Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Patent
1997-08-05
1999-11-09
Niland, Patrick D.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
524458, 524460, 524500, 524502, 525193, 525263, 5253295, 5253297, 525387, C08J 302, C08K 320, C08L 904, C08L 908
Patent
active
059816422
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method of grafting an oligomer to a polymer in latex form, and to an aqueous latex of an oligomer-grafted polymer where grafting has been effected using such a method.
The use of aqueous emulsions of organic polymers, commonly known as aqueous polymer latices, is well known in the art for numerous applications, and in particular for the provision of the binder material in various coatings and adhesives applications.
It is known for some applications to be advantageous to employ an aqueous emulsion of a polymer system which comprises a hydrophilic oligomer and an emulsion polymer which is (often) hydrophobic in nature, the hydrophilic polymer being (often) solubilised is in the aqueous medium. In some cases, the polymer system is produced by a sequential polymerisation process, examples of which are described in patent publications such as U.S. Pat. No. 4,894,397, U.S. Pat. No. 4,954,558 and WO 95/04767.
Such latices may provide improvements in mechanical, physical or other performance properties in comparison to more conventional emulsion polymers.
It is, moreover, also known that it is often advantageous for the oligomer and polymer components of the latex to be intimately associated, and in particular to be grafted or at least strongly physically bound (e.g. by adsorption) to one another. This often achieves desirable improvements such as: greater latex stability in various applications, conditions, or formulations; avoiding problems of unwanted reactions or effects of the free oligomeric component with other materials which might occur in certain formulations; and the provision of desired rheological effects.
It is of course known that grafting or strong physical association may in fact take place to a certain degree when the polymer system is made sequentially (i.e. when the polymerisation to form the emulsion polymer is carried out in the presence of the oligomer or vice versa), particularly if the oligomeric material is unsaturated, as in the use e.g. of an unsaturated oligomeric polyester or an addition oligomer made using free radical polymerisation in the presence of a cobalt chelate catalyst as a molecular weight control material which often results in a proportion of terminal unsaturation in the resulting oligomer (see later).
However, the use of sequential polymerisation process to form the grafted oligomer/emulsion polymer combination does have certain disadvantages.
Thus, there is a certain loss of freedom to control various parameters and components when making the oligomer and emulsion polymer in a sequential operation such as the choice of initiator types, amount of initiator, emulsifier types and amounts, and type of monomers used, since one must be mindful of the effect thereof on the subsequent polymerisation (which could be a detrimental one). It is also necessary to employ a carefully controlled polymerisation set-up when making the second-formed polymer (usually emulsion polymer) whereas, ideally, one would often prefer to use an already existing polymer (e.g available commercially, or otherwise ready to hand). Further still, the use of a sequential process tends to result in a relatively small particle size for an emulsion polymer formed in the presence of oligomer, since the latter in many respects itself acts as an emulsifier (becoming adsorbed on the surface of the growing polymer particles and hence limiting their size); ideally one would prefer the choice of using an emulsion polymer with a very wide range of average particle size. Yet further, it may be necessary to carefully control the amount of oligomer present in the subsequent polymerisation process to form emulsion polymer, since in some cases the use of above a certain oligomer concentration may encourage flocculation or coagulation in the polymerising reaction medium.
Apart from all the foregoing, in our experience the use of the sequential polymerisation technique to achieve grafting in aqueous polymer systems is sometimes rather inefficient and in some cases may only occur to a low
REFERENCES:
patent: 4151143 (1979-04-01), Blank et al.
patent: 4894397 (1990-01-01), Morgan et al.
patent: 4954448 (1990-09-01), Wiegand et al.
patent: 4954558 (1990-09-01), Tsaur
Bedells Alison Dawn
Overbeek Gerardus Cornelis
Padget John Christopher
Niland Patrick D.
Zeneca Limited
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