Polymerization bulk reactions

Bead Polymerization Bulk reaction proceeds in independent droplets of 10 to 1,000 [Lm diameter suspended in water or other medium and insulated from each other by some colloid. A typical suspending agent is polyvinyl alcohol dissolved in water. The polymerization can be done to high conversion. Temperature control is easy because of the moderating thermal effect of the water and its low viscosity. The suspensions sometimes are unstable and agitation may be critical. Only batch reaciors appear to be in industrial use polyvinyl acetate in methanol, copolymers of acrylates and methacrylates, polyacrylonitrile in aqueous ZnCh solution, and others. Bead polymerization of styrene takes 8 to 12 h. 

In mass polymerization bulk monomer is converted to polymers. In solution polymerization the reaction is completed in the presence of a solvent. In suspension, dispersed mass, pearl or granular polymerization the monomer, containing dissolved initiator, is polymerized while dispersed in the form of fine droplets in a second non-reactive liquid (usually water). In emulsion polymerization an aqueous emulsion of the monomer in the presence of a water-soluble initiator Is converted to a polymer latex (colloidal dispersion of polymer in water). 

The vast majority of commercial apphcations of methacryhc acid and its esters stem from their facile free-radical polymerizabiUty (see Initiators, FREE-RADICAl). Solution, suspension, emulsion, and bulk polymerizations have been used to advantage. Although of much less commercial importance, anionic polymerizations of methacrylates have also been extensively studied. Strictiy anhydrous reaction conditions at low temperatures are required to yield high molecular weight polymers in anionic polymerization. Side reactions of the propagating anion at the ester carbonyl are difficult to avoid and lead to polymer branching and inactivation (38—44). 

It may also be possible to crosslink the acrylic PSA with the help of multifunctional acrylates or methacrylates [87], These monomers can simply be copolymerized with the balance of the other monomers to form a covalently crosslinked network in one step. Since the resulting polymer is no longer soluble, this typ)e of crosslinking is typically limited to bulk reactions carried out as an adhesive coating directly on the article or in emulsion polymerizations where the crosslinked particles can be dried to a PSA film. 

Another factor in step-growth polymerizations is cyclization versus linear polymerization.1516 Since ADMET is a step-growth polymerization, most reactions are carried out in the bulk using high concentrations of the reactant in order to suppress most cyclic formation. A small percentage of cyclic species is always present but is dependent upon thermodynamic factors, typical of any polycondensation reaction. 

Poly(boronic carbamatejs were prepared by alkoxyboration polymerization of diisocyanates with mesityldimethoxyborane (scheme 33).59 The polymers obtained have boronic carbamate functions in their repeating units and can be expected to be novel reactive polymers. First, alkoxyboration polymerization between mesityldimethoxyborane and 1,6-hexamethylene diisocyanate was examined, and the optimized reaction conditions were bulk reactions at 140°C. Both aliphatic and aromatic diisocyanates gave the corresponding polymers. When aromatic diisocyanates were employed, the... 

It is not practical to stir all reaction systems, for example, bulk polymerizations, postpolymerization reactions, fixed-bed catalytic reactors, and plug-flow reactors. Although multipoint temperature sensing is often used as a key solution to determine a runaway in nonagitated vessels, the occurrence of hot spots may not always be detected. 

Monomer and initiator must be soluble in the liquid and the solvent must have the desired chain-transfer characteristics, boiling point (above the temperature necessary to carry out the polymerization and low enough to allow for ready removal if the polymer is recovered by solvent evaporation). The presence of the solvent assists in heat removal and control (as it also does for suspension and emulsion polymerization systems). Polymer yield per reaction volume is lower than for bulk reactions. Also, solvent recovery and removal (from the polymer) is necessary. Many free radical and ionic polymerizations are carried out utilizing solution polymerization including water-soluble polymers prepared in aqueous solution (namely poly(acrylic acid), polyacrylamide, and poly(A-vinylpyrrolidinone). Polystyrene, poly(methyl methacrylate), poly(vinyl chloride), and polybutadiene are prepared from organic solution polymerizations. 

Because of the highly exothermic nature of acrylonitrile polymerization, bulk processes arc not normally used commercially. Howevei. a commercially feasible process lor bulk polymerization in a continuous stirred lank reactor has been developed. The heat nl reaction is controlled hy operating at relatively low conversion levels and supplementing the normal jacket cooling with reflux condensation of umcaclcd monomer... 

ATMET of a triglyceride-based multifunctional monomer [125]. The ring opening of epoxidized soybean oil with 4-vinyl benzene sulfonic acid provided monomers suitable for metathesis polymerization. The bulk reaction of this monomer in the presence of C5 afforded a thermosetting material with a Tg of — 1.6°C. 

As the ion concentration in the acid grows toward a steady state value, alkylation and polymerization-cracking reactions occur which generate a distribution of C5" " to Cg" " ions in the acid. An estimate of this "homogeneous" alkylate distribution in the bulk acid can be made from the product distribution at the earliest times shown in Figures 8 to 11. 

The kinetic schemes described in this chapter apply to free-radical polymerizations in bulk monomer, solution, or in suspension. Suspension polymerizations ([Section 10.4.2.(iii)]) involve the reactions of monomers which are dispersed in droplets in water. These monomer droplets contain the initiator, and polymerization is a water-cooled bulk reaction in effect. Emulsion systems also contain water, monomer and initiator, but the kinetics of emulsion polymerizations are different from those of the processes listed above. Chapter 8 describes emulsion polymerizations. 

Most emulsion polymerizations are free-radical reactions. The main difference from alternative free-radical polymerizations, such as those in bulk, solution, and suspension systems, is that the propagating macroradicals in emulsion reactions are isolated from each other. Encounters between macroradicals are hindered as a consequence, and termination reactions are less frequent than in comparable systems in which the reaction mixture is not subdivided. Emulsion polymerizations thus often yield high-molccular-wcight products at fast rates when suspension or bulk reactions of the same monomers are inefficient. 

Bulk reactions are attractive for step-growth polymerizations. Heat removal is not a serious problem, because such polymerizations are not highly exothermic. Mixing and stirring are also not difficult until the last stages of the reaction, since the product molecular weight and the mixture viscosity remain relatively low until high conversions are reached. 

If the monomer and polymer are not mutually soluble, the bulk reaction mixture will be heterogeneous. The high pressure free radical process for the manufacture of low density polyethylene is an example of such reactions. This polyethylene is branched because of self-branching processes illustrated in reaction (6-89). Branches longer than methyls cannot fit into the polyethylene crystal lattice, and the solid polymer is therefore less crystalline and rigid than higher density (0.935-0.96 g cm ) species that are made by coordination polymerization (Section 9.5). 

Suspension polymerizalion is also known as pearl or bead polymerization. Ki-netically, suspension polymerizations are water-cooled bulk reactions. Monomer droplets with dissolved initiator are dispersed in water. As the polymerization proceeds the droplets become transformed into sticky, viscous monomer-swollen particles. Eventually, they become rigid particles with diameters in the range of about (50-500) 10 cm. The final reaction mixture typically contains 25-50% of polymer dispersed in water. The viscosity of the system remains fairly constant during the reaction and is determined mainly by the continuous water phase. 

Bulk polymerization. Bulk polymerization is the simplest and most direct method (from the standpoint of formulation and equipment) for converting monomer to polymer. It requires only monomer (and possibly monomer-soluble initiator or catalyst), and perhaps a chain transfer agent for molecular weight control, and as such gives the highest-purity polymer. However, extra care must be taken to control the process when the polymerization reaction is very exothermic and particularly when it is run on a large scale. Poly(methyl methacrylate), polystyrene, or low-density (high pressure) polyethylene, for example, can be produced from... 

The fundamental difficulty in constructing a theory for the MWD in emulsion polymers is to account for the compartmentalized nature of the system- In the commouly occurring situation where particles contain only a few free radicals at any given time, it is obviously incorrect to consider that each latex particle behaves like a mini-bulk reaction vessel, and so the conventional methods used for bulk polymerizations are inapplicable. Nevertheless, some assumptions which introduce only minor errors may often be made. The most important such assumptions is that the evaluation of the MWD may be separated from that of the PSD. In other words, provided that the MWD being produced at any given moment is the same as would be formed in an equivalent set of monodispersed latex particle systems [as expressed in Eq. (27) below], then the MWD evolved in a system that is polydispersed in size may be computed trivially. Formally, this is expressed as follows. Let S(M,a,t) be the MWD formed in a monodisperse system of size o at time f here M is the molecular weight variable. In a polydisperse system with PSD n([Pg.115]

These equations are perfectly general and therefore are applicable to solution, bulk, suspension, and emulsion polymerization systems. In the case of solution and bulk systems there is, in effect, only one particle with a volume of that of the whole reaction mixture. In emulsion and suspension polymerizations, the reaction mixture is subdivided into a large number of small particles and the influence of the state of subdivision is expressed by the factor z. 

Higher molecular weight polycarbonate was enzymatically synthesized from diethyl carbonate.223 The lipase CA-catalyzed bulk reaction of an excess of diethyl carbonate with 1,3-propanediol or 1,4-butanediol under ambient pressure gave oligomeric products followed by polymerization under vacuum to give aliphatic polycarbonates with Mw higher than 4 x 104. 

Enzyme regioselectivity also enables the conversion of multifunctional monomers (functionality >3) to linear or nearly linear homo- and copolymers. In 1991, Dordick and co-workers [60] reported that, by using the protease Proleather, condensation polymerizations (45 °C, 5 days) performed in pyridine between sucrose and bis(2,2,2-trifluoroethyl) sebacate proceed with high regioselectivity giving sucrose oligoesters (DP 11) in 20% yield (see also Chapter 1). This inspired subsequent work by others that demonstrated such copolymerizations with polar multifunctional polyols could be performed under bulk reaction conditions without activation of carboxylic acids (see below). 

Apart from CALB other enzymes were shown to be able to successfully polymerize lactones. For instance Lipase PS-30, immobilized on Celite, was used as catalyst to study PDL-ROP under bulk reaction conditions. Poly(PDL) with M = 62000 and PDI 1.9 was reported [76]. Gross and coworkers could show that Humicola insolens cutinase (HiC) showed a high catalytic activity for enzymatic ROP of e-CL and PDL [87]. Poly(e-CL) with M n = 16000 (M /lVf = 3.1), in >99% yields was produced in bulk (70 °C, 24h) with 0.1% w/w immobilized HiC. Furthermore, using immobilized HiC in toluene (70 °C, 24h), PDL was converted to poly(PDL) (99% yield) with M = 44600 and Mw/M = 1.7. 

Polyanhydrides have been synthesized by the following methods a) bulk melt condensation of activated diadds, b) ring opening polymerization, c) reaction between dibasic acid and diacid chlorides, and d) interfacial polymerization. A detailed study of these polymerization methods and various polymerization conditions for a range of diadds were previously described [25-27],... 

Field and Schaefgen (5) demonstrated that a high molecular weight poly (vinylene carbonate) (PVCA) was obtained if the first step of the synthesis, photochlorination of ethylene carbonate, was carried out in CC14 instead of bulk reaction and if the monomer was distilled from NaBH4 shortly before polymerization. On the other hand, bulk chlorination led invariably to poor quality VCA. 

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