Production of Polyols for High Performance Polyurethanes
The polyols produced by the ring-opening polymerization
of epoxides are one of the core raw materials for various polyurethane applications.
Most of the current epoxide based polyols are being produced by simple base catalysts like KOH.
The PPG produced through a base-catalyzed process has been studied as a soft segment material for foams,
with less spectacular properties for elastomers.
However, in the early 1990s, advances in zinc hexacyanocobaltate-based double metal cyanide (DMC) catalyst used to produce PPG diols,
resulted in a substantial improvement in the levels of polyfunctionality and molecular weight (MW), a narrowing of the molecular weight distribution (MWD), and a lowering of viscosity.
The resulting PPG polyols of narrow MWD
and ultra-low monol content (< 0.02 meq/g) allow them to yield polyurethane with superior mechanical properties.
Prussian blue analogues possess structures based upon a simple cubic M[M (CN)6] framework,
in which octahedral [M (CN)6]n- complexes are linked via octahedrally coordinated, nitrogen-bound Mn+ ions (Figure 1).
Figure 1. Octahedral [M2(CN)6]n- complexes are linked via octahedrally coordinated, nitrogen-bound [M1]n+ ions. M1 = Zn(II), Fe(II), Co(II), Ni(II), Mn(II); Sn(II), Pb(II), etc. M2 = Co(III), Fe(III), Fe(II), Ni(II), Mn(II), Mn(III), etc.
Double metal cyanide (DMC) complexes base upon Zn3[Co(CN)6]2 framework are well-known catalyst for the polymerization of epoxides
and the synthesis of propylene oxide based polyether polyols (PPGs) that are one of the main raw materials in a wide range of polyurethane applications (Figure 2).
While DMC catalysts offer significant advantages over conventional base catalysts, they must be activated for a long time (e.g. several hours)
at high temperature above 100 oC together with starter (or initiator) molecules, usually low molecular weighr PPG polyols,
which control the functionality of the resulting polyols, before epoxide monomer can be added continuously to the reactor for
propagation. This long induction period increases cycle time, which undercuts the economic advantage of the DMC-catalyzed polymerizations.
In addition, initial heating of the catalyst during the long induction period at high temperature can reduce its activity or deactivate it completely.
Numerous trials have been made to make up this shortcoming of DMC catalysts by modifying formulations of the catalyst, remaining unsolved.
Figure 2. Developments of highly functional and high-performance polyurethane based on polyols produced by double metal cyanide (DMC) catalysts.
Recently, we developed a simple but very effective way to tune polymer properties as well as polymerization activity and induction period by
combining DMC catalyst with quaternary ammonium salts (QASs) as simple external additives (Figure 3). Polyurethanes produced by the reaction of polyols developed by our laboratory with isocyanate compounds shows very
nice physical properties that are not achievable with conventional polyols. We showed that the reduction of monol content in PPG is a key factor to achieve high-performance PU elastomer.
The reduction of monol results in PU elastomers showing much higher final molecular weight and thus improved
mechanical properties, approaching to those of the poly(tetramethylene ether glycol) (PTMEG) derived PU. Note that PTMEG is much more expensive than PPG polyols.
Figure 3. Polymerization rate curves obtained by using Zn-Co double metal cyanide (DMC) catalyst and
DMC/quaternary ammonium salt (QAS) binary catalysts: (a) DMC catalyst alone, (b) DMC/tetrapropyl ammonium chloride,
(c) DMC/tetrabutyl ammonium chloride, (d) DMC/tetrabutyl ammonium bromide, (e) tetrahexyl ammonium chloride,
(f) DMC/tetrabutyl ammonium iodide, (g) DMC/tetraoctyl ammonium chloride, and (h) DMC/tetradodecyl ammonium chloride.
Polymerization conditions: temperature = 115 PoPC, PPG starter = 70 g, catalyst = 0.1 g (0.4 mmol Zn), and QAS = 0.5 mmol.
The narrow MWD of PPG together with low monol content results in a reduction of viscosities of both PPG and
resulting polyurethane prepolymer. Figure 4 shows a compartive stress/strain graph of PTMEG and various polyols.
A fundamental understanding of the monol effect allows one to obtain the maximum benefits from the low monol PPG
and to realize the opportunity for designing new high performance polyurethane products.
Figure 4. Polyurethane elastomer stress/strain curves derived from various PPG. PPG-1: conventional KOH-based polyol; PPG-2 to PPG-4: DMC-catalyzed polyols with different unsaturation developed in our laboratory; and PTMEG: poly(tetramethylene ether glycol).
1. I. Kim and S. H. Lee, US 6627575 (2003).
2. I. Kim and S. Lee, WO 2004045764 (2004).
3. I. Kim, J.-T Ahn, C.-S. Ha, C.-S. Yang, and I. Park, Polymer, 44, 3417 (2003).
4. I. Kim, J.-T. Ahn, S.-H Lee, C.-S. Ha, and D.-W. Park, Catal. Today, 93-95, 511 (2004).
5. I. Kim, S.H. Byun, J. Polym. Sci., Part A. Polym. Chem., 43, 4393 (2005).
6. I. Kim, M.J. Yi, K.J. Lee, D.-W. Park, B.U. Kim, and C.-S. Ha, Catal. Today, 111, 292 (2006).
7. S. H. Lee, C.-S. Ha, and I. Kim, Macromol. Res., 15, 202 (2007).
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Environmentally benign polycarbonates by carbon dioxide/epoxide copolymerizations
Chemical fixation of CO2 is of great interest in connection with the development of a truly environmentally benign process,
since there are many possibilities for CO2 to be used as a safe and cheap C1 building block in organic synthesis.
One of the most promising methodologies in this area is the synthesis of biodegradable polycarbonates via CO2/epoxide copolymerizations.
We are studying highly effective catalysts, heterogeneous and homogeneous ones, for these alternating copolymerizations.
Recently, carbon dioxide (CO2) along with other gases, such as methane, nitrous oxide, and FreonTM
gases in the atmosphere has seriously been considered to be a greenhouse gas causing the global warming that may contribute to the climate change.
The contribution to the climatic warming is estimated to be 66% from CO2, 18% from methane, 11% from Freon gases, and 5% from nitrous oxide.
Human activities annually add about 24 billion tons of CO2 to the atmosphere, with 22 billion tons coming from the burning of fossil fuels.
About 15 billion tons is removed by plants, the soil, and the oceans, leaving a net addition of 9 billion tons per year.
The concentration of CO2 is, therefore, increasing at a rate of 1 ppm per year.
Thus, the reduction of CO2 emissions now is seriously considered by all the nations.
As a kind of potential approach, one of the most promising areas of CO2 utilization is its application as a direct material for polymer synthesis.
Since 1969, when Inoue first reported the copolymerization of CO2 with propylene oxide aliphatic polycarbonate produced directly from CO2
has been a topic of increasing interest. These polymers received much attention not only because they exhibited good mechanical properties
comparable with commercial products but also because they are relatively easy to degrade. Thereafter, a number of catalysts were developed
to catalyze the copolymerization of CO2 and epoxide such as cyclohexene oxide and propylene oxide (Scheme 1).
Scheme 1. Various types of polycarbonate produced by CO2/epoxide copolymerizations.
The use and production of polycarbonates has seem tremendous growth in the last thirty years.
This is not surprising, given the attractive properties of this material. Polycarbonates are very tough and have good thermal and dimensional stability.
Also, they are good electrical insulators and gave excellent optical properties Taken together, this accounts for the widespread and diverse application of polycarbonates.
They are used as lenses in a variety of optical devices; they are used as substrate materials for data storage devices,
such as CD’s and DVD’s; they are also used in many applications in the medical industry such as membranes for the dialysis of blood.
With such a variety of application, polycarbonates are ranked second in overall production of the engineering thermoplastics
(with a global demand of over, 1,000,000 tons per year).
However, there are drawbacks to the tremendous volume of commercial production associated with polycarbonates.
The production of these materials proves to be both costly and hazardous, as a consequence of the need for extremely toxic starting materials,
requiring significant investment in the areas of safety and environmental protection.
The most common method for production is the interfacial polycondensation of phosgene and diols.
By far, the leading polycarbonate made is bisphenol-A polycarbonate.
The process involves feeding phosgene into an aqueous alkali bisphenol-A solution in a halogenated hydrocarbon (e.g. methylene chloride).
This is shown in Scheme 2.
Scheme 2. Polycarbonate by polycondensation.
Therefore this method, while more benign for a specific production line, eliminates neither the need for phosgene nor the associated cost.
Another method for the production of selected polycarbonates has been the coupling reaction of epoxides and CO2.
This is certainly more environmentally friendly.
However, the problem here has been to eliminate side reactions and competing processes while producing a polymer with
properties similar to those described for bisphenol-A polycarbonate.
One of the most compelling aspects of this approach is the possibility for the wide-scale use of CO2 as a C1 starting material.
This has obvious economic and environmental advantages due to the ubiquitous nature of CO2 as well as its role in the relatively
little use as a starting material in the synthesis of organic compounds. Indeed, many of its more attractive attributers
(it is nontoxic, and nonflammable) are a result of its stable, unreactive nature (Scheme 3).
Although the process of photosynthesis efficiently fixes scientists have developed little in the way of effective uses for this simple molecule.
However, there have been breakthroughs in the area, as it applies to polymer chemistry (Scheme 1).
Of course, the type of catalyst is a key to achieve polycarbonates starting from CO2.
Scheme 3. Mechanisms for CO2/epoxide copolymerizations
Among all the catalysts reported, homogenous single-site zinc catalysts containing beta-diimine ligands are known to produce polycarbonate,
which has high molecular weight and narrow molecular weight distribution, at mild conditions (Figure 1).
These homogeneous single-site zinc complexes can give different activity and structure of the resulting copolymer according to beta-diimine ligand structure.
Figure 1. Highly effective catalysts for CO2/cyclohexene oxide copolymerizations.
We have also developed highly effective homogeneous (Scheme 4) and heterogeneous catalysts for CO2/epoxide copolymerizations.
Scheme-4. Highly effective homogeneous catalysts for CO2/epoxide copolymerizations developed in our laboratory.
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Green Chemistry-Valuable Chemicals from Renewable Resources
Oils and fats are the most important renewable raw materials of the chemical industry.
They make available fatty acids in such purity that they may be used for chemical conversions and for the synthesis of chemically pure compounds.
Their interesting new industrial applications are the usage as environmentally friendly industrial fluids and lubricants, insulating fluid for electric utilities
such as transformers and additive to asphalt. Modern methods of synthetic organic chemistry including enzymatic and microbial transformations
were applied extensively to fatty compounds for the selective functionalization of the alkyl chain. Syntheses of long-chain diacids, omega-hydroxy fatty acids,
and omega-unsaturated fatty acids as base chemicals derived from vegetable oils were developed.
Interesting applications were opened by the epoxidation of C-C double bonds giving the possibility of photochemically initiated
cationic curing and access to polyetherpolyols. Enantiomerically pure fatty acids as part of the chiral pool of nature can be used
for the synthesis of nonracemic building blocks.
Average annual world oil production in the years 1996 to 2000 amounted to 105.0×106 t and will increase in the years 2016 to 2020 to 184.7×106 t.
Eighty to eighty-one percent of the produced oils and fats are consumed as human food; 5–6% as feed.
Approximately 14%, 15–17 million tonnes are used by industry. In contrast, the world consumption of fossil mineral oil was approximately 4,000×106 t in the year 2002.
The chemical share was about 11% in the European Union (EU).
About 80% of the global oil and fat production were vegetable oils and only 20%, with declining tendency, were of animal origin (Table 1).
About one quarter of global production came from soybean, followed by palm oil, rapeseed, and sunflower.
Coconut and palm kernel oil (laurics) contain a high percentage of saturated C12 and C14 fatty acids and are most important for the production of surfactants.
Table 1. Composition of Oils from Renewable Resources
These commodity oils make available fatty acids in such purity that they may be used for chemical conversions and for the synthesis of chemically
pure compounds such as oleic acid from 'new sunflower' linoleic acid from soybean, linolenic acid from linseed, erucic acid from rapeseed,
and ricinoleic acid from castor oil (Figure 1).
Figure 1. Valuable chemicals obtained by from oleic acid from sunflower.
Polyurethane materials created from vegetable oils such as cast resins and rigid foams has been in exist for some time.
Two types of soy polyols can be prepared, one with secondary OH groups resulted from epoxidation of soybean oil followed by methanolysis (polyol type I)
and the other with primary OH groups created from hydroformylation of soybean oil followed by hydrogenation (polyol type II) (Figure 2).
Cast polyurethane resins were prepared from these two types of polyols with various isocyanate compounds,
and rigid polyurethane foams were prepared from a blend of soy polyol and glycerol. Polyol II is much more reactive than polyol I towards polyurethane formation.
This is evidenced from studies on polyurethane gel-times, glass transitions and rigid foam mechanical strengths.
The reaction for the polyurethane formation is more complete for polyol II resulted from its higher reactivity than polyol I,
although a less rigid polyurethane material is resulted from polyol II than from polyol I. Polyol type II also requires lower amounts of
catalysts for rigid foam formulation. Both rigid foam systems produce foams having the required mechanical strength.
The polyol II foam system behaves much like conventional rigid foam systems where the strength are proportional to system OH content,
while the less reactive polyol I system does not.
Figure 2. Rigid polyurethanes using polyols from soybean oil via both hydroformylation and epoxidation.
Epoxidized soybean oil was effectively converted to carbonated soybean oil (CSBO) containing five membered cyclic carbonates by reaction with
carbon dioxide in the presence of tetrabutylammonium bromide as catalyst at 110°C in high yield. CSBO could easily react with di- or tri- primary amines
to give the corresponding nonisocyanate polyurethane networks (Figure 3). A model reaction between CSBO and n-butylamine showed the effective
ring opening of five-membered cyclic carbonate moieties in the triglyceride molecules by the amine to form hydroxyurethane systems.
The data from our research confirmed the network character of all materials and also showed how the levels of extractables,
Tg, and mechanical properties varied with type of amine and, in the case of ethylenediamine, the effect of stoichiometry.
Figure 3. Schematics of the reaction of epoxidized soybean oil with CO2
to form carbonated soybean oil and model reaction of nonisocyanate polyurethane networks with diamine.
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Supramolecular materials that naturally assemble themselves
One of key aims of modern chemistry is to explore and exploit the phenomenal complexity of matter that seems to arise
spontaneously within ambient environments like that of our planet. Biology, of course, is an ultimate manifestation of a universal chemical canon encompassing
interactions both at the molecular and supramolecular level. Inorganic building blocks play a significant role in the self-organized assembly of many biological structures
at various scale-lengths but the details of their chemical behaviour and interaction with organic compounds are still not well-understood.
We are probing the ground rules for biomineralization in the hope of applying them to the self-assembly of practical materials with complex hierarchical structures.
It seems truly extraordinary that Nature can assemble, with such exquisite control, a wide variety of functional mineral structures with highly specific
morphologies-elegant skeletal frameworks, optical lenses (in trilobites), or gravity sensors in the inner ear from just two kinds of mundane inorganic ions (Figure 1).
It is fascinating factor that gets us into a limited number of solid-state inorganic materials such as calcium carbonate,
silica and iron oxides could form new materials that bear no relation to the underlying crystallographic structure.
We wanted to understand biomineralization in a general sense from a chemical point of view, and develop overarching
concepts that could be exploited to make new materials. It was clear that biology offered a confined and controlled-and,
of course, highly non-equilibrium-environment able to modulate the movement of ions and their destination, particularly in
relation to crystal growth. Organic components such as proteins, lipid structures (Figure 2) and larger macromolecular frameworks
play a key role in directing the aggregation or nucleation of ions and their sequestration, either on a specific crystal face to create
larger-scale morphologies with a lower symmetry than that of the basic unit cell, or to form part of a supramolecular organic-inorganic
composite. Various dynamic combinations of interactions, often with feedback-chemical bonding, electrostatic attraction or repulsion,
mechanical stress, spatial confinement come into play to generate a specific reaction field at a defined length scale. In this way,
macroscopic hierarchical structures can be autonomously built up from assemblies of smaller units formed at the nano and
meso-scale the process of morphogenesis.
Figure 2. Various lipid molecules that are commercially available
We showed that the ferrihydrite cores can be removed from the protein cages and replaced with other nanoparticles of technological
interest such as semiconductors or ferromagnets (Figure 3). In addition, we made various nanoparticles, using various lipid molecules
shown in Figure-2 as a template, for various applications (Figure 4,Figure 5).
Figure 3. Artificial ferritins containing MnOOH, magnetic Fe3O4 or CdS can be prepared from apoferritin (demineralised ferritin).
Figure 4. Various kinds of nanoparticles prepared by using biomacromolecules as templates.
Figure 5. TEM image of gold nanoparticles prepared in our group.
Some biological structures such as bone may be assembled as mutually interacting organic–inorganic
composites in which each component modifies the behaviour of the other through interfacial recognition.
Recently we showed the assembly of a silica–lipid nanocomposite from an unusual surfactant diacetylenic
phosphatidyl choline (23:2 DIYNE PC) (see Figure 2) and tetraethoxysilane (Si(OEt)4), or TEOS.
The phospholipid has a zwitterionic headgroup and two hydrocarbon tails, each containing diacetylenic units.
Its overall chiral structure generates bending and twisting stresses which force the aligning lipid bilayers into
strips that wind into a tubeshaped helical structure, rather like a drinking straw (Figure 6).
These pre-formed tubules can then be used as templates for making ultra-thin metal or inorganic cylinders
by depositing the appropriate mineral and burning off the lipid. However, if 23:2 DIYNE PC is added to
water already containing TEOS, the two components co-assemble.
The TEOS hydrolyses to produce silicate anions which interact with the lipid’s cationic headgroups and
deposit along the lipid bilayers as they twist into the helical shape—in this case forming an open secondary
architecture rather than a closed tube (Figure 7 and Figure 8).
The resulting lipid nanotubules could be utilized for the nano-array of various nanoparicles as illustrated in Figure 9.
Figure 6. Possible formation mechanism of lipid nanotubes based on chiral molecular self-assembly by using diacetylenic phosphatidyl choline (23:2 DIYNE PC ).
Figure 7. Lipid nanotubules by the self-assembly of diacetylenic phosphatidyl choline (23:2 DIYNE PC ).
Figure 8. Silica–lipid mineralized nanotubules.
Figure 9. Gold nanoparticle-lipid nanotubules array.
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Polyolefins are the world's most widely-used thermoplastics materials family and they are polymers of
simple olefins such as ethylene, propylene, butenes, isoprenes, and pentenes, and copolymers and modifications thereof.
Polymerization catalyst technologies are fundamental to the production of polyolefins, in fact, final polymer product
properties are tailored by the catalytic system and further optimized by the specific industrial process.
Higher linear a-olefins, by oligomerization process, of chain lengths C4-C18 are of utmost importance for the chemical industry
as they are highly valuable and versatile feedstocks and building blocks for a variety of refining processes(Figure 1).
In general coordination polymerization involves a catalyst/cocatalyst system. The active site can be visualized as a
co-ordinatively unsaturated cationic species having a metal-carbon formed by the reaction between metal complex and cocatalyst.
A typical mechanistic pathway involving Ni(II) catalyst for the production of polyethylene
for polymerization is depicted in Scheme-1 and a schematic monomer insertion is depited belowas an animated figure.
Scheme 1. Mechanism of Ni catalyzed polymerization of ethylene
Advanced catalysis group primarily focuses its research by combining the areas of organometallic chemistry,
homogeneous catalysis and polymer chemistry. The key aspects addressed include:
1. Ligand effect on catalytic activity and polymer properties are evaluated in order to aid the development of novel ligand sytems.
2. Application of different metals and metallating routes for the formation of active sites (cationic and neutral)
in the production of value added materials ranging from oligomers to polymers.
3. Polymer microstructure analysis in correlation with catalyst architecture to device polymers fit for specialty application.
4. Development of new protocols for cost-effective heterogenization by tethering homogenous catalysts to support via non- alkyl aluminum route.
5. Synthesis of multicentre single site natured catalysts envisaged by the introduction of multiple ligating sites on dentrimers.
6. Coordiantion polymerization protocol for developing functional polymers by homo and copolymerization methodology of polar monomers.
An overview of our recent works:
We have reported an efficient synthetic routes to (pyCAr2O)2M(NR2)2 complexes (M=Ti, Zr, Hf) and elucidated its structure.
X-ray crystallographic analyses establish that complexes adopt distorted octahedral structures with a trans-O, cis-py,
cis-amide arrangement of ligands .Treatment of (pyCAr2O)2M(NMe2)2 complexes with Al(iBu)3 and methylaluminoxane (MAO) yields active,
multisite ethylene polymerization catalysts.In another study we designed new amine moiety for alpha-diimine nickel system
with varied bulkiness and presence of a remote substituents which interacts both electronically to the metal center and chemically
with cocatalysts resulting in unique polymerization behavior (Figure 2). The resulting polyethylene was characterized by
high molecular weight and relatively broad molecular weight distribution and their microstructure varied with the structure of catalyst and cocatalyst.
The identification of active species is essential in aiding to develop new ligand architecture.
In an effort to identify the active center we have carried out UV/VIS spectroscopic analysis of the modified diimine Ni(II) catalysts.
The absorption maximum around 520 nm is of activated species and that around 700 nm is due to the deactivated species,
formed by partial reduction of Ni(II) species (Figure 3). UV-Vis spectra for Co- salicylaldimine catalyst for
butadiene polymerization revealed active center at 800 nm and a dormant one at 600 nm (Figure 3).
To adapt these highly active catalysts in commercial process it is required to support these catalysts on inorganic support materials.
Conventional method is to tether the catalyst to support through expensive aluminum alkyls. But we reprted a cost-effective route by
covalently attaching Fe(II) and Co(II) to silica gel through silicone ethoxide functionalized ligands (Scheme 2).
Presently we are performing a macro ligation strategy to achieve this goal by funtionalizing dendrimers and designing of polymeric ligand.
1. S. Abraham, C. S. Ha, and I. Kim, Macromolecular Rapid Communications, 27, 1386 (2006).
2. K. B. Bijal., D. W. Park, C. S. Ha, and I. Kim, Catalysis Surveys from Asia, 10, 65 (2006)
3. I. Kim, C. H. Kwak, J. S. Kim, and C. S. Ha, Applied Catalysis, A: General, 287, 98 (2005)
4. I. Kim, B. H. Han, Y. S. Ha, C. S. Ha, and D. W. Park, Catalysis Today, 93-95, 281 (2004).
5. I. Kim, B. H. Han, C. S. Ha, J. K. Kim, and H. Suh, Macromolecules, 36, 6689 (2003).
6. I. Kim, and C. S. Ha, Applied Catalysis, A: General, 251, 167 (2003).
7. I. Kim, J. M. Zhou, and H. Chung, Journal of Polymer Science, Part A: Polymer Chemistry 38, 1687 (2000).
8. I. Kim, Y. Nishihara, R. F. Jordan, R. D. Rogers, A. L. Rheingold, and G. P. A. Yap, Organometallics, 16, 3314 (1997).
9. I. Kim, Jordan, and R. F. Jordan, Macromolecules, 29, 489 (1996).
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