Cores polysiloxane

Masamune et al. constructed a polysiloxane dendrimer with an oligosilane core unit [98]. A repetitive synthetic strategy, consisting in catalytic oxidation of the terminal SiH to SiOH groups and substitution of the hydroxyl groups by a spacer, provided access to polysiloxane dendrimers of up to the third generation. 

The bromosilane obtained by reaction of the phenylsiloxane 1 with bromine in the presence of triethylamine or sodium siloxide led Kakimoto et al. to the siloxane core building block 4. It contains three phenylsilane-terminated disilox-ane branching units, which should minimise steric hindrance on construction of subsequent generations. A sequence of bromination, amination, and alcoholysis ultimately leads to the third-generation polysiloxane 5 (Fig. 4.50) [99]. 

Masamune et alJ1001 reported the preparation of the first series of high molecular weight, silicon-branching macromolecules by means of the procedure shown in Scheme 4.21. Their iterative procedure utilized two differently branched synthetic equivalents a trifunctional, hydrido-terminated core 71 and a trigonal monomer 72. Syntheses of the polysiloxane core 71 and building block 72 were each accomplished by the treatment of trichloromethylsilane with three or two equivalents of the siloxane oligomers, HO[Si-(Me)20]5Si(Me)2H and H0[Si(Me)20]3Si(Me)2H, respectively. 

Repetitive silicon-based transformations were then employed for dendritic construction. Palladium-catalyzed silane hydroxylation of the core 71 afforded triol 73, which was then treated with three equivalents of monochloropolysiloxane 72 to generate the hexa-hydrido, first generation dendrimer 74. Further application of the Pd-mediated hydroxylation, followed by attachment of monochloro-monomer 72, led to the second (75) and third (76) generation polysiloxane cascades. 

Examples of the synthesis of polysiloxane nanocomposites reported in the literature include Work by Ma et al (6) who modified montmorilIonite with short segments of PDMS and blended this into a polymer melt/solution to yield examples of fully exfoliated or intercalated PDMS/clay nanocomposites. Pan, Mark et al (7) synthesized well defined nano-fillers by reacting groups of four vinyl terminated POSS cages with a central siloxane core. These materials were subsequently chemically bonded into a PDMS network yielding a significant improvement in the mechanical properties of the polymer. 

The mesogenic behavior of 43 emphasizes the role played by the oc-tasilsesquioxane core when comparing with the related side-chain liquid-crystalline polysiloxanes [95,96]. It is remarkable that the thermal stability of the chiral nematic phase is similar in both the polymer and the dendrimer, suggesting that the cubic core does not perturb significantly the associations between the mesogens necessary to support the chiral nematic phase. 

A number of polymer and fiber modifications have been devised to overcome this problem, although none has been successful enough to allow acrylics to compete in successfully easy-care apparel markets. The fibers may be treated with compounds such as ammonium sulfide [433], hydrazine derivatives [434,435], thiosemicarbazides [436], silicone oils [437], and emulsions of polysiloxane and polyepoxide [438]. Some success has been achieved by incorporating comonomers that increase the wet glass transition temperature of the polymer or make the copolymer more water-resistant [439-444]. Sheath-core fibers have been reported [445] in which the core polymer is stable under hot-wet conditions and the sheath polymer is used to compensate for deficiencies in dyeability. 

Polysiloxane dendrimers T ris-[(phenyldimethylsiloxy) dimethylsiloxy]methylsilane core bis[(phenylimethylsiloxy)methyl siloxy] dimethylsilanol as the building block Three generations [r]]-M relationship/Mark-Houwink constants, NMR, molecular diameter discussed [276]... 

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