Viscoelastic and Mechanical Properties of Epoxy/Multifunctional Polyhedral Oligomeric Silsesquioxane Nanocomposites and Epoxy/Ladderlike Polyphenylsilsesquioxane Blends

Abstract

Aliphatic epoxy composites with multifunctional polyhedral oligomeric silsesquioxane (POSS) ((C 6H5CHCHO)4(Si8O12)(CHdCHC6H5)4) nanophases (epoxy/POSS 95/5 and 75/25) and epoxy blends with the prepolymer of ladderlike polyphenylsilsesquioxane (PPSQ) (95/5, 90/10, and 85/15) were prepared by solution casting and then curing. These composites and blends were studied by dynamic mechanical thermal analysis (DMTA) and mechanical testing. The POSS units incorporated into the epoxy network are well dispersed in the composite, probably on the molecular scale, even at high POSS content (25 wt %) based on TEM observations. However, the aliphatic epoxy/PPSQ blends exhibit good miscibility only at low PPSQ content (e10 wt %). Phase separation was clearly observed when the PPSQ content was 15%. Incorporation of the POSS macromer into this epoxy network by curing at upper temperatures of 120 and 150 °C broadened the temperature range of glass transition of the resulting composites but has almost no influence on their T g (the tan δ peak temperature). The Tg of epoxy/PPSQ blends containing e10 wt % PPSQ increased slightly with increasing PPSQ content. However, the Tg of epoxy/PPSQ 85/15 is lower than that of the neat epoxy resin because cross-linking density is reduced in the blend. Inclusion of PPSQ into the epoxy resin has no effect on the width of their glass transition range. The storage moduli E′ of both epoxy/POSS composites and epoxy/PPSQ blends at T > Tg are higher than those of neat epoxy resin and increase with the POSS or PPSQ content, improving their thermal dimensional stability. The flexural modulus of the epoxy resin is raised by POSS incorporation or PPSQ addition. Modification of the epoxy resin's flexural modulus is larger for composites with molecularly dispersed POSS than for those containing PPSQ. The magnitude of this increase goes up as more POSS or PPSQ was added. But, the flexural strengths of epoxy/POSS nanocomposites and epoxy/PPSQ blends are lower than that of neat epoxy.

Viscoelastic properties and residual stresses in polyhedral oligomeric silsesquioxane‐reinforced epoxy matrices

“…The epoxy/POSS nanocomposite with 10% POSS was further postcured at T g þ 10 C (190 C) for 36 h to reach full conversion; a longer cure time and/or higher cure temperature has also been found in other work 30 to be required for the nanocomposites to reach the same degree of crosslinking as the neat system. The samples were cured in their glass tubes under air atmosphere, but the top few centimeters of sample (that was potentially exposed to air) were not used.…”

“…37 The moduli of the POSS-filled nanocomposites similarly depend on the POSS structures. The glassy modulus of the nanocomposites is found to either increase due to the nanoreinforcement of the nanoparticles 27,31,39 or decrease; 37 furthermore, the rubbery modulus also either increases presumably due to the increased crosslink density or the reinforcement of the nanoparticles 28,30,43 or decreases due to the decreased crosslink density associated with the flexible structure of the POSS. 27 One study also showed that the instantaneous modulus of the nanocomposites is not affected by the incorporation of POSS, although the physical aging process of the composites in the glassy state was found to be retarded.…”

“…It has been found that the glass transition temperature of POSSreinforced epoxy nanocomposites either increases, 24,28,29,35,38 decreases, 27,31,[38][39][40] stays unchanged, 30,32,37,39 , or even disappears 37 with the addition of POSS depending on the chemical structure of the functional group (R group) on the POSS and the POSS loading. In general, the glass transition temperature of the nanocomposites decreases when the R group on the POSS is long and flexible and a ''soft'' interface can be formed between the nanoparticle and matrix; 27,32,40,45 on the other hand, T g increases if the interface is rigid and the polymer chain motions are hindered by their covalent bonding to POSS clusters.…”

DEA and DSC study of cubic silsesquioxane epoxy resin nanocomposites

“…To overcome these drawbacks, many types of polymer-filler composites have been developed, in which the epoxy resins are reinforced with modifying agents, such as fillers, polyhedral oligosilsesquioxanes, dendrimers etc. [8][9][10][11][12][13][14][15][16][17][18].…”

“…In these materials the cubes can be connected to one another by organic components with known architecture and lengths of the order of 3-5 nm, forming composites with completely defined interfacial component between organic and inorganic phase [19][20][21][22][23][24]. Nanocomposite materials can offer novel properties, such as significant improvements in tensile modulus, fracture toughness, thermal and oxidation resistance, and reduced flammability that can only be explained by extensive organic-inorganic interfacial interactions [10][11][12][13][14][19][20][21][22][23][24].…”