Introduction to Modified Silicone Resins

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The structure of organic silicon has Si-O key whose key energy could reach 425kh/mol, which is way larger than C-C (345kj/mol) and C-O (351kj/mol). Also, it is hard to happen that silicon combined with other atoms. This means organic silicone compound has properties like low and high temperature resistance, dirt resistance, weather resistance and oxidation resistance. It also has good breathability. Organic polysiloxane consists of inorganic Si-O chain and organic C-H chain. It is to plus the Si-O-Si key angle is a larger one and low bending force, these have promoted much to the flow ability of organic silicone chains to lower its vitrification temperature. All kinds of organic composited resins have their own pros and cons. Their weaknesses are just the advantages of organic silicone polymers.  To lead organic silicone to organic composited resins could improve their weaknesses and perfect the modified resins. Therefore, it is the hot spot and difficulty to use advantage of organic silicon to improve organic composited silicone resins.

The ways to modify silicone composited resins include physical co-mixing and chemical structure modification. It is due to molecules have their own properties, many organic silicone resins have bad compatibility with organic silicon. Therefore, physical co-mixing cannot achieve perceived modification result. Only chemical way could be used to achieve very good modification target. There are two types of compounds which could lead Si-O keys into organic polymers: the silane compound like coupling agent; the silane monomers and low polymers contain reactive functional groups. By using organic silicon and different resin molecules could get modified silicone resins with different properties.

Alkyd Resin Modified Organic Silicone Resin

Alkyd resin is one composited polymer which could produce excellent resin on surface coating by adjusting different components of the polymer. It consists of polyol, polybasic acid and fatty acid as the main components to do the condensation to get oil or fatty acid modified polyester resin.

By the number and structure of two-key of fatty acid molecules, they could be divided into dry, half-dry and non-dry. Dry alkyd resin could have solidification in the air; non-dry could only be solidificated by being heated and be mixed with amino resin.

For the modification of alkyd resin, the physical way is the earliest one. By adding organic silicone resin to the end of the reaction. Organic silicone resin could be connected to alkyd resin in high temperature. However, it is also possible that most organic silicone resin is only soluble in alkyd resin. It is in order to improve the solubility of organic silicone resin, organic silicone resin always contains some long-chain alkyl. By the simple mixing, the outdoors weather resistance of alkyd resin will be improved. Generally, to mix high phenyl silicone resin which contains better compatibility with alkyd resin which is low or medium oiliness in cold condition could provide better thermal plasticity, faster air dry and better solubility. However, the modification result is still not good and the physical is been abandoned gradually.

Now the modification of alkyd silicone resin mainly applies chemical way. There are usually three ways: The first is to the put the silicone intermediaries, acid and alcohol together and just react them once for all; the second is that to react silicone intermediaries with alcohol firstly and react with acid; the third is to react alcohol with acid firstly and react with acid then. In practice, the third way is applied mostly.

Silicone Resin Modified Polyester Resin

In modern industries, polyester resin is the raw material to produce polyester fiber, pigment, slim film and engineering plastics. It is according to the acid saturation of raw materials, production could be divided into saturated polyester and unsaturated polyester. Both of them could be used to modify silicone resin but the main one is the saturated polyester type.

This kind of polymer has a common characteristic that the links between chains of the big molecules are linked by ester groups thus called polyester. Polyester contains the advantages like polished, high hardness, good physically mechanical properties and better corrosion resistance. However, it has weaknesses like bad waterproof and bad processing properties which will influence the further application in rolling material coating pigments; however, organic silicone resins contain excellent heating resistance, weather resistance, waterproof and lower tensile strength, but it also has bad solvent resistance and high solidification temperature. Organic silicone modified polyester resin is one type of thermosetting resin, which could allow the advantages of two polymer materials to help mutually. It has excellent heating resistance, weather resistance, corrosion resistance, electrical isolation and bending resistance and it could highly improves the properties of silicone resins and expands the scope of application.

At present, there are also two ways to modify organic silicone resin and the chemical way is generally better than the physical way.

Physical co-mixing is the method to mix polyester resin and silicone resin physically. Generally, the compatibility between these two polymers is pretty bad and will influence much on the hardness, stability and mechanical properties of the modified silicone resin and it is hard to fulfill the requirement of high-quality products on silicone modified polyester and this will definitely influence the promotion and application of itself.

The chemical modification is to use chemical key to link the two polymers which have bigger difference in polarities. This method could improve their compatibility and curb the moving of polysiloxane molecules and to distribute silicone resin and polyester resin averagely from a micro perspective.

Of course, there is a certain ratio between polyester resin and organic silicone resin. The modified resin’s property is between organic silicone resin and polyester silicone resin. As the percentage of organic silicon increases, the property moves to organic silicone resin side but with a higher cost; if the polyester takes the most part, the advantages of organic silicon will not appear. Therefore, it is according to the requirement of the final products, the percentage of organic silicone is between 15% ~ 30%.

Summary

Today we have introduced two main types of modified silicone resins. These modified new products have made the applications of silicone resins to be more varied and effective.