Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Patent
1996-12-17
2000-02-29
Buttner, David
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C08F29704
Patent
active
060310537
DESCRIPTION:
BRIEF SUMMARY
Block copolymers of vinylaromatics (eg. styrene) and dienes (eg. butadiene) are copolymers of a plurality of polymer molecular segments (ie. blocks) which are linked to one another in series or in some other manner and have a more or less uniform composition. Depending on the structure and content of diene monomers, they may have, at a certain temperature, generally elastomeric properties or are rigid and have nonelastomeric properties, ie. they behave externally in general either as elastomeric materials, similar to a polydiene, and are important, for example, as SB rubber, or like transparent, impact-resistant styrene polymers. In line with the terminology for toughened polystyrene, it is usual to define the molecular moieties which determine the elastomeric behavior as a flexible phase and the rigid molecular moieties (the pure polystyrene component) as the rigid phase. SB rubbers cannot be processed in the same way as thermoplastics but must be vulcanized for use, in the same way as conventional diene polymers, which greatly restricts their use.
The present invention relates to usually transparent block copolymers of vinylaromatics and dienes, which copolymers can be processed by a purely thermoplastic method and have elastomeric behavior and particular mechanical properties.
In this context, the following may be said at the outset:
The anionic polymerization which leads to living polymers and in which the growth of a chain molecule takes place at a chain end which lives (remains polymerizable) for an infinitely long term in theory owing to a lack of spontaneous chain termination or chain transfer reactions, and the reaction of the living polymer with monofunctional or polyfunctional reactants, are known to provide a wide range of possibilities for the synthesis of block copolymers, although the choice of monomers is limited; only block copolymers of vinylaromatic compounds, ie. styrene and its derivatives, on the one hand, and dienes, essentially butadiene or isoprene, on the other hand, have become important in practice. Block copolymers are obtained by effecting polymerization in each case up to virtual exhaustion of a monomer stock and then changing the monomer or monomers. This process can be repeated several times.
Linear block copolymers are described, for example, in U.S. Pat. Nos. 3,507,934 and 4,122,134. Star block copolymers are disclosed, for example, in U.S. Pat. Nos. 4,086,298, 4,167,545 and 3,639,517.
The property profile of these block copolymers is characterized essentially by the content of polymerized diene monomers, ie. the length, arrangement and ratio of polydiene and polystyrene blocks. In addition, the type of transition between different blocks plays an important role: well defined and tapered transitions are known, depending on whether the change in monomer takes place abruptly or gradually. In the latter case, a more or less random distribution of sequence lengths occurs.
With identical molecular weight and diene content, block copolymers having sharply separated blocks are less tough than those having tapered block transitions. If tougher block copolymers are desired, block transitions having a random distribution of sequence lengths of diene and vinylaromatics in the transition region are consequently preferred (cf. U.S. Pat. No. 4,122,134 and EP-A-0 316 671).
In morphological investigations of block copolymers, it has been found that, in the case of tapered block transitions, the sequence length of the pure diene phase is shifted relative to the polystyrene phase and hence the volume ratio is altered in favor of the diene phase. The toughness of a polymer can thus be increased by the type of block transition without the diene content having to be increased. This may be advantageous since, with growing diene content, the flow of the melt and the heat stability of the polymers decrease and the danger of crosslinking of the diene phase increases. During processing by injection molding and extrusion, the crosslinking is evident from gel formation and turbidity in the polymer.
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Bender Dietmar
Gausepohl Hermann
Knoll Konrad
Naegele Paul
Niessner Norbert
BASF - Aktiengesellschaft
Buttner David
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