Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Patent
1991-05-01
1992-09-08
Seccuro, Jr., Carman J.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
524474, 524484, 524485, 524518, 525194, 525210, 5253596, C08L 2328, C08L 4500
Patent
active
051458977
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to polynorbornenebased rubbery compositions with an improved heat stability and to thermally stable thermoplastic elastomers obtained from these compositions.
Formulated and vulcanised polynorbornene is a rubber which is quite sensitive to thermal degradation because of its high degree of unsaturation. When the vulcanising system employed is sulphur-based, it results in bridges containing sulphur-sulphur bonds which make the vulcanised polynorbornene proportionately more vulnerable to temperature. Thus, it is known that rubbers formulated from polynorbornene generally lose the essential part of their mechanical properties (especially tensile strength and elongation at break) after long-term aging periods at temperatures above 80.degree. C.
A number of solutions have already been proposed to improve the thermal aging behaviour of polynorbornene-based formulated rubbers. Among these solutions there may be mentioned especially the addition to the formulated rubber of at least one antioxidant of phenolic type or else such as the zinc salt of mercaptobenzoimidazole. It is also possible to mention the use of reactive compounds capable of forming carbon-oxygen or carbon-carbon bonds, such as phenolic resins, generally coupled with accelerating compounds such as Lewis acids or some metal oxides (in particular those of zinc and of magnesium). As an example of such a reactive system there may be mentioned the combination of stannous chloride with a phenolic resin of formula: ##STR2## in which: n=4 or 5 and R denotes an alkyl radical. The abovementioned solutions for improving the thermal aging behaviour of polynorbornene-based formulated rubbers can naturally be combined to strengthen their effects However, even in this case it is generally observed that the said rubbers lose more than 80% of their tensile strength after an aging period of 7 days at 100.degree. C. and lose virtually all of their mechanical properties (elongation and tensile strength) after 14 days' aging at 100.degree. C. This situation quite obviously impedes the use of polynorbornene-based formulated rubbers in a number of applications.
A first objective of the present invention consists therefore in developing an effective means for improving the thermal aging behaviour of polynorbornene-based formulated rubbers, and in particular for maintaining the essential part of their mechanical properties after long-term aging at temperatures above 80.degree. C.
Furthermore, patent U.S. Pat. No. A-4,203,884 teaches that compositions comprising a mixture of a thermoplastic crystalline polyolefin, polynorbornene and a sufficient quantity of plasticiser for polynorbornene to lower its glass transition temperature to the range of rubbers have advantageous properties. More particularly, this document discloses compositions comprising a mixture of 75 to 10 parts by weight of polyolefin, 25 to 90 parts by weight of polynorbornene, and 30 to 400 parts by weight of plasticiser per 100 parts by weight of polynorbornene, the said compositions being elastoplastic, that is to say that they have elastomeric properties while being capable of being converted like thermoplastics. In the molten state, according to this technique, some of the plasticiser may be present in the thermoplastic polyolefin phase. After cooling, the plasticiser migrates substantially from the crystalline polyolefin phase towards the polynorbornene phase, to form part of the latter. In this way, the plasticiser improves the thermoplasticity or the processability of the composition. As a general rule, for a given degree of thermoplasticity, the composition requires proportionally less polyolefin, the greater the quantity of plasticiser.
U.S. Pat. No. A-4,203,884 also discloses compositions comprising a mixture of 10 to 90 parts by weight of crystalline polyolefin and 90 to 10 parts by weight of crosslinked polynorbornene dispersed in the form of small-sized particles, and plasticiser in a sufficient quantity to lower the glass transition temperature of the polynorbornene
REFERENCES:
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patent: 4203884 (1980-05-01), Coran et al.
patent: 4874808 (1989-10-01), Minami et al.
patent: 4918133 (1990-04-01), Moriya et al.
patent: 4990559 (1991-02-01), Shiraki et al.
Chemical Abstracts, 1981, vol. 94, page 64.
Coupe Frederic
Levif Gabriel
Atochem
Seccuro, Jr. Carman J.
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