Tertiary amines with styrenes

It is interesting to compare the rapid growth from the tertiary amines with that of more traditional AIBN-type initiators. For instance. Fig. 8c represents the polymerization of styrene from SAMs of (24) on gold. The amino initiator yields much thicker films in about half the time. The rate of polymer film growth is important in manufacturing processes and it is usually desirable to minimize the UV exposure time. Partially for this reason, Riihe... 

Decomposition in the presence of styrene at 60°C or with a tertiary amine in the presence of methyl methacrylate gives the corresponding ABA active block copolymer or ABBA active block copolymer, respectively. When both active block copolymers are used as polymeric initiators in another vinyl polymerization, an ABCBA type multiblock copolymer is obtained [34]. 

Aromatic electrophilic substitution is used commercially to produce styrene polymers with ion-exchange properties by the incorporation of sulfonic acid or quaternary ammonium groups [Brydson, 1999 Lucas et al., 1980 Miller et al., 1963]. Crosslinked styrene-divinyl-benzene copolymers are used as the starting polymer to obtain insoluble final products, usually in the form of beads and also membranes. The use of polystyrene itself would yield soluble ion-exchange products. An anion-exchange product is obtained by chloromethylation followed by reaction with a tertiary amine (Eq. 9-38) while sulfonation yields a cation-exchange product (Eq. 9-39) ... 

On stirring at room temperature ozonides of terminal alkenes (prepared in dichloromethane at — 70 °C) with a polymer-supported tertiary amine obtained from chloromethylated poly(styrene/divinylbenzene) and piperidine, followed by filtration and concentration under reduced pressure, the products (aldehydes or ketones) can be obtained easily in almost pure form in high yields <2003T493>. However, yields are low for cycloalkenes because apparently they form monomeric and polymeric ozonides. 

As a preliminary step in the manufacture of unsaturated polyester thermoset plastic one uses low molecular weight linear polyester (Mr 10,000) obtained by a polycondensation of polyglycols with saturated and unsaturated dicarboxylic acids. The precondensate can then be dissolved and stored in the stabilized comonomer, e.g. styrene, with which it will be crosslinked later. The crosslinking polymerization reaction between the polyester chains and the styrene bridges is initiated with the help of organic peroxides which are added dispersed in plasticizers. The reaction begins at 60-90 °C and then proceeds exothermally. In addition to this a cold hardening reaction can also be carried out. For this reaction cold accelerators are necessary, e.g. tertiary amines or cobalt naphthenate. 

Table 14.6 illustrates typical improvements noted in epoxy hybrid formulations with vinyl chloride, acrylic, and styrene butadiene lattices. Tensile strengths of cured, latex-saturated paper substrates are listed in absolute numbers while those of latex-epoxy hybrids are listed as percent increases in tensile strength over that of the latex alone. The mechanisms believed responsible for these improvements are (1) cocuring of the epoxy group with carboxyl and amine functional groups present on the latex backbone and/or (2) homopolymerization of the epoxy catalyzed by the tertiary amine included in some hybrid formulations. 

The equilibrium constants with nucleophiles such as tertiary amines are so large, that carbenium ions practically do not exist. Thus, tertiary amines and pyridine apparently react with carbenium ions irreversibly and therefore terminate carbocationic polymerizations. Somewhat weaker nucleophiles such as 2,6-dimethylpyridine (lutidine), sulfides, and tris(p-chlorophenyl)phosphine are good deactivators in vinyl ether polymerizations because they react reversibly with monomer, thus maintaining a low concentration of carbenium ions without causing elimination. However, the equilibrium constants in styrene and isobutene polymerizations with amines, sulfides, and phosphines are too large to generate a sufficient stationary concentration of carbenium ions to complete polymerization in a reasonable amount of time. 

Tazuke reported the carboxylation of the radical anions of aromatic hydrocarbons that are generated by photoinduced electron- transfer from the tertiary amines to the excited singlet aromatic hydrocarbons (Scheme 36) [119]. Toki and his coworkers reported the photofixation of COj with styrene using tertiary amines as electron donors [120]. Tomioka reported the photoaddition of tertiary amines to electrophilic cyclopropanes [115]. 

Benzophenone with tertiary amines has been used to polymerize bis 2-[2-(methacryloyloxy)ethoxy]ethyl phthtilate and triethylene glycol dimethacrylate in bulk, while mixtures of ZnO and l,8-diamino-3,6-diazaoctane have been used to emulsion-polymerize styrene. An internal keto-imine compound,... 

Combinations of benzophenone and tertiary amine groups, one of which was anchored to a polymer matrix, have also been checked in the photoinduced polymerization and photografting of 2-ethylhexyl methacrylate (EHMA) [52]. Indeed, poly(VBP-co-St)s, in the presence of 7V,Af-diethylaniline (DEA), are found to display lower photoinitiation activity and photografting efficiency than the corresponding copolymers of styrene with 4-(Af,Af-diethylamino) styrene [poly(St-co-DEAS)] in the presence of benzophenone (BP), as revealed by conversion and fractionation data (Table 10). 

The photoreduction of aromatic ketones by polymeric systems having tertiary amine end groups provides an ele nt way for the preparation of block copolymers with high efficiency [138]. The method consists of the synthesis of the bifimctional azo-derivative 4,4 -azobis (iV,i -dimethylaminoethyl-4-cyano pentanoate) (ADCP), successively used as fiee radical thermal initiator for the preparation of tertiary amine-terminated poly(styrene). 

The resulting poly(styrene), which is expected to have tertiary amine groups attached at each end of the polymer chain, due to the well established termination mechanism by radical-radical combination, are used, under UV irradiation, in conjunction with 9-fluorenone as a photo-redox system for the free radical polymerization of MMA to yield MMA/St/MMA block copolymers (Scheme 37) ... 

The ion exchange resins can be obtained either from the polymerization of substituted styrene or by the chemical modification of the polymer. For example, styrene/divinylbenzene (SDVB) polymer can be modified by chloromethylation (using HCl and formaldehyde in the presence of ZnCb) followed by reaction with a tertiary amine. This derivatization leads to a strong anion exchange material. Sulfonation of SDVB leads to a strong cation exchanger. The idealized structure of SDVB and of the anion and cation exchangers obtained from this material are shown below ... 

Details about ILs properties are covered in this book in the contributions by Seddon, Chiappe and Scott. However, two features deserve a comment for their possible consequences on reactivity and catalysis. First, depending on a delicate balance of entropie and enthalpic factors, including the polarity of the transition state structures with respect to regents, a reaction can be either speeded up or decelerated when carried out in an ionic liquid medium compared to a molecular solvent. An elegant study by Welton shows that in S-,2 reactions, primary, secondary and tertiary amines are more reactive as nucleophiles in ionic liquids, while halides react faster in conventional molecular solvents such as CH2CI2. In particular in a series of [Bmim] salts the order of nucleophilicity of halides is determined by the anion partner. To the same direction moves a kinetic study by Dyson on a cationic Ru(II) complex-catalysed hydrogenation of styrene in ILs, where it is clearly demonstrated that both the cation and the anion of the IL can inhibit or accelerate the formation of the active catalytic species. ... 

Zirconium complexes, generated in situ by addition of HZrCp2Cl to alkenes, can be animated with <9-(mesitylenesulfonyl)hydroxylamine an example is shown in Eq. 41.116 When the initial hydrozirconation is not regioselective, as with styrene, mixtures of amines are formed. A reaction that permits animation at the tertiary carbon in a similar substrate is discussed below (Eq. 49). 

---