Poly post-polymerization reactions

The concept of PO macroinitiators centers on the introduction of an initiation moiety into an olefinic polymer chain for polymerization. The most effective route for preparing PO macroinitiators is by employing functional polyolefins containing hydroxyl groups or other reactive groups. These functional POs are prepared by copolymerization of olefins with functional monomers and post-polymerization reaction, as mentioned above. In the case where an initiation moiety was at the chain-end of the polyolefins, a block type copolymer is produced. It has been reported that thiol-terminated PP was used as polymeric chain transfer agent in styrene and styrene/acrylonitrile polymerization to form polypropylene-b/odc-polystyrene (PP-b-PS) and polypropylene-btock-poly(styrene-co-acrylonitrile) (PP-b-SAN) block copolymer [19]. On the other hand, polymer hybrids with block and graft structures can be produced if initiation moieties are in the polymer chain. 

The most common example of macromonomers in this category are polyethylene oxide and propylene oxide. From their method of preparation they have one or two end -OH groups which can be used for post-polymerization reactions. Acryloylchloride, methacryloylchloride, p-vinyl benzyl chloride, and iso-cyanatomethylmethacrylate are some of the reagents reacted with PEO or poly(propylene oxide) (PPO) to prepare macromonomers. A few of these reactions [195,196] are presented in the following schemes (Scheme 61). 

Combination of anionic polymerization and post polymerization reactions has been used for the synthesis of poly(acrylic acid-b-N,N-diethylacrylamide) (PAA-PDEA) copolymers [9]. Initially the synthesis of a precursor poly(tert-butylacrylate-b- N,N-diethylacrylamide) (PtBMA-PDEAAm) block copolymer was realized via sequential anionic polymerization of the tert-butyl acrylate and diethylacrylamide monomers. However, an amount of PtBMA homopolymer was detected in the crude reaction product. In order to remove the vast majority of the homopolymer, the authors proposed the precipitation of the crude product in hexane, where the homopolymer is highly soluble, in contrast to the block copolymer. The piuified block copolymer was subjected to deprotection of the tert-butyl group in acidic media, leading to the desirable DHBC. The final block copolymer showed pH and thermosensitive solution aggregation. 

Macromonomers have been also prepared by post-polymerization reactions. Poly(ethylene oxide) (PEO) or poly(propylene oxide) (PPO) has one or two —OH end groups depending on the method of their preparation. These —OH groups may react with (meth)acryloyl chloride, p-vinyl benzyl chloride, norbomenyl chloride, 4-vinyl benzoyl chloride, etc. for the synthesis of the corresponding macromonomers (109,110) (eq. 33). 

A number of hydrophobically modified water-soluble polymers have been prepared via post-polymerization reaction. For example, Straus [21] has prepared polysoaps by the quarternization of poly(2-vinylpyridine) with n-dodecyl bromide (Eq. 1.3). 

Poly (ethylene terephihalate) and nylon-6,6 manufacture are homogeneous bulk step-growth reactions. The molecular weight of the polymer produced is limited by the high viscosity of the reaction mixture at very high conversions. Post polymerization techniques such as that described in connection with reaction (5-39) can be used to increase the polymer molecular weight for some applications. 

Monomers Not Polymerizable by Plasma Initiation. When styrene and a-methy1styrene were subjected to plasma treatment, the monomers became yellowish and only trace amounts of insoluble films were formed. The discoloration was intensified and extensive formation of dark films were observed if carbon tetrachloride was added as the solvent. No post-polymerization was detectable for these monomers. Generally styrene and a-methylstyrene readily undergo thermal polymerization. However, no thermal polymerization was possible for these monomers after having been subjected to plasma treatment for one minute or less. It has been demonstrated from the emission spectra of glow discharge plasma of benzene (6) and its derivatives (7 ) that most of the reaction intermediates are phenyl or benzyl radicals which subsequently form a variety of compounds such as acetylene, methylacetylene, allene, fulvene, biphenyl, poly(p-phenylenes) and so forth. It is possible that styrene and a-methylstyrene also behave similarly, so that species from the monomer plasma are poor initiators for polymerization. 

To furnish a convenient reaction platform, polymer chemists have explored the utility of non-isocyanide-based MCRs in order to avoid the use of isocyanides. For example, Tao and coworkers focused intensively on the employment of non-isocyanide MCRs such as the BigineUi reaction [70] and the three-compmient reaction between aldehydes, amines, and mercaptoacetic acid [71]. In additimi, the utility of the Kabachnik-Fields reaction was demonstrated independently by the groups of Theato [72] and Tao [73]. To be precise, Kakuchi and Theato showed that the Kabachnik-Fields post-polymerization modification reaction on poly(4-vinyl benzaldehyde) with amines and phosphites proceeded very efficiently to afford polymers featuring a-amino phosphonate pendant groups (Scheme 3) [72]. Furthermore, the group of Tao succeeded in synthesizing polymeric a-amino phosphonates via concurrent Kabachnik-Fields reactions of vinyl compounds and RAFT polymerization of the vinyl monomers in a one-pot process [73]. 

Keywords Amphipathic polymers Bifunctionalized homopolymers Dual-func-timial polymers Poly(glycidyl methacrylate) Post-polymerization modification Sequential reactions siRNA delivery Thiol-epoxy reaction... 

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