Utilizing thiol–ene coupling kinetics in the design of renewable thermoset resins based on d-limonene and polyfunctional thiols

Mauro Claudino,Mats Johansson,Mats Jonsson

doi:10.1039/c3ra47922f

Abstract

Off-stoichiometric manipulations on the initial thiol–terpene composition strongly favor the formation of di-addition product (a) over mono-additions (b + c) when the reaction system contains an equimolar or relative excess of thiol.

Highlights

The search for valuable compounds from renewable resources to prepare non-petroleum plastic materials has grown into an important topic in the polymer eld on grounds of increasing environmental awareness and issues of sustainable development and because fossil-oil reserves are dwindling at an increasingly faster rate
Macromolecular ultraviolet (UV)-curing thiol–ene systems are acquiring high popularity in industry and scienti c research community due to industrially favoring characteristics such as: resistance to inhibition by ambient oxygen which is a serious problem affecting conventional acrylic-based chain-growth radical polymerizations; relatively rapid cure rates leading to highly cross-linked networks; solventless processing when thiol and ene co-reactants are miscible; improved photocuring control; ability to initiate polymerization without addition of photoinitiator enabling the cure of thick geometries; and, a step-wise radical growth mechanism leading to delayed gel-point which results in thermosets with uniform cross-link density, narrow glass-transition temperatures, reduced volume shrinkage and low stress development at high monomer conversions.[4,5,6]
Each method promotes the intramolecular cleavage of the starting initiator boosting the production of thiyl radicals (RSc) that initiate the cycles of thiol–ene coupling reactions

Summary

Introduction

The search for valuable compounds from renewable resources to prepare non-petroleum plastic materials has grown into an important topic in the polymer eld on grounds of increasing environmental awareness and issues of sustainable development and because fossil-oil reserves are dwindling at an increasingly faster rate. An extensive array of starting materials comprised of vegetable oils, lignin, polysaccharides (e.g., cellulose and starch), sugars/carbohydrates, polycarboxylic acids, glycerol, macrocyclic lactones, furans, etc., have all been explored either as they are found natively or modi ed to prepare bio-based polymers and biocomposites using a wide variety of chemistries and enzymatic methods.[1,2] The use of natural ole ns, most of which are biodegradable, have been studied[3] and their combination with environmentally friendly and economically favorable UV technology offers a viable ‘green’ alternative to Macromolecular ultraviolet (UV)-curing thiol–ene systems are acquiring high popularity in industry and scienti c research community due to industrially favoring characteristics such as: resistance to inhibition by ambient oxygen (acting as chain stopper) which is a serious problem affecting conventional acrylic-based chain-growth radical polymerizations; relatively rapid cure rates leading to highly cross-linked networks; solventless processing when thiol and ene co-reactants are miscible; improved photocuring control (both spatial and temporal); ability to initiate polymerization without addition of photoinitiator enabling the cure of thick geometries; and, a step-wise radical growth mechanism leading to delayed gel-point which results in thermosets with uniform cross-link density, narrow glass-transition temperatures, reduced volume shrinkage and low stress development at high monomer conversions.[4,5,6] thiol–ene photopolymers are transparent and exhibit enhanced physical properties such as mechanical exibility and good adhesion to several substrates.[6,7] This makes thiol–ene photopolymers ideal for organic coating applications

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Conclusion