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
1995-02-06
2002-04-23
Wilson, D. R. (Department: 1713)
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
active
06376613
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to polyolefinic compositions having elastic properties and to the use thereof for the manufacture of shaped articles for biomedical use.
2. Description of the Prior Art
The most used material for the manufacture of flexible articles for biomedical use is represented by the plastified poly-vinyl chloride (PVC). The high characteristics of flexibility of the plastified PVC are due to the plasticizers contained in it.
However, the migration and extractability of plasticizers in biological liquids, with the consequent possible negative effects on the health of the patient represent a still unsolved drawback.
In addition, it has to be taken in mind the surface migration of the additives based on organo-polysiloxane oils used in PVC as external lubricants to give to the PVC surface a critical surface tension intended to avoid blood coagulation phenomena. In fact, the organo-polysiloxane compounds tend to exude from the PVC surface thus causing problems deriving from their poor compatibility with blood (see European patent application EP-A-287 482).
Therefore, the need of materials substitutive of PVC in these fields is highly felt.
Other materials suitable for the manufacture of flexible devices for biomedical use are the styrene-ethylene-butene-styrene block copolymers (SEBS). SEBS modified with polysiloxanes have been for example suggested as substitutive of PVC and silicon resins for the realization of some devices, such as endotracheal tubes (U.S. Pat. No. 4,386,179). These copolymers combine good properties of optical transparency and flexibility also at low temperatures.
U.S. Pat. No. 4,335,225 describes the preparation of high molecular weight polypropylene showing elastomeric characteristics and processable by the technologies of thermoplastic materials and suggests a possible use of this polypropylene for the manufacture of some articles for biomedical use. The polymerization is carried out using as catalyst the product of the reaction of an organic derivative of zirconium, generally tetra-neophil-zirconium, with hydroxilated alumina. However, the content of aluminium in the polymer obtained is always very high, higher than 1000 ppm. Till now, the above mentioned materials did not find any meaningful application in the biomedical field.
SUMMARY OF THE INVENTION
It has now unexpectedly been found a new polymeric material suitable for the manufacture of articles for biomedical applications, which combines a good set of mechanical properties with good optical properties and that, furthermore, does not show problems related to the extractability of metals in biological fluids.
Therefore, an object of the present invention is a thermoplastic composition comprising:
(A) from 1 to 99% by weight of a propylene amorphous polymer having the following characteristics:
[&eegr;]>1 dl/g
% syndiotactic diads (r)−% isotactic diads (m)>0;
less than 2% of the CH
2
groups contained in sequences (CH
2
)
n
, with n>2;
Bernouillianity index (B)=1±0.2;
(B) from 1 to 99% by weight of a component selected from:
(B
1
) a copolymer of propylene with at least a comonomer selected from ethylene and the &agr;-olefins of formula CH
2
═CHR wherein R is an alkyl radical containing from 2 to 8 carbon atoms, said copolymer containing at least 85%, preferably 90-99%, by weight of units deriving from propylene, and
(B
II
) a polyolefinic composition comprising:
(a) 10-50%, preferably 10-40% and more preferably 20-35%, by weight of at least a polymer selected from a propylene homopolymer having an isotactic index higher than 80, preferably higher than 85, and a copolymer of propylene with at least a comonomer selected from ethylene and the &agr;-olefins of formula CH
2
═CHR wherein R is an alkyl radical containing from 2 to 8 carbon atoms, said copolymer containing at least 85%, preferably 90-99%, by weight of units deriving from propylene,
(b) 0-20%, preferably 0-15%, by weight of a copolymer containing ethylene, insoluble in xylene at room temperature, and
(c) 40-80%, preferably 50-70%, by weight of a copolymer containing 10-40% by weight of units deriving from ethylene, 90-60% by weight of units deriving from at least a comonomer selected from propylene and the &agr;-olefins of formula CH
2
═CHR wherein R is an alkyl radical containing from 2 to 8 carbon atoms, 0-5% of units deriving from a diene, said copolymer being soluble in xylene at room temperature and having an intrinsic viscosity comprised between 1.5 and 4 dl/g;
wherein the sum of components (b) and (c) is. comprised between 50 and 90% by weight on the polyolefin olefinic composition and the ratio of the amounts by weight of components (b)/(c) is lower than 0.4.
Another object of the present invention is a shaped article for biomedical use, obtainable from a thermoplastic composition according to the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The ratio of the amounts by weight of components (A)/(B) in the composition of the present invention is preferably comprised between 10:90 and 90:10 and, more preferably, between 25:75 and 75:25.
The propylene polymers of the component (A) in the composition of the invention, together with the process for the preparation thereof, are described in the European patent application EP-A-604 917, the content of which is intended included in the present description.
These propylene polymers are amorphous, can be obtained directly from the polymerization reaction of propylene, and have the following characteristics:
(a) intrinsic viscosity [&eegr;] greater than 1 dl/g;
(b) the percentage of syndiotactic diads (r) minus percentage of isotactic diads (m) is greater than 0;
(c) less than 2% of the CH
2
groups are contained in sequences (CH
2
)
n
, with n greater than or equal to 2;
(d) Bernouillianity index (B)=1+0.2.
These propylene polymers are essentially free of crystallinity. Their melting enthalpy values are generally lower than 20 J/g and, preferably, lower than 10 J/g. In most cases, they have melting enthalpy values of 0 J/g.
Preferably, the above mentioned propylene amorphous polymers show intrinsic viscosity values higher than 1.5 dl/g and more preferably higher than 2 dl/g.
13
C-N.M.R. analysis carried out on the above mentioned ethylene amorphous polymer gives information on the tacticity of the polymeric chains, that is, on the distribution of the configurations of the tertiary carbon atoms.
The structure of these polymers appears substantially atactic. Nevertheless, it is observed that syndiotactic diads (r) appear to be more numerous than the isotactic ones (m). Preferably, %r−%m>5.
The Bernouillianity index (B), defined as:
B=4[mm] [rr]/[mr]
2
has values near the unit, in particular comprised within the range 0.8-1.2 and preferably comprised within the range 0.9-1.1.
The structure of these propylene polymers appear to be highly regioregular. In fact, from the
13
C-N.M.R. analysis signals relating to sequences (CH
2
)
n
, wherein n>2, are not detectable. Therefore, less than 2% and preferably less than 1% of CH
2
appears contained in sequences (CH
2
)
n
, wherein n>2.
Molecular weights of the above mentioned propylene polymers are not only high, but distributed within rather narrow ranges. An index of the distribution of molecular weight is represented by the ratio M
w
/M
n
which appears to be generally lower than 5, preferably lower than 4 and more preferably lower than 3.
The polyolefinic compositions which form the component (B
II
) of the composition according to the present invention, together with the process for the preparation thereof, are described in European patent application EP-A-472 946, the content of which is intended included in the present description.
The thermoplastic compositions according to the invention can contain additives able to give particular properties to the articles for the manufacture of which the composition is designed.
Additives useable are thos
Braga Vittorio
Pelliconi Anteo
Resconi Luigi
Silvestri Rosanna
Basell Technology Company BV.
Cave LLP Bryan
Wilson D. R.
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