Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2000-08-29
2002-04-09
Mullis, Jeffrey (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S098000
Reexamination Certificate
active
06369160
ABSTRACT:
The invention relates to polymer mixtures comprising
P1) from 1 to 85% by weight of an elastomeric block copolymer which has been built up from hard blocks S made from vinylaromatic monomers and from random soft blocks B/S made up from dienes and from vinylaromatic monomers, and which contains at least the block structure S-B/S-S, where the diene content is less than 50 percent by weight and the proportion of the soft phase formed from the blocks B/S is at least 60 percent by weight, based in each case on the entire block copolymer,
P2) from 5 to 89% by weight of a block copolymer differing from P1) and made from vinylaromatic monomers and from dienes,
P3) from 10 to 94% by weight of glass-clear or impact-modified polystyrene or mixtures thereof, and
P4) from 0 to 84% by weight of other additives,
where the total of components P1) to P4) is 100%.
The invention also relates to the use of the polymer mixtures for producing fibers, films or moldings, and also to the resultant fibers, films and moldings.
WO 96/20248 describes impact-modified, thermoplastically processable mixtures of elastomers and thermoplastics. The elastomers used may be styrene-butadiene block copolymers with a flexible soft block B/S with a random styrene-butadiene sequence and hard blocks S made from styrene. These block copolymers are used in thermoplastics for impact modification. The thermoplastics mentioned are, inter alia, glass-clear or impact-modified polystyrene or styrene-butadiene block copolymers. During processing these exhibit improved mechanical properties and low shrinkage of the moldings. The use of such polymer mixtures for producing flexible, transparent films is described in WO 96/23823.
The toughness of thermoplastics can be increased by adding butadiene rubbers or styrene-butadiene block copolymers. However, with this there is usually an associated reduction in stiffness. In addition, high butadiene proportions in the polymers used for impact modification can lower heat resistance and weathering resistance. High proportions of rubbers or of block copolymers also make the corresponding thermoplastic molding compositions more expensive.
It is an object of the present invention to provide polymer mixtures which are easy to process and have high ultimate tensile strength together with stiffness which can be adjusted over a wide range. Compared with conventional polystyrene mixtures, the polymer mixtures should have the same elongation at break with a very low proportion of butadiene-containing polymers.
We have found that this object is achieved by means of the polymer mixtures mentioned at the outset.
The novel polymer mixtures comprise, as component P1), from 1 to 85% by weight, preferably from 2 to 62% by weight, particularly preferably from 5 to 35% by weight, of an elastomeric block copolymer which has been built up from hard blocks S made from vinylaromatic monomers and from random soft blocks B/S made from dienes and from vinylaromatic monomers, and which contains at least the block structure S-B/S-S, where the diene content is less than 50 percent by weight and the proportion of the soft phase formed from the blocks B/S is at least 60 percent by weight, based in each case on the entire block copolymer.
A feature of the block copolymers P1) is that a block B/S of random structure and made from diene units and from vinylaromatic units occurs as soft phase instead of a pure polydiene block in a vinylaromatic-diene block copolymer made from blocks forming hard (block type S) and soft phases. The structure here along the chain may, on average statistically, be homogeneous or inhomogeneous.
An elastomeric block copolymer of this type according to the invention is obtained within the abovementioned parameters by forming the soft phase from a random copolymer of a vinylaromatic compound with a diene. Random copolymers of vinylaromatic compounds and dienes are obtained by polymerization in the presence of a polar cosolvent or of a potassium salt.
The random incorporation of the vinylaromatic compound into the soft block of the block copolymer and the use of Lewis bases during the polymerization affect the glass transition temperature (T
g
). The glass transition temperature of the soft block B/S is preferably from −50 to +25° C., preferably from −50 to +5° C., particularly preferably from −50 to −15° C.
The glass transition temperature of the hard block S is preferably above 25° C., particularly preferably above 50° C.
The molar mass of a block S is preferably from 1000 to 200,000 g/mol, in particular from 5000 to 50,000 g/mol. It is very particularly preferable for the molar mass of a block S to be from 10,000 to 20,000 g/mol. Blocks S within a molecule may have various molar masses.
The molar mass of the block B/S is usually from 2,000 to 250,000 g/mol and preferably from 20,000 to 150,000 g/mol.
Block B/S, like block S, may assume various molecular weights within a molecule.
Preferred polymer structures are S-B/S-S, X-[-B/S-S]
2
and Y-[-B/S-S]
2
. X is the radical of a bifunctional coupling agent and Y is the radical of a bifunctional initiator. The random block B/S may itself again be subdivided into blocks (B/S)
1
-(B/S)
2
-(B
3
/S)
3
- . . . The random block is preferably composed of from 2 to 15 random sub-blocks, particularly preferably from 3 to 10 sub-blocks. Dividing the random block B/S into very many sub-blocks (B/S)
n
has the important advantage that the B/S block overall behaves as an almost perfect random polymer even if there is a gradient in its make-up within a sub-block (B/S)
n
, as is difficult to avoid in anionic polymerization under industrial conditions (see below). It is therefore possible to use less than the theoretical amount of Lewis base. This increases the proportion of 1,4-diene linkages, lowers the glass transition temperature T
g
and reduces the tendency of the polymer to crosslink.
Preference is given to a block copolymer of one of the formulae S-B/S-S,
where
S is a vinylaromatic block and
B/S is the soft phase made from a block built up randomly from diene units and vinylaromatic units.
The soft phase may be subdivided into blocks (B/S)
1
-(B/S)
2
, where the indices 1 and 2 represent different structures in the sense that the vinylaromatic/diene ratio is different in the individual blocks B/S or changes continuously within a block within the limits (B/S)
1
(B/S)
2
, where the glass transition temperature T
g
of each sub-block is less than 25° C.
Particular preference is given to a soft block B/S which has been subdivided into more than one block (B/S)
n
of identical make-up.
Preference is also given to a block copolymer which has, in each molecule, more than one block B/S and/or S with different molar mass.
Preferred vinylaromatic compounds for the purposes of the invention are styrene and also &agr;-methylstyrene and vinyltoluene, and also mixtures of these compounds. Preferred dienes are butadiene and isoprene, and also piperylene, 1-phenylbutadiene and mixtures of these compounds.
A particularly preferred monomer combination is butadiene and styrene. All of the weight and volume data below are based on this combination. If the technical equivalents of styrene and butadiene are used, the data must be recalculated as appropriate.
The soft block B/S is preferably composed of 75 to 30% by weight of styrene and from 25 to 70% by weight of butadiene. A particularly preferable soft block B/S has a butadiene proportion of from 35 to 70% and a styrene proportion of from 65 to 30%.
In the case of the monomer combination styrene/butadiene, the proportion by weight of the diene in the entire block copolymer is from 15 to 50% by weight, and that of the vinylaromatic component is correspondingly from 85 to 50% by weight. Particular preference is given to butadiene-styrene block copolymers with a monomer make-up of from 25 to 40% by weight of diene and from 75 to 60% by weight of vinylaromatic compounds.
The block copolymers P1) are obtainable by anionic polymerization in a non-polar solvent with addition of
Gausepohl Hermann
Knoll Konrad
Niessner Norbert
Wünsch Josef
BASF - Aktiengesellschaft
Keil & Weinkauf
Mullis Jeffrey
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