Experimental Method Determination of Osmotic Pressure Polymer Solubility

Experimental Method: Determination of : Osmotic Pressure Polymer Solubility 1

The osmotic pressure data for cellulose tricaproate in dimethylformamide at three temperatures. The Flory temperature was determined to be 41 ± 1°C Polymer Solubility 2

Modified Flory-Huggins theory Is temperature dependent Therefore, any temperature which causes =1/2 will be the Flory temperature Polymer Solubility 3

Flory-Huggins Parameters Polymer Solubility 4

An Example Polymer Solubility 5

Applications of The Chain Expansion Ratio and -Temperature The Expansion Ratio, r Polymer Solubility 6

Applications of ar depends on balance between i) polymer-solvent and ii) polymer-polymer interactions If (ii) are more favourable than (i) ar < 1 Chains contract Solvent is poor If (ii) are less favourable than (i) ar > 1 Chains expand Solvent is good If these interactions are equivalent, we have theta condition ar = 1 Same as in amorphous melt Polymer Solubility 7

Applications of For most polymer solutions ar depends on temperature, and increases with increasing temperature At temperatures above some theta temperature, the solvent is good, whereas below the solvent is poor, i. e. , T> ar > 1 T= ar = 1 T< ar < 1 Often polymers will precipitate out of solution, rather than contracting Polymer Solubility 8

Applications of The Solvent Goodness: • • A Positive A 2 indicates a good solvent, i. e. a solvent that gives rise to an exothermic enthalpy of mixing. This arise when <1/2. When A 2=0 the solvent is nearly Ideal. This is important for use of osmotic pressure to measure molar mass. A negative A 2 indicates a poor solvent ( >1/2). The entalpy of mixing is positive here. The goodness of solvent can be adjusted by changing the temperature. Polymer Solubility 9

Applications of Recall: Note that the energy terms w 11, w 22 and w 12 are attractive terms and are usually negative. When Hmix =0 for a solvent -polymer system, thus w 11=w 22 and the cohesive energy density. Polymer Solubility 10

Summary Solubility Parameters: Thermodynamics of Mixing Polymer Solubility 11

Summary Free Energy of Mixing: Polymer Solubility 12

Summary Chemical Potential and Osmotic Pressure: Polymer Solubility 13

Summary Other Forms of Flory-Huggins Eqs: 0. 35 (in older literature), or zero Polymer Solubility 14

Properties of the value of is below 0. 5, the polymer should be soluble if amorphous and linear. When equals 0. 5, as in the case of the polystyrene–cyclohexane system at 34°C, then the Flory conditions exist. If the polymer is crystalline, as in the case of polyethylene, it must be heated to near its melting temperature, so that the total free energy of melting plus dissolving is negative. For very many nonpolar polymer–solvent systems, is in the range of 0. 3 to 0. 4. If Polymer Solubility 15

Properties of many systems, has been found to increase with polymer concentration and decrease with temperature with a dependence that is approximately linear with, but in general not proportional to, 1/T. �For a given volume fraction 2 of polymer, the smaller the value of , the greater the rate at which the free energy of the solution decreases with the addition of solvent. �Negative values of often indicate strong polar attractions between polymer and solvent. �For Polymer Solubility 16

Properties of The polymer–solvent interaction parameter is only slightly sensitive to the molecular weight. Polymer Solubility 17

Molecular Weight Averages Polymer Solubility 18

Molecular Weight Distribution Polymer Solubility 19

Determination of Number Average Mw a) End-group Analysis b) Colligative Properties Polymer Solubility 20

Osmotic Pressure Polymer Solubility 21

Flory -Temperature Polymer Solubility 22

Intrinsic Viscosity Polymer Solubility 23

Some Definitions Polymer Solubility 24

The Mark-Houwink Relationship Polymer Solubility 25

Experimental Techniques Polymer Solubility 26

Example Polymer Solubility 27

Example (cont. ) Polymer Solubility 28

Gel Permiation Chromatography Size Exclusion Chromatography Polymer Solubility 29

Schematic View Polymer Solubility 30

Calibration GPC is a relative Molecular Weight Method Narrow molecular weight distribution, anionically polymerized polystyrenes are used most often. Other Polymers: PMMA, Polyisoprene, polybutadiene, Poly(ethylene oxide) and sodium salts of PMA. Polymer Solubility 31

Calibration Method Polymer Solubility 32

Molecular Weight of a Suspension Polymerized PS Polymer Solubility 33

GPC of a Blend Polymer Solubility 34

End of Chapter 2 Polymer Solubility 35