Alkyl chain end groups

M. A. Elrehim, S. Said, A. Ghonerm and G. Turky, Dielectric properties of hyperbranched polyesteramide with long alkyl chain end groups , Macromol Symp, 2007,254,1-8. 

In the cases of PLLA samples with alkyl ester chain ends with 12-14 carbons, the PLLA molecules on the film surface are degraded by the enzyme. The alkyl chain end groups are not readily hydrolyzed by proteinase K and remain on the film surface. As a result, during the initial stage of the... 

Reactions of quinones with radicals have been explored, and alkylation with diacyl peroxides constitutes an important synthetic tool (68). Although there are limitations, an impressive range of substituents can be introduced in good yield. Examples include alkyl chains ending with functional groups, eg, 50% yield of (70) [80632-67-3] (69,70). 

In some cases it is possible to differentiate between the various alkyl substituents. Primary, secondary and tertiary nitrates and nitrites all show clearly different infrared absorptions. The spectra of acid fluorides can be used to differentiate chain-end groups from pendant acid groups. Furthermore, the loss of all -OH species upon sulfur tetrafluoride exposure allows the reliable estimation of ketones, esters and lactones without the complication of hydrogen-bonding induced shifts in the spectra. Preliminary results from the use of these reactions to characterize y-ray oxidized polyethylene and polypropylene are used to illustrate the scope of the methods. 

Chain termination has been discussed by Drent. At higher temperatures both ester and alkyl chain ends are formed, thus leading to polymer chains with two esters, two ketones, or one of each as end groups.468... 

The second termination reaction is alkyl chain end transfer from the active species to aluminium [155]. This termination becomes major one at lower temperatures in the catalyst systems activated by MAO. XH and 13CNMR analysis of the polymer obtained by the cyclopolymerization of 1,5-hexadiene, catalyzed by Cp ZrCl2/MAO, afforded signals due to methylenecyclopentane, cyclopentane, and methylcyclopentane end groups upon acidic hydrolysis, indicating that chain transfer occurs both by /Miydrogen elimination and chain transfer to aluminium in the ratio of 2 8, and the latter process is predominant when the polymerization is carried out at — 25°C [156]. The values of rate constants for Cp2ZrCl2/MAO at 70°C are reported to be kp = 168-1670 (Ms) 1, kfr = 0.021 - 0.81 s 1, and kfr = 0.28 s-1 [155]. 

Matrix-assisted laser desorption/ionization (MALDI) mass spectrometry has contributed remarkably to unravelling the termination and initiation steps of the styrene/CO copolymerisation catalysed by the highly active bis-chelated complex [Pd(bipy)2](Pp5)2 in TFE [40]. Chain-end group analysis of the material produced in the absence of BQ showed that the termination by P-H elimination is accompanied by three different initiators two palladium alkyls from Pd-H formed by reaction of the precursor with CO and water (a and b) and a palladium carboalkoxy species formed by reaction of the precursor with the fluorinated alcohol and CO (c) (Chart 7.4). The suppression of the chain-transfer by alcoholysis was proposed to be responsible for the enhanced stability of the palladium acyl intermediates and hence for the high molecular weight of the copolymers produced. 

THF polymerization was initiated with triethyloxonium tetrafluoroborate. BF anions are known to decompose during THF polymerization, producing dead polyTHF carrying an alkyl fluoride end-group. Another reason for the formation of polyTHF may be chain transfer to polymer during THF polymerization, yielding dead blocks and dicationically living chains ... 

Two mechanisms for the first step of biodegradation of alkylmethylammonium salts are described. The first of these is oxidation of the methyl groups at the far end of the alkyl chain end a stepwise shortening of the latter. The second is a fission of the bond between the nitrogen atom and the alkyl chain, followed by the oxidation of the alkyl chain to the carbon acid which is further metabolized through 0-oxidation. It was proven in laboratory tests that alkylmethylammonium compounds are subjected to a primary degradation with an approximate half-life of 2.5 h. The ultimate degradation requires 28-40 h half-life. 

Determination of the number of labeled alkyl groups bound to the polymer chains (end groups) of polymers obtained with catalysts prepared in the presence of " C-labeled aluminum alkyls [268,279]. 

Figure 4 The first rolaxane (4) bearing transition metal complex fragments as stoppers. It is also the first cyclodextrin-based rotaxane the a-cyclodextrin ring is threaded onto an alkyl chain ended by amino groups, which bind cobalt(III) centres coordinated to cthylcncdiaminc chelates [4a].

A central core of benzene rings is linked by a fuactioaal group X. The most common end groups at the para sites, and R2, are alkyl (—C H2 ) or alkoxy (—OC H2 + ), or acyl chains C SI NO2 cinnamate (—CH=CHCOOC H2 ) or halogens. Cyclohexane rings can sometimes replace one or more of the benzene rings without loss of Hquid crystallinity. 

Fluorocarbons with a hydrophilic functional group are very active surfactants [23]. Less than 1% of ionic or nonionic surfactants with perfluoroalkyl groups can reduce the surface tension of water from 72 to 15-20 dyne/cm, compared with 25-35dyne/cm for typical hydrocarbon surfactants [24] Perfluoroether surfactants are about as active as their perfluoroalkyl counterparts of similar chain length [25, 26], but fluorosurfactants with more polar alkyl end groups are considerably less active than their perfluoroalkyl analogues (Table 7)... 

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