No abstract

Flexible, self-extinguishing silicone foams (SFs) with a relatively low density (0.25-0.45 g/cm 3 ) were obtained from a mixture of a,x-(dihydroxy)polydimethylsiloxanes, water, flame retardants (melamine and/or expanded graphite), and polyisocyanates [poly(diphenylmethane isocyanate)]. These compositions were crosslinked at room temperature with branched polymethylhydrosiloxanes with the structure (MeSiO 1.5 ) 3 (MeHSiO) 102 (Me 3 SiO 0.5 ) 5 in the presence of tin octoate as a catalyst. The SFs were modified by the addition of linear or graft carbofunctional polysiloxanes containing chydroxypropyl groups. Only the SFs prepared by means of a dehydrocondensation reaction had a good homogeneity of pores, whereas the foams formed with two kinds of blowing agents (hydrogen and carbon dioxide, generated in the reaction of water with isocyanate groups) had lower densities but a poor homogeneity of pores. Unmodified SFs showed a tensile strength of 20 kPa or less, whereas the foams formed with the addition of poly(diphenylmethane isocyanate) and water had a tensile strength of 23-25 kPa. The SFs with 15 and 30% contents of melamine or expanded graphite had tensile strengths in the ranges 38-45 and 51-54 kPa, respectively. All of the prepared SFs were combustible materials. The SFs without the addition of flame retardants had a limiting oxygen index of approximately 21%, whereas the SFs with a 30% content of fire retardant had self-extinguishing properties and a limited oxygen index of 41-43%.

141 Crystal structure analysis of (Et4N),. 7 . C H X N (the values in brackets represent results of a structure determination on a second data set obtained from an independently grown new crystal): a = 16.557(!) [16.563(4)], b = 18.915(6) [18.879(6)], C = 17.110(6) [17.108(5)] A, a = / f = y = 9 0 " ; space group, Pbcm, 2 = 4 , pCalcd=1.35 g cm-,, pl,hu,= 1.40 g cm-,, p=12.9 cm-', 2Q,,,=4O0 (MoKa, L=O.71069A); 2620 unique reflections; used in refinement with F~z > 3 u ( F~) : 1290 [1376]; parameters 198. Final R=0.0699 I0.07331, R, =0.0647 10.06891. The low number of observed reflections for both data sets is due to the fact that crystals of high crystallographic quality could not be isolated. This problem, coupled with positional disorders encountered with two of the three [Et4N]" cations, accounts for the rather high temperature factors obtained for some of the carbon atoms. Further details of the crystal structure investigation are available on request from the Fachinformationszentrum Energie, Physik, Mathematik GmbH, D-7514 Eggenstein-Leopoldshafen 2 (FRG), on quoting the depository number CSD-53 196, the names of the authors, and the journal citation. [IS] H. Beinert, A. Dedicated to Professor Hans Bock on the occasion of his 60th birthdayAlthough the chemistry of the silanediyls is well developed and of continuing interest,"] there are few convenient methods for generating these species on a preparative scale. We had need for a variety of methods for making di-rert-butylsilanediyl (2) and in this communication we report three convenient routes for generating this intermediate, possibly in a complexed form like 8, in high yields.'21 2 has been proposed as a product of the photolyses of hexa-tert-butylcy~lotrisilane~~~ and di-tert-butylsilyldi-a~i d e . '~] We have found [Eqn. (a)] that when di-tert-butyl-dichlorosilane ( l a ) and lithium in T H F in the presence of excess of triethylsilane, were irradiated with ultrasonic waves using an ultrasonic cleaning bath, the di-tert-butylsilanediyl insertion product l,l,l-triethyl-2,2-di-tert-butyldisilane (3) was isolated in 60% yield.[51 The same product was obtained in comparable yields from l b and l c . This is the first example of a metal-promoted a-elimination of dihalosilanes on a preparative scale. tBu2SiX2 + Li a [tBu,Si:] E13S'H * Et,Si-SiHtBu2 (a) l a , X = C1 2 Ib, X = Br lc, x = 1 3We have investigated the reactions of l a and lithium with other trapping agents and in the absence of a quenching agent. With trans-butene for example, 1,l-di-tert-butyltrans-2,3-dimethylsilirane (4), was isolated in 65-70% yield. None of the cis isomer was detected by gas chromatography. When cis-butene was used as a trap, 1,l-di-tertbutyl-cis-2,3-dimethylsilirane was also isolated in 65-70% yield.16] A small amount (< 5%) of 4 was detected along with 5 but was understood to arise from the presence of 2-5% trans-butene in our samples of cis-butene.

Copolymers and homopolymers containing silicon atoms connected to three and four other silicon atoms have been prepared and characterized. We report the first evidence of dendritic polymers with silicon backbones. Copolymers made from RSiCl3 and R1R2SiCl2 resemble hybrid materials of polysilyne and polysilanes. Polymers, which contain tetrasilyl‐substituted Si atoms, [(SiMe2)4Si]n and (Si)m(Me2Si)n, have also been synthesized. These molecules appear to be the first hyperbranched polymers, which have applications based on their electronic properties. The properties of these molecules fit into the hierarchy of 1‐D to 3‐D topologies known for Si materials.