Polymers from Substituted Styrene

Many derivatives of styrene can be readily synthesized. Some are commercially available. One of them is a-methyl styrene. It is formed fi om propylene and benzene by a process that is very similar to st5n ene preparation  

Due to the allylic nature of a-methyl styrene it cannot be polymerized by free-radical mechanism. It polymerizes readily, however, by an ionic one. Resins based on copolymers of a-methyl styrene are available commercially. Other styrene derivatives that can be obtained commercially are  

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In the 1960s, after Kennedy and Thomas [25] had established the isomerisation polymerisation of 3-methylbutene-l, this became a popular subject. From Krentsel s group in the USSR and Aso s in Japan there came several claims to have obtained polymers of unconventional structure from various substituted styrenes by CP. They all had in common that an alleged hydride ion shift in the carbenium ion produced a propagating ion different from that which would result from the cationation of the C C of the monomer and therefore a polymer of unconventional structure the full references are in our papers. The monomers concerned are the 2-methyl-, 2-isopropyl-, 4-methyl-, 4-isopropyl-styrenes. The alleged evidence consisted of IR and proton magnetic resonance (PMR) spectra, and the hypothetical reaction scheme which the spectra were claimed to support can be exemplified thus ... 

Synthetic applications of carbon radical additions to allenes cover aspects of polymerization, selective 1 1 adduct formation and homolytic substitutions. If heated in the presence of, e.g., di-tert-butyl peroxide (DTBP), homopolymerization of phenylal-lene is observed to provide products with an average molecular weight of 2000 (not shown) [58]. IR and 1H NMR spectroscopic analyses of such macromolecules point to the preferential carbon radical addition to CY and hence selective polymerization across the 2,3-double bond of the cumulene. Since one of the olefinic jr-bonds from the monomer is retained, the polymer consists of styrene-like subunits and may be... 

Fig. 3. Variation of the dimensions of the a axis of isotactic polystyrene as a function of the content of copolymerized units of differently substituted styrenes. Abscissa molar fraction of CH,=CH—C6H4—R (from Natta, G., et al. J. Polymer Sci.

Table 23.2 Molecular characteristics of hydrogenated substituted Styrenic polymers—(CH2CHR)—[20]". Reproduced from Gehlsen et al., J. Polym. Sci., Part B Polym. Phys., 33, 1527(1995) by permission of John Wiley Sons, Inc.

Another approach to the preparation of polymer-supported metal Lewis acids is based on polymerization of functional monomers. If synthesis of the functional monomer is not difficult, polymerization should afford structurally pure functional polymers, because the polymer formed requires no further complicated chemical modification. A variety of substituted styrene monomers are now commercially available styrene monomers with an appropriate ligand structure can be prepared from these. Several other interesting functional monomers such as glycidyl methacrylate, 2-hydr-oxyethyl methacrylate, and other acrylics have also been used extensively to prepare functional polymers. 

Poly(styrenes) and poly(a-substituted styrenes) can bear various substituents on the aromatic ring. These substituents may affect other properties of the polymer, but their thermal stability is not very different from that of unsubstituted poly(styrene). Some of the idealized structures of the polymers in this group are shown below ... 

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 ... 

Phenolic ion exchangers derived from a phenol-formaldehyde condensation reaction appeared in the first generation of ion-exchange polymers. More recently, styrene-divinylbenzene copolymers incorporating azo-substituted cresol and salicylic acid, catechol, hydroquinone, and benzoquinone have been described. The quinone-type polymers selectively sorb Hg(III) and the catechol resins sorb Cr(VI). 

Recently, blocked polymeric isocyanates useful in the preparation of polyurethanes, have been prepared by direct carbonylation of a nitro-substituted polymer based on styrene with carbon monoxide in the presence of a catalyst at 60-200 "C and a pressure from atmospheric to 2000 psi in a hydrogen-donor solvent [64]. Catalysts such as PdL2X2 (X = halogen, L = heterocyclic ligand, e.g. pyridine) in the presence of [NEt4][Cl] have been used. However, from the abstract it is not clear if polynuclear ruthenium, iron, and platinum carbonyls are... 

Another method of preparing functionalized polymers involves copolymerization of substituted styrene monomers plus styrene and/or DVB to give the functionalized polymer directly (Table 2-4). Introduction of functional groups into styrene polymers by copolymerization of suitably substituted styrene monomers is reported to give polymers of more uniform functionalization. In addition, they are not contaminated by small proportions of other functional groups remaining from incomplete prior chemical transformation. 

Polystyrene is a polymer (Section 12-15) whose subunits are derived from ethenylbenzene (styrene). Although beads of polystyrene are insoluble and rigid when dry, they swell considerably in certain organic solvents, such as dichloromethane. The swollen material allows reagents to move in and out of the polymer matrix easily. Thus, its phenyl groups may be functionalized by electrophihc aromatic substitution. For peptide synthesis, a form of Friedel-Crafts alkylation is used to chloromethylate a few percent of the phenyl rings in the polymer. 

If the above argument is valid, the bimodal MWD is not specific to the styrene/C104 system but should be generally the case for such polymerization systems where the interaction between the propagating carbocation and its counteranion is suitably strong. This interrelationship is supported by the formation of polymers with a bimodal MWD from a series of p-substituted styrenes (Table 2) With perchlorate... 

Comparing our results with other published reports it is clear that removal of carbazole moiety from polymer backbone by any kind of spacer group eliminates the formation of excimer emission sites. This applies even to bomopolymers of the rather rigid carbazole-substituted styrenes 11 and 12... 

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