Mastering the chaos: The ultimate guide Free radical POLYMERIZATION
LIST OF AUTHORS
We would like to express our sincere gratitude to everyone who helped us finish this E-book, "Mastering the Chaos: The Ultimate Guide to Free Radical Polymerization." Firstly and foremost, we would like to thank Dr. Norlinda binti Daud for her invaluable assistance and experience throughout the project. She gave us the information and resources we needed to explore the fascinating field of polymer science. We sincerely thank each and every member of our team who put in countless hours to finish this Ebook. Without the combined efforts and enthusiasm of Bethaniea Aedell, Cliffina Cordelia, and Nurul Hidayah, this E-book would not have been possible. We appreciate the contributions of all those who helped make this E-book a reality, no matter how modest or large. Our endeavor to finish this E-book has been greatly impacted by your assistance. ACKNOWLEDGE i
Welcome to "Mastering the Chaos: The Ultimate Guide to Free Radical Polymerization," a guide that will teach you about an important process in polymer chemistry. This E-book is intended for anybody interested in polymer science, from students and researchers to professionals wishing to expand their knowledge base. Free radical polymerization is a major process for producing numerous common materials such as plastics, rubbers, and adhesives. Despite its importance, the procedure might appear difficult. This E-book attempts to explain things in a straightforward and easy manner. Our exploration began with basic information about polymers and different types of polymerization. Also, we will talk about about mechanisms, kinetics, thermodynamics of Free Radical Polymerization, polymerization techniques and finally its applications. You'll find diagrams, examples, and exercises throughout the book to help you understand and apply the concepts. We hope it sparks your curiosity and helps you learn more about this fascinating topic. Thank you for choosing this E-book. Enjoy your journey into the world of free radical polymerization! PREFACE ii
TABLE OF CONTENTS CONTENTS PAGES Acknowledgement Preface Introduction to free radical polymerization (FRP) Mechanism of FRP Kinetics of FRP Thermodynamics of FRP Techniques of FRP Applications of FRP Answer Schemes References i ii 4 7-18 19-21 22 23-28 29-30 31-38 39
lET'S LOOK AT THIS CONVERSATION FIRST BEFORE WE LEARN ABOUT WHAT IS POLYMERIZATION 1
Message (Today) 12:21PM Messages CHATTINGWITHCLIFFINA Details HeyBethaniea! What’sup? HeyCliffina! Iwannaaskaboutourpolymerclasstheotherday. I stillcannotunderstandaboutwhatispolymerand polymerization.Canyouhelptoexplainittome? Sure.Letmeexplain aboutpolymerfirstbyusingapicture. So actually, a polymer is a large molecule made up of monomers, or repeating structural units, joined together in a long chain by covalent bonds. Therefore, polymers made up of thousands of monomers joined together. AhhIsee..... Now,forpolymerization,let’slookatthispicture. 2
Inordertogetapolymer,a chemicalprocesscalledpolymerizationwas done.Thisiswherealargenumberofmonomersbecomeconnectedby covalentbondstoformasinglelongmoleculecalledpolymer. Thereare2typesofpolymerisationwhichare step-growthpolymerisation (addition)andchainpolymerization(condensation).Thisisoneofexampleof additionpolymerizationandcondensationpolymerization. Messages CHATTINGWITHCLIFFINA Details Icanunderstanditnow.Thanksforyourhelpcliff! YouraremostwelcomeBeth! Howmanytypesofpolymerizationprocess? Polyaddition Polycondensation 3
Polymerization Step-growth Chain Polycondensation Polyaddition Free radical polymerization Coordinative polymerization Cationic polymerization Anionic polymerization A polymer is a large molecule made up of monomers, or repeating structural units, joined together in a long chain by covalent bonds. Polymerization is the chemical process by which tiny molecules called monomers unite to produce a big, chain-like molecule known as a polymer. There are 2 types of polymerisation which are step-growth polymerization (addition) and chain polymerization (condensation). INTRODUCTION Summary from the conversation...... types of polymerization ? 4
EXERCISE 1 4. Give two examples of polymerization. POLYMERIZATION 1. Explain the term polymer and monomer. 2. Explain the term polymerization. 3. How can you differentiate between addition and condensation polymerization? 5
IN THIS E-BOOK, WE WILL LEARN ABOUT FREE RADICAL POLYMERIZATION IN THIS E-BOOK, WE WILL LEARN ABOUT FREE RADICAL POLYMERIZATION 6
FREE RADICAL POLYMERIZATION FREE RADICAL POLYMERIZATION A polymerizing technique called free radical polymerization involves adding free radicals one after the other to create polymer units. It's a kind of polymerization that grows in a chain and can be cationic, anionic, or coordinated. There are three stages involved in free radical polymerization: initiation, propagation, and termination. Mechanism of Free Radical Polymerization Termination of Free Radical Initiation of Free Radical Propagation of Free Radical 7
2 steps stage First: The formation of free radicals from an initiator. Second: The addition of one of these free radicals to a monomer molecules. Generating free radical from initiator and monomer INITIATION Primary radical Monomer CHAIN POLYMERIZATION Radical from initiator/primary radical Active centre/Activated monomer 8
CHAIN POLYMERIZATION EXAMPLE BENZOYL PEROXIDE, DICUMYL PEROXIDE (DCP) BENZOYL PEROXIDE, DICUMYL PEROXIDE (DCP) INITIATOR TYPE ORGANIC PEROXIDE/ HYDROPEROXIDE ORGANIC PEROXIDE/ HYDROPEROXIDE REDOX AGENT PERSULFATES + REDUCING AGENTS HYDROPEROXIDE + FERROUS ION PERSULFATES + REDUCING AGENTS HYDROPEROXIDE + FERROUS ION AZOBISISOBUTYRONITRILE (AIBN) AZOBISISOBUTYRONITRILE (AIBN) AZO COMPOUND ORGANOMETALLIC REAGENTS ORGANOMETALLIC REAGENTS SILVER ALKYLS HEAT, LIGHT, UV OR HIGH ENERGY RADIATION HEAT, LIGHT, UV OR HIGH ENERGY RADIATION ELETROLYTIC ELECTRON TRANSFER ELETROLYTIC ELECTRON TRANSFER INITIATOR COMMON USED An effective initiator is a molecule which subjected to heat, electromagnetic radiation or chemical reaction will readily undergo homolytic fission into radicals These radicals must stable long enough to react with monomer and form a reactive centre 9
CHAIN POLYMERIZATION thermally unstable initiators decomposed into radicals Organic peroxides/hydroperoxides used for polymerization in bulk and suspension (organic) dissolved in organic solvent used for polymerization in solution and emulsion stable at room temperature decomposed thermally >40 C, photochemically <40 C, giving substituted alkyl halides and liberating nitrogen suited as initiator in bulk and or in organic solvent production of free radicals by one electron transfer reaction Redox initiators can be proceed at relatively low temperature with high rates, with formation high molecular weight polymer usually carried with aqueous solution, suspension and emulsion Azo compounds 10
The addition of monomer molecules to the active center to grow the polymer chain. A polymer spends most of its time expanding its chain length or propagating. After initiation of free radical, it attacks another monomer subunit. Has 3 modes of propagation. CHAIN POLYMERIZATION PROPAGATION The product must be a chain radical (growing polymer radical) and the process can be repeated NOTES: 11
Head to head Tail to tail Head to tail CHAIN POLYMERIZATION 3 MODES OF PROPAGATION 12
Chain radical reacts with primary radical. This type of termination process is unproductive and can be controlled by maintaining a low rate for initiation. CHAIN POLYMERIZATION TERMINATION Termination is the final step in the polymerization process. Destruction of the growth activity of the chain. Has 2 types (primary and mutual). PRIMARY 13
CHAIN POLYMERIZATION one polymer chain is saturated and the other is unsaturated polymer chain Chain radical reacts with another chain radical MUTUAL COMBINATION/ COUPLING COMBINATION/ DISPROPORTIONATION COUPLING a labile atom (usually hydrogen) is transferred from one polymer radical to another produce a single polymer results in two polymers from the two reacting polymer chain radicals two growing polymer chains react with the mutual destruction of growth activity 14
CHAIN POLYMERIZATION COMBINATION/ COUPLING COMBINATION/ COUPLING DISPROPORTIONATION 15
CHAIN POLYMERIZATION CHAIN TRANSFER a growing polymer chain is deactivated or terminated by transferring its growth activity to a previously inactive species. SOLVENT The transfer reaction involves the transfer of an atom between the radical and the molecule. solvent MONOMER If the molecule is unsaturated, like a monomer , the atom can be transferred to either the monomer or the chain radical. For a saturated molecule, like a solvent, an atom is transferred to the chain radical. assumed to have the same reactivity as the primary radicals formed by initiation. may undergo a rearrangement reaction, which destroys the double bond site 16
If the chain end radical attacks an atom on the backbone of the same or another chain the result is a new radical that can reinitiate to form a branch. CHAIN POLYMERIZATION INITIATOR POLYMER This reaction reduces molecular weight and wastes initiator. Common side reaction for the peroxide initiators, but happens less often with azo initiators. always generates a long chain branch 17
CHAIN POLYMERIZATION EXERCISE 2 Write the initiation, propagation and termination reactions of the following: 1. a) Initiatior = Benzoyl Peroxide b) Monomer = Methyl methacrylate Benzoyl Peroxide Methyl methacrylate 4.Propose a mechanism for synthesis of polystyrene. 5.Write the mechanism of addition polymerization with ditert-butyl peroxide as initiator and ethene as monomer. 2.Which of the following monomers cannot undergoes growth polymerization? A) CH2═ CH2 B) CH2═CHCN C) CH2═CHCOOR D) COOH−CH2−COOH 3.What does chain initiation step of free radical polymerization consists of? A) decomposition of initiator B) addition of free radical to monomer C) all of the mentioned D) none of the mentioned 18
I Ri = dt P i P + KINETICS OF FREE RADICAL POLYMERIZATION KINETICS OF FREE RADICAL POLYMERIZATION Initiation n R R + M RM1 slow fast d[R Propagation Mi + M Mi+1 Rp = d[M] dt = kp[M1 ][M] + kp[M2 ][M] + . . . +kp[Mi][M]+. . . = kp[M][M ] Termination Mi + Mj ktc ktd Pi + j j Rt = d[M ] - dt =2ktc [M ][M ] +2ktd[M ][M ] =2kt[M ] 2 kt= k tc + ktd . .] . . . . . . . . . . . . . . . 19
= p k ( rate of polymerization = rate of propagation R = p [M][M ] =kp ( R KINETICS OF FREE RADICAL POLYMERIZATION KINETICS OF FREE RADICAL POLYMERIZATION Steady-state condition (approximation) i R 1/2 = [M ] t Ri 2kt ) Ri t 2k ) 1/2 [M] . . 20
KINETICS OF FREE RADICAL POLYMERIZATION KINETICS OF FREE RADICAL POLYMERIZATION EXERCISE 3: 1.How many initiator fragments are present in the dead polymer formed by combination mode of chain termination? A) 2 B) 1 C) 3 D) 0 2.What is the expression rate of termination reaction of free radical polymerization? A) k [M ] t . 2 B) 2k [M ] t . 2 C) 2fk [M ] t . D) fk [M ] t . 3.How does polymerization rate at a given monomer concentration vary, if rate of chain initiation is tripled? A) doubled B) tripled C) increment by factor of 3 D) remains constant 0.5 4. Which order kinetics does the rate of polymer formation, in free radical polymerization, follow corresponding to monomer concentration? A) 1 B) 0 C) 2 D) 3 21
The thermodynamics of the polymerization process can be used to estimate the equilibrium point in chaingrowth polymerization. The Gibbs free energy (ΔGp) of a polymeric reaction is calculated to identify its tendency. THERMODYNAMICS OF FREE RADICAL POLYMERIZATION THERMODYNAMICS OF FREE RADICAL POLYMERIZATION If ΔGp < 0, polymerization will occur. If ΔGp > 0, depolymerization will occur. Thermodynamic equation states that, ΔG = ΔH – TΔS A negative enthalpy and an increasing entropy will favour polymerization. Polymerization is favoured at low temperatures. Therefore, TΔSp is small. Depolymerization is favoured at high temperatures. Therefore, TΔSp is large. When the rate of polymerization = rate of depolymerization, equilibrium is attained. This temperature is known as the ceiling temperature (Tc). 22
TECHNIQUES OF POLYMERISATION Suspension polymerization Emulsion polymerization Homogeneous techniques Bulk polymerization Solution polymerization. Heterogeneous techniques TECHNIQUES OF POLYMERIZATION TECHNIQUES OF POLYMERIZATION 23
High purity High viscosity The polymerization is obtained with a broad molecular weight distribution due to the high viscosity and lack of good heat transfer Molecular weight distribution can be easily changed with the use of the chain transfer agent Heat transfer and mixing become difficult as the viscosity of reaction mass increases The system is simple and requires thermal insulation Removal of last traces of unreacted monomer is difficult Product can be used directly and no isolation is required due to its resistance towards solvents Hot spots may form and explosion may possible Longer polymerization time for high molecular weight polymers (nearly 10-16 hrs.) ADVANTAGES DISADVANTAGES TECHNIQUES OF POLYMERIZATION Bulk polymerization involves using a liquid monomer with initiators and chain transfer agents. The purpose of the chain train transfer reagent is to produce a homogeneous phase and regulate the molecular weight of the final polymer. To start the polymerization process, the resulting mass is heated or subjected to radiation of a certain wavelength. The drawback is that as the polymerization reaction continues, the medium's viscosity rises therefore making mixing more challenging. As the polymerization progresses, the medium's viscosity increases, making mixing difficult. This results in products with a broad molecular weight dispersion, making the reaction entirely exothermic. Batch reactors are used for polymerization. Heterogeneous Techniques 01 Bulk polymerization 24
High molecular weight polymers cannot be manufactured by this process because addition of solvent lowers monomer concentration which lowers the rate of polymerization Heat transfer easy due to presence of solvent Mass transfer is easy Polymer obtained is impure Complete removal of solvent is moredifficult Stirring is easy because the solution is low viscous Requires drying to be used as solid The product obtained is in liquid form and can be directly used for applications such as adhesives The monomer is dissolved in a suitable inert solvent along with chain transfer agents, if needed. The free radical initiatoris also dissolved in the solvent medium. The solvent announces the heat capacity so that it reduce the viscosity and promotes proper heat transfer. After the reaction is over, the polymer is used the polymer is used as such in the form of polymer solution orthe polymeris isolated by evaporating the solvent. Polymer so formed can be used for surface coating. Besides that, it is used for the production of Polyacrylonitrile, PVC, Polyacrylic acid, Polyacrylamide, Polyvinyl alcohol, PMMA, Polybutadiene and so on. TECHNIQUES OF POLYMERIZATION 02 Heterogeneous Techniques Solution polymerization ADVANTAGES DISADVANTAGES 25
The method can be adopted only for water insoluble monomers. The process is comparatively cheap as it involves only water instead of solvents The method cannot be used for tacky polymers such aselastomers because of the tendency for agglomeration of polymer particles Product isolation is easy since the product is insoluble in water Polymer purity is low due to the presence of suspending& stabilizing additives that are difficult to remove completely Viscosity increase is negligible Viscosity increase is negligible It is difficult to control polymer size ADVANTAGES DISADVANTAGES In suspension polymerization, the monomer is dispersed in a dispersing medium and polymerization occurs in the monomer droplets suspended in the dispersing medium, water soluble monomer cannot be used unless a salting out procedure is used. This method is used with free radical polymerization where the initiator is dissolved in the monomer, which is then dispersed in the water using emulsifying agent. Polymerization is initiated in the monomer droplets dispersed in the aqueous medium. TECHNIQUES OF POLYMERIZATION 03 Homogeneous Techniques Suspension polymerization 26
The method can be adopted only for water insoluble monomers. High molecular weight polymers Designed to operate higher conversion of monomer to polymer. This can result in significant chain transfer to polymer Viscosity remains close to that of water and is not dependent on molecular weight For dry (isolated) polymers, water removal is an energy-intensive process Fast polymerization rates and allow removal of heat form the system Cannot be used for condensation, ionic or Ziegler-Natta polymerization The final product can be used as such does not need to be altered or processed ADVANTAGES DISADVANTAGES In emulsion polymerization, the technique used is for the production of large number of commercial plastics and elastomers. The monomer is dispersed as droplets in an immiscible liquid (e.g., water) and an emulsifier (a soap) forms micelles with suitable agitation. The initiatoris water-soluble, not monomer-soluble. Micellar aggregates of emulsifier molecules containing monomers in their hydrophobic part are formed in water. Polymerization initiation occurs in water, and the radicals formed penetrate and activate the micelles. Each droplet or micelle is a polymerization microreactor. The resulting product is a latex, a continuous phase (water) in which polymer particles are suspended TECHNIQUES OF POLYMERIZATION 04 Homogeneous Techniques Emulsion polymerization 27
TECHNIQUES OF POLYMERIZATION TECHNIQUES OF POLYMERIZATION EXERCISE 4 1.Which does heat dissipation in bulk polymerization becomes progressively difficult with high conversions? A) increase in medium viscosity B) solubilization of polymer in the monomer C) precipitation of polymer in the monomer D) all of the mentioned 2. Which of the following monomer mixture is used in bulk polymerization? A) undiluted monomer B) monomer –solvent mixture C) monomer-water mixture D) none of the mentioned 3. How is the solvent in solution polymerization, more useful to overcome the disadvantages of bulk polymerization? A) it reduces the viscosity gain B) increases the rate of reaction C) causes chain transfer D) all of the mentioned 4. Which of the following is used as a stabilizer in suspension polymerization? A) gelatin B) peroxides C) water D) carbon tetrachloride 5. What kind of initiators is used in the process of suspension polymerization? A) oil-soluble B) water-soluble C) oil-water insoluble D) none of the mentioned 28
Applications of free radical polymerization APPLICATIONS OF FREE RADICAL POLYMERIZATION APPLICATIONS OF FREE RADICAL POLYMERIZATION It is used in synthesizing polystyrene and elastomers. It is used in synthesizing chemical surfactants, lubricants It is used in manufacturing cardiovascular stents. It is used in synthesizing nanocomposite hydrogels. 29
APPLICATIONS OF FREE RADICAL POLYMERIZATION APPLICATIONS OF FREE RADICAL POLYMERIZATION EXERCISE 5 1.How is free radical polymerization used in the production of plastics? 2.What role does free radical polymerization play in the creation of synthetic rubber? 3.What is the significance of free radical polymerization in the packaging industry? 4.Can free radical polymerization be used in the medical field? 5.How is free radical polymerization utilized in water treatment? 30
ADDITION POLYMERIZATION CONDENSATION POLYMERIZATION EXERCISE 1 ADDITION POLYMERIZATION CONDENSATION POLYMERIZATION ANSWERS Question 1 Question 2 Ans : Polymerization is the process of forming high molecular mass macromolecules, which consists of repeating structural units derived from monomers. In a polymer, various monomer units are joined by strong bonds Polymers are high molecular mass macromolecules composed of repeating structural units derived from monomers. Polymers have a high molecular mass . in polymers, various monomer units are joined by strong covalent bonds. Polymers can be natural as well as synthetic. Polythene, rubber, and nylon6,6 are examples of polymers. Monomers are simple, reactive molecules that combine with each other in large numbers through covalent bonds to give rise to polymers. For example ethene, propene, vinyl chloride Ans: Question 3 Question 4 *Accept any answer as long as relevant Monomers must have either a double bond or triple bond Produces no by-products Monomers must have two similar or different functional group By-products such as ammonia water and HCI are produced 31
Initiation ANSWERS Propagation n n+1 EXERCISE 2 Question 1 Notes: R=COOCH3 32
n m n m ANSWERS Termination m n n m Question 2 Ans: D Explanation: Dicarboxylic acid undergoes condensation polymerization Question 3 Ans: C Explanation: The first step in chain initiation is decomposition of initiator to free radicals and the second step is addition of free radical to the monomer unit 33
The initiator radicals (R*) add to the C=C bond of styrene to produce a new, benzyl-type free-radical. ANSWERS Question 4 Initiator benzoyl peroxide decomposes at 80-90C with the cleavage Oxygen-Oxygen bond to give two benzoyloxy radicals, which then losses carbon dioxide to form two benzyl radicals. Initiation: This radical then adds to another molecule of styrene, and the process continuous during which the polymer chain starts to grow. Propagation: Termination: Polymer chain is terminated by the combination of two radicals (either both polymer radicals or one polymer radical and one initiator radical). 34
Initiation: @2R RCH CH RCH CH 2 2 Propagation: n R-CH CH -CH -CH 2 2 2 2 n R-CH CH -CH -CH 2 2 n 2 CH-CH-CH CH -R 2 2 2 m R 2 2 ANSWERS Question 5 Termination: R-CH CH -CH -CH-CH-CH-CH CH -R n 2 2 2 2 2 2 2 2 35
ANSWERS EXERCISE 3 Multiple Choice Question Answer: 1. A 2. B 3. C 4. A Explanation: 1. (A) - The combination reaction is given by R~~~CH2-CHY + YH C-CH2~~~~~R --> R~~~CH2 -CHY-CHY-CH2~~~R 2. (B) - The rate expression for termination reaction is given by R = 2k [M ] . The factor 2 is used for the disappearance of chain radicals at each incidence of termination reaction. t . 2 t 3. (C) - The rate equation of overall polymerization clears that the polymerization rate at a given monomer concentration is dependent on the square root of rate of chain initiation. 4. (A) - The rate of polymer formation is given by: R = [(k /k )fk ] [I] [M]. This proves that rate of polymer formation is first order in monomer concentration. p p 2 t d 0.5 0.5 36
ANSWERS EXERCISE 4 Multiple Choice Question Answer 1. D 2. A 3. A 4. C 5. A Explanation: (D) - The stirring process and heat dissipation become progressively difficult due to gain in viscosity medium or due to solubilization or precipitation of polymer in the monomer, more so in higher conversions. 1. (A) - Bulk polymerization is the polymerization of undiluted monomer and is the simplest technique of polymer synthesis. 2. (A) - The solvent reduces the viscosity gain, thus allowing more efficient stirring of the medium and proper heat dissipation of the heat liberated. The chain transfer to solvent causes a problem for solution polymerization. 3. (C) - The process of suspension polymerization requires water soluble polymer stabilizers like CMC, PVA or gelatin, etc. to raise medium viscosity and stabilize the suspension. 4. (A) - In suspension polymerization, oil-soluble initiators like peroxides, hydroperoxides and azo-compounds are used. 5. 37
ANSWERS EXERCISE 5 Answer for Question 1: Free radical polymerization is commonly used to produce a wide variety of plastics such as polyethylene, polystyrene and polyvinyl chloride (PVC). These plastics are used in everyday items like packaging materials, containers, toys and household goods. Answer for Question 2: Synthetic rubbers, such as styrene-butadiene rubber (SBR), are produced through free radical polymerization. SBR is widely used in the manufacturing of automobile tires, shoe soles, and various rubber goods. Answer for Question 3: The packaging industry relies heavily on polymers like polyethylene and polypropylene, which are produced through free radical polymerization. These materials are used to make bottles, bags, films, and other packaging solutions that provide protection and convenience for a wide range of products. Answer for Question 4: Yes, free radical polymerization is used to produce biomedical polymers such as poly(methyl methacrylate) (PMMA), which is used in applications like bone cement, dental implants, and contact lenses due to its biocompatibility and mechanical properties. Answer for Question 5: Polymers produced via free radical polymerization, such as polyacrylamide, are used as flocculants in water treatment processes. These polymers help in aggregating suspended particles, making it easier to remove contaminants from water. 38
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