前言：硅胶是化工生产中的一大领域，在工业、手术、日化中均有运用。本文以两种硅油（端氢硅油&甲基氢硅油）为典例，研究了在硅氢合成有机硅弹性体时，硅油分子含氢量、分子结构及乙烯基-硅氢键摩尔比对于反应物交联的影响，并探讨了现象后因由。

1.1 浅谈硅胶弹性体

交联硅胶是一类低交联密度的液体硅橡胶，耐高温（200℃），耐低温（-50℃~-80℃），绝缘，无副产物，收缩率小，无毒无味，无腐蚀，安全卫生，机械密度低，低交联密度又赋予其良好的吸震性，粘合性，密封性，防潮性及防污性。由于性状柔软，交联硅胶受到轻微压力即可引起形变，无色透明，流动性好，宜填充精密结构，故有其以下三种特殊用途。

1）LED电子封装胶

2）医疗整容

3）化妆品成分

1.1 Background

Additional silicone gel is a kind of liquid silicone rubber with low crosslinking density. It possesses the properties of high (200℃) and low (-50℃~-80℃) temperature resistance, electrical insulation, low shrinkage and mechanical strength without by-products, poison, smell and corrosion while ensuring safety and health. Low crosslinking density gives good shock absorption, adhesiveness, airtightness, moisture and soil resistance. Because of the soft character, it can easily change its shape under small load and low pressure. Meanwhile, its colorless and transparent appearance and  good liquidity, which make it easy to fill in into fine parts of precise structures, lead to its specific end use as listed below:

1) Electronic Packaging for Light Emitting Diodes

2) Medical and Cosmetic Surgery

3) Cosmetic Products

1.2 有机硅弹性体的结构

三维网状聚合物的形成被称之为交联。交联键可被看作长硅链分支。 交联键数量庞大, 故形成能黏性的不溶性网状结构或凝胶。

铂催化水解反应能形成网状结构，故常被用于含≡Si-H的低分子量聚硅氧烷与含≡Si-Vi的高分子量聚硅氧烷之间的反应。

1.2 The Chemical Structure of Silicone Elastomers

Cross-links are junctions of polymer strands in a three-dimensional network. They may be viewed as long-chain branches that are numerous enough to form insoluble network or gel. 

Platinum catalyzed hydrosilylation reactions, which are used to form network structures, are typically involved in reactions between a low molecular weight polysiloxane containing ≡Si-H groups, and a high molecular weight polysiloxane containing ≡Si-vinyl groups, vice versa.

2. 有机硅弹性体化学结构与性能关系的实验验证

2.1 实验方法：

提前将 Gvi (甲基乙烯基硅橡胶)溶解于D5 (十二甲基环环硅氧烷) 中。分别加入不同摩尔比的 DH1000 和 MHS。观察反应过程和结果。

2.2 实验器材：

电子天平;玻璃棒;汞温度计;烧杯;恒温水浴

2.3 反应物：

DH1000-------------端氢硅油 (Mw=1000 1000, H%= 0.2%)

MHS----------------甲基氢硅油 (H%=1.6%, 梳状结构)

Gvi------------------甲基乙烯基硅橡胶 (Mw= 570000, Vi%= 0.22%)

D5------------------十二甲基环戊硅氧烷

H2PtCl6/IPA(1%)---氯铂酸的异丙醇溶液

2.4 溶液：

在实验过程中使用相同的乙烯基胶,即Gvi/D5 (20/80), Mw=570000, Vi%=22%

乙烯基胶制备：取20克 Gvi, 然后倒入80克 D5。搅拌不止至Gvi溶解，亦可室温下静置一宿。

2.5 操作示范--实验1

Gvi/D5 (20/80)------10g (0.000157mol -Vi)

DH1000-------------0.08g (0.00016mole -H)

Pt/IPA---------------0.014g (5ppm)

称量10克 Gvi/D5 (20/80), 0.08g DH1000。滴入 H2PtCl6, 搅拌。将烧杯放置在70-90℃恒温水浴池。20分钟内，溶液发生交联。将溶液在恒温水浴中保留2小时, 形成透明、柔软的凝胶。

2.6 实验结果与比较

2 Experiments to verify the relationship between chemical structure and properties of silicone elastomers

2.1 Experimental methods

Dissolve Gvi (methyl vinyl silicone rubber) in D5 (decamethylcyclopentasiloxane) in advance. Add DH1000 and MHS of different proportion of moles respectively. Observe reaction processes and results.

2.2 Laboratory apparatus

Electronic balance; Glass stick; Mercury thermometer; Beaker; Thermostatic water bath

2.3 Reagents

DH1000----------Hydrogen-terminated silicone oil (Mw=1000, H%=0.2%)

MHS------------ Methylhydrogen silicone oil (H%=1.6%， comb structure)

Gvi--------------Methyl vinyl silicone rubber (Mw=570000, Vinyl%=0.22%)

D5--------------Decamethylcyclopentasiloxane

H2PtCl6/IPA(1%) ---Chlorideplatinum acid dissolved in Isopropyl alcohol

2.4 Pre-solution

During the experiment, use the same vinyl gum, or Gvi/D5 (20/80), Mw=570,000, Vi%=0.22%.

Preparation： Take 20 grams of Gvi, then pour 80 grams of D5 into it. Stir until dissolved. 

2.5 Operation Demo—Example 1

Gvi/D5 (20/80)-------10 grams (0.000157mole Vinyl)

DH1000--------------0.08 grams (0.00016mole -H)

Pt/IPA----------------0.014 gram (5ppm)

Weight 10 grams of Gvi/D5 (20/80), 0.08g DH1000. Add H2PtCl6 and stir in a beaker.The beaker was placed in a 80-90℃ thermostatic water bath. Gelation took place within 20 minutes. The gel was left in thermostatic water bath for 2 hours, resulting in a clear and soft gel.

2.6 Comparison of experiment results

3.1 结果与分析

1)交联时，≡Si-H与≡Si-Vi物质的量相同

现象：DH1000（端氢硅油）的反应比MHS(甲基氢硅油)更快、更容易。

推论：DH1000（端氢硅油）活性较高。

猜想：乙烯基与MHS的交联反应受阻, 完全反应困难而缓慢。

2)交联时，≡Si-H 过量

现象：乙烯基与MHS（甲基氢硅油）反应产物坚硬，而与DH1000（端氢硅油）的产物是液体。

推论：乙烯基与MHS中的≡Si-H完全反应，使该产品具有较高的交联密度。

猜想：DH1000中硅氢反应未充分进行，仅有单端反应。故该产品交联程度非常低。

3.1 Results and Discussions

1) ≡Si-H groups and ≡Si-Vi groups are equimolar.

The reactions Hydrogen-terminated siliconeapplied are faster and easier than Methyl hydrogen silicone oil (H%=1.6% combstructure). Hydrogen-terminated is with higher activity. 

Due to hindered reaction with MHS, the complete reaction is difficult and slowly.

2）Excess ≡Si-H groups

Reaction product with MHS is hard, vinyl reacted completely.Theproduct is provided with high crosslinking density.

Due to only partial hydrosilylation reaction with Vinyl-Si≡, only single end reacts. The product is rarely crosslinked.

4.1 总结

以DH1000(端氢硅油)为交联剂, 仅有两个官能团。交联产品可以是二维网状结构，亦可是三维立体网络结构。在使用MHS(甲基氢化硅油)作为交联剂的同时, 参与交联的多个官能团, 形成了具有较高交联密度的三维网络结构产物。

4.1 Conclusion

There are only two functional groups,when using Hydrogen-terminated silicone as crosslinking agent. The crosslinking products can form a two-dimensional network structure, or a three-dimensional network structure. When using methyl hydrogenated silicone oil as crosslinking agent, multiple functional groups are involved in the crosslinking stimutaniously, resulting in a three-dimensional network structure with higher crosslinking density.

参考文献

1. 电子封装中使用的有机硅弹性体

    <www.wap.alighting.cn/webapp/view.aspx>

2. 辛松民， 有机硅合成工艺及产品应用，化工出版社，2000

3. Kadlec, Donald Anthony, et al. US 6770708.2004

Works Cited

1. Silicone elastomers used in electronic packaging www.wap.alighting.cn/webapp/view.aspx?CategoryID=1&ContentID=158534  Accessed on 5 December, 2018.

2. Xin,Songmin, 辛松民.YoujiguiHechengGongyi Ji ChanpinYingyong有机硅合成工艺及产品应用[Organic Silicon Synthesis Process andItsProductApplication].ChemicalIndustry Press, 2000.

3. Kadlec,Donald Anthony, et al. US 6770708.2004

来源：小v化学实验室