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02/13/2006

Chemical Business Div. Yokkaichi Research Laboratory Develops Dendrimer Manufacturing Technique in Collaboration with NICT

The Chemical Business Division of Hakuto and the National Institute of Information and Communications Technology (hereinafter referred to as NICT; URL: http://www.nict.go.jp/index.html) conducted a joint research on the commercial manufacturing technique of a polymeric material called `dendrimer,' which is drawing attention as a new material suited for forming plastic-based information and telecommunication elements, and established a simple, quick and safe manufacturing technology of the ester dendrimer.

What is dendrimer?
Dendrimer is a spherical molecule with a regularly radiating branched architecture. Since it was first reported in 1984, dendrimer applications have grown in the field of medicine including bioreagents and cancer therapeutic agents as well as general industrial fields including molecular sensors, catalytic materials, plastic modifiers, solvent-free coating, organic light emitting displays and dye-sensitized solar cells, with further expansion into various other fields expected.

Developmental background
Dendrimer has a branched structure based on the regular repetition of a constitutive unit radiating outward spherically from the central core. The core molecule synthesized by a combination of multiple reactions is referred to as generation zero and each successive repeat of the synthesis forms the next generation. Since the dendrimer is synthesized in such a stepwise manner by repeating a sequence of reactions, any complex and time-consuming reaction has resulted in higher cost as well as an extremely long time for synthesis. Due to this major impediment in the development of dendrimer applications, the establishment of a commercial manufacturing technique of dendrimers has long been awaited.

Ester Dendrimer
The dendrimer that Hakuto and NICT worked on for establishing a commercial manufacturing technique is poly (glycerol-succinic acid) dendrimer, one of ester dendrimers, with the conventional and common divergent synthesis method (in which the molecular weight is increased by stepwise repetition of reactions from the core to the peripheral). Since propagation of the ester dendrimer branches is radial and extends from the center of the core molecule by repetition of protection and deprotection steps, new development of reaction conditions and the method for purifying generated dendrimers and their precursors led to the establishment of the commercial manufacturing technique.

Specifically, the step of protecting functional groups required time for purification/separation processes as well as a large amount of solvent, which also require efforts for processing it. Improvement of catalysts and solvents to be used as well as reaction conditions helped achieve reducing the required time by half. On the other hand, the deprotection step had a problem of requiring approximately 10 hours for reaction using palladium catalyst and high pressure hydrogen. Development of reaction conditions that completes reaction by approximately one hour and a half helped reduce the reaction time dramatically in addition to establishing a highly safe manufacturing method which eliminates the use of a special pressure vessel.

The zero to fourth generation (the number of the layer of repeating unit) poly (glycerol-succinic acid) dendrimer can be synthesized arbitrary, resulting in the molecular mass of 266 (with four end hydroxyl groups) at the generation zero and 10706 (with 64 end hydroxyl groups) at the fourth generation, which characterizes its water solubility. Having many end hydroxyl groups at its end, the polyglycerol-succinic acid dendrimer offer various modifications for different purposes, which will lead to applications leveraging the structure and properties different from commercially available amine dendrimers such as Poly (amideamine) and Poly (trimethyleneimine). For example, NICT is engaged in research and development of plastic elements for telecommunications use by applying the lithography technique that uses the low viscosity and high reactivity properties of the dendrimer and is viewing the poly (glycerol-succinic acid) dendrimer as a promising advanced material for lithography.

Characteristics
Dendrimers in general have characters absent in other existing polymeric molecules and therefore have potential to largely contribute to the development of new materials in the future.
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(1) Polymeric molecules of a single molecular weight
(2) Low viscosity for its molecular weight
(3) Amorphous
(4) A high number of reactive sites on the shell surface
(5) Solubility and reactivity controllable by chemical modification of the shell surface
(6) Increase of functionality possible at the core and the shell
(7) Formation of a unimolecular micelle possible by making the surface end groups hydrophilic and internal groups hydrophobic
(8) Higher generation dendrimer can be deemed as a spherical molecule.
(9) 10 nanometers or lower in diameter
(10) Capable of encapsulating metals or other molecules


For more details, please contact:
Chemical Business Div. Yokkaichi Research Laboratory
contact person: Taketsuji
Phone: +81-59-334-1200 / FAX: +81-59-334-1214
e-mail Hakuto