Drying agent

 

Drying agent is a chemical that usually used in absorbing the water present in the organic solvent. This is because the presence of water may cause the ineffective reaction or any other undesirable reactions.

The efficiency of drying agent is measured by capacity and rate. The maximum number of moles of water that the drying agent can absorb is called capacity. The rate of water absorption is another factor that affects the efficiency of drying agent. Some of the examples of drying agents are shown in below.

 

Magnesium Sulfate:

Advantage: Magnesium sulfate is a rapid and efficient drying agent with high capacity.

Disadvantage: Sensitive to epoxide, need to be filtered out due to its fine powder form

 

Sodium Sulfate:

Advantage: less reactive, present in granule form which is easier to be removed, high capacity  

Disadvantage: lower efficiency and lower completeness than magnesium sulfate

 

Calcium Sulfate:

Advantage: High completeness, high efficiency

Disadvantage: low capacity

 

Calcium Chloride:

Advantage: High completeness, high efficiency

Disadvantage: low capacity

 

Potassium Carbonate:

Advantage: moderate capacity, moderate efficiency

Disadvantage: Not sure

 

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Polymer solubility parameter and solubility of polymer

Questions:

1. Calculate the polymer solubility parameter, δ₂ for PVC, LDPE, PS and PMMA by using the equation below, where the molar attraction constant per unit for the functional groups are referring to the appendix 1.

 

 

 

Type of polymers and their repeating unit	Molecular weight, M (g mol-1)	Sum of molar attraction constant, ∑E (J1/2 cm3/2 mol-1)	Density, ρ (g cm-3)	Solubility parameters, δ2 (J1/2 cm-3/2)
-(CH2CHCl)- Poly(vinyl chloride)	62.50	891.00	1.41	20.10
-(CH2CH2)- Low Density Polyethylene	28.00	560.00	0.85	17.00
-CH2CHΦ)- Polystyrene	104.00	1937.00	1.05	19.56
-[CH2CH(COOCH3)]- Poly(methyl methacrylate)	86.00	1352.00	1.17	18.39

 

2. Explain how solubility is affected by polymer chain structure.

When molecular weight of polymer increases, its solubility will decrease. Crosslinked polymers do not dissolve but they only swell when the solvent diffuse into the polymers. Lightly crosslinked polymers swell extensively in solvent in which unvulcanized material would dissolve. When crosslinking degree increases, the solubility decreases. This is because the strong cross-linked polymers will inhibit interaction polymer chains and solvent molecules.

 

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