Precipitation polymerization pdf

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Control Rel — However, substantially all of the prior heterogeneous methods have been unable to produce a product in which the objectionable and contaminating monomeric residue is reduced to less than 0.

Reduction to practically exclusion of the monomer, e. Finally, many of the prior polymerizations produce low molecular weight products since they are carried out under conditions which provide a short propagation stage resulting from the formation of a highly viscous reaction mixture thus hindering agitation and tending to terminate the reaction. Accordingly, it is an object of this invention to overcome the above deficiencies by providing a commercially feasible and economical process for the precipitation polymerization of monomers.

Another object of this invention is to provide a process for producing polymer containing significantly less than 0. Still another object is to provide a commercially acceptable process for producing particulate copolymers and terpolymers from any proportion of monomeric mixtures. Another object is to produce finally divided colorless products containing not more than ppm residual monomer. These and other objects of the invention will become apparent from the following description and disclosure.

Examples of homopolymerizable monomers included in this invention are N-vinylpyrrolidone, alkyl substituted N-vinylpyrrolidones, N-vinyl caprolactam, alkyl substituted N-vinyl caprolactams, acrylic acid, methacrylic acid, acrylamide, methacrylamide, etc. Copolymers within this group are also suitable candidates for the present high temperature polymerization reaction. Suitable comonomers may also include cross-linking agents such as the divinyl ether of diethylene glycol, N,N-divinyl-imidazolidone, pentaerythritol triallyl ether, triallyl-1,3,5-triazine-2,4,6- 1H,3H,5H trione, ethylene glycol diacrylate, 2,4,6-triallyloxy-1,3,5-triazine, 1,7-octadiene, 1,9-decadiene, divinyl benzene, methylene bis acrylamide , ethylene bis methacrylamide and the like.

In the process of this invention the monomer or monomeric mixture is predissolved in from about 50 to about 90 wt. Suitable solvents include cyclohexane, heptane, benzene, toluene, xylene, ethyl benzene, and linear, branched or cylic alkanes having from 2 to 20 carbon atoms.

In the initial stage of the process, i. Such low temperature initiators include diacyl peroxides such as diacetyl peroxide, dibenzoyl peroxide, dilauroyl peroxide; peresters such as t-butylperoxy pivalate, t-butyl peroctoate, t-amylperoxy pivalate, t-butylperoxyethyl hexanolate; percarbonates such as dicyclo hexyl peroxy dicarbonate, as well as azo compounds such as 2,2'-azo-bis isobutyrolnitrile , 2,2'-azo-bis 2,4-dimethylvaleronitrite , 2,2'-azo-bis cycanocyclohexane and mixtures thereof, the organic peroxides being preferred.

The reaction is carried out under anhydrous conditions in the absence of oxygen which is maintained by purging the reaction zone with an inert gas, such as nitrogen, throughout the reaction. In carrying out the. The monomer or monomeric mixture in solution is then introduced, e. It is essential that the high temperature initiator be present at this stage of the reaction.

Hence, in cases where it is absent in the precharge of initiator solution, the high temperature initiator is introduced at this stage. The pressure in the reactor during polymerization may vary from atmospheric up to psi, more often between about atmospheric and about 50 psi, depending upon the monomeric species selected Although the total initiator solution can be added as the precharged mixture, it is more desirable to add initiator solution throughout the reaction either by gradual addition or at separate stages of conversion as desired.

The polymerization reaction is carried out over a period of from about 2 to about 48 hours, more often a reaction time of from about 6 to about 12 hours is sufficient to achieve complete conversion of the monomeric species. Toward the end of the reaction, the polymerization mixture may become too viscous for good agitation. However, this step is optional. Another expedient which improves contact between the monomer and initiator involves introducing the monomeric species below the level of the initiator solution in the reactor.

Porous monodisperse poly divinylbenzene microspheres by precipitation polymerization Journal of Polymer Science Part A: Polymer Chemistry, A short summary of this paper.

Download Download PDF. Translate PDF. These microspheres have di- ameters between 4 and 7 mm, total pore volumes of up to 0. As no surfactant nor stabilizer was used in the preparation of these particles, their surfaces are free of any such residues. This broad size distribution can reduce their phy by Moore at Dow Chemical in As a In recent years, mono- or narrow-dispersed result, crosslinked polystyrene particles have be- porous resins have been developed for use in high- come the most widely used insoluble polymeric performance chromatography and elsewhere.

Permanent hydrocarbons activation followed by a mixture small and large pores can be introduced into these of monomer, crosslinker, initiator, and optional particles through the use of solvent or polymeric porogen. The resulting suspensions are polymer- porogens as reviewed by Guyot and Bartholin. In a previous paper, we described the dried under vacuum at C overnight. The fil- formation of highly crosslinked and monosized trate from the reaction was concentrated and an poly divinylbenzene particles by polymerization excess amount of methanol was added to precipi- of commercial divinylbenzene in neat acetonitrile tate the soluble polymer sol fraction.

This sol using AIBN as initiator. In this paper we report the introduction of po- The preparation of the DVB suspension rosity into these precipitation polymer particles. The reactions are Particle Characterization again carried out in absence of steric and ionic stabilizers. Agitation must be gentle in order to Particle diameters and particle size distributions prevent particle coagulation.

The internal texture of Chemical Co. Here, the parti- merization. General Procedure for Preparation of Microspheres The sol fractions were analyzed by size exclusion For a typical polymerization, 0. Up to 12 such bottles were attached to a tometer were used with tetrahydrofuran as the mo- rotor plate. The rotor plate was submerged in a bile phase. The temper- less steel column 4. Finally, these overlap or aggregate to form the final porous polymer bead. Pore Formation in Suspension and Seeded Swelling This explanation of the pore generation process Polymerizations accounts well for the broad pore size distribution generally observed in suspension polymerization.

In both suspen- sion polymerizations and seeded swelling poly- Precipitation Polymerization merizations, the porogen and monomer s to- gether constitute the dispersed organic phase. As The mechanisms of precipitation polymerization the polymerization proceeds, phase separation oc- of DVB have been discussed earlier. This leads to porogen- merization mixtures are initially homogeneous rich domains, or pores, distributed within the fi- solutions of monomer DVB and initiator nal polymer beads.

With a nonsolvent porogen AIBN in acetonitrile. Monomer loadings must such as dodecanol, phase-separation occurs early be kept low 2—5 vol.

Polymerization starts in the homoge- pores. With toluene as a porogen on the other neous phase, and the oligomers aggregate to form hand, phase separation occurs late and leads to colloidally stable particles. These particles grow small pores. Mixtures of solvent and nonsolvent by capturing oligomers and monomer, to ulti- porogens can be used to give intermediate pore mately form monodispersed, crosslinked particles sizes.

Below we describe the crosslinked nuclei dispersed within the droplet. The particle size maximum around 25 vol. As well, the shape of the particle size distribu- tion changes from columnar to a more rounded form at higher toluene fractions.

In presence of 45 or 50 vol. Only soluble polymer was isolated from polymeriza- tions in neat toluene, without any precipitate be- ing formed.

These results are in agreement with the formation of soluble polymer microgels re- ported by Walczynski et al. The molecular weight and the amount of the sol fractions, in general, increase with toluene volume fraction, reflecting the increasing solvency of the medium Table I. This sol fraction resembles the Staudinger micro- Figure 1. Particle size distributions of precipitation poly divinylbenzene particles prepared in the pres- gels recently reviewed by Antonietti.

The last three entries in Table I indicate that the average particle size increases with the mono- the suspension polymer particles prepared earlier mer loading. Monomer loadings above 5 vol.

Mono- or narrow-dispersed particles were ob- tained in presence of 0—40 vol. The average particle diameter increased from 4. Particle size distributions of suspension po- vol. The suspension microspheres in sequent polymerizations, by simply adding the the last sample Fig. The nonsolvent porogen have a visibly porous struc- resulting microspheres are again mono-, or nar- ture.

Electron Microscopy The four types of particles described above were External Particle Morphology by Scanning Electron embedded in Spur epoxy resin and microtomed to Microscopy SEM produce 50—60 nm thick sections for transmission Figure 3 shows the SEM images of poly divinyl- electron microscopy.

Figure 4A,B corresponds to benzene particles prepared by precipitation poly- the precipitation particles prepared in neat merization in neat acetonitrile Fig. No apparent pores Fig. The precipitation parti- hard, crosslinked particles.

The porous precipita- cles prepared in neat acetonitrile Fig. The have nonspherical shapes Fig. In contrast, the suspen- ene volume fractions. Addition of toluene ization with suspension polymerization. These grow and crosslink to form micro- dioxane, methyl ethyl ketone MEK , and xylenes spheres.

Spherical particles At this point the two processes diverge: in sus- with bimodal size distributions were obtained pension polymerizations, with their high mono- from polymerizations in acetonitrile mixtures con- mer loadings of around 40 vol.