Addition polymers styrene

To produce the Type 2 polymers, styrene and acrylonitrile are added to polybutadiene latex and the mixture warmed to about 50°C to allow absorption of the monomers. A water-soluble initiator such as potassium persulphate is then added to polymerise the styrene and acrylonitrile. The resultant materials will be a mixture of polybutadiene, polybutadiene grafted with acrylonitrile and styrene, and styrene-acrylonitrile copolymer. The presence of graft polymer is essential since straightforwsird mixtures of polybutadiene and styrene-acrylonitrile copolymers are weak. In addition to emulsion processes such as those described above, mass and mass/suspension processes are also of importance. 

Addition of styrene to a green solution of naphthalene" Na+ in tetrahydrofuran leads to an instantaneous change of color from green to red. Styrene polymerizes rapidly and quantitatively within a few seconds, and when the reaction is completed, addition of water converts the red solution of polystyryl carbanions into colorless solution of polystyrene. After precipitation of the polymer it was shown spectroscopically25 that the residual solution contains an amount of naphthalene equal to that used in the preparation of the initiating catalyst. This observation confirms the proposed mechanism of initiation of the polymerization. 

The observation of Tsuji et al. 148) concerned with copolymerization of 1- or 2-phenyl butadiene with styrene or butadiene illustrates again the importance of the distinction between the classic, direct monomer addition to the carbanion, and the addition involving coordination with Li4. The living polymer of 1- or 2-phenyl butadiene initiated by sec-butyl lithium forms a block polymer on subsequent addition of styrene or butadiene provided that the reaction proceeds in toluene. However, these block polymers are not formed when the reaction takes place in THF. The relatively unreactive anions derived from phenyl butadienes do not add styrene or butadiene, while the addition eventually takes place in hydrocarbons on coordination of the monomers with Li4. The addition through the coordination route is more facile than the classic one. 

Nonlinear addition polymers are readily obtained by copolymerizing a divinyl compound (e.g., divinylbenzene) with the vinyl monomer (e.g., styrene), as already mentioned. Products so obtained exhibit the insolubility and other characteristics of space-network structures and are entirely analogous structurally to the space-network polymers produced by the condensation of polyfunctional compounds. Owing to... 

This reaction includes modified acrylates with or without addition of styrenes in combination with one or more initiators in a solvent [126], In an example, tetrahydrofuran was used as solvent and the polymer concentrations amounted to about 5.6 g Thus, the polymerization is carried out as solvent process. 

At the end of the polymerisation, when species IA has disappeared and ions are present, the addition of styrene makes the ions vanish instantaneously and they remain absent whilst polymerisation proceeds. Moreover, this polymerisation has the same rate constant as the first. This means that it cannot have been initiated only by the acid that was free at that time and that the acid bound as ions must also have become available. These facts are represented by the reaction paths leading to esters IB and IC, which complete the cycle whereby eventually ions are formed again, and can be destroyed again by addition of more monomer. Of course, reaction of the freshly added monomer with the then free acid leads to formation of ester IA. The maximum concentration of carbonium ions increases after each addition because of the increasing double bond concentration, as the polymer concentration increases. Thus the final value of the equivalent conductance and... 

Most addition polymers are formed from polymerizations exhibiting chain-growth kinetics. This includes the typical polymerizations, via free radical or some ionic mode, of the vast majority of vinyl monomers such as vinyl chloride, ethylene, styrene, propylene, methyl methacrylate, and vinyl acetate. By comparison, most condensation polymers are formed from systems exhibiting stepwise kinetics. Industrially this includes the formation of polyesters and polyamides (nylons). Thus, there exists a large overlap between the terms stepwise kinetics and condensation polymers, and chainwise kinetics and addition (or vinyl) polymers. A comparison of the two types of systems is given in Table 4.1. 

The blocks of 4-vinylpyridine must not be too long, otherwise the polymer is no longer completely soluble in THE.This can easily be observed when 20 ml lots of 4-vinylpyridine are used instead of 5 ml the solution then becomes cloudy, but after fresh addition of styrene it turns clear again. 

Other latexes which have been produced by this method include poly(butyl methacrylate), poly(butyl acrylate) and poly(styrene/DVB) [161]. Additionally, polymer blends were produced by mixing, under high shear, HIPEs of partially polymerised monomer, followed by completion of polymerisation. The conversion prior to blending had to be less than 5%, to allow efficient mixing of the highly viscous emulsions. The materials thus produced resembled agglomerates of latex particles, due to copolymerisation at the points of contact of partially polymerised droplets. 

Styrene-1,3-butadiene-styrene (SBS) or styrene-isoprene-styrene (SIS) triblock copolymers are manufactured by a three-stage sequential polymerization. One possible way of the synthesis is to start with the polymerization of styrene. Since all polystyrene chains have an active anionic chain end, adding butadiene to this reaction mixture resumes polymerization, leading to the formation of a polybutadiene block. The third block is formed after the addition of styrene again. The polymer thus produced contains glassy (or crystalline) polystyrene domains dispersed in a matrix of rubbery polybutadiene.120,481,486... 

The copolymer styrene-butadiene rubber (SBR), shown here, is used for making tires as well as bubble gum. Is it an addition polymer or a condensation polymer ... 

Note the similarities between the structure of SBR and polyethylene and polystyrene, all of which possess no heteroatoms. SBR is an addition polymer made from the monomers 1,3-butadiene and styrene mixed together in a 3 1 ratio. Notably, SBR is the key ingredient that allows the formation of bubbles within bubble gum. 

The addition of styrene (S) to a polymer possessing CH2.C(Ph)2, Na+ end group was also investigated in a stirred-fiow reactor (47). The process involves two steps... 

Polymerization of styrene initiated by trifluoro-acetic acid (3) is another example of the same phenomenon. Addition of styrene to tri-fluoroacetic acid yields polystyrene of M. W. 20,000 to 30,000 while the addition of trifluoro-acetic acid to styrene does not produce any polymer Trifluoro-acetate counter ions, formed in the first process, are strongly stabilized by the solvent (trifluoro-acetic acid) through powerful hydrogen bonds, and hence their capacity to recombine with the growing carbonium ion is greatly reduced. In the second process, the counter ions are formed in a hydrocarbon millieu (styrene) of low solvation power. Their recombination with carbonium ions remains therefore unhindered and consequently the formation of a polymer is prevented. 

Biostable polymers have been chosen for use in the majority of DES that are marketed or in clinical development. The main attractiveness of biostable polymers is their physical stability, inertness toward the drug, and predictable drug kinetics. In Cypher, a blend of poly(ethylene-co-butyl methacrylate) (PEVAc/PBMA) is used as the drug carrier. This hydrophobic polymer, along with additional polymer process steps, effectively controls the release of sirolimus, eluting 80% of the drug over 30 days after implantation. In the case of Taxus, atri-block copolymer of styrene-isobutylene-styrene (SIBS) is used as the hydrophobic polymer matrix that releases 10% of incorporated paclitaxel in the first 30 days (20). 

Anionic polymerization is widely used to prepare polymers with narrow molecular weight distribution. Addition of styrene to the living poly(l,l-dialkylsilabutane)s provided a poly(l,l-dialkylsilyl-/ -styrene) block copolymer (Scheme 11) in 99% yield with MJMn = 1.19 C1997PSA3207, 1995MM7029>. 

Asymmetric PS stars of the type (PSA)n(PSB)n were also prepared by the divinyl-benzene (DVB) method [9]. Living PS chains, prepared by sec-BuLi initiation, were reacted with a small amount of DVB producing star homopolymers. The DVB core of the stars contains active anions which, if no accidental deactivation occurs, are equal to the number of the arms that have been linked to this core. These active sites are available for the polymerization of an additional quantity of monomer. Consequently further addition of styrene produced asymmetric star polymers... 

Styrenic copolymers are materials capable of thermoplastic processing which, in addition to styrene (S), also contain at least one other monomer in the main polymer chain. Styrene-acrylonitrile (SAN) copolymers are the most important representative and basic building blocks of the entire class of products. By adding rubbers to SAN either ABS (acrylonitrile-butadiene-styrene) or ASA (acrylate-styrene-acrylonitrile) polymers are obtained depending on the type of rubber component employed. These two classes of products yield blends composed of ASA and polycarbonate (ASA -f PC) or ABS and polyamide (ABS -(- PA). 

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