I working with silicon-based polymer which is crosslinked to obtain solid polymer as i am a mechanical engineer i am not sure of this, can someone kindly oblige
additionally if molecular weight changes how can we estimate molecular weight and degree of crystallinity ?
Linear polymers before crosslinking have a molecular mass ditribution that can be deterrmined by various methods, such as gel permeation chromatography. The average molecular mass can be determined by light scattering, viscometry, etc. Once you begin to use a crossliker first you will get branched molecules with increased molecular mass. Then you reach the gel point, where the end-to-end distance in the molecules becomes comparable with the sample size, i.e. you will have an infinite nework. In this case it is meaningless to speak about molecular weight, th material becomes insoluble, you will have elasticity instead of viscosity. What is meaningful, however, is the average molecular mass of the chains between the crosslink points. That can be estimatd form mechanical tests above the glass transition temperature or by swelling tests. the higher the corsslink density the harder the network becomes, the elongaton at break and the average molecular mass between the network points decrease.
Linear polymers before crosslinking have a molecular mass ditribution that can be deterrmined by various methods, such as gel permeation chromatography. The average molecular mass can be determined by light scattering, viscometry, etc. Once you begin to use a crossliker first you will get branched molecules with increased molecular mass. Then you reach the gel point, where the end-to-end distance in the molecules becomes comparable with the sample size, i.e. you will have an infinite nework. In this case it is meaningless to speak about molecular weight, th material becomes insoluble, you will have elasticity instead of viscosity. What is meaningful, however, is the average molecular mass of the chains between the crosslink points. That can be estimatd form mechanical tests above the glass transition temperature or by swelling tests. the higher the corsslink density the harder the network becomes, the elongaton at break and the average molecular mass between the network points decrease.
By cross linking, you are essentially connecting two materials, to put it in the simplest term.
The definitions of the molecular weight of the linear and crosslinked polymers are different. Of course the degree of crosslinking influeneces the molecular weight.
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