有機超強塩基およびその協奏型触媒を用いる
高純度ポリプロピレングリコールの開発
井
山
森
常
石

上
本
藤
橋

善
敏
勝
透
圭

彰＊ 1
秀＊ 1
朗＊ 2
朗＊ 3
太＊ 4

High Purity Polypropylene Glycol using Organic Superbase andits Cooperative Catalyst
Yoshiaki INOUE
Toshihide YAMAMOTO
Katsuaki MORI
Yukio TSUNETOH
Keita ISHIBASHI

Polypropylene glycol (PPG) is widely used as raw material for polyurethane (PU)-based products such as flexible
foam, rigid foam, coatings, adhesives, sealants, and elastomers. PPG is generally synthesized by using potassiumhydroxide (KOH) as base catalyst. However, the unsaturated value (USV) of PPG synthesized by conventional KOH
catalysis is relatively high due to the occurrence of side reactions. For example, the USV of a PPG synthesized by
KOH is 〜 0.10 meq/g for the OH value (OHV) of 24 mg KOH/g. In addition, high-USV PPG induces low crosslink
density in the PU thereof, which sometimes results in undesirable physical properties.
We found that iminophosphazenium hydroxide (IPZOH), which is an organic superbase, is an effective basecatalyst for the preparation of PPG. Thus, we succeeded in obtaining PPG with an OHV of 24 mg KOH/g by using
IPZOH as catalyst. From the corresponding analysis, we found that the USV of the PPG was drastically decreased
to less than 0.03 meq/g, which was one third of that of conventional PPG. Moreover, we discovered that theperformance of the catalyst for“high purity PPG (low-USV PPG)”could be further enhanced by using a cooperative
catalyst based on IPZOH (organic base) and an aluminum compound (Lewis acid). The USV of the PPG (OHV= 24 mg KOH/g) synthesized by the cooperative catalyst (<0.005 meq/g) was found to be lower than that of any
commercial PPG. The flexible PU foams based on this low-USV PPG showed excellent durability and comfort.

1． Introduction
Polypropylene glycol (PPG) is a main raw material
＊1
＊2
＊3
＊4

ファンクショナルポリマー研究所 機能高分子グループ
研究企画部
ファンクショナルポリマー研究所 情報材料グループ
ウレタン研究所 機能性フォーム第 2 グループfor polyurethane (PU). PPG is generally synthesized byusing potassium hydroxide (KOH) as base catalyst1).
However, the occurrence of side reactions during
27

TOSOH Research & Technology Review Vol.64（2020）

conventional KOH catalysis renders the unsaturatedof PPG and produce high molecular weight PPG 5), 6).

value (USV) of the PPG relatively high (Fig. 1) 2), 3).

Furthermore, phosphazene (PZN), which is a strong

Thus, the USV of a PPG synthesized by KOH is 〜0.10

organic base, has also been used as effective catalyst for

4)

low-USV PPG 7). In order to achieve low-USV PPG, we

meq/g for the OH value (OHV) of 24 mg KOH/g .
Since the physical properties of PU are strongly

focused on iminophosphazenium hydroxide (IPZOH)

influenced by the USV of the starting PPG, someas catalyst due to its strong basic character and bulky

catalysts for low-USV PPG have been developed in

substituents (Fig. 2) 8), 9).

recent years (Table 1). For example, a double metal

On the other hand, flexible PU foams for automotive

cyanide complex (DMC) can greatly reduce the USV

seating are required to improve properties such

Main reaction

OH
OH
OH

KOH catalyst

O
O
O

O

O K
OH
OH
O

H

OH
O
Allyl terminated mono-ol

Side reaction

Fig.１

OH
OH
OH
PPG

Main and side reactions at PPG preparation

Table １

Properties of catalysts for PPG a)
KOH

DMC

PZN

0.043－0.045 0.006－0.019 0.013－0.017

USV［meq ／g］
maximum molecular weight

7,000＞20,000＞20,000a) T. Hayashi, S. Yamasaki, T. Urakami and T. Nobori, Catalysts &Catalysis, 43(7), 532(2001)

NMe2
Me2N

N

N

N C C C NORN C C C N
Zn
Co
Zn
Co
Zn
OR
N C C C N
N C C C N
RO
RO

Me2N P

N P

N

P

NMe2

NMe2

NMe2 N
Me2N P

DMC

NMe2

NMe2

NMe2

Me2N

OH

NMe2

NMe2 N

N

N

P

Me2N
Me2N

OH

N
N P N
N
Me2N

NMe2

NMe2

IPZOH

PZN

Fig. ２

Structures of catalysts for PPG

OH

OH

conventional
PPG

OH
PPG

＋ OCN
OH

mono-ol

NCO
isocyanate
low -USVPPGHigh crosslink density

Fig. ３28

Influence of the presence of mono-ol on the crosslink density of PU

NMe2
NMe2

東ソー研究・技術報告

as weight reduction, riding comfort, durability,
incombustibility, and volatile organic compounds(VOC) reduction. In this context, low-USV PPG can

第 64 巻（2020）

3．Results and discussion［1］Synthesis of PPG by using IPZOH as catalyst

afford enhanced riding comfort and durability due to

We investigated (1) the influence of thehigh crosslink density (Fig. 3). This technology canpolymerization temperature, (2) the influence ofcontribute to weight reduction of automotive seating

the molecular weight, and (3) ethylene oxide (EO)

and improvement of fuel efficiency.

copolymerization using IPZOH.

2．Experimental［1］Preparation of PPG⑴

Influence of polymerization temperatureFirstly, the polymerization using a catalytic amountof IPZOH relative to initiator were carried out at 90,

IPZOH and hydroxyl group-containing compound

110, and 130 ºC. All reactions were successful, andas initiators were added into an autoclave at r.t. andthe catalytic activity was high in all cases (500 − 1300

vacuumed. Then, propylene oxide (PO) was added at 90

g/mol･min). The USV of the obtained PPG was in–130 ºC under 0.3 MPa. After aging and removal of free

the range from 0.03 to 0.06 meq/g. Fig. 4 shows thePO, crude PPG was obtained, from which clear PPG

catalytic activity at various temperatures (90, 110, andwas obtained after purification.

130 ºC). As can be seen, the catalytic activity increased
with temperature. Similarly, it was found that the USV［2］Analysis of PPG⑴

also increased with temperature (Fig. 5). We believe

USV
PPG was dissolved in chloroform-d (CDCl 3), andCZ400S/LI by JEOL) was recorded. The amount of
mono-ol was calculated from the allyl peak (5.1–5.4ppm) and the methyl peak (0.8–1.5 ppm).
⑵

OHV
PPG was reacted with an acetylating reagent (1.3mol/L) of acetic anhydride in imidazole pyridine
solution (25 mL) at 108 ºC for 1 h. Then, the reaction

1500
Catalytic activity［g ／ mol・min］

the 1H-nuclear magnetic resonance spectrum (JNM-E

1200
900
600
300
0

mixture was titrated with sodium hydroxide solution (1.080mol/L). The OH value was calculated according to JIS
K 1557-1.

90

100

110

120

130

140

Polymerization temperature［℃］

Fig.４

Polymerization temperature vs catalytic activity⑶ M w/M n
PPG was dissolved in tetrahydrofuran and analyzed

0.08

by Tosoh). The corresponding value of M w/M n was
calculated by comparison with polystyrene standards.
⑷

Aldehydes
PPG was dissolved in acetonitrile and2,4-dinitrophenylhydrazine (DNPH) reagent was

USV［meq ／ g］

via gel permeation chromatography (HLC-8320GPC

0.06

0.04

0.02

mixed. The obtained solution was analyzed by highperformance liquid chromatography (Prominence-i LC-

0.00

2030 by Shimadzu). Formaldehyde, acetaldehyde and

90

100

110

120

130

140

Polymerization temperature［℃］propionaldehyde were calculated by comparison withaldehyde-DNPH standard reagents.

80

Fig.５

Polymerization temperature vs USV

29

TOSOH Research & Technology Review Vol.64（2020）

that the side reaction that generated the mono-ol wasusing IPZOH as catalyst. The interest of the PO/EO

accelerated at high temperature.

copolymerization lies on the fact that a high primary
OH ratio is necessary to produce flexible PU foam⑵

(Fig. 8). In general, although KOH can catalyze

Influence of molecular weight
Secondly, we synthesized various PPG of different

the copolymerization of PO and EO, the USV of themolecular weights by controlling the ratio PO toobtained copolymers is high. On the other hand, it isinitiator. The USV of the obtained PPGs was found to

known that the DMC can decrease the USV, but blockincrease slightly with the molecular weight, reaching

PO/EO copolymers are difficult to achieve under these

one third of the value corresponding to the PPG

conditions.

synthesized by KOH catalysis (Fig. 6). The viscosity ofIn the reaction using IPZOH, EO was added after thethe PPGs increased proportionally with the molecularpolymerization of PO, and a clear PPG was obtained.

weight, as extracted from Fig. 7.

Fig. 9 shows the plot of primary OH ratio for various
EO/OH ratios. It was found that the primary OH ratio⑶

could be controlled by the EO/OH ratio.

Copolymerization of PO and EO
Next, we tried the copolymerization of PO and EO

4,000

0.10

USV［meq ／ g］

0.08

Viscosity［mPa・s］

IPZOH
KOH
1
3

0.06
0.04
0.02
0.00

0

2000

4000

6000

3,000

2,000

1,000

0

8000

0

Molecular weight［g ／ mol］

Molecular weight vs USV

Fig.７

PO

OH +
OH
initiator

O

O

OH

O

catalyst

O

O

n

nH

O

O

catalyst

15,000O

nH

O

Copolymerization of PO and EOPrimary OH ratio［％］

90
85
80
75

Fig.９

4

5

7
8
9
6
EO ／ OH［mol ／ mol］

O
O
O

O mH

n

O mH

n
n

H
primary OH

95

70

Molecular weight vs viscosityOsecondary OH

Fig.８

30

10,000

EO
O

Fig.６

5,000

Molecular weight［g ／ mol］

10

Amount of EO vs primary OH ratio東ソー研究・技術報告第 64 巻（2020）［2］Synthesis of PPG by using IPZOH and aluminum

was due to the effect of the aluminum compound. In any

as cooperative catalyst

case, the synthesis of low-USV PPG could be performed

To further reduce the USV, we focused on acooperative catalyst consisting of an organic base anda Lewis acid10) - 12)with high catalytic activity at high polymerization
temperature.

. As a result of our investigation,
Catalytic activity［g ／ mol・min］

we discovered that IPZOH/aluminum compoundconstituted an excellent cooperative catalyst for lowUSV PPG. We investigated (1) the influence of thecatalyst ratio, (2) the influence of the polymerization
temperature, (3) the influence of the aluminumcompound and, (4) the aldehyde of PPG in the reaction
using IPZOH and aluminum compound.
⑴

1500
1200
900
600
300
0

Influence of catalyst ratio

80

90

100

110

120

130

140

Polymerization temperature［℃］Firstly, we used the cooperative catalyst comprisingof IPZOH and triisobutyl aluminum (TiBAL) in a molar

Fig.10

Polymerization temperature vs catalytic activity

ratio IPZOH:TiBAL of 1:1, but the reaction did notproceed (Table 2; Run 1). When we used a 1:2 molar

0.08

ratio, the reaction proceeded with the same activity as

IP ZOH
USV［meq ／ g］

that obtained using IPZOH as catalyst. It was foundthat the USV of the obtained PPG (OHV = 24 mg KOH/g) was only 0.002 meq/g, which is the lowest level
exhibited by commercial PPG (Table 2; Run 2). A
similar result was obtained when a 1:3 molar ratio of
IPZOH:TiBAL was used (Table 2; Run 3). Incidentally,

0.04

0.02

0

the reaction did not proceed when using only TiBAL as80

Fig.11

Run

90

100

110

120

130

140

Polymerization temperature［℃］a catalyst (Table 2; Run 5).

Table 2cooperative

0.06

Polymerization of PO using IPZOH and TiBAL
as catalysts

IPZOH:TiBAL
activity
USV[mol:mol] [g/mol･min] [meq/g]

Mw/M n

1

1：1

0

－

－

2

1：2

530

0.002

1.05

3

1：3

520

0.002

1.05

4

1：0

460

0.028

1.05

5

0：1

0

－

－

⑶

Polymerization temperature vs USV

Influence of aluminum compounds
We also investigated the influence of using

different aluminum compounds on the reaction.
The polymerization was carried out using TiBAL,
triphenyl aluminum (AlPh3), aluminum tri-isopropoxide(Al(Oi Pr) 3), and aluminum trichloride (AlCl3). Highcatalytic activities were obtained in all cases. In addition,
the USVs of the obtained PPGs were very low (0.002
meq/g) (Table 3).

⑵

Influence of polymerization temperature

Fig. 12 shows the elution curves of gel permeation

Then, we investigated the influence of thechromatography (GPC) for the obtained PPGs. Impurity

polymerization temperature on the reaction using thecomponents with low molecular weight were detected incooperative catalyst. It was found that the catalytic

amounts that depended on the aluminum compounds.

activity increased with temperature (Fig. 10), whereas

Thus, when TiBAL or AlPh3 were used, the amounts

the USV remained unaltered upon temperature variationof impurities were small. Conversely, when Al(Oi Pr)3

(Fig. 11), which contrasts with the result obtained foror AlCl 3 were used, the impurities were obtained in

IPZOH. It seems reasonable to assume that this result

relatively large amounts.
31

TOSOH Research & Technology Review Vol.64（2020）

Intensity［mV］

15

10― IPZOH+TiBAL― IPZOH+AlPh3

5― IPZOH+Al(Oi Pr)3
― IPZOH+AlCl30･･･ IPZOH only
3

4

5

logM

Fig.12

Table３Run

GPC analysis of impurities

Properties of the PPG synthesized by IPZOH andaluminum compounds

shown in Fig. 13, in which allyl terminated mono-ol

aluminum
activity
USV
impurity a)compounds [g/mol･min] [meq/g] [area%]

terminated diol (C) were detected. We believe that

1

TiBAL

520

0.002

0.8

2

AlPh3

480

0.002

1.3

3

Al(OiPr)3

510

0.002

2.3

4

AlCl3

530

0.002

9.0

(A), isopropoxy terminated mono-ol (B), and hydroxy
impurity (A) was generated by side reaction, impurity(B) derived from the aluminum compound, and impurity(C) from H2O.
⑷

a) Calculated by GPC.

Aldehydes of PPG
We analyzed aldehydes of PPG synthesized by

To identify the structure of the impurities, a sample

IPZOH or its cooperative catalyst, because requirementof the impurity obtained in the synthesis of PPG

to reduce aldehydes of PU foams for automotive seatingiusing IPZOH and Al(O Pr)3 was analyzed with matrix-

have been increasing 13). The results are shown in Table

assisted laser desorption/ionization time-of-flight4, propionaldehydes of PPG synthesized by IPZOH or

mass spectrometry (MALDI-TOF/MS). The result is

IPZOH/TiBAL catalyst were much lower than that ofB

PPG catalyzed by
IPZOH and Al(Oi Pr)3

C

H
O
O n
A (m/Z=1532.0572)iH
O n
B (m/Z=1534.0725)

A

m/z=58.04

1530

Fig.13

Table４
Run

32

1570

1550

1590

1610

PrO

H
HO
O n
C (m/Z=1550.0686)

Analysis of impurities with MALDI-TOF/MS

Aldehydes of PPG synthesized by various catalyst

catalyst

formaldehyde acetaldehyde propionaldehyde
[ppm]
[ppm]
[ppm]

1

IPZOH

1.2

11.1

7.5

2

IPZOH+TiBAL

1.2

1.5

7.9

3

KOH

1.4

5.6

1,590

東ソー研究・技術報告

PPG synthesized by KOH catalyst. Furthermore, an
acetaldehyde of PPG synthesized by IPZOH/TiBAL
catalyst was lower than that of PPG synthesized by

第 64 巻（2020）

4．Conclusions［1］We found that IPZOH was an effective base catalyst
for the preparation of PPG, which exhibited

IPZOH catalyst.

OHV and USV of 24 mg KOH/g and 0.03meq/g,［3］Evaluation of flexible foam based on low-USV PPG

respectively. Most interestingly, this USV was one⑴

third of that of conventional PPG.

Synthesis of PPG for flexible foam
We synthesized a PPG that could be applicable as［2］We discovered that a cooperative catalyst of IPZOH

flexible PU foam. The OHV and USV were 24.1 mg

and aluminum compound exhibited enhanced,

KOH/g and 0.029 meq/g, respectively. It is worth

excellent performance in the synthesis of low-USV

noting that the latter value was only one third of

PPG. The USV of the PPG (OHV = 24 mg KOH/g)that corresponding to the PPG synthesized by KOH

was only 0.002 meq/g, which was lower than thatcatalysis.

of any commercial PPG.
［3］The flexible PU foams based on this low-USV PPG⑵

showed excellent hysteresis loss, ball rebound, andEvaluation of flexible foam
In the evaluation of flexible PU foam (formulation

compression set.

is shown in Table 5), we found that the foams basedon low-USV PPG showed excellent hysteresis loss,
ball rebound, and compression set (CS) in comparison
with those based on conventional PPG, which could be
attributed to the increase of the crosslink density (Table

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Chem. Soc ., 81(13), 3374(1959)
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Formulation

phr

PPG

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POP

25

cell opener

4.0

cross linker

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TEDA L33

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TOYOCAT ET

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surfactant

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H2O

4.0

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Table６

Properties of PPG and flexible foam

catalyst
PPG

foam

A. Kutt, I. Koppel, V. Maemets and I. Leito, J. Am.

Chem. Soc ., 127(50), 17656(2005)

low-USV
PPG

conventional
PPG９）Y. Kondo and Y. Tanaka, Kagaku , 61(10), 66(2006)

IPZOH

KOH

10）C.Billouard, S. Carlotti, P. Desbois and A. Deffieux,

OHV［mg KOH/g］

24.1

24.0

USV［meq/g］

0.029

0.091

density［kg/m3］

45

45

hardness［N/314cm2］

252

248

hysteresis loss［％］

28

31

ball rebound［％］63

59

CS wet［％］

8.6

10.2

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