Photoinitiated cross-linking of a thiol–methacrylate system

Lecamp, Laurence; Houllier, F.; Youssef, B.; Bunel, Claude

doi:10.1016/s0032-3861(00)00700-x

Cited by 108 publications

(120 citation statements)

References 23 publications

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“…The results as shown in Figure 4B have been observed experimentally in thiol-acrylate and thiol-methacrylate systems with and without photoinitiators. [4,5,26] The disadvantage of more rapid vinyl group consumption is the incomplete conversion of the thiol groups after the thiol-ene reactions. To obtain equivalent conversion of both functional groups, one has to alter the feed ratio of thiol and vinyl groups, r 0 .…”

Section: Resultsmentioning

confidence: 99%

Kinetic Modeling of Thiol‐Ene Reactions with Both Step and Chain Growth Aspects

Okay

Bowman

2005

Macro Theory & Simulations

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Summary: A kinetic model is presented for thiol‐ene cross‐linking photopolymerizations including the allowance for chain growth reaction of the ene, i.e., homopolymerization. The kinetic model is based on a description of the average chain lengths derived from differential equations of the type of Smoluchowski coagulation equations. The method of moments was applied to obtain average properties of thiol‐ene reaction systems. The model predicts the molecular weight distribution of active and inactive species in the pre‐gel regime of thiol‐enes, as well as the gel points depending on the synthesis parameters. It is shown that, when no homopolymerization is allowed, the average molecular weights and the gel point conversion are given by the typical equations valid for the step‐growth polymerization. Increasing the extent of homopolymerization also increases the average molecular weights and shifts the gel point toward lower conversions and shorter reaction times. It is also shown that the ratio of thiyl radical propagation to the chain transfer kinetic parameter (kp1/ktr) affects the gelation time, tcr. Gelation occurs earlier as the kp1/ktr ratio is increased due to the predominant attack of thiyl radicals on the vinyl groups and formation of more stable carbon radicals. The gel point in thiol‐ene reactions is also found to be very sensitive to the extent of cyclization, particularly, if the monomer functionalities are low.Number‐average chain length of carbon radicals $\bar X_1 \bullet$ (solid curves) and thiyl radicals $\bar X'_1 \bullet$ (dashed curves) plotted against the vinyl group conversion, xM, during thiol‐ene polymerization. Calculations were for six different kp/ktr ratios.magnified imageNumber‐average chain length of carbon radicals $\bar X_1 \bullet$ (solid curves) and thiyl radicals $\bar X'_1 \bullet$ (dashed curves) plotted against the vinyl group conversion, xM, during thiol‐ene polymerization. Calculations were for six different kp/ktr ratios.

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Section: Resultsmentioning

confidence: 99%

Kinetic Modeling of Thiol‐Ene Reactions with Both Step and Chain Growth Aspects

Okay

Bowman

2005

Macro Theory & Simulations

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“…However, with 365 nm initiating light source, the initiation rates were proportional to the double bond groups. Cramer et al [14] and Lecamp et al [15] also studied the thiol-ene photopolymerization of thiol and acrylate. The rate of homopolymerization of acrylate is %1.5 times greater than that of hydrogen abstraction from thiol.…”

Section: Full Papermentioning

confidence: 99%

Influence of the Thiol Structure on the Kinetics of Thiol‐ene Photopolymerization with Time‐Resolved Infrared Spectroscopy

Wutticharoenwong

Soucek

2008

Macro Materials & Eng

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Photopolymerization kinetics of difunctional thiols with alkenes were studied. Two of the thiols, trans‐1,4‐bis(mercaptomethyl)cyclohexane (CHDMT) and 1,4‐bis(mercaptomethyl)benzene (BDMT) were synthesized. The CHDMT was synthesized via a two step process using potassium thioacetate and hydrochloric acid as reagents. The BDMT was synthesized by a one step process using 1,4‐benzenedimethanebromine with thiourea and potassium hydroxide as reagents. Three types of alkenes (divinyl ether, diallyl ether, and dimethacrylate) were reacted with CHDMT, BDMT or 1,8‐octanedithiol (ODT). The photopolymerization was investigated with and without a photoinitiator. The kinetics of the thiol‐ene photopolymerization was investigated by time‐resolved infrared spectroscopy. It was proposed that the steric hindrance of the cyclohexane (CHDMT) resulted in a lower rate of photopolymerization compared to BDMT and ODT. The vinyl ether (alkene) exhibited the highest activity compared to allyl ether and acrylate which was attributed to a high electron density of the alkene. Incorporation of photoinitiator increased the reaction rate and final conversion of the system, particularly in the ODT system.

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“…[16,17] In addition, the inclusion of thiols and amines to monomer systems is known to diminish the harmful effects of oxygen. [25,[28][29][30] Owing to the great importance of the photopolymerization process, it is necessary to fully understand the impact of oxygen on photopolymerization in order to combat its inhibitory effects. Previous research has recognized the effect of oxygen, principally concentrating on the polymerization rate reduction.…”

Section: Introductionmentioning

confidence: 99%

Modeling the Effect of Oxygen on Photopolymerization Kinetics

O’Brien

Bowman

2006

Macro Theory & Simulations

103

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Summary: A comprehensive one‐dimensional photopolymerization model was utilized to investigate the effect of oxygen on the free‐radical photopolymerization kinetics. The spatial profiling aspect of the model provided insight into the heterogeneity of the cure kinetics due to oxygen inhibition, specifically the variance in the concentration profile of monomer and oxygen. Double bond conversion was negligible for the top ten microns of the film due to continuous oxygen diffusion, and increased with increasing depth. Similarly, the oxygen concentration decreased with increasing depth due to the competition between oxygen diffusion time and the polymerization rate. The effect of initiation rate on the extent of oxygen inhibition was investigated for various oxygen concentrations. As the initiation rate increased, the polymerization rate increased, and eventually approached that of a sample in an inert environment. Similarly, as the oxygen concentration was decreased, the polymerization rate increased. The effect of varying the initiation rate on the cure profile in the oxygen‐exposed film was also studied. It was found that the unpolymerized tacky layer decreased from 50 µm to 5 µm with a 3 order of magnitude increase in initiation rate. Using the pseudo steady state approximation, the relationship between polymerization rate and initiation rate was derived for films in an oxygen environment. A direct relationship between the polymerization and initiation rate was found for films in air. The polymerization model supported this derivation and found that as the oxygen concentration was decreased, the dependence on initiation rate, or alpha, decreased, reaching the accepted value of 0.5 for alpha in inert environments.Double bond conversion versus film depth and cure time.imageDouble bond conversion versus film depth and cure time.

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Photoinitiated cross-linking of a thiol–methacrylate system

Cited by 108 publications

References 23 publications

Kinetic Modeling of Thiol‐Ene Reactions with Both Step and Chain Growth Aspects

Kinetic Modeling of Thiol‐Ene Reactions with Both Step and Chain Growth Aspects

Influence of the Thiol Structure on the Kinetics of Thiol‐ene Photopolymerization with Time‐Resolved Infrared Spectroscopy

Modeling the Effect of Oxygen on Photopolymerization Kinetics

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