Swelling and drying kinetics of polytetrahydrofuran and polytetrahydrofuran–poly (methyl methacrylate) gels: A photon transmission study

A bifunctional polytetrahydrofuran (PTHF) macromonomer was synthesized by termination of the living polymerization of tetrahydrofuran (THF) initiated by triflic anhydride and the subsequent termination by sodium methacrylate. The PTHF macromonomer thus prepared was polymerized and copolymerized with methyl methacrylate (MMA) by free‐radical polymerization to yield a network and a segmented network of PTHF, both being homogeneous, respectively. These PTHF and PTHF–PMMA gels were used for swelling experiments in chloroform and chloroform vapor. Drying processes were monitored after removing the gels from the solvent and solvent vapor. Photon transmission from PTHF and PTHF–PMMA gels was monitored during swelling and drying processes using a UV‐visible (UVV) spectrophotometer. Transmitted light intensities, I_tr, from these gels increased when they were immersed in chloroform and/or subjected to its vapor. The increase in I_tr was attributed to the homogeneous lattice structure of PTHF and PTHF–PMMA gels which appeared during swelling. The increase in I_tr was modeled using the Li–Tanaka equation from which time constants, τ₁, and cooperative diffusion coefficients, D_C, were determined. A decrease in I_tr after removing choloform and/or its vapor from the cell was observed and attributed to the decrease in homogeneity of lattice structures during drying of the corresponding gels. Time constants, τ2, for the drying processes were also determined. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 632–640, 2003     

Small molecule desorption prior to dissolution of a polymeric glass

Poly(methyl methacrylate) (PMMA) discs in various molecular weights (M_w) were prepared by free‐radical polymerization. Pyrene (Py) was introduced during polymerization as a fluorescence probe. In situ steady state fluorescence experiments were performed to monitor desorption processes in chloroform solvent. When the PMMA discs were in chloroform, desorption of Py molecules were monitored by observing the change of Py fluorescence intensity I_P. To understand the mechanism of desorption, two different experiments were carried out in the meantime. In the first experiment, the weight of swelling and dissolving PMMA discs against dissolution time was monitored. The parallel experiment was conducted by measuring fluorescence intensity I_P from the desorbing Py molecules. Then, a set of desorption experiments were performed by monitoring I_P for various discs with different molecular weight of PMMA. A Fickian diffusion model was employed to quantify the fluorescence data produced from the swelling PMMA discs to measure desorption coefficients D_d. The measured D_d values decrease as the molecular weight of PMMA is increased in the swelling glass. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 908–912, 2006     

Fluorescence quenching method for monitoring oxygen diffusion into PS/CNT composite films

Oxygen permeabilities of nanocomposite films consisting of multi wall carbon nanotubes (MWNT) and polystyrene (PS) were determined to investigate the oxygen diffusion depending on MWNT and temperature. A method which is based on quenching of an excited phosphorescent by oxygen was applied for the measurements. The composite films were prepared from mixtures of (MWNT) and surfactant-free pyrene (P)-labeled (PS) latexes of various compositions at room temperature. These films were then annealed at 170 °C which is well above the glass transition (T_g) temperature of polystyrene, for 10 min. Diffusion experiments were performed for eight films with different MWNT content (0, 1.5, 3, 5, 10, 15, 25 and 40 wt%) to evaluate the effect of MWNT content on oxygen diffusion. Diffusion coefficients were found to increase from 1.1 × 10⁻¹² to 41 × 10⁻¹² cm² s⁻¹ with increasing MWNT content. On the other hand, to examine the effect of temperature on oxygen diffusion, diffusion measurements were performed over a temperature range of 24–70 °C for three different MWNT contents (3, 15, and 40 wt%) within the films. The results indicated that the values of the diffusion coefficient D are strongly dependent on both temperature and MWNT content in the film. It was also observed that the diffusion coefficients obey Arrhenius behavior, from which diffusion energies were determined, which increased with increase of MWNT content and temperature.     

Effect of molar size and solubility parameter of solvent molecules on swelling of a gel: a fluorescence study

Gels were swollen in various solvents with different molar volume V and solubility parameter δ. In situ steady state fluorescence (SSF) measurements were performed for swelling experiments in gels formed by free radical crosslinking copolymerization (FCC) of methyl methacrylate (MMA) and ethylene glycol dimethacrylate (EGDM). Gels were prepared at 75 °C with pyrene (Py) as a fluorescence probe. After drying these gels, swelling and slow release experiments were performed in various solvents with different V and δ at room temperature by time monitoring of the Py fluorescence intensity. The Li–Tanaka equation was used to produce time constant τ₁ values. Cooperative diffusion coefficients (D_c) were measured and found to be strongly correlated to the molar volume of the solvents used. Solvent uptake and degree of swelling were found to be dependent on the solubility parameter of the solvent. © 2000 Society of Chemical Industry     

Effects of annealing on morphology of polymer/polymer (PS/PMMA) blend; a fluorescence study

Steady state fluorescence (SSF) technique conjunction with optical microscopy were used to study the morphology of polystyrene (PS)/poly(methyl methacrylate) (PMMA) blend upon annealing above glass transition in elevated time intervals. The PS/PMMA blends were prepared from dissolution of pyrene (P) and naphthalene (N) labeled PS and PMMA particles, respectively. Monte Carlo simulations were performed to model the N and P fluorescence intensities (I_N and I_P), using photon diffusion theory. Number of N and P photons (N_N and N_P) emerging from the front surface of the blend are calculated when only N is excited, where N_P photons are combined of photons from radiative (N_PR) and nonradiative (N_PNR) energy transfer processes. Optical microscopy images were taken at each annealing step to support our findings from fluorescence measurements. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2104–2110, 2006     

Volume changes and relaxations within the interphase domain of blendlike polymer particles

The behavior of volume changes upon solvent swelling and annealing was studied within the interphase domain of poly(methyl methacrylate) (PMMA) Particles sterically stabilized with polyisobutylene (PIB). Transient fluorescence technique was applied on these micronsized particles labeled in the PMMA phase with naphthalene (N) groups. Mean decay times 〈τ〉, obtained from fluorescence decay measurements, were used to examine volume changes within the PMMA–PIB interphase domain. The mathematical model proposed by Inokuti–Hirayama for the quenching of lifetimes was employed to quantify the individual volume changes and relaxations at this particular domain. © 1995 John Wiley & Sons, Inc.     

Comparison of the uroprotective efficacy of mesna and HBO treatments in cyclophosphamide-induced hemorrhagic cystitis

The aim of this research was to compare the protective effects of mesna, hyperbaric oxygenation (HBO), and their combination in cyclophosphamide-induced hemorrhagic cystitis in guinea pigs. Following one dose of i.p. 21.5 mg./kg. mesna administration 20 minutes before i.p. 68.1 mg./kg. cyclophosphamide, 3 additional doses of mesna were given every three hours. A total of 8 HBO exposures, 5 of which were applied prophylactically before cyclophosphamide, were performed at 2.8 ATA for 90 minutes 2 times a day. Although mesna or HBO provided significant protection for cyclophosphamide-cystitis in animal bladders, there was also significant damage compared with controls. The combination of mesna and HBO, which act through independent mechanisms, resulted in complete protection, since mean histological scores and hematuria levels in this group were not different from controls (p >0.05). Therefore, this combination may be a useful tool in the prophylaxis and treatment of cyclophosphamide-induced hemorrhagic cystitis.     

Synergistic effect of the locust bean gum on the thermal phase transitions of κ-carrageenan gels

Synergism between κ-carrageenan and locust bean gum (LBG) was studied using the photon transmission technique. Synergistic effects in these polymeric mixtures strongly affected the physical properties of the gel structure. The transmitted light intensities, I_tr, versus temperature variations were investigated during the gelation and liquefaction processes. Slight synergistic peaks were detected in gel–sol and sol–gel transition temperatures for high κ-carrageenan/LBG ratios (approx. 80/2). Moreover, apparent synergistic peaks were observed in gel–sol and sol–gel transition activation energies for the mixtures approximately with the ratios of 80/10.     

Film formation from nano‐sized polystrene latex covered with various TiO2 layers

Steady‐state fluorescence technique was used for studying film formation from TiO₂ covered nano‐sized polystyrene latex particles. The composite films were prepared from pyrene (P)‐labeled PS particles by covering them with various layers of TiO₂ at room temperature. These films then annealed at elevated temperatures in 10 min time interval above glass transition (T_g) temperature of polystyrene. Five different composite films were studied in various TiO₂ layer contents. Fluorescence emission intensity, I_P from P was measured after each annealing step to monitor the stages of film formation. Films present significant increase in I_P above the certain onset temperature called minimum film forming temperature, T₀. However, at higher annealing temperatures, I_P showed a decrease. Increase and decrease in I_P were modeled by void closure and interdiffusion processes and related activation energies were determined, respectively. Dissolution of annealed PS film, with high TiO₂ content presented a nice, ordered nano‐sized ceramic structure, which may predict the construction of nano‐layer photonic crystals. POLYM. COMPOS., 27:651–659, 2006. © 2006 Society of Plastics Engineers