Polymer Synthesis: Free Radical Polymerization and Transfer Reactions

Sustainable Polymer Chemistry

SPC Sustainable Polymer Chemistry Polymer Synthesis Chapter 3: Free Radical Polymerization free radical polymerization (8 CC 8 8 ) 8) 8) SPC UNIVERSIT OF TWENTE. Sustainable Polymer Chemistry Frederik Wurm frederik.wurm@utwente.nl www.utwente.nl/en/tnw/spc

Chapter 2: Step-Growth Reactions Reminder

Chapter 2: step-growth reactions SPC Sustainable Polymer Chemistry polycondensation polyaddition A-B -> A-B-(A-B)n-A-B A-B -> A-B-(A-B),-A-B + (n-1) condensate e.g. polyesters, polyamides e.g. polyurethanes, epoxy resins

Polycondensation A polymerization in which the growth of polymer chains proceeds by condensation reactions between molecules of all degrees of polymerization.

Polyaddition is a polymerization reaction that forms polymers via individual independent addition reactions. www.utwente.nl/en/tnw/spc 2 UNIVERSITY OF TWENTE. REMINDER

Chapter 3: Free Radical Chain Growth Polymerisation

Chapter 3: Free Radical Chain Growth Polymerisation SPC Sustainable Polymer Chemistry · Vinyl monomers = Chain growth repeating unit CH2=CH CH2=CH CH2=CH styrene -CH2-CH-CH2-CH- CH2-CH- n polystyrene a chain-growth polymer Careful: "chain growth polymers" also called "addition polymers" - do not confuse with "polyaddition" (Chapter 2) UNIVERSITY OF TWENTE. www.utwente.nl/en/tnw/spc 3

Propagation Mechanisms in Chain Growth Reactions

Propagation mechanisms in chain growth reactions REMINDER SPC Sustainable Polymer Chemistry initiator + reactive monomer polymer

• radical polymerization

• anionic polymerization

• cationic polymerization

• coordinative polymerization

K. RO R + MVILn radical former (e.g., peroxo- compounds) anions (e.g., BuLi) cations (e.g., TosOMe) metal complexes (e.g., Ti-complex) UNIVERSITY OF TWENTE. Lecture 3 & 8 Lecture 5 & 7 Lecture 9 www.utwente.nl/en/tnw/spc

Topics Chapter 3

Topics Chapter 3 SPC Sustainable Polymer Chemistry

• Radical Chain-growth reaction

• Free radical polymerization (Monomers, initiators, mechanism)

• Thermodynamics, kinetics

• Mayo-Equation

• Chain Transfer & Inhibitors/Retarders

• Some Examples of polymers UNIVERSITY OF TWENTE. www.utwente.nl/en/tnw/spc 5

Chain-Growth: Acyclic Monomers and Their Uses

Chain-Growth : Acyclic Monomers SPC Sustainable Polymer Chemistry Table 28.1 Some Important Chain-Growth Polymers and Their Uses

Monomer	Repeating unit	Polymer name	Uses
CH2=CH2	-CH2-CH2-	polyethylene	film, toys, bottles, plastic bags
CH2=CH CI	-CH2-CH-	poly(vinyl chloride)	"squeeze" bottles, pipe, siding, flooring
CH2=CH-CH3	-CH2-CH- CH3	polypropylene	molded caps, margarine tubs, indoor/outdoor carpeting, upholstery
CH2=CH	-CH2-CH-	polystyrene	packaging, toys, clear cups, egg cartons, hot drink cups
CF2=CF2	-CF2-CF2-	poly(tetrafluoroethylene) Teflon®	nonsticking surfaces, liners, cable insulation
CH2=CH C=N	-CH2-CH- C=N	poly(acrylonitrile) Orlon®, Acrilan®	rugs, blankets, yarn, apparel, simulated fur
CH2=C-CH3 COCH3 O	CH3 -CH2-C- COCH3 O	poly(methyl methacrylate) Plexiglas®, Lucite®	lighting fixtures, signs, solar panels, skylights
CH2=CH OCCH3 =0	-CH2-CH- OCCH3 =O	poly(vinyl acetate)	latex paints, adhesives

UNIVERSITY OF TWENTE. vente.nl/en/tnw/spc

Chain-Growth: Examples of Alkenes for Radical Polymerization

Chain-Growth : Acyclic Monomers SPC Sustainable Polymer Chemistry Table 28.2 Examples of Alkenes That Undergo Radical Polymerization

• CH2=CH OCCH3 II Ö vinyl acetate

• CH2=CCH3 - COCH3 II D methyl methacrylate

• CH2=CH 1 Cl vinyl chloride

• CH2=CH 1 C=N acrylonitrile

• CH2=CH CH=CH2 1,3-butadiene

CH2=CH styrene Caution: not all vinyl monomers can be polymerized by free radical polymerization (compare Chapter 1)! UNIVERSITY OF TWENTE. www.utwente.nl/en/tnw/spc

Kinetic Steps in Chain Growth Reactions

Kinetic steps in chain growth reactions follow the same recipe REMINDER SPC Sustainable Polymer Chemistry monomers

1. addition of initiator

2. initiating of a monomer > "reactive monomer"

3. growing chain

4. Termination ("automatically" or "on purpose")

reactive polymer chains "dead" polymer chains (re)combination disproportionation reaction with a molecule, which catches the active species UNIVERSITY OF TWENTE. www.utwente.nl/en/tnw/spc

Chain Growth Polymerisation: Thermodynamics

Chain Growth Polymerisation: Thermodynamics SPC Sustainable Polymer Chemistry Thermodynamics determines whether a polymerization takes place : AG = AH - TAS AG must be negative for polymerization to occur Vinyl polymerizations are exothermic AS always negative for polymerizations · A chemical reaction (and a polymerization) takes plase when AG negative - Either with: - AH < 0,45 > 0 or - AH > 0,45 >> 0 or - AH << 0 that neg. AS is compensated - for polymerizations: loss of entropy increases with increasing temperature (TAS increases) - There is a temperature at which AH = TAS i.e. AG = 0 UNIVERSITY OF TWENTE. www.utwente.nl/en/tnw/spc

Ceiling Temperature in Chain Growth Polymerisation

Chain Growth Polymerisation: Thermodynamics SPC Sustainable Polymer Chemistry "Ceiling temperature": above this temperature polymerization is not possible !

• methyl methacrylate 220 ℃

• methyl styrene 61 ºC

• styrene 310 ℃ (temperatures for bulk polymerisation)

Kdp Rate kp[M] Kp[M]-Kdp Temperature UNIVERSITY OF TWENTE. Rev. Chem. Soc. 12, 61 (1958). www.utwente.nl/en/tnw/spc

Thermodynamics of Vinyl Monomers and Dienes

Chain Growth Polymerisation: Thermodynamics SPC Sustainable Polymer Chemistry Thermodynamics determines whether a polymerization takes place : AG = AH - TAS AG must be negative for polymerization to occur Vinyl polymerizations are exothermic AS always negative for polymerizations . The reaction entropies for vinyl monomers and dienes are nearly structure independent and are at 25℃:

• AS = - 25 cal/mol T => TAS = - 7,5 kcal/mol . The reaction enthalpies for the following monomers are:
• styrene: -16 kcal/mol
• acrylonitrile: -17 kcal/mol
• vinylchloride : - 27 kcal/mol UNIVERSITY OF TWENTE. www.utwente.nl/en/tnw/spc

Free Radical Polymerization: General Recipe

Initiator Decay and Start Reaction

Free radical polymerization : the general recipe SPC Sustainable Polymer Chemistry 1) Initiator decay - this is the slowest step (rate determining!) and depends on the type of initiator! R __ X .K + X. R __ R . . R + R. Homolytic cleavage of a weak bond: one or more reactive radical(s) are formed 2) Start reaction/ Initiation R' .R + R R' addition of initiator radical to monomer > reactive monomer

Chain Growth

3) Chain growth (propagation) - fast build-up of molecular weight! R' R' + R addition of monomers > growing polymer chain R R' R' R' R' R. + R . UNIVERSITY OF TWENTE. R' R' R' R' n www.utwente.nl/en/tnw/spc

Termination I: Reaction with Another Radical

Free radical polymerization : the general recipe SPC Sustainable Polymer Chemistry 4) Termination I Reaction with another radical: · R + .Y _ R Y R' R' R' R' R' R' n n Disproportionation: H R' R + R R' R' R' R' R' n m H + R H R' R' R' R' R' R' m n UNIVERSITY OF TWENTE. www.utwente.nl/en/tnw/spc R

Termination II: Short Lifetime of Free Radicals

Free radical polymerization : the general recipe SPC Sustainable Polymer Chemistry 4) Termination II : free radicals have a short lifetime - termination is happening "all the time"! (re)combination R' R + R R' R' R' R' n n R' R' R R R' R' R' R' n n termination depends on monomer and temperature: styrene (up to 160 ℃) MMA (> 60 ℃) acrylonitrile vinylacetate mainly recombination mainly disproportionation recombination disproportionation termination influences molar mass dispersity: Ideal: disproportionation Mw/Mn ca. 1.5 Recombination Mw/Mn ca. 2 In reality: side reactions (transfer) broaden Mw/Mn SoS 20_14 UNIVE OF TWENTE. www.utwente.nl/en/tnw/spc R

Molar Mass Distributions

Molar Mass Distributions SPC Sustainable Polymer Chemistry 0.014 Đ = 1.01 0.013 0.012 0.011 0.010 0.009 probability 0.008 0.007 Đ = 1.04 0.006 0.005 Đ = 1.1 0.004 Đ = 1.2 0.003 Đ = 1.3 Đ = 1.5 0.002 -- 0.001 Đ = 2 - 0.000 0 20000 40000 60000 80000 100000 120000 140000 molar mass [g/mol] Fig. 2 Representation of theoretical Gaussian distributions of PHPMA with a degree of polymerisation of 300 (Mn = 40 kg mol-1) with a vari- ation in the dispersity from 1.01, 1.04, 1.1, 1.2, 1.5 to 2. UNIVERSITY OF TWENTE. Polym. Chem., 2011, 2, 1900-1918 twente.nl/en/tnw/spc

Initiator Types for Radical Polymerization

Radical Production Methods

Initiator Types for Radical Polymerization SPC Sustainable Polymer Chemistry Initiator types: a) Radicals are produced by homolytic thermal decomposition of:

• organic and inorganic peroxides (R-O-O-R)
• Azoinitiators (R-N=N-R)

b) by redox reactions c) by high energetic radiation (e.g. UV-light or gamma-radiation)

Peroxides & Azo Compounds

a) Peroxides & Azo compounds

• Organic peroxides/ azo compounds are potentially explosive!
• Inorganic peroxides for aqueous polymerization
• Organic peroxides are used in technical scale
• e.g. bulk polymerization of styrene, ethylene, vinylchloride
• Both radicals can initiate the polymerization (efficiency influenced by environment, monomer)

CH3 CH3 CH3CO-OH -> CH3CO. 1 1 + .OH CH3 CH3 O O KOSO-OSOK O II =0 > 2 KOSO· !! O CH3 CH3 CH3 CH3CO-OCCH3 -> 2 CH3CO. - CH3 CH3 CH3 O O O II CO-OC > 2 CO· CH3 CH3 CH3 1 CH3C-N=N-CCH3 > - 2 CH3C. + N2 I C=N CEN C=N UNIVERSITY OF TWENTE. www.utwente.nl/en/tnw/spc

Commercially Available Radical Starters

Initiator Types for Radical Polymerization SPC Sustainable Polymer Chemistry Many different radical starters commercially available (solubility, decomposition temperature, functional groups, etc.)

step1 Is polymerization process a radical reaction? Radical polymerization initiator

step2 Is the solvent an organic solvent or water? Organic solvent Water

step3 Polymerization Method Suspension polymerization Solution polymerization Bulk polymerization Emulsion polymerization A polymerization method to heat the oil-soluble monomers in a dispersed condition in water (The initiator solves in monomers.) A polymerization method under which the initiator, monomers and formed polymers are all dissolved status. A polymerization method under which liquid mono- mers are polymerized by itself or with adding the initia- tor. A polymerization method under which oil-soluble monomer is dispersed in water with emulsifying agent. (The initiator dissolves in water.)

step4 Polymerization Temperature 88℃ V-40 86°℃ VA-086 56°℃ V-50 44℃ VA-044 etc 10-hour Half-life Temperature Azo Nitrile Azo Ester Azo Amidine Azo Alkye 110℃ O CH, CHO C-C-N-N-C-C CHACH-CH_CHANH CH, он, висконценск, CH3 CH, CH3 V-40(88℃) CN 80℃ -N=N-7 VE-073(73℃) NC V-59(67℃) N=N H,COOC COOCH3 70°℃ CH3 CH3 CH3CH2-C-N=N-C-CH2CH3 CN CN VEF-066(66℃) CH3 CH3 0 C-C-N=N-C-C CH30 CH3 CH3 OCH3 *Metal-content-control-grade products are also available. AIBN(65℃)O 60℃ CH3 CH3 CH3-C-N=N-C-CH3 CN CN *Metal-content-control-grade products are also available. V-65(51℃) O 50℃ CH3 CH, CH, CH, CHCH2-C-N=N-C-CHICH CH, CN CH *Metal-content-control-grade products are also available. V-70(30℃) 30°℃ OCH, СН, сн, ОСН, CH,-C-CH2-C-N=N-C-CH,-C-CH: CH, CN ČN CH3 VAm-110(110℃) VR-110(110℃) O CHS CH, CH CH3 CH ;- C-CH .- C-N=N-C-CH2-C-CH, CH3 UNIVERSITY OF TWENTE. https://specchem-wako.fujifilm.com/asia/azo-polymerization-initiators/ www.utwente.nl/en/tnw/spc 66°℃ V-601 51ºC V-65 etc V-601(66℃)