A general method for introducing various side chains onto a highly branched polysilaethylene (HBPSE) backbone is described. This method starts with a commercial oligomer mixture which has a highly branched structure, consisting of [H3SiCH2], [SiH2CH2], [SiH(CH2)2], and [Si(CH2)3] subunits combined to give an overall "SiH2CH2" average formula. Several alkyl-, aryl-, and allyl-substituted HBPSEs were prepared by first converting the parent HBPSE into a highly reactive bromo-substituted derivative which was then treated with organolithium reagents (RLi, R ) C4H9, C6H13, C8H17, C6H5, C6H4N(Me)2) or Grignard reagents (RMgBr, R ) Et, allyl). The parent HBPSE and its derivatives were characterized by means of NMR and IR spectroscopy, as well as elemental analysis, DSC, GPC, and VPO. It was shown that the allyl-substituted HBPSE can be used as a synthetic platform for attaching functional side chains via the hydrosilation reaction.
The molecular structure of the monosilicon analog of
poly(ethylene), poly(silylenemethylene),
CH3[SiH2CH2]
n
SiH3,
or poly(silaethylene) (PSE), was characterized by means of
high-resolution 1H, 13C,
and 29Si NMR spectroscopy. The average molecular
weight of this polymer was also determined from
the NMR spectra by integration of the −SiH3 and
−CH3 end groups, relative to the main-chain
−SiH2CH2− units. All of the peaks in the NMR spectra were
assigned with the help of a model compound,
CH3SiH2CH2SiH3,
and PSE with added SiCH2SiH3 or
SiCH3 side groups. In addition to the
main-chain
−SiH2CH2− species, the
−CH3 and −SiH3 end groups and a small
concentration (ca. 1 per 200 Si atoms
in the polymer chain) of −SiHCH3− branch sites were
evidenced in the NMR spectra of the “parent”
PSE. These −SiHCH3− groups were concluded to arise
from a small amount of dimethyldichlorosilane
in the methyltrichlorosilane starting material used in the synthesis of
the 1,1,3,3-tetrachloro-1,3-disilacyclobutane monomer.
Work carried in the authors' laboratory on Si-CH 2-Si bridged polycarbosilanes is reviewed. In pursuit of high-yield polymeric precursors to silicon carbide, convenient synthetic routes to both linear and hyperbranched polycarbosilanes having a '[SiH 2 CH 2 ] n ' compositional formula have been developed. The linear [SiH 2 CH 2 ] n polymer was prepared by ring-opening polymerization of a substituted disilacyclobutane, and was studied both as an analogue of polyethylene and as a high-yield precursor to SiC. Elaboration of the methods employed to prepare this polymer has yielded a wide range of new poly(silylenemethylene)s (PSMs) of the type [SiRR'CH 2 ] n , where R and R' can be a wide range of different groups, including a series of symmetrically disubstituted polymers with R = R' = F, alkyl and alkoxy which form crystalline solid phases and various amorphous, atactic polymers having different R and R' groups. By using (Si)-Cl replacement reactions analogous to those developed previously for polydichlorophosphazene, as well as hydrosilation reactions similar to those used for [Si(H)(Me)O] n , a series of side-chain polymers having various groups attached to Si through Si-C or Si-O bonded linkages were obtained. Similar polymer modification reactions have recently been developed for the branched oligomer/polymer analogue of these linear polycarbosilanes, leading to hyperbranched species with functional substituents, including a di(ethyleneoxy) methyl ether-terminated derivative which readily dissolves lithium salts. The results of studies of these novel 'inorganic/organic' hybrid polycarbosilanes are described and their properties are compared with those of related carbon-backbone and siloxane polymers.
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