A phenolic resin with a new structure was synthesized by reacting phenols with divinylbenzene (“DVB”), a compound having two vinyl groups in its molecule, using the electrophilic substitution reaction of vinyl group to the phenolic nuclear. DVB purity, phenol types, and catalysts together with reaction mechanism, structural analyses were discussed on the reaction and its products. Also was performed an evaluation of the resin as a hardener for epoxy resins. DVB reacts selectively with various phenols without self-polymerization, by the electrophilic substitution reaction of a cation, which forms on the α carbon of the vinyl group, to the high electron density site of the phenol nuclear. Compounds formed by this mechanism were detected by ¹³C-NMR and GC-MASS. Also, molecular weight distribution was controlled by adjusting molecular ratio, catalyst, and temperature of the reaction. Epoxy resins cured with this resin had low water absorption, and BPA/DVB resins were enhanced in heat resistance. The new resins obtained in this study also have the features of low heat expansion which leads to withstand thermal strains, and of good oxidization resistance which is attributed to the low weight loss on heating caused by the low oxygen content. With these features, a wide application in new fields is expected.

View full abstract

A flexible polyurethane foam consists of soft and hard segments. The soft segment mainly made from polyols is mobile, while the hard segment mainly made from urethane and/or urea is rigid. The balance of these two components decides the property of the polyurethane foam. In this research, water-blown flexible polyurethane foams were prepared by varying the content of water, on which the structure of hard segment depended. The solid-state NMR technique was applied to characterize the segment distribution in the flexible foam.
Results of¹³C spinlattice relaxation time showed that moleculer mobility was about 10⁹Hz at room temperature. Broad-line NMR and spin diffusion data showed that the amount of hard segment increased with increasing the content of water. It is considered that, using much water, more reacting points are generated, thus resulting in an increase in the amount of hard segment. As a result, the hard segment domains are more finely distributed, and this lowers the resilience of the foam.

View full abstract

The FTIR spectroscopic examination of aromatic polyimide (PI), poly (p-phenylene biphenyltetracarboxydiimide) (BPDA-PDA) prepared under different (thermal and chemical) imidization conditions, revealed a number of IR active vibrational modes sensitive to molecular (conformational and packing) order. The spectral criteria obtained were employed to characterize the structure organization in the BPDA-PDA films cured in a free-standing state as a function of their thermal histories : temperatures of imidization (T_i = 150-400°C) and annealing (T_a = 300-400°C); cure protocol (one-step/stepwise), and film thickness (t = 1-100μm). The investigation revealed that the conformational changes toward the crystalline preferred chain conformation could be observed even at early stages of imidization - at T_i's as low as 150-170°C, whereas the spectral features of the crystal-like order appeared for the samples cured at T_i's close to or above the Tg. It was found that annealings at T_a's as high as 350-400°C do not completely erase the effects of former processing history, suggesting that the thermally induced molecular mobility is not the only factor governing the structure organization processes. For samples obtained under the same processing conditions, thicker films always displayed much higher order, indicating the plasticizing action of the volatiles retained in the film as another important factor. The results are also presented and discussed on the relative contributions to the molecular mobility of the traces of the casting solvent [N, N-dimethylacetamide (DMAc) / N-methyl-2-pyrrolidone (NMP)] as well as that of the by-products of imidization [H₂O - for polyamic acid (PAA) / CH₃OH - for polyamic ester (PAE)].

View full abstract

N,N,N′-Tribenzyl-N″-cyanoguanidine (TriBCG), a trisubstituted derivative of N″-cyanoguanidine (CG), was prepared from dimethyl (N-cyano) carbonimidodithioate, benzylamine, and dibenzylamine via N-benzyl-N′-cyano-S-methylisothiourea according to the method reported by Suyama et al. TriBCG was identified by elemental analysis, ¹H-and¹³C-NMR spectrometry, and FD mass spectrometry. The structure was determined by the X-ray crystal analysis and compared with those of CG and its derivatives, such as 4-cyanoimino-3-metoxymethylperhydro-1,3,5-oxadiadine (CG-1Mcyc2F), and N,N,N′,N′-tetrabenzyl-N″-cyanoguanidine (TetraBCG). The crystal is orthorhombic, space group P2₁2₁2₁, a = 9.740 (3), b = 22.755 (4), c = 8.807 (4) Å, V = 1952 (1) ų, Z = 4, Dc = 1.206g·cm^-3, μ (MoK α) = 0.68cm^-3. The final R value is 0.061 for 1374 reflections.
The carbon and nitrogen atoms in the cyano group in TriBCG as well as in TetraBCG, are relatively remote from the least-square plane comprising of guanidine moiety. On the other hand, the carbon and nitrogen atoms in the cyano group in CG-1Mcyc2F and CG are placed approximately on the plane comprising of guanidine moiety. These results suggest the following : in the phase-transfer reaction of CG with benzyl chloride and hydroxymethylation of CG with formaldehyde, it may depend on the difference of the position of the carbon and nitrogen atoms in cyano group between TriBCG and CG-1Mcyc2F, whether the tetrasubstituted derivative of CG can be produced or not.

View full abstract