Chapter 5:Polymerization Techniques Bulk polymerization Solution polymerization Suspension polymerization Emulsion polymerization Interfacial condensation polymerization Etc. Polymer Technology (A. Cattaleeya)

1. Bulk Polymerization : In the reactor:- Liquid monomer Initiator Inhibitors Chain transfer agents Homogeneous : polymer remains dissolved in monomers. Ex. PMMA Heterogeneous : aka. Precipitation polymerization polymer is insoluble in its monomers. Ex. Polyacrylonitrile, PVC Problem : heat transfer not good Make objects with a desirable shape by polymerization in a mold. Polymer Technology (A. Cattaleeya)

Model of Batch Polymerization Monomer

Pros & Cons of Bulk Polymerization Advantage Disadvantage Obtain purest possible polymer Conveniently cast to shape Obtain highest polymer yield per reactor volume Difficult to control Reaction has to be run slowly Cannot get high rate and high MW at the same time Difficult to remove last traces of unreacted monomer

Ex. 1 The maximum possible temperature rise in a polymerizing batch may be calculated by assuming that no heat is transferred from the system. Estimate the adiabatic temperature rise for the bulk polymerization of styrene, Hp = -16.4 kcal/mol, molecular weight = 104 Solution Hp for polymerization of styrene = 16,400 cal/mol (assuming complete conversion)  meaning that polymerization of 1 mol styrene release heat in the amount of 16,400 calories. In the absense of heat transfer, all this energy heats up the reaction mass. To a reasonable approximation, the heat capacity of most liquid organic systems may be taken as 0.5 cal/g-oC From Q = mc T (Note that- Boiling point of styrene = 146 oC)

2. Solution Polymerization Solution Polymerization : Monomer dissolved into inert- solvent / inhibitor Monomer Initiator CTA Inert solvent Solvent helps controlling heat transfer from reaction. Use for : Thermosetting condensation polymer (stop before gel point) Ionic polymerization Ziegler-Natta solution process

Model of Solution Polymerization Monomer I I Initiator I I I Solvent

The effect of solvent solubility on the molecular weight of polyurethane produced by solution method Viscosity of polymer solution Precipitation of polymer out of the solution Xylene Chlorobenzene Nitrobenzene Dimethyl sulfoxide 0.06 0.17 0.36 0.69 Precipitate immediately Precipitate within 0.5 hr. Polymer remain dissolved in solution Viscosity of polymer  MWpolymer  High viscosity = high molecular weight !

Pros & Cons of Solution Polymerization Advantage Disadvantage solvent Rate [M]  reduce rate, chain length xn Solvent waste Need solvent separation & recovery Have traces of solvent, monomer Lower yield Solvent may not be really inert (May interfere w/ rxn.-act as CTA) Reduces the tendency toward autoacceleration Increases heat capacity/heat- transfer Reduces viscosity Minimize runaway reaction

Ref: S.L. Rosen, John Wiley & Sons 1993

Ex. 2 Estimate the adiabatic temperature rise for the polymerization of a 20% (by weight) solution of styrene in an inert organic solvent Solution In 100 g of the reaction mass, there are 20 g of styrene, so the energy liberated on its complete conversion to polymer is Temperature rise is calculated from Q = mc T Therefore, the adiabatic temperature rise is then

Ref: S.L. Rosen, John Wiley & Sons 1993

Ref: S.L. Rosen, John Wiley & Sons 1993

3. Suspension Polymerization : Monomer into water, suspending agents (Ex.Ionic detergent, barium sulfate) Model of suspension polymerization Water monomer (Hydrophilic) Initiator + (Hydrophobic) Suspending agent - Ex. Polyvinyl alcohol - Beads of polymer ( 10-1000 m)

Monomer (hydrophobic) Initiator (dissolved in monomer) Monomer phase Typical Composition: Monomer (hydrophobic) Initiator (dissolved in monomer) Monomer phase Chain-transfer agent (dissolved in monomer) Water – suspending medium Protective Colloid Suspending agent Insoluble inorganic salt

Pros & Cons of Suspension Polymerization Advantage 1. Easy heat removal and control 2. Obtain polymer in a directly useful from Disadvantage Low yield / reactor volume Traces of suspending agent on particle surfaces Cannot run continuously Cannot be used for -condensation polymers -ionic or Ziegler-Natta polymerization

Ref: S.L. Rosen, John Wiley & Sons 1993

4. Emulsion Polymerization Emulsion Polymerization : Use emulsifier / soap monomer Water Soap Initiator (Hydrophilic) Reaction occurs in water phase until polymer gets very hydrophobic and then dissolve back in the monomer region. Ex. Latex - very very small particle stable in solution - particle size << 1 m - can generate very high MW. polymer

Emulsion Polymerization (cont.): Typical ingredient 100 part (by wt.) monomer (water insoluble) 180 part water 2-5 parts acid soap 0.1-0.5 part water-soluble initiator 0-1 part CTA (monomer soluble)

Steps in Emulsion Polymeriztion Water-soluble initiator Polymer born in water Monomer swollen micelle Polymer moves to micelle growing polymer particle Monomers inside the micelle decrease Unreacted monomers in other micelles and in droplets diffuse through water to the growing particles Reaction terminates when 2nd radical gets in reaction starts again for the 2nd chain when 3rd particle gets in.

Ref: S.L. Rosen, John Wiley & Sons 1993

Ref: S.L. Rosen, John Wiley & Sons 1993

5. Interfacial Polycondensation water CCl4 Advantage : = Monomer1 : Hexamethlyene diamine Monomer2 : Sebacoyl chloride Polymer formed at interface Commercial scale  easier to stir the phases together Reaction  rapid at room temperature (no need for high T., vacuum P.) Interfacial Polycondensation of Nylon 6/11

Interfacial Polycondensation of Nylon 6/11 Experiment on Interfacial Polycondensation of Nylon 6/11 การดึงเส้นใยไนลอนจากผิวสัมผัสของสารละลาย

Pros & Cons of some polymerization techniques Bulk - easy - No contamination - Difficult to control temp. and heat transfer - High viscosity Solution -good heat transfer -easy to control reaction temp. -low viscosity -polymer produced may be used directly in the solution form - Need to use solvent –adding cost Difficult to eliminate solvent entirely Solvents sometimes act as chain transfer agent  leading to lower MW polymer Suspension - Good heat transfer - easy to control reaction temp. - low viscosity - polymer produced may be used directly as polymeric suspension -Need extra process in washing out suspending agent/contaminants and drying the polymer beads -Polymer beads may stick together and maybe contaminated with suspending agent -Good only for addition polymerization using hydrophobic free radical initiator. Emulsion -- Good heat transfer - polymer produced may be used directly as polymer latex -Need extra process in washing out emulsifier/ contaminants and drying -Good only for addition polymerization using hydrophilic initiator. Interfacial Reaction is fast at room temp. and pressure.  No need for high temp. like in normal polycondensation. Can produce polymer in fiber form Limited to polycondensation where the two reactants are insoluble in each other ex. Acid chloride (quite expensive) Need extra process in recovering solvent and excess reactants

Comparing different techniques for Polycondensation conditions บัลค์ (bulk) สารละลาย (solution) ระหว่างผิว (interfacial) Temp สูง จำกัดอยู่ที่จุดหลอมเหลวและจุดเดือดของตัวทำละลายโดยทั่วไปทำที่อุณหภูมิห้อง Heat stabilization จำเป็น ไม่จำเป็น Kinetic of Reaction สมดุล เป็นขั้น บ่อยครั้งไม่สมดุล คล้ายปฏิกิริยาลูกโซ๋ Reaction time 1 ชั่วโมงถึงหลายวัน หลายนาทีถึง 1ชั่วโมง Productivity ต่ำถึงสูง Equality of reactants ไม่ค่อยจำเป็น Purity of reactants Equipment พิเศษ ระบบปิด ง่ายๆ ระบบเปิด Pressure สูง, ต่ำ บรรยากาศ

6. Gas-Phase Olefin Polymerization : Use Zieler-Natta catalyst Moderate P (7-20 atm) Low temperature ( < 100 oC) Use fluidized bed reactor Good Point : No solvent Monomer separation is easy Low capital + operating cost

Ref: S.L. Rosen, John Wiley & Sons 1993

Ref: S.L. Rosen, John Wiley & Sons 1993