Polymer Chemistry

Basic Principles and Introduction

Prof. Y.M. Lee School of Chemical Engineering, College of Engineering Hanyang University

Spring 2004 WeWe livelive inin aa polymerpolymer age!!age!!

RubberRubber Elastomers PlasticsPlastics Elastomers

FibersFibers CoatingsCoatings

ProteinProtein CelluloseCellulose

AdhesivesAdhesives

Spring 2004 Polymer: large molecules made up of simple repeating units Greek poly, meaning many, and mer, meaning part Synonymous Term: Macromolecules

Synthesis of Polymer: Synthesized from simple molecules called “monomers”

1) Addition Polymerization

Ethylene H C CH 2 2 * CH2 CH2 n *

CH CH Styrene H2C CH * 2 n *

Spring 2004 2) Condensation Polymerization

-H O 2 Ethylene glycol OCH CH HOCH2CH2OH * 2 2 n *

4-Hydroxymethyl HOCH CO H benzoic acid 2 2

O -H2O * O CH2 C n *

Spring 2004 Historical Milestones in Polymer Science

• Prehistory – 19th Century Mankind relies on natural polymeric materials like wood, bone, and fur.

•1833 Polymer was first used by the Swedish chemist Berzelius.

• 1839 Charles Goodyear vulcanizes natural rubber with sulfur, launches rubber industry. The polymerization of styrene was firstly reported.

•1860s Poly(ethylene glycol) and poly(ethylene succinate) was published. O O * * n * * n O

Spring 2004 Historical Milestones in Polymer Science

•1870 John Wesley Hyatt invents Celluloid through chemical treatment of natural cellulose (nitrated cellulose).

•1887 Count Hilaire deChardonnet spins cellulose nitrate into Chardonnet silk

•1909 American inventor Leo Baekeland (who had already earned considerable success with his light-sensitive photographic paper) treated phenol with formaldehyde to produce Bakelite, the first successful fully synthetic polymer material.

Spring 2004 Historical Milestones in Polymer Science

•1920 German chemist Hermann Staudinger proposes his Macromolecular Hypothesis, claims giant molecules exist (revealing view is that plastics are assemblies of small molecules). Staudinger is widely criticized but eventually becomes the first polymer chemist to win the Nobel Prize in Chemistry (in 1953).

•1928 German chemists Kurt Meyer and Herman Mark confirm the existence of macromolecules through x-ray studies.

Spring 2004 Historical Milestones in Polymer Science •1928 DuPont hires Professor Wallace Hume Carothers from Harvard to start first basic R&D lab in the USA. •1930s - An explosion of new materials. Wallace Carothers -Polyamide (Nylon) Polychloroprene (Neoprene) Waldo Semon - Polyvinyl chloride (PVC) Roy Plunket - Polytetrafluoroethylene (Teflon) Paul Flory - Theory of gelation •1940s WWII leads to synthetic rubber program Professor Peter Debye develops light scattering for MW measurement Flory and Huggins develop theory of polymer thermodynamics

Spring 2004 Historical Milestones in Polymer Science

•1953 German chemist Karl Ziegler and Italian chemist Giulio Natta develop effective catalysts for olefin polymerization allowing large scale production of polyethylene and polypropylene. They receive the Nobel Prize in 1963.

• 1974 Professor Paul Flory is awarded the Nobel Prize in Chemistry for his many contributions to polymer science.

•1986 Chemical Engineering Professor Robert Langer and Medical Doctor Joseph Vacanti demonstrate the use of polymers in tissue engineering. Liver cells grown on a special polymer can be transplanted and still function.

Spring 2004 Historical Milestones in Polymer Science

•2000 The Nobel Prize in Chemistry is given “for the discovery and development of electrically conductive polymers.”

Professor Alan J. Heeger at the University of California at Santa Barbara, USA

Professor Alan G. MacDiarmid at the University of Pennsylvania, USA

Professor Hideki Shirakawa at the University of Tsukuba, Japan

Polymer Science and Technology remains a vital and exciting field!

Spring 2004 Important Advances in Polymer Science

• High thermal and oxidation-stable polymer: high performance aerospace applications

• Engineering plastics – polymers designed to replace metals

• High strength aromatic fibers – a variety of applications from tire cord to cables for anchoring oceanic oil-drilling platforms

• Non flammable polymers – emit a minimum of smoke or toxic fumes

• Degradable polymers – allow controlled release of drugs or agricultural chemicals

• Polymer for a broad spectrum of medical applications – from degradable sutures to artificial organs

• Conducting polymers – exhibit electrical conductivities comparable to those of metals

• Polymer that serve as insoluble support for catalysts or for automated protein or nucleic acid synthesis (Bruce Merrifield, who originated solid-phase protein synthesis, was awarded the Nobel Prize in Chemistry in 1984)

Spring 2004 Chap 2. Types of Polymers & Definitions

Polymer: a large molecule whose structures depends on the monomer or monomers used in preparation Oligomer: low-molecular weight polymer (a few monomer units)

Repeating unit (RU): monomeric units (examples: polyethylene) Degree of polymerization (DP): the total number of structural units, including end groups. It is related to both chain length and molecular weight

n CH C H2C CH * n -2-2* Vinyl acetate O O (a important industrial C O C O monomer)

CH3 CH3 If DP (n) = 500, for example, M.W.= 500 × 86(m.w. of structural unit) = 43,000 Because polymer chains within a given polymer sample are almost always of varying lengths (except for certain natural polymers like proteins), we normally refer to the average degree of

Polymerization (DP). Spring 2004 Definitions

Homopolymer: -A-A-A-A-A-A-A-A-A-

Copolymer: (1) Alternating copolymer: -A-B-A-B-A-B-A-B-A-B-A-B- (2) Random copolymer: -A-A-B-A-B-B-A-B- (3) Block copolymer: -A-A-A-A-A-A-B-B-B-B-B-B- (4) Graft copolymer: -A-A-A-A-A-A-A-A-A-A-A-A- B B-B-B-B-B-B-B-

Spring 2004 Representation of polymer types

(a) Linear (b) Branched (c) Network

(a) Star (b) Comb

(c) Ladder (d) Semiladder

Spring 2004 Network Polymers (Crosslinked polymers)

Network polymers arise when polymer chains are linked together or when polyfunctional instead of difunctional monomers are used. Ex) Vulcanized rubber

1. Excellent dimensional stability Polymer crosslink 2. X-polymers will not melt or flow and cannot be molded. Chains (thermosetting or thermoset ÅÆ thermoplastic) 3. Usually insoluble, only swelling

Spring 2004 Polymerization processes (traditional)

Traditionally, polymers have been classified into two main groups: 1) addition polymers and 2) condensation polymers (first proposed by Carothers)

1. Polyester from lactone and ω-hydroxycarboxylic acid:

2. Polyamide from lactam and ω-amino acid

Spring 2004 3. Polyurethane from diisocyanate and diol

4. Hydrocarbon polymer from ethylene and α,ω-dibromide by the Wurtz reaction

Spring 2004 Polymerization processes (recent)

In more recent years the emphasis has changed to classifying polymers according to whether the polymerization occurs in a stepwise fashion (step reaction or step growth) or by propagating from a growing chain (chain reaction or chain growth).

1. Step reaction polymerization

AB * ABn * Reactive functional group in one molecule

AA+ BB Two difunctional monomers * A A B B n *

Ex) Polyesterification Å diol + dibasic acid or intermolecularly between hydroxy acid molecules

Spring 2004 Carothers’ equation

If one assumes that there are No molecules initially and N molecules (total) after a given reaction period, then amount reacted is No-N. The reaction conversion, p, is then given by the expression

No − N p = or N = No (1− p) No

N 1 o = DP = N 1− p

Ex) At 98% conversion, p = 0.98 Æ DP = 50

Spring 2004 2. Chain-reaction polymerization

Chain-reaction polymerization involves two distinct kinetic steps, initiation and propagation.

Initiation . R . + H2C CH2 RCH2CH2 Propagation . RCH CH CH CH . RCH2CH2 + H2C CH2 2 2 2 2

In both addition and ring-opening polymerization, the reaction propagates at a reactive chain end and continues until a termination reaction renders the chain end inactive (e.g., combination of radicals), or until monomer is completely consumed.

Spring 2004 3. Comparison of step-reaction and chain-reaction polymerization

Step reaction Chain reaction

Growth occurs throughout matrix by reaction Growth occurs by successive addition of monomer between monomers, oligomers, and polymers units to limited number of growing chains

DP low to moderate DP can be very high

Monomer consumed rapidly while molecular Monomer consumed relatively slowly, but molecular weight increases slowly weight increases rapidly

No initiator needed; same reaction mechanism Initiation and propagation mechanisms different throughout

No termination step; end groups still reactive Usually chain-terminating step involved

Polymerization rate decreases steadily as Polymerization rate increases initially as initiator units functional groups consumed generated; remains relatively constant until monomer depleted

Spring 2004 Nomenclatures Vinyl polymers

Spring 2004 Nonvinyl polymers

Spring 2004 Nonvinyl polymers

Spring 2004 Industiral polymers

Plastics

Commodity plastics

Spring 2004 Engineering plastics

Spring 2004 Thermosetting plastics

Spring 2004 Fibers Synthetic fibers

Spring 2004 Rubber (elastomers)

Synthetic rubber

Spring 2004 Chap 3. Bonding in Polymers

Primary Covalent Bond C C C H H δδ_ + O C O H N Hydrogen Bond δ _ H O δ + δ_ Dipole Interaction C N

N C δ+

CO Ionic Bond O +1 _ Zn O CO

Van der Waals CH2

CH2

Spring 2004 PE

γm r

Attraction

Repulsion

Spring 2004 Chap 4. Stereoisomerism Activity (Tacticity)

CH3 CH3 Atactic C C C C C C C C C

CH3 CH3 CH3

Isotactic C C C C C C C C C

CH3 CH3 CH3 CH3

CH3 CH3 Syndiotactic C C C C C C C C C

CH3 CH3

Spring 2004 Chap 5. Crystallinity

Six crystal system

• Isometric; 3 mutually perpendicular axes of equal length. • Tetragonal; 3 perpendicular axes are equal in length. • Orthogonal; 3 perpendicular all of different length. Unit cell • Monoclinic; 3 axes of unequal length.

2 are not ⊥ to each other both are ⊥ to the third • Triclinic; all 3 axes of different length.

• Hexagonal; 4 axes, 3axes in the same plane & symmetrically spa and of equal length.

Spring 2004 Polyethylene: a = 7.41Å , b = 4.94Å , c = 2.54Å

Chain axes

CH 2

H2C CHCH2 2 CH 2 CH 2 CH 2 CH 2 H2C CH 2 CH 2 CH CH 2CH2 CH22 CH 2 CH 2 H2C CH 2

Unit cell volume = a×b×c = 93.3 Å3

Mass in cell corner = 8 CH2’s shared / 8 cells = 1 CH2 2 sidewall CH2’s = 2/2 = 1 CH2 Top & bottom face CH2’s =

24 o mass 4 14 AMU gm 10 3 ρ = = A c volume o 3 23 93.3 A 6.023 10 AMU cm3

3 = 0.997 gm / cm Crystal density

Spring 2004 결정화의 조건

1. 정규 결정 격자로 사슬이 packing 되려면 ordered, regular chain structure가 필요. 따라서 stereoregular structure 를 가진 고분자가 irregular structure 를 가진 고분자보다 결정화가 될 확률이 높다.

2.결정격자간 2차 간력이 강해서 열에너지에 의한 무질서 효과(엔트로피 효과)를 극복할 수 있어야 함.

biaxial stress(stretching) is stronger than uniaxial stretch ∵different arrangement of chain.

Spring 2004 Crystallizability

고분자의 화학구조에 의한 고유의 성질

• 구조의 규칙성 • 강한 친화력

Crystallinity

가공history 에직접의존

• Temperature/time • Stress/time

Spring 2004 몇가지 결정 MODELS

1. Fringed-Micelle Model fringed-micelle(or crystallites) 가 amorphous matrix 내에 퍼져 있음

orientation

Spring 2004 2. Folded-Chain Crystallites

희박용액으로부터 single crystal 이성장하여polymer crystal 이 생성됨을 발견. 냉각 또는 solvent 가 evaporation함으로서 thin, pyramidal, or platelike polymer crystal(lamellae)가생성. 이 결정들은 두께 약 100Å에 수십만 Å 길이를 가짐. X-ray 결과로는 chain axis가 flat surface에수직으로배열됨이알려짐. 또한 각자 사슬들이 1000Å 이상의 길이를 가짐. 따라서 chain이 folded back and forth 할수밖에없다는 결론. Dilute solution으로부터 뿐 아니라 melt로부터도이같은lamellae 형성 model이 적용됨.

Spring 2004 3. Extended-Chain X-tal melt 상태에서 extension(stress)을 가하면서 결정화가 일어날 때 확장하는 방향으로 사슬이 배열하며 fibrillar 구조를 형성. 이들은 extended-chain crystals로알려져있고 이들은 먼저 서로 평행으로 배열되어 있고 chain folding은 minimum.

“Shish-Kebab”

Spring 2004 4. Spherulites

고분자 사슬들은 crystallites를 형성할 수 있도록 배열되어 있으며 이들 crystallites들은 spherulites라고 하는 커다란 집합체로 되어 있다. 이들 spherulites는 핵형성점 으로부터 원형으로 성장. 따라서 각개 spherulites는 존재하는 핵의 숫자로부터 조절될 수 있으며 핵이더있으면더많은작은spherulites가됨. Spherulites가 큰 것들은 고분자의 brittleness . Brittleness를적게하려면nucleating agent를 첨가하든가 고분자를 shock cooling 함.

Spring 2004 Spring 2004 Specific volume

V = Vc wc + Va (1 wc)

c : calculated x-ray(1 / V ρc ) wc : wt ftaction of xtalls

Spring 2004