End-capping reagent

Table 22.5 Properties which can be adjusted in the 2nd stage of the PEER polymer synthesis by varying the end-capping reagent to improve the molecular weight and backbone stiffness...

Table 1. Oligomerization and polymerization of compound 1 by Glaser-Hay coupling. Catalyst formation CuCI, TMEDA, and 02 in 1,2-dichlorobenzene [5, 12]. The reaction was performed in the presence of molecular sieves (4 A). If PhC=CH was available immediately at beginning ofthe coupling process (procedure C) an equal amount was added again 1 h before the end of the reaction. (tr is the total reaction time and tadd is the time until addition of the end-capping reagent.)...

In cationic polymerization end-capping was first applied by Saegusa in the polymerization of THF and then of other cyclic ethers sodium phenoxide was used as the end-capping reagent and the phenoxy end groups were determined by UV. End-capping is sufficiently fast and the phenolate is exclusively formed in reaction with the growing species ... 

Figure 3.4. Structures of the typical bonding and end-capping reagents and diagram of the bonded silica with residual silanols.

Sulfonated PAES random copolymers can be prepared by the by potassium carbonate mediated direct aromatic nucleophilic substitution polycondensation of disodium 3,3 -disulfonate-4,4 -dichlorodiphenyl sulfone, 4,4 -dichlorodiphenyl sulfone and BP. The condensation reaction proceeds quantitatively to high molecular weight in A-methyl-2-pyrroUdone (NMP) at 190°C. In addition, a monofunctional monomer, 4-tert-butyl-phenol, can be used as an end capping reagent. The phenol functional group has a similar reactivity as biphenol. In this way, the molecular weight can be controlled. 

Optical Storage. For the purpose of reversible optical storage, a hyperbranched PEEK has been developed. The polymer is terminated with azobenzene chromophores. 1,3,5-Tris(4-(4-fluorobenzoyl)pheno-xy)benzene is a core molecule with a functionality of three, additionally 4,4 -(hexafluoroisopropylidene)-diphenol is used, and 4-(4-hydroxyphenylazo) ben-zonitrile acts as the end capping reagent [96]. The monomer is shown in Figure 6.14. 

N-substituted pyrroles as potential end-capping reagents in the quasiliving carbocationic polymerization of PIBs. The TiCl4-co-initiated polymerization of PIB was quenched with N-methylpyrrole to form a mixture of 2- and 3-PIB-N-methyl-pyrrole-fimctionalized polymer in quantitative yield as determined by Catalytic hydrogenation of the... 

A group at IBM prepared (Scheme 51) polymers 108 end-capped with vinyl groups by addition of bromostyrene as an end-capping reagent to a Yamamoto polycondensation [212]. These polymers can be thermally cross-hnked at 150-200 °C to produce insoluble materials which show stable blue emission [212]. This is attributed to a reduction in chain mobihty, due to the cross-hnking, which hinders exciton migration to the defect sites. 

The doubly end-capped polyfluorenes 216 and 217, with phenol or carboxylic acid functional groups at the chain termini, have been made by addition of 13 mol % of suitable end-capping reagents to the Yamamoto polymerisation of a dibromofluorene followed by conversion of the protected functionalities (Scheme 98) [315]. The materials appeared to be totally end-capped by NMR analysis. 

Formaldehyde (anhydrous) is also the major reactant for polyacetal resins, important for engineering components. The chemical structure is essentially R0(CH20) R, with co-monomers or end-capping reagents incorporated to prevent slow reversion to formaldehyde. 

The studies of the crosslinking reaction of a nadic end-capped imide, N, N -(ox-ydi-3,4 -phenylene)bis(5-norbornene-2,3-dicarboximide) in thermal and micro-wave processes were performed by Scola at al. (Fig. 14) [80]. The investigated starting resin (RP-46) consisted of polyimide precursors, 3,3, 4,4 -benzophenonetet-racarboxylic acid methyl ester (BTDE), 3,4 -oxydianiline (3,4 -ODA), and end capping reagent, 5-norbornene-2,3-dicarboxylic acid monomethyl ester (NE). The cure process proceeds in two steps imidization (1) and a thermally induced (retro-diene Diels-Alder) decomposition-recombination crosslinking step (2) (Fig. 14). 

Because of the reversibility of the polymerization and the high reactivity of the oxonium functions, bi- and trifunctional PTHFs are not easy to use. However, addition of a nucleophile to a solution of living polymer yields telechelics that are easier to handle (300). End-capping reagents and the resulting end groups are shown in Table 7. 

Table 10 End Capping Reagents and the Resulting End Groups Used in the Synthesis of PTHF...

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