Contents lists available at ScienceDirect Computational Materials Science journal homepage: www.elsevier.com/locate/commatsci Critical role of tetrasilanolphenyl–POSS moieties in competing mechanism of rigid cages and soft segments and its effect on the glass transition temperature of epoxy hybrids Rui Pan a, ⁎ , Robert Shanks b , Qiongfen Yang a , Hong Luo a a Chemistry and Material Science College, Sichuan Normal University, Key Laboratory of Special Waste Water Treatment, Chengdu City, Sichuan Province 610066, PR China b School of Science, RMIT University, GPO Box 2476, Melbourne VIC 3001, Australia ARTICLE INFO Keywords: POSS Epoxy Molecular mechanics Molecular dynamics ABSTRACT Molecular mechanics (MM) and molecular dynamics (MD) simulations were adopted to further investigate the competing mechanism of rigid cages and soft segments in epoxy hybrids with tetrasilanolphenyl polyhedral oligomeric silsesquioxane (TSP–POSS) copolymerized at various moieties. Calculated conformational energy and mean square displacement (MSD) delineated that rigid cage of TSP–POSS unit as an anchoring substituent, inhibited and rigidified polymer chains apparently. The degree of such reinforcement depended on TSP-POSS moieties plays a critical role in determining the final glass transition temperature (Tg) by competing with the effect of epoxy soft segments in bulk structures. At TSP–POSS loading less than 30%·w/w, rigid cages tended to approach mutually and the anchoring effect was strengthened. The restricted mobility and reinforced rigidity of chains led to an improvement of Tg. At TSP–POSS loading over 30%·w/w, increasing rigid cages were fixed by soft segments of epoxy unit and thus, the anchoring effect was weakened and mobility of chains was released to some extent. Additionally, with a steady plasticization mechanism, Tg was slightly decreased in 40%·w/w TSP–POSS embedded in epoxy, which was confirmed by experiments. 1. Introduction Due to the excellent mechanical strength, perfect chemical re- sistance and simple processing process, epoxy resins as the important thermosetting resin are widely used as adhesives, coatings and elec- tronic encapsulates [1,2]. Meanwhile, as a kind of good inorganic na- noparticle fillers, polyhedral oligomeric silsesquioxane (POSS) has been received huge attention since the introduction of POSS particles at various moieties into epoxy can lead to apparent improvements in properties including the glass transition temperature, thermal stability, anti-corrosion and flame retardation as well as ablation resistance in coating application [3–6]. Wenchao Zhang and his research group re- ported that a novel polyhedral oligomeric silsesquioxane containing 9,10-dihydro-9-oxa-10-phosphaphenanthrene–10–oxide was used to improve the flame retardation of diglycidyl ether of bisphenol A epoxy resins, which was apparently depending on the POSS content [7]. Yanli Ma et al. showed that thermo-mechanical property discrepancies with three polysiloxane-epoxy hybrids obtained by dispersing cage- or linear-structured polysiloxane into polyglycidyl methacrylate (PGMA) matrix. The introduction of polysiloxane into an epoxy matrix has achieved high thermal-stability as expected [8]. Jun Kai Herman Teo et al. reported that a novel epoxy-based hybrid composite was suc- cessfully synthesized by incorporating 1,2–di- methyl–3–(benzyl–heptaisobutyl–POSS) imidazolium chloride (POS- S–IMC) and POSS-IMC-modified clay (POSS–MMT) into a resin based on 3,4–epoxycyclohexylmethyl 3,4-epoxycyclohexane carboxylate (ECHM) and hexahy-drophthalic anhydride (HHPA) with reduction of thermal expansion coefficient (CTE) [9]. Shree Meenakshi et al. carried on the development of high functionality siloxane based on tetra- glycidyl epoxy resin and characterized the structure of nanocomposites, which indicated that modified tetraglycidyl epoxy nanocomposites showed the superior flame retardancy to the unmodified epoxy resin [10]. Magdalena Perchacz et al. reported two types of pre-condensed silica-based precursors with epoxy groups in liquid, which has been verified as novel composites with the enhanced thermoxidative stability [11]. An investigation from Adriana Lungu et al. presented the synth- esis of simultaneous interpenetrating polymer networks based on di- methacrylic-epoxy resins with or without polyhedral oligomeric sil- sesquioxane (POSS), and which was demonstrated the tailored thermal decomposition with various POSS concentration [12]. Ian Hamerton https://doi.org/10.1016/j.commatsci.2018.05.036 Received 21 February 2018; Received in revised form 17 May 2018; Accepted 18 May 2018 ⁎ Corresponding author. E-mail address: panrui@sicnu.edu.cn (R. Pan). Computational Materials Science 152 (2018) 78–84 0927-0256/ © 2018 Elsevier B.V. All rights reserved. T