Giuseppina Conio

Chitosan : chain rigidity and mesophase formation

Abstract Light-scattering measurements on samples of chitosan with degrees of acetylation (d.a.) of 42 and 15% have been performed in 0.1 m acetic acid-0.2 m sodium chloride. From the values of R G °, a persistence length q t ° of ∼ 220 A has been deduced, which is lower than that (∼ 350 A) of chitin and indicates a decrease of rigidity with decrease in d.a. The existence of a cholesteric mesophase above a critical value of [polymer] has been demonstrated.

Physical-chemical characterisation of acrylic polymers grafted on cellulose

An oxidative reaction of cellulose with sodium metaperiodate was performed. The oxidised groups were decomposed by treatment with UV light into free macroradicals. In the presence of acrylic monomers, in the vapour phase, these reactive sites become the starting points for the graft copolymerisation of the cellulose substrate. In this study we examined the graft yield as a function of the polymerisation time and the oxidation degree of cellulose. The grafted polymer was characterised using several analytical techniques, DSC analysis, GPC analysis, viscosity, FTIR and 13C CP-MAS. Information on the morphology of grafted chains with respect to the bulk cellulose was obtained, measuring the dynamic parameters in a careful 13C CP-MAS NMR study. All proposed chemical reactions, if properly conducted, do not affect the crystallinity of cellulose and introduce only a very modest amount of oligomers, therefore they seem suitable for the consolidation and protection of precious cellulose based materials, which are of historical interest.

On the synthesis of poly(p-benzamide) block copolymers by the phosphorylation reaction

The multistep method suggested in the literature for the synthesis of poly(p-benzamide) (PBA) block copolymers has been critically re-examined. The reaction products after each step have been isolated and characterized, and the extent of competitive processes evaluated. Under the chosen experimental conditions, almost no PBA copolymer is formed in the presence of terephthalic acid and p-aminobenzhydrazide. The increase of the limiting viscosity number has been attributed to coupling reactions between PBA chains by the difunctional reagents used in steps 2 and 3.

Isolation and characterization of multiple forms of renin from bull kidney.

Different forms of renin have been purified from bull kidney by combined gel filtration, affinity chromatography and ion-exchange chromatography. The specific activity of the enzyme was determined by a biochemical method of synthetic substrate and by radioimmunoassay on both synthetic and natural substrates; molecular characterization was carried out by molecular weight determinations, polyacrylamide gel electrophoresis, isoelectric focusing, amino acid analysis and optical rotatory dispersion. Three forms (renin C, D, E) are distinct on the basis of amino acid composition and chromatographic behavior, while possessing the same molecular weight, and displaying only minor differences in specific activity, alpha-helix content and isoelectric point; the occurrence of a group of renin isoenzymes may be suggested. Another form (A) has a lower specific activity and a higher molecular weight (57 000) compared with C, D and E and further differs markedly in chromatographic behavior, amino acid composition, alpha-helix content and isoelectric point, as well as in substrate specificity; it may be regarded as a pseudorenin. The fifth form (B) possesses the highest specific activity and does not correspond to a single molecular form; the presence of two components of different molecular weight (27 000 and 46 000 respectively) has been established both by polyacrylamide gel electrophoresis and isoelectric focusing.

Solution properties and mesophase formation of 4‐phenyl‐benzoylcellulose

Cellulose samples were derivatized in dimethylacetamide/LiCl (DMAc/LiCl) to give 4‐phenyl‐benzoylcelluloses (PBCs). The process is quantitative and leads to an highly substituted product, as verified by elemental analysis, IR and 13C‐NMR spectroscopy. PBC samples were characterized by viscometric and light scattering measurements in DMAc. The persistance length q is used to evaluate the theoretical critical volume fraction for mesophase formation (v′th, which has been found higher than the experimental critical one (v′exp)

Synthesis of block copolymers based on poly(p-benzamide) with a polyamide benzimidazole

Abstract A diblock copolymer based on poly( p -benzamide) (PBA) and poly(2-phenylene-(5-benzimidazole))isophthalamide (PABI) was synthesized by direct coupling reaction between acylchloride and amino end groups of the two homopolymers. Soxhlet extraction with N,N 1- dimethylacetamide completely removed unreacted PABI and allowed determination of copolymer content and composition of the unextracted fraction (by u.v. data and viscosity measurements). Preliminary results on phase behaviour are given and analysed in terms of block length.

Lyotropic block copolymers of poly(p-benzamide) and poly[2-phenylene (5-benzimidazole)]: The ternary system copolymer/poly(p-benzamide)/dimethylacetarnide—lithium chloride

New rigid-flexible copolymers based on poly( p -benzamide) (PBA) and poly[2-phenylene (5-benzimidazole)] (PABI) were synthesized, varying the molecular weight of the flexible block. Ternary solutions in dimethylacetamide—3% LiCl show the peculiar behaviour expected theoretically for this kind of system. In particular, it was demonstrated that more copolymer enters the anisotropic phase as the PABI chain length becomes shorter. Comparison with homopolymer mixtures shows the usefulness of the copolymer in improving the amount of flexible chains inside the mesophase.

Poly[2-phenylene-(5-benzimidazole)] isophthalamide : macromolecular characterization

Two different synthetic routes have been used to synthesize poly[2-phenylene-(5-benzimidazole)] isophthalamide (PABI), an aromatic polyamide that shows good compatibility with rigid chain polymers such as poly(p-benzamide). The influence of the conditions of synthesis in determining the molecular weight of PABI has been investigated in order to use this polymer for rigid—flexible copolymers with specific characteristics. Values of [η] and Mw have been determined in 96% H2SO4 and dimethylacetamide, and conformational properties have been investigated by viscometry and molecular dynamics simulations.

Cellulose-polyacrylonitrile blends: 2. Effect of graft copolymer on the phase properties in dimethylacetamide/LiCl

Abstract The effect of a graft copolymer based on cellulose (CE) and polyacrylonitrile (PAN) on the compatibility of the two homopolymers in solution was analysed. Samples of copolymers containing different proportions of CE and PAN were synthesized. In order to reduce the degradation of the cellulose chain we tested different synthetic routes. After extraction of PAN homopolymer, the reaction products were composed of pure CE and copolymer; the percentage of PAN with respect to the total weight varied between 13 and 32.2%. A significant increase in compatibility was obtained by using graft copolymers in mixtures with the homopolymers, as evident from ternary phase diagrams and morphology of solution-cast films. Moreover, solutions containing the graft copolymer showed a liquid crystalline phase at high concentration.