Analysis of Network Structures in Thiol-Ene UV Curing System Using Reworkable Resins

Area of Science:

• Polymer Chemistry
• Materials Science
• Photochemistry

Background:

• Thiol-ene UV curing offers a versatile method for creating polymer networks.
• Reworkable resins with tertiary ester linkages enable post-curing modification.
• Understanding network structure is crucial for tailoring material properties.

Purpose of the Study:

• To analyze the network structures of reworkable thiol-ene UV curing resins.
• To investigate the influence of crosslinking parameters on network architecture.
• To correlate network structure with material properties like molecular weight and chain length.

Main Methods:

• Synthesis of reworkable resins using di(meth)acrylate monomers and thiol compounds.
• UV irradiation (365 nm) for photopolymerization.
• Post-curing degradation via heating after UV irradiation (254 nm).
• Analysis of degraded samples using Size Exclusion Chromatography (SEC) and proton Nuclear Magnetic Resonance (¹H NMR) after methylation.

Main Results:

• Crosslinking conditions significantly affected network structures.
• Degraded samples exhibited molecular weights ranging from 250 to 2700 Da.
• Higher thiol functionality led to increased molecular weights but suggested reduced reactivity due to steric hindrance.
• Network chain lengths were proportional to (meth)acrylate monomer concentration.
• Reactive diluents enhanced reactivity and increased chain length.

Conclusions:

• Thiol functionality, monomer concentration, and reactive diluents are key factors controlling network structure in thiol-ene UV curing.
• Steric hindrance in highly functional thiols impacts reactivity and network formation.
• The study provides insights into designing reworkable polymer networks with tunable properties.