It has been considered that the flow of the viscoelastic fluid in a nozzle of a uniform diameter almost fully develops from the inlet to the outlet of the nozzle. But according tothe experimental results, the Barus effect which is to be a function of the ratio of lengthto diameter of the nozzle tends to constant values in case with long nozzles. It is presumedthrough the analogy of Newtonian fluids that these experimental results suggestthe existence of the calming section in the case of viscoelastic fluids.
Therefore, the main purpose of this study is to see whether the calming section existsor not, and whether the flow at the outlet of the nozzle fully develops or not.
The photoelastic method, which has been used to study the stress distribution in elasticsolids, is applied to measuring the isochromatic patterns in the rectangular nozzles.
The measurement of the isochromatic patterns leads to the following conclusions. 1) Itmay be rightly said that the calming section exists. 2) The flow at the outlet of thenozzle doesn't occur in an equilibrium state of flow.
The second phenomenon seems to be concerned with the facts that, the values of thenormal stress difference calculated by the swelling indexes of the Barus effect, are very smallin comparison with the values calculated by other methods. Moreover, the concentrationof the isochromatic patterns on the wall at the outlet of the nozzles seems to prove theexistence of the residual pressure at the point in the viscoelastic fluid.

View full abstract

Commercial chlorinated rubbers were fractionated by successive fractional precipitation method from the dilute solution of tetrahydrofuran with water as precipitant. Viscosity and light scattering measurements of the fractions in tetrahydrofuran were made at 30°C and room temperature respectively. The intrinsic viscosity-molecular weight relationship was obtained as[η]=1.98×10^-4M_ω0.68.
In addition the solution viscosities of the fractions were measured in various solvents. The unpertured molecular dimensions of the chlorinated rubber, calculated by the Stockmayer-Fixman method for each solvent, were found to depend on the solvent nature.

View full abstract

The authors studied the mechanical denaturation of Poly-L-glutamic acid (PGA) in aqueous soltions by means of shearing force.
The experiment was done with a shaking method and the Hercules High Shear Viscometer. The coagulation of PGA caused by shearing force was observed in the aqueous solutionsof the pH range from 3.5 to 4.4, in which the molecule initialy is not completely of α-helical conformation, but in part of random-coil conformation.
These coagulated molecules were proved to have the β-structure by IR and X-ray diffractionmethods.
The process of the mechanical denaturation of PGA in the aqueous solution can be interpretedas that intramolecular hydrogen bonding in α-helical conformaton changes into intermolecularhydrogen bonding in β-structure by means of the shearing force.

View full abstract

The statistically designed experiments were carried out to study the effects of molding conditions, molecular weights and synthesis methods on the density and heat shrinkage at120°C of the injection molded polycarbonate disks. These properties were strongly affectedby the mold temperature and the holding pressure. The density became high with theincrease in holding pressure and with the decrease in mold temperature. The heat shrinkageat 120°C became small with the increase in holding pressure and mold temperature. Thestock temperature and injection rate did not affect these properties. The treatment of thespecimen at 120°C extinguished the effect of mold temperature and holding pressure on thedensity and in most of the cases, decreased the density. The properties of the specimenmolded at high mold temperature were similar to those of the specimen treated at 120°C.The effects of the mold temperature and holding pressure on the properties of injectionmolded polycarbonate were related to the short range order or local mode motion of polycarbonate mclecule.

View full abstract

The kinetics of isoprene polymerization with n-butyllithium in n-heptane solution has been constructed on the basis of the elementary reactions characterized in the preceding paper.
The concentration of Li attached to the polymer end [P_t] is directly proportional to avariable τ(τ=∫[M] dt) giving an equation.
_??_where P₀ is first step product of initiation involving n-butyllithium and monomer. The concentration of consumed monomer ([M] ₀-[M]) is directly proportional to the τ² as expressed in the following equation,
_??_where [C₁] ₀ is initial concentration of non-associated n-butyllithium and K₄ is equilibrium. constant of a cross-associatiation between n-butyllithium and polymer-end-Li. The concentration of the first step product of initiation [P] increases as the initial n-butyllithium concentration increases and [P₀]/(1+K₄ [C₁] ₀²) decreases as the initial n-butyllithium concentration increases.
Thus, these results explain satisfactorily the experimental results including the polymerization rate retardation as well as the sigmoidal conversion curve caused by excess of n-butyllithium. The calculated molecular weight distribution based on these kinetic equations agree well with those determined by the column fractionation method.

View full abstract

The elementary reactions of isoprene polymerization initiated with sec-butyllithium and with low molecular weight polyisoprenyllithium have been studied in n-heptane solution.
The concentration of Li attached to the polymer end (polymer-end-Li)[P_i] with these initiators increases more rapidly than with n-butyllithium and reaches to the concentration of charged initiator [C] ₀. The rate constant of initiation reaction k_i is determined from the relation between [C] ₀ and [P_i] at the increasing step of [P_i] which is expressed in the following equation.
where τ is a variable defined as τ=∫[M] dt.The rate constant k_i is obtained as 7.4×10^-2and 6.1×10^-2 (l/momin) for sec-butyllithium and polyisoprenyllithium, respectively. These values are fairly small in comparison with the rate constant of propagation reactionk_p=10 (l/molmin) determined previously.
The calculated molecular weight distributions based on these rate constants and the equilibrium constant of sixfold association of polymer-end-Li agree well with those determined by the column fractionation method.

View full abstract

The copolymerizations of maleic anhydride and tetrahydrofurfuryl acrylate were carriedout in benzene at 30 or 70°C. The plots of f (F1)/F against f²/F and (F1)/f against F/f² were not linear, but the plots of f (F-2)/(F-1) against f²/(F-1) and (F-2)/f against (F1)/f² were linear, where F and f were the molar ratios of the two monomersin the copolymer and in the monomers. Therefore, the relationships between the monomercompositions and the copolymer compositions were rationalized on the basis of the penultimateeffect. The monomer reactivity ratios were found to be 1.25 (r_t), 41.6 (r_t), 0 (r_m) and 0 (r_m) at 30°C, and 1.65 (r^t), 2.08 (r_t), 0 (r_m), and 0 (r_m) at 70°C.

View full abstract

Acrylonitrile (AN) was grafted onto polyvinyl alcohol (PVA) in aqueous solution using ceric ammonium nitrate as an initiator, where graft copolymer latexes were obtained.
The number of the latex polymer particles increased with an increase in ceric-ion concentration and slightly with PVA concentration, but was not affected by AN amount. The grafting efficiency (% grafted polyacrylonitrile based on polymerized AN) was high as 70-90%, and the reaction extent of PVA (% grafted PVA based on PVA added) increased with an increase in molar ratio of ceric-ion to PVA.
The film-forming ability of the graft copolymer latex and the mechanical properties of the latex films were corelated with polymer composition (polyacrylonitrile component C_N, grafted-PVA component C_AG, and free PVA component C_AN). The graft copolymer latexes, except of having low C_AG or high C_N, produced continuous, transparent latex-films under drying temperature of 20°C. The latex film whose tensile strength was close to or over 4kg/mm² was obtained from the latex having C_N/(C_AG+C_AH) =3 and containing an appreciable amount of grafted PVA. Elongation of the latex film at break increased with an increase in C_AG and with a decrease in C_N.
From the above results and the texture of the latex film observed by means of an electron microscope, a mechanism of film formation from the graft copolymer latex is proposed, where the role of PVA component of the graft copolymer is very important.

View full abstract