Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From carboxylic acid or derivative thereof
Reexamination Certificate
2000-07-23
2001-12-04
Hampton-Hightower, P. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From carboxylic acid or derivative thereof
C528S354000, C528S355000, C528S359000, C502S152000
Reexamination Certificate
active
06326459
ABSTRACT:
This application is an application under 35 U.S.C. Section 371 of International Application Number PCT/FR98/02181 filed on Oct. 12, 1998.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a catalytic composition based on a grafted metal oxide, to its preparation and to its use in a process of polymerization by opening oxygenated rings.
2. Description of the Related Art including information disclosed under 37 C.F.R. 1.97 and 1.98
Polymerization by opening oxygenated rings, for example lactones or lactides, is well known. Metal alkoxides are used as initiators, for the reaction. These initiators are used in homogeneous medium and they have been found to be effective. However, they have drawbacks. Firstly, their solubility is low. In addition, during their use, aggregations of the alkoxide molecules occur, leading to the existence of several families of active centres, which has the consequence of producing a wider molecular mass distribution of the polymer obtained. Finally, it is occasionally difficult to separate the initiator from the polymer formed, thereby compromising the purity of this polymer.
It would thus be desirable to have available a heterogeneous catalyst.
One object of the invention is to provide such a catalyst.
BRIEF SUMMARY OF THE INVENTION
With this aim, the composition of the invention comprises a support chosen from the group of metal oxides capable of containing hydroxyl functions, onto which is grafted a group of formula (1) —M(OR)
n
in which M is an element chosen from scandium, zirconium, hafnium, niobium, tantalum, rare-earth metals and actinides, R is an organic group and n is an integer greater than or equal to 1.
The invention also relates to a process for preparing this composition, which is characterized in that a suspension of the abovementioned support is formed and this suspension is then placed in contact and reacted with a compound of formula (2) M(OR)
n+1
in which M, R and n are defined as above.
Finally, the invention relates to a process of polymerization by opening oxygenated rings, which is characterized in that a composition as defined above is used as catalyst, in the presence of a protic compound.
Other characteristics, details and advantages of the invention will emerge even more fully on reading the description which follows, as well as the various concrete but non-limiting examples intended to illustrate it.
DETAILED DESCRIPTION OF THE INVENTION
The composition of the invention comprises a support which is chosen from the group of metal oxides capable of containing hydroxyl functions (—OH functions). Oxides of this type which may be mentioned are silica SiO
2
, alumina Al
2
O
3
, zirconium oxide ZrO
2
, cerium oxide CeO
2
, titanium oxide TiO
2
and thorium oxide. Mention may also be made of supports based on combinations or mixtures of these oxides. CeO
2
/ZrO
2
mixtures may be indicated more particularly, the respective proportions of the two oxides possibly varying within wide ranges. Mention may also be made of silica/alumina combinations or zeolites.
The support for the composition of the invention comprises, grafted to its surface, a group of formula (1) —M(OR)
n
. The term “grafted” means that the group is chemically bonded to the support, in particular by a bond of covalent type. This grafting takes place using the hydroxyl groups of the support to give a bonding sequence A—O—M(OR)
n
, A representing the metal element of the support. In the case of silica, for example, and using the silanol groups thereof, this will give Si—O—M(OR)
n
bonding sequences on the surface of the support.
In the group of formula (1), M is chosen from scandium, zirconium, hafnium, niobium, tantalum, rare-earth metals and actinides.
The expression “rare-earth” means the elements of the group consisting of yttrium and the elements of the Periodic Table of atomic number between 57 and 71 inclusive. The element M can be, more particularly, yttrium, lanthanum, samarium or neodymium.
In the case of the actinides, M can be, more particularly, uranium.
R is an organic group. It is generally a group containing from 1 to 100 carbon atoms, in particular from 1 to 50 carbon atoms. R can comprise one or more hetero atoms such as halogens, nitrogen, oxygen, sulphur, and phosphorus. R can be, more particularly, a saturated or unsaturated, linear or branched alkyl group, an aryl group, an aralkyl group or an alkaryl group. According to one specific embodiment, R is an alkyl group comprising from 1 to 18 carbon atoms such as a propyl group.
The value of n is not more than v−1, v being the maximum valency of the element M.
Preferably, the support is a support which has undergone a heat treatment, the purpose of which is to remove the free or adsorbed water, on the one hand, and, on the other hand, to control the density or the content of hydroxyl functions in the support. This content can be assayed chemically, for example by reaction of triethylaluminium and measurement of the volume of ethane gas evolved. It is thus sought by this heat treatment to obtain a density of hydroxyl functions which allows the metal to be bound to the support as far as possible by a single chemical bond.
In the case of silica, a silica with a BET specific surface from about 100 to about 700 m
2
/g, more particularly between 250 and 350 m
2
/g, is preferably used. For alumina, this surface can be between 150 and 250 m
2
/g.
The expression “specific surface” means the BET specific surface determined by adsorption of nitrogen in accordance with ASTM standard D 3368-78 established from the Brunauer-Emmett-Teller method described in the periodical “Journal of the American Chemical Society, 60, 309 (1938)”.
The process for preparing the composition of the invention will now be described.
This process comprises the formation of a suspension of the support and the reaction of this suspension with a compound of formula (2) M(OR)
n+1
. The reaction takes place between the hydroxyl groups of the support and this compound to give the bonds which have been described above.
Preferably, the suspension is formed and the reaction is carried out under anhydrous conditions and in a solvent for the compound of formula (2). The solvent is generally a polar or non-polar anhydrous aprotic liquid. It can be chosen more particularly from products that are liquid under normal temperature and pressure conditions, for example hexane, benzene, toluene, xylenes, 1,2-dichloroethane, acetonitrile, dimethyl, sulphoxide, dimethylformamide and hexamethyl-phosphorotriamide.
The reaction is preferably carried out with an excess of the compound of formula (2) relative to the number of hydroxyl (—OH) sites present at the surface of the support. This excess can be from 1.5 to 2 times the number of hydroxyl sites.
The reaction is carried out by heating the reaction medium to a temperature which is not critical, which depends in particular on the nature of the solvent and which can be, for example, between 40 and 100° C.
After the reaction, the product obtained is separated from the reaction medium by any known means and maintained under an anhydrous atmosphere. After separation from the reaction medium, it can be washed with the abovementioned solvent. It is finally dried. If necessary, it can be stored in this same solvent.
According to one preferred variant, the support is subjected to a prior heat treatment. As indicated above, the purpose of this heat treatment is to obtain, a support without free or adsorbed water and with a controlled content of hydroxyl functions. This heat treatment is usually carried out by heating to temperatures of between 130° C. and 900° C. under vacuum or under inert gas. These temperatures depend on the nature of the support. They should be high enough to allow the removal of the free or adsorbed water and the control of the content of hydroxyl functions, but they should not exceed the temperatures of onset of sintering of the support concerned. Infrared analysis, for example, of the heat-treated support makes it possible to check whether
Delaite Christelle
Hamaide Thierry
Spitz Roger
Tortosa Karine
Hampton-Hightower P.
Rhodia Chimie
Seugnet Jean-Louis
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