What Determines Organic Silicone Resin's Properties

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As we introduced in last article, silicone resins do have many excellent physical and chemical properties which could be directly applied in industries. Today we will introduce more on each unique property and we will also introduce what factors will influence each of them.

Heat Resistance and Cold Resistance

Silicone resin is thermosetting resin, when it is in the thermal oxidation under high temperature, the breaches only occur on the functional groups of the side chains. The breaches will release oxides and the Si-O chemical chain of the main chain is hardly broken. Thus it has higher thermal stability. The main reasons are:

1.      It is due to the big molecular chains of silicone resins are made of –Si-O-Si- chemical keys, and Si-O chemical key has better key energy (373kj/mol). Therefore, it has excellent thermal oxidation stability and heat resistance, heat resistance is generally better than organic silicone resin, in other words, Si-O key’s covalent bond energy is higher than the C-C key’s in the general organic macro polymers.

2.      However, it is since silicon atoms are linked to organic functional groups, organic silicon’s thermal stability is worse than some inorganic matters like quartz. Difference from electronegativity in the silicon atoms and oxygen atoms in Si-O chemical key is big, therefore Si-O key has big polarity and it improves the stability of oxidation brought by hydrocarbon base; it has better stability than normal organic macro polymers; In other words, Si-O-Si chain could provide isolation effect for the oxidation from the linked hydrocarbon base.

3.      Normal organic macro polymers’ C-C main chain has been thermal oxidated to breach into micro molecular structure; However, when the hydrocarbon base which is linked to silicon atom of organic silicone macro polymer has been thermal oxidated, the produce product is highly crosslinked more stable Si-O-Si key which could prevent its main chain to be breached.

4.      During the process of thermal oxidation, the organic silicon macro polymer’s surface has formed a stable protection film which contains a rich of Si-O-Si keys. This reduces the influences into its inside. Therefore, silicone resin has high thermal decomposition.

Electrical Properties (Isolation)

Another outstanding property of silicone resin is its excellent electrical property. In the normal form, silicone resin coating film has similar properties with organic silicon resins. However, in high temperature or humid environment, the former one’s electrical property is way higher than the latter one. It is due to most macromolecular main chains of silicone resins have a layer of non-polar organic functional groups around its outside, and the macromolecular chains have symmetry, therefore, it has excellent electrical isolation. It could perfectly fulfill requirements from H-grade materials; it is one of the best electrical isolation materials. Its dielectric loss, voltage resistance and some other relevant properties are at the best level to compare with other isolation materials. Therefore, they are stable isolation materials and they are widely applied in electronical and electrical industries.

Silicone resins not only have high insulation resistance, but also it performs very well in some other fields as well.

Weather Resistance

Silicone resin has excellent weather resistance. No other organic resins could compare it with silicone resin. It is one of the main features of silicone resin. It is because the main chain of silicone resin is –Si-O-, and there are no existences of double keys, therefore it is hard to be decomposed by odors or UV light, and the length of Si-O key chain is one and half times more than C-C key chain. The longer key length makes silicone resin has better thermal stability, radiation resistance and weather resistance to compare with other macromolecular materials. Silicone resins could have a product life cycle over tens of years.

Methyl silicone resin hardly absorbs UV light; phenyl silicone resin also only absorbs rays which is lower than 280nm. Therefore, the sunlight which is over 300nm has little influence on silicone resins. Even though in the strong sunshine of UV light, silicone resin will not turn to be yellow and the functional groups will not be reacted and basically no oxidation reaction will occur. If to use light-resistance pigments and the coating materials made of silicone resins, the colors could be kept for years.

Organic resin modified silicone resin’s weather resistance is worse than pure silicone resin, but to add some type of silicone resin into organic resins, it could evidently increase its weather resistance. The more polysiloxane modified silicone resin contains, the better weather resistance it has.

Mechanical Properties

It is due to the molecular structure and intermolecular force of organic silicone polymer is small, effective crosslinking density is low, therefore, silicone resin’s general mechanical properties like bending, tension and shock resistance are weak. However, as the silicone resin to be used for electrical isolation coating materials, the key mechanical properties are focusing on its softness, hardness, thermal plasticity and adhesion. Silicone resin film’s hardness and softness could be modified by changing its resin structure to fulfill the specific requirements. Also, when the structures are similar, methyl phenyl resin’s softness and thermal plasticity are better than methyl silicone resin.

Compatibility

The main chain of organic silicon is very soft, this excellent softness comes from its basic geometric molecular configuration. It is due to its intermolecular force is way smaller than some other chemicals, therefore, it has lower surface tensile strength, low surface energy, and it has stronger film formability, demoudling and adhesion resistance. It could be used as the heat resistance and permanent demoulding agent.  

Summary

As we could see from the descriptions and discussions above, most of silicone resin’s properties are determined by it molecular structure or component. Therefore, more and more people do more researches on the modification at the molecular level or use some other ways to change silicone resin’s molecular structure to fulfill the needs from their industries.

All of these methods have expanded the categories of silicone resins and also make its market to be larger and larger, and more and more types of silicone resins will be applied in the foreseeable future.