Polymethylenic series

With all six series of polyester illustrated in Figure 25.14, as the number of methylene groups in the repeating unit increases so the polymer becomes more like a linear polyethylene (polymethylene). Thus the melting points for five of the six classes are seen to converge towards that of the melting point of polymethylene. In the ca.se of the sixth class, the poly(alkylene adipates), there would appear no reason to believe that additional data on other specific members of the class would not lead to a similar conclusion. 

Oligo- and polymethylene-bridged complexes can be prepared by reaction of metal carbonyl anions with w.w -dihaloalkanes. This method proved to be a simple entry to the iron series /j,-(CH2)j.][(t75-C5H5) Fe(CO)2]2 (x s 3) (283), but yielded quite different products in the case of Na[(T 5-C5H5)Mo(CO)3] (283) and Na[Mn(CO)s] (284). An alternative two-step synthesis of the iron compounds involves the preparation of the mononuclear w-haloalkyls LXM—(CH2)X—X, and a subsequent... 

The equation for the diffusion coefficient in a gaseous state, Dc, is the starting point for the derivation of an equation for diffusion coefficients in an amorphous solid state (S). The homologous series of n-alkanes is used as a reference class of chemical compounds which asymptotically reach an unlimited molecular chain in the form of poly methylene. The diffusion coefficient, DSji, is derived theoretically for a member of the series with j carbon atoms at infinite dilution in a matrix of a n-alkane with i carbon atoms in the molecule. In addition, the diffusion in polymethylene, which is considered as the reference structure for all polymers is also derived theoretically. 

Linear capsiacinoids with a C9/C12 chain are only trace constituents of capsicum oleoresin, which mainly contains branched capsaicinoids. The acyl moiety of these compounds is produced by the branched chain fatty acids pathway (Scheme 4.1) [30[. Depending on the nature of the amino acid that acts as the acyl starter precursor, different capsaicinoids are formed. Thus, capsaicinoids of the iso series such as CPS and homocapsaicin I are derived from valine and leucine via isobutyrylCoA and isovalerylCoA, respectively, while those from the anteiso series such as homocapsaicin II originate from isoleucine via 2-methylbutyrylCoA (Scheme 4.1) [31[. The polymethylene moiety of norcapsaicin has one less carbon than capsaicin. The... 

The polyhomologation of 1-boraadamantane THF by dimethylsulfoxonium methylide formed a series of new macrocyclic trialkylboranes 24, oxidation generated a three-armed star polymethylenic polymer, based on a c/s,m-l,3,5-trisubstituted cyclohexane core <03JA12179>. 

A series of compounds, illustrated by (137), was evaluated for in vitro affinity for a, and a,-adrenoceptors by radioligand-binding assays (83). All compounds showed good affinities for the a, adrenoceptor, with K- values in the low nanomolar range. The polymethylene chain spacer between furoylpiperazinylpyradiz-inone and aryl piperazine moieties was shown to influence the affinity and selectivity of these compounds. A gradual increase in affinity for the a, adrenoceptor was observed, by length-... 

Figure 27. Polymethylene-linked dyads. For longer members of the series, added to ensure the chain was kept in the extended conformation [86].

Recent studies have shed light on the distance dependence of the rates of ET reactions proceeding through polymethylene chains. The rates of photoinduced forward and thermal charge recombination ET in the series of dyads 34(n) (Figure 27) have been measured for various chain lengths, n = 1-5, 7, and 8 [86],... 

A similar study has been carried out on the series of polymethylene dyads 35( ) and 36(b) in which n = 3-12 [87]. The rate data fitted an exponential decay with increasing values of n, provided that the experiments were carried out in the presence of /S-cyclodextrin for dyads with n > 7 (vide supra). The damping factor was calculated to be ... 

Most of the subject polymers that have been studied to date have contained flexible spacers composed of polymethylene chains. The monomers or precursors for these spacers are readily available as either diols or diacids or as dihalides, and this availability has led to the preparation of several homologous series of thermotropic polymers with different mesogenic units. Indeed, the first reported main chain, thermotropic LC polymer contained a polymethylene flexible spacer... 

Another series of polymers was prepared by reaction of the diacetoxy ester of meso-genic structure 33 in Table 1 with a series of a,(B-polymethylene diacids The spacer length was increased from 3 to 12 methylene groups, and examples with spacers of 14 and 20 repeat units were also prepared. These polymers had a mesogenic unit that was shorter than that for the series just discussed (18A vs 13A), and this probably led to the reported formation of only the nematic mesophase in this polymer series. 

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