Mechanical and thermal properties of UV cured mixtures of linear and hyperbranched urethane acrylates

https://doi.org/10.1016/j.porgcoat.2011.12.004Get rights and content

Abstract

The properties of urethane acrylate resin mixtures based on the linear and hyperbranched aliphatic polyesters were examined. Linear polyester was synthesized from neopentil glycol and adipic acid. Hyperbranched polyester of the third generation was synthesized from 2,2-bis(hydroxymethyl)propionic acid and di-trimethylol propane. The modification of 60% of hyperbranched aliphatic polyester OH end groups was carried out with isononanoic acid or with soybean fatty acids. Two hyperbranched urethane acrylates, with the same degree of acrylation, and one linear urethane acrylate were obtained by reaction of appropriate polyester and isophorone diisocyanate and 2-hydroxyethyl acrylate. The influence of added amount of HUA and nature of non-acrylic end groups on the rheological, mechanical and thermal properties of the uncured and UV cured mixtures diluted with 20 wt.% hexanediol diacrylate was examined. The nature of non-acrylic end groups have great effect on the interaction between linear and hyperbranched urethane acrylates, which further has a crucial influence on the examined properties of uncured and UV cured mixture samples.

Highlights

► UV curable mixtures of linear and hyperbranched urethane acrylates. ► Hyperbranched urethane acrylates with the same degree of acrylation and different non-acrylic end-groups. ► Non-acrylic end groups originating from isononanoic acid and soybean fatty acids. ► The nature of non-acrylic end-groups has great influence on the properties of uncured and UV cured mixtures.

Introduction

Hyperbranched polymers, due to their highly branched molecular architecture and high functionality possess unique and different properties compared to their linear counterparts, such as low viscosity, high solubility and low entanglement degree [1], [2], [3], [4], [5], [6]. Beside the nature and structure of the backbone, their physical and chemical properties are to a large extent dependent on the number and nature of their end-groups, so the chemical modification of end groups gives the possibility of designing the macromolecules with desired properties for any particular application [7], [8], [9].

One possible application of hyperbranched polymers is in the radiation curable coatings where it is required to have multifunctional, high reactivity, low viscosity oligomers, which can be obtained by simple chemistry at very high yields. The use of acrylated aliphatic hyperbranched polyesters as oligomeric components in the radiation curable coatings has been studied by Hult and co-workers [10], [11], [12], [13]. Hyperbranched polymers, bearing different functional groups, were used in UV curable waterborne polyurethane dispersions [14], [15], as component of interpenetrating networks [16], [17], in UV curable coatings containing different nanofillers [18], [19], etc.

Urethane acrylates are one of the major types of resins used in UV curable formulations. Their properties are influenced by their functionality, type of isocyanate, type and molecular weight of polyol used in the synthesis. The higher functionality gives greater reactivity and harder cured films with good scratch and chemical resistance, but at the same time increases resin viscosity. The aliphatic urethane acrylates give more flexible coatings with better weather resistance than their aromatic counterparts. Polyester urethane acrylates exhibit better weathering characteristics than polyether urethane acrylates. With the increase of molecular weight of the used polyol, the reactivity of urethane acrylates decreases and flexibility of cured film increases [20], [21]. In our previous papers, the most attention was addicted to urethane acrylates based on partially modified aliphatic hyperbranched polyesters (HUA) and the influence of the generation number, degree of modification and type of end groups of the used aliphatic hyperbranched polyester (HBP) cores and degree of acrylation on the properties of uncured and cured resins was examined [22], [23], [24], [25], [26], [27]. It is well known that addition of some amount of dendritic acrylate to conventional acrylate based UV curable formulation greatly improves final conversion, significantly reduces the amount of extractables, and considerably reduces film shrinkage during curing, giving coatings with enhanced adhesion and low residual stress and improved mechanical properties. Those properties depend on the generation number of hyperbranched polymer, degree of acrylation of hyperbranched polymer and of type and amount of non-acrylic end groups.

Therefore, in this paper we examined properties of UV curable formulation based on the mixture of conventional linear polyester-based urethane acrylates and urethane acrylates based on partially modified aliphatic hyperbranched polyester. Linear polyester was synthesized from neopentyl glycol and adipic acid. Two different HUA based on partially modified HBP of the third generation with the same degree of acrylation (8 acrylic groups per HBP molecule) were used. Modification of 60% end OH groups of HBP, synthesized from 2,2-bis(hydroxymethyl)propionic acid with di-trimethylol propane as a core, was carried out with soybean fatty acids or with isononanoic acid (3,5,5-trimethylhexanoic acid). The urethane acrylates were obtained from appropriate polyesters, isophorone diisocyanate and 2-hydroxyethyl acrylate. Linear polyester contains side methyl groups and thus has the structure more similar to the HBP core with end groups originating from isononanoic acid. This should further enable better interaction between LUA and HUA based on HBP partially modified with isononanoic acid than between LUA and HUA based on HBP partially modified with soybean fatty acids. On the other side, except saturated, soybean fatty acids also contain unsaturated oleic, linoleic and linolenic fatty acids so the cross-link density of UV cured mixtures is enhanced by reaction of those additional double bonds. Main goal of the present work was to investigate the influence of replacement of certain amount of linear urethane acrylate with HUA and nature of their non-acrylic end groups on the rheological, mechanical and thermal properties of uncured and UV cured formulations.

Section snippets

Materials

2,2-Bis(hydroxymethyl)propionic acid (bis-MPA) and di-trimethylol propane were purchased from Perstorp AB, while methanesulphonic acid (MSA) was obtained from Aldrich. Isophorone diisocyanate (IPDI) was purchased from Hüls and 2-hydroxyethyl acrylate (2-HEA) from Laporte Performance Chemicals. Neopentil glycol and adipic acid were obtained from BASF, while FASCAT 4100 from ELF ATOCHEM. Hexanediol diacrylate (HDDA) was obtained from BASF. Dibutyltindilaurate (DBTDL) was purchased from Merck and

Synthesis of urethane acrylates and mixtures preparation

Linear urethane acrylate was obtained by reaction of the linear polyester, synthesized by polycondensation of neopentil glycol and adipic acid, and adduct, obtained by reaction of the same amount of IPDI and 2-HEA. That reaction was monitored using IR spectroscopy. The disappearance of the absorption peak at 2267 cm−1, assigned to the isocyanate group, is indicative of the completion of the reaction. The molecular weight and molecular weight distribution of the synthesized LPe and LUA are given

Conclusion

The mixtures of two hyperbranched urethane acrylates, with the same degree of acrylation and different non-acrylic end-groups and linear urethane acrylate, were used as oligomeric components in UV curable formulation. The mixtures of LUA and HUAIA have higher viscosity than LUA/HUASFA mixtures with the same amount of LUA because higher degree of hydrogen bonding interaction was achieved between LUA and HUAIA than between LUA HUASFA, where modification of OH groups was carried out with linear

Acknowledgement

This work was financially supported by the Ministry of Education and Science of the Republic of Serbia (Project Nos. 172062 and 45020).

References (38)

  • E. Žagar et al.

    Prog. Polym. Sci.

    (2011)
  • J. Lange et al.

    Polymer

    (2001)
  • M. Johansson et al.

    Prog. Org. Coat.

    (2003)
  • H. Claesson et al.

    Prog. Org. Coat.

    (2004)
  • Y. Zhang et al.

    Prog. Org. Coat.

    (2011)
  • S. Simić et al.

    Prog. Org. Coat.

    (2008)
  • S. Marinović et al.

    Prog. Org. Coat.

    (2010)
  • R.S. Mishra et al.

    Eur. Polym. J.

    (2009)
  • M. Sangermano et al.

    Polymer

    (2009)
  • R. Schwalm et al.

    Prog. Org. Coat.

    (1997)
  • E. Džunuzović et al.

    Prog. Org. Coat.

    (2005)
  • E. Džunuzović et al.

    React. Funct. Polym.

    (2006)
  • D.M. Crawford et al.

    Thermochim. Acta

    (2000)
  • A. Asif et al.

    Polymer

    (2005)
  • S. Oprea et al.

    Polymer

    (2001)
  • S. Oprea

    Polym. Degrad. Stabil.

    (2002)
  • F. Burel et al.

    Thermochim. Acta

    (1999)
  • D.K. Chattopadhyay et al.

    Prog. Polym. Sci.

    (2009)
  • Y.H. Kim

    J. Polym. Sci. Part A: Polym. Chem.

    (1998)
  • Cited by (35)

    • Flowable polysilsesquioxanes as robust solvent-free optical hard coatings

      2021, Reactive and Functional Polymers
      Citation Excerpt :

      Solvent-free processing is also facing many difficulties in that not all polymers could be processed by melt-state processing, or that the viscosity of room temperature liquid-state pourable polymers fall between the acceptable range for coating. [2,3] Optical hard coatings are a widespread technology in various electronic devices to protect the exterior of displays, requiring a combination of thermal stability, surface mechanical hardness, optical transparency, and low surface roughness after coating. [15–20] The prerequisite combination of these properties limited to the material selection to organic-inorganic hybrid siloxane materials [21–23] which cannot be easily processed without organic solvents as the sol-gel based hydrolysis-polycondensation reaction conventionally yields either a high viscosity liquid or polymeric-like powder material without melting or glass transition temperature. [24,25]

    • Fabrication of castor oil-based hyperbranched urethane acrylate UV-curable coatings via thiol-ene click reactions

      2019, Progress in Organic Coatings
      Citation Excerpt :

      Previous studies have demonstrated that hyperbranched urethane acrylates (HBUAs) not only exhibited relatively low viscosity and an abundance of terminal functional groups as HBPs, but they also possessed the excellent photo-reactivity, mechanical properties, solvent resistance and adhesion of polyurethane acrylates (PUAs) [9–12]. Dzunuzovic et al. [13–15] synthesized a series of HBUAs that exhibited Newtonian fluid behavior upon dilution with 20 wt% of a reactive diluent. The obtained UV-cured films were found to exhibit good mechanical properties and a low amount of extractable components.

    • Synthesis and viscoelastic properties of acrylated hyperbranched polyamidoamine UV-curable coatings with variable microstructures

      2017, Progress in Organic Coatings
      Citation Excerpt :

      Physical and chemical properties of dendritic polymers depend on the chemical nature of their backbone, as well as the type and population of end groups of shell. Therefore, chemical modification of terminal groups made possible design of macromolecule with different architectures [13,14]. Despite exceptional features of dendritic polymers, serious difficulties are associated with identifying and characterizing their microstructure, and understanding branching mechanism and structure-performance relationship.

    • Studying the effect of hyperbranched polymer modification on the kinetics of curing reactions and physical/mechanical properties of UV-curable coatings

      2016, Progress in Organic Coatings
      Citation Excerpt :

      Beside the nature and the structure of the backbone, the physical and chemical properties of hyperbranched polymers are largely dependent on the number and the nature of their end-groups, so the chemical modification of the end-groups gives the possibility of designing the macromolecules with desired properties for any particular applications. Chemical modification of end-groups can result changes in the solubility, reactivity, rheological behavior and polarity of the molecule [2,15–20]. In this present research, the effects of end-group modification of a hyperbranched polymer (polyester-amide based) by the aid of acrylic acid on the viscosity of monomeric and oligomeric systems have been studied.

    View all citing articles on Scopus
    View full text