Precipitation mass polymerization

Another close analogy is the precipitation mass polymerization system for polyvinyl chloride (PVC). In that case, the polymer does precipitate from the monomer, but it does not go through a self-adhering sticky stage. This allows... 

Polymerization Kinetics of Mass and Suspension PVC. The polymerization kinetics of mass and suspension PVC are considered together because a droplet of monomer in suspension polymerization can be considered to be a mass polymerization in a very tiny reactor. During polymerization, the polymer precipitates from the monomer when the chain size reaches 10—20 monomer units. The precipitated polymer remains swollen with monomer, but has a reduced radical termination rate. This leads to a higher concentration of radicals in the polymer gel and an increased polymerization rate at higher polymerization conversion. 

For both suspension and mass polymerizations ar less than 2% conversion, PVC precipitates from its monomer as stable primary particles, slightly below 1-p.m dia. 

For both suspension and mass polymerizations at less than 2% conversion, PVC precipitates from its monomer as stable primary particles, slightly below 1-jlm dia (4,10—12). These primary particles are stabilized by a negative chloride charge (4,13). Above 2% conversion, these primary particles agglomerate. Sectioning the PVC grains of either suspension or mass resins readily shows the skins primary particles at 1-jim dia, and agglomerates of primary particles at 3—10-jJm dia (4,7,8,14). 

The unique solubility characteristics of CO2 limit the types of polymerization techniques that can be successfully employed. While amorphous fluoropolymers may be synthesized homogeneously in CO2, most other polymers are insoluble in CO2 and must be made via heterogeneous processes such as precipitation, dispersion, and emulsion techniques or via mass polymerizations swollen by CO2. 

Bulk or mass polymerization" Gas-phase pol3mierization Precipitation polymerization Suspension polymerization Microsuspension polymerization Dispersion polymerization Emulsion polymerization Miniemulsion polymerization Microemulsion polymerization... 

M-PVC mass polymerization of vinyl chloride (precipitation polymerization). 

In 1994, we reported the dispersion polymerization of MM A in supercritical C02 [103]. This work represents the first successful dispersion polymerization of a lipophilic monomer in a supercritical fluid continuous phase. In these experiments, we took advantage of the amphiphilic nature of the homopolymer PFOA to effect the polymerization of MMA to high conversions (>90%) and high degrees of polymerization (> 3000) in supercritical C02. These polymerizations were conducted in C02 at 65 °C and 207 bar, and AIBN or a fluorinated derivative of AIBN were employed as the initiators. The results from the AIBN initiated polymerizations are shown in Table 3. The spherical polymer particles which resulted from these dispersion polymerizations were isolated by simply venting the C02 from the reaction mixture. Scanning electron microscopy showed that the product consisted of spheres in the pm size range with a narrow particle size distribution (see Fig. 7). In contrast, reactions which were performed in the absence of PFOA resulted in relatively low conversion and molar masses. Moreover, the polymer which resulted from these precipitation... 

Syntheses. The polymerization reaction of poly(2-methyl pentene-1 sulfone) (PMPS) was carried out at -78°C. Purified 2-methyl pentene-1 (42 grams) and condensed SO, (about 125 grams) at a molar ratio of 1 to 4 were charged into the reaction system under atmospheric pressure, and the reaction was Initiated by 2 milliliters of butyl hydroperoxide. The white polymer mass was purified by dissolving 1n acetone, then precipitating Into methanol (8). 

Membranes used for the pressure-driven separation processes, microfiltration, ultrafiltration and reverse osmosis, as well as those used for dialysis, are most commonly made of polymeric materials 11. Initially most such membranes were cellulosic in nature. These are now being replaced by polyamide, polysulphone, polycarbonate and a number of other advanced polymers. These synthetic polymers have improved chemical stability and better resistance to microbial degradation. Membranes have most commonly been produced by a form of phase inversion known as immersion precipitation. This process has four main steps (a) the polymer is dissolved in a solvent to 10-30 per cent by mass, (b) the resulting solution is cast on a suitable support as a film of thickness, approximately 100 11 m, (c) the film is quenched by immersion in a non-solvent bath, typically... 

POE 6000 was used as polymeric support, a soluble polyethylene glycol derivative functionalized at both termini with an amino group and with an average molecular mass of 6000 Da [62-63]. After completion of the homogeneous reactions it can be precipitated, filtered off, and washed with diethyl ether, thereby facilitating the separation of surplus reagents and the side products. Furthermore it allows for NMR spectroscopic monitoring of the reactions [64]. 

There are two different ways for carrying out polyreactions in a solvent. When both the monomer and the resulting polymer are soluble in the solvent, one speaks of a homogeneous solution polymerization on the other hand, if the polymer precipitates during the course of the reaction, it is called precipitation polymerization. By addition of a solvent, different effects are obtained Basically, the viscosity of the reaction mixture is decreased in comparison to a bulk polyreaction this facilitates heat transfer, mass transport, and handling. 

Microspheres are particles ranging between 1 and 100 pm. They are typically formed from degradable polymeric materials such as albumin, polysaccharides, or poly(a-hydroxy acids) by precipitation or phase-separation emulsion techniques [6, 332]. The relatively large diameters of microspheres make their extravasation into the tumor mass difficult and the uptake of microspheres by the RES is very rapid. 

Preparation of Poly(p-formyloxystyrene) (IV) A sample formyloxystyrene and 0.0652 g AIBN were combined in a bottomed flask equipped with an air cooled condenser and N2 bubbler, and heated at 80 C overnight. The resulting polymeric mass was dissolved in THF and precipitated in petroleum ether. Repeated washing, followed by drying of the polymer overnight in a vacuum oven at room temperature yielded 4.85 g (79%) of poly(/>-formyloxystyrene) (M = 1.09 x 104, Mz = 1.65 x 104, polydispersity =1.51 (gpc)). 

Micro-encapsulation, as obtained by continuous SAS techniques, is a physical process, guided both from thermodynamics and kinetics. The entire process involved is not clear. Mass-transfer kinetics and thermodynamic equilibria related to polymer-particle precipitation from a solution expanded by supercritical CO2 are currently being investigated [9,10], Many empirical observations are now available, suggesting that for a given polymeric solution, both pressure and temperature play an important role in determining the precipitated particles morphology. 

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