1-Phenylethyl isocyanide

The mechanism for the initiation step of the polymerization was investigated using the stoichiometric reaction of 73-allylnickel trifluoroacetate (14) with 1-phenylethyl isocyanide labeled with 13C at the isocyano carbon atom (Scheme 18) [24, 25]. 13C NMR measurements revealed that addition of three... 

The existence of a non-racemic helical conformation in poly(isocyanide)s was first suggested by Millich et al. in 1969 [37]. They carried out polymerizations of optically pure d- and /-1-phenylethyl isocyanide 29 in the presence of an acidic ground glass catalyst (Scheme 26). The observation of a... 

The copolymerization of isocyanides, such as cyclohexyl, phenyl, p-toluyl and (r-toluyl—singly with diazomethane (6), or as mixtures of two isocyanides (7)—has been reported. These products are largely insoluble in common organic solvents but are dispersed in dichloroacetic add. Millich and Wang copolymerized sec-butyl isocyanide with a-phenylethyl isocyanide, and obtained a copolymer sparingly soluble in common solvents (8). Recently, Millich and Chenvanij copolymerized a phenylethyl isocyanide with methyl a-isocyanopropionate, and obtained copolymers which have solubilities suitable to conventional solution characterization methods (8,9). 

The concept of a unique hydrodynamic volume for all rodlike polymers was derived from examination of the Mark-Houwink constants, K and a, of the equation [rj ] = KMa. Macromolecules with values of a greater than unity are commonly accepted to be stiff or rigid rods. However, it was also found that such molecules (even for values of a less than unity) obey a relation illustrated by close concordance with the curve in Fig. lb (13) flexible, branched or otherwise irregular polymers, on the other hand, show dispersion around the upper part of the curve. The straight line curve in Fig. lb implies that the constants K and a are not independent parameters for the regular macromolecules to which they apply. Poly (a- and polyQJ-phenylethyl isocyanide) fall on this line the former has a value of a > 1 while the latter has a value a < 1 (14) both polymers give linear concentration dependence of reduced specific viscosity for fractionated samples... 

The rotation of alkyl and aryl substituents about the N-R single bond may be severely restricted on steric grounds in most polyisocyanides, (which usually contain branching at the a-carbon of substituent R). This is consistent with the observation that the NMR spectrum of whole samples of J-poly(a-phenylethyl isocyanide) in tetrachloroethylene undergoes little change upon heating between room temperature and 128° C (4). 

The early characterizations were carried out on unfractionated polymer samples of poly(d,/-a-phenylethyl isocyanide) of two origins ... 

One additional aspect of complexity in defining the molecular structure of polyisocyanides arises, especially wherein the substituent R group is aralkyl and contains hydrogen on the benzylic a-carbon atom, as in poly(a-phenylethyl isocyanide). The possibility of tautomeric shift of the hydrogen atom on the a-carbon is reasonably likely (5), whereby the 7t-electrons of the original... 

Homopolymers of simple alkyl and aryl isocyanides (Mv.p.osm > 1000-4000) are insoluble in all common solvents. This statement, however, requires elaboration of the fact that trichloroacetic acid successfully disperses these polymers. Observations with poly(cr-toluyl isocyanide) are informative, since the polymer is canary yellow in color, and turns to dark brown in trichloroacetic acid—acting in the manner of an acid-base indicator dye. Dilution with water of the trichloroacetic acid solution of poly(aqueous alkali produces the original yellow color. It appears that the polyisocyanide is dispersed in trichloroacetic acid as a pro-tonated species. Conductimetric experiments on poly(a-phenylethyl isocyanide) in dichloroacetic acid confirm this view (25). 

Distinctly different is the solubility behaviour of poly(a-phenylethyl isocyanide), which can be dispersed truly by thermodynamic mixing. It is soluble is more than 40 solvents, as shown in the mode of representation following Hansen s treatment (27), (Fig. 5). The well known Hildebrand-Scott solubility parameter by this treatment is divided into three indices which separately account for cohesive energy contributions from dispersion, permanent dipole-dipole, and hydrogen bonding forces. Thus, the conventional Hildebrand-Scott parameter equals 9.56 (cal/cm3) for an unfractionated sample of poly(a-phenylethyl iso-... 

Fig. 5. Lower surface of the solubility zone of unfraetionated poly(a-phenylethyl isocyanide) of Afn = 72000 (large solid sphere) in terms of Hansen s three parameter spectrum. Compatible solvents are shown by small solid spheres non-solvents by open circles. The greatest latitude...

Fig. 6. Concentration dependences of a apparent molecular weights ", and b freezing-point depression 6 per unit concentration c in benzene of poly(a-phenylethyl isocyanide) of Mn = 34800. [Reproduced from Ref. (21), with permission of J. Wiley and Sons, Publ.]...

Poly(/j-phenylethyl isocyanide), similarly, gave a first impression of random coil behavior (33) which belies a tendency of the polymer, once fractionated, to precipitate from diluted solution. 

Unfractionated poly(a-phenylethyl isocyanide), [ ]tS°c = 0.41 dl/g, A n = 30000, also displays a similar decay in dichloroacetic acid at 30° C, where rjt of a 1.16% solution decreases from 1.515 to 1.165 in 5 days (19). This polymer, therefore, shows common properties in regular solutions, in which it has been... 

Thermogravimetry and gel permeation chromatography data show that poly[(a-carboxymethyl)alkyl isocyanides) also undergo degradation which becomes rapid at temperatures above 50° C. However, at room temperature this process is sufficiently slow so as not to confuse the observations reported above. Other polyisocyanides, including copolymers of the above with a-phenylethyl isocyanide, are being synthesized which may prove less complex subjects of study of the phenomena described above. 

Poly(a-phenylethyl isocyanide), however, yields complex products distinguishable from monomer upon thermal degradation at 20 mm Hg (13). At 300° C a viscous condensate is produced which is free of isocyanide absorption in its infrared spectrum and appears very similar to the recently synthesized oligo-isocyanides, a,co-dihydrotri(a-phenylethyl isocyanide) and a,co-dihydrohexa(a-phenylethyl isocyanide) (15). Pyrolysis at 500° C produces an intense broad infrared absorption band in the range about 3300 cm-1, which is the range of associated N il bonds. Pyrolysates obtained at 700° C reveal nitrile absorption at 2270 cm"1, that becomes more intense in pyrolysates produced at temperatures up to 1300° C. A slow pyrolysis at 200-300° C is indicated for the study of primary structural changes in poly(a-phenylethyl isocyanide). Pyrolysates of poly(<7-... 

The arrangement of helices in the solid and liquid crystalline states of poly(a-phenylethyl isocyanide) were determined by X-ray and electron diffraction. Well-defined diffraction patterns were obtained from oriented films using selected area electron diffraction. Intermolecular and intramolecular patterns were calculated from the five Debye-Scherrer rings. All the reflections were indexed in terms of a pseudo-hexagonal triclinic unit cell, with... 

Preliminary polarizing microscope studies on poly(/ -phenylethyl isocyanide) show the spontaneous reversible formation of a highly birefringent mesophase in concentrated solutions. These observations suggest that small differences in conformations due to concentration changes give rise to the occurrence of a phase separation and molecular ordering. 

Poly(a-phenylethyl isocyanide) was prepared in 55-80% batch yields, using the sulfuric acid droplet dispersion method (20), and a series of fractions with a polydispersity ratio of MJMn of 1.1-1.3 were obtained by precipitation from... 

Poly(/ -phenylethyl isocyanide) was similarly prepared and fractionated (14). A comparison between the hydrodynamic properties of poly(/T and poly(a-phenylethyl isocyanide) showed, that while the latter was characterized by its intrinsic lack of molecular flexibility, the former was relatively a flexible chain. This was manifested in the values estimated for the shape factor and the radius of gyration. Accordingly, two general conformations in dilute solution are ascribed to poly(phenylethyl isocyanides) a nearly rigid, rodlike helix to poly(a-phenyl-ethyl isocyanide), and an undulating, more randomly orienting chain to poly(/l-phenylethyl isocyanide). 

Poly(l-a-phenylethyl isocyanide) initiator H2SO4, O2, glass dibenzoyl 32 (7)... 

R)-poly(a-phenylethyl isocyanide), in tetrahydrofuran, room temperature (RS)-poly(a-phenylethyl isocyanide), in toluene, room temperature,... 

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