres of reorientation may be related to the flexibility of the molecular chain of the polymer. The ratio of two effective volumes of the polymer obtained from the unperturbed chain molecular dimension and from the dielectric relaxation time, τ_m agreed with that of the two effective volumes obtained from the K value in Onogi's treatment and from the τ_m value.