SynopsisFour novel symmetric tri-n-alkyltin fluorides were prepared. In this homologous series, melting point decreases with increase in the carbon chain length while an x-ray diffraction study shows an increase in amorphousness. 'H-NMR spectra in cyclohexane, a nonpolar solvent in which these compounds form long polymeric chain, show a peak broadening effect due to high solution viscosity at very low solute concentration. Contrary to this, the spectra in CDCI,, a polar solvent in which these compounds are monomeric, show well resolved and narrow peaks. IR frequencies for Sn-C vibrations have been assigned.

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While the effects of ionizing radiation on homopolymers are well de~cribed,'-~ few studies of copolymer systems have been reported. The most serious effort in this area was by Alexander and Charle~by,~ who noted that when styrene-isobutylene copolymers are irradiated in a pile, the system initially degrades to an extent proportional to the styrene concentration, then crosslinks; even copolymers containing 0.7 mole fraction styrene separated into a sol and gel fraction after doses of the order of 10 Mrep. A more recent note6 reported that radiation protection occurs in emulsion copolymers of butadiene with styrene and acrylonitrile (dose range, 10 to 100 Mrep; probably irradiated in air). Survey experiments are reported for systems of the more common monomers.6-'2 Experiments in this laboratory indicated that viscosity data were not a reliable index of radiation protection, and the large doses necessary to effect measurable solubility changes obscured truly initial effects. It appeared that mass analysis of the gases liberated as a function of copolymer composition would afford additional useful data; accordingly, styrene-methyl methacrylate (STY-MMA) and styrene-methyl acrylate (STY-MAC) copolymers were yirradiated in vacuo, and, in addition to viscosities, the decomposition gases were examined. EXPERIMENTALAppropriate mixtures of redistilled monomers were degassed in 5-inch polymerization tubes and polymerized thermally to less than 5% conversion; the products were reprecipitated repeatedly from benzene solution with methyl alcohol, dried in vacuo for 4 hours at lOO", then analyzed for the elements to determine the composition. Intrinsic viscosities were determined in solvent benzene a t 25'; the values for the starting materials were about 1.3 for the STY-MMA and 2.2 for the STY-MAC copolymers. A weighed amount of the dry polymer (about 0.1 gra.m) in an ampule was maintained at 80" for 1 hour at a pressure of about loF5 mm.; the tube was then sealed. Mass analysis prior to irradiation failed to reveal the presence of any gas.A dose rate of 2.4 X lo5 rep per hour (CoG0 source; FeS04 dosimetry) was employed for all the experiments; doses ranged from 1.0 Mrep to 10.0 Mrep.It was assumed that one gram of polymer absorbed 58 X lo1* e.v. when given a dose of 1.0 Mrep.About 1 day after irradiation, the ampules were sealed into a Consolidated Model No. 21-103 mass spectrometer, the conventional inlet system of which was modified to permit analysis of about 10-lo moles of gas.13 The actual quantities measured were a t least fifty times this value. Absolute quantities are believed to be within 10% of the true values; relative concentrations within a few per cent. Usually more than 90% of the gases in each tube were accounted for; in the case of PMMA, the analysis was about 98% complete. When the gas content of the low dose sample (1.0 Mrep) was too small for accurate analysis, these values were omitted from the average determinations. It is estimated that the mass data are reproducible to within f10%, with the exception ...

The radiation-induced solid phase polymerization of hexamethylcyclotrisilosane ( I ) has been described by Lawton, Grubb, and Balwit.1 It was reported that for doses high enough to cause gel formation ( a ) the rate increases with temperature, exhibits a discon-

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