Polymerization Introduction Radical polymerization Steps Kinetics Chain-transfer reaction Ionic polymerization Cationic Anionic Stereo-specific polymerization Co-polymerization Industrial polymerization technologies

Polymerization Type Chain Monomers Chain polymerization Step polymerization Chain Radical Anionic Cationic Stereo-selective (coordination) Monomers Vinyl Vinylidene R1 and R2: Hydrogen, halogen, alkyl, alkenyl, aryl, Examples: methyl, phenyl, vinyl The polymerization process determines the structure, properties and stability of the polymer

Radical polymerization The active sites are the free radicals Radicals react in each steps of polymerization Initiation (generating the free radicals) Example: decomposition of peroxides

Radical polymerization Decomposition of azo-derivatives Redox-initialization Rate-determinant step

Radical polymerization Propagation The addition of monomer onto the active site is very fast Consequently, the concentration of active sites is very small

Radical polymerization Termination (end of propagation) Interaction of two active sites Reaction of an active site and a radical from initiator Reaction with other active molecule Contamination Recombination Disproportion

Radical polymerization The rate of propagation and termination is significantly larger than the rate of initiation Consequently the lifetime of active sites is extremely short (10-9 s) The molecular mass is constant during polymerization The molecular mass can be influenced by the modification of polymerization conditions

Radical polymerization Kinetics I – initiator, M – monomer, R – active site, k – rate constant and f represents the fraction of radicals formed during initiation that is successful in initiating chains Assumption: the reactivity of active site is independent on its size Initiation Propagation

Radical polymerization Chain-transfer reactions Monomer, initiator – reaction rate does not change, but polymerization degree decreases Polymer – polymerization degree does not change, but branching occurs Solvent – considerable decreased molecular mass Chain-transfer molecules can influence molecular mass

Radical polymerization Chain transfer molecules Influencing the molecular mass

Radical polymerization Inhibition and retardation

Radical polymerization Gel-effect Hindered termination due to diffusion control Increasing polymerization rate

Ionic polymerization - cationic Catalyst – Lewis acids BF3, AlCl3, TiCl4, SnCl4 Co-catalyst – nucleofil agent: water Initiation Propagation Termination – contaminations, chain transfer covalent ion pair separated ion pair free ions Living polymerization, telechelic polymers

Ionic polymerization - anionic Catalyst – possatium-amide, n-butyl lithium, Grignard compound: alkyl-magnesium bromide Initiation Propagation – addition to the carbanion Termination – contamination, chain transfer Living polymerization

Ionic polymerization Factors Contamination Temperature Polarity of solvent Character and strength of ionic pair Resonance Geometry Contamination Temperature Living polymerization

Stereo-specific (coordination) polymerization Chain structure – regularity, branches etc. Isomerism – cis- and trans-isomers Asymmetric monomers – orientation Head-to-tail, head-to-head and tail-to-tail Stereo-isomerism

Stereo-specific polymerization May also be occured in ionic polymerization Requires appropriate substituents Never occurs in radical polymerization Coordination polymerization Heterogeneous catalyst system (AlEt3 – TiCl3, TiCl4) Amount of atactic polymer, catalyst efficiency 5. Generation – metallocene catalyst system Regularity, phase structure, properties

Stereo-specific polymerization Mechanism

Chain polymerization techniques Monomer Mechanism of polymerization Radical Cationic Anionic Coordination Ethylene + + – + Propylene – – – + Isobutylene – + – – Diene + – + + Styrene + + + + Vinyl-chloride + – – + Vinylidene-chloride + – + – Vinyl-fluoride + – – – Tetrafluoro-ethylene + – – + Acrylates + – + +

Copolymerization At least two kind of monomers Types Reactions Statistic Alternating Grafted Block Reactions Mechanism – radical or ionic

Copolymerization Kinetics – constant conditions Reactivity of monomers Alternating r values – different composition Example (VC-VAC copolymer) 50-50 wt% solution r1 = k11/k12 and r2 = k22/k21 Temperature Composition t1 9:3 t2 7:3 t3 5:3 t4 5:7

Copolymerization – reactivity ratio Monomer 1 Monomer 2 r2 r1 T (°C) akryl-nitryl 1,3-butadyene 0,02 0,30 40 methyl-metacrylate 0,15 1,22 80 styrene 0,04 0,40 60 vinyl-chloride 2,70 0,04 60 methyl-metacrylate styrene 0,46 0,52 60 vinyl-acetate 20 0,015 60 vinyl-chloride 10 0,10 68 styrene vinyl-acetate 55 0,01 60 vinyl-chloride 17 0,02 60 vinyl-acetate vinyl-chloride 0,23 1,68 60

Copolymerization- composition 1. Ideal polymerization r1 = r2 = 1 Nearly ideal r1r2 = 1 and r1 ≠ r2 Alternating 0 < r1r2 < 1 Reality azeotropic Small conversion, continuous addition of monomers

Copolymerization - processing Statistic, alternating: radical Block Radical if r1r2 >> 1 Ionic if the reactivity of monomers is different Living polymerization (fine regulation of stucture) Combination of active end-groups Grafting From chain To chain Mechano-chemical grafting

Industrial polymerization techniques Gas phase Conditions: High T and p Initiator: Oxygen Product struct.: long chain branched Example: PE Bulk Initiator: soluble in the monomer Product: powder or chunk Advantage: clean Disadvantage: gel-effect Example: PVC, PMMA, PAN Solution Product: solution or precipitate Advantage: heat Disadvantage: contamination, solvent, chain transfer Example: ionic, stereo-specific PP Suspension Initiator: soluble in the monomer Medium: water Product: powder Advantage: heat transfer Disadvantage: contamination Example: PVC, PS, PMMA

Industrial polymerization techniques Emulsion Initiator: soluble in water Medium: water Product: powder Advantage: diffusion Disadvantage: contamination Example: PVC, SBR, PMMA Monomer droplet Micelle Emulgeator Aqueous media Polymer droplet