Course Syllabus for English-Taught Majors

Polymer Synthesis and Modification TechnologyCourse Syllabus

Course Code09040003

Course CategoryMajor Selective

MajorsIntensive Training Class

SemesterSpring

Total Hours36 Hours         Credit2

Lecture Hours36 Hours          Lab Hours0         Practice Hours0

InstructorsYouliang Zhao

 

TextbooksContemporary Polymer Chemistry, H. R. Allcock, F. W. Lampe, J. E. Mark, Chemical Industry Press 2006, ISBN: 7502576444.

References

1) Polymer Science and Technology, J. R. Fried, Chemical Industry Press 2005, ISBN: 7502568255.

2) Principles of Polymer Chemistry, A. Ravve, Chemical Industry Press 2008, ISBN:  9787122009845.

3) New techniques of polymer synthesis (the second edition), editor: Jianguo Wang, Chemical Industry Press 2004, ISBN: 7502553150.

4) Polymer modification, editors: Yaguang Qi and Xuming Xue, Chemical Industry Press 2005ISBN: 7502563237/G.1618.

5) Synthetic technique of polymers, Deren Zhao, Weisheng Zhang, Chemical Industry Press 2004, ISBN: 7502516816.

6) Engineering plastics by blending modification, Rusheng Deng, Chemical Industry Press 2005ISBN: 750254416x.

7) Polymer modification, Guoquan Wang, Xiufeng Wang, China Light Industry Press 2008, ISBN: 9787501963621.

8) Principles and applications of polymer blending modification, Guoquan Wang, China Light Industry Press 2007, ISBN: 9787501957415.

9) PMMA resins and their applications, Zhanbiao Ma, Chemical Industry Press 2002, ISBN: 7502533885.

 

Teaching Aim

Polymer synthesis and modification technology is a major selective course in College of Chemistry, Chemical Engineering and Materials Science at the Soochow University. It can be also regarded as a special and basic course for students in different specialties. By taking this course, the students can master the basic concepts, theories and methods of polymer synthesis and processing and will understand the characteristics of different kinds of polymers.

  Polymer chemistry is aimed at synthesis and reaction of polymers, and polymer modification underlies wide use of polymeric materials, so both of them are very important to each other. This course will be focused on a) basic theory of polymer reactions, b) relationships among reaction theory, structures, properties and applications, and c) basic technology of polymer modification preparation. The students are expected to master the following contents after attending this course: 1) to understand some basic concepts such as polymerization rate, average degree of polymerization, macromolecular microstructure and copolymer composition and some important reagents such as monomer, initiator, catalyst, chain transfer agent, inhibitor, emulsifier and dispersant; 2) to learn basic polymerization methods such as normal and “living”/controlled free radical polymerization, step-growth polymerization, and ionic polymerization; 3) to learn classification of topological polymers including dendrimers and their self-assembly; 4) to master basic theory and methods of polymer modification, molding and production.

  After taking this course, the students will learn how to synthesize polymers from the raw materials, can under the different characteristics of various polymeric materials and can handle the modification process of common polymers. The students can also be capable to solve the engineering problems and can make up the gap between the theoretical knowledge of polymer chemistry and practical production.

  To study the present course, the students had better possess the basic knowledge of differential courses, such as polymer structure and properties, polymer chemistry, polymer physics and materials science and engineering. The students should also have the basic understandings of mechanics and engineering. The course will be very useful for their further studies and future employment.

Chapter One  Free radical polymerization

   Hourstwo weeks4 hours in total

 

Contents

1-1 Chain polymerization family

Classified by the nature of reactive center: radical polymerization, cationic polymerization, anionic polymerization, coordinating ionic polymerization.

Chain polymerization consists of a sequence of three steps: Initiation reaction, Propagation reaction, Termination reaction.

Examples on polymers prepared via free radical polymerization.

 

1-2 Mechanism of radical polymerization

Generation of free radicals: thermal decomposition, photochemical decomposition, oxidation-reduction (redox) reaction, high energy particle radiation.

The activity of a free radical is determined by its structure.

Reactions of the free radical: addition reaction, coupling reaction, disproportionation reaction, dissociation reaction, and transfer reaction.

 

1-3 Monomer structure and types of polymerization

Most of the mono olefin, conjugated diolefin, alkyne and carbonyl compounds, and some of the heterocyclic compounds can be polymerized from the thermodynamic viewpoint.

However, the selectivity of various monomers to different polymerization mechanisms varies greatly and depends on some factors such as the electronic effect of the substituents involving the inductive or resonance effect and steric effect.

 

1-4   Elementary reactions of the radical polymerization

They normally refer to chain initiation, chain propagation, and chain termination.

Perhaps the polymerization is accompanied by chain transfer reaction and so on.

 

1-5 Characteristics of the radical polymerization

The rate of initiation is the lowest one, which controls the overall rate of polymerization.

In conclusion, the characteristics of radical polymerization are slow initiation, fast propagation, fast termination, and easy transfer.

 

1-5   Initiators and initiation

Types of initiators: azo initiator, organic peroxide initiator, inorganic peroxide initiator, redox initiation system.

Kinetics of initiator decomposition: initiator decomposition rate, initiator efficiency, and choice of initiator.

Other initiation systems: thermal-initiated polymerization, light initiated polymerization, and high energy radiation initiated polymerization.

 

1-6 Rate of radical polymerization

Polymerization rate and measuring method, steady-state polymerization rate equation, effect of temperature on polymerization rate, rate constants of elementary reaction and main parameter, autoacceleration, types of rate changing during the polymerization process, inhibition and retardation.

 

1-7 Molecular weight and chain transfer reaction

Molecular weight is an important parameter to characterize polymers.

Factors affect the rate of polymerization, such as the concentration of initiators, the concentration of monomers, the polymerization temperature, and so on, which also affect the molecular weight.

Chain transfer reaction usually doesn’t affect the rate of the polymerization, however, affects the molecular weight very much.

Molecular weight is also an important part in kinetics study.

Kinetic chain length and the degree of polymerization.

 

Problems:

1 What are molecular weight and polydispersity of polymers?

2 Please list the repeating unit of the following polymers and monomers to synthesize them: PSt, PMMA, PAA, PVA, PIP, PTFE.

3 Please list the resources to generate free radicals.

4 Please list main reactions of radicals.

5 Please list three monomers which can be polymerized via radical, ionic and coordination polymerizations.

6 Can 1,1-diphenylethylene be subjected to polymerization? Why?

7 Please draw chemical structures of poly(styrene-alt-maleic anhydride).

8 Please list elemental reactions of chain polymerization.

9 Please list the types of microstructures for monosubstituted vinyl monomers.

10 Please list the types of chain transfer reaction in free radical polymerization and give two examples of chain transfer agents.

11 What are the characteristics of radical polymerization?

12 Notions: efficiency of initiation, kinetic chain length, autoacceleration (gel effect), radical life, polymerization rate, inhibition, retardation

13 Chemical structures: AIBN, BPO, KPS, cumyl hydroperoxide

14 Please list the relationship between degree of polymerization and kinetic chain length.

15 Please explain basic principles of dilatometer method.

 

Chapter Two  “Living”/controlled radical polymerization

   Hourstwo weeks4 hours in total

 

Contents

2-1   Living and controlled systems

Living systems: constant number of polymer chains, no permanent chain stopping reactions, dormant and active state, control of chain-growth, narrow MWD (Poisson), Mn vs. monomer conversion is linear.

Controlled systems: side reactions do occur, however still have a control over end groups, topology, monomer sequence.

 

2-2 Living polymerization

Living polymerization is a form of addition polymerization where the ability of a growing polymer chain to terminate has been removed.

Chain termination and chain transfer reactions are absent, and the rate of chain initiation is much larger than the rate of chain propagation.

The result is that the polymer chains grow at a more constant rate than seen in traditional chain polymerization and their lengths remain very similar.

Living polymerization is a popular method for synthesizing block copolymers since the polymer can be synthesized in stages, each stage containing a different monomer.

Additional advantages are predetermined molecular weight and control over end groups. 

 

2-3 Types of living polymerizations

Living anionic / cationic polymerization

Ring-opening methathesis polymerization

“Living”/controlled free radical polymerization

Group transfer polymerization

Living Ziegler-Natta polymerization

2-4 How to realize a living system?

Reversible activation, chain transfer processes, and combination of both.

Ionic polymerization:

Easy design of polymeric architectures: Very selective reactions, requires extreme reaction conditions such as low temperatures and high purity solvents and reagents, expensive to undertake for industry (catalysts cost, various requirements).

Free radical polymerization: Good tolerance towards impurities, wide range of (functionalized) monomers, widely employed in industry via bulk, solution, emulsion/suspension polymerization, inhibition by oxygen, and lack of selective reactions.

 

2-5 Iniferter method

Developed by Otsu in 1982

Thermal-initiated iniferter: Most of them belong to derivatives of 1,2-disubstituted tetraphenylethanes

Photo-initiated iniferter: Compounds comprising diethyldithiocarbamate

 

2-6   Catalytic chain transfer polymerization (CCTP)

Certain low-spin cobalt complexes, typical [Mon]/[Co] ratio of ca. 106

 

2-7 Nitroxide mediated living radical polymerization

Typical nitrooxy radical is 2,2,6,6-tetramethylpiperidinyl-1-oxy (TEMPO)

High temperature is required (>110 oC), and there are limited number of monomers

 

2-8 Transition metal mediated living radical polymerization (Atom transfer radical polymerization, ATRP)

ATRP process using CuBr/bpy catalytic system

Application of ATRP: To prepare well-defined macromolecules with predetermined MW and low polydispersity (1.04 < Mw/Mn <1.50, 300 < Mn < 200,000), to control macromolecular architecture, to control microstructure of macromolecules, and to prepare macromonomers and functionalized polymers with COOH, OH, NR1R2 and vinyl groups.

 

2-9 Reversible addition-fragmentation chain transfer (RAFT) polymerization

Control over MW & architecture

Wide range of monomers

Ambient reaction conditions

One-step process

Simple purification of product

RAFT agents: only a few agents are available commercially (expensive!!)

Thio-chemistry: hazardous and smelly

Application of RAFT process

 

Problems:

1 What are basic features of living polymerization systems?

2 Please list the main types of “living”/controlled radical polymerization.

3 Please list the basic mechanism and application of ATRP.

4 Please list the basic mechanism and application of RAFT polymerization, and describe the primary roles of Z and R groups of RAFT agent.

 

Chapter Three  Ionic polymerization

   Hourstwo weeks4 hours in total

 

Contents

3-1   Overview

Some monomers, like alkenes and substances with rings, can undertake ionic chain polymerization with an ionic initiator.

According to the sorts of the active center at the end of long chain, ionic polymerization can be classified into three categories: cationic, anionic and coordination.

The active center of cationic polymerization is a carbocation, and the active center of cationic polymerization is a carbocation.

 

3-2 Cationic Polymerization

Initiator and monomer

Alkenes with electron-donating substituents are cationic polymerizable

A cationic catalyst or initiator could react with the above-mentioned monomer to produce a carbocationic active center.

The cationic initiators can be classified into two categories: strong proton acid and Lewis acid.

Cationic polymerization mechanism: Cationic polymerization belongs to chain polymerization, and it contains initiation, propagation, transfer, and termination.

The feature of the cationic polymerization is fast initiation, rapid propagation, very extremely easy transfer and comparatively hard to termination, in which a terminator is often indispensable.

Reaction kinetics

 

3-3 Polymerization

Initiator and monomer

Typical anionic polymerizable monomers: styrene, MMA and acrylic nitrile etc.

All types of monomers are p-p conjugated system or that with electron attracting group, making the density of electron cloud of double bond decline

The anionic active center reacts with double bond by addition reaction

Mechanism: The anionic polymerization still belongs to the chain polymerization. It consists of 3 elementary reactions: initiation, propagation, and termination.

Living polymer:

As long as no termination occurs, though all monomers are used up, the polymer still remains activity. When new monomer is added, the polymerization restarts. When another kind of monomer is added, a block copolymer produces.

Many initiators can be used in the living polymerization. The most convenient is metal Na and naphthalene natrium initiator.

Alkali metal Na transfers the electron of the outer layer to the monomer, to form a monomer anion radical, which is produced, through the radical double-group termination, double anion to take on the living polymerization.

Reaction kinetics

Application: To synthesize monodisperse polymers, to measure the anionic polymerization rate constant, to prepare block copolymers, and to prepare telechelic polymers.

 

3-4 Comparison between radical & ionic polymerizations

Monomer and initiator

Mechanism

Kinetics

Temperature

Effect of solvent and other chemicals

 

Problems:

1 Take Na-naphthalene based anionic polymerization of styrene for example, please describe the basic mechanism and application of living anionic polymerization. How about the relationship between polymerization degree and kinetic chain length?

2 Please describe the main applications of living anionic polymerization.

3 Please compare the similarity and differences among anionic polymerization, cationic polymerization and free radical polymerization.

 

Chapter Four  Dendrimer and hyperbranched polymer

   Hoursthree weeks6 hours in total

 

Contents

4-1   Overview of dendritic polymers

Dendritic polymers are highly branched polymer structures, with complex secondary architectures and well-defined spatial location of functional groups.

They can be used in applications such as targeted drug-delivery, as macromolecular carriers, for catalysis, as sensors, for light harvesting, for surface engineering, as biomimetic materials.

Dendritic polymers exhibit very different properties compared to their linear analogues.

Dendritic materials sub-classes: dendrimers, dendrons, hyperbranched polymers, dendrigraft polymers, dendronized polymers.

 

4-2 Dendrimers

When dendritic polymers are perfectly branched they are either dendrons or dendrimers.

The dendrimers comprise a single core that is capped with layers of repeat units which are radially branched. Each layer is called a generation.

Much like proteins and natural products, dendrimers are near monodisperse with predictable molecular weights and nano-scale dimensions.

The unique properties of dendrimers are attributed to their globular structure, resulting from internal structures in which all bonds emerge radially from a central core, and a large number of end-groups are present at its surface.

Dendrimers consist of a series of chemical shells built on a small core molecule. Each shell consists of two chemicals, always in the same order and is called a generation.

Dendrons: Dendrons represent a structural component of the parent dendrimer, and are monodisperse, wedged-shaped sections of a dendrimer.

Examples of dendrimers:

Tomalia-type poly(amidoamine) (PAMAM)

Fréchet-type poly(benzylether)

Newkome’s arborol dendrimers

Phosphorus-containing dendrimers

Poly(2,2-bis(hydroxymethyl)propionic acid) dendrimer

 

4-3 Dendrimer synthesis

Divergent synthesis - Multiplicative growth from a central core.

Convergent synthesis - Preparation starting from what will become the periphery of the molecule and progressing inward.

 

4-4 Dendrigraft polymers

Dendrigraft polymers, sometimes referred to as arborescent polymers, are a relatively new addition to the dendritic family, combining features of dendrimers and hyperbranched polymers with linear polymers.

Dendrigraft polymers are grown in generations, much like dendrimers, but the repeating unit is an oligomer or a polymer chain, rather than a small monomer unit.

As dendrigraft polymers flexible polymers with very high molecular weights are obtained rapidly.

Examples of dendrigraft polymers are: Comb-bursts, arborescent polybutadiene.

 

4-5 Dendronized polymers

Dendronized polymers, sometimes termed “rod-shaped polymers”, are structures having a linear backbone with dendritic side chains.

Dendronized polymers are a sub-class of comb-polymers where the “comb’s teeth” are dendrons instead of linear polymer chains.

Depending on the density and size of the attached dendrons, the dendronized polymers can have either random coil or fully stretched out conformation.

Fully stretched out dendronized polymers are rod-like cylindrical polymers (nanotubes) and are believed to have new and interesting properties, since they have dimensions reminiscent of several biological functional units, such as the mosaic virus (lengths up to 400 nm and diameters up to 6 nm)

 

4-6 Hybrid structures

Polymers containing both linear chains and dendritic parts are often referred to as “dendritic–linear polymer hybrids” or just “hybrid materials”.

One approach to obtain hybrid structures is by turning the core or the multiple end-groups of the dendritic polymer into initiating moieties for polymerization.

Another method utilizes a grafting-to strategy, in which pre-formed polymer linear chains are coupled to a dendritic core.

 

4-7 Hyperbranched polymer

General method to synthesize hyperbranched polymer: ABn monomer, AB*

Other routes: inimer-based SCVP via NMP, ATRP and RAFT, Ax + By (or more monomers) type condensation or adductive polymerization

 

4-8 Applications of dendrimers

Suprachemistry, catalyst, biomedicine, optics, and other fields.

 

Problems:

1 Please describe main subclasses of dendritic polymers.

2 What is dendrimer? How about its main applications?

3 Please list three types of dendrimers? What is the repeating unit of Tomalia-type poly(amidoamine) dendrimer?

4 Please list the main methods to synthesize dendrimers?

5 By assuming the core functionality is m, and each branching point has three linking positions, please calculate the surface functionality of dendrimer with generation n.

6 Please describe the advantage of synthesis of dendrimers via orthogonal strategy.

7 Please describe the similarity and difference of dendrimer and hyperbranched polymer. How to calculate the degree of branching?

 

Chapter Five  Polymer self-assembly

   Hoursthree weeks6 hours in total

 

Contents

5-1 Overview

Phase diagram of a diblock copolymer

Triblock copolymers: Even more options

 

5-2 Polymer and nanostructure

Supramolecular chemistry: To construct polymer materials via non-covalent bonds such as hydrogen bond, ionic bond and coordination bond.

Polymer self-assembly: Hollow polymer sphere, polymer tube, molecular wire, molecular device

Nanostructure: Suprahydrophobic materials

 

5-3 What is supramolecular chemistry

Supramolecular chemistry is the chemistry of the intermolecular bond, concerning the structure and functions of the entities formed by the association of two or more chemical species. (Jean-Marie Lehn)

Molecular Chemistry: covalent, ionic and metal-metal bonds - Intramolecular bonding

Supramolecular chemistry: charge groups, dipoles, H-bonds, hydrophobic/hydrophilic interactions, p-p interactions, non-bonding electronic repulsion - Intermolecular bonding

Molecular aggregates: held together by intermolecular forces

Major intermolecular forces:

    non-directional: van der Waals interactions,

    directional: H-bonds, p-p interactions

Strength: Intermolecular forces–––usually less than 10 kJ/mol

Distance: 0.3-0.5 nm

 

5-4 Making nanostructures: nanomanufacturing

“Top down” versus “bottom up” methods

 

5-5 What drives self-assembly?

Static assembly (thermodynamic free energy minimum) - once formed it is stable

Dynamic assembly (kinetically formed, not necessarily thermodynamic minimum) - not necessarily stable

Forces of chemical bonding (4): covalent, ionic, van der Waals, hydrogen

Other forces (magnetic, electrostatic, fluidic)

Polar/Nonpolar (hydrophobicity)

Shape (configurational)

Templates (guided self-assembly)

Kinetic conditions (e.g., diffusion limited)

 

5-6 Typical aggregates

Langmuir Film of an amphiphilic molecule

Langmuir-Blodgett Film

SAM: Self assembled monolayer

Self-assembly with diblock copolymers

5-7   Characteristics of soft matter

i) Length scales:

- Structures of ≈10-1000 nm determine the properties

ii) Time scales: processes from 10-12 - 103 s

- Dynamics processes over a wide time scales 10-12 - 103 s

- Very slow processes in non-equilibrium configurations

iii) Weak interactions    

- Interactions between molecules and molecular structures ≈ kT

iv) Self-assembly

- Hierarchical arrangement of structures

- Competition between interaction energy and entropy

Surfactants and amphiphiles

Shape of aggregates

Basic shapes: spheres, cylinders, bilayers, vesicles

Superstructures: micellar crystals, lamellar phases, bicontinuous networks

 

5-8   Suprastructures from surfactants

Micelles: sphere, rodlike

Vesicles

Complex structures: LB film and multilayer membrane, onionlike, rodlike micelles

 

5-9 Polymer self-assembly

Phase behaviour of polymers: LCST/UCST behaviour

Colloidosomes

Encapsulation of “Material” by colloidal shells

Micelles: Two extremes, hairy micelles and crew cut micelles

Assembly into colloidal structures: polymersomes

Shell-crosslinked polymer assemblies

Toroidal triblock copolymer assemblies

Peptide-amphiphilic nanofibers

Supramolecular self-assembly of macroscopic tubes

 

Problems:

1 Please list four types of morphologies of diblock copolymers via self-assembly in bulk.

2 Please list three types of morphologies observed in polymer aggregates.

3 Please describe the main driving forces of self-assembly.

4 Please describe the differences between hairy micelle and crew cut micelle.

5 Please list four individual examples of hydrophobic and hydrophilic polymers at ambient temperature.

 

Chapter Six  Polymer structure and properties

   Hourstwo weeks4 hours in total

 

Contents

6-1 Overview

Polymers are organic, chain molecules.

They can vary from a few, to hundreds of thousands of atoms long.

There are three classes of polymers that we will consider in turn:

Thermoplastic: flexible linear chains

Thermosetting: rigid, 3-D networks

Elastomeric: linear, cross-linked chains

Representing polymer structures

Molecular shape

Molecular structure

Molecular configurations

Polymer crystallinity

Thermoplastic polymers go through a series of changes with changes in temperature. (Similar to ceramic glasses)

In their solid form they can be semi-crystalline or amorphous (glassy).

 

6-2 Thermoplastics

Bonding along the “backbone” of the chain is covalent.

In simple thermoplastic polymers, the chains are bound to each other by weaker Van der Waal’s forces and mechanical entanglement.

Therefore, the chains are relatively strong, but it is relatively easy to slide and rotate the chains over each other.

 

6-3 Amorphous thermoplastics

Glassy polymers (T < Tg): Below the glass transition temperature, amorphous polymers are hard and brittle.

Rubbery or leathery polymers (Tg < T < Tm): Between Tg and Tm, when a stress is applied, the polymer deforms elastically and plastically at the same time. When the stress is removed the elastic deformation is recovered, but the polymer is permanently deformed because of the movement of the chains.

Liquid polymers (T > Tm): Bonds between chains are very weak, and chains slide past each other with almost no force.

 

6-4 Polymer crystallinity

Similar to metals and ceramics, polymers can be made to exhibit some long-range order (crystallize).

For polymers to crystallize, entire chains must be ordered.

Crystalline thermoplastics: Linear polymers never completely crystallize. However, some polymers partially crystallize. Neighboring chains become aligned and fold back on themselves to form thin plates.

These plates are connected to each other by amorphous chains and often form spherulites.

The ability of a polymer to crystallize is affected by:

1. Complexity of the chain: Crystallization is easiest for simple polymers (e.g. polyethylene) and harder for complex polymers (e.g. with large side groups, branches)

2. Cooling rate: Slow cooling allows more time for the chains to align

3. Annealing: Heating to just below the melting temperature can allow chains to align and form crystals

4. Degree of Polymerization: It is harder to crystallize longer chains

5. Deformation: Slow deformation between Tg and Tm can straighten the chains allowing them to get closer together.

 

6-5 Deformation of polymers

Polymers can be:

A. Elastic – Brittle

B. Elastic – Plastic

C. Highly elastic

1 Deformation of amorphous polymers

Deformation of thermoplastic polymers is more complicated than in metals or ceramics– It depends on the applied stress and the strain rate.

Elastic deformation is the result of stretching the covalent bonds of the chain and the rotation of the curved chains.

On unloading, the strain due to stretching the chains is recovered immediately, and the strain due to the rotation of the chains takes longer.

Plastic deformation in polymers does not occur by the motion of dislocations, and deformation is accomplished by the motion of polymer chains relative to each other. If the polymer is not brittle, after yielding the chains begin to disentangle, straighten and slide past each other.

Necking begins almost immediately after yield, but this is different from necking in metals.

Necking in Amorphous Thermoplastics

2 Deformation of semi-crystalline thermoplastics

Elongation occurs first in the amorphous regions between crystalline lamellae.

Crystalline lamellae begin to align in the direction of the applied stress and then break into smaller segments.

Under an applied stress, small voids can open up in bands perpendicular to the applied load. This is known as crazing. In a transparent material, these voids can appear as an opaque band through the material. A craze is not a crack and can still support a stress.

As the voids elongate, the ligaments between them are subjected to higher stresses and eventually fracture causing the craze to grow.

Eventually, the crack grows to a size that causes rapid fracture.

 

6-6 Time dependent deformation

Deformation is accomplished by the motion of polymer chains relative to each other.

Sliding polymer chains past each other takes some time.

This is viscoelastic behavior.

At high temperatures or low strain rates – More ductility

At low temperatures or high strain rates – Less ductility

Creep and stress-relaxation are time dependent phenomena.

Creep: change in length at constant load

Stress-Relaxation: change in load at constant extension

 

6-7 Temperature dependence of deformation

Increasing temperature:

Decreases Young’s Modulus

Decreases the Yield Strength

Increases ductility

 

6-8 Controlling the strength of thermoplastics

Plastic deformation in thermoplastics is due to the rotation and sliding of chains over each other.

To increase the strength of a thermoplastic, we have to make it harder for the chains to move.

There are essentially three ways that we can control this: 1. Alter the length of the chains; 2. Change the strength of the bonds within the chains; 3. Change the strength of the bonds between the chains

 

6-9 Features of typical polymers

Elastomers

Thermoplastic elastomers

Thermosetting polymers

 

Problems:

1 At room temperature, which types of polymers will act as glassy polymers, rubbery or leathery polymers, and liquid polymers? Please give two individual examples of these polymers.

2 Please list three polymers which can crystallize.

3 Please describe the main factors to affect the crystallizability of polymers.

4 Notions: glass transition temperature, melting temperature, thermoplastic elastomer, thermoplastic polymer, thermosetting polymer.

 

Chapter Seven  Polymer modification

   Hourstwo weeks4 hours in total

 

Contents

7-1 Polymerization techniques

Bulk: no solvent just monomer + catalysts

Solution polymerization: in solvent

Suspension: micron-millimeter spheres

Emulsion: ultrasmall spheres

Less common polymerization techniques:

Solid state polymerization: Polymerization of crystalline monomers, diacetylene crystals

Gas Phase polymerization: light olefin, parylene polymerizations

Plasma polymerization: Put anything in a plasma

 

7-2 Feature and weakness of polymers

Plastics: fragile, unable to bear impact, poor heat-resistant

Rubber: need to improve intensity, anti-freezing and oil-resistance

 

7-3 Polymer modification

The polymer performance could be greatly enhanced, and new functions could be bestowed by modification.

The polymers are hence of greater industrial importance and could be used in various applications.

There are various kinds of methods for polymer modification. Generally speaking, it can be classified into five categories: blending modification, filling modification, composition modification, chemical modification and surface modification.

 

7-4 Blending modification

The original idea of blended polymers is the mixing of two or more kinds of polymers, and macroscopically homogeneous materials are concocted thereafter.

Basic methods for blending modification: physical blending, chemical blending, and physicochemical blending.

Implementation of blending modification: melt blending, solution blending, and emulsion blending

Mixing: Polymer and Additives

Usually, polymers are mixed with added ingredients (serve a variety of purposes)

2 types of additives: Modifying additives, Protective additives

Types of Mixing Process

Based on 2 basic mixing functions:

1 Blending: Stirring together/blending of a number of solids, e.g. polypropylene powder, pigment, antioxidant, etc. The result is to form a mixture of powders; the individual powder remains and can be separated (in principle).

2 Compounding: Blending mixing is used when the fabrication process will be followed by compounding process (pigments must be mixed into granules/powder followed by injection molding process), thermosetting powders and fillers are often blends which disperse upon fusion of the resin during molding.

Compounding mixing is used when accurate distribution & dispersion of ingredients are required (e.g. in rubber compounding, 4-5 additives have to act together for efficient cross-linking of the rubber)

 

7-5 Chemical modification

In the treatment of polymeric surfaces, chemical composition of polymer surfaces can be modified either by direct chemical reaction with a given solution (wet treatment) or by the covalent bonding of suitable macromolecular chains to the sample surface (grafting).

Main methods: hydrolysis, oxidation, photochemistry, chemical crosslinking, chemical modification.

 

7-6 Surface modification

Corona treatment

Flame treatment

Flame treatment

Ion beam treatment

Metallization

 

Problems:

1 Please list main types of polyethylene.

2 Notions: filling modification, surface modification, chemical modification.

3 What is solution blending? What are the features of solution blending?

4 What is blending modification? Please describe its features, classifications and techniques.

5 Please describe main methods and principles of polymer modification.

 

Chapter Eight  Polymer processing

   Hourstwo weeks4 hours in total

 

Contents

8-1 Overview

Source of strength of polymers

Advantages of polymer

Properties of polymer melt

 

8-2 Extrusion

A compression process in which the material is forced to flow through a die orifice to provide long, continuous product with regular shape controlled by the orifice shape.

Extrusion characteristics:

The extrusion machine forms the basis of nearly all other polymer processes.

Basically involves melting polymer pellets and extruding them out through a two dimensional die.

Produces long, thin products: coating for electrical wire, fishing line, tubes, etc.

Extrusion defects

 

8-3 Injection Molding

Typical cycle time: 10 - 30 seconds

Most widely used process

Two units: Injection unit, clamping unit

The injection molding process depends on the injection pressure, injection velocity, melt temperature, mold temperature, and holding time.

Molding cycle: (1) mold closing; (2) melt injection into cavity; (3) screw retraction; (4) mold opening and part ejection

Reaction Injection Molding

Thermoplastics foam injection molding

Multi-injection molding process

Injection molding of thermosets

 

8-4 Compression and transfer molding

 

8-5 Blow Molding

Extrusion blow molding

Injection blow molding

Stretch blow molding

 

8-6 Other techniques

Rotational molding

Thermoforming

Casting

Polymer foaming

 

8-7 Polymer recycling

 

8-8 Processing of polymer composites

 

Problems:

1 Please describe main polymer processing methods.

2 What is extrusion molding? How about its features and applications?

3 What is injection molding? How about its features and applications?

4 What is reaction injection molding? How about its features and applications?

 

 

Assessment MethodsPaper writing

 

 

                                 Made by Youliang Zhao

                                    Date:  Oct-8-2016