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
1999-07-08
2001-02-06
Dawson, Robert (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C528S015000, C528S031000, C528S035000, C424S010400
Reexamination Certificate
active
06184313
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to silane and carbosilane dendrimers having bridge moieties at the periphery, and to star polymers formed by attaching arms to sites on the bridge. The arms are polymers formed in situ from monomers at initiator sites on the bridge, or preformed polymer attached at reactive sites on the bridge. The bridge may be selected alkyl, cycloalkyl, aryl, alkaryl, aralkyl, small polyether or small polysulfide groups. The arms may be polyethers, polysulfides or polyesters. Copolymers of these polymer types may be used.
BACKGROUND AND PRIOR ART
Recently polyethers of the type of poly(ethylene oxide) (PEO) and poly(ethylene glycol) (PEG) have found application in biological and pharmaceutical contexts because of properties including water solubility, biocompatibility e.g. non-thrombogenic, and terminal hydroxy groups to attach various entities including drugs, prodrugs and other biological agents.
These polyethers (PEO, PEG) have been used as outer arms in star polymers where the cores have been divinylbenzene (may be cross-linked), poly(ethylene imine), poly(amidoamines) and heptaphenyl. See for instance:
U.S. Pat. No. 5,275,838, Jan. 4,1994, Merrill; and
U.S. Pat. No. 5,648,186, Jul. 15, 1997, Daroux et al.
Polyester arms formed by ring-opening polymerization of lactones, lactides and glycolides have been used with cores of polyesters, sugar type molecules or inositol, to form star polymers. See for instance:
U.S. Pat. No. 5,225,521, Jul. 6, 1993, Spinu.
Carbosilane dendrimers have been used as cores in hybrid dendrimer-star polymers. These dendrimers provide a non-polar and chemically inert scaffold that is advantageous when thermal and hydrolytic stability is required, and in hydrophobic environments. See for example:
U.S. Pat. No. 5,276,110, Jan. 4, 1994, Zhou et al.
When these carbosilane dendrimers, having peripheral silane termini, were used as cores with arms of poly(alkylene oxide), it was found that the core-arm interface was unduly susceptible to hydrolysis in some applications. It would be desirable to reconfigure this interface in order to reduce susceptibility to hydrolysis.
The periphery of carbosilane dendrimers having outer allyl silane groups, has been modified to introduce hydroxy groups by controlled oxidation. See Lorenz et al in: Macromolecules 28, 6657-6661 (1995). No outer arms of any type of polymer were incorporated in this reference.
We have studied modifying the outer surface of carbosilane dendrimers to reduce hydrolytic cleavage at the core-arm interface when arms of polyalkylene oxide and the like are used in hybrid dendrimer-star polymers.
SUMMARY OF THE INVENTION
It has now been found that by inserting selected bridge molecules at the core-arm interface (when the core is silane or carbosilane and the arm is polyether, polysulfide or polyester) the susceptibility to hydrolysis is reduced significantly. In this context by hydrolysis is meant the breaking of chemical bonds at the dendrimer periphery and the release of functional groups or polymer chains from the dendrimer-polymer hybrid.
The invention includes a silane- or carbosilane-based, periphery-modified dendrimer, adapted to serve as core in hybrid dendrimer-star polymers, comprising:
a) an inner structure having a central silane nucleus and, optionally, multiple carbosilane branches extending outwardly from the nucleus in a repetitive generational manner yielding silane termini;
and, attached to the silane or silane termini by a hydrolysis-resistant bond;
b) bridge moieties comprising groups selected from alkyl of at least 4 C atoms, cycloalkyl, aryl including aralkyl and alkaryl, and polyether and polysulfide of up to about 6 repeating units, the moieties having reactive groups enabling attachment of polymer arms thereto.
The invention also includes a hybrid dendrimer-star polymer, comprising:
(i) the modified dendrimer described in the previous paragraph except that the alkyl bridge moiety has at least 2C atoms, and
(ii) outer arms comprising polymer chains selected from polyethers, polysulfides, polyesters and copolymers thereof, the arms being attached to the dendrimer at the sites of the bridge reactive groups.
The invention further includes a process of preparing a hybrid dendrimer-star polymer including a modified silane or carbosilane dendrimer and selected polymer outer arms, comprising:
a) attaching bridge moieties to reactive silane sites in a silane or carbosilane dendrimer, the bridge comprising a group selected from alkyl, cycloalkyl, aryl, aralkyl, alkaryl, small polyether and small polysulfide, the bridges having reactive groups thereon; and
b) reacting a selected form of the bridge reactive groups with one of:
(i) monomer selected from alkylene oxide, alkylene sulfide, alkylene glycol, alkylene dithiol, and hydroxyalkanoic acid and lactone thereof, under polymerization conditions, said selected form serving as initiator, to form polymer arm attached to the bridge; and
(ii) functionalized prepolymer selected from polyether, polysulfide, polyester and copolymers thereof, to attach prepolymer to the bridge, thereby to form the star polymer.
A primary aspect of the invention may be defined as: in a star polymer having a silane or carbosilane core and outer arms comprising polymer selected from polyether, polysulfide, polyester and copolymers thereof, the improvement comprising selected bridge inserts positioned between the core and the arms, with the bridge attached to silicon atoms in the core or dendrimer by a Si—C bond, the length and type of the bridge and of the arm being selected to give desired properties e.g. hydrophilic/hydrophobic balance or solubility, to the polymer-dendrimer hybrid.
DETAILED DESCRIPTION
The silane or carbosilane core has a regular usually dendritic structure and is built up in stages or generations from a central silane or disilane nucleus e.g. by alternating hydrosilylation and vinylation or allylation reactions. Various dendritic carbosilanes are known and any would be operative provided that the bridges can be formed at the peripheral silane group. The core size can range from generation zero to generation 5 or even higher e.g. to 8. For generation zero, one or up to 5 silicon atoms can suffice.
The carbosilane dendrimers provide a non-polar and relatively inert scaffold that can be used under various reaction conditions including anionic polymerization conditions.
The bridge moiety is bonded to silane or to peripheral silane sites in the carbosilane dendrimer by a hydrolysis-resistant Si—C bond.
Preferably the bridge moiety is selected from
(1) —R—X; where R is selected from alkyl and cycloalkyl having from 4 to 18 C atoms; aryl, aralkyl and alkaryl having from 6 to 18C atoms; and X is hydroxyl, thiol, amine, carboxyl, aldehyde, halide or a protecting group therefor;
and
where R′ is alkyl having from 2 to 4C atoms, Y is oxygen or sulfur and n is 2 to 6, and the bridge-core attachment comprises the hydrolysis-resistant bond Si—C.
Preferred bridge members include (C
4
-C
9
alkyl)—Z, cyclohexyl, phenyl or benzyl or para-methylenephenyl)—Z, and
H where Z is a reactive group such as OH, —NH
2
or —COOH and n=2-6, as well as the corresponding thiols and thioethers. In the aryl, aralkyl and alkaryl bridge moieties the aryl may be phenyl or lower alkyl-substituted phenyl, naphthyl, biphenyl (may be alkyl-substituted) or pyridine, and the alkyl may be C
1
to C
6
straight chain or branched.
Where the bridge is cycloalkyl or aryl it is possible to have two reactive groups at selected locations on the ring or rings. This allows for doubling the number of arms and facilitates masking or isolation of the core, reduction of influence of core properties and/or increasing the number of modifiable functional groups.
Suitable protecting groups for the reactive groups on the bridge moiety are illustrated as follows:
Reactive Group
Protecting Group
hydroxyl
tetrahydropyran,
thiol
(S) -benzyl
amino
2,2,5,5-tetramethyl-1-aza-2,5-
disilacyclopentane
carboxylic acid
4,4′-dimethyl-2-oxazoline
aldehyde
acetal su
Comanita Bogdan
Roovers Jacques
Anderson J. Wayne
Dawson Robert
National Research Council of Canada
Zimmer Marc S.
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