Process for microgel preparation

Details Process for microgel preparation Process for microgel preparation

2001-01-12

2003-04-08

Nutter, Nathan M. (Department: 1711)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Mixing of two or more solid polymers; mixing of solid...

C525S193000, C525S194000, C525S195000, C525S196000

Reexamination Certificate

active

06545095

ABSTRACT:

The present invention relates to a process for the preparation of microgels and to a composition for use in such a process.
Microgels are macromolecules which possess a combination of very high molecular weight and a solubility and viscosity similar to linear or branched polymers of relatively low molecular weight. Microgels are an intermediate structure between conventional linear or branched polymers such as polyethylene or polycarbonate and networks such as vulcanised natural rubber. The dimensions of microgels are compatible with high molecular weight linear polymers but their structure resembles a network.
The properties of microgels make them particularly useful in a wide range of applications such as in additives, in advanced material formulations for foams or fibres, in coating compositions, binders and redispersible latexes. Microgels may also be used to improve the ease of processing and to improve the structural strength and dimensional stability of the final products. A further potential use for microgels is as additives for high impact polymers. Microgels embedded in a matrix of conventional linear polymer may act to stabilise the whole structure by distributing mechanical tension. Microgels are also useful in biological systems and as pharmaceutical carriers.
A number of methods have been used for the preparation of microgels, however these methods generally have a number of serious deficiencies. For example, extreme care is required in preparing microgels as the multiple double bonds present within these systems may readily undergo intermolecular reactions which can lead to intractable networks. Other procedures such as those described by OKay, O. and Funke, W. in
MACROMOLECULES,
1990, 23 at 2623-2628 require high purity solvent and reagents as well as an inert atmosphere and are complicated by undesirable side reactions. Despite the unique properties of microgels the difficulties in preparing them have limited their potential and commercial use.
Our copending application PCT/AU98/00015 discloses a process for microgel preparation involving reacting an alkoxy amine with a cross-linking agent.
SUMMARY OF THE INVENTION
We have now found that Microgels may be prepared using a range of living radicals or macromonomers allowing the formation of microgels with a vast range of monomers and under a wide range of conditions.
Accordingly, we provide a process for producing a microgel composition comprising reacting a living prepolymer component with a monomer component including a multi-olefinic monomer. The microgel product typically comprises a cross-linked core and a multiplicity of polymeric chains appended to the cross-linked core. The polymeric chains appended to the core have free ends and may interact with solvent.
The term living prepolymer where used herein refers to a polymer having a radical-terminating group adapted to reversibly cleave from the polymer under activating conditions to provide a reactive prepolymer radical.
The reaction between the living prepolymer and monomer component may be conducted in the presence of an initiator and/or catalyst.
The proportion of cross-linked core in the microgel composition is determined by the ratio of living prepolymer to monomer component. Preferably, the molar ratio of living prepolymer to monomer component is in the range of from about 0.05/1 to about 5/1.
The monomer component used in the process of the invention comprises a multi-olefinic monomer. In the preferred embodiments of the invention the monomer component additionally includes a mono-olefinic monomer. The ratio of the number of moles of multi-olefinic monomer to the number of moles of mono-olefinic monomer will determine the density of the cross-linked core. The mono-olefinic monomer acts as a spacer and in high proportions reduces the density of the core.
A range of known techniques may be used to prepare the living propolymer component. Typically, the process includes reacting a mono-olefinic monomer and initiator optionally in the presence of a catalyst. The mono-olefinic monomer used in preparation of the living prepolymer component may include monomer containing more than one double bond and which reacts to provide chain extension rather than cross-linking. Examples of such monomers include conjugated dienes and 1,5-dienes.
Throughout the description and claims of this specification, the word “comprise” and variations of the word, such as “comprising” and “comprises”, is not intended to exclude other additives or components or integers.
Methods for Preperation of Living Prepolymer
The living prepolymer may have a radical terminating group adapted to reversibly cleave from the prepolymer under activating conditions to provide a reactive prepolymer radical.
Examples of radical terminating group precursors include Lewis acids, mercaptans, disulfides, thiocarbamates and dithiocarbamates, dithioesters, transition metal carbonyls, stabilized carbon radicals, peroxides and azo initiators.
Typical examples of Lewis acid radical terminating group precursors include metal complexes such as CuX/2,2′-bipyridines, Mn(CO)
6
RuX
x
/PPh
3
, AR(OR)
3
, NiX/O,O′—(CH
2
Nme
2
)C
6
H
3
, NiX
2
/PPh
3
and FeX
2
/N(n-Bu)
3
wherein X is halogen and preferably chlorine or bromine. Lewis acid terminated prepolymer radicals may be prepared by a method of atom transfer radical polymerization which is hereinafter described.
The method of atom transfer radical polymerization (ATRP) may be represented as shown in the following scheme:
Initiation:
Propagation:
Initially, the transition metal species, M
t
n
, abstracts the halogen atom X from the organic halide, R—X, to form the oxidized species, M
t
n+1
X, and the carbon-centered radical R. In the subsequent step, the radical R., reacts with unsaturated monomer, M, with the formation of the intermediate radical species, R—M. The reaction between M
t
n+1
X and R—M results in the target product, R—M—X, and regenerates the reduced transition metal species, M
t
n
, which further reacts with R—X and promotes a new redox cycle. When polymeric halides, R—M—X, are reactive enough toward M
t
n
and monomer is in excess, a number of atom transfer radical additions, i.e., a “living”/controlled radical polymerization occurs. Further, details of this mechanism are described in the reference: Macromolecules, 1995, 28, 7901.
Another embodiment of ATRP is described in Macromolecules, 1995,28,7970 and Macromolecules, 1996,29,3665. These references report on the formation of “living” polymers using a combination of an arylsulfonyl chloride and a transition metal compound.
One part of the polymerization system in the process is an arylsulfonyl halide or an alkyl sulfonyl halide of the formula A
1
SO
2
X wherein A
1
is an aryl, substituted aryl group, an alkyl group or a substituted alkyl group, and X is chlorine, bromine or iodine. Included within the meaning of arylsulfonyl halide and alkylsulfonyl halide is any adduct, such as a 1:1 adduct, which is a reaction product of an aryl or alkyl sulfonyl halide and any polymerize vinyl monomer. In effect, such an adduct is one of the initial products in the polymerization process itself.
Another component of the ATRP system is a compound containing a lower valent transition metal atom. By this is meant a compound containing at least one transition metal atom that is capable of existing in a higher valent state. Included within the definition of a compound containing a transition metal atom in a lower valent state is a compound or combination of compounds that under the polymerization process conditions can form in situ the desired compound containing a transition metal atom in a lower valent state. In some cases this can include metal itself (or an alloy or a metal oxide thereof) which can either be dissolved or slightly dissolve in the process medium.
Suitable lower valent metals include Cu[I], Ru[I], Ni[II], Re[II], Pd[II], Cu[
0
], Ni[
0
], Fe[
0
], Pd[
0
], and Rh[II]. The

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