Isothermal crystallization of PVA was studied by differential scanning calorimeter (DSC). Sigmoidal shapes of the isotherms for crystallization of PVA obtained at different temperatures of 205°C to 223°C are very similar to one another and are superposable. The value of exponent n in Avrami's equation of PVA is 1.75±0.25 irrespective of degree of polymerization and configuration of PVA. The value of n for mixture of PVA and triethylene glycol is 3.82. This value suggests that spherulites are grown. Half time of crystallization is dependent remarkably on the crystallization temperature and degree of polymerization. Multipeaks are observed in DSC thermogram of PVA film which was stepwise annealed.
The rapid photodegradation of polyether-polyester block copolymers was studied under ultraviolet (UV) irradiation in air for a short duration under which the effect of oxygen was neglected, and the degradation mechanism is discussed in relation to the photochemical reaction. (1) The intrinsic viscosity of block copolymers decreased markedly as a result of the degradation. The number of carboxyl groups resulted from the chain scission increased with irradiation time. (2) From the results obtained, it seems resonable to assume that n-π* transition caused by UV-irradiation may promote the chain scission at the sites of ester linkages formed between polyether block chains and polyester ones. (3) The rate of increase of carboxyl groups with the degradation was proportional to the concentration of ester linkages between two types of block chains, and the process of chain scission obeyed the first order kinetics. (4) When the acid or ether component at the site of ester linkages between two block chains was replaced with other ones, respectively, the rate of chain scission varied, and the variation agreed with that of the photoreaction between the carbonyl group and the hydrogen atom of γ-position. (5) The activation energy of this degradation process was approximately 14 Kcal/mol. It was concluded from the results that the degradation is principally governed by the chain scission at the site of ester linkages fromed between the polyether and the polyester block chains.
Influence of soft segments, i.e., polyether and polyester, on the elastic recovery and the characteristics of heat set has been studied of the linear polyurethane elastomers prepared by the usual method. It has been found that the variation in soft segment does not influence very much on the degree of heat set, but significantly on the elastic recovery. The fine structure, orientation and crystallization was investigated by the X-ray diffraction method. It has been concluded that the elastic recovery is greatly attributed to the orientation and crystallization of the soft segment, because of the orientation and crystallization of the soft segment by drawing the sample and the low elastic recovery of the highly crystalline sample after removal of the tension.
The interactions between solvents and poly (ethylene terephthalate) (PET) fiber were discussed on the basis of swelling behavior of PET fibers with different fine structures in trichloroethylene, tetrachloroethylene, chloroform, 1, 2-dichloroethane and acetone. Results obtained were as follows; (1) The diffusion behavior of solvents in heat treated PET fibers is classified in the following cases; i. e. 1) the diffusion coefficient is constant in the whole process of diffusion, 2) it gradually increased in the first step and then reaches a constant value and 3) it gradually increased in the whole process of diffusion. (2) It is considered that the increase of the diffusion coefficient is caused by the retardation of the relaxation of the interchain bond of PET by the diffusion of solvent. (3) The activation energy of diffusion varies with the heat treating temperature of PET fiber. The higher the ability of solvent to relax PET chains, the smaller becomes the effect of annealing. (4) The above-mentioned results are interpreted by the interaction power and the steric effect of solvent to the fine structure of the amorphous region of heat treated PET fibers. These support the results of the previous paper. 1)
A fatigue tester to which a pen-galvanometer was applied was deviced. This tester is characterised by the electronic feedback system of tension and by the rate feedback system to chose the suitable damping ratio for the spring constant of the specimen. By examining the frequency and indicial responses of this fatigue tester, the following results were obtained. (1) In the case of a nylon 180D yarn, the tension well followed the input signal up to 80Hz, while the damping ratio has the small effect on the indicial response. (2) In the case of a rubber string, the tension followed the input signal and the damping ratio has significant effects on the gain and indicial response.
On the basis of the theoretical expressions on the melting of two component copolymers reported in our preceding papers, the related thermodynamic quantities were investigated for two kinds of copolyamides. In particular, the heat and the entropy of transition in the amorphous regions for these copolymers were compared quantitatively with those for the homopolymers.
Piperazine polyamides were prepared from piperazine and dicarboxylic acid (adipic, suberic, sebacic, terephthalic and isophthalic acid) by interfacial, low-temperature solution and melt polycondensation methods. Polymers thus prepared have fairly low moisture regains. Polyamides from suberic and sebacic acid were hot-pressed and subjected to dynamic mechanical measurement. Temperature of tan δmaz of these polymers is found at around 100°C, which is relatively high in comparison with nylons, and does not shift appreciably by water absorption, which probably is due to the vaporization of water during measurement, but small shoulder appeares at 40_??_50°C in tan δ curve. These moisutre absorption and dynamic mechanical behaviors are discussed in relation to the characteristic structures, such as the lack of N-hydrogen atom and the rigidity of piperazine ring.