Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2000-11-30
2002-01-22
Pezzuto, Helen L. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S207000, C526S236000, C526S320000, C525S303000
Reexamination Certificate
active
06340733
ABSTRACT:
The present invention relates to a functionalised polymer, a method of producing same and curable compositions containing same.
Conventional curable compositions, in particular those susceptible to curing by exposure to radiation such as UV light, contain functionalised oligomeric species. Such oligomeric species tend to be based on acrylated-epoxy, acrylated-polyester or acrylated-urethane resins and to have molecular weights (number average) of from 500 to 2000. The composition is cured by the reaction of the acrylate functional groups.
Additionally, such conventional curable compositions may also contain reactive monomeric species such as isobornyl acrylate, hexanediol diacrylate, tripropylene glycol diacrylate and trimethylol propane triacrylate.
These conventional curable compositions often shrink during curing. However, this tendency may be combated by the inclusion of a relatively high molecular weight (number average) copolymer, i.e. greater than 2000. The copolymer is present as a solute and the oligomeric species and (when present) reactive monomeric species act as a solvent. The copolymer is typically a random copolymer formed from two or more of methyl methacrylate, n-butyl methacrylate, ethyl methacrylate and methacrylic acid monomers.
In order to further improve the properties of the curable composition, it would be very desirable to cross-link the copolymer with the functional, e.g. acrylate, groups of the oligomeric species and (when present) reactive monomeric species during curing. However, such cross-linking would require the copolymer to have pendant reactive groups of similar structure to the functional groups of the oligomeric species and also of the reactive monomeric species. This would be difficult to achieve by using multifunctional monomers to make the functional copolymer because pendant reactive groups present on the monomers, which would participate in such a cross-linking reaction, would also participate in the polymerisation process to provide a prematurely cross-linked structure. In order to overcome this problem a copolymer with a suitable pendant group could be functionalised by esterification at 80-100 deg C for example as described in CHEMISTRY & TECHNOLOGY OF UV & EB FORMULATION FOR COATINGS. INKS & PAINTS, VOLUME 2. Prepolymers and Reactive Diluents for UV and EB Curable Formulations, N. S. Allen et al, page 124—Formation of a Polyester Acrylate. However at the reaction temperature for esterification the functionalised pendant reactive groups may react to form a prematurely cross-linked structure.
It is also desirable to be able to functionalise the copolymer in a solvent which is the functionalised oligomeric species and possibly the reactive monomeric species but this is currently not possible because at such high esterification temperatures the oligomeric and monomeric species would be likely to polymerise and react with the functionalised copolymer leading to premature polymerisation and cross-linking. Thus far no practical method of preparing such a functionalised copolymer has been identified.
It is an object of the present invention to provide such a functionalised copolymer, a new method for its preparation and a curable composition containing such a functionalised copolymer.
Accordingly in a first aspect the present invention provides a copolymer of general formula (I)
wherein A is a residue of at least one (meth)acrylate monomeric species, B is a residue of at least one monomeric species copolymerisable with A, R is a (meth)acrylate functionalised pendant ester group, X
1
and X
2
are terminal groups which may be the same or different, n and p are both at least one and are chosen such that the copolymer has a number average molecular weight of more than 2000.
In a second aspect, the present invention provides a process for the preparation of a copolymer (I)
wherein A is a residue of at least one (meth)acrylate monomeric species, B is a residue of at least one monomeric species copolymerisable with A. R is a (meth)acrylate functionalised pendant ester group, X
1
and X
2
are terminal groups which may be the same or different, n and p are both at least one and are chosen such that the copolymer has a number average molecular weight of more than 2000 which process comprises the steps of
(i) polymerising by free radical polymerisation the at least one (meth)acrylate monomeric species providing residue A with the monomeric species providing residue B to form a copolymer of general formula (II)
wherein A, B, X
1
, X
2
, n and p are as defined above and Y is a pendant reactive group capable of undergoing esterification;
(ii) dissolving the copolymer (II) in a solvent; and thereafter
(iii) esterifying the pendant group Y with a moiety that carries both a reactive group Q capable of undergoing esterification with the group Y and also a (meth)acrylate group so as to form groups R in the presence of a reagent of the general formula (III)
Z
1
−N=C=N−Z
2
(III)
wherein Z
1
and Z
2
are end groups which are capable of assisting in the solubilisation of the reagent by the solvent.
In a third aspect, the present invention provides a curable composition which comprises a solution of a copolymer of general formula (I)
wherein A is a residue of at least one (meth)acrylate monomeric species, B is a residue of at least one monomeric species copolymerisable with A, R is a (meth)acrylate functionalised pendant ester group, X
1
and X
2
are terminal groups which may be the same or different, n and p are both at least one and are chosen such that the copolymer has a number average molecular weight of more than 2000 in a solvent, which solvent is a functionalised oligomeric species having number average molecular weight of 2000 or less and/or a reactive monomeric species.
In a fourth aspect, the present invention provides a coating formed by curing a curable composition comprising a solution of a copolymer of general formula (I)
wherein A is a residue of at least one (meth)acrylate monomeric species, B is a residue of at least one monomeric species copolymerisable with A, R is a (meth)acrylate functionalised pendant ester group, X
1
and X
2
are terminal groups which may be the same or different, n and p are both at least one and are chosen such that the copolymer has a number average molecular weight of more than 2000 in a solvent, which solvent is a cross-linkable oligomeric species and/or reactive monomeric species having number average molecular weight of less than 2000.
Suitable (meth)acrylate monomeric species which can provide residues A include lower alkyl, i.e. C
1
to C
20
alkyl, (meth)acrylates, e.g. methyl methacrylate, ethyl methacrylate, propyl methacrylate, n-butyl methacrylate, iso-butyl methacrylate, t-butyl methacrylate, 2-ethyl hexyl methacrylate, octyl methacrylate, ethyl acrylate, butyl acrylate. Additionally, cyclic alkyl monomeric species may be used such as cyclohexyl methacrylate and isobornyl methacrylate. Preferably, mixtures of such monomeric species are used in order to optimise the characteristics of the copolymer. In particular, combinations of methyl methacrylate with one or more of n-butyl methacrylate and ethyl methacrylate may be used to good effect.
Suitable monomeric species which can provide residues B include hydroxy alkyl (meth)acrylates such as hydroxyethyl methacrylate (HEMA), hydroxypropyl methacrylate, hydroxybutyl methacrylate, hydroxyethyl acrylate, hydroxypropyl acrylate and hydroxybutyl acrylate; acid containing monomers such as methacrylic acid and acrylic acid; and amine containing monomers such as amino ethyl methacrylate and amino ethyl acrylate.
A and B may be the same or different.
The terminal groups X
1
and X
2
are determined by the monomeric species used and also the reagents used in the free radical polymerisation of the monomers. Additionally, it may be possible to further functionalise the copolymer so that one or other or both are a group R.
The group R is a (meth)acrylate functionalised pendant ester group. Preferably the (meth)acr
Chisholm Michael Stephen
Harte Helen
Slark Andrew Trevithick
Imperial Chemical Industries PLC
Pezzuto Helen L.
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