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Thiol-Yne Photopolymerizations: Novel Mechanism, Kinetics, and Step-Growth Formation of Highly Cross-Linked Networks.

Fairbanks BD, Scott TF, Kloxin CJ, Anseth KS, Bowman CN - Macromolecules (2008)

Bottom Line: Chain-growth polymerization of alkyne and vinyl functionalities was only observed for reactions in which the alkyne was originally in excess.A tetrafunctional thiol was photopolymerized with a difunctional alkyne, forming an inherently higher cross-link density than an analogous thiol-ene resin, displaying a higher glass transition temperature (48.9 vs -22.3 degrees C) and rubbery modulus (80 vs 13 MPa).Additionally, the versatile nature of this chemistry facilitates postpolymerization modification of residual reactive groups to produce materials with unique physical and chemical properties.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemical and Biological Engineering and the Howard Hughes Medical Institute, University of Colorado, Boulder, Colorado 80309-0424.

ABSTRACT
Radical-mediated thiol-yne step-growth photopolymerizations are utilized to form highly cross-linked polymer networks. This reaction mechanism is shown to be analogous to the thiol-ene photopolymerization; however, each alkyne functional group is capable of consecutive reaction with two thiol functional groups. The thiol-yne reaction involves the sequential propagation of a thiyl radical with either an alkyne or a vinyl functional group followed by chain transfer of the radical to another thiol. The rate of thiyl radical addition to the alkyne was determined to be approximately one-third of that to the vinyl. Chain-growth polymerization of alkyne and vinyl functionalities was only observed for reactions in which the alkyne was originally in excess. Analysis of initial polymerization rates demonstrated a near first-order dependence on thiol concentration, indicating that chain transfer is the rate-determining step. Further analysis revealed that the polymerization rate scaled with the initiation rate to an exponent of 0.65, deviating from classical square root dependence predicted for termination occurring exclusively by bimolecular reactions. A tetrafunctional thiol was photopolymerized with a difunctional alkyne, forming an inherently higher cross-link density than an analogous thiol-ene resin, displaying a higher glass transition temperature (48.9 vs -22.3 degrees C) and rubbery modulus (80 vs 13 MPa). Additionally, the versatile nature of this chemistry facilitates postpolymerization modification of residual reactive groups to produce materials with unique physical and chemical properties.

No MeSH data available.


Related in: MedlinePlus

Concentrations of the various reactive species, thiol (◻), alkyne (○), and vinyl sulfide (Δ), during curing of two different initial stoichiometric ratios of reactive groups including (A) 6:5 thiol:alkyne (excess alkyne) and (B) 10:3 thiol:alkyne (excess thiol). Samples were formulated with 3 wt % Irgacure 184 and irradiated at 365 nm, 30 mW/cm2.
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fig3: Concentrations of the various reactive species, thiol (◻), alkyne (○), and vinyl sulfide (Δ), during curing of two different initial stoichiometric ratios of reactive groups including (A) 6:5 thiol:alkyne (excess alkyne) and (B) 10:3 thiol:alkyne (excess thiol). Samples were formulated with 3 wt % Irgacure 184 and irradiated at 365 nm, 30 mW/cm2.

Mentions: Measurements of the functional group concentrations during stoichiometrically unbalanced reactions demonstrate that when the alkyne is in excess, the accumulation of vinyl sulfide is more pronounced than in stoichiometrically balanced reactions (3), whereas no vinyl sulfide accumulation is observed when the thiol is initially in excess (3).


Thiol-Yne Photopolymerizations: Novel Mechanism, Kinetics, and Step-Growth Formation of Highly Cross-Linked Networks.

Fairbanks BD, Scott TF, Kloxin CJ, Anseth KS, Bowman CN - Macromolecules (2008)

Concentrations of the various reactive species, thiol (◻), alkyne (○), and vinyl sulfide (Δ), during curing of two different initial stoichiometric ratios of reactive groups including (A) 6:5 thiol:alkyne (excess alkyne) and (B) 10:3 thiol:alkyne (excess thiol). Samples were formulated with 3 wt % Irgacure 184 and irradiated at 365 nm, 30 mW/cm2.
© Copyright Policy - open-access - ccc-price
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2651690&req=5

fig3: Concentrations of the various reactive species, thiol (◻), alkyne (○), and vinyl sulfide (Δ), during curing of two different initial stoichiometric ratios of reactive groups including (A) 6:5 thiol:alkyne (excess alkyne) and (B) 10:3 thiol:alkyne (excess thiol). Samples were formulated with 3 wt % Irgacure 184 and irradiated at 365 nm, 30 mW/cm2.
Mentions: Measurements of the functional group concentrations during stoichiometrically unbalanced reactions demonstrate that when the alkyne is in excess, the accumulation of vinyl sulfide is more pronounced than in stoichiometrically balanced reactions (3), whereas no vinyl sulfide accumulation is observed when the thiol is initially in excess (3).

Bottom Line: Chain-growth polymerization of alkyne and vinyl functionalities was only observed for reactions in which the alkyne was originally in excess.A tetrafunctional thiol was photopolymerized with a difunctional alkyne, forming an inherently higher cross-link density than an analogous thiol-ene resin, displaying a higher glass transition temperature (48.9 vs -22.3 degrees C) and rubbery modulus (80 vs 13 MPa).Additionally, the versatile nature of this chemistry facilitates postpolymerization modification of residual reactive groups to produce materials with unique physical and chemical properties.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemical and Biological Engineering and the Howard Hughes Medical Institute, University of Colorado, Boulder, Colorado 80309-0424.

ABSTRACT
Radical-mediated thiol-yne step-growth photopolymerizations are utilized to form highly cross-linked polymer networks. This reaction mechanism is shown to be analogous to the thiol-ene photopolymerization; however, each alkyne functional group is capable of consecutive reaction with two thiol functional groups. The thiol-yne reaction involves the sequential propagation of a thiyl radical with either an alkyne or a vinyl functional group followed by chain transfer of the radical to another thiol. The rate of thiyl radical addition to the alkyne was determined to be approximately one-third of that to the vinyl. Chain-growth polymerization of alkyne and vinyl functionalities was only observed for reactions in which the alkyne was originally in excess. Analysis of initial polymerization rates demonstrated a near first-order dependence on thiol concentration, indicating that chain transfer is the rate-determining step. Further analysis revealed that the polymerization rate scaled with the initiation rate to an exponent of 0.65, deviating from classical square root dependence predicted for termination occurring exclusively by bimolecular reactions. A tetrafunctional thiol was photopolymerized with a difunctional alkyne, forming an inherently higher cross-link density than an analogous thiol-ene resin, displaying a higher glass transition temperature (48.9 vs -22.3 degrees C) and rubbery modulus (80 vs 13 MPa). Additionally, the versatile nature of this chemistry facilitates postpolymerization modification of residual reactive groups to produce materials with unique physical and chemical properties.

No MeSH data available.


Related in: MedlinePlus