Separation of Polymers by Solvent Fractionation

 

Separation of Polymers by Solvent Fractionation Objectives: 1. To under underst stand and the the co conc ncept ept of polym polymer er so solu lubi bili lity ty an and d fr frac acti tion onat atio ion n an and d it itss re rela late ted d  parameters. 2. To expose to aste aste polymers polymers hich are also also pollutin! pollutin! a!ents" a!ents" e!. Plastic Plastic and rubber. rubber. #ntroduction The dissolution of polymers depends not only on their physical properties but also on the chemical chemi cal structure" structure" such as polarity polarity"" molecular molecular ei!ht" branchin!" branchin!" crosslin$ crosslin$in! in! de!ree and crystallinity. Solvent fractionation is that different solubility of polymers in different solvent ill  precipitate the polymer pol ymer from the polymer mixture. Polar macromolecules li$e poly%acrylic acid&"  poly%acrylamide& and polyvinyl alcohol are soluble in ater. On the other hand" non'polar   polymers or polymer shoin! lo polarity such as polystyrene" poly%methyl methacrylate&"  poly%vinyl chloride& and poly%isobutylene& are soluble in non'polar solvents. ( macr macrom omol olec ecul ulee be beco come mess a si sin! n!le le ph phas asee in solu soluti tion on ac acco cord rdin in! ! to th thee sa same me thermo the rmody dynami namics cs las las as the micro micromol molecu ecular lar soluti solution on sub subst stance ances. s. )oeve )oever" r" differ differenc ences es in molecular si*e influence the solubility properties of both these substances. For example" a macromolecule dissolves sloly due to its entan!led constitution opposin! the penetration of the solvent" but most polymer'solvent pairs can mix in all of the proportions. On contrary" the solubility of micromolecules is !enerally limited to saturated solution. The solvent of a macromolecule can be considered !ood by one of these to standards hich are the $inetic standard or the thermodynamic standard. ( !ood solvent from the $inetic  point of vie is a solvent that easily dissolves the polymer in a short time. The solubility can be made faster by decreasin! the particle si*e of the polymer sample. From the thermodynamic  point of vie" a !ood solvent has to be able to stron!ly interact ith the solution substances. Thus" a !ood solvent in terms of $inetics is fast hile in terms of thermodynamics is efficient. +enerally" solubility of synthetic polymers increases as the molecular ei!ht decreases. )oever" )oeve r" proper propertie tiess such such as viscos viscosity ity"" str stren! en!th th and fl flexi exibil bility ity are found found to im impro prove ve ith ith increasin! molecular ei!ht. The solubility of matrix and polymers in the same solvent is critical for polymer analysis. ,ertain non'a-ueous polymers can simply be dissolved in acetone or  methanol. ased on their solubility" synthetic polymers can be divided in four !roups as follos:

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/ater'soluble polymers: poly%acrylic acid& and poly%ethylene !lycol" P0+& /ater'soluble Polar or!anic'soluble polymers: acrylics and poly%methyl methacrylate" P(&.  on'polar or!anic'soluble polymers: polystyrene %PS&" polyvinyl chloride and

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 polyethylene. 3o solubility polymers: cured polyimide.

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Polymer Polym er frac fracti tiona onati tion on is de defi fine ned d as the the se sepa para rati tion on of po poly lyme mers rs in or order der to obtai obtain n a homo!eneous fraction or component. Fractionation based on the solubility properties is done by  precipitatin! polymer from its solution solution throu!h various methods such as: • • •

ixin! solvent Separatin! solvent by vapourisation Temperature Temperature reduced

The solvent and precipitate should be chosen so that precipitation occurs over a ide ran!e of  solvent composition" yet is complete before too hi!h a ratio of precipitant to solvent is reached. Other important considerations are the stability and volatility of the li-uids and their ability to form a hi!hly sollen" mobile !el phase. (pparatus: Filter paper" bea$er" boilin! tube" !lass rod" heater" uchner funnel. aterials: Toluene" acetone" methanol" cyclohexanone" P4, 5Poly %4inyl ,hloride&6" 37P0 53o 7ensity Polyethylene6" P( 5Poly %ethyl ethacrylate&6" PS 5Polystyrene6 8esult: Table 1: /ei!ht of polymers Polymer

37P0 P4, PS

Initial weight Final weight (g) (g) Filter paper + watch glass product 9.192 ;.

'O' %epoxy&

1 ! mol'1 P( A 199 ! mol'1 7ensity %K& of: 37P0 A 9.@ ! cm'; P4, A 1.>1 ! cm'; PS A 1.9! cm'; P( A 1.1. I1E2 cm;E2 mol'1& E %19> ! mol '1&

  A 1