Professor Ito Kohzo and his team at the University of Tokyo, developed novel, so–called sliding gel polymers that comprises a polyethylene glycol (PEG) threaded alpha-cyclodextrin polyrotaxanes where some CD rings of the rotaxanes are covalently bound together resulting in a new supramolecular polymer structure with unique properties like pulley effect. ( Reference Okumura Y. and K. Ito, Adv. Mater 13, 485-487. 1992)
Figure 1 Suggested structure of slige-ring polymers (Ref. 1.)
This concept has lead to the development and optimization of new polymeric materials called Shinayaka Polymers.
Shinayaka polymers were used for making special plastic materials that are characterized by highly improved toughness, mechanical resistance, flexibility, very low brittleness, and significantly reduced weight. No wonder that Ito’s team soon applied this polymer system for making future cars in the frame of the ImPACT program. This program named ItoP (Iron to Polymers, besides the name of main inventor and program manager Professor Kozho Ito) has built a mutually rewarding co-operation between academic research groups and industrial partners representing prestigious university research centers and large Japanese companies (e.g. Bridgestone, Nissan, Mitsubishi Chemicals, Sumitomo Chemicals, Tory, etc.)
The introduction of such Shinayaka polymer-based plastic materials in car industry is forecasted a great industrial expansion of the use of polymer materials in automobiles by 47% and this expected to reduce environmental green gas emission by 11 %, when compared with cars made of traditional materials. A prototype concept car built by this slide-ring polymers containing plastics is depicted in Figure 2.
In November 22 2018, the „University News” of Hokkaido University reported on the cover about „Brand-new concept car „ItoP” that debuted at the Campus of the University. (see Figure 2)
Figure 2. The ItoP displayed in front of the Hokkaido University Museum. (Photo courtesy Yu Kikuchi.)
About 80 percent of the components used to build the new concept car, including the entire body frame, the tires windows are made from different types of polymers the team has developed, successfully reducing the body weight by 38% and greenhouse gas emissions by 11% to those of a conventional car. Their polymer technologies are also used in the ItoP’s fuel cell, its Li ion battery as well as its front and rear suspensions.
The rubber used for the tires was developed by the Bridgestone corporation based on the double network gel technology devised by Professor Jian Ping Gong’s laboratory at Hokkaido University. The technology integrates two different kinds of polymers, one rigid and brittle and the other flexible and stretchable, to make the material much tougher than traditional polymer-based materials. This made possible that the ItoP’s tires were much lighter and thinner than conventional tires, contributing to higher fuel efficiency and lower emission.
Also a novel type of ductile polymer based glasses have been created from thermoplastic polyrotaxanes, The inorganic hard glass having a Young modulus of 1 GPa, shows crazing necking and strain hardening with a total elongation of 330 %. The stress concentration is prevented by a unique stretch force induced intramolecular phase separation of the cyclodextrin constituents and the exposed backbone. (See Figure 3 below)
Figure 3: Schematic representation of the structure and transparency of polyrotaxane-based ductile polymer glass (Ref: Kato et al. ACS Appl. Mater. Interfaces 2017, 9, 32436−32440)
Among sixteen ImPACT programs, Professor Kohzo Ito from The University of Tokyo leads the project called “Realizing Ultra-Thin and Flexible Tough Polymers,” involving more than 20 universities and corporations in Japan. This program attempts to develop tough and yet flexible polymers that achieve a level of both thinness and toughness which exceeds conventional limits. Such polymers are expected to help realize a more energy-efficient, safe, and sustainable society.