Isomeric poly

PHOST represents poly(4-hydroxystyrene). The properties of the isomeric poly(2-hydroxystyrene) and poly(3-hydroxystyrenes) differ substantially (87). 

TABLE 2.7 Melting Temperatures of Isomeric Poly(alkylene terephthalate)s and... 

Isomeric poly(alkylene terephthalate)s, melting temperatures of, 36 Isophthalaminonitrile, polymerization of, 344... 

Different mechanistic interpretations of the formation of an alternating propylene/carbon monoxide copolymer of poly(spiroketal) structure were considered [107, 478, 480, 481, 489]. Any reasonable proposal, however, needs to take into account the nature of the end groups in the copolymer chains. To date this has not been possible owing to the low solubility of the copolymer in solvents other than hexafluoroisopropanol however, this solvent, probably because of its acidic nature, causes transformation of the poly(spiroketal) structure into an isomeric poly(ketone) structure [489]. The formation of a cyclic polymeric structure could be favoured by minor entropy loss due to the intramolecularity of the process [480,481] and by the peculiar conformational situation of the poly(ketone) structure [491]. 

Some data deal with the stabilizing efficiency of polymers and copolymers bearing a stabilizing functionality. Three isomeric poly(vinylphenols) provided a better resistance to oxidation than the corresponding monomers (the o-hydroxy isomer provided the best protection). All tested poly(vinylphenols) were however slightly inferior to 2,6-di-rerr-butyl-4-methylphenol [330]. The presence of the... 

In this compound we have a substance approaching the proteins in complexity and it has been found to resemble the proteins and the proteoses and peptones in its physical properties. Furthermore, a simpler synthetic poly-peptide, viz., a tetra-peptide has been found to be almost identical with an isomeric poly-peptide obtained by the hydrolysis of a silk protein. This synthetic tetra-peptide has the following constitution ... 

The possibility that olefin-carbon monoxide copolymers can exist in the isomeric poly-spiro ketal structure (Scheme 8.5) was recognized soon after the first synthesis of the copolymers of propene. Using dialkyl diphosphines as the modifying ligands [27], copolymers were obtained with blocks with the spiroketal form [28]. 

Figure 2. UV spectra in CHjCl, of isomeric poly(acetonaphthyl...

The chemical shifts of the characteristic carbon signals in acyclic terpenes, polyprenols, and cis-trans isomerized poly-isoprenes are plotted in Fig. 3. Here, the chemical shifts are correlated using the w C-5 methyl carbon signal at 17.66 ppm as an internal standard (except for isomerized polyisoprenes) in order to compensate for the effect of solution concentration. It is clear that these chemical shifts are independent of the chain length of the compounds and can be used for the determination of the arrangement of isoprene units as well as the terminal units in various isoprenoid compounds (8). 

Figure 5-9. Conformations, lattice constants (fl, and c), density p, and crystal forms of the four isomeric poly(butadienes) (after G. Natta and P. Corradini).

Table 3. Degradation products of isomeric poly( jutyl acrylate)s...

The l,4-poly(butadienes) corresponding to the butene-2 compounds, however, differ in their melting points by almost 140°C (Table 1-2). 1,4-c/s-Poly(butadiene) is an elastomer l,4-trans-poly(butadiene) is thermoplastic. The other isomeric poly(butadienes) likewise show a marked difference in their properties. Aromaticized l,2-poly(butadiene), although not an isomer of poly(butadiene), shows semiconductor properties because of its conjugated double bonds. 

Starch grains also contain an isomeric poly(glucose), amylopectin, that is quite variable and much less soluble in warm water containing starch grains. This substance introduces another key concept in polymer science that was recognized by Haworth, Meyer and Mark. Glucose is not just bifunctional, it is polyfunctional. Amylopectin has been shown to be a highly branched macromolecule of maltose (Fig. 2.13). 

Monomer-isomerization poly- or oligomerization by a cationic mechanism appears to be specific for oxo-acid initiators, because facile monomer isomerization requires a rapid proton elimination from a protonated olefin. No examples of monomer-isomerization polymerization have been reported for MX initiators. The following examples of cationic monomer-isomerization oligomerization may be helpful to demonstrate another characteristic of oxo-acid initiators. 

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