Yasar Yilmaz

Real time monitoring of polymerization rate of methyl methacrylate using fluorescence probe

The steady-state fluorescence technique was used to study the polymerization rate and the autoacceleration due to the gel effect in free-radical polymerization of methyl methacrylate. Pyrene was used as a fluorescence probe for the in situ polymerization experiments. The times required for the onset of the gel effect were recorded for various polymerization temperatures. A simple kinetic model was used to validate the experimental data. The results show that the fluorescence technique can be used to follow the onset of the gel effect and the activation energy during the polymerization processes.

Fluorescence technique for studying the sol-gel transition in the free-radical crosslinking copolymerization of methyl methacrylate and ethylene glycol dimethacrylate

Abstract The steady-state fluorescence technique was used to study the free-radical crosslinking copolymerization of methyl methacry- late and ethylene glycol dimethacrylate in the absence and presence of toluene at 75°C. A sol-gel phase transition was observed and monitored by an excited aromatic molecule during the gelation of the above system. Bond percolation theory was employed to quantify the results. The critical exponent and gel point were found to be around 0.45 and 0.36 both in bulk and solution polymerization.

In situ fluorescence experiments to test the reliability of random bond and site bond percolation models during sol-gel transition in free-radical crosslinking copolymerization

Sol-gel phase transition during the free-radical crosslinking copolymerization of methyl methacrylate and ethylene glycol dimethacrylate was studied using the steady-state fluorescence method. Copolymerization was performed both in the absence and presence of toluene at 75°C. Sol-gel phase transitions were monitored by observing the direct intensity of an excited pyrene methyl pivalate during in situ fluorescence experiments. Random bond and site bond percolation models were employed to quantify the results of bulk and solution polymerizations, respectively, during the sol-gel phase transition. Gel points were determined and the β exponents were found to be around 0.37 and 0.38 during gelation in bulk and solution polymerizations, respectively.

Elucidation of multiple-point interactions of pyranine fluoroprobe during the gelation

We have studied the multiple-point interactions of the pyranine (8-hydroxypyrene-1,3,6-trisulfonic acid, trisodium salt; 3sPyOH) fluoroprobe with polymer chains during the free-radical polymerization of acrylamide (AAm) by using the steady state fluorescence measurements. We observed a considerable blue shift from 515nm to 406nm in the emission spectra due to a C-O ether bond formation between the hydroxylic oxygen of 3sPyOH and a terminal C-atom of the growing AAm chain. Furthermore ionic (electrostatic) interactions occur between the three ionized sulfonic acid groups (SO(3)(-)) of 3sPyOH and protonated amide groups on the AAm chains. These electrostatic interactions also cause a gradual red shift in the maximum of the short-wavelength-peak, from 406nm to 430nm. The results showed that the pyranine can be used as a probe for real time monitoring of the polymerization process of AAm system since it monitors both the progression of the polymerization via chemical binding over OH group and the change in the local density of the polymerizing sample by means of the gradual red shift in the short-wavelength-peak via ionic interactions over SO(3)(-) groups.

Real-time monitoring of swelling and dissolution of poly(methyl methacrylate) discs using fluorescence probes

Abstract A new technique, based on steady state fluorescence measurements is introduced for studying swelling and dissolution of polymer discs. These discs are formed by free radical polymerization of methyl methacrylate (MMA). Pyrene (Py) was introduced as a fluorescence probe during polymerization. Swelling and dissolution of disc shape poly(methyl methacrylate) (PMMA) samples in chloroform-heptane mixtures were monitored in real-time by the Py fluorescence intensity change. The effects of solvent quality and agitation (stirring) on film dissolution were studied. Sorption and desorption coefficients of solvent and Py molecules were measured respectively during dissolution of films, and found to be between 10 −7 and 10 −6 cm 2 s −1 .

Slow regions percolate near glass transition

Abstract:A nanosecond scale in situ probe reveals that a bulk linear polymer undergoes a sharp phase transition as a function of the degree of conversion, as it nears the glass transition. The scaling behaviour is in the same universality class as percolation. The exponents γ and β are found to be 1.7±0.1 and 0.41±0.01 in agreement with the best percolation results in three dimensions.

Determination of reaction activation energy during gelation in free radical crosslinking copolymerization using the steady-state fluorescence method

SYNOPSIS The steady-state fluorescence technique was used to study the sol-gel transition in free radical crosslinking copolymerization of methyl methacrylate and ethylene glycol dimethacrylate (EGDM). Pyrene methyl pivalate was used as a fluorescence probe for the in situ polymerization experiments. The times required for the onset of gelation t, and the critical exponent /3 were recorded for various EGDM contents and at different polymerization temperatures. A simple kinetic model was used to interpret the experimental gel point data. The results show that the fluorescence technique can be used to measure the critical exponent /3, the gel point tc, and the activation energy during sol-gel phase transition processes. 0 1996 John Wiley & Sons, Inc.

Ffast Transient Fluorescence Technique to Study Critical Exponents at the Glass Transition

The fast transient fluorescence (FTRF) technique was used to study critical exponents at the glass transition in free-radical crosslinking copolymerization (FCC) for two different monomeric systems, methyl methacrylate (MMA) and styrene (S). Pyrene (Py ) was used as a fluorescence probe. The fluorescence lifetimes of Py from its decay traces were measured and used to monitor the gelation process. Changes in the viscosity of the pregel solutions due to glass formation dramatically enhance the fluorescent yield of aromatic molecules. This effect is used to study the glass transition upon gelation of MMA and S monomeric systems as a function of time, at various temperatures and crosslinker concentrations. The results are interpreted in the view of percolation theory. The gel fraction and weight average degree of polymerization exponents β and γ are found to be 0.37 ± 0.02 and 1.66 ± 0.07 in agreement with percolation results.

Modeling of swelling by fluorescence technique in poly (methyl methacrylate) gels

A novel technique based on in-situ steady-state fluorescence (SSF) measurements is introduced for studying swelling processes in gels formed by free radical cross-linking copolymerization (FCC) of methyl methacrylate (MMA) and ethylene glycol dimethacrylate (EGDM) in toluene. Gels were prepared at 75°C for various toluene contents with pyrene (Py) as a fluorescence probe. After drying these gels, swelling and desorption experiments were performed in toluene at 50°C by real-time monitoring of Py fluorescence intensity. A correction method was developed to obtain pure swelling curves, by using desorption curves of Py molecules. Li-Tanaka equation was employed to produce swelling parameters. Cooperative diffusion coefficients (D c ) were measured and found to be around 10 -6 cm 2 /s for gels swollen in toluene.

Probing the swelling kinetics in polymer gels by fluorescence technique

Abstract A method based on in situ steady-state fluorescence (SSF) measurements is introduced for studying swelling processes in gels formed by free radical cross-linking copolymerization (FCC) of methyl methacrylate (MMA) and ethylene glycol dimethacrylate (EGDM) in toluene. Cooperative diffusion coefficients (Dc) were measured and found to be around 10−6 cm2/s for gels swollen in toluene.