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
1998-03-25
1999-11-30
Cain, Edward 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...
C08K 501
Patent
active
059944463
DESCRIPTION:
BRIEF SUMMARY
This invention relates to new and technically superior gel compositions.
Gels made from oil-extended poly(styrene)-poly(alkylene)-poly(styrene) triblock copolymers are known. For example, WO-A-9305113 (RK451) describes gels of poly(styrene)-poly(ethylene/butylene)-poly(styrene) (SEBS) triblocks with addition of diblocks (preferably poly(styrene)-poly(ethylene/propylene) diblocks) to improve resistance to exudation of the extender oil from the gel under pressure. WO-A-9323472 (RK469) describes gels of poly(styrene)-poly(ethylene/propylene)-poly(styrene) triblocks. The softening temperature of these gels may be undesirably low for some purposes, and WO-A-8800603 (RK308) describes polyphenylene ether additives for improving the softening temperature.
For brevity, triblock copolymers will hereinafter be identified by reference to the block-forming unit without repetition of the word "poly", for example the above SEBS triblocks would be shown as styrene-ethylene/butylene-styrene triblocks. Gels will preferably be identified as such by the physical test criteria described in WO-A-8800603.
The present invention provides a new class of triblock gel compositions, some of which may have advantageous softening temperatures and other characteristics. The invention provides a gel composition comprising a methacrylate (preferably alkyl- or aryl-methacrylate)-alkylene-methacrylate (preferably alkyl- or aryl-methacrylate) triblock copolymer having number average molecular weight Mn of at least 50,000, preferably at least 60,000, more preferably at least 70,000, and at least 200 (preferably at least 300, more preferably at least 400) parts by weight of extender liquid per 100 parts by weight of the triblock copolymer, which liquid extends and softens the polyalkylene mid-block of the triblock copolymer. In this invention, the term "alkylmethacrylate" includes cycloalkylmethacrylates; and the term "alkylene" referring to the mid-blocks includes hydrogenated alkylene.
In these methacrylate-alkylene-methacrylate (MAM) triblock copolymers, it is preferred that the methacrylate end blocks have Mn within the range from 6,000 (preferably 7,000) to 40,000, preferably 10,000 to 30,000. It is also preferred that the polyalkylene mid-blocks of the triblock copolymer have Mn within the range from 38,000 (preferably 40,000) to 150,000, preferably 50,000 to 140,000, more preferably 60,000 to 130,000. Within these molecular weight ranges, it has surprisingly been found possible to make gels from the MAM triblock copolymers having number average molecular weight Mn as low as 50,000, preferably at least 60,000 or 70,000, these being much lower than the usual molecular weights of the known styrene-alkylene-styrene (SAS) triblock copolymers used for making gels. Better gels are obtained when Mn of the MAM triblock is at least 80,000 and superior gels are obtained when Mn is at least 90,000. The molecular weights and composition of the triblocks will preferably be selected to give the methacrylate end blocks a glass transition temperature Tg of at least 90.degree. C., preferably at least 100.degree. C., with a view to making some MAM triblock gels with softening points considerably higher than those of the corresponding SAS triblock gels.
These new MAM gel compositions according to the present invention not only have higher softening temperatures than corresponding SAS triblock gels, but also tend to be unexpectedly softer and tackier. The gels may be formed either by masticating suitable exender liquid into the MAM triblocks in the heat-softened or molten state or by incorporating the extender liquid in a solution of the MAM triblock in a suitable solvent, then removing the solvent. The gels may be used in ways similar to those known for other gels, especially the aforementioned SAS triblock gels.
The preferred end blocks for these gel-forming MAM triblocks include polymethylmethacrylate (PMMA), and C.sub.2 -(preferably C.sub.4 -)-or-higher alkylmethacrylates, for example poly-t-butylmethacrylate, polycyclohexylmethacrylate, and isobornylmet
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Graulus Hendrik
Hammond Philip James
Hudson John
Overbergh Noel
Perkins Anthony
Burkard Herbert G.
Cain Edward J.
Chao Yuan
Raychem Limited
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