Isocyanates nco oh
Sponsored Links
This presentation is the property of its rightful owner.
1 / 18

異氰酸鹽 (Isocyanates, -NCO ) 和羥基 (-OH ) 化合物的 反應性極高 ,但在有些應用上需要延遲異氰酸鹽與羥基的反應,並在適當的步驟下適放異氰酸鹽官能基。 PowerPoint PPT Presentation


  • 138 Views
  • Uploaded on
  • Presentation posted in: General

Introduction. 異氰酸鹽 (Isocyanates, -NCO ) 和羥基 (-OH ) 化合物的 反應性極高 ,但在有些應用上需要延遲異氰酸鹽與羥基的反應,並在適當的步驟下適放異氰酸鹽官能基。 封閉型異氰酸鹽是 異氰酸鹽 和 帶有活性氫的封閉劑 (Blocked agegnt BH) 反應生成一個 弱鍵結 的化合物;在一定溫度下釋放出 (-NCO) 官能基。. Introduction. 封閉型聚異氰酸鹽, 對於水氣有良好的抵抗性 及 較佳的儲存性 。

Download Presentation

異氰酸鹽 (Isocyanates, -NCO ) 和羥基 (-OH ) 化合物的 反應性極高 ,但在有些應用上需要延遲異氰酸鹽與羥基的反應,並在適當的步驟下適放異氰酸鹽官能基。

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


Introduction

  • 異氰酸鹽(Isocyanates, -NCO)和羥基(-OH)化合物的反應性極高,但在有些應用上需要延遲異氰酸鹽與羥基的反應,並在適當的步驟下適放異氰酸鹽官能基。

  • 封閉型異氰酸鹽是異氰酸鹽和帶有活性氫的封閉劑(Blocked agegnt BH)反應生成一個弱鍵結的化合物;在一定溫度下釋放出(-NCO)官能基。


Introduction

  • 封閉型聚異氰酸鹽,對於水氣有良好的抵抗性及較佳的儲存性。

  • 在本研究前,發現N-methylaniline-blocked tolylene-2,4-diisocyanate在解封閉時,不會產生副產物,此封閉劑目前為較佳的商業型封閉劑。

  • 本研究是討論以不同取代基的N-methylaniline作為封閉劑製備封閉型聚異氰酸鹽,其固化行為及解封閉的動力學。


Materials

  • N-Methylaniline (Lancaster)

  • Methyl 2-methylaminobenzoate(Lancaster)

  • Methyl 4-methylaminobenzoate(Lancaster)

  • N-methyl-o-anisidine (Aldrich)

  • Nmethyl-p-anisidine (Aldrich)

  • N-methyl-o-toludine(Aldrich)

  • N-methyl-p-toludine (Aldrich)

  • 2-chloro-N-methylaniline (Aldrich)

  • 4-chloro-N-methylaniline(Aldrich)

  • N-methyl-4-nitroaniline (Aldrich)


Materials

  • 4,4-Methylenebis(phenylisocyanate) (MDI; Lancaster)

  • Phenyl isocyanate(Aldrich)

  • Poly(tetrahydrofuran) (Terathane; Mn=2000;Aldrich)

  • Dibutylamine (Fluka)

  • Hydroxyl-terminated polybutadiene(HTPB; Mn=2500), obtained from Vikram SarabhaiSpace Centre, was used after drying for 2 hat 80 ℃ in vacuo.

  • Toluene (Merck), methanol(Merck), and chloroform (Merck) were purifiedaccording to standard procedures.


Synthesis

N-methylanilinemethod

50 ℃ 2hr

PTHF

N2

N2

1hr

70 ℃ 3hr

40 ℃

MDI

Blocked agent


Synthesis


Results and discussion

有內子分氫鍵

The electron-donating substituents rendered the nitrogen atom of N-methylaniline more basic for its easy attack on the partially positive carbon atom of the -NCO group, thereby increasing the rate of the blocking reaction. The slow blocking reaction of N-methylaniline substituted with electron-donating substituents at the ortho position may be attributed to the steric factor.


Results and discussion

Urea:153.69 ppm

urethane:154.39 ppm


Results and discussion

Polyisocyanate 2


Results and discussion

經由實驗證實,並非如此,而是四級化過渡態上的氫鍵,會產生自催化效應,使C=O和N的鍵結變更弱。

The use of phenol as a blocking agent for isocyanates is understandable because phenol is less nucleophilic toward isocyanate groups; as a result, the bond that forms between the carbonyl carbon of isocyanate and the oxygen atom of phenol is labile.

NMA上氮的親核性較phenolic system高,和羰基的碳形成的鍵結較穩定,因此,可從電荷差異來看鍵的強弱。


Results and discussion

At low temperatures, the hydrogen-bonded proton has a dipolar attraction between the positively polarized hydrogen and the negatively polarized nitrogen of the blocking agent, which leads to intramolecular association with consequent lengthening and weakening of the original -NH bond.

由此可證實,Urea的質子與分子內氫鍵有關,而在解封閉反應中會形成氫鍵及四級化過渡態的錯合物。

The electron density around the proton is reduced, and this deshielding moves the proton signal to a higher frequency.

As the temperature increases, the hydrogen bond becomes weak, and the original -NH bond is shortened; this leads to increased electron density around the proton, and this shielding move the proton to a lower frequency.

Variable-temperature 1H NMR spectra of blocked polyisocyanate 2, showing a frequency shift of (a) hydrogen-bonded urethane and (b) urea protons in CDCl3.


Results and discussion

在鄰位有極化的取代基,降低氫鍵的自催化反應

BH的N上電子密度↑


Results and discussion

Urea : 1685 cm-1

Ureathane : 1685 cm-1

FTIR spectrum of (A) blocked isocyanate 12, (B) blocked polyisocyanate 2 recorded at 140℃, and (C) blocked polyisocyanate 2 recorded after 120 min at 140℃.


Results and discussion

Carbonyl regions of FTIR spectra of blocked polyisocyanate 2 recorded at 140 ℃ for different time intervals.


Results and discussion

(A)

(C)

(B)

Changes in the intensities of (A) NCO, (B) urea C=O, and (C) allophanate C=O absorption of blocked polyisocyanate 2 at 125 ℃ with respect to time.


Results and discussion

The entropies of activation are highly negative because of the formation of a hydrogen-bonded, four-centered, rigid complex in the transition state.

In the case of blocked polyisocyanate 10, the peak of urea carbonyl is partly merged with the adjacent allophanate carbonyl absorption; thus, there was difficulty in the calculation of the kinetic parameters.


Conclusions

  • 一系列不同取代基的N-methylanilines封閉劑與異氰酸酯被合成出來,且解封閉的溫度、固化時間及解封閉動力學在這篇研究報告出來。

  • N-methylanilines經過解封閉後殘留在系統中,與酚類化合物相比,其腐蝕性較低,較適合用來製作熱固型聚胺酯。


  • Login