Carboxy end groups

An implication of the kinetic analysis presented in Sec. IV.A is that the rate of chain scission of polyesters can be retarded by endcapping to reduce the initial carboxylic acid end-group concentration. Alternatively, the rate may be increased by acidic additives that supplement the effect of the carboxy end groups. The first expectation was confirmed by partial ethanolysis of high molecular weight... 

FIGURE 25 Reduction in the rate of hydrolytic chain scission of PCL achieved by ethoxylation of the carboxy end groups of the polymer. The experimental result is compared with calculated predictions of the effect of varying degrees of ethoxylation. (From RGf. 49.)... 

In these processes hydroxy and carboxy end groups and salts capable to reinitiate copolymerization are generated. New end groups can again be formed in termination reactions. In fact, Eqs. (77) and (78) describe a chain transfer. This is also supported by the fact that during copolymerization about 10 chains are formed per one molecule of the tertiary amine at equimolar epoxide — to — anhydride ratio 39-44). 

Deffieux et al. have already prepared a-styrenyl-cw-acetal heterodifunctional vinylic polymers using living anionic polymerizations [26-30]. The heterotelechelic polystyrene chains containing a-hydroxy-cw-carboxy end groups using free radical polymerization were also prepared, and the intramolecular cyclization (unimolecular process) was examined [37]. The... 

Styryl carbanions readily react with carbon dioxide 31) to yield carboxy end groups. These terminal groups are also introduced by reaction with anhydrides 19) whereas the use of oxirane 23) leads to the formation of hydroxy end groups esters and nitriles are used to introduce carbonyl functions at the chain end. These reactions can be carried out at low temperature in THF solution and proceed quantitatively if no deactivation by protons occurs. 

In addition, telomers which exhibit carboxy end-groups have been esterified with telechelic polyether diols and a,co-difunctional PDMS have been mainly used as the central block, as in the three following examples [132-134] ... 

Such polyesters are prepared by condensation in xylene of isophtalic acid with a slight excess of 1,5-pentanediol. The molecular weights are adjusted by the ratio diol/diacid. The carboxy end groups are... 

Size, Surface Occupied by Carboxy End Groups and Conformation... 

MALDI-TOF spectra were obtained of carboxy-terminated oligostyrene samples, prepared by radical polymerization usinga dicarboxylated initiator and efficiently fractionated by HPLC. The data show that in addition to the carboxy end-groups, further end-groups are formed due to contamination of the initiator or else to side reactions during the polymerization process. ... 

Epoxies modified with butadiene acrylonitrile copolymers with (32) amine or carboxy end groups have disadvantages. They are susceptible to thermal and oxidative degradation and also have poor hot/wet properties, i.e., they soften when exposed to heat and moisture for long periods. Polysiloxane rubbers such as polydimethylsiloxane have been considered as a possible alternative. 

The synthesis of heterotelechelic PS chains containing a-hydroxy-co-carboxy end groups and their intramolecular cyclization have been described. The controlled free radical polymerization of styrene was carried out using 4,4 -azobis(4-cyanovaleric add) as the initiator and 4-hydroxy-2,2,6,6-tetra-methylpiperidin-l-oxyl,nitroxyl-2 (TEMPO) as the terminator to generate difunctional macromolecules with molar masses in the range of 1-10 kg mol" The cydization reaction was dearly evidenced by infrared spectrometry and SEC. The yield of... 

The formation of such grafts must modify the interfacial tension in a similar way to block copolymers, as discussed in chapter 6. The mechanical effect of grafting has been studied by Norton et al. (1995), who looked at the effect on fracture energy of grafting polystyrene with a carboxy end-group at an interface between polystyrene and a thermosetting epoxy resin. The unmodified... 

Nitrile rubber is used to increase impact strength of epoxy resins. It is made as a low-molecular-weight liquid oligomer with carboxy end-groups (CTBN) and used as a curing agent for the epoxy resin. 

The synthesis of these oligomers with iunctional groups on the two terminal phenyl units, especially those with amino, hydroxy or carboxy end-groups, can be used in the recently opened field of segmented block copolymers of the rigid-rod type or the soft-hard... 

Besides the amide interchange reaction shown above, propagation may also involve reaction of amine and carboxy end-groups ... 

Hydroxy and carboxy end-groups, and oxydiethylene units are already present in the initial PEG and are obviously present in final copolyester. The vinyl ester function of the E series can be formed by a degradation reaction during heating (Equation 5.7) ... 

To say that one polymer is or is not different from another will always require some arbitrary judgment of what is or is not significant in polymer identification. For example, are the two polymers represented by the source-based expressions shown as Figures 3(a) and 3(c) sufficiently different to be worthy of two separate representations In terms of source-based polymer registration, CAS regards them as two separate polymers. Some industrial consumers of PET may find that the presence of carboxy end groups rather than methoxycarbonyl ones makes no difference for their particular application, while others may find that end group composition makes an appreciable difference to product properties thus, the answer may depend upon many factors. 

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