On the Role of Tin Catalysts in Step-Growth Polymerization Reactions

Abstract

Organotin compounds have been used to catalyze the condensation of various a,x-dihydroxyl terminated organosiloxane diols. This tin catalyzed reaction extends the length of siloxane chains and it also produces narrow molar mass distribution polyorganodisilanols (M w /M n = 1.4). The reaction occurs between a variety of siloxanes that are terminated with hydroxyl groups and it does not depend on the organic side groups connected to silicon for the systems studied here. These systems include silicon atoms bearing dimethyl, methylphenyl or methyl 1,1,1 trifluoropropyl substituents. The organotin catalyst in the reaction facilitates the organosilanol condensation releasing water as a byproduct. However it does not appear to facilitate the opening of siloxane bonds nor the redistribution of siloxane bonds under the conditions employed here. Copolymerization of linear oligomeric dimethylsiloxane diol and linear oligomeric methylphenylsiloxanediol was found to give a relatively equal reactivity of homo polymerization and hetro polymerization in the condensation and randomly alternating segmented block copolymers that were formed. The reaction kinetics of the polymerization was used to experimentally verify the fact that there is a chain length dependence of the reacting silanol endgroups. The molar mass values during the polymerizations were determined using gel permeation chromatography.The chromatography, viscosity and FTIR results demonstrate that the reactivity of the hydroxyl end-groups in the polycondensation reaction decreases upon increasing the chain length of the siloxane. It therefore appears that these tin catalyzed siloxane systems deviate from the widely demonstrated hypothesis of Paul Flory on the ''equal reactivity of functional groups'' for step-growth polymerizations.

(Me3N)Mo(CO)5-Catalyzed Reduction of DMF by Disiloxane and Disilane Moieties: Fate of the Silicon-Containing Fragments

“…The sole formation of cyclic polysiloxanes is presumably related to the use of such organotins as catalysts for the condensation of siloxane diols and functional silanes, leading to useful polysiloxanes under mild conditions . Certainly many cyclic stannasiloxanes have been reported and have a thermodynamic and kinetic stability suggesting that under our reaction conditions they should be observed . At present we have not further investigated this aspect of the new chemistry.…”

Dialkyltin(IV)bis(O–tolyl/benzyldithiocarbonate) complexes: Spectroscopic, thermogravemetric, antifungal and crystal analysis of n–Bu2Sn(S2COCH2C6H5)2

“…The 1 H and 13 C NMR spectra were recorded in CDCl 3 on a Bruker Avance III spectrophotometer (400 MHz) using TMS as internal reference. The 119 Sn NMR spectra were recorded on a Bruker Avance II (400 MHz) spectrometer using Me 4 Sn as an external standard. The thermogram was analyzed by using Perkin Elmer, diamond TG/DTA instrument.…”

“…Inorganic and organotin compounds have found industrial use as catalysts like in heterogeneous oxidation catalysts based on tin(IV) oxide [1][2] and homogeneous catalysts for industrial organic and polymeric reactions. [3][4] Apart from the well-established uses of tin catalysts in polyurethanes, 5 RTV silicones 6 and esterification reactions, 7 new developments have included their use as anti-tumor drugs, [8][9] ion carriers in electrochemical membrane, 10 in synthetic vitamin E production 11 and in the manufacture of certain novel polymeric materials. 12 A remarkable but little known fact about tin is to save energy and reduce emissions when added to fuel 13 and are effective premixed methane flame inhibitors.…”