Tetsuo Yokoyama

The Relation between Structure and Physical Properties in Polyurethans

Abstract The field of polyurethans is rapidly growing in commercial importance, especially in form and elastomer applications. This group of polymers includes a very broad region of chemical structures and chain length. In many cases polyurethans are synthesized from polyester glycols or polyether glycols and diisocyanates so that the urethan groups are even fewer in number than other functional groups. This process of synthesis enables us to deal with a very wide range of polymer properties, adding interest to the studies of relation between structure and properties. Though a considerable number of publications dealing primarily with the properties of urethan polymers have been published, few of them contribute to better understanding of the relation between these properties and the corresponding polymer structure. Within the last few years information of value has become available, and Saunders has established some semi-quantitative relations by the use of such data. He also discusses in his reports gen...

Methods for the Determination of Internal Energy Contribution to Rubber Elasticity

Abstract In order to determine exactly the contribution of internal energy component to retractive force (fe/f), two methods (one is Single Specimen Method [Successive Contraction Method] and the other Multi Specimen Method), two different reference lengths (one is the initial length of undeformed specimen and the other the final length including permanent set), and two instruments of different type (one is automatic balance type relax-o-meter [ROM] and the other tensile tester) were examined by using natural rubber, cis-1,4-polyisoprene, and polyurethane rubber. The apparent mechanical and thermo-dynamic properties were significantly dependent upon these methods and reference lengths. In spite of the variation of C1 and C2 in Mooney-Rivlin plot, fe/f was almost unaffected and the sign of this value coincided with that expected from the chain conformation as far as ROM-Single or Multi Specimen Method and the final length were adopted. The influences of permanent set, the time used to attain equilibrium, e...

Activities of Anionic Catalysts in Network Formation of Diisocyanate through lsocyanurate Formationt

The catalytic activities of the sodium salts of Br6nsted acids sodium cyanide, sodium benzoate, sodium phenoxide, etc in the network formation of 4, 4 -diphenylmethane diisocyanate (MDI)by the formation Of isocyanurate were studied in DMF at 30 C determining the gelation time of the reaction mixture. The activities of the sodium salts some increased with mcreasmg pKa of the conjgate acids. However, the activity of salts, such as sodium thiosulfate and sodium trichloroacetate was found tobe greater than that predicted from their pKa values. In cases of alkoxides, mercaptides and carboxylate salts, the catalysts with aromatic substituents showed higher activity in spite of their lower Z Ka values than those with aliphatic ones. The activities of substituted benzoate salts were found to decrease with increasing electrondonating character of ther substituents. From these results, it was concluded that the catalytic activities of the sodium salts depend not only on the basities of the nucleophiles, but also on the polarizabilities of the nucleophiles as well as on the degrees of dissociation of the salts. In the series of lithium, sodium, and potassium benzoates, the activity increased with decreasing electronegativities of alkali metals. The gelation of MDI was accelerated in aprotic solvents in the order of hexamethylphosphoramidedimethylacetamide dimethylformamide but the acceleration was not observed in dimethylsulfoxide.

Network Formation of Polyether-diisocyanate with Anionic Catalystt

It was found that urethane prepolymers, that is, diisocyanate adducts of polyether glycol, in DMF solution were rapidly crosslinked by the catalytic action of sodium cyanide. By evapolating to dryness, three-dimensional polymers were obtained. Anionic catalysts such as nbutyl lithium, sodium benzophenone ketyl and sodium benzoate were also found to be effective for the crosslinking of prepolymers. The crosslinking reactions of prepolymers with sodium cyanide in DMA solution were studid by determining the gel point. Gelation time decreased with increasing catalyst concentration and prepolymer concentration. The apparent activation energy of gelation was ca.18 kcal for polypropylene glycol-tolylene diisocyanate at 0∼25°C and ca.35 kcal for polypropylene glycol-hexametylene diisocyanate at 55∼80°C. The crosslinking reaction of prepolymers, prepared from polypropylene glycol and tolylene diisocyanate, in DMA solution with sodium cyanide catalyst was followed at 25°C by the titration of unreacted isocyanate groups, and was found to obey apparent third-order. The infrared spectrum of the resulting polymer shows an absorption at 1410 cm-1 corresponding to isocyanurate ring. From these results, it was considered that the crosslinking is effected by trimerization of isocyanate groups. The resulting network polymers were rubbery at room temperature and gel fractions of these polymers were mostly near 1. Densities, swelling properties, glass transition temperature, Youngs modulus, tensile strengths and elongations were also measured. Polyurethanes prepared from hexametylene diiscyanate have good mechanical properties (tensile strength 130∼320 kg/cm2 and elongation 450∼1000%). DTA and TGA measurement showed these polymers were stable up to 280∼320°C.

Network Structure of Three-dimensional Polyurethane.

線状の高分子グリコール(I)とジイソシアネート(II)から得られる連結延長物(III)の構造,およびそれが網状化剤(IV)と反応して生成する網目の構造について考察を行なった。(I)と(II)の配合比をK,(III)と(IV)の配合比をM,ポリオールの分子の数をν0とすると,網状化反応の反応率が1の場合,M≧1/3では(III)の末端は付加のため消失し完全網目構造となり, 内部鎖の数νiは式(1,2) で表わされた。M＞ 1/3 νi=3ν0(K-1) (1-2M) (1)M=1/3 νi=ν0(K-1) (2)M＜1/3の場合は(III)の末端が自由端として残り,式(3)となった。M＜1/3 νi=ν0(K-1)(6M-1) (3)またこれに(III)の重合度分布を考慮した式もたてられた。また弾性に有効な要素鎖の数νeは,網状化反応により生じる閉回路の数の計算から求められ,式(4),(5)が得られた。M ≧ 1/3 νe = 2ν0(K-1)(1-2M) (4)M＜1/3 νe=2ν0(K-1)(4M-1) (5)