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 60-80 ℃ Petroleum ether The reaction was monitored using FTIR, and the procedure was stopped when complete disappearance of absorption due to -NCO group in the FTIR spectrum. N2 Filtered,dried in air and recrystallized from toluene. NMA/CH2Cl

Synthesis MDI TDI IPDI HMDI Adduct 1 2 3 4 Prepolymer 5 6 7 8 Synthesis of prepolymer N-methylaniline-blocked polyisocyanates (5-8) based on poly(tetrahydrofuran) (Terathane-2000) 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 N-methylaniline 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), N-methylaniline 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 isocy-anates 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. The low deblocking temperature of N-methylaniline- blocked isocyanates is due to the auto-catalytic effect of the tertiary nitrogen atom of blocked isocyanate moiety through the formation of an intramolecularly hydrogen bonded four-centered complex. If the blocked isocyanate is based on aromatic isocyanate, the aromatic ring drains the electron density of the nitrogen atom of isocyanate moiety and makes the labile bond formed between the isocyanate and blocking agent more 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 2,4-diisocyanate 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。