Process for preparing polymeric microgels

Details Process for preparing polymeric microgels Process for preparing polymeric microgels

1999-09-07

2001-10-09

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...

C526S217000, C526S328000, C526S335000, C526S336000, C526S341000, C526S346000

Reexamination Certificate

active

06300443

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 internal 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.
According to the present invention we provide a process for preparation of a microgel comprising reacting an alkoxyamine with an unsaturated monomer composition comprising a cross-linking agent comprising at least two double bonds and optionally one or more further monomer selected from mono-unsaturated monomers and conjugated dienes.
In a particularly preferred aspect the invention provides a process for the preparation of a microgel polymer including the free radical polymerization of a composition including:
an alkoxyamine comprising an oligomer containing an aminoxy substituent; and
a cross-linking agent comprising at least two double bonds.
The microgel prepared by this aspect of the invention generally has linear arms which are linked via the cross-linking agent to provide a core in the form of a cross-linked network. This type of microgel may conveniently be referred to as a star microgel.
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.
The process of the invention may be carried out using various additives such as solvent, promoters or radical species. In some instances the efficiency of the process may be improved by the addition of nitroxide radical species such as TEMPO (tetramethyl-1-oxyl radical) or other nitroxide radical which is hereinafter described. It is believed that the nitroxide radical enables the molecular weight distribution to be controlled and provides rate enhancement in many cases. The use of nitroxide radicals in the process of the invention is particularly preferred when, in the alkoxy amine of Formula I n is zero or less than about 5. Radical initiators such as AlBN may also be used to provide rate enhancement.
The alkoxyamine used in the present invention is preferably of Formula I
wherein —(A)
n
X is a radical species capable of polymerising in the presence of the monomer component comprising the cross-linking agent. In the initiators of formula (I) the groups R
1
, R
2
, R
5
and R
6
are the same or different straight chain or branched substituted or unsubstituted alkyl groups of a chain length sufficient to provide steric hindrance and weakening of the O—(A)
n
X bond, and
R
3
and R
4
are the same or different straight chain or branched alkyl or substituted alkyl groups or R
3
CNCR
4
may be part of a cyclic structure which may have fused with it another saturated or aromatic ring. Mixtures of alkoxyamines may be used if desired.
In the group (A)
n
X the unit A is a monomer unit which, when there is more than one A, may be the same or different;
n is zero or greater than zero; and
X is an initiator fragment residue.
The proportion of components used in the process of the invention will generally depend on the desired properties of the microgel and the intended application. Generally the microgel is prepared using up to 60 mole percent of cross-linking agent based on moles of polymerizable components. More preferably the cross-linking agent will comprise up to 50 mole % of the total of the polymerizable components. Typically the alkoxyamine will compose from about 5 to about 95 mole % of the polymerizable components.
The present invention allows a higher proportion of cross-linking agent than has previously been possible for microgel compositions. Prior art microgels have generally been restricted to using no more than several mole percent of cross-linking agent. The ability to use high concentrations of cross-linking agent enables microgels to be prepared with a high density conferring significant advantages in rheology control. Accordingly it is preferred that the process of the invention use at least 5 mole percent of cross-linking agent based on total of the polymerizable components and most preferably from 10 to 50%.
In the process of the invention when the alkoxyamine contains from zero to 5 monomeric units (ie. n is from 0 to 5) then it is particularly preferred that the monomer composition include a further monomer such as a mono-unsaturated monomer or conjugated diene monomer. As the number of monomer units decreases the improvement provided by using a mono-unsaturated monomer increases. When n is 0 or 1 a further monomer is typically used.
Typically when the number of monomeric units is less than 5 the mono-unsaturated monomer will be present in up to 80 mole % based on the total number of moles of polymerizable components and more preferably from 10 to 80%. In this embodiment the alkoxyamine is typically present in an amount of at least 5 mole % and preferably in an amount of from 5 to 60%.
When preparing star microgels it is preferred that the number of monomeric units (A) in the alkoxyamine is at least 3 and more preferably at least 5. In this embodiment the alkoxyamine will typically comprise from 50 to 95 mole % of the total polymerizable component and the mono-unsaturated monomer may comprise from 0 to 45 mole %.
The one or more further monomers when used in the process of the invention, may be any well known monounsaturated monomer such as an alkene, acrylate, methacrylate, styrene or styrenic monomer, acrylonitrile or substituted acrylonitrile, or a conjugated diene monomer such as butadiene, isoprene, chloroprene, cyclopentadiene vinyl acetate, vinylidene chloride and polyvinylidene dichloride.
The properties of the microgel and its reactivity in subsequent applications may be controlled by the choice of monomers and their functional groups. Examples of monomers include C
1
to C
10
alkenes, alkylacrylates, alkylmethacrylates, hydroxyalkylacrylates, hydroxyalkylmethacylates, haloalkylacrylates, haloalkylmethacrylates. alkoxyalkylacrylates, alkoxyalkylmeth acrylates, optionally mono N-substituted or di-N-substituted aminoalkylmethacrylates, cycloalkylaerylates, cycloalkylmethacrylates, phenoxyacrylate, phenoxymethacylate, alkylene glycolacrylate, alkylene glycol methacrylate, polyalkyleneglycolacrylate, polyalkyleneglycolmethacrylate, acrylamides, methacrylamides, derivatives of acrylamid

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