Preparation of Functional Polymers

The attachment of functional groups to polymers is frequently the first step towards the preparation of speciality polymers, for example, for biomedical applications or as supported reagents. In the latter category particularly, polymers containing the m- and / -isomers of chloromethylstyrene are widely used and the syntheses of many functionalized polymers based on these starting materials have been described.  

Some cross-linking occurs as a side reaction but this is probably less disadvantageous than the extensive chain scission which accompanies photochemical boronation with BBrs. 

Phosphorus-containing polystyrenes have been used for a variety of purposes and can be prepared either by copolymerization or by chemical modification methods. The latter are limited in number and often lead to unacceptable 

Useful brominating resins (containing vinylpyridinium hydrobromide per bromide units) were prepared by functionalizing terpolymers of styrene, 4-vinyl-pyridine and divinylbenzene with bromine and HBr. The resins were stable over long periods and gave excellent yields in the bromination of alkenes and ketones. The spent reagent was readily removed after reaction and could be regenerated easily.  

The reaction of AICI3 vapour at 115 °C with cross-linked poly(styrenesulphonic acid) yields complexes within the resin having proton donor properties comparable with the sup eracid solution of SbF, and FSO3H. The modified resin is capable of isomerizing and cracking n-hexane. The polymers probably contain structures (7), (8), and (9). Structure (9) could account for the powerful proton donor properties. 

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Scheme 5. Synthetic routes used for the preparation of functional polymers containing pendant 2-oxazoline and bromobenzyl groups.

With respect to the polymeric backbone, two approaches exist for the preparation of functional polymers, the polymerization or copolymerization of monomers which carry the desired functionality, and secondly the chemical modification of preformed polymers. The former concept, the polymerization of prefunctionalized monomers, was often tested in the early days of polymer-assisted syntheses, e. g. in the preparation of polymers containing pyridine [12] or quinone [13] residues, and benzaldehyde [14] or phosphine [15] functionalities. Although the latter approach demands that the synthetic organic chemist acquires profound knowledge of polymers and polymerization, this strategy can have advantages because... 

PREPARATION OF FUNCTIONALIZED POLYMERS BY REACTIONS OF POLY(VINYLBENZYL CHLORIDE)... 

If, however, the polymerization process is aimed at the preparation of functional polymers (telechelics, macromonomers), then the problem of cyclization becomes much more important, because cyclic oligomers do not contain functional end groups. 

The quantitative character of initiation and the living character of active species permits the preparation of functional polymers (telechelic oligomers) as well as block copolymers (cf., Section IV.A.). 

The intermolecular chain transfer to polymer (scrambling), however, is detrimental for preparation of functional polymers, leading to disproportionation of monofunctional macromolecules, as shown schematically below ... 

Macromonomers are polymers or oligomers with polymerizable end groups, widely investigated for the preparation of functional polymers and polymer microspheres by dispersion polymerization. For microspheres, the macromonomers should be designed to copolymerize with the main monomers in such a way as to produce graft chains that serve as efficient stabilizers in other words, their main chain should be firmly bound to the particle surface and the graft chains should extend into the polymerization medium. 

Two different approaches can be used for the preparation of functionalized polymers Polymerization of functionalized monomers and chemical modification of preformed resins. Initially we selected this second approach, using polystyrene-divinylbenzene resins, as this allows to work with materials of well known structural characteristics. 

The methodology of active ester synthesis, as shown in Fig. 2, is generally applicable and covers a wide range of nucleophiles, including primary, secondary and aromatic amines, primary alcohols and phenols. Thus, chemical modification d polymeric active esters (i.e. active ester synthesis) provides a single-step route for the preparation of functional polymers in general. The syntl sis of various polymer types by the active ester method is advanced in Sects. 5-7. Here, an example of a relativdy simpk fiinctional group (OH) is discussed to illustrate the versatility of the active ester method, as compared with conventional methods of polymer functionalization. 

ATRP is an excellent method for the preparation of functional polymers. Polymers with molecular weights up to M =100,()00 can be obtained with narrow molecular weight distribution. Many functionalized styrenes, acrylates and other functional monomers were successfully polyineiized using a wide range of functional initiators or macroinitiators. Furthermore chain-end halogens can be displaced. Because of all these possibilities, ATRP can find applications in solventless coatings, adhesives, lubricants, surfactants and additives. 

Jo, S., Shin, H. Mikos, A. G. (2001a) Modification of oligo(poly(ethylene glycol) fumarate) macromer with a GRGD peptide for the preparation of functionalized polymer networks. Biomacromolecules, 2, 255-61. 

In the last few years, click reactions, as termed by Sharpless et al. [280] received attention due to their high specificity, quantitative yields, and good fidelity in the presence of most functional groups. The click chemistry reaction includes a copper-catalyzed Huisgen dipolar cycloaddition reaction between an azide and an alkyne leading to 1,2,3-triazole. Recent publications on this click reaction indicate that it is a useful method for preparation of functional polymers [281]. 

Preparation of Functionalized Polymers by Reactions of Poly(Vinylbenzyl Chloride).97... 

Two new synthetic methods for the preparation of functional polymers containing 2-oxazoline pendant groups were developed. The first concerns the synthesis of m- and p-vinylbenzyl ethers of 2-(p-hydroxyphenyl)-2-oxazoline, followed by their radical poljnnerization. 2-(p-Hydroxyphenyl)-2-oxazo-line was reacted with a mixture of m- and p-chloromethylstyrene (60% m and 40% p) under phase transfer catalysis conditions at room temperature. The m-and p-vinylbenzyl ethers of 2-(p-hydroxyphenyl)-2-oxazoline obtained were separated by selective crystallization from methanol. Radical polymerization of these ethers was carried out in dioxane at 60 C, giving polymers with pendant 2-oxazoline groups. 

The preparation of functional polymers by chemical modification has been extensively used to modify the properties of polymers for various technological applications [53-58]. Chemical modification affords new classes of polymers which cannot be prepared by direct polymerization of monomers owing to their instability or nonreactivity. Also it is possible to modify the structure and physical properties of commercial polymers making them more suitable for specific applications [3]. For example, attempts to prepare linear poly(A-alkylethylenimine)s directly by ringopening polymerization of A-alkylethylene imines were unsuccessful but these... 

These polymers constitute the largest group to be discussed in this report and this is mainly because polystyrene and poly(chloromethylstyrene), often crosslinked with divinylbenzene, continue to be widely used in the preparation of functional polymers and resin-supported reagents. In fact most of the examples given here refer to the preparation of functional polymers rather than to new materials. This is a rapidly growing area of polymer chemistry and it is not possible to refer, in a compressed review of this nature, to all reports of functionalized styrene-based resins that have appeared in the past two years. This section falls naturally into three parts the first deals with styrene polymers and copolymers, the second with reactions on chloromethylated polystyrenes, and the third deals with styrene-related polymers. 

ATRP is a particularly attractive approach for the preparation of polymer brushes, because of its tolerance to a wide range of functional monomers and less stringent experimental conditions. As a living polymerization, ATRP allows for control of molecular weight and molecular weight distribution and affords the opportunity to prepare block copolymers. For the preparation of functional polymer brushes onto PET surfaces via surface-initiated ATRP, the presence of alkyl halide initiators on the surfaces is indispensable. ATRP initiators are often introduced onto PET surfaces via reaction of the reactive functional groups (as described in Section 5.2) with functional alkyl halides, such as bromoisobutyryl bromide or 3-trichlorosilyl-propyl-2-bromo-2-methyl propanoate. Farhan and Huck modified PET films by plasma oxidation to create hydroxyl groups on their surfaces, followed by... 

Yamauchi, A. (1987). Artificial Vitreous Preparation of Functional Polymer Gels and Their Applications, M. Irie, ed., CMC, pp. 169-179. 

The preparation of functional polymers is an area of organic-polymer chemistry which continues to receive much attention in view of the numerous new and imaginative applications which are discovered for specialty polymers with reactive functionalities ... 

The two main approaches which can be used in the preparation of functional polymers consist of the polymerization or copolymerization of suitably functionalized monomers or the chemical modification of pre-formed polymers The first approach is often considered to be the most attractive due to its apparent simplicity, although it is often ill suited for the preparation of polymers with fairly complex functionalities In some cases, even simple polymers such as poly(vinyl alcohol) are only accessible via a chemical modification route In other cases it may be desirable to effect a simple chemical modification reaction to prepare a less common or more reactive polymer such as poly(iodomethyl styrene) from a more readily accessible but less reactive precursor such as polyCchloromethyl styrene). 

Figure 19 Schematic illustration of the concept for the preparation of functional polymer brushes via polymer-analogous transformation of reactive groups.

Both methods, the post-sulfonation of preformed polyfarylene ether sul-fone)s and the preparation of functionalized polymers by the use of sulfonated monomers, have been widely described in the hterature and will be discussed in the following sections. 

The second route to obtain functionahzed polymers is by the use of monomers aheady bearing functional groups, for example, sulfonic acid groups. This method has the advantage that (a) the site of functionalization, (b) the number of functional groups, and (c) the distribution of functional groups, either randomly or blockwise, can be easily controlled in the polymer chain. Both methods, the postsulfonation of preformed poly(arylene ether sulfone)s and the preparation of functionalized polymers by the use of sulfonated monomers, have been widely described in the literature and wdl be discussed in the following sections. 

SI-ATRP facilitates preparation of functional polymer brushes. Functional groups can either be an inherent part of the monomer molecule, thus being present along the polymer backbone, or can be introduced to previously prepared polymer chains. Chain-end functional groups can be converted into other functional groups and provide an opportunity for conducting click chemistry to the brush end. 

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