End-capped polymers

This interesting class of polymers, which could be considered telechehc, is one of the clear examples in which the introduction of only one or two units of at the 

The first example of polystyrenes capped with a Qo moiety was reported in 1995 by Frey [32]. All the materials easily formed transparent and homogeneous films with increased conductivity. 

Nevertheless, two groups have strongly helped the development of this class of polyfullerenes Goh s, which has focused mainly on the mechanical behavior, miscibility properties and interpolymer complexes of C )-end-capped polymers (Chapter 4) [33], and Tam s, which has emphasized the aggregation behavior and self-assembly of endopped polymers under appropriate conditions (Chapter 3) 

However, other groups are still working on this topic and, recently, an interesting thermosensitive end-capped C -polymer with radical scavenging properties 

The first example of a fullerene covalently linked to a dendrimer was reported by Frechet and Wudl in 1993 [37]. Since then, several studies have been carried out, mainly by the groups of Hirsch, who have focused on the synthesis and properties of water-soluble C o-dendrimers and on globular dendrimers [38], Nierengarten, who have developed several synthetic routes for a number of different fulleroden-drimers and their applications (Chapter 10) [39], and Deschenaux, who have studied, in detail, aU aspects regarding C ,-dendrimers with liquid crystal properties (Chapter 11) [40]. 

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Polymer is separated from the polymerisation slurry and slurried with acetic anhydride and sodium acetate catalyst. Acetylation of polymer end groups is carried out in a series of stirred tank reactors at temperatures up to 140°C. End-capped polymer is separated by filtration and washed at least twice, once with acetone and then with water. Polymer is made ready for extmsion compounding and other finishing steps by drying in a steam-tube drier. 

Traces of formaldehyde, present in neat end-capped polymer or produced by processing polymer under abusive conditions, detract from polymer stabihty. Commercial resins typically contain formaldehyde scavengers. Nitrogen compounds, especially amines and amides, epoxies, and polyhydroxy compounds, are particularly efficacious scavengers. 

A very efficient energy transfer (producing emission at 613 nm) was observed in PL spectra of the perylene end-capped polymer 361 in solid films. This material had the highest QE (>60%) among the fluorene- perylene polymers, although the performance of its PLED has not yet been reported [434],... 

The facile addition of primary and secondary amines to Cjq has been used to synthesize polymer-bound Cjq [126-133]. Solutions of precursor polymers containing primary amino groups in the side chain or secondary amino groups in the main chain [132] were allowed to react with CgQ in a "buckybalT fishing process. Fullerene end capped polymers (type V) are accessible by reaction of amino-terminated polystyrene [128], poly(ethylene glycol) or poly(propylene glycol) [129] with Cgo. 

The triphenyl methyl or trityl radical behaves as a radical trap and favors the polymerization-termination which is thermoreversible and thus allows the insertion of a new polymeric sequence. In 1982, Otsu et al. [49,213,214] proposed an interesting example involving phenylazotriphenylmethane as Initer (initiator-terminator) able to initiate a free radical polymerization from the phenyl radical. Alternatively, the trityl end-capped polymer can be utilized as an original macroiniter for the polymerization of a second monomer and yields block copolymers as follows ... 

A mixture consisting of poly(s-caprolactone-co-trimethylene carbonate) (0.129 mmol), the Step 3 product (1.79 mmol), pyridine (0.62 mmol), and 20.5 ml of CH2CI2 were stirred overnight at ambient temperature. The end-capped polymer was precipitated in diethyl ether and then purified by fractionation using DMF and diethyl ether/methanol, 8 2 the product was isolated in 86% yield. 

After freeze-drying the end-capped PSa branch, the excess silane was removed under high vacuum by heating the resulting porous material at 50 °C for at least 3 days. After the silane was removed the end-capped polymer was dissolved in benzene, which was introduced directly by distillation from the vacuum line. 

On the other hand, Scherf and coworkers used N,N-bis(4-methylphenyl)-N-phenylamine as the end-capper to yield the polymer 16 (end-capper concentration 3 mol%) its single-layer device (ITO/PEDOT PSS/16/Ca/Al) exhibited maximum luminance of 1600cdm 2 and efficiency of 1.1 cdA-1, with CIE coordinates (0.15, 0.08) at 8.5 V [29]. This efficiency is higher than that of non-end-capped polymer 3 (that is, bromine exists at each chain end) by one order of magnitude and was attributed to an efficient hole trapping at the... 

Linear poly(dimethylsiloxane)s are used in a number of refinery applications. They are normally trimethylsilyl end-capped polymers of the type MDnM. They are made by reaction of dimethylsilicone fluid (DM) and a source of chain terminator, (CHj SiO- (M). The ratio of M to D controls the molecular weight and viscosity of the product (9). 

Styrene-(ethylene-butylene)-styrene fiiblock copolymer, 165 Capcure 3-800 Thiol end-capped polymer, 508 Caprolan ... 

A blend of the tweezer-end-capped polymer with 8 exhibited essentially the same tensile modulus (1.8 MPa) as the analogous healable blend (1.2 MPa) supported by weaker interactions (7 and 8, Fig. 12). This finding confirms that the major contributing factor to the tensile modulus of the material is the nature of the... 

This type of functionalization is common in polysaccharide chemistry but it also has applications in other fields. It has been employed for the introduction of self-fluorescence of nanocomposites as well as for the transformation of aldehyde end-capped polymers into amine end-capped ones. ... 

A triazole crosslinked polymer can be formed by the cycloaddition of an azide end-capped polymer with dipolarophile acetylenic curing agent [31]. 

Block Copolymers. Block copolymers (qv) have been made in two-step processes. First a mixture of chloroprene and p-xylene-bis-AT,A -diethyl dithiocarbamate was photopol5nnerized to form a dithiocarbamate-terminated pol5mier which was then photopol5nnerized with styrene to give the block copolymer. The block copolymer had the expected morphology of spherical polystyrene domains within the polychloroprene matrix (31). Other routes to block copolymers involved hydrolysis of xanthate or thiocarbamyl end-capped polymers followed by oxidative coupling of the two different homopolymers. Core-shell technology is another potential route to block copolymers. 

A broad variety of difunctional allylic olefins have been used for the synthesis of amino-, carboxyl-, and halide-terminated polybutadienes by means of the Grubbs catalyst I (396-398). With the same catalyst, commercially interesting hydroxy telechelic polybutadienes could be obtained by the cleavage of the acetyl end-capped polymer or the copolymer, as depicted in Figure 14 (399,400). 

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