Peroxide-initiated suspension polymerization styrene

A mathematical model for styrene polymerization, based on free-radical kinetics, accounts for changes in termination coefficient with increasing conversion by an empirical function of viscosity at the polymerization temperature. Solution of the differential equations results in an expression that calculates the weight fraction of polymer of selected chain lengths. Conversions, and number, weight, and Z molecular-weight averages are also predicted as a function of time. The model was tested on peroxide-initiated suspension polymerizations and also on batch and continuous thermally initiated bulk polymerizations. 

The choice of the proper peroxy initiator largely depends on its decomposition rate at the reaction temperature of the polymerization. BPO is the major initiator for bulk polymerization of polystyrene or acrylic ester polymers, where temperatures from 90°C to 220°C are encountered. Dilau-royl, dicaprylyl, diacecyl, and di- err-butyl peroxides are also used. In the case of suspension polymerization of styrene, where temperatures between 85°C and 120 C are applied, the initiators also range in activity from BPO to di-tm-butyl peroxide. In suspension polymerization of vinyl chloride (reaction temperatures of 45-60°C for the homopolymer), thermally very labile peroxides such as diisopropyl peroxydicarbonate and rm-butyl peroxy-pavilate are used. 

Literature data for the suspension polymerization of styrene was selected for the analysi. The data, shown in Table I, Includes conversion, number and weight average molecular weights and initiator loadings (14). The empirical models selected to describe the rate and the instantaneous properties are summarized in Table II. In every case the models were shown to be adequate within the limits of the reported experimental error. The experimental and calculated Instantaneous values are summarized in Figures (1) and (2). The rate constant for the thermal decomposition of benzoyl peroxide was taken as In kd 36.68 137.48/RT kJ/(gmol) (11). 

The Instantaneous values for the initiator efficiencies and the rate constants associated with the suspension polymerization of styrene using benzoyl peroxide have been determined from explicit equations based on the instantaneous polymer properties. The explicit equations for the rate parameters have been derived based on accepted reaction schemes and the standard kinetic assumptions (SSH and LCA). The instantaneous polymer properties have been obtained from the cummulative experimental values by proposing empirical models for the instantaneous properties and then fitting them to the cummulative experimental values. This has circumvented some of the problems associated with differenciating experimental data. The results obtained show that ... 

The computer program simulates the batch polymerization of styrene and has been applied to the relatively low temperature peroxide-initiated polymerization typical of suspension processes and to higher temperature bulk, thermal conditions. It has been useful in the design of new suspension processes and for more general process analysis. 

Styrene-divinyl benzene copolymer with 15% crosslinking was synthesised by the suspension polymerization technique using benzoyl peroxide as an initiator [5]. After polymerization the beads were washed with distilled water, water ethanol (1 1) mixture and ethanol. It was finally, soxhlet extracted with ethanol benzene (1 1) mixture. 

EPDM elastomer, type C and elastomer in starting solution, 10%. Initial polymerization T = 100°C styrene conversion, 30% and initiator, tert-butyl peracetate, 0.09%. Suspension polymerization suspending agent, 0.6% ferf-butyl peroxide, 0.4% and water/(rubber -f monomer) = 1.2. Suspension cycle 2 hrs at 120°C, l hr at 140°C, and 2 hrs at 155°C. 

Classification Organic peroxide Empirical C13H26O3 Properties M.w. 230.35 Uses Initiator for vinyl polymerization, bulk/sol n./suspension polymerization, for cure of polyester resins and acrylic syrup Manuf./Distrib. Akzo Nobel http //www.akzonobel.conr, Aztec Peroxides Trade Name Synonyms Aztec TAPEH [Aztec Peroxides] Esperox 570 [Crompton/Olefins Styrenics] Lupersol 575 [Atofina N. Am./Org. Peroxides Atofina SA http //www.atofina.com, Trigonox 121 4tAkzo Nobel http //www.akzonobel.com]-, Trigonox 121-BB75 [Akzo Nobel http //www.akzonobel.com] t-Amylperoxy 2-ethylhexyl carbonate CAS 70833-40-8... 

The suspension polymerization of styrene is mostly carried out with dibenzoyl peroxide. Bulk polymerization is often no longer carried out purely thermally high-temperature initiators such as 1,2-dimethyl-1,2-diethyl-1,2-diphenyl ethane or vinyl silane triacetate, CH2=CH—Si(OOCCH3)3, are added. 

Suspension polymerization processes were developed to solve the heat generation problems that occur in bulk polymerization and the volatile organic recycling problem that oeeurs in the solution processes. In a suspension process, a monomer/water mixmre is stirred to form a suspension of styrene monomer droplets with the aid of suspending agents or surfactants (i.e. surface active agents). When an organie soluble initiator such as a peroxide is added to the suspension, the peroxide diffuses into the monomer droplets and initiates styrene polymerization. 

Quarternary salts in combination with benzoyl peroxide are known to induce vinyl polymerization in emulsion systems [79,80]. Quartemary salts are also potential photoinitiators for vinyl polymerization [81]. The use of quarternary salts in combination with peroxides as redox initiators for suspension polymerization of styrene [82] and polymerization of methyl methacrylate [83,84] in bulk or in solution have been explored. 

At present all commercial polystyrene (with average molecular weights between 100,000 and 400,000) is manufactured by radical polymerization, which yields atactic polymers.476 Peroxides and azo compounds are commonly used initiators. The suspension process (usually as a batch process in water at 80-140°C) produces a product with relatively high residual monomer content.223 More important is the continuous solution process (usually in ethylbenzene solvent at 90-180°C), which yields high-purity product. Styrene can be copolymerized with numerous other monomers.477 One of these copolymers, the styrene-divinylbenzene copolymer produced by free-radical polymerization, has a crosslinked stucture and is used in... 

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