Photo-crosslinked coatings from an acrylate terminated non-isocyanate polyurethane (NIPU) and reactive diluent

Highlights

• Preparation of an acylate terminated non-isocyanate polyurethanes (NIPUA).

• Formulation of NIPUA with several reactive diluents at various proportions.

• Preparation of coatings by photocuring.

• Physical properties of coatings in line with those of commercial analogues.

Abstract

Non-isocyanate polyurethane acrylate coatings (NIPUAs) were prepared by photocrosslinking of mixtures of an acrylate terminated NIPU oligomers (A-Ol) and reactive (meth-)acrylate diluents. A-Ol were prepared by a transurethane polycondensation pathway followed by an acrylation reaction of the resulting hydroxy chain-ends. The influence of the reactive diluent content and chemical structures on the thermal and mechanical properties of these coatings has been investigated. The obtained materials exhibited thermal stabilities above 255 °C, Young modulus ranging from 2.6 to 9.2 MPa, tensile strength from 2.69 to 25.5 MPa and elongation at break from 56 to 470%.

Introduction

Polyurethanes (PUs) are a class of very important polymer materials possessing versatile properties allowing them to be used in various application fields. Polyurethane acrylate systems (PUAs) are based on acrylate-terminated prepolymers that are crosslinked to afford protective coatings displaying very good abrasion and chemical resistances and very flexible mechanical properties [1], [2].

The attention towards UV-curable coatings is continually increasing owing to their fast curing and low energy consumption [3]. Their formulations are usually composed of three major components: photoinitiator, reactive oligomer and reactive diluent [4]. The reactive diluent decreases the viscosity of the formulation and copolymerizes with the oligomer. The chemical structure of the oligomer defines the viscoelastic properties of the final crosslinked material [5].

Epoxy acrylate, polyester acrylate and urethane acrylate oligomers (PUAs) are commonly used in the preparation of free radical UV-curable coatings [6]. PUAs are conventionally prepared by acrylation of telechelic polyurethane oligomers, synthesized by the conventional reaction between polyols and toxic diisocyanates, which are obtained from diamines and toxic phosgene [7]. During the two last decades, some research groups have proposed alternatives to prepare PUA materials by non-isocyanate and non-phosgene routes (NIPUAs) [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18].

Recently, the photo-curing of poly(hydroxyurethane) acrylate (PHU) oligomers, obtained by the polyaddition of cyclic dicarbonate with diamine monomers followed by acrylation have been studied [12], [13], [16], [18]. However, as far as we know, the photo-crosslinking of NIPUA oligomers obtained by the transurethane polycondensation, which is one of the most promising free isocyanate pathways to polyurethanes, has not yet been described [19], [20], [21], [22], [23], [24], [25]. This pathway consists in the reaction of dialkyl dicarbamates [19], [20], [21], [22] or dihydroxyethyl dicarbamates [23], [24], [25] with diols, in presence of organic or organo-metallic catalysts. However, with dihydroxyethyl dicarbamates, a weak proportion of urea functions are formed owing to a back-biting side reaction [23], [24], [25]. On the other hand, the transurethane polycondensation gives conventional PU structures and not poly(hydroxyurethane) structures (PHUs) [26], [27], [28], [29], [30].

In this work, we describe the preparation of UV-curable coatings from several urethane and non-urethane reactive diluents and a NIPU-acrylate oligomer (NIPUA), obtained by the transurethane polycondensation approach. The impact of the reactive diluent chemical structure and content on the mechanical and thermal properties of the resulting coatings is investigated.