Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Styrene-type monomers

In cationic polymerization the active species is the ion which is formed by the addition of a proton from the initiator system to a monomer. For vinyl monomers the type of substituents which promote this type of polymerization are those which are electron supplying, like alkyl, 1,1-dialkyl, aryl, and alkoxy. Isobutylene and a-methyl styrene are examples of monomers which have been polymerized via cationic intermediates. [Pg.411]

The rate of polymerization with styrene-type monomers is directly proportional to the number of particles formed. In batch reactors most of the particles are nucleated early in the reaction and the number formed depends on the emulsifier available to stabilize these small particles. In a CSTR operating at steady-state the rate of nucleation of new particles depends on the concentration of free emulsifier, i.e. the emulsifier not adsorbed on other surfaces. Since the average particle size in a CSTR is larger than the average size at the end of the batch nucleation period, fewer particles are formed in a CSTR than if the same recipe were used in a batch reactor. Since rate is proportional to the number of particles for styrene-type monomers, the rate per unit volume in a CSTR will be less than the interval-two rate in a batch reactor. In fact, the maximum CSTR rate will be about 60 to 70 percent the batch rate for such monomers. Monomers for which the rate is not as strongly dependent on the number of particles will display less of a difference between batch and continuous reactors. Also, continuous reactors with a particle seed in the feed may be capable of higher rates. [Pg.9]

Ionic polymerizations are remarkable in the variety of polymer steric structures that are produced by variation of the solvent or the counter ion. The long lived nature of the active chain ends in the anionic polymerization of diene and styrene type monomers lends itself to studies of their structure and properties which might have relevance to the structure of the polymer produced when these chain ends add further monomer. One of the tools that, may be used in the characterization of these ion pairs is the NMR spectrometer. However, it should always be appreciated that, the conditions in the NMR tube are frequently far removed from those in the actual polymerization. Furthermore NMR observes the equilibrium form on a long time scale, and this is not necessarily that form present at the moment of polymerization. [Pg.177]

Styrene-type Monomers." Product Bulletin of the Dow Chemical Company. [Pg.211]

The generic name hydrocarbon resins designates several families of low molar mass polymers (M from 600 to 104) obtained by polymerization of petroleum, coal tar, and turpentine distillates [80-82], In most cases, these products are obtained by cationic polymerization of mixtures either of aliphatic and/or aromatic mono and diolefins present in the more or less enriched Cs and C9 feedstreams, or of pure aromatic monomers generally of the styrene type. They are complex mixtures of polymers ranging from viscous liquids and tacky fluids to hard, brittle thermoplastics, and are used as additives in adhesives, printing inks, rubbers, coatings, etc. [80-82], They are obviously amorphous and are characterized by their softening point (0 to —150° C), determined by standardized methods (i.e.,... [Pg.703]

Thermal degradation of plastics can be classified as depolymerization, random decomposition and mid chain degradation [54, 55], In the process of depolymerization, the conjunction bonds between monomers are broken up, which leads to the forming of monomers. Depolymerization type plastics mainly include a-polymethyl styrene, polymethyl methacrylate and polytetrachloroethylene. In the random decomposition process, scission of carbon chains occurs randomly, and low-molecular hydrocarbons are produced. Random-decomposition-type plastics include PP, PVC and so on. In most cases, both decompositions take place. To be more specific, the degradation of polyolefins can be classified as the following three types ... [Pg.734]

Storage and Handling of Styrene-Type Monomers, Form No. 115-575-79, Oiganic Chemicals Dept., Dow Chemical USA, Midland, Mich., 1979. [Pg.492]

The formulation of two types of ion-pair is an attractive hypothesis which has been used for other systems [130] to explain differences in reactivity. The polymerization of styrene-type monomers in ether solvents, all of which solvate small cations efficiently, seems to be a particularly favourable case for the formation of thermodynamically distinct species. Situations can be visualized, however, in which two distinct species do not exist but only a more gradual change in properties of the ion-pair occurs as the solvent properties are changed. These possibilities, together with the factors influencing solvent-separated ion-pair formation, are discussed elsewhere [131, 132]. In the present case some of the temperature variation of rate coefficient could be explained in terms of better solvation of the transition state by the more basic ethers, a factor which will increase at lower temperatures [111]. This could produce a decrease in activation energy, particularly at low temperatures. It would, however, be difficult to explain the whole of the fep versus 1/T curve in tetrahydrofuran with its double inflection by this hypothesis and the independent spectroscopic and conductimetric evidence lends confidence to the whole scheme. [Pg.37]

Reactor and Reactor Conditions. A 5-litre glass reactor (15 cm diameter) fitted with four stainless steel baffles (10 cm x 1.5 cm) immersed in a thermostatted oil bath at 80 °C (reflux temperature of methyl acrylate) was used for polymerisation. Stirring was by means of a marine type impeller (6 cm diameter and pitch 45°). The overall reaction rate was sufficiently slow to ensure isothermal conditions. Additions of solutions of the more reactive monomer (styrene, of molar concentration 0.8) to the reactor were made using a computer controlled positive displacement pump (Precision Metering Ltd.) with four long-stroke pump heads, 90 out of phase to minimise pulsation of the flow. [Pg.124]

A substituted linear triamine (L-24) is effective for three types of monomers, styrene, MA, and MMA, to give relatively narrow MWDs (MwIMn = 1.1 —1.4), where the polymerizations of styrene and MA are faster than those with L-l.108 A cyclic triamine (L-25) with ethylene linkers is similarly effective.81 A perfluoroalkyl-substituted triamine (L-26) is useful... [Pg.465]

The system may be modelled initially by considering a system in which all the fimctional groups are the same type chemically and so have the same reactivity. Some typical systems would be monomer styrene (PhCH=CH2) and crosslinker divinyl benzene (CH2=CH Ph CH=CH2), and monomer methyl methacrylate (CH2=CMeCOOMe) and crosslinker ethylene glycol dimethacrylate (CH2=CMeC00CH2CH200CMeC=CH2). [Pg.100]

Polymerizable Ultraviolet Stabilizers — Miscellaneous Types. In our research on polymerizable ultraviolet stabilizers, we have decided to prepare styrene-type monomers in which the vinyl (or isopropenyl) group is directly attached to the phenyl group of the stabilizer, which might be polymerized similarly to styrene. These monomers can indeed be polymerized and copolymerized successfully with styrene, acrylic and methacrylic acid derivatives with azobisisobutyronitrile (AIBN) as the radical initiator (12-Ut-). [Pg.201]

Styrene-Type Monomers, Technical Bulletin No. 170-151B-3M-366, The Dow Chemical Company, Midland, Mich, (no date). [Pg.491]

These authors concluded that the differences in the hydrophobicity of the oil and the polymer turned out to be the driving force for the formation of nanocapsules. Due to the pronounced difference of polarity of PMMA and hexadecane, the system was very well suited for the formation of nanocapsules. With more hydrophobic monomers such as styrene, however, it was more difQcult to create nanocapsules as the cohesion energy density of the polymer phase was close to that of the oil, and adjustment of parameters to influence the interfacial tensions and spreading coefficients became critical in order to form nanocapsules. The parameters studied were monomer concentration, type and amount of surfactant and initiators, and the addition of functional comonomers. For example, addition of 10 wt% acrylic acid as a comonomer in the miniemulsion leads to an increase in the number of close-to-perfect nanocapsules. [Pg.320]

Another type of controlled radical polymerization employs a reversible termination with a nitroxide compound [21]. Rosenfeld et al. [22] reported details of the nitroxide-mediated radical polymerization of styrene and butyl acrylate at 140 °C in a 2.9 m tubular micro-reactor with an inner diameter of 900 gm. Whereas, for the low-heat-producing monomer, styrene, the differences between a batch process and the microtubular reaction were small, in the case of butyl acrylate the difference was high. This situation, which may have been due to the Trommsdorff effect in the batch reaction (Figure 14.11), indicated that the polymerization was no longer under control. By contrast, no such effect was observed in the tubular micro-reactor, and the degree of conversion remained quite low under the applied conditions. [Pg.433]

Acrylate and methacrylate co-monomers participate in the nitrile reaction [182] but styrene type monomers act as a blocking agent. Chlorinated co-monomers degrade the AN units at lower temperatures [184] by a dehydrochlorination mechanism (Scheme XXV) ... [Pg.244]

For a binary system, D j is the binary mutual diffusion coefficient Dp. The FRRPP process, however, is essentially a ternary system of the polymer/monomer/ precipitant type (such as polystyrene/styrene/water or poly(methacrylic acid)/ methacrylic acid/water). Let us designate the polymer (poly(methacrylic acid) or polystyrene) as component 1 precipitant (such as water or ether) as component 2 and the monomer (methacrylic acid or polystyrene) as component 3. Therefore, for the FRRPP process, we have four mutual diffusivities in the mixture Dn is approximated as the mutual diffiisivity of the polymer and precipitant D22 is approximated as the mutual diffiisivity of the monomer and the precipitant D 2 is the mutual dif-fusivity for the mass transfer of the polymer due to composition gradient of the monomer and D21 is the mutual diffiisivity for the mass transfer of the monomer... [Pg.61]

A typical composition for BMC and SMC includes base resins, catalysts, peroxides accelerators, fillers/chopped GF, thickeners and other additives. The base resins that are usually used are either polyester-based (orthophthalic or isophthalic), which are used with styrene, acrylic, vinyl toluene or di-allyl-phthalate (DAP) monomers, as crosslinkers, or styrene type monomers for general purpose products. Acrylic base resins are used for low shrinkage, while vinyl type monomers for high hot strengths (heat deflection temperatures). Catalysts are used for polyester type resins. Peroxides, such as benzoyl peroxide (BPO) and butyl perbenzoate are used as high temperature catalysts. [Pg.339]

To improve the strength and elastic properties as well as fill in open areas, eliminate defects, and control water permeation, a series of vinyl, acrylic, and styrene type monomers were incorporated via an emulsion technique.After polymerization, a semi-I IPN is formed if the vinyl monomer mix contain no crosslinker, and a full IPN is formed if a crosslinker is incorporated. [Pg.216]

The polymerization behavior of Schemes (81a), (81b) and (81c) is similar to that of unsubstituted monomers [384]. Copolymers of Schemes (81a), (81b) and (81c) with 1,3-butadiene [427], acrylonitrile [428], acryl ester [426], and styrene [426] are of technical interest, due to their fire-retarding properties. Detailed investigations are available on monomers of type (81a), which are particular interesting as models for phospholipide-analogous biological membranes [429]. Table 9 shows selected structure variations of those monomers. [Pg.653]


See other pages where Styrene-type monomers is mentioned: [Pg.202]    [Pg.528]    [Pg.61]    [Pg.15]    [Pg.297]    [Pg.106]    [Pg.81]    [Pg.106]    [Pg.262]    [Pg.8]    [Pg.471]    [Pg.17]    [Pg.9]    [Pg.200]    [Pg.158]    [Pg.203]    [Pg.204]    [Pg.212]    [Pg.106]    [Pg.1780]    [Pg.1018]    [Pg.200]    [Pg.298]    [Pg.188]    [Pg.163]    [Pg.235]    [Pg.4]    [Pg.561]   
See also in sourсe #XX -- [ Pg.9 ]




SEARCH



Monomer type

Styrene monomer

© 2024 chempedia.info