Thermogravimetric study of the vacuum depolymerization of polydimethylsiloxane

Tatrishvili

2007

ABSTRACT:The catalytic dehydrocondensation reaction of ␣,-bis(trimethylsiloxy)methylhydridesiloxane and of ␣,-bis(trimethylsiloxy)methylhydridesiloxane-dimethylsiloxane with ␣-hydroxy--trimethylsiloxydiorganosilylenes, in the presence of anhydrous caustic potassium, at 1:35 and 1:33 ratio of initial compounds has been investigated and polyorganosiloxanes with rigid polydiorganosilylenes fragment in the side chain, completely soluble in organic solvents, have been obtained. The catalytic dehydrocondensation reaction order, activation energies, and rate constants have been determined. The synthesized copolymers were characterized by thermogravimetric, gel permeation chromatographic, differential scanning calorimetric, and wideangle X-ray analyses. It was shown that during modification of ␣,-bis(trimethylsiloxy)methylhydridesiloxane-dimethylsiloxane with ␣-hydroxy--trimethylsiloxydiorganosilylenes in synthesized block-copolymers, microdomain structure (phase incompatibility) was observed.

Section: Figurementioning

confidence: 86%

Section: Figurementioning

confidence: 95%

Comb‐type methylsiloxane copolymers with diorganosilylene fragments as a lateral group

Tatrishvili

2007

“…We showed that inserting the silaoxadihydrophenanthrene-diphenylsiloxanes fragments in the DMS chain caused the thermal-oxidative stability of the copolymers to rise and the main destruction process proceeds at 80 -100°C higher than the destruction of unblocked PDMSs. 12,13 The microheterogeneous structure of the BCs is observed by DSC and X-ray investigation at definite values of the length of the flexible DMS chain.…”

Section: Discussionmentioning

confidence: 99%

“…3 It was shown that by the insertion of silaoxadihydrophenanthrene fragments in the DMS chain the thermaloxidative stability of copolymers increases compared with the linear unblocked poly(DMS) (PDMS). This may be explained by the presence of aromatic phenyl groups that are highly resistant to oxidation and have an inhibiting effect on the oxidation of methyl groups 2,3 and by the break of the spiral structure of the linear PDMS. 4 At the same time, it is known that introduction of groups distinct from 'SiOOO links into the PDMS backbone leads to breakdown of the destruction processes of the depolymerization mechanism, because of the impossibility of formation of a transitive complex.…”

Section: Introductionmentioning

confidence: 95%

“…There is some information in the literature about the card-type organic silicon copolymers cyclotrisiloxane 1 and cyclocarbosiloxane 2 and with silaoxadihydrophenanthrene fragments in the linear dimethylsiloxane (DMS) chain. 3 It was shown that by the insertion of silaoxadihydrophenanthrene fragments in the DMS chain the thermaloxidative stability of copolymers increases compared with the linear unblocked poly(DMS) (PDMS).…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Synthesis and investigation of properties of silaoxadihydrophenanthrene‐diphenylsiloxane fragments containing block copolymers

Samsonia

Karchkhadze

et al. 2002

ABSTRACT:The reaction of heterofunctional condensation of 1,1-dichloro-1-sila-2-oxadihydrophenanthrene with dihydroxydiphenylsilane at various ratios of initial compounds in the presence of pyridine is investigated. ␣,-Dihydroxysilaoxadihydrophenanthrene-diphenylsiloxane oligomers with various degrees of condensation are obtained. Organosiloxane block copolymers with the regular arrangement of silaoxadihydrophenanthrene-diphenylsiloxanes fragments in the main linear dimethylsiloxane chain are produced by the reaction of heterofunctional condensation of ␣,-dihydroxysilaoxadihydrophenanthrene-diphenylsiloxanes with ␣,-dichlorodimethylsiloxanes in the presence of anhydrous pyridine, as an acceptor of hydrochloric acid. Thermogravimetry, differential scanning calorimetry, gel permeation chromatography, and wide-angle X-ray analysis are carried out on the synthesized block copolymers. The microheterogeneous structure of block copolymers is observed at definite values of the length of the flexible dimethylsiloxane chain by DSC and X-ray investigation.

Thermal stability of in situ filled siloxane elastomers

Sohoni

Mark

1992

SYNOPSISPoly (dimethylsiloxane) elastomers that had been filled with in situ precipitated silica were studied by thermogravimetric analysis, under nitrogen and in air. Both types of measurements indicated that the filler raises the temperature of thermooxidative degradation of the polymer, possibly by inactivating the terminal -OH groups on the chains. Commercial fume silica was found to cause more severe degradation problems than did the in situ precipitated silica. In all cases, the degradation was more pronounced in air than in the inert atmosphere provided by nitrogen. 0 1992 John Wiley & Sons, Inc. I NTRODU CTI 0 NThe need for elastomeric materials in a variety of applications has resulted in the development of highperformance materials that can be used over a wide range in temperature and under different environmental conditions, some of which are quite hostile. Organosiloxane polymers, of repeat unit [ -SiRR'O -1, have long been known to be very good materials in this regard' because of their low glass transition temperatures and high thermal stabilities compared with those of most carbon-based elastomer^.^,^ Among these, elastomers of poly (dimethylsiloxane) (PDMS) are by far the most used.Thermal effects on elastomers can be either reversible or irrever~ible.~ More specifically, raising the temperature of an elastomer generally affects it in two ways: There is an immediate effect, which is reversible, followed by a long-term effect known as "heat-aging,'' which is irreversible. The reversible effects of temperature are physical in origin, for example, changes in the nature or degree of polymer crystallinity. Examples of irreversible change would be additional ( inadvertent ) curing, and degradative interactions with oxygen or ozone.