Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2002-02-06
2003-09-09
Lu, Caixia (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S160000, C526S165000, C526S293000, C525S242000, C525S288000
Reexamination Certificate
active
06617410
ABSTRACT:
The present invention relates to random copolymers of propylene as main recurring units comprising recurring units deriving from styrene. The present invention also relates to functionalized copolymers and graft copolymers. The invention, moreover, relates to processes for the production of said copolymers.
The present invention lies in the technical field of the production of thermoplastic materials.
As it is well known, plastic materials based on isotactic polypropylene are among the most interesting ones from the technology viewpoint. In fact, they are not only competitive from a cost perspective, but are also suitable for various applications due to suitable chemical and physical modifications.
The chemical modification mostly used in the industry is the random copolymerisation of propylene with small amounts of one or more comonomer(s), generally ethylene or butene-1. Said modification allows to obtain materials that have a lower melting temperature (above all used for producing films with thermoweldable layers), lower stiffness, higher impact resistance at low temperatures and a higher transparency than the isotactic propylene homopolymer.
The above mentioned variations in physical properties with respect to the homopolymer are due to lower crystallinity and smaller size of crystallites caused by the comonomer units.
It is worth noting that ethylene and butene-1 recurring units have a sterical hindrance similar enough to propylene recurring units. Consequently, although they cause a decrease in packing energy, they are partially enclosed as defects in the crystalline phase. As it is well known, generally speaking, in semicrystalline polymeric materials one obtains a more efficient decrease in crystallinity and size of crystallites when one uses comonomer units with much higher hindrance than the basic monomer units, i.e. such that they have inevitably to be excluded from the crystalline phase.
In this connection, there is however the problem that hindered and cheap comonomers, such as styrene, are not easily copolymerisable with propylene, because generally catalytic sites suitable for the isotactic polymerisation of propylene are not capable of polymerising styrene and vice-versa. In fact, generally speaking, catalytic systems suitable for the polymerisation of 1-alkenes to isotactic polymers, such as metallocene- and methylalumoxane-based catalysts, are not capable of polymerising styrene. On the contrary, styrene tends to act as a poison in such processes. It is worth noting that in case of heterogeneous catalysts, which typically contain different types of catalytic sites, it is possible to polymerise mixture of the said two monomers but mixtures of the two homopolymers are mostly obtained.
Another disadvantage of known random copolymers based on propylene produced by heterogeneous catalysts is that macromolecules do not have a homogenous content of the comonomer units, so that the fractions with a higher comonomer content are more easily extractable with solvents. This evidently limits their use for preparing articles to be used in contact with foods.
European patent application EP-A-872 492 discloses catalytic systems based on stereorigid metallocenes that contain a metallic atom belonging to the IV group of the Periodic Table and whose substituted cyclopentadienyl groups are bridged through a single atom. Said metallocenes are capable of copolymerising olefins with vinyl aromatic compounds. As disclosed in the patent application, such catalyst systems, however, produce copolymers containing blocks of styrene units. This is, for instance, shown by the Nuclear Magnetic Resonance spectrum of
FIG. 29
, therein.
It has now been produced a random copolymer of propylene that has a homogeneous distribution of recurring units deriving from styrene in the polymer chain.
Thanks to the homogeneous distribution of the styrene recurring units in the polymer chain, the copolymers of the instant invention essentially show no variation of the glass transition temperature compared with isotactic polypropylene. For example, in the case of propylene copolymers of the present invention, no increase of the glass transition temperature higher than 10° C. compared with isotactic polypropylene is observed, e.g., if the T
g
is measured by Differential Scanning Calorimetry at a rate of 10° K per minute, its value does not exceed 0° C.
It is important to note that possible random copolymers of propylene with styrene or substituted styrenes would present a substantial increase of the glass transition temperature (T
g
) in comparison with the propylene homopolymer, approximately according to the Fox relation:
1
/T
g
=W
prop
/T
g prop
+W
styr
/T
g styr
where W
prop
and W
styr
are respectively propylene and styrene fractions by weight and T
g prop
and T
g styr
are respectively the glass transition temperatures of polypropylene and polystyrene homopolymers. Since the glass transition temperatures of the styrene polymers are much higher than that of polypropylene and the molecular mass of the styrenic units is much larger than that of the propylene unit, a substantial increase of the glass transition temperature should be observed also in cases of a low content by mole of the styrenic units and this would make said materials unusable in applications which demand a low running temperature.
As another advantage, some of the copolymers of the present invention can be used for preparing functionalized polypropylene as well as graft copolymers.
The present invention provides, therefore, new isotactic-polypropylene-based copolymers having a homogenous distribution of recurring units of the formula (1):
where R is a hydrogen, halide radical or a hydrocarbyl radical optionally containing an atom selected from oxygen, nitrogen, sulphur, phosphorus and silicon and n is an integer ranging from 1 to 3.
The copolymers of the present invention contain the recurring units of formula (1) preferably in amounts ranging from 0.1 to 30% by weight.
Said copolymers have a
13
C-NMR spectrum wherein the resonance signals attributed to the links between different monomeric units fall around 30, 34, 35, 45 and 47 ppm and present intensities at least 2 times higher than the resonance signals attributed to styrene—styrene sequences around 41 ppm and 44-46 ppm (all chemical shifts are relative to tetramethylsilane). In particular, for the case where R of formula (1) is hydrogen, that is for styrene-ethylene comonomer units, the resonance signals attributed to the links between different monomeric units fall at 30.3, 33.9, 34.6, 44.8, and 46.9 ppm.
The polymerisation degree of the copolymers of the present invention is normally at least 50.
When R is a substituent containing carbon atoms, it can be selected from C
1
-C
20
alkyl radicals, linear or branched, C
3
-C
20
cycloalkyl radicals and C
6
-C
20
aryl radicals. The alkyl radicals may be saturated or unsaturated radicals. The preferred radicals are metyl, ethyl, isopropyl, vinyl and allyl radicals.
Said substituent R may contain a functional group, such as —NR
2
, where R is an alkyl group as above defined.
Preferably the sequences of propylene recurring units are mainly isotactic. Generally, the content of meso diads (m) is higher than 80%.
The amount of the structural units of formula (1) in the copolymer may be determined on the basis of the intensity of specific signals in the
13
C nuclear magnetic resonance spectra. For example, in the case of propylene copolymers with styrene the presence of said structural units is put in evidence by signals in the aliphatic region at 33.9 and 25.2 ppm (chemical shift from tetramethylsilane, TMS) and the molar fraction of the styrenic units (X
s
), equal to the molar fraction of the connected ethylenic units, can be obtained by the following relation:
X
s
=
0.5
A
33.9
+
A
25.2
(
0.5
A
33.9
+
A
25.2
)
+
(
0.5
A
33.9
+
A
25.2
+
A
24.4
)
+
(
A
44.8
+
0.5
A
34.6
+
A
45.4
+
0.5
A
36.9
)
where A
x
is the intensity of the signal at x ppm.
Depending on the polymerization conditions, random
Caporaso Lucia
Guerra Gaetano
Izzo Lorella
Oliva Leone
Resconi Luigi
Basell Polyolefine GmbH
Lu Caixia
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