Key Aspects of Novel Catalyst Systems in all-Water Blown Integral Skin Foams-Related Catalytic Activities in the Isocyanate Reaction

This paper will focus on the generalization of catalytic activities of a variety of typical amine and tin catalysts in the isocyanate reaction of gelation, blowing and crosslinking Secondly the relationship between catalytic activities and foaming behavior, as well as foam properties, will be discussed from the stand-point of developing novel catalyst systems for all-water blown integral skin foams (ISF).

Catalysts play an important role in the control and balance between the gelation and blowing reactions. Especially in ISF systems, this control becomes increasingly important for the improvement of surface skin formation in all-water blown systems, which are now required for eliminating CFC. That is to say, skin formation and cure become inferior when using water as a blowing agent, primarily because the role of CFC is to aid in skin formation. Moreover, other than the two primary reactions, it will be considered that the catalytic activity of the crosslinking reactions such as allophanate, biuret and isocyanurate formation will have some effect on foaming behavior as well as foam properties. Therefore, it will be important to know the crosslinking activities for the design of novel catalyst systems.

Concerning the catalytic activities for the primary gelation and blowing reactions, many reports have been presented in the past where the relationships between catalytic activities and foaming behaviors, as well as foam properties, have been reported. On the other hand, several reports have been recently presented on the crosslinking activities, based on the method using HPLC analysis techniques in a model reaction. Few reports, however, describe the reaction kinetic analysis of the catalytic crosslinking activities and the systematic examination of its relation to foaming behavior and foam properties.

In this paper, the catalytic activity of a variety of typical amine and tin catalysts will be generalized with a review on gelation and blowing activities and a reaction kinetic analysis of the crosslinking activities using HPLC analysis in a model reaction.

In addition, the relationship between these catalytic activities and foaming behaviors, as well as foam properties, will be discussed in an all-water blown ISF system. As to the foaming reaction, the relationship between viscosity rise profiles, which may have a large relation to cure, will also be discussed. Concerning foam properties, the relation to cure and skin formation will be discussed. As a result, it will be shown that strong gelling catalysts with high crosslinking activities provide improvement in skin formation. This report will intro-duce novel catalyst systems in all-water blown ISF systems by suggesting the effectiveness of catalytic activities in the selection of a suitable catalyst system.

An Insight into the Characteristics of a Nucleation Catalyst in CFC-Free Rigid Foam Systems

The establishment of CFC-free polyurethane foam systems, aimed at total CFC elimination by the year 1995, is of paramount importance in the present day polyurethane foam technology. Especially in rigid foam systems, the attempts to apply a variety of alternative blowing agents such as HCFC-22, -141b, and -142b, HFC-134a and -356, and hydrocarbons such as n-pentane, isopentane and cyclopentane, as well as all-water blown systems, are being examined.

In all cases of alternative blown systems, however, there exist differences in foaming behavior as well as inferior foam properties compared to traditional CFC-11 blown systems. Especially in HCFC-141b and cyclopentane blown systems, which have gained the greatest interest among the above-mentioned options, the following three subjects are of major concern. The requirements involved in achieving the resolution of these problems are dependent not only on the development of major raw materials but also on the selection of suitable auxiliary intermediates such as catalysts and foam stabilizers. (1) Thermal Conductivity; HCFC-141b, cyclopentane and carbon dioxide, which is generated from the reaction of water and isocyanate, have high thermal conductivity compared to CFC-11, thereby causing inferior insulation performance of the foam. Fine cell technology is now being examined in order to improve the thermal conductivity. For the achievement of the fine cell structure, the selection of suitable amine catalyst systems is important, although the effect of foaming stabilizers has an especially large contribution. (2) Dimensional Stability; not only in all-water blown systems, but also in HCFC-141b and cyclopentane blown systems which use water in high concentration, dimensional stability becomes a large problem due to the diffusion of carbon dioxide gas from the foam cell. For the improvement of dimensional stability, there exists the option to increase the foam strength; moreover, it is important to improve the isotropy of cell structure by adjusting amine catalyst systems. (3) Foam density; since 141b and cyclopentane have relatively higher boiling points and less blowing efficiency, lowering the foam density becomes rather difficult. Moreover, lower foam density normally provides poor dimensional stability. It can be said that the catalytic activity ratio in blowing/gelling of amine catalysts play an important role for the lowering of foam density with improved dimensional stability.

It is very difficult to improve these three factors simultaneously. In this report, however, the improvements of these subjects are discussed from a standpoint of amine catalysts; also special newly developed nucleation catalyst systems are introduced for cyclopentane and HCFC-141b blown systems.

Evidence for structural differences between the two highly homologous actin-regulatory proteins, destrin and cofilin

The amino acid sequences of destrin and cofilin are very similar (84% homology) throughout the entire range of proteins, but they have different functions. In this study, we constructed a new cofilin expression plasmid, which had high expression frequency, and the structures of destrin and cofilin were analyzed by limited proteolysis and circular dichroism (CD). When destrin was digested by trypsin, two fragments of 17.0 kDa and 9.2 kDa were obtained, whereas only one 8.4 kDa fragment was obtained from cofilin. In spite of the overall sequence homology, an N-terminal amino acid sequence analyses of the fragments revealed the cleavage sites on destrin and cofilin to be different. These results suggest that destrin and cofilin differ in their overall tertiary folds. Cofilin showed activity similar to destrin at high pH values, although no pH-dependent structural change in cofilin was confirmed by using limited proteolysis and CD.

Different effects of vitamin E on the growth and morphological differentiation of 4 murine neuroblastoma cell lines in vitro

The effects of vitamin E (vit.E, d-alpha-tocopherol acid succinate) on the growth and the morphological differentiation of 4 representative murine neuroblastoma cell lines: C1300 (wild type), NS-20 (cholinergic type), N-18 (inactive type), N1E-115 (adrenergic type), and the combined effects of vit.E and cis-diamminedichloroplatinum(II)(cisplatin, CDDP) were studied in culture. Vitamin E inhibited the growth of all clonal cells in a dose-dependent manner, especially that of NS-20 cells, and it caused significant morphological differentiation only in NS-20 cells. In addition, vit.E enhanced the growth inhibition of C1300 cells by cisplatin in an additive manner, but not that of NS-20 cells. These suggested that both phenomena induced by vit.E may not always occur in parallel in each clonal neuroblastoma, and both mechanisms might be different.

Combined effects of vitamin E (alpha-tocopherol) and cisplatin on the growth of murine neuroblastoma in vivo

Combined effects of vitamin E (alpha-tocopherol) and cisplatin on the growth of two murine neuroblastomas (C1300, NS-20) was investigated in vivo. Five groups of mice were prepared; group 1 were fed the control diet, group 2 were fed a vitamin E-deficient diet, group 3 were fed a vitamin E-supplemented diet, group 4 were fed the control diet and plus vitamin E solution given intraperitoneally during the treatment (solvent i.p. group), and group 5 were given vitamin E in the same manner (20 mg/kg/day; vitamin E i.p. group). Cisplatin (6 mg/kg) was injected intraperitoneally into the mice of each group during the treatment. In case of the C1300 neuroblastoma, the antitumor activity of cisplatin was most enhanced in the mice receiving vitamin E i.p., and the intra-tumor vitamin E and platinum levels were significantly higher in this group than in the other groups (P less than 0.01, and P less than 0.05 respectively). In contrast, in animals transplanted with the NS-20 murine neuroblastoma, which proved to be a cisplatin-tolerant tumor in separate experiments, no combined effect of those drugs was observed, although the intra-tumor level of platinum was elevated. The possibility was that vitamin E increases the influx of cisplatin into the tumor cells and acts after incorporation of cisplatin through the plasma membrane. Vitamin E did not accentuate the cisplatin-induced renal impairment in vitamin E-loaded groups. Those results suggested that vitamin E should be considered as a co-agent of cisplatin for the treatment of neuroblastoma.

Different clonal drug sensitivity of murine neuroblastoma cells in vivo

Four cloned murine neuroblastomas were implanted intramuscularly into the left thigh of adult A/Jax mice. Cyclophosphamide, cisplatin, adriamycin, imidazole carboxamide, and vincristine were administered intraperitoneally, in a dose of one third to one fourth of a median lethal dose, every week after the implantation until all the mice died. The effects of continuous long-term chemotherapy, particularly on clonal differences, were then assessed. Cyclophosphamide was most effective for four murine neuroblastomas, and cisplatin was the next most effective drug. Cisplatin was not effective in the NS-20 cell line, a cholinergic cloned neuroblastoma. The C 1300 cell line (wild type) was tolerant to adriamycin, imidazole carboxamide, and vincristine. The N-18 cell line (an inactive clone) exhibited tolerance of adriamycin and imidazole carboxamide. In the N1E-115 cell line, an adrenergic clone, tumor growth was inhibited by all the drugs given. We conclude from this study that drug sensitivity differs with the clone, and that there are clones resistant to each drug.