Cross-linking, representative scheme

Polynuclear clathrochelate hydrazonates can be synthesized by the same reaction pathways as those described for oximehydrazonates (Schemes 88 and 137) using formaldehyde, triethyl orthoformate, chloral, and others as cross-linking agents. Scheme 142 represents the formation of a binuclear double-decker complex. 

Cross-linking in polyethene may be induced in the presence of a sen-sitiser such as benzophenone. The mechanism is outlined in Scheme 9.4, where the symbol Pn-H represents any C-H bond in polyethene. 

The intramolecular C-H insertion reaction of phenyldiazoacetates on cyclohexadiene, utilizing the catalyst Rh2(S-DOSP)4, leads to the asymmetric synthesis of diarylacetates (Scheme 8). Utilizing the phenyl di azoacetate 38 and cyclohexadiene, the C-H insertion product 39 was produced in 59% yield and 99% ee. Oxidative aromatization of 39 with DDQ followed by catalytic hydrogenation gave the diarylester 40 in 96% ee. Ester hydrolysis followed by intramolecular Friedel-Crafts gave the tetralone 31 (96% ee) and represents a formal synthesis of sertraline (5). Later studies utilized the catalyst on a pyridine functionalized highly cross-linked polystyrene resin. ... 

Oxetanes have also been synthesized by the immobilization of 2,2 -disubstituted 1,3-diols with polymer-bound sulfonyl chloride, followed by intramolecular cyclization/cleavage from the solid support (Scheme 17) <2005TL643>. One percent divinylbenzene (DVB) cross-linked polystyrene and polyethylene glycol (PEG) (average Mn 3400) were used as polymer support in this reaction, and in both cases the properties of the polymer support allowed rapid purification of the intermediate. Intermediates on the insoluble cross-linked polystyrene support could be washed with a range of organic solvents to remove insoluble impurities, whereas the soluble PEG supported products could be purified by recrystallization from isopropanol. This is thought to represent the first reported polymer-supported synthesis of oxetanes. 

Fig. 7.1 General scheme representing peroxidase-mediated reactions (a) homopolymerization, (b) heteromolecular coupling, (c) cross-linking, and (d) surface functionalization...

Fig. 9.11. Reaciion scheme for the synthesis of network-polymeric CSPs and representative chromatograms, (a) Derivatization of A, A -diallyl-(R.R)-tartaric acid diamide (DATD) to give the bifunctional monomers used as chiral SO units, (b) Cross-linking and immobilization by hydrosilylation with multifunctional hydrosilane (alternatively, cross-linking and immobilization can be performed first with DATD followed by O-derivatization). (c) Enantioseparation of 2-(octylsulphinyl)benzoic acid. The chromatograms illustrate the column performance under non-overloadcd (left) and overloaded conditions (right). CSP network polymer from /V. -diallyl-i/il.Rl-tartaric acid diamide fc/.s-. i.S-dimethylbenzoatc bound to. ) pm 1.50 A Kromasil. Mobile phase hexane-THF (80 20 v/v) with 0.0.55 - of TFA (reprinted with permission from Ref. [194]).

Cross-Linking Reactions of Polymers. Bisdichloromaleimide-amine polymers contain (a) a double bond in the maleimidyl group, (b) chlorine, and (c) secondary amine group (-NH-). It may be possible to cross-link them either by the opening of the double bond (thermal polymerization) or by the nucleophilic displacement of chlorine by the secondary amine. The representative reaction scheme for such reactions is shown in Figure 6. The extent of such reactions may be evaluated by solubility measurements in dimethyIformamide. 

Figure 6. Representative scheme of cross-linking reactions.

The poly(vinyl cinnamate) (I) (see Scheme 6.1) resist represents the simplest example of cross-linking in a negative resist system by an excited chromophore. 

Figure 17.9 The chemistry of the CARL process scheme. x may stand for hydroxystyrene, acrylates, and alicyclic monomeric units, etc. R represents an alkyl group. Structure (I) is the alkaline-insoluble resist resin, consisting of an alternating polymer of maleic anhydride and an appropriate monomer. Structure (II) is the product of the base-catalyzed hydrolysis of the anhydride resin. Structure (III) is the bis-diaminoalkyl-oligo-dimethylsiloxane, the CARL process silylating agent. Structure (IV) is the cross-linked product of silylating agent and the hydrolyzed anhydride resist resin.

Reactions 10-12 in Scheme 12.3 represent the termination of free radical sites which may have the character of cross-linking (reaction 12) and/or formation of diaUtyl peroxides (reactions 10 and 11) which may act as new initiating species. The first parallel reaction in reaction 10 is typical for tertiary peroxyl radicals, while... 

Figure 19 Representative scheme for the preparation of hollow nanotubes with one open end from a bottlebrush block copolymer, (a) Chemical structure of a bottlebrush copolymer, (b) AFM height image of the corresponding shell-cross-linked copolymer adsorbed on mica, (c) TEM characterization of organic nanotubes obtained after core degradation. Reproduced with permission from Huang, K. Rzayev, J. J. Am. Chem. Soc. 2009, 131 (19), 6880-6885. ...

Figure 29 Representative scheme for the preparation of organic-inorganic hybrid nanocylinders through bulk self-assembly followed by cross-linking via sol-gel. (Left) Chemical structure of block copolymers used. (Right) TEM images of films and nanostructures obtained from a series of PTEPM-b-PS block copolymers. Reproduced with permission from Zhang, K. Gao, L. Chen, Y. M. Macromolecules 2001, 40,5916-5922, and Zhang, K. Gao, L. Chen, Y. M. Macromolecules 2m, 41 (5), 1800-1807. ...

Supramolecular gels can also be formed using coordination interactions and gels represent a way to control the positioning of metal ions, for example, in nanoparticle synthesis. The reaction of Fe(N03)3 with 1,3,5-benzenetricarboxylic acid (BTC), for example, forms a coordination polymer gel within minutes. There is extensive cross-linking between the Fe and the tricarboxylic acid which leads to voids within the coordination polymer structure (Scheme 5.10). This gel may be used as a polymerisation template. Methyl methacrylate may be polymerised within the gel matrix by UV irradiation of the monomer, resulting... 

According to the results [239,240], this large impact of small 3D ND additive could be associated with formation of the peculiarly cross-linked structure in these nanocomposites, due to the effect of double chemical hybridization between three network constituents. A simplified scheme of such a structure is represented in Fig. 61. 

The special feature of this scheme is the reaction represented by the second equation with rate coefficient k since this acts to quench vulcanization by using up the active cross-link precursor B. Hence if... 

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