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指導教授:王振乾教授
研究生:符昌中
Introduction
• 聚氨酯(Polyurethane,PU)包含異氰酸鹽與羥
基化合物，在工程材料上應用廣泛，且幾
乎每天都有新的用途出現。
• 由於異氰酸鹽和羥基化合物反應性高，因
此產生雙組成(Two package)的構想，而雙
組成聚氨酯在設備及成本上需要較多的花
費。
Introduction
• 封閉型聚氨酯，是一個經由熱硬化方式所獲得的聚
氨酯，此可降低異氰酸鹽對水氣的敏感性，及毒性。
• 本研究是探討不同結構的異氰酸鹽在封閉、解封閉
和硬化反應中的熱力學和動力學反應。
Materials
• N-methylaniline (NMA) (Lancaster)
• 4,4-Methylenebis(phenylisocyanate) (MDI) (Lancaster)
• Toluene 2,4-diisocyanate(TDI) (Aldrich)
• 1,6-Diisocyanatohexane (HMDI) (Fluka)
• Isophorone diisocyanate (IPDI) (Aldrich)
• Phenyl isocyanate(Aldrich)
Materials
• Polytetrahydrofuran (PTHF,Mn =2000) (Aldrich)
• Polypropylene glycol (PPG, Mn = 2000)(Aldrich)
• Poly(e-caprolactone diol) (PCL, Mn = 2000)
(Aldrich)
• Dibutyl amine (Fluka) were used as received.
Materials
• Hydroxyl-terminated polybutadiene (HTPB,
Mn = 2500) obtained from Vikram Sarabhai
Space Centre, was used after drying for 2 h at
80℃ under vacuum.
• Toluene (Merck), methanol (Merck) and
chloroform (Merck) were purified according to
standard procedures.
Synthesis
Synthesis of adduct
Diisocyanate/
CH2Cl
N2
NMA/CH2Cl
The reaction was monitored using FTIR,
and the procedure was stopped when
complete disappearance of absorption
due to -NCO group in the FTIR spectrum.
Filtered,dried in air and
recrystallized from toluene.
Synthesis
Synthesis of prepolymer
N-methylaniline-blocked polyisocyanates (5-8)
based on poly(tetrahydrofuran) (Terathane2000) were prepared according to a
procedure described in our pervious report.
MDI
TDI
IPDI
HMDI
Adduct
1
2
3
4
Prepolymer
5
6
7
8
Results and discussions
In the case of aromatic isocyanates, carbonyl carbon of -NCO group is more electro
positive because the aromatic ring drains the electron density of the nitrogen atom
and this facilitates the blocking reaction. In the case of the aliphatic isocyanates,
the carbonyl carbon is less electro positive and the nucleophile attack by the Nmethylaniline is more difficult. Therefore, the use of catalyst is inevitable for the
preparation of blocked isocyanates 3 and 7.
Results and discussions
The aromatic moiety drains electron
density present in the nitrogen atom of
-NH and this makes urea nitrogen atom
less basic, thus, hydrogen atom
attached to the nitrogen atom undergo
deshielding. Similarly aliphatic moiety
makes the nitrogen atom of -NH more
basic and hence the proton attached to
the nitrogen atom is more shielded.
1H
NMR spectra of N-methylaniline (a), Nmethylaniline blocked HMDI (b), MDI (c)
and TDI (d).
Results and discussions
13C
NMR spectrum of blocked polyisocyanate 6.
1H
NMR spectra of each of the blocked
isocyanates shows urethane proton at
6.78 ppm and the 13C NMR spectra
show urea and urethane carbonyl
carbon at 153.69 ppm and at 154.39
ppm, respectively. This confirms the
formation of amine-blocked isocyanates and their structures.
1H
NMR spectrum of blocked polyisocyanate 6.
Results and discussions
The blocked aromatic diisocyanate adducts deblocks relatively at high
temperature, the reactivity of regenerated isocyanate group with HTPB will be
high.
If the
The
low
blocked
deblocking
isocyanate
temperature
is based
of N-methylanilineon aromatic isocyanate,
blocked isocyanates
the aromaticis ring
due
to the auto-catalytic
drains
the electron density
effect ofofthethe
tertiary
nitrogen
nitrogen
atomatom
of isocyanate
of blockedmoiety
isocyanate
and
moietythe
makes
through
labile bond
the formation
formed between
of an intramolecularly
the isocyanate and
hydrogen
blocking
bonded
agent more
fourcentered complex.
labile.
Results and discussions
TDI based blocked isocyanate
undergo deblocking at lowest
temperature and are due to
the methyl group present in
the isocyanate moiety, which
accelerates the deblocking
reaction, through steric factor.
Variable temperature FTIR spectra of
N-methylaniline-blocked toluene 2,4diisocyanate adduct (a) and poly
toluene 2,4-diisocyanate (b).
Results and discussions
3
2
1
FTIR spectra of N-methylaniline-blocked poly 4,40-methylenebis( phenyl isocyanate) (a) and
4,40-methylenebis(phenyl isocyanate) adduct (b) recorded at 145 C at different time intervals.
Results and discussions
All the blocked polyisocyanates and blocked diisocyanate adduct
based on IPDI were found to be readily soluble in room
temperature in all the four polyols. This is due to the presence of
large number of aliphatic groups in the blocked isocyanates.
Conclusions
• 經由此研究發現，封閉聚氨酯的硬化行為
視解封閉溫度和釋放出的-NCO官能基而定。
• 芳香族異氰酸鹽的反應性較脂肪族來的快，
且解封閉的速度也快。