Proportion Of Monomers Research Articles

A model of flow‐through pore formation in methacrylate ester‐based monolithic columns

The main factors affecting the porosity of methacrylate-ester based monolithic columns were investigated. We prepared 23 monolithic capillary columns with porosity controlled by varying the proportions of butyl methacrylate and ethylene dimethacrylate monomers and of 1,4-butanediol and 1-propanol as the porogen solvent in the polymerization mixtures by thermally initiated in-situ polymerization in fused-silica capillaries. Using mixture design software, we systematically varied the composition of the polymerisation mixtures to find significant factors affecting flow-through pore formation. Multivariate analysis of the experimental data obtained for the fabricated columns yielded a model for prediction of the flow-through porosity in monolithic beds as a function of the composition of the polymerization mixture used to prepare polymethacrylate monolithic capillary columns. The mean error of prediction was lower than 8% for eight columns prepared independently of the original set of 15 columns used to derive the flow-through model. The flow-through porosity increases with increasing concentration of the binary porogen solvent mixture, the concentration of 1,4-butanediol being the main factor enhancing flow-through pore formation. On the other hand, increasing concentrations of the hydrophobic monomer butyl methacrylate and increasing concentrations of 1-propanol have a negative effect on flow-through pore formation. The capillary columns prepared with a high proportion of flow-through pores and a minimum amount of mesopores can be used for fast gradient separations of both low-molecular weight compounds and biopolymers.

Resilient Bioresorbable Copolymers Based on Trimethylene Carbonate, l-Lactide, and 1,5-Dioxepan-2-one

The new combinations of monomers presented in this work were evaluated in order to create an elastic material for potential application in soft tissue engineering. Thermoplastic elastomers (TPE) of trimethylene carbonate (TMC) with L-lactide (LLA) and 1,5-dioxepan-2-one (DXO) have been synthesized using a cyclic five-membered tin alkoxide initiator. The block copolymers were designed in such a way that poly(trimethylene carbonate-co-1,5-dioxepan-2-one) formed an amorphous middle block and the poly(L-lactide) (PLLA) formed semicrystalline terminal blocks. The amorphous middle block consisted of relatively randomly distributed TMC and DXO monomer units, and the defined block structure of the PLLA terminal segments was confirmed by 13C NMR. The properties of the TMC-DXO-LLA copolymers were compared with those of triblock copolymers based either on LLA-TMC or on LLA-DXO. Differential scanning calorimetry and dynamic mechanical analysis data confirmed the micro-phase separation in the copolymers. The mechanical properties of the copolymers were evaluated using tensile testing and cycling loading. All of the copolymers synthesized showed a highly elastic behavior. The properties of copolymers could be tailored by altering the proportions of the different monomers.

The Peroxisomal Acyl-CoA Thioesterase Pte1p from Saccharomyces cerevisiae Is Required for Efficient Degradation of Short Straight Chain and Branched Chain Fatty Acids

The role of the Saccharomyces cerevisae peroxisomal acyl-coenzyme A (acyl-CoA) thioesterase (Pte1p) in fatty acid beta-oxidation was studied by analyzing the in vitro kinetic activity of the purified protein as well as by measuring the carbon flux through the beta-oxidation cycle in vivo using the synthesis of peroxisomal polyhydroxyalkanoate (PHA) from the polymerization of the 3-hydroxyacyl-CoAs as a marker. The amount of PHA synthesized from the degradation of 10-cis-heptadecenoic, tridecanoic, undecanoic, or nonanoic acids was equivalent or slightly reduced in the pte1Delta strain compared with wild type. In contrast, a strong reduction in PHA synthesized from heptanoic acid and 8-methyl-nonanoic acid was observed for the pte1Delta strain compared with wild type. The poor catabolism of 8-methyl-nonanoic acid via beta-oxidation in pte1Delta negatively impacted the degradation of 10-cis-heptadecenoic acid and reduced the ability of the cells to efficiently grow in medium containing such fatty acids. An increase in the proportion of the short chain 3-hydroxyacid monomers was observed in PHA synthesized in pte1Delta cells grown on a variety of fatty acids, indicating a reduction in the metabolism of short chain acyl-CoAs in these cells. A purified histidine-tagged Pte1p showed high activity toward short and medium chain length acyl-CoAs, including butyryl-CoA, decanoyl-CoA and 8-methyl-nonanoyl-CoA. The kinetic parameters measured for the purified Pte1p fit well with the implication of this enzyme in the efficient metabolism of short straight and branched chain fatty acyl-CoAs by the beta-oxidation cycle.

Acrylic acid level and adhesive performance and peel master‐curves of acrylic pressure‐sensitive adhesives

AbstractThree series of pressure‐sensitive adhesives were prepared with constant glass‐transition temperature, using emulsion polymerization. The monomers chosen were butyl acrylate, 2‐ethylhexyl acrylate (EHA), methyl methacrylate (MMA), and acrylic acid (AA). Within each polymer series, the proportion of AA monomer was held constant for each polymer preparation but acrylic ester monomer levels were varied. Adhesion performance was assessed by measurement of loop tack, static shear resistance, and through the construction of peel master‐curves. Peel master‐curves were generated through peel tests conducted over a range of temperatures and peel rates and through application of the time–temperature superposition principle. Bulk effects dominated by polymer zero shear viscosity change as AA and EHA levels were varied were attributed to the observed effect on static shear resistance and the horizontal displacements of peel master‐curves. Static shear resistance was found to strongly correlate with log(aC), a parameter introduced to horizontally shift peel master‐curves to form a superposed, “super master‐curve”. An interfacial interaction was proposed to account for deviations observed when loop tack was correlated with log(aC). Surface rearrangements via hydrogen bonding with the test substrate were suggested as responsible for the interfacial interaction. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1237–1252, 2006

Influence of Regulator, Temperature and Monomer Proportion on the Microstructure and Sequence Distribution of Random Isoprene-Styrene Copolymer

The linear random isoprene-styrene copolymer (L-SIR) was prepared by solution polymerization with cyclohexane—n-hexane mixture as solvent and n-BuLi as initiator in the presence of the polar regulator—tetrahydrofuran (THF). Microstructures of L-SIR have been studied by 1H-NMR.

Radiation Grafting of 2-Hydroxy Ethyl Methacrylate (HEMA)/Glycidyl Methacrylate (GMA) onto Polyethylene-Coated Polypropylene Non-woven Fabric

The paper presents results of an investigation of the possibility of applying polyethylene-coated polypropylene (PE-co-PP) nonwoven fabric for treating dye wastes resulting from wastewater of the textile industry. For this purpose the radiation-induced graft copolymerization of binary mixtures of 2-hydroxy ethyl methacrylate (HEMA)/glycidyl methacrylate (GMA) onto polyethylene-coated polypropylene by the pre-irradiation method has been investigated. The effect of different factors that may affect the grafting percent such as solvent type and comonomer compositions were studied. Two solvents, dimethyl sulphoxide (DMSO) and 1-butanol were used. It was found that the degree of grafting depend upon the type of solvent and the composition of the comonomer mixture. Morphology of grafted nonwoven fabric was examined by scanning electron microscope (SEM). The hydrophilic properties in terms of swelling percent and water uptake were investigated. The higher swelling and water uptake percent were achieved at 100% HEMA diluted with 1-butanol. The use of these modified samples as absorbents for different classes of dyestuffs normally released from textile factories was achieved. The results obtained showed that the highest percentage of dye sorption was found in the case of basic dye and the lowest one in the case of reactive dye, depending on the reactive groups on the dye. Copolymers with a higher proportion of HEMA monomer diluted with 1-butanol as solvent showed the highest hydrophilic properties and higher dye uptake.

Controlling Drug Release from Imprinted Hydrogels by Modifying the Characteristics of the Imprinted Cavities

The aim of this study was to analyse the influence of the template/functional monomer proportion on the achievement of molecularly imprinted hydrogels with cavities with a high enough affinity for the drug to sustain drug release. Imprinted hydrogels were prepared from N,N-dimethylacrylamide and tris(trimethylsiloxy)sililpropyl methacrylate (DMAA and TRIS; main components), methacrylic acid (MAA; functional monomer), ethylene glycol dimethacrylate (EGDMA; cross-linker), and timolol (template drug). Photo-polymerization of the monomer solutions was carried out in poly(propylene) molds (0.3 mm thickness) to obtain contact lens-like devices. Non-imprinted control hydrogels were also prepared in the same way but without the addition of timolol. The imprinted hydrogels showed a higher affinity for timolol and a slower release rate than the non-imprinted hydrogels. The release rate decreased by increasing the MAA/timolol ratio in the gel recipe. Hydrogels prepared with 400 x 10(-3) M MAA, 600 x 10(-3) M EGDMA, and a timolol/MAA mole ratio of 1:16-1:32 had drug diffusion coefficients two orders of magnitude below those of non-imprinted hydrogels. The results obtained clearly indicate that the timolol release rate is critically affected by the conditions under which the hydrogels were synthesized. These effects are discussed on the basis of the influence of drug proportion on the conformation of the imprinted cavities.

Artificial Neural Networks Associated to Calorimetric Measurements Used as a Method to Predict Polymer Composition of High Solid Content Emulsion Copolymerizations

Inspired by biological systems, artificial neural networks (ANN) have demonstrated to be powerful tools to model non-linear systems, such as high solid content latexes produced by emulsion polymerization which have a great importance in the polymeric industry, essentially for environmental reasons, since they usually have water as a continuous phase. The quality of the produced polymer is closely related to the structure of the polymeric chain. In order to propose technical and economically feasible alternatives to control a polymeric structure, this work is aimed to develop a new methodology based on ANN associated with calorimetry to predict the polymeric structure. The designed ANN presented excellent results when tested with process condition variations (such as temperature and reaction time) as well as when they were submitted to test concerning the variation on the proportion of monomers in the latex formulation. Hence, it was possible to conclude that ANN, associated to calorimetry, lead to an efficient method to predict the polymer composition in emulsion copolymerizations.

Polysaccharides of Algae 58. The polysaccharide composition of the Pacific brown alga Alaria fistulosa P. et R. (Alariaceae, Laminariales)

Quantitative determination of mannitol, fucoidan and alginate in different parts of the thallus (the blade, the midrip, the sporophylls, and the stipe with rhizoids) of the brown alga Alaria fistulosa, collected from the coastal waters of Paramushir Island, was carried out. Sporophylls were shown to differ considerably in carbohydrate composition from all other parts of the plant. In particular, the fucoidan content in sporophylls is several times as high as that in the blade. Alginate preparations isolated from sporophylls and from blade have different proportions of monomers (mannuronic acid and guluronic acid residues) and different molecular masses. Fucoidan preparations isolated from these parts of the plant differ slightly in the sulfate content. Their specific feature is a rather high galactose content comparable with the content of fucose. The sporophylls of A. fistulosa may be regarded as a rich source for practical isolation of fucoidan.

Egg-White Protein Fractionation Using New Weak Anion-Exchange Resins Based on Poly(Glycidyl Methacrylate-co-Ethylendimethacrylate). Preparation and Characterization

A new formulation for a poly(glycidyl methacrylate-co-ethylendimethacrylate)-based resin with a 11:9 proportion of monomer to crosslinker is developed and amino-functionalized in order to obtain new particulate materials suitable for egg-white protein fractionation. Functionalization is carried out using three different chemical reagents: diethylamine (DEA), DEA-tetrahydrofuran (THF) (1:1), and concentrated ammonia. The ammonia- and DEA-THF-treated polymers are used to fractionate egg-white proteins, in particular lysozyme and ovalbumin, by anion-exchange chromatography in packed column experiments, the latter resin showing better performances. Finally, both supports, working at semipreparative scale and step-gradient elution, separate pure ovalbumin with a yield of 83%.

Temporary restorative resins using non-phthalate ester plasticizers

This study examined temporary restorative resins that use non-phthalate ester plasticizers. Three non-phthalate plasticizers were tested: tri-ethyl citrate (TEC), tri-butyl citrate (TBC), and di-butyl sebacate (DBS). The experimental resins were compared with resins that use a phthalate ester plasticizer (di-butyl phthalate, DBP) and commercial products (Dura Seal, Plast Seal, and Fit Seal). For the experimental resins, the ratio of plasticizer to PMMA/MMA resin was varied from 30 to 60% (wt). The mechanical properties of the experimental resins were evaluated using a modified diametral compressive strength and the resistance to explorer insertion. The strengths of the experimental resins with plasticizer concentrations ranging from 40 to 50% (TEC, TBC, and DBP) or from 30 to 40% (DBS), by weight, were equivalent to the strengths of commercial temporary restorative resins. A similar tendency was seen for the resistance to explorer insertion. The results suggest that new temporary restorative resins can be prepared by choosing the appropriate proportions of resin monomer and non-phthalate ester plasticizer.

Nonsense Suppression in Yeast Cells Overproducing Sup35 (eRF3) Is Caused by Its Non-heritable Amyloids

The [PSI+] prion determinant of Saccharomyces cerevisiae causes nonsense suppressor phenotype due to a reduced function of the translation termination factor Sup35 (eRF3) polymerized into amyloid fibrils. Prion state of the Rnq1 protein, [PIN+], is required for the [PSI+] de novo generation but not propagation. Yeast [psi-] [PIN+] cells overproducing Sup35 can exhibit nonsense suppression without generation of a stable [PSI+]. Here, we show that in such cells, most of Sup35 represents amyloid polymers, although the remaining Sup35 monomer is sufficient for normal translation termination. The presence of these polymers strictly depends on [PIN+], suggesting that their maintenance relies on efficient generation de novo rather than inheritance. Sup35 polymers contain Rnq1, confirming a hypothesis that Rnq1 polymers seed Sup35 polymerization. About 10% of cells overproducing Sup35 form colonies on medium selective for suppression, which suggests that the proportion of Sup35 monomers to polymers varies between cells of transformants, allowing selection of cells deficient for soluble Sup35. A hybrid Sup35 with the N-terminal domain replaced for 66 glutamine residues also polymerizes and can cause nonsense suppression when overproduced. The described polymers of these proteins differ from the [PSI+] polymers by poor heritability and very high frequency of the de novo appearance, thus being more similar to amyloids than to prions.

The synthesis of hydroxybutyrate and hydroxyvalerate copolymers by the bacterium Ralstonia eutropha

The paper deals with the study of the synthesis of 3-hydroxybutyrate (3HB) and 3-hydroxyvalerate (3HV) copolymers by the bacterium Ralstonia eutropha B-5786 grown under different carbon nutrition conditions (growth on carbon dioxide, fructose, and CO2-valerate and fructose-valerate mixtures). The parameters to be analyzed included the yield of biomass, the yield, synthesis rate, and composition of copolymers, the activity of the key enzymes of polyhydroxyalkanoate (PHA) synthesis (beta-ketothiolase, acetoacetyl-CoA reductase, and PHA synthase), the maximum tolerable concentration of valerate to the bacterium, and the conditions that govern the incorporation of hydroxyvalerate to copolymers. This allowed the relationship between cultivation conditions and the proportion of monomers in the copolymers to be deduced. We were able to synthesize a range of 3HB/3HV copolymers and found that the thermal characteristics and the degree of crystallinity of these copolymers depend on the molar fraction of 3HV.

The Effect of Chain Transfer Agent Level on Adhesive Performance and Peel Master‐Curves for Acrylic Pressure Sensitive Adhesives

AbstractSummary: Three series of pressure sensitive adhesives were prepared with fixed glass transition temperature, using emulsion polymerisation. Monomers chosen were butyl acrylate, 2‐ethylhexyl acrylate, and methyl methacrylate, along with a small amount of acrylic acid. The proportion of acrylic acid monomer was held constant for each polymer preparation while acrylate ester monomer levels were varied. The chain transfer agent level used was varied for each series of polymerisations. Adhesion performance was assessed by measurement of loop tack, static shear resistance, and through construction of peel master‐curves. Peel master‐curves were generated through peel tests conducted over a range of temperatures and peel rates and through application of the Boltzmann superposition principle. The presence of high levels of polymer gel was found to obscure the influence of monomer composition on adhesion performance. For polymers with low levels of gel, adhesion performance was correlated with changes in viscosity as comonomer composition was varied. In cohesive failure regions of peel master‐curves for polymers with high levels of chain transfer agent, the shift factors aT were found to closely fit the Williams‐Landel‐Ferry (WLF) equation and allowed the calculation of the WLF parameters, C1 and C2. The cohesive failure regions were successfully shifted to provide a “super” master‐curve and the values of aC used to generate the “super” master‐curve were applied to accurately predict relative static shear resistance levels. For low gel content polymers, loop tack was correlated with log(aC) as EHA levels were increased.Peel master‐curve for formulation AA4M91‐3.magnified imagePeel master‐curve for formulation AA4M91‐3.

The effect of varied monomer composition on adhesive performance and peeling master curves for acrylic pressure‐sensitive adhesives

AbstractA group of pressure‐sensitive adhesives were prepared with constant glass transition temperature, using emulsion polymerization. The monomers chosen were butyl acrylate, 2‐ethylhexyl acrylate, and methyl methacrylate, along with a small amount of acrylic acid. The proportion of acrylic acid monomer was held constant for each polymer preparation but acrylic ester monomer levels were varied. The glass transition temperatures of the acrylate copolymers were measured by using differential scanning calorimetry. Drying and weighing the tetrahydrofuran‐insoluble polymer fractions were used to determine the polymer gel fractions. Films of constant coating thickness were applied to poly(ethylene terephthalate) film and adhesive properties (tack and shear) were examined. Peel was examined through the construction of master curves derived from peel tests conducted over a range of temperatures and peel rates. As the 2‐ethylhexyl acrylate content increased, the latex gel fractions were found to increase. With increasing EHA and gel fraction, peel shear was found to increase. When peel force master curves were compared, divergence in peel master curves occurred as peel rates increased where polymers with higher butyl acrylate contents reached greater peel stress values. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2909–2917, 2004

Oxidative electropolymerizations of carbazole derivatives in the presence of bithiophene

N-Ethylcarbazole (NECZ) or carbazole (CZ) and bithiophene (BT) have been used as a mixture of monomers for the formation of electrodeposited polymer and copolymer films on platinum electrode. When beginning with a NECZ–BT mixture, the peak intensity resulting from the composite film cycling decreases with increasing initial NECZ proportion until that proportion reaches 40%. For higher NECZ proportions, no deposit could be obtained. Infrared spectra of the deposits show the presence of the characteristic bands of both monomer units in the material. In the case of CZ–BT mixtures, the electrochemical behaviours of the composite films are close to those displayed by the homopolymers, i.e. polybithiophene or dicarbazyle, containing respectively low and high proportions of CZ. Furthermore, infrared and ultraviolet-visible studies of deposits obtained for various CZ proportions yield spectra that vary according to monomer proportion.

Tsp36, a tapeworm small heat-shock protein with a duplicated alpha-crystallin domain, forms dimers and tetramers with good chaperone-like activity.

Small heat shock proteins (sHSPs), which range in monomer size between 12 and 42 kDa, are characterized by a conserved C-terminal alpha-crystallin domain of 80-100 residues. They generally form large homo- or heteromeric complexes, and typically have in vitro chaperone-like activity, keeping unfolding proteins in solution. A special type of sHSP, with a duplicated alpha-crystallin domain, is present in parasitic flatworms (Platyhelminthes). Considering that an alpha-crystallin domain is essential for the oligomerization and chaperone-like properties of sHSPs, we characterized Tsp36 from the tapeworm Taenia saginata. Both wild-type Tsp36 and a mutant (Tsp36C-->R) in which the single cysteine has been replaced by arginine were expressed and purified. Far-UV CD measurements of Tsp36 were in agreement with secondary structure predictions, which indicated alpha-helical structure in the N-terminal region and the expected beta-sandwich structure for the two alpha-crystallin domains. Gel permeation chromatography and nano-ESI-MS showed that wild type Tsp36 forms dimers in a reducing environment, and tetramers in a non-reducing environment. The tetramers are stabilized by disulfide bridges involving a large proportion of the Tsp36 monomers. Tsp36C-->R exclusively occurs as dimers according to gel permeation chromatography, while the nondisulfide bonded fraction of wild type Tsp36 dissociates from tetramers into dimers under nonreducing conditions at increased temperature (43 degrees C). The tetrameric form of Tsp36 has a greater chaperone-like activity than the dimeric form.

Solubilization of DMPC-d54and DMPG-d54vesicles with octylglucoside and sodium dodecyl sulfate studied by FT-IR spectroscopy

The solubilization of deuterated dimyristoylphosphatidylcholine (DMPC-d54) and dimyristoylphosphatidylglycerol (DMPG-d54) vesicles by the surfactants sodium dodecyl sulfate (SDS) and octylglucoside (OG), respectively, was studied by Fourier transform infrared spectroscopy (FT-IR) at 30 °C. In order to obtain separate information about the structural changes of both, the lipid and the surfactant component during the solubilization process, isotopically labelled lipids (DMPC-d54 and DMPG-d54) were used. With increasing surfactant concentration, the shift of the CD2 stretching mode towards higher wavenumber indicates an increasing disorder of the lipid alkyl chains during the incorporation of the surfactants into the lipid bilayer. At the same time the frequency of the antisymmetric CH2 stretching mode of the surfactant alkyl chains shifts towards lower wavenumber with increasing amount of surfactant. This occurs due to the decreasing proportion of surfactant monomers until the saturation limit is reached. In the coexistence region the frequency of the CH2 vibration stays constant, which indicates no change in the monomer concentration of the surfactant. Only the proportion of micelles increases at the expense of the vesicles. Above the coexistence region no further frequency shift is observed except for the DMPC/SDS system, which show an additional frequency decrease of the CH2 stretching mode. This is due to the decreasing amount of SDS monomers according to the decrease of the CMC for charged systems. In DMPG/SDS mixtures, prepared in 0.1 mM NaCl, the surfactant charge is screened by the salt and no frequency shift is observed. The carbonyl vibrations show a pronounced frequency shift towards lower wavenumber exclusively for the DMPG/SDS system with high net charge. This indicates an increasing degree of hydration of the lipid head-group with increasing amount of surfactant due to the effort to separate the negative charge of the lipid head-group from the negatively charged surfactant head-group.

Monolithic valves for microfluidic chips based on thermoresponsive polymer gels.

The direct preparation of thermoresponsive monolithic copolymers by photopatterning of a liquid phase consisting of an aqueous solution of N-isopropylacrylamide, N-ethylacrylamide, N,N'-methylenebisacrylamide, and 4,4'-azobis(4-cyanovaleric acid) has been studied and the products used as valves within the channels of microfluidic devices. The volume change associated with the polymer phase transition at its lower critical solution temperature (LCST) leads to the rapid swelling and the deswelling of the 2.5% cross-linked monolithic gel thus enabling the polymer to close or open the channel and to function as a nonmechanically actuated valve. The LCST at which the valve switches was easily adjusted within a range of 35 degrees C-74 degrees C by varying the proportions of the monovinyl monomers in the polymerization mixture. The closed valve holds pressures of up to 18 MPa without noticeable dislocation, structural damage, or leakage. In contrast, following deswelling by raising the temperature above LCST the valve offers no appreciable flow resistance since its large, micrometer-size pores are open. Laser-triggered photobleaching of a fluorescent dye contained in the liquid phase enabled monitoring of flow through the device and determination of the times required to open and close the valve. The valves are characterized by very fast actuation times in a range of 1-4 s depending on the type of device. No changes in performance were observed even after repeated open-close cycling of the valves.

FTIR and ESR Spectroscopic Studies of the Photopolymerization of Vinyl Ester Resins

The reaction kinetics during photopolymerization of bisGMA/styrene blends were investigated using FTIR and ESR spectroscopy. Increased styrene concentration reduced the polymerization rate of both methacrylate and styrene due to an increase in the termination rate and due to the stability of the styryl radical. Raised styrene concentrations also increased the final methacrylate conversion, but the final styrene conversion decreased because styrene plasticized the network, allowing methacrylate conversion to rise at higher styrene concentrations; however, the copolymerization did not proceed far enough to achieve increased conversions of styrene. The final concentration of radicals was reduced at higher styrene concentrations because of an increase in the bimolecular termination rate for networks with low cross-link densities. The proportion of styryl radicals trapped in the vitrified matrix was found to be markedly higher than the proportion predicted from the proportion of styrene monomer in the feed resin or from the copolymerization rate constants, due to the higher mobility of styrene relative to the methacrylate groups. Increased isothermal cure temperature resulted in a raised polymerization rate, increased conversion, and a decreased final concentration of radicals. This was attributed to the effects of an increase in the propagation rate and the bimolecular termination rate. The proportion of styryl radicals trapped in the vitrified matrix was found to increase with raised isothermal cure temperature because the fraction of styrene reacting increased relative to the methacrylate groups. The concentration of radicals released by photocleavage of the photoinitiator was sufficient to account for the increase in the concentration of radicals even after the sample entered the vitrification region.