Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1999-10-15
2001-09-18
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S529000, C524S457000, C524S458000, C526S201000, C526S329700
Reexamination Certificate
active
06291553
ABSTRACT:
This invention relates to the production of monodisperse spherical polymers having a weight-averaged average particle diameter of 1-50 &mgr;m by a seed/feed process.
Spherical polymers having an average particle size of 1 to 50 &mgr;m are widely used, for example as spacers for film materials, as supports for catalysts, as calibration materials for light scattering measurements or as starting materials for chromatographic resins and ion exchangers. Polymers having the most uniform possible particle size (herein-after referred to as “monodisperse”) are desired for many applications.
Monodisperse, spherical polymers having particle sizes of 1 to 10 &mgr;m may be produced by so-called dispersion polymerisation. A suitable process is described, for example, in EP 80 225, 610 522, U.S. Pat. Nos. 4,861,818 and 4,614,708. In dispersion polymerisation, a solvent is used, in which the monomers used are soluble, but the polymer formed is not. It has, however, been found that a predetermined particle size is not easy accurately to produce by dispersion polymerisation and that it is difficult even to produce relatively large particles (for example larger than 8 &mgr;m). Another characteristic feature is that the particle size distribution becomes distinctly wider as particle size increases, i.e. it becomes less monodisperse.
Spherical polymers having a particle size of approx. 10 to 1000 &mgr;m may be obtained by suspension polymerisation. Suspension polymerisation is taken to mean a process in which a monomer or monomer mixture, which contains an initiator soluble in the monomer(s), is dispersed in droplet form, optionally mixed with small, solid particles, in a phase which is substantially immiscible with the monomer(s) and contains a dispersant, and polymerisation is performed by increasing the temperature with stirring. Further details of suspension polymerisation are described, for example, in the publication
Polymer Processes
, edited by C. E. Schildknecht, published in 1956 by Interscience Publishers Inc., New York, in the chapter “Polymerization in Suspension” on pages 69 to 109. One disadvantage of suspension polymerisation is the broad particle size distribution of the resultant bead polymers.
There was accordingly a requirement for a process for the production of monodisperse spherical polymers of specific particle sizes of 1 to 50 &mgr;m.
It is known according to DE 196 34 393 that a seed/feed process may give rise to spherical polymers of a specific particle size. The term seed/feed process is taken to mean a process in which a polymer (so-called seed) is swollen with a monomer or monomer mixture (so-called feed) and is then polymerised. The process may be performed statically or dynamically. In the static process, the entire quantity of monomer or monomer mixture is added at once to the seed at room temperature. Once the seed has swollen, polymerisation is performed by increasing the temperature. In the dynamic process, the monomer or monomer mixture is added continuously to the seed under polymerisation conditions over a certain period of time.
One disadvantage of the seed/feed process, in particular of the static process, is the occurrence of a new generation of particles, which are produced by unabsorbed monomer. The particle size distribution of the resultant seed/feed polymer thus does not always correspond to the particle size distribution theoretically achievable from the seed, but is instead generally somewhat wider. Since a monodisperse polymer is required for many applications, the new generation of particles must be separated from the desired seed/feed polymer by additional process steps.
In order to increase the efficiency of the seed/feed process and thus suppress the occurrence of a new generation of particles, it is possible according to EP 101943 to add the monomer or monomer mixture under polymerising conditions, by the so-called dynamic seed/feed process. The term efficiency is taken to mean the proportion of the monomer which soaks into the seed and polymerises therein relative to the total quantity of monomer added. However, with conventional seed polymers, as are known from EP 448 391, the efficiency is limited. The so-called static seed/feed process according to DE 196 34 393, in which the monomer is added completely to the seed before it is polymerised by increasing the temperature, provides a robust, reproducible, widely applicable seed/feed process. However, a microencapsulated seed must be used in this process.
Special variants for increasing the efficiency of the general static seed/feed process are known. According to U.S. Pat. Nos. 4,459,378, 4,336,173, EP 709 400 and EP 308 864, the seed, which consists of normal high molecular weight polymer, is swollen by means of special, lower molecular weight organic compounds (so-called swelling auxiliaries). The monomer is then added to the treated seed and polymerised. Treating the seed with the swelling auxiliary is, however, very complex and demands numerous steps. Another disadvantage of this process is that the organic compounds used as swelling auxiliaries are enclosed in the finished seed/feed polymer and have a negative effect on the mechanical properties of the seed/feed polymers. The seeds treated with the swelling auxiliary are furthermore usually no longer spherical, which gives rise to non-spherical seed/feed polymers.
In another variant of the static seed/feed process according to EP 190 886, the monomer feed is added as a microemulsion to the normal, high molecular weight spherical seed. However, in this variant, the particle size of the monomer droplets in the feed emulsion is extraordinarily critical to the success of the process. Moreover, due to the microemulsion which is required, the process has only limited applicability on the larger scale.
It is known to use special seeds in order to be able to perform a technically simple static seed/feed process while nevertheless achieving elevated efficiency. According to U.S. Pat. Nos. 5,189,107, 4,186,120 and 4,952,651, seeds are used which consist of polymers having a molecular weight (M
w
) of below 10000 g.mol
−1
. One disadvantage of this process resides in the poor availability of the seed. According to the prior art, it is not possible to produce such a seed with a high monodispersity. The use of such seeds accordingly does not give rise to monodisperse seed/feed polymers.
It has now been found that both the static and the dynamic seed/feed processes may be performed very simply with elevated efficiency and yield monodisperse, spherical polymers having a particle size distribution which is an exact, enlarged reproduction of the introduced monodisperse, spherical seed, if the seed consists of a polymer having a comb structure.
The present invention provides a process for the production of monodisperse spherical polymers having a weight-averaged average particle diameter of 1 to 50 &mgr;m using a seed/feed process, characterised in that the seed used is a monodisperse, spherical seed which consists of a polymer which has a comb structure.
A polymer having a comb structure is taken to mean a polymer which consists of a main chain and a plurality of long side chains. For the purposes of the invention, a comb structure is present, for example, in graft polymers and in polymers having long-chain or short-chain branches. Highly suitable polymers having a comb structure are also copolymers with comonomers containing long-chain residues. Copolymers prepared from methyl (meth)acrylate and C
2
to C
22
alkyl (meth)acrylates are preferred. Particularly preferred copolymers are those prepared from methyl (meth)acrylate and C
6
-C
22
alkyl (meth)acrylates which in particular have a solubility in water of at most 0.03 wt. % at 25° C. (cf EP 615 158 for definition). The term (meth)acrylate is intended to mean both acrylate and methacrylate. Particularly preferred copolymers are those prepared from
a) 99.5 to 80 wt. %, in particular 99 to 85 wt. %, of methyl (meth)acrylate, preferably 98 to 90 wt. % of methyl (meth)acrylate,
b) 0.5 to 20 wt. %
Harrison David Bryan
Louwet Frank
Podszun Wolfgang
AGFA-GEVAERT
Connolly Bove & Lodge & Hutz LLP
Egwim K C
Wu David W.
LandOfFree
Production of monodisperse spherical polymers using seed... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Production of monodisperse spherical polymers using seed..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Production of monodisperse spherical polymers using seed... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2450551