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

Haruyuki Okamura,Kyohei Nakata,Masashi Yamagaki

doi:10.3390/polym11010005

Haruyuki Okamura, Kyohei Nakata + Show 1 more

Open Access

https://doi.org/10.3390/polym11010005

Copy DOI

Journal: Polymers	Publication Date: Dec 20, 2018
Citations: 4	License type: CC BY 4.0

Affiliation: Osaka Prefecture University

Abstract

An analysis of the network structures in thiol-ene UV curing resins was carried out using reworkable resins composed of di(meth)acrylate monomers having tertiary ester linkages. The effect of the functionality of the thiols, the functional ratio of the thiol and ene functions, their conversions and curing atmosphere on the chain lengths was discussed. A mixture of (meth)acrylates, thiol compounds, a photoradical initiator, and a photoacid generator was cured by irradiation at 365 nm. The cured samples were degraded by heating after irradiation at 254 nm. Size exclusion chromatography (SEC) and 1H NMR analyses of the degraded samples were carried out after the methylation. The crosslinking conditions strongly affected the network structures. The degraded samples have molecular weights between 250 and 2700. The molecular weights of the degraded resins increased with the functionality of the thiol compounds. The chain length dependence suggests that thiol compounds with a high functionality have a low reactivity due to steric hindrance. The chain lengths of the degraded networks were nearly proportional to the concentration of the (meth)acrylate monomers. The addition of reactive diluents enhanced the reactivity and increased the chain length.

Highlights

We focused on the thiol-ene UV curing system which reduces oxygen inhibition, and a reworkable monomer, which was used for the analysis of the network structures
The molecular weights of the degraded resins increased with the functionality of the thiol compounds
The chain length dependence suggests that thiol compounds with a high functionality have a low reactivity due to steric hindrance

Summary

Introduction

Degradable thermosets [1,2,3,4,5,6,7,8,9,10,11,12,13,14] have attracted much attention for environmental aspects [4,5,6,7], and for interesting investigations such as biomedical applications [8], adhesives [9], optical properties [10], and structural analysis of the networks in the thermosets [11,12,13,14].Especially, UV curable resins, a very important class of thermosets, are widely used as adhesives, printing plates, coatings, etc., due to their toughness and high reactivity. Multifunctional monomers having reactive units were irradiated to form UV cured resins in the presence of a photoinitiator. The UV curing system is roughly categorized into three units, i.e., the radical system, cationic system, and anionic system. The demand for a higher reactivity and reduced oxygen inhibition still remain. We focused on the thiol-ene UV curing system which reduces oxygen inhibition, and a reworkable monomer, which was used for the analysis of the network structures

Methods

Results

Discussion

Conclusion