Local motion of crosslinks for poly (methyl methacrylate) gels by the fluorescence depolarization method

Poly(methyl methacrylate) (PMMA) gels labeled at crosslinks with anthracene were prepared. Anthracene fluorescence depolarization was monitored to probe the local motion of crosslinks for PMMA gels at different equilibrium swelling states. The relaxation times and the activation energies of local motion were measured for PMMA gels at the swollen states in various solvents through fluorescence anisotropy decays. The local motion of PMMA gel at crosslinks became faster with the increase of swelling ratio. When the swelling ratios were almost the same, the mobility of crosslinks was the same irrespective of the molecular weights between crosslinks. These results indicate that the local motion of crosslinks for PMMA gel is mainly governed by the segment density of network chains in the vicinity of crosslinks. Received: 31 March 1997/Revised: 11 April 1997/Accepted: 21 April 1997     

Fast transient fluorescence technique for studying swelling of gels made at various crosslinker contents and exposed to organic vapour

Fast transient fluorescence technique (FTRF) was employed for studying swelling of disc‐shaped poly(methyl methacrylate) (PMMA) gels, which were prepared by free radical copolymerization of methyl methacrylate (MMA) using various ethylene glycol dimethacrylate (EGDM) contents at 60 °C. Pyrene (P) was introduced as a fluorescence probe during polymerization. Swelling experiments were performed by using P‐doped PMMA gels under chloroform vapor. Decay curves of P were measured during in situ swelling experiments. Exponential fits were performed to measure pyrene lifetimes, τ, inside the PMMA gels. It was observed that τ values decreased as swelling proceeded. An equation is derived for low quenching efficiencies to interpret the behaviour of P lifetimes during swelling. The Li–Tanaka equation was used to determine the cooperative diffusion coefficients, D_c, for the gels made at various crosslinker contents. It is observed that D_c values decrease as the crosslinker content is increased. © 2002 Society of Chemical Industry     

In situ fast transient fluorescence technique (FTRF) to study swelling of gels made of various crosslinker contents

The fast transient fluorescence technique (FTRF), which uses the strobe master system (SMS), was employed to study the swelling of disc‐shaped PMMA [poly(methyl methacrylate] gels. Seven gels were prepared by free radical copolymerization (FCC) of methyl methacrylate (MMA) with various ethylene glycol dimethacrylate (EGDM) contents. Pyrene (P_y) was introduced as a fluorescence probe during polymerization. After drying these gels, swelling experiments were performed in chloroform at room temperature. P_y lifetimes were measured from fluorescence decay traces during the in situ swelling experiments. An equation was derived for low quenching efficiencies to interpret the behavior of lifetimes in the gel during swelling. It was observed that P_y lifetimes in the gel decreased as swelling proceeded. The Li–Tanaka equation was used to determine the cooperative diffusion coefficients, D_c, which were found to decrease as the crosslinker content was increased. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 464–472, 2003     

Preparation and properties of silicone‐containing poly(methyl methacrylate) gels

Poly(methyl methacrylate) (PMMA) gels with varying amounts of silicone and solvent and constant amounts of crosslinker were prepared by solution free radical crosslinking copolymerization of methyl methacrylate (MMA), ethylene glycol dimethacrylate (EGDM), tetraethoxysilane (TEOS) and vinyltriethoxysilane (VTES) comonomer systems. They were then studied in benzene at a total monomer concentration of 3.5 mol L^?1 and 70 °C. The conversion of monomer, volume swelling ratio, weight fraction and gel point were measured as a function of the reaction time, silicone concentration and benzene content up to the onset of macrogelation. Structural characteristics of the gels were examined by using equilibrium swelling in benzene, gel fraction and Fourier‐transform infrared (FTIR) analysis. The morphology of the copolymers was also investigated by SEM. Based on the obtained results, it was concluded that the FTIR data did not have the capacity to show the presence of the VTES or TEOS moiety in these kinds of copolymers. On the other hand, the variation of weight fraction of gel, W_g, and its equilibrium volume swelling ratio in benzene, q_v, exhibited the same behaviour as that of MMA/EGDM copolymers. Also, the dilution of the monomer mixture resulted in an increase in the gel point and swelling degree and a decrease in the percent of conversion and gel fraction. Finally, TEOS is not an ideal silicone compound for reaction in the MMA/EGDM copolymerization system, whereas VTES is a suitable silicone comonomer for this system and it has been proved useful. Copyright © 2005 Society of Chemical Industry     

A fluorescence study on dissolution of polymeric glasses prepared in various molecular weights

Poly(methyl methacrylate) (PMMA) discs in various molecular weights, M_w, were prepared by free-radical polymerization of methyl methacrylate (MMA). Pyrene (P) was introduced during polymerization as a fluorescence probe to monitor the gelation and dissolution processes in chloroform vapor and solvent, respectively. In-situ steady state fluorescence (SSF) experiments were performed to monitor vapor uptake and chain desorption processes. Direct illumination of PMMA discs were performed to excite the P molecules embedded inside the PMMA glass. Variation in P intensity, I, was monitored during the swelling of the PMMA material exposed to chloroform vapor. It was observed that PMMA film swells like a crosslinked polymeric gel at early times by obeying the Li-Tanaka equation. Swelling time constants, τ_c, of PMMA discs were measured and found to have a strong correlation with the molecular weight, of PMMA. In a separate experiment, when the PMMA discs were in chloroform, desorption of PMMA chains from glass discs was monitored by observing the change of pyrene fluorescence intensity. A diffusion model with a moving boundary was employed to quantify the fluorescence data observed from dissolving PMMA discs made at various molecular weights. It was observed that desorption coefficient, D, decreased by increasing M_w by obeying the D≈M_w ⁻¹ law. Presented at the 80th Annual Meeting of the Federation of Societies for Coatings Technology, October 30–November 1, 2002, New Orleans, LA. Department of Physics, 80626 Maslak, Istanbul. Turkey.     

Percolation cluster on partially dissolving polymer film

Steady state fluorescence (SSF) technique was used for studying dissolution of UV-induced polymer films. These films are formed from poly(methyl methacrylate) (PMMA) chains labeled with pyrene (P) which was introduced as a fluorescence probe to monitor the dissolution processes. PMMA films in various ethylene glycol dimethacrylate (EGDM) content, cured by UV radiation, were dissolved in chlorofrom-heptane (20-80%) mixtures. Dissolution of the films were monitored in real-time by the P fluorescence intensity change in the solvent reservoir. It is observed that P intensity decreased dramatically above a critical EGDM content, which was atributed to the formation of a percolation cluster. The measured percolation threshold, (p_c=0.25) was found to be in accord with the bond percolation model. Desorption coefficients, D_d were measured for films prepared with various EGDM content and it was observed that D_d values are much lower above p_c than below p_c.     

Formation and structure of poly(methyl methacrylate) gels containing triphenyl vinyl silane

A series of Poly(methyl methacrylate) gels (PMMA) were prepared for making optical lenses by solution free radical crosslinking copolymerization of 2,2,2,‐trifluoroethyl methacrylate (TFEMA), methyl methacrylate (MMA), ethylene glycol dimethacrylate (EGDM), and triphenyl vinyl silane (TPVS) comonomer systems. They were then studied in toluene at a total monomer concentration of 5 molL^?1 and 70°C. The conversion of monomer, volume swelling ratio, weight fraction, and gel point were measured as a function of the TPVS concentration, temperature, and chain transfer agents up to the onset of macrogelation. Structural characteristics of the gels were examined by using equilibrium swelling in toluene, gel fraction, and Fourier‐transform infrared (FTIR) analysis. The morphology of the copolymers was also investigated by Scanning electron microscopy (SEM). The dilution of the monomer mixture resulted in an increase in the gel point and swelling degree and a decrease in the percentage of conversion and gel fraction. Finally, TPVS is a compatible vinyl type silicone comonomer for this system. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Molecular weight effect on polymer dissolution: a steady state fluorescence study

In situ steady state fluorescence (SSF) technique was used to study the dissolution of disc-shaped polymer glasses in various molecular weights, M_W. The glass discs were formed by free-radical polymerization of methyl methacrylate (MMA). Pyrene (P) was introduced during polymerization as a fluorescence probe to monitor the dissolution process in chloroform. Desorption of poly(methyl methacrylate) (PMMA) chains from discs were monitored simultaneously by observing the change of P fluorescence intensity, I. Diffusion model with a moving boundary was employed to quantify the fluorescence data observed from dissolving PMMA discs made at various molecular weights. It is observed that desorption coefficient, D decreased by increasing molecular weight, M_W by obeying D≈M⁻¹ law.     

Gel formation in free-radical crosslinking copolymerization

Polymer gels with varying amounts of crosslinker and solvent were prepared by solution free-radical crosslinking copolymerization of methyl methacrylate/ethylene glycol dimethacrylate (MMA/EGDM) and styrene/p-divinyl benzene (S/p-DVB) comonomer systems. The structural characteristics of the gels were examined using equilibrium swelling in toluene and gel fraction measurements. Experimental results were compared with the predictions of a kinetic model developed recently for free-radical crosslinking copolymerizations. Experimental data on S/EGDM networks reported by Hild, Okasha, and Rempp were also used to test this model. It was found that the model correctly predicts the development of the gel properties in free-radical crosslinking copolymerization. © 1995 John Wiley & Sons, Inc.     

Preparation and characterization of graft copolymers of methyl methacrylate and poly(n-hexyl isocyanate) macromonomers

Living poly(n-hexyl isocyanate) (PHIC) was deactivated with methacryloyl chloride to produce methacryl-terminated poly(n-hexyl isocyanate) (PHIC-MA) rodlike macromonomers. Radical copolymerization of methyl methacrylate (MMA) with PHIC-MA was performed using 2,2′-azobis(isobutyronitrile) as an initiator in benzene at 60 °C to prepare poly(methyl methacrylate)-graft-poly(n-hexyl isocyanate) (PMMA-graft-PHIC) graft copolymers. The monomer reactivity ratios of MMA (M₁) and PHIC-MA (M₂) were evaluated as r₁=11.5 and r₂=∼0, exhibiting remarkably lower reactivity of PHIC-MA macromonomer than that of common macromonomers. The resultant graft copolymers were characterized using gel permeation chromatography equipped with low-angle laser light-scattering to determine the molecular weights, and equipped with a refractive index detector and an ultraviolet light detector to estimate a PHIC weight fraction of PMMA-graft-PHIC at the ith elution volume of the GPC chromatogram. There are 2-3 PHIC grafts per PMMA molecule, and the PHIC rodlike chains might be difficult to introduce into the PMMA main chains having higher molecular weights. A specific dimension of PMMA-graft-PHIC in solution was discussed in detail.     

Poly(methyl methacrylate)/poly(ethylene glycol)/poly(ethylene glycol dimethacrylate) micelles: Preparation,characterization, and application as doxorubicin carriers

A crosslinked amphiphilic copolymer [poly(ethylene glycol) (PEG)–poly(methyl methacrylate) (PMMA)–ethylene glycol dimethacrylate (EGDM)] composed of PMMA, PEG, and crosslinking units (EGDM) was synthesized by atom transfer radical polymerization to develop micelles as carriers for hydrophobic drugs. By adjusting the molar ratio of methyl methacrylate and EGDM, three block copolymer samples (P0, P1, and P2) were prepared. The measurement of gel permeation chromatography and ¹H‐NMR indicated the formation of crosslinked structures for P1 and P2. Fluorescence spectroscopy measurement indicated that PEG–PMMA–EGDM could self‐assemble to form micelles, and the critical micelle concentration values of the crosslinked polymer were lower than those of linear ones. The prepared PEG–PMMA–EGDM micelles were used to load doxorubicin (DOX). The drug‐loading efficiencies of P1 and P2 were higher than that of P0 because the crosslinking units enhanced the micelles' stability. With increasing drug‐loading contents, DOX release from the micelles in vitro was decreased, and in the crosslinked formulations, the release rate was also slower. An in vitro release study indicated that DOX release from the micelles for the linear samples was faster than that for crosslinked micelles. The drug feeding amount increased and resulted in an increase in the drug‐loading content, and the loading efficiency decreased. These PEG–PMMA–EGDM micelles did not show toxicity in vitro and could reduce the cytotoxicity of DOX in the micelles; this suggested that they are good candidates as stable drug carriers. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39623.     

Kinetics of emulsifier–free emulsion polymerization of methyl methacrylate

The influences of polymerization temperature, initiator and monomer concentrations, ionic strength of the aqueous phase, as well as ethylene glycol dimethacrylate (EGDM) co-monomer, on the kinetics of the emulsifier-free emulsion polymerization of methyl methacrylate (MMA) and on the properties of the resulting poly(methyl methacrylate) (PMMA) lattices were studied. The polymerizations were carried out using potassium persulfate (KPS) as the initiator. Monodisperse PMMA lattices with particle diameters varying between 0.14–0.37 μm and polymer molecular weights of the order 0.4 × 10⁶ to 1.2 × 10⁶ g/mol were prepared. The initial rate of polymerization increases with increasing temperature, KPS-MMA mole ratio, EGDM content, or with decreasing ionic strength of the aqueous phase. It was shown that the bead size can be limited by reducing the monomer concentration or by using the cross-linking agent EGDM. The ionic strength of the aqueous phase has a dominant effect on final particle diameter and polymer molecular weight. The uniformity of the latex particles increases as the temperature increases or as the initiator concentration decreases. The experimental results can be reasonably interpreted by the homogeneous nucleation mechanism of the emulsifier-free emulsion polymerization of MMA. © 1996 John Wiley & Sons, Inc.     

Thermal properties, specific interactions, and surface energies of PMMA terpolymers having high glass transition temperatures and low moisture absorptions

We have prepared a series of poly(methyl methacrylate) (PMMA)-based terpolymers that have high glass transition temperatures and low moisture absorptions by the free radical copolymerization of methyl methacrylate, methacrylamide, and styrene in dioxane. We have investigated the effects of the styrene content on the glass transition temperatures, hydrogen bonding interactions, surface energies, moisture absorption, and molecular weights of these poly(methyl methacrylate-co-methacrylamide-co-styrene) (Poly(MMA-co-MAAM-co-S)) terpolymers by differential scanning calorimetry, Fourier transform infrared and X-ray photoelectron spectroscopies, contact angle measurements, and gel permeation chromatography. The results indicate that the glass transition temperatures, hydrogen bonding strengths, surface energies, molecular weights, and the moisture absorption decreased upon increasing the PS content in most of the terpolymer systems. In addition, the moisture absorptions of some selected terpolymers decreased even through they possess higher values of T_g than pure PMMA. These selected terpolymers have the potential to replace pure PMMA in optical device applications.     

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     

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.     

Association and physical gelation of ABA triblock copolymer in selective solvent

Association behavior and physical gelation mechanism of ABA triblock copolymer dissolved in B-selective solvent have been studied systematically from dilute to moderately concentrated solutions. Static and dynamic light scattering and nuclear magnetic resonance measurements for dilute solutions of poly(methyl methacrylate)-block-poly(tert-butyl acrylate)-block-poly(methyl methacrylate) (PMMA-PtBuA-PMMA) in 1-butanol (PtBuA selective solvent) indicated that PMMA-PtBuA-PMMA chains are molecularly dissolved above 50 °C. With decreasing temperature, the triblock copolymers form associated micelles consisting PMMA associated core and PtBuA shell. Linear dynamic viscoelastic measurements for solutions with moderate concentration (3.9-12.0 wt%) revealed that the system was viscous sol state at 60 °C. Drastic increase of shear storage modulus (G′) occurred with decreasing temperature, and at 25 °C, G′ showed rubbery plateau with weak frequency dependency, means the formation of elastic physical gel. The consistency between the temperature for micelle formation and that at the increase in G′ indicates that the physical gelation is owing to the network formation as the result of the association of PMMA chains and the bridging PtBuA chains connecting the PMMA cores. Master curves for the dynamic moduli were derived by time-temperature superposition along the frequency axis. Just above sol-gel transition concentration (C_gel), the master curves suggest the existence of fairy amount of aggregate that is not incorporated in the macroscopic network. With the increase in polymer concentration, the master curves become to reveal Maxwell-type viscoelasticity with narrow relaxation time distribution, suggesting the formation of transient network with easily generation and destruction of crosslinks. Concentration dependency of the plateau modulus is stronger than the theoretically expected, means the macroscopic transient network grows with polymer concentration by increasing the fraction of elastically effective bridging PtBuA chain above C_gel.     

Fast transient fluorescence method for measuring swelling and drying activation energies of a polystyrene gel

The time-resolved, fast transient fluorescence (TRF) technique which uses a strobe master system (SMS), was employed for studying swelling and drying of disc-shaped polystyrene gels. Disc-shaped gels were prepared by free-radical crosslinking copolymerization of styrene and ethylene glycol dimethacrylate. Pyrene was introduced as a fluorescence probe during polymerization and lifetimes, τ of pyrene were measured during in situ swelling and drying processes. Chloroform was used as an organic vapor agent to induce gel swelling at various temperatures. It was observed that τ values decreased as swelling is proceeded. Li-Tanaka equation was used to determine the swelling time constant, τ_c and cooperative diffusion coefficients, D_c for the swelling processes. It is observed that lifetimes, τ of pyrene increased during drying process and an empirical equation was introduced to determine the desorption coefficient, D for drying at various temperatures. The activation energies, ΔE were measured for the swelling and drying processes and found to be 80.0 and 33.5 kJ mol⁻¹, respectively.     

Swelling behavior of amphiphilic gels based on hydrophobically modified dimethylaminoethyl methacrylate

The amphiphilic gels based on hydrophobically modified dimethylaminoethyl methacrylate with different 1-bromoalkanes (1-C_nH_2n+1Br, n = 2, 4, 6, 8, 12) were synthesized by radiation-induced polymerization and crosslinking. The length of alkyl side chains had significant influence on the swelling behavior of the resulting gels. The swelling degree of the gels decreased with the increase of side chain length, and the gel hardly swelled when n = 12. The effect of temperature and ionic strength on the swelling behavior of the resulting gels revealed that (1) the gels with longer side chains (n ≥ 8) had upper critical solution temperature, while other gels were not thermo-sensitive. (2) Antipolyelectrolyte effect was observed when immersing the gels (n ≥ 8) in NaCl solutions in certain concentration range. The dramatic difference in swelling behavior was attributed to the different gel structures. The gels with short side chains (n ≤ 6) had cellular structure of normal polyelectrolyte gels. The gels (n ≥ 8) had an aggregation gel structure caused by the hydrophobic interaction among alkyl groups and the formation of ion-cluster between tetra-alkyl ammonium cation and Br⁻, which had been analyzed with the aid of SEM, Br⁻-selective electrode and fluorescence molecular probe.     

Synthesis of porous poly[oligo(ethylene glycol) methyl ether methacrylate] gels that exhibit thermosensitivity in highly concentrated aqueous NaCl solution

The polymerization of 2-(2-methoxyethoxy)ethyl methacrylate (MEO₂MA) in 20 wt% aqueous ethanol solution and oligo(ethylene glycol) methyl ether methacrylate (OEGMA₃₀₀, M_n = 300 g mol^?1) in water was carried out in the presence of a crosslinker. Polymerization at temperatures above the lower critical solution temperature (LCST) yielded the corresponding porous poly[oligo(ethylene glycol) methyl ether methacrylate] gels by polymerization-induced phase separation. The resulting porous gels showed rapid swelling-deswelling in water. The temperature dependency of the equilibrium swelling ratio of the gels was investigated in several concentrated aqueous NaCl solutions. At 20 °C, the equilibrium swelling ratios of the POEGMA₃₀₀ gel obtained from OEGMA₃₀₀ were largely unaffected by NaCl concentration; however, above 30 °C, they decreased with increasing NaCl concentration. Therefore, the POEGMA₃₀₀ gel showed sharp and high thermosensitivity in highly concentrated aqueous NaCl solutions. Similar swelling behaviors were observed for PMEO₂MA gel, which was prepared from MEO₂MA.     

Investigation on the early and late stage phase-separation dynamics of poly(methyl methacrylate)/poly(α-methyl styrene-co-acrylonitrile) blends through rheological and scattering functions

The phase-separation behavior of poly(methyl methacrylate)/poly(α-methyl styrene-co-acrylonitrile) (PMMA/α-MSAN) blends with two different compositions was studied by time-resolved small angle light scattering (SALS) in the spinodal decomposition (SD) regime from 160 to 210 °C. The rheological function (WLF-like equation) was introduced into the processing of light scattering data. It was found that the WLF-like equation was applicable to describe the temperature dependence of apparent diffusion coefficient D_app and the relaxation time τ of normalized scattering intensity (I(t)−I(0))/(I_m−I(0)) at the early stage of SD, as well as the relaxation time τ of maximum scattering intensity I_m and characteristic scattering vector q_m with I_m at the late stage of SD for PMMA/α-MSAN blends with two different compositions. This is in consistence with the phase-separation behavior of PMMA/SAN reported in our previous paper.