Polyhedral Oligomeric Silsequioxanes

With the recent development of nanostructmed chemical feedstocks based on polyhedral oligomeric silsequioxane (POSS), POSS-based hybrid nanocomposites have received increasing attention because of the unique three-dimensional 

FIGURE 10.5 Effect of TiOa nanoparticle concentration on the heat release rate of PMMA at 35 kW/m. (From Ref. 19, copyright 2005, Elsevier, with permission.) 

The thermal analysis study above demonstrated the enhanced thermal stability of POSS-polymer nanocomposites and suggested that there is a potential to improve the flammability properties of matrix polymers. However, studies clearly demonstrating such improvement by means of the use of POSS-based 

Thermally and chemically robust hybrid — (organic-inorganic) framework 

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Cole-Hamilton el al. reported one of the first dendritic effects. Dendrimers based on polyhedral oligomeric silsequioxane (POSS) cores were synthesized (Figure 4.26) the dendrons of this dendrimer were functionalized on the periphery with 8, 24 and 72 PR2 arms respectively (R = Me, Et, hexyl, Cy, or Ph).[36]... 

The synthesis of poly(St-h-IB-h-St) triblock copolymer has been accomplished by many research groups [195-201]. The synthesis invariably involved sequential monomer addition using a difunctional initiator in conjunction with TiCU in a moderately polar solvent mixture at low (—70 to —90°C) temperatures. As already mentioned at the synthesis of poly(IB-f)-St) it is important to add St at 100% IB conversion. The selection of the solvent is also critical, coupled product that forms in intermolecular alkylation during St polymerization cannot be avoided when the solvent is a poor solvent (e.g., hexanes/MeCl 60/40 (v/v)) for polystyrene [202]. The formation of coupled product is slower in wBuCl or in MeChx/MeCl 60/40 (v/v) solvent mixture however, to obtain block copolymers essentially free of coupled product it is necessary to stop the polymerization of St before completion. Detailed morphological and physical properties of poly(St-h-IB-h-St) triblock copolymer have been reported [199, 203-206]. The two step sequential monomer addition method has also been employed to obtain poly(p-chlorostyrene-f)-IB- )-p-chlorostyrene) [68, 207], poly(indene-f)-IB- )-indene) [208], poly(p-tert-butylstyrene-f)-IB-h-p-tert-butylstyrene) [209], poly((indene-co-p-methylstyrene)-h-IB-f)-(indene-co-p-methylstyrene)) [210], poly(p-MeSt-f)-IB- )-p-MeSt) [202], and poly(styryl-POSS-i -IB-h-styryl-POSS) (POSS=polyhedral oligomeric silsequioxane) [211] copolymers. 

Different types of biostable PURs have been used in heart valve components, including polyether urethanes (PEUs), polyether urethane ureas (PEUUs), polycarbonate urethane (PCUs), polycarbonate urethane ureas (PCUUs), polycarbonate-based materials that contain polyhedral oligomeric silsequioxane nanoparticles (POSS) (Ghanbari et al., 2010 Kidane et al 2009b), and those that contain polysiloxane soft segments (Bezuidenhout et al 2015). 

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