338
catalyzed by TFA, while phenyl modified PDMS-PMHS copolymers containing
both internal Si-H and end SiH 2 and MeSiO 3/2 (T) units were prepared by Yang et al.
(2004) via ROP of D
H 4.5 + hexamethylcyclotrisiloxane (D 3 ) + D
Ph 3 with n-BuLi, and
the sequential microstructures of these copolymers were determined by
29
Si-NMR.
14.2.2 Synthesis of PHS and PMHS with Branched, Cage,
Dendritic, Ladder and Star Structures
An increasing interest in the preparation and applications of PMHS of branched,
dendritic and star structures has been especially observed in the last three decades.
A star tetrakis(dimethylsiloxy)silane (Si(OSiMe 2 H) 4 ), cage T
H 8 , and octakis
(dimethylsiloxy)octasilsesquioxane (((HMe 2 SiO)SiO 1.5 ) 8 ) are commercial products
(Hoebbel and Wieker 1971; Hasegawa and Motojima 1992, Hasegawa 1993,
Hasegawa et al. 2003; Moran et al. 1993; Majoros et al. 1997; Provatas et al. 1998;
Constantopoulos et al. 2004; Laine 2005; Soh et al. 2007; Hessel et al. 2006).
Uchida et al. (1990) elaborated a multistep synthesis of polysiloxane dendrimer
from siloxane oligomers containing different functional groups: Si-Br, Si-Cl, Si-H
and Si-OH. Through many consecutive condensation reactions, the liquid dendritic
polysiloxane of third generation, (MeSiO 1.5 ) 22 (Me 2 SiO) 162 (M
H
) 24 , having 24 Si-H
end functional groups on the globular-like surface was obtained (Uchida et al. 1990).
A branched H-siloxane, {-OSi[(OSiMe 2 O) n SiMe 2 H] 2 -} 6 , was prepared by
Sargent and Weber (2000) through the equilibration of hexakis(dimethylsiloxy)
cyclotrisiloxane (((HMe 2 SiO) 2 SiO) 3 ) with D 4 , towards TFA. Six- and eightmembered ring-star silicates were synthesized by Cai et al. (2004) with low yields:
[(HMe 2 SiO) 2 SiO] 3 was obtained in reaction of DMCS with pseudowollastonite
(Ca 3 Si 3 O 9 Cl 6 ), while octakis(dimethylsiloxy)cyclotetrasiloxane (((HMe 2 SiO) 2 SiO) 4 )
was obtained by Sargent and Weber (2000) from octakis(trimethylsiloxy)cyclotetrasiloxane (((Me 3 SiO) 2 SiO) 4 ) and M
H 2 in the presence of TFA.
The equilibration of star octamethylpentasiloxane (Si(OSiMe 2 H) 4 ) with D 4
towards TFA gave liquid tetraarm star polysiloxanes (Si((OSiMe 2 ) n OSiMe 2 H) 4 ) with
Si-H end groups (and a number-average molecular weight (M n ) = 2,800–10,940 g/
mol). Similarly, tetraarm star oligofluorosiloxanes have been synthesized by the
equilibration of 1,3,5-trimethyl-1,3,5-tris(3,3,3-trifluoropropyl)cyclotrisiloxane
with Si(OSiMe 2 H) 4 in the acidic medium (Cai and Weber 2004; Grunlan et al. 2006).
The ROP of 2,4,6,8-tetramethyltetrahydrocyclotetrasiloxane (D
H 4 ) with
tris(pentafluorophenyl)borane (B(C 6 F 5 ) 3 ), in toluene, was reported by Chojnowski
et al. (2012). The Si-H multifunctional branched polysiloxane, composed of rings
and macrocycles of different size, was soluble. A gaseous side product, methylsilane (MeSiH 3 ), was formed, and in the bulk process gelation was observed. A
hydride transfer led to a rearrangement of linear MeHSiO units into branching
MeSiO 1.5 units (Chojnowski et al. 2012).
The poly(hydrosilsesquioxane) (PHSSQ) precursors were synthesized from
triethoxysilane (HSi(OC 2 H 5 ) 3 , HSi(OEt) 3 , TES) at pH 1–4. The molecular structures
J. J. Chruściel
catalyzed by TFA, while phenyl modified PDMS-PMHS copolymers containing
both internal Si-H and end SiH 2 and MeSiO 3/2 (T) units were prepared by Yang et al.
(2004) via ROP of D
H 4.5 + hexamethylcyclotrisiloxane (D 3 ) + D
Ph 3 with n-BuLi, and
the sequential microstructures of these copolymers were determined by
29
Si-NMR.
14.2.2 Synthesis of PHS and PMHS with Branched, Cage,
Dendritic, Ladder and Star Structures
An increasing interest in the preparation and applications of PMHS of branched,
dendritic and star structures has been especially observed in the last three decades.
A star tetrakis(dimethylsiloxy)silane (Si(OSiMe 2 H) 4 ), cage T
H 8 , and octakis
(dimethylsiloxy)octasilsesquioxane (((HMe 2 SiO)SiO 1.5 ) 8 ) are commercial products
(Hoebbel and Wieker 1971; Hasegawa and Motojima 1992, Hasegawa 1993,
Hasegawa et al. 2003; Moran et al. 1993; Majoros et al. 1997; Provatas et al. 1998;
Constantopoulos et al. 2004; Laine 2005; Soh et al. 2007; Hessel et al. 2006).
Uchida et al. (1990) elaborated a multistep synthesis of polysiloxane dendrimer
from siloxane oligomers containing different functional groups: Si-Br, Si-Cl, Si-H
and Si-OH. Through many consecutive condensation reactions, the liquid dendritic
polysiloxane of third generation, (MeSiO 1.5 ) 22 (Me 2 SiO) 162 (M
H
) 24 , having 24 Si-H
end functional groups on the globular-like surface was obtained (Uchida et al. 1990).
A branched H-siloxane, {-OSi[(OSiMe 2 O) n SiMe 2 H] 2 -} 6 , was prepared by
Sargent and Weber (2000) through the equilibration of hexakis(dimethylsiloxy)
cyclotrisiloxane (((HMe 2 SiO) 2 SiO) 3 ) with D 4 , towards TFA. Six- and eightmembered ring-star silicates were synthesized by Cai et al. (2004) with low yields:
[(HMe 2 SiO) 2 SiO] 3 was obtained in reaction of DMCS with pseudowollastonite
(Ca 3 Si 3 O 9 Cl 6 ), while octakis(dimethylsiloxy)cyclotetrasiloxane (((HMe 2 SiO) 2 SiO) 4 )
was obtained by Sargent and Weber (2000) from octakis(trimethylsiloxy)cyclotetrasiloxane (((Me 3 SiO) 2 SiO) 4 ) and M
H 2 in the presence of TFA.
The equilibration of star octamethylpentasiloxane (Si(OSiMe 2 H) 4 ) with D 4
towards TFA gave liquid tetraarm star polysiloxanes (Si((OSiMe 2 ) n OSiMe 2 H) 4 ) with
Si-H end groups (and a number-average molecular weight (M n ) = 2,800–10,940 g/
mol). Similarly, tetraarm star oligofluorosiloxanes have been synthesized by the
equilibration of 1,3,5-trimethyl-1,3,5-tris(3,3,3-trifluoropropyl)cyclotrisiloxane
with Si(OSiMe 2 H) 4 in the acidic medium (Cai and Weber 2004; Grunlan et al. 2006).
The ROP of 2,4,6,8-tetramethyltetrahydrocyclotetrasiloxane (D
H 4 ) with
tris(pentafluorophenyl)borane (B(C 6 F 5 ) 3 ), in toluene, was reported by Chojnowski
et al. (2012). The Si-H multifunctional branched polysiloxane, composed of rings
and macrocycles of different size, was soluble. A gaseous side product, methylsilane (MeSiH 3 ), was formed, and in the bulk process gelation was observed. A
hydride transfer led to a rearrangement of linear MeHSiO units into branching
MeSiO 1.5 units (Chojnowski et al. 2012).
The poly(hydrosilsesquioxane) (PHSSQ) precursors were synthesized from
triethoxysilane (HSi(OC 2 H 5 ) 3 , HSi(OEt) 3 , TES) at pH 1–4. The molecular structures
J. J. Chruściel