Synthesis of cellulose-polyacrylonitrile copolymers has been studied in a homogeneous solution of... more Synthesis of cellulose-polyacrylonitrile copolymers has been studied in a homogeneous solution of N,N-dimethylacetamide/LiCl. The method is based on the preliminary reaction of a portion of OH cellulosic groups with acryloyl chloride to give cellulose with a certain number of pendant double bonds. Successively, acrylonitrile is grafted onto the unsaturated groups by free radical polymerization using azobisisobutyronitrile as initiator. The optimum grafting conditions are evaluated by changing reaction temperature, as well as monomer/ initiator and monomer/unsaturated group molar ratios. The products are characterized by size exclusion chromatography, i.r. and 13 C n.m.r. spectroscopy and a possible reaction mechanism is deduced.
The reactivity ratios for the free radical copolymerization of styrene and methyl methacrylate at... more The reactivity ratios for the free radical copolymerization of styrene and methyl methacrylate at 50°C have been evaluated in dioxane, acetone and dimethylformamide solutions. In all these systems there is a marked solvent effect on both r 1 and r 2, which can be correlated to the variation in the dielectric constant of the solvent. The role of solvents in enhancing the polarization of growing chains and the alternation tendency is discussed.
Abstract The use of a UV spectrometer for evaluating the chemical composition of styrene-methyl m... more Abstract The use of a UV spectrometer for evaluating the chemical composition of styrene-methyl methacrylate random co-polymers is conditioned by the presence of a marked hypochromism at 2695 Å. The composition range where the hypochromic effect appears is ...
Aromatic polyamide (aramid) copolymers having a highly branched architecture were prepared by dir... more Aromatic polyamide (aramid) copolymers having a highly branched architecture were prepared by direct polycondensation of an AB
The kinetics of e-caprolactam fast-activated anionic polymerization in the bulk under quasi-adiab... more The kinetics of e-caprolactam fast-activated anionic polymerization in the bulk under quasi-adiabatic conditions is analyzed in terms of three semiempirical schemes. Malkin's model, the most frequently quoted approach in the literature, provides an excellent simulation of the polymerization kinetics in our experimental conditions, but the values of the derived parameters do not remain constant, as predicted by the model when different experimental conditions are chosen, and do not allow any correlation with the physical and chemical aspects of the reaction. The same limit exists for Lin's model, with a poorer agreement between simulation and experimental data. Only Kamal-Sourour's model provides almost constant values of the parameters present in the equation and can be considered a valid approach for the description of the whole course of the reaction in our experimental conditions. The relevance of the auto acceleration step is compared for two very fast activators and related to the most accredited interpretation of its occurrence. V
A number of anomalies, found in studies on the free-radical copolymerizations of a variety of mon... more A number of anomalies, found in studies on the free-radical copolymerizations of a variety of monomers are attributed to the globular state of growing macroradicals, the monomer mixture composition inside and outside of which differ markedly. An account of such partitioning of monomers (the Harwood Bootstrap Effect) is performed within the framework of a new quantitative theory of copolymerization which interprets the dependence of the composition of copolymers obtained at low conversions on their molecular weights, as well as explains the pronounced intramolecular and compositional inhomogeneity of these copolymers. A theoretical approach has been elaborated to describe the copolymerization of an arbitrary number of monomers which is easy to verify experimentally because along with reactivity ratios its only other input parameters are the Flory-parameters of pair interactions between monomer units, monomers, and solvent molecules.
The multistep method suggested in the literature for the synthesis of poly(p-benzamide) (PBA) blo... more The multistep method suggested in the literature for the synthesis of poly(p-benzamide) (PBA) block copolymers has been critically reexamined. 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.
The direct synthesis of poly(p-phenyleneterephthalamide) has been successfully performed by polym... more The direct synthesis of poly(p-phenyleneterephthalamide) has been successfully performed by polymerizing its dimer, N-(4-aminophenyl)terephthalamic acid, instead of p-phenylenediamine and terephthaloyl chloride or terephthalic acid, as commonly carried out. An intrinsic viscosity much higher than those typical of the commercial fibres (Kevlar®) has been obtained. The procedure and the advantages of the method are highlighted.
The influence of initiator and activator concentrations on the anionic polymerization of c-caprol... more The influence of initiator and activator concentrations on the anionic polymerization of c-caprolactam and, in particular, on the methanol-extractable fraction of the final polymer has been w idely studied.Dueto the increasing interest ofthis polymerization in the field of reaction injection molding(R1M) technology, a thorough investigation has been also carried out to find the best experimental conditions for this reaction in the mold. The effectof post polymerization annealingonthe overall amount of low-molecular mass substances, among which cyclic oligomers, has been evaluated. Thermal properties as well as crystallinityofthe resultant materials have been examined.Acomparison with literature data is given; the suggested correlation between the amount ofthe oligomeric fraction and the molecular arrangement ofthe polymer in the solid state is discussed.
Samples of polycaprolactam, obtained by anionic polymerization of caprolactam in bulk under adiab... more Samples of polycaprolactam, obtained by anionic polymerization of caprolactam in bulk under adiabatic conditions and in presence of different amounts of lithium chloride, have been fractionated using a method based on summative fractionation of the polyamide in the amorphous ...
For comparison, the characteristics of the above blends have been matched to those based on PA6 a... more For comparison, the characteristics of the above blends have been matched to those based on PA6 and the HB aramid synthesised from an AB 2 monomer (namely 5-(4-aminobenzoylamino)isophthalic acid, named ABZAIA), which was the topic of a ...
Random copolymers from ethylene and carbon monoxide, containing different numbers of carbonyl gro... more Random copolymers from ethylene and carbon monoxide, containing different numbers of carbonyl groups in the main chain, have been crystallized from dilute solutions. The self-seeding technique has been applied. Monolayer single crystals are obtained and some results concerning their morphology and the unit cell dimensions as functions of the carbonyl content are reported. The annealing treatment supports a structural transition previously noted for other polymers.
Branched PET samples with a high content of trifunctional comonomer units were prepared by additi... more Branched PET samples with a high content of trifunctional comonomer units were prepared by addition of suitable amounts of mono-and trifunctional monomers to dimethyl terephthalate and diethylene glycol. The samples were fully characterized in terms of structural parameters ...
Synthesis of cellulose-polyacrylonitrile copolymers has been studied in a homogeneous solution of... more Synthesis of cellulose-polyacrylonitrile copolymers has been studied in a homogeneous solution of N,N-dimethylacetamide/LiCl. The method is based on the preliminary reaction of a portion of OH cellulosic groups with acryloyl chloride to give cellulose with a certain number of pendant double bonds. Successively, acrylonitrile is grafted onto the unsaturated groups by free radical polymerization using azobisisobutyronitrile as initiator. The optimum grafting conditions are evaluated by changing reaction temperature, as well as monomer/ initiator and monomer/unsaturated group molar ratios. The products are characterized by size exclusion chromatography, i.r. and 13 C n.m.r. spectroscopy and a possible reaction mechanism is deduced.
The reactivity ratios for the free radical copolymerization of styrene and methyl methacrylate at... more The reactivity ratios for the free radical copolymerization of styrene and methyl methacrylate at 50°C have been evaluated in dioxane, acetone and dimethylformamide solutions. In all these systems there is a marked solvent effect on both r 1 and r 2, which can be correlated to the variation in the dielectric constant of the solvent. The role of solvents in enhancing the polarization of growing chains and the alternation tendency is discussed.
Abstract The use of a UV spectrometer for evaluating the chemical composition of styrene-methyl m... more Abstract The use of a UV spectrometer for evaluating the chemical composition of styrene-methyl methacrylate random co-polymers is conditioned by the presence of a marked hypochromism at 2695 Å. The composition range where the hypochromic effect appears is ...
Aromatic polyamide (aramid) copolymers having a highly branched architecture were prepared by dir... more Aromatic polyamide (aramid) copolymers having a highly branched architecture were prepared by direct polycondensation of an AB
The kinetics of e-caprolactam fast-activated anionic polymerization in the bulk under quasi-adiab... more The kinetics of e-caprolactam fast-activated anionic polymerization in the bulk under quasi-adiabatic conditions is analyzed in terms of three semiempirical schemes. Malkin's model, the most frequently quoted approach in the literature, provides an excellent simulation of the polymerization kinetics in our experimental conditions, but the values of the derived parameters do not remain constant, as predicted by the model when different experimental conditions are chosen, and do not allow any correlation with the physical and chemical aspects of the reaction. The same limit exists for Lin's model, with a poorer agreement between simulation and experimental data. Only Kamal-Sourour's model provides almost constant values of the parameters present in the equation and can be considered a valid approach for the description of the whole course of the reaction in our experimental conditions. The relevance of the auto acceleration step is compared for two very fast activators and related to the most accredited interpretation of its occurrence. V
A number of anomalies, found in studies on the free-radical copolymerizations of a variety of mon... more A number of anomalies, found in studies on the free-radical copolymerizations of a variety of monomers are attributed to the globular state of growing macroradicals, the monomer mixture composition inside and outside of which differ markedly. An account of such partitioning of monomers (the Harwood Bootstrap Effect) is performed within the framework of a new quantitative theory of copolymerization which interprets the dependence of the composition of copolymers obtained at low conversions on their molecular weights, as well as explains the pronounced intramolecular and compositional inhomogeneity of these copolymers. A theoretical approach has been elaborated to describe the copolymerization of an arbitrary number of monomers which is easy to verify experimentally because along with reactivity ratios its only other input parameters are the Flory-parameters of pair interactions between monomer units, monomers, and solvent molecules.
The multistep method suggested in the literature for the synthesis of poly(p-benzamide) (PBA) blo... more The multistep method suggested in the literature for the synthesis of poly(p-benzamide) (PBA) block copolymers has been critically reexamined. 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.
The direct synthesis of poly(p-phenyleneterephthalamide) has been successfully performed by polym... more The direct synthesis of poly(p-phenyleneterephthalamide) has been successfully performed by polymerizing its dimer, N-(4-aminophenyl)terephthalamic acid, instead of p-phenylenediamine and terephthaloyl chloride or terephthalic acid, as commonly carried out. An intrinsic viscosity much higher than those typical of the commercial fibres (Kevlar®) has been obtained. The procedure and the advantages of the method are highlighted.
The influence of initiator and activator concentrations on the anionic polymerization of c-caprol... more The influence of initiator and activator concentrations on the anionic polymerization of c-caprolactam and, in particular, on the methanol-extractable fraction of the final polymer has been w idely studied.Dueto the increasing interest ofthis polymerization in the field of reaction injection molding(R1M) technology, a thorough investigation has been also carried out to find the best experimental conditions for this reaction in the mold. The effectof post polymerization annealingonthe overall amount of low-molecular mass substances, among which cyclic oligomers, has been evaluated. Thermal properties as well as crystallinityofthe resultant materials have been examined.Acomparison with literature data is given; the suggested correlation between the amount ofthe oligomeric fraction and the molecular arrangement ofthe polymer in the solid state is discussed.
Samples of polycaprolactam, obtained by anionic polymerization of caprolactam in bulk under adiab... more Samples of polycaprolactam, obtained by anionic polymerization of caprolactam in bulk under adiabatic conditions and in presence of different amounts of lithium chloride, have been fractionated using a method based on summative fractionation of the polyamide in the amorphous ...
For comparison, the characteristics of the above blends have been matched to those based on PA6 a... more For comparison, the characteristics of the above blends have been matched to those based on PA6 and the HB aramid synthesised from an AB 2 monomer (namely 5-(4-aminobenzoylamino)isophthalic acid, named ABZAIA), which was the topic of a ...
Random copolymers from ethylene and carbon monoxide, containing different numbers of carbonyl gro... more Random copolymers from ethylene and carbon monoxide, containing different numbers of carbonyl groups in the main chain, have been crystallized from dilute solutions. The self-seeding technique has been applied. Monolayer single crystals are obtained and some results concerning their morphology and the unit cell dimensions as functions of the carbonyl content are reported. The annealing treatment supports a structural transition previously noted for other polymers.
Branched PET samples with a high content of trifunctional comonomer units were prepared by additi... more Branched PET samples with a high content of trifunctional comonomer units were prepared by addition of suitable amounts of mono-and trifunctional monomers to dimethyl terephthalate and diethylene glycol. The samples were fully characterized in terms of structural parameters ...
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