Thermal degradation studies of poly(urethane–siloxane) thermosets based on co-poly(dimethyl)(methyl, 3-glycidoxypropyl)siloxane and epoxy-terminated urethane oligomer
Introduction
Poly(urethane–siloxane) copolymers (PU–Si) are a class of hybrid materials, which are situated on a boundary between organic and inorganic materials. They consist of organic segments derived from polyurethane and inorganic siloxane structures. PU–Si materials combine advantages of both homopolymers, i.e., good tensile strength and abrasion resistance which are specific for polyurethane, with low free surface energy and glass transition, great elasticity (especially at low temperature) as well as good thermal, chemical and biological stability which are due to polysiloxanes. Owing to their properties, PU–Si are widely used as protection coatings, membranes or medical implants [1], [2], [3], [4], [5].
The chemical modification of polyurethanes by siloxane is mostly achieved by introduction of usually linear polydimethylsiloxane into PU backbone as soft segments or as a part of them [6], [7]. However, the investigations on polyurethanes with other siloxane structures including polydimethylsiloxane chains terminated only at one side with two hydroxyl groups [5] or polyhedral oligomeric silsesquioxane (POSS) [8] have been recently developed. The thermal degradation studies were also carried out for poly(urethane–siloxane) networks obtained by sol–gel process [9], by cross-linking with hyperbranched polyester [10], or by moisture curing [11]. Moreover, detailed studies on kinetics of the thermal decomposition of poly(urethane–siloxane) semi-interpenetrating polymer networks (semi-IPNs) [12] and networks based on comb-like structure co-poly(dimethyl)(methyl, hydroxypolyoxyethylenepropyl) siloxane cured with aliphatic diisocyanates [13] have been recently developed.
However, in the 21st century, technologies designed for manufacturing any kind of products must also be analyzed in terms of broadly understood ecological aspects, at the stage of synthesis, safe application and final waste management of the specific product. The previously reported modification of polyurethanes in order to obtain hybrid polymer materials occurred mainly via polyaddition reaction of reactive isocyanate groups originating from diisocyanates with hydroxyl or amino groups of respective polysiloxanes. Due to the high viscosity of the obtained copolymers, synthesis reactions usually required organic solvent to be used in significant amounts, exceeding even 70% of the total weight of the basic raw materials. Significantly less frequently water, which is definitely less toxic, was the reaction medium [14].
This study has employed a new approach for obtaining of hybrid poly(urethane–siloxanes) based on reactive epoxy and amino groups. Obtaining of a lower viscosity system by employing epoxy-functional urethane oligomer which at later stages is crosslinked by means of an amine at the presence of functionalized polysiloxane has a beneficial pro-environmental effect involving reduction of volatile organic compounds (VOC) in the final product. While synthesis of polyurethane thermosets from urethane derivatives containing epoxy groups has been reported [15], [16], [17], this approach has never been employed in obtaining of hybrid poly(urethane–siloxanes). Additionally, a novel type of functionalized polysiloxane with a comb-like chain structure was employed, which has not been used for polyurethane modification.
Hence, the aim of this work is to investigate the effect of the composition of poly(urethane–siloxane) thermosets composed of epoxy-terminated urethane oligomer, co-poly(dimethyl)(methyl, 3-glycidoxypropyl) siloxane, cured with diethylenetriamine on their thermal stability, including evolved gases analyses and detailed kinetic studies.
Section snippets
Materials
Isophorone diisocyanate (IPDI), poly(oxytetramethylene) diol (PTMO, Mn = 1000), glycidol (Gly), diethylenetriamine (DETA), dibutyltin dilaurate (DBTDL) and Karstedt catalyst solution in xylenes (2% Pt) were purchased from Aldrich. Co-poly(dimethyl)(methyl, 3-glycidoxypropyl) siloxane (EPS) was synthesized in the hydrosilylation reaction of allyl glycidyl ether with co-poly(dimethyl)(methyl, hydrogen) siloxane according to the procedure comprehensive described in Ref. [18]. The epoxy-terminated
Thermal degradation in nitrogen
The samples of crosslinked poly(urethane–siloxane) were investigated by thermogravimetric analysis to determine their thermal stability. TG and DTG curves recorded at 10 °C min−1 heating rate in nitrogen were presented in Fig. 2, whereas Table 3 provides interpretation of both profiles obtained at 5, 10, 20, 40 °C min−1.
On the basis of thermogravimetric analyses one may conclude, that crosslinked urethane oligomer (PUS0) decomposes at least in two main stages in the range of 205–500 °C. The first
Conclusions
In this work a series of crosslinked hybrid poly(urethane–siloxane) networks based on comb-like structure co-poly(dimethyl)(methyl, 3-glycidoxypropyl) siloxane and epoxy-terminated urethane oligomer cured with aliphatic diicocyanates was submitted for thermal degradation investigations. The thermal stability of crosslinked polyurethane is improved by the addition of siloxane. With the increase of siloxane the temperature of 5% weight loss of the poly(urethane–siloxane) thermosets increases. The
Acknowledgement
The author thank Dr. Michał Dutkiewicz from Adam Mickiewicz University for preparation of co-poly(dimethyl)(methyl, 3-glycidoxypropyl)siloxane.
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