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This is the complete lecture note for ICH 455 Macromolecular Chemistry II. You can read it online below, open it in the full viewer, or download the PDF for offline study. It pairs with the course's video lectures, so you can read and watch together.
LA-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS
LA-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS Course code: ICH 455 Course title: Macromolecular Chemistry Course unit: 3 Units Series 1: Mechanism and Kinetics of Polymerization Part 1 Free radical polymerization 1.1.1 Initiation, propagation, and termination steps 1.1.2 Kinetic equations and rate expressions 1.1.3 Factors influencing free radical polymerization Part 2 Ionic polymerization 1.2.1 Mechanism of cationic polymerization 1.2.2 Mechanism of anionic polymerization 1.2.3 Kinetics and stability considerations Part 3 Stereo-specific polymerization 1.3.1 Role of catalysts (e.g. Ziegler–Natta catalysts) 1.3.2 Mechanism of stereo-regular polymer formation 1.3.3 Industrial and laboratory applications Part 4 Comparative kinetics and mechanistic analysis 1.4.1 Comparison of free radical, ionic, and stereo-specific mechanisms 1.4.2 Influence of reaction conditions on kinetics 1.4.3 Practical implications for polymer design Introduction Polymers are at the heart of modern materials, from plastics and fibres to biological macromolecules. To appreciate how these substances are formed and controlled, it is essential to understand the mechanisms and kinetics of their polymerisation. This Series sets the stage for your study of macromolecular chemistry by examining the fundamental processes that govern how monomers link together, how reaction rates are determined, and how different pathways influence the properties of the resulting polymers.
LA-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS The aim of this Series is to introduce you to the major mechanisms of polymerisation and to equip you with the ability to analyse their kinetics. By the end, you should be able to explain free radical, ionic, and stereo-specific polymerisation, and evaluate how reaction conditions affect polymer formation. We shall commence this Series by exploring free radical polymerisation, focusing on initiation, propagation, and termination steps, as well as the kinetic equations that describe them. Next, we will move on to ionic polymerisation, considering both cationic and anionic mechanisms and their stability factors. Following that, we will examine stereo-specific polymerisation, highlighting the role of catalysts and the formation of stereo-regular polymers. Finally, we will wrap up by comparing the kinetics and mechanisms across these processes, drawing out their practical implications for polymer design and application. Series Learning Outcomes Upon completing this Series, you should be able to: define the initiation, propagation, and termination steps in free radical polymerisation, explain the kinetic equations and rate expressions governing free radical polymerisation, analyse the factors influencing the rate and efficiency of free radical polymerisation, describe the mechanism of cationic polymerisation, describe the mechanism of anionic polymerisation, evaluate the kinetic and stability considerations in ionic polymerisation, explain the role of catalysts in stereo-specific polymerisation, demonstrate how stereo-regular polymers are formed through stereo-specific mechanisms, assess the industrial and laboratory applications of stereo-specific polymerisation, and compare the kinetics and mechanisms of free radical, ionic, and stereo-specific polymerisation processes. 1.1 Free Radical Polymerisation 1.1.1 Initiation, propagation, and termination steps Free radical polymerisation is a chain reaction process in which monomers are linked together through the action of highly reactive free radicals. A free radical is a chemical species with an unpaired electron, making it highly reactive and capable of initiating polymerisation. The process occurs in three main stages: initiation, propagation, and termination. Initiation involves the generation of free radicals, often through the decomposition of an initiator such as benzoyl peroxide or azobisisobutyronitrile (AIBN). Propagation is the stage where the free radical reacts with a monomer, creating a new radical that continues to add successive monomers. Termination occurs when two radicals combine or disproportionate, ending the chain growth.
LA-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS Fill in the blank: The stage where free radicals are first generated from an initiator is called __________. Figure 1.1 Stages of free radical polymerisation 1.1.2 Kinetic Equations and Rate Expressions The kinetics of free radical polymerisation can be described using rate equations. The rate of polymerisation depends on the concentration of monomer, the concentration of initiator, and the efficiency of radical generation. The rate of initiation is proportional to the square root of the initiator concentration, while the rate of propagation depends on both monomer concentration and the propagation rate constant. Overall rate of polymerisation: Rp = kp [M][R•] Where: Rp = rate of polymerisation
LA-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS kp = propagation rate constant [M] = monomer concentration [R•] = radical concentration Fill in the blank: The rate of polymerisation is directly proportional to the __________ Key kinetic expressions in free radical polymerisation Rate of initiation: Ri = 2 f kd [I] Rate of propagation: Rp = kp [M][R•] Rate of termination: Rt = kt [R•]² 1.1.3 Factors influencing free radical polymerisation Several factors influence the efficiency and outcome of free radical polymerisation. These include: Temperature: Higher temperatures increase initiator decomposition but may also accelerate termination. Initiator concentration: Too little initiator slows polymerisation, while too much increases termination events. Solvent effects: Solvents can stabilise radicals or alter reaction rates. Monomer structure: Substituents on monomers affect reactivity and chain growth. Fill in the blank: Increasing initiator concentration generally increases radical formation but also increases __________ events.
LA-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS Plate 1.1 Laboratory setup for free radical polymerisation Pilot questions 1.1 Define free radical polymerisation. List the three main stages of free radical polymerisation. Write the general expression for the rate of polymerisation. State one factor that influences free radical polymerisation. What happens during the termination stage of free radical polymerisation? 1.2 Ionic Polymerisation 1.2.1 Mechanism of cationic polymerisation Cationic polymerisation is a chain reaction process in which the active centre of the growing polymer chain is a positively charged ion (cation). It is typically initiated by strong acids or Lewis acids, which generate carbocations from monomers such as isobutylene or styrene. The carbocation then reacts with successive monomer units, propagating the chain. Termination may occur through chain transfer or reaction with impurities.
LA-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS Fill in the blank: In cationic polymerisation, the active centre of the growing chain is a __________. Figure 1.2 Mechanism of cationic polymerisation 1.2.2 Mechanism of anionic polymerisation Anionic polymerisation is a chain reaction process in which the active centre is a negatively charged ion (anion). It is initiated by strong bases or organometallic compounds, which generate carbanions from monomers such as styrene, butadiene, or acrylates. Anionic polymerisation is unique because it can proceed without termination under ideal conditions, leading to living polymerisation, where chains continue to grow as long as monomer is available. Fill in the blank: Anionic polymerisation can proceed without termination under ideal conditions, a process known as __________ polymerisation.
LA-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS Plate 1.2 Laboratory setup for anionic polymerisation 1.2.3 Kinetics and Stability Considerations The kinetics of ionic polymerisation depend strongly on the stability of the ionic active centres. In cationic polymerisation, carbocation stability is influenced by the nature of the monomer and the solvent. Polar solvents stabilise cations, while non-polar solvents may destabilise them. In anionic polymerisation, carbanion stability is affected by substituents on the monomer and the presence of counter-ions. Rate of Polymerisation For cationic polymerisation: Rp = kp M][C⁺]
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