Research

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18 pages, 3264 KiB

Open AccessArticle

Epoxy-Thiol Systems Filled with Boron Nitride for High Thermal Conductivity Applications

by John M. Hutchinson, Frida Román and Adrià Folch

Polymers 2018, 10(3), 340; https://doi.org/10.3390/polym10030340 - 20 Mar 2018

Cited by 19 | Viewed by 4405

An epoxy-thiol system filled with boron nitride (BN), in the form of 80 µm agglomerates, has been investigated with a view to achieving enhanced thermal conductivity. The effect of BN content on the cure reaction kinetics has been studied by differential scanning calorimetry [...] Read more.

An epoxy-thiol system filled with boron nitride (BN), in the form of 80 µm agglomerates, has been investigated with a view to achieving enhanced thermal conductivity. The effect of BN content on the cure reaction kinetics has been studied by differential scanning calorimetry (DSC) and the thermal conductivity of the cured samples has been measured by the transient hot bridge method. The heat of reaction and the glass transition temperature of the fully cured samples are both independent of the BN content, but the cure reaction kinetics is not: with increasing BN content, the reaction first advances and is then delayed, this behaviour being more pronounced than for the same system with 6 µm BN particles, investigated previously. This dependence on BN content is attributed to the effects of heat transfer, and the DSC results can be correlated with the thermal conductivity of the cured systems, which is found to increase with both BN content and BN particle size. For a given BN content, the values of thermal conductivity obtained are significantly higher than many others reported in the literature, and achieve a value of over 4.0 W/mK for a BN content of about 40 vol %. Full article

(This article belongs to the Special Issue Thermosets)

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15 pages, 5620 KiB

Open AccessArticle

Thermal and Mechanical Characterization of EMA-TEGDMA Mixtures for Cosmetic Applications

by Ruben Donoso, Jose Antonio Reina, Marta Giamberini, Silvia De La Flor, Francesc Ferrando and Pierfrancesco Cerruti

Polymers 2018, 10(3), 256; https://doi.org/10.3390/polym10030256 - 01 Mar 2018

Cited by 5 | Viewed by 6694

Abstract

Mixtures of methacrylic polymers are the most common materials for making composites to be used as resins for dental and cosmetic applications. Some of these mixtures are composed by poly(ethyl methacrylate) (PEMA) and poly(methyl methacrylate) (PMMA), which constitute a solid component to be [...] Read more.

Mixtures of methacrylic polymers are the most common materials for making composites to be used as resins for dental and cosmetic applications. Some of these mixtures are composed by poly(ethyl methacrylate) (PEMA) and poly(methyl methacrylate) (PMMA), which constitute a solid component to be mixed with a liquid component made out of methacrylate monomers. The reaction between the thermal initiator benzoyl peroxyde (BPO) present in the solid component and the activator of the polymerization process, N,N-dimethyl-p-toluidine (DMT) present in the liquid component, gives rise to thermoset materials. In the present study, different liquid formulations composed by a mixture of two methacrylic monomers, ethyl methacrylate (EMA) and triethylene glycol dimethacrylate (TEGDMA) for cosmetic applications, were prepared and characterized, using a commercial powder (POW) composed by PEMA and PMMA. With the aim of improving workability during final application of the material, it was necessary to slow down the polymerization rate of liquid formulations. Their thermal behavior was investigated by differential scanning calorimetric (DSC) in order to check the polymerization rate. Thermal stability of final materials was determined by thermogravimetric analysis (TGA). Dynamic mechanical thermal analysis (DMTA), microindentation hardness and impact tests were performed on final materials, to assess their performance with respect to standard formulation. The combination of thermal and mechanical properties allows choosing which formulations could be suitable for use in cosmetics. Full article

(This article belongs to the Special Issue Thermosets)

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13 pages, 3600 KiB

Open AccessArticle

Ring-Opening Polymerization of 1,3-Benzoxazines via Borane Catalyst

by Mustafa Arslan, Baris Kiskan and Yusuf Yagci

Polymers 2018, 10(3), 239; https://doi.org/10.3390/polym10030239 - 27 Feb 2018

Cited by 38 | Viewed by 6838

Abstract

Tris(pentafluorophenyl)borane was used as Lewis acid catalyst to lower the ring opening polymerization temperature (ROP) of 1,3-benzoxazines. Dynamic scanning calorimeter studies revealed that on-set ROP temperatures were decreased as much as 98 °C for model benzoxazine compounds. Catalytic polymerization was traced by both [...] Read more.

Tris(pentafluorophenyl)borane was used as Lewis acid catalyst to lower the ring opening polymerization temperature (ROP) of 1,3-benzoxazines. Dynamic scanning calorimeter studies revealed that on-set ROP temperatures were decreased as much as 98 °C for model benzoxazine compounds. Catalytic polymerization was traced by both FTIR and ¹H NMR, and revealed that tris(pentafluorophenyl)borane acted rapidly and fast curing achieved. Moreover, thermal properties of resulting polybenzoxazines were investigated by thermogravimetric analysis (TGA) and found out that the catalyst has high impact on char yield and even 3 mol % catalyst augmented char yields up to 13%. Full article

(This article belongs to the Special Issue Thermosets)

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14 pages, 3305 KiB

Open AccessArticle

Special Resins for Stereolithography: In Situ Generation of Silver Nanoparticles

by Gabriele Taormina, Corrado Sciancalepore, Federica Bondioli and Massimo Messori

Polymers 2018, 10(2), 212; https://doi.org/10.3390/polym10020212 - 22 Feb 2018

Cited by 42 | Viewed by 7281

Abstract

The limited availability of materials with special properties represents one of the main limitations to a wider application of polymer-based additive manufacturing technologies. Filled resins are usually not suitable for vat photo-polymerization techniques such as stereolithography (SLA) or digital light processing (DLP) due [...] Read more.

The limited availability of materials with special properties represents one of the main limitations to a wider application of polymer-based additive manufacturing technologies. Filled resins are usually not suitable for vat photo-polymerization techniques such as stereolithography (SLA) or digital light processing (DLP) due to a strong increment of viscosity derived from the presence of rigid particles within the reactive suspension. In the present paper, the possibility to in situ generate silver nanoparticles (AgNPs) starting from a homogeneous liquid system containing a well dispersed silver salt, which is subsequently reduced to metallic silver during stereolithographic process, is reported. The simultaneous photo-induced cross-linking of the acrylic resin produces a filled thermoset resin with thermal-mechanical properties significantly enhanced with respect to the unfilled resin, even at very low AgNPs concentrations. With this approach, the use of silver salts having carbon-carbon double bonds, such as silver acrylate and silver methacrylate, allows the formation of a nanocomposite structure in which the release of by-products is minimized due to the active role of all the reactive components in the three dimensional (3D)-printing processes. The synergy, between this nano-technology and the geometrical freedom offered by SLA, could open up a wide spectrum of potential applications for such a material, for example in the field of food packaging and medical and healthcare sectors, considering the well-known antimicrobial effects of silver nanoparticles. Full article

(This article belongs to the Special Issue Thermosets)

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16 pages, 5121 KiB

Open AccessArticle

Epoxy Vitrimers: The Effect of Transesterification Reactions on the Network Structure

by Facundo Ignacio Altuna, Cristina Elena Hoppe and Roberto Juan José Williams

Polymers 2018, 10(1), 43; https://doi.org/10.3390/polym10010043 - 03 Jan 2018

Cited by 68 | Viewed by 9809

Abstract

Vitrimers are covalently crosslinked polymers that behave as conventional thermosets below the glass transition temperature (T_g) but can flow above a particular temperature, T_v > T_g, by bond exchange reactions. In epoxy vitrimers, transesterification reactions are responsible for [...] Read more.

Vitrimers are covalently crosslinked polymers that behave as conventional thermosets below the glass transition temperature (T_g) but can flow above a particular temperature, T_v > T_g, by bond exchange reactions. In epoxy vitrimers, transesterification reactions are responsible for their behavior at T > T_v that enables flow, thermoforming, recycling, self-healing and stress relaxation. A statistical analysis based on the fragment approach was performed to analyze the evolution of the network structure of epoxy vitrimers during transesterification reactions. An analytical solution was obtained for a formulation based on a diepoxide and a dicarboxylic acid. A numerical solution was derived for the reaction of a diepoxide with a tricarboxylic acid, as an example of the way to apply the model to polyfunctional monomers. As transesterification acts as a disproportionation reaction that converts two linear fragments (monoesters) into a terminal fragment (glycol) and a branching fragment (diester), its effect on network structure is to increase the concentration of crosslinks and pendant chains while leaving a sol fraction. Changes in the network structure of the epoxy vitrimer can take place after their synthesis, during their use at high temperatures, a fact that has to be considered in their technological applications. Full article

(This article belongs to the Special Issue Thermosets)

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1617 KiB

Open AccessArticle

Preparation, Characterization and Application of UV-Curable Flexible Hyperbranched Polyurethane Acrylate

by Hongping Xiang, Xiaowei Wang, Guanghong Lin, Lu Xi, Yan Yang, Dehua Lei, Haihui Dong, Jiahui Su, Yanyan Cui and Xiaoxuan Liu

Polymers 2017, 9(11), 552; https://doi.org/10.3390/polym9110552 - 25 Oct 2017

Cited by 56 | Viewed by 7806

Abstract

A novel UV-curable hyperbranched polyurethane acrylate (FHBPUA) with excellent flexibility is successfully synthesized based on a reaction of hydroxyl terminated hyperbranched polyurethane (regarded as core) with flexible semiadduct urethane monoacrylate (regarded as arms). The structure and property of FHBPUA is firstly analyzed and [...] Read more.

A novel UV-curable hyperbranched polyurethane acrylate (FHBPUA) with excellent flexibility is successfully synthesized based on a reaction of hydroxyl terminated hyperbranched polyurethane (regarded as core) with flexible semiadduct urethane monoacrylate (regarded as arms). The structure and property of FHBPUA is firstly analyzed and then utilized as functional additives to ameliorate the UV-curing and mechanical properties of epoxy acrylate resin. The degree of branching of FHBPUA turns out to be 0.82. Its thermal decomposition process consists of three different stages, and the glass transition temperature is around 65 °C. The freestanding FHBPUA film (~30 μm thickness) can be UV-cured within 3 s, and its flexibility is up to 1 mm. With the increase of FHBPUA content to 10 wt %, the UV-curing time of UV1000 film decreases from 6 to 3 s, flexibility strikingly increases from 10 to 1 mm, and adhesive force also improves from 5 to 3 grades, meanwhile its glossiness is not influenced by FHBPUA. In addition, a certain amount of FHBPUA can improve the tensile strength and elongation at break of UV1000 film. This novel FHBPUA can be used not only to develop flexible UV-curable freestanding films but also as functional additives to perfect other UV-curable compositions like coatings, inks and 3D printed parts. Full article

(This article belongs to the Special Issue Thermosets)

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Review

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24 pages, 3266 KiB

Open AccessReview

State of the Art in Dual-Curing Acrylate Systems

by Osman Konuray, Xavier Fernández-Francos, Xavier Ramis and Àngels Serra

Polymers 2018, 10(2), 178; https://doi.org/10.3390/polym10020178 - 12 Feb 2018

Cited by 84 | Viewed by 16788

Abstract

Acrylate chemistry has found widespread use in dual-curing systems over the years. Acrylates are cheap, easily handled and versatile monomers that can undergo facile chain-wise or step-wise polymerization reactions that are mostly of the “click” nature. Their dual-curing processes yield two distinct and [...] Read more.

Acrylate chemistry has found widespread use in dual-curing systems over the years. Acrylates are cheap, easily handled and versatile monomers that can undergo facile chain-wise or step-wise polymerization reactions that are mostly of the “click” nature. Their dual-curing processes yield two distinct and temporally stable sets of material properties at each curing stage, thereby allowing process flexibility. The review begins with an introduction to acrylate-based click chemistries behind dual-curing systems and relevant reaction mechanisms. It then provides an overview of reaction combinations that can be encountered in these systems. It finishes with a survey of recent and breakthrough research in acrylate dual-curing materials for shape memory polymers, optical materials, photolithography, protective coatings, structured surface topologies, and holographic materials. Full article

(This article belongs to the Special Issue Thermosets)

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8 pages, 2747 KiB

Open AccessReview

New Horizons in Cationic Photopolymerization

by Marco Sangermano, Ignazio Roppolo and Annalisa Chiappone

Polymers 2018, 10(2), 136; https://doi.org/10.3390/polym10020136 - 31 Jan 2018

Cited by 82 | Viewed by 6984

Abstract

In this review, we report some recent advances and new horizons in UV-induced cationic photopolymerization. In particular, after a brief introduction on the discovery and affirmation of the cationic photopolymerization process, new efforts in the synthesis of cationic photoinitiators are reported. Subsequently, an [...] Read more.

In this review, we report some recent advances and new horizons in UV-induced cationic photopolymerization. In particular, after a brief introduction on the discovery and affirmation of the cationic photopolymerization process, new efforts in the synthesis of cationic photoinitiators are reported. Subsequently, an interesting and absolutely new application is reported, related to the combination of Radical-Induced Cationic Photopolymerization with Frontal Polymerization, achieving the cross-linking of epoxy composites. Full article

(This article belongs to the Special Issue Thermosets)

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