Segmental motion of stereoregular poly(methyl methacrylates) in a homologous series of n-alkyl acetate solvents by nmr relaxation measurements

The ¹³C spin-lattice relaxation times, T₁s, of both stereoregular poly(methyl methacrylates) (PMMA) and homologous series of n-alkyl acetate solvents in solution have been measured at 40°C. It was observed that the motion of polar side-chains was highly affected by the degree of interaction with solvent molecules. The stronger polymer-solvent interactions in predominantly syndiotactic PMMA solutions than in isotactic PMMA solutions were shown from the T₁ values for the carbonyl, methoxy, and quaternary carbons in polymer segments and also from the carbonyl T₁s of solvent molecules. By relating the solvent dependences of the T₁ data in syndiotactic polymer solutions to that of the known dissolution rate data of atactic PMMA, it was found that the solvent dependences of the T₁ values of those carbon groups in which the polymer-solvent interaction is not significant, e.g., methylene and α-methyl carbon groups, were consistent with the solvent dependence of the dissolution rate of polymer. This result suggested that the dissolution of polymer is mainly governed not by the sorption process related to the polymer-solvent interaction but by the transport process related to the local motions of polymer segments and solvent molecules.     

Fast transient fluorescence technique (FTRT) for studying dissolution of polymer glasses

The fast transient fluorescence technique (FTRT) was used for studying the swelling and dissolution of a glassy polymer formed by free‐radical polymerization of methyl methacrylate (MMA). Anthracene (An) was introduced during polymerization as a fluorescence probe to monitor swelling and dissolution. Swelling and dissolution processes of disc‐shaped poly(methyl methacrylate) (PMMA) glasses in a chloroform–heptane mixture were monitored by measuring the fluorescence lifetimes of An from its decay traces. A method is developed for low quenching efficiencies for measuring lifetimes, τ, of An, and it was observed that τ values decreased as the dissolution process proceeded. Desorption, D, and mutual diffusion, D_m, coefficients of An molecules were measured during dissolution of PMMA and found to be around 5.4 × 10⁻⁶ (cm²/s) and 2.2 × 10⁻⁵ (cm²/s), respectively. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 948–957, 1999     

Rheology of solvent-cast polymer films

This paper describes and analyzes the results of an experiment where various thin polymeric films are continuously sheared between smooth glass substrates. The shear force per unit area has been measured as a function of mean uniaxial stress and temperature using representative “good” and “poor” casting solvents followed by a range of heat treatments. The polymers studied include high density polyethylene, polybisphenol-A–carbonate, poly(ethylene terephthalate), atactic polystyrene, isotactic polystyrene, atactic poly(methyl methacrylate), isotactic poly(methyl methacrylate), poly(vinyl acetate), poly(vinyl alcohol), poly(vinyl pyrrolidone), poly(vinyl chloride), and polytetrafluoroethylene. The results indicate that the casting solvent has a very pronounced influence upon the rheology of the film. The casting solvents may apparently confer either ductile or brittle failure in the film and also influence the nature of the temperature and pressure dependence of the shear stress. The data have been analyzed using Eyring theory and also by reference to relevant published literature on the influence of solvent and thermal treatments on the morphology and deformation behavior of polymers. “Good” solvents generally tend to promote a brittle mode of failure with little temperature dependence. The same type of solvents also produced films which have higher shear strengths and show greater increases in shear strength with pressure. These data are adequately rationalized using free volume and entanglement notions.     

Configuration dependence of carbon-13 spin-lattice relaxation times of poly(α-methylstyrene)

Carbon-13 n.m.r. spin-lattice relaxation times have been measured for atactic poly(α-methylstyrene) in 25% (w/v) solution in o-dichlorobenzene-d₄ as a function of temperature from 100° to 163°C and the results were compared with those for a syndiotactic poly(α-methylstyrene). It was concluded that the carbon-13 spin-lattice relaxation time is dependent on the stereochemical configuration over a relatively short range, but is not sensitive to longer range effects.     

Influence of tacticity of poly(methyl methacrylate) on the compatibility with poly(vinyl phenol)

Isotactic, atactic, and syndiotactic poly(methyl methacrylate) (PMMA) were mixed with poly(vinyl phenol) (PVPh) separately in tetrahydrofuran to make three polymer blend systems. Differential scanning calorimetry (DSC) and Fourier transform infrared (FTIR) spectroscopy were used to study the miscibility of these blends. Isotactic PMMA was found to be more miscible with PVPh than atactic or syndiotactic PMMA. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1773–1780, 1997     

Nature of PMMA dissolution process by mixtures of acetonitrile/alcohol (poor solvent/nonsolvent) monitored by FTIR-imaging

The dissolution process of poly(methyl methacrylate), PMMA, in mixtures of the binary systems: acetonitrile/alcohol (methanol, ethanol and 1-propanol), individually poor and nonsolvents respectively for the polymer, was studied at 25 °C using FTIR imaging spectroscopy. To investigate this cosolvency phenomenon and the kinetics of the dissolution process, the spatial resolution and sensitivity of FTIR imaging were used. It has been found that the PMMA dissolution rate anomalously increases almost in a parabolic way independently of the solvent system used in this study. These results were interpreted assuming that the dissolution of a polymer by a mixture of solvents is governed by a complex dependence of the solvent molecules size and their thermodynamic characteristics. The kinetics of the PMMA dissolution by AcN/alcohol solvent mixtures were interpreted using conventional Arrhenius behavior in which the activation energy has a simple dependence on the thermodynamic quality and the molecular weight of the solvent mixture.     

Effect of polymer microstructure on methyl group torsional vibrations

Fundamental torsional frequencies of methyl groups have been measured with neutron incoherent inelastic scattering for isotactic poly(methyl methacrylate)-COOCD₃, and heterotactic, syndiotactic and head-to-head isomers of poly(α-methylstyrene). The measurements confirm that the spectrum of isotactic PMMA differs considerably from the syndiotactic polymer in the region of the fundamental vibration, but no difference is found for the two stereoregular forms of poly(α-methylstyrene). However, the torsional frequency of the methyl group in the head-to-head configuration of α-methylstyrene lies at lower wavenumbers than that observed in the head-to-tail.     

Decay Lifetimes of Para-Substituted Polystyrene in Solid Films and in Dichloromethane

The fluorescence decay times of polystyrene, poly(4-bromostyrene), poly(4-chlorostyrene), poly(4-methylstyrene), poly(α-methylstyrene), poly(4-methoxystyrene), and poly(4-tert butylstyrene) were measured in solid films and in dichloromethane solution. A detailed analysis of the emission profile performed by nanosecond time resolved fluorescence spectroscopy confirmed the presence of monomer fluorescence as well as excimer fluorescence in both media. Monomer fluorescence decay times gave shorter times compared with that of excimer decay times in dichloromethane solution. Fluorescence from substituted polystyrene was mainly excimer fluorescence with shift of maximum emission to longer wavelength. The ratio of monomer to excimer contributions was found to be dependent on the emission wavelength, but was not affected by polymer concentration. Both monomer and excimer fluorescence lifetimes as well as excimer intensity increase with increasing emission wavelength. An accompanying decrease in monomer contribution is also observed is solution in comparison with that in solid films.     

Solvent-, ion- and pH-specific swelling of poly(2-acrylamido-2-methylpropane sulfonic acid) superabsorbing gels

Homopolymer hydrogel of 2-acrylamido-2-methylpropane sulfonic acid (AMPS) and its nanocomposite counterpart were prepared to study their swelling properties. The hydrogels showed ability to absorb and retain electrolytes as well as binary mixtures of water and organic solvents (i.e., methanol, ethanol, acetone, ethylene glycol (EG), polyethylene glycol, N-methyl-2-pyrrolidone (NMP), and dimethylsulfoxide (DMSO). The nanocomposite gel exhibited lower swelling in all solvent compositions in comparison with non-composite gel. Unlike conventional acrylic acid-based hydrogels, the poly(AMPS) gels showed superabsorbing capacity in pure ethanol, methanol, EG, DMSO and NMP. Meanwhile, swelling capacity of poly(AMPS) hydrogel in DMSO-water mixtures was surprisingly found to be even higher than that in water. This extraordinary superswelling behavior was explained based on the interactions involved in solvation as well as the solubility parameters. The gels showed pH-independent superabsorbency in a wide range of pH (3–11). Saline-induced swelling transitions were also investigated and the ionic interactions were confirmed by FTIR spectroscopy.     

Effect of the tacticity of poly(methyl methacrylate) on the phase diagram of its ternary blends

Previously, isotactic and atactic poly(methyl methacrylates) (PMMAs) were found to be miscible with poly(vinyl phenol) (PVPh) and poly(hydroxy ether of bisphenol‐A) (phenoxy) because all the prepared films were transparent and showed composition‐dependent glass transition temperatures (T_g's). However, syndiotactic PMMA was immiscible with PVPh because most of the cast films had two T_g's. On the contrary, syndiotactic PMMA was still miscible with phenoxy. According to our preliminary results, PVPh and phenoxy are not miscible. Also to our knowledge, nobody has reported any results concerning the effect of the tacticity of PMMA on its ternary blend containing PVPh and phenoxy. The miscibility of a ternary blend consisting of PVPh, phenoxy, and tactic PMMA was thus investigated and reported in this article. Calorimetry was used as the principal tool to study miscibility. An approximate phase diagram of the ternary blends containing different tactic PMMA was established, probably for the first time, based on differential scanning calorimetry data. Immiscibility was found in most of the studied ternaries but a slight difference due to the effect of tacticity of PMMA was definitely observed. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2720–2726, 2002     

Swelling measurement of polymers in high pressure carbon dioxide using a spectroscopic reflectometer

We developed an in situ thickness monitor using a spectroscopic reflectometer to measure the swelling behaviors of polymer thin films in carbon dioxide up to 30 MPa. Because the change in thickness was measured under high-pressure CO₂, the measurement was performed through a sapphire window with a relatively high refractive index. We found that the window effect on the reflectivity can be successfully eliminated. To confirm the accuracy of the analysis, we measured the swelling behaviors of four polymers (poly(methyl methacrylate) (PMMA), polystyrene (PS), poly(n-butyl methacrylate) (PBMA), and poly(dimethylsiloxane) (PDMS)), and compared the swelling measurements with reported data. The swelling ratios of the polymers were in reasonable agreement with literature data. Notably, anomalous swelling was observed for PBMA and PDMS, although anomalous swelling has been observed in films much thinner than those of our samples, probably due to the low glass transition temperatures and high swelling ratios of PBMA and PDMS.     

Preparation and stress-strain properties of aba block copolymers of α-methylstyrene and butadiene

ABA-type “tapered” block copolymers of α-methylstyrene (monomer A) and butadiene were prepared using four commercially available dilithio initiators. Polymerizations were run at 25°C in benzene solvent, or at 40°C with butadiene dissolved in neat α-methylstyrene. Although α-methylstyrene has a rather low ceiling temperature, triblock copolymers could be made at these temperatures by using α-methylstyrene concentrations well in excess of the [M]_e values at the respective temperatures. Its concentration was such that molecular weights of at least 15,000–20,000 for the A blocks could be attained. The course of the copolymerization at 40°C was followed, showing that copolymers containing about 40% α-methylstyrene could be formed in 4–8 hr, depending on the initiator used. They showed the usual behavior of triblock thermoplastic elastomers, with tensile strengths > 3000 lb/in.² at 24°C. However, because of the high T_g of poly(α-methylstyrene) (172°C), they also had tensiles of several hundred lb/in.² at 100°C, unlike comparable polymers with polystyrene end blocks, which have practically no strength at this temperature. Microstructures of polybutadienes made with these initiators are also given.     

A study on the dissolution rate of irradiated poly(methyl methacrylate)

A detailed study of the factors affecting the dissolution rate of poly(methyl methacrylate), PMMA, showed that the magnitude of the increase in the dissolution rate of irradiated PMMA could not be entirely attributed to the reduction in the molecular weight, MW. The formation of non-polymeric volatile fragments by radiation exposure, i.e., CO, CO₂H₂, CH₃OH and CH₄ causes a large increase in the solvent flux into the polymer matrix, thereby causing a large increase in the dissolution rate of exposed PMMA. The volatilization of these low molecular weight fragments cause an increase in the “excess free volume” (microporosity) of the glassy PMMA. The relative magnitudes of the contribution of the MW reduction and the formation of volatile matter on the increase in the solubility rate of the irradiated polymer were found to depend on the molecular size of the solvent, and also on the enthalpy of mixing.     

Preparation of Tethered Half-Titanocene Complex on Syndiotactic Poly(styrene-<Emphasis Type="Italic">co</Emphasis>-<Emphasis Type="Italic">p</Emphasis>-methylstyrene) for Using in Syndiospecific Polymerization of Styrene

Abstract  

In this work the syndiotactic polystyrene copolymer, poly (styrene-co-p-methylstyrene) was prepared by the copolymerization of styrene and p-methylstyrene with cyclopentadienyltitanium trichloride/methylaluminoxane catalyst. This copolymer was functionalized with silyl-hydride groups. The structure of copolymer and functionalized copolymer were characterized by FT-IR, ¹H-NMR and ¹³C-NMR spectroscopy. The obtained results revealed that the functionalization reaction successfully proceeds at low temperatures. Tethering of half-titanocene complex on polymeric support was done by the hydrosilylation reaction of 1-allylindenyltrichlorotitanium with silyl-hydride functionalized copolymer in the presence of Karstedt catalyst as a coupling reagent. The polymer-supported catalyst was tested for syndiospecific polymerization of styrene using methylaluminoxane as a cocatalyst. The results of styrene polymerization showed that the polymer-supported catalyst exhibited high activity for syndiospecific polymerization of styrene. The polymer prepared with supported catalyst was characterized by carbon nuclear magnetic resonance (¹³C-NMR) and differential scanning calorimetry (DSC). The results confirmed the syndiotacticity of obtained polymers. X-ray diffraction (XRD) analysis showed the δ-form crystalline structure of obtained syndiotactic polystyrene.     

Solubility and diffusion in latex films formed from high glass transition temperature particles

In situ steady-state fluorescence measurements were used to study the dissolution of polymer films. These films were formed from pyrene labeled poly(methyl methacrylate) (PMMA) latex particles that were sterically stabilized by polyisobutylene. Annealing was performed above the glass transition temperature at 180°C at 1-h time intervals for film formation. Desorption of pyrene labeled PMMA chains was monitored in real time by the change of pyrene fluorescence intensity. Dissolution experiments were performed in various solvents with different solubility parameters, δ, at room temperature. Diffusion coefficients, D, in various solvents were measured and found to be around 10⁻¹⁰ cm²/s. A strong relation between D and δ was observed. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 1493–1502, 1998     

Influence of microstructure on dynamic mechanical behaviour of polymeric composites with complex inclusions

The dynamic mechanical properties of polymeric composites composed of crosslinked poly(n-butyl methacrylate) continuous-phase and crosslinked polystyrene dispersed phase with poly(n-butyl methacrylate) occlusion have been examined. The composite samples were prepared by mixing and swelling of the crosslinked polystyrene particles obtained by emulsifier-free emulsion polymerization, with n-butyl methacrylate and crosslinker, then photopolymerizing at the desired temperature. The composite microstructure was varied by either changing the crosslink density of polystyrene, and temperature of swelling and polymerization, or using different sizes and contents of polystyrene particles. The tan δ peak positions of composite samples are found to be dependent on morphological characteristics as well as the properties of the dispersed phase while the peak height seems to be dependent on the effective volume of dispersed phase composed of polystyrene and poly(n-butyl methacrylate) occlusions. Special attention has been paid to the comparison among composite, homonetworks, and bulk IPN samples that are expected to have the identical structure with the complex dispersed phase of the composite samples. © 1993 John Wiley & Sons, Inc.     

Miscibility of poly(α-methyl siyrene-co-acrylonitrile) with polyacrylates and polymethacrylates

A copolymer formed from 30 percent acrylonitrile and 70 percent α methyl styrene by weight, or αMSAN, has been examined for miscibility in blends with various polyacrylates and polymethacrylates. None of the polyacrylates or poly(vinyl acetate) were miscible with α-MSAN at room temperature or above. The methyl and ethyl esters of the polymethacrylate series (PMMA, PEMA) proved to be miscible with α MSAN, but none of the higher homologues were miscible under these conditions. Blends of both PMMA and PEMA with α MSAN exhibited lower critical solution temperatures. The observed cloud points decreased as PMMA molecular weight increased up to 10⁵ where kinetic effects caused an apparent reversal of this trend. Atactic PMMA interacts more strongly with αMSAN than does either isotactic PMMA or atactic PEMA. These structural effects are compared with similar trends found in other systems.     

Phase structure in the blend of atactic poly(vinyl alcohol) with atactic poly(vinyl alcohol‐block‐vinyl acetate)

An almost fully saponified atactic poly(vinyl alcohol) and an atactic poly(vinyl alcohol‐block‐vinyl acetate) of which degree of saponification is 89 mol % were blended by a solution casting method. The phase structure of the blend film was analyzed by optical microscopy, ¹³C‐NMR, and differential scanning calorimetry. The most remarkable structure of the blend was composed of cylindrical domains penetrating the film. The swelling behavior of the blend films was also investigated in the dimethylsulfoxide and water mixed solvents to find differences in solubility and diffusion behavior between the matrix and the domain. The cylindrical domains could be selectively dissolved away in water and the film became porous. We tried to change the size of the cylindrical domain with various film preparation conditions. This aimed to turn the film into the useful filter membrane. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1807–1815, 2002     

Dissolution rates for thin films of miscible polymer blends

The dissolution rates of thin polymer films were measured and compared. Mixtures of various ratios of poly(methyl methacrylate), PMMA, and poly(p-hydroxystyrene), PPHS, were dissolved in methyl isobutyl ketone, MIBK. The polymer solutions were then spun into thin films on silicon wafers and dried. The coated wafers were immersed in an MIBK bath and the rate of dissolution was observed using laser interferometry. The results show that pure PPHS films have dissolution rates 1000 times greater than films of pure PMMA at comparable molecular weights. However, for films containing both PPHS and PMMA, a minimum dissolution rate occurs for a mixture with about 20% (by weight) PPHS. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 2015–2020, 1997     

Dynamics of macromolecular chains. Excimer formation of poly(α-methylstyrenes) in solution

Intramolecular excimer formation has been investigated in two samples of poly(α-methylstyrenes) over the temperature range ?80° to +80°C. The ratio of the emission intensities of dimer and monomer ($\text{I}{}_{\mathrm{D}}\text{I}{}_{\mathrm{M}}$) is very sensitive to the tacticity of the polymer. The results reveal a rather large difference in excimer stability between polystyrene and poly(α-methylstyrene). On the other side, poly(α-methylstyrene) exhibit a higher efficiency of excimer formation than polystyrene. Activation energy for excimer formation in the case of a syndiotactic diad is lower in poly(α-methylstyrene) than in polystyrene. This is consistent with conformational energy calculations.