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
1983-06-07
1985-07-23
Michl, Paul R.
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...
524460, 526 80, 526 87, C08F 216
Patent
active
045309566
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a new process for preparing oligomer and/or oligomer-polymer particles and the use of these for the preparation of polymer dispersions and, if desired, dispersions with monodisperse polymer particles.
The preparation in aqueous dispersion or in a mixture of water and organic solvents of particles which are capable of absorbing much more of low molecular substances than ordinary polymer particles, has been described in previous patents.
In Norwegian Pat. No. 142.082 there is described a process which comprises the preparation of particles which are characterized in that they are capable of taking up large amounts of low molecular substance, such as a monomer. In a special process this is attained by adding to a dispersion of polymer particles in water, a liquid Substance I having a very low solubility in water, or a solution of the same which in advance has been homogenized to become rapidly absorbed in the polymer particles. In order to further increase the rate of absorption, a water soluble solvent for Substance I, such as acetone, is added in certain cases. The amount of Substance I which may be absorbed in the initial polymer particles, is in practice limited to about 10 times the volume of polymer, for large particles somewhat more. For small particles the limit is normally 2-3 times. The obtained particles which contain polymer + said Substance I having a very low solubility in water, are capable of absorbing more than a 1000 times its own volume of a more water soluble Substance II, depending on the size of the particles. It is emphasized that an essential feature for this swelling capacity, is that the conditions during the swelling with Substance II are such that the only transport which can take place, is the transport of Substance II through the outer phase into the particles, while the transport of said Substance I having a very low water solubility out of the particles, is hindered. A condition for this is that the difference in solubility in the outer phase between Substance II and I is a factor of >10, preferably >100. It is emphasized that in the use of solvents to increase the diffusion of Substance I into the particles, it is later necessary to prevent the diffusion out of the particles either by removing the solvent added in the first step or dilution with water before addition of Substance II.
Norwegian Pat. No. 141.367 describes a method for preparing swellable particles by preparing an oligomer by means of a chain transfer agent. By adjusting the amount of chain transfer agent and using it in amounts far above those which are commonly used in processes in which chain transfer agents are employed, it is possible to obtain particles which exclusively or predominantly contain oligomer of a molecular weight <5000. The weakness of this method is that it is necessary to use relatively large amounts of chain transfer agent with a chain transfer constant equal to the rate constant for the growth of the growing radical. This is a condition for obtaining a constant ratio between the concentration of monomer and the concentration of chain transfer agent during the polymerization, in order to ensure that the mean degree of polymerization in the oligomers formed, is constant. If the transfer constant is higher than the growth constant, the chain transfer agent will be rapidly consumed and the molecular weight will increase. If the transfer constant is lower than the growth constant, there will be a considerable amount of chain transfer agent left after all the monomer has reacted, and the molecular weight of the oligomers will decrease markedly as the monomer is consumed.
According to the present invention there is provided a process in which particles which exclusively or predominantly consist of oligomer having a desired and relatively constant molecular weight, are prepared in a first step by providing a high ratio between the rate of radical formation and the rate of polymerization. Particles which have been prepared in this manner, and which contain o
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Berge Arvid
Ugelstad John
Michl Paul R.
Sintef
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