Postpolymerization reactions

Postpolymerization Reactions. Copolymers can also be formed by postpolymetization reactions on polymers. A well-known example is the partial hydrolysis of polyacrjiamide (PAM) to hydrolyzed polyacrylamide (HPAM). The product becomes a random copolymer of acrylamide and acryUc acid (44) (see Acrylamide polya rs). 

Ethylene-acrylic acid copolymers are converted to ethylene ionomers in a separate, postpolymerization reaction. 

It is not practical to stir all reaction systems, for example, bulk polymerizations, postpolymerization reactions, fixed-bed catalytic reactors, and plug-flow reactors. Although multipoint temperature sensing is often used as a key solution to determine a runaway in nonagitated vessels, the occurrence of hot spots may not always be detected. 

The incorporation of comonomers into PET and other polyesters, with the intent that these comonomers would then serve as the site for additional, postpolymerization reactions, has not been widely explored. A potential difficulty in such an approach is that the reactive comonomer cannot react under PET synthesis conditions of ca. 285 °C/2h/Lewis acid catalyst if the modification is to be effective. Two such systems, stable under PET synthesis, and then subjected to post-polymerization reactions, have been recently reported. 

Note 2 Physical aging, crystallization, physical crosslinking and postpolymerization reactions are sometimes referred to as curing . Use of the term curing to describe such... 

The preparation of polyacrylamides and postpolymerization reactions oti polyacrylamides arc usually conducted in water. Reactions on the amide groups of polyacrylamides are often more complicated than reactions of simple amides because of neighboring groups effects. 

Our second motivation for utilizing CDs with polymers is to alter their functionalities through incorporation of CDs into their backbones during polymerization or to attach them to polymer side chains via postpolymerization reactions. The presence of covalently bonded CDs in polymers serves to increase their acceptance and retention of additives, such as dyes, fragrances, antibacterials, etc. They may also be further reacted or treated through their covalently bonded CDs to cross-link and form networks or to form blends with other polymers having a propensity to thread through their attached CD cavities. 

The branching sites can be introduced onto the backbone either by postpolymerization reactions or by copolymerization of the main backbone monomer ) with a suitable comonomer, with the desired functional group (unprotected or in a protected form if this functional group interferes with the polymerization reaction). Branches of comb-shaped polymers are commonly prepared by anionic polymerization, and backbones with electrophilic functionalities such as anhydrides, esters, pyridine, or benzylic halide groups are employed.88 The actual average number of branches in the final copolymer can be found by the determination of the overall molecular weight of the copolymer and the known molecular weights of the backbone and the branches. 

The reaction takes place in dilute THF solutions (2-3 w/v %) at 70 C for several days using an excess of the sultone over the amine groups (sultone/amine = 10/1). For the PBd samples inert atmosphere was used. Under these conditions this postpolymerization reaction is free of side reactions (crosslinking, degradation etc.) as was verified by SEC. Similar peaks with the corresponding amine-capped polymers were observed in CHCI3 in all cases. 

As indicated earlier, another powerful tool for upgrading polymer properties is the postpolymerization reaction of preformed polymers. These reactions may occur on reactive sites dispersed in the polymer main chain. Such reactions include chain extensions, cross-linking, and graft and block copolymer formation. The reactions may also occur on reactive sites attached directly or via other groups/chains to the polymer backbone. Reactions of this type are halogenation, sulfonation, hydrolysis, epoxidation, surface, and other miscellaneous reactions of polymers. In both cases these types of reactions transform existing polymers into those with new and/or improved properties. 

FIGURE 9.8 Statistical copolymers of caprolactone and caprolactone derivates that are further functionalized via postpolymerization reactions [64,65]. 

The choice of the particular monomers is based on the fact that PI is a nonpolar low Tg polymer, P2VP is a relatively more polar material with a coordinating ability, due to the presence of nitrogen in the side phenyl ring, with high Tg and the potential to be transformed into a water-soluble polyelectrolyte by postpolymerization reaction. On the other hand, PEO is a semicrystalline polymer, water-soluble (polar), and biocompatible. The incorporation of all these diverse properties in the same molecule makes these materials very interesting in terms of their self-organization in solution, bulk, and thin films. 

EDOT monomers bearing w-iodo-alkyl and w-iodo-polyether side chains (80) have been electro-polymerized into corresponding polymers. These polymers can be rapidly and quantitatively converted into functionalized polymers under mild conditions by postpolymerization reaction with functional blocks bearing a thiolate group, as demonstrated in the case of tetrathiafulvalene (81) [ 151 ]. Application of the same procedure led to a modified electrode containing a tetrathiafulvalene core substituted by two polyether chains (82). It was shown that the binding of Pb by the polymer 82 could be electrochemicaUy driven [185]. 

Olefmic end-functionalized PIBs provide a platform for the preparation of a variety of end-fiinctionalized polymers via postpolymerization reactions. Olefmic end-fiinctionalized polymers have been prepared by a variety of methods, including end-quenching. Kennedy et first prepared olefmic... 

Scheme 37 Synthetic routes to exo-olefin-functionalized PIB and various postpolymerization reactions to form end-functionalized polymers.

An amphiphilic ABCA terpolymer has been prepared by the sequential monomer addition route and modified by postpolymerization reactions. The PSt-PIP-PBd-PSt precursor was synthesized by anionic polymerization followed by hydrogenation of double bonds using Ni-Al catalyst. Accordingly, the PSt outer blocks were sulfonated and neutralized with NaOH. A novel aggregate morphology was achieved in water, showing the influence of the ABCA asymmetric architecture in copolymer self-assembly. ... 

VBFP pentafluorophenyl 4-vinylbenzyl ether) was synthesized by a three-step sequential monomer addition, using benzyl dithio benzoate as CTA (Scheme 23). By postpolymerization reaction, the PVBCl block was quaternized by N-methylmorpholine yielding the cationic amphiphilic PVBM-PSt-PVBFP terpolymer comprising two highly incompatible hydrophobic blocks. The interest in this terpolymer stems from its ability to form multicompartment micelles of a novel nanostructure in aqueous media. 

Postpolymerization reactions, where a linear (or branched) polymer is cross-linked after synthesis is complete. An example is the vulcanization of rubber with sulfur, which will be considered further below. 

Bruk et al. [716] described the low-temperature radiation polymerization of crystalline TFE in detail. It has been established that three solid-phase postpolymerization reactions can take place when irradiated specimens are heated above the melting point low-temperature polymerization (in the interval 77 to IlOK), slow polymerization close to the melting point (in the interval 128 to 138 K), and rapid polymerization during melting of the crystal (142 K). Tabata et al. [717] have found that a significant post-polymerization takes place even in the liquid phase. Kinetic analysis has been made of the in-source and post-polymerizations [718,719]. Post-polymerization is explained by a long lifetime of polymer radicals in the hquid phase at —78 °C due to the slow combination rate of the polymer radicals caused by their rod-like shape. 

A variety of postpolymerization reactions should be feasible. These include the ability to quantitatively functionalize the polymer chain end, add another monomer, or react the chain ends for the purpose of creating various architectures. In the case of block copolymers, it is important that initiation (crosspropagation) be fast relative to the subsequent propagation. 

Postpolymerization reactions, such as grafting, cross-linking, acid and base hydrolysis, quatemization, amination, and pegylation, represent attractive alternatives to using... 

---