Polymer ~ a large molecule built up by the constitutional repeating units(structural units)

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Maximilian Richard
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1 Polymer ~ a large molecule built up by the constitutional repeating units(structural units) Fundamental characteristics of polymers chemical structure and molecular mass distribution pattern ~ determine all the properties of the polymer hemical structure of a polymer a) the nature of the repeating units b) the nature of the end groups c) the composition of possible branches and cross-links d) the nature of defects in the structural sequence Molecular mass distribution ~ average molecular size and its regularity ~ may vary greatly depending on the method of synthesis of the polymer

2 Geometrical arrangements of the atoms in a polymer chain onfiguration: arrangements fixed by the chemical bonding cannot be altered unless chemical bonds are broken or reformed Examples: head to head, head to tail, tail to tail configuration in vinyl polymers stereoregular arrangement: cis- and trans-isomer, 1,2- and 1,4-addition, or d- and l-forms onformation: arrangements arising from rotation about single bonds In dilute solutions the molecules are in continuous motion and assume different conformations in rapid succession(random coils) In the solid state many polymers have typical conformations, such as folded chains and helical structures

3 ead to ead, ead to Tail R R R or l l l l

4 Stereoisomerism cis/trans Isomer cis cis-isoprene (natural rubber) bulky groups on same side of chain trans trans-isoprene (gutta percha) bulky groups on opposite sides of chain

5 Substitutional isomer R = 2 Optical isomer = 2 1,2-addition R 1,4-addition A A B D E E D B mirror plane

6 Tacticity stereoregularity of chain R R R R R R R R R R R R isotactic all R groups on same side of chain syndiotactic R groups alternate sides atactic R groups random

7 omopolymer ~ the structural units are identical opolymer ~more kinds of basic units(e.g. two or three) Alternating copolymer ~ considered as homopolymers with a composed structural unit Random copolymer ~ obtained from two or more monomers which are present simultaneously in one polymerization reactor Graft copolymer ~ a homopolymer is prepared first and in a second step one or more monomers are grafted onto this polymer the final product consists of a polymeric backbone with side branches Block copolymer ~ one monomer is polymerized, after which another monomer is polymerized on to the living ends of the polymeric chains the final product is a linear chain with a sequence of different segments

8 opolymers two or more monomers polymerized together random A and B randomly vary in chain alternating A and B alternate in polymer chain block large blocks of A alternate with large blocks of B graft chains of B grafted on to A backbone random alternating block A B graft

10 Polymer Blends Fig. A chronology of the discovery of polymers and their modification. [ourtesy of Prof. ans G. Fritz of IKT Stuttgart, Stuttgart, Germany]

11 Two Types of Plastics 1. Thermoplastics hemical structure remains unchanged during heating and shaping More important commercially, comprising more than 70% of total plastics tonnage 2. Thermosets Undergo a curing process during heating and shaping, causing a permanent change (called cross linking) in molecular structure Once cured, they cannot be remelted

15 Amorphous Polymer ~ below Tg, like ordinary inorganic glass hardness, stiffness, brittleness, transparency rystalline Polymer ~ crystallize below Tm, geometrically regular structure, strong, tough, stiff, more resistant to solvents and chemicals Glass Transition Temperature(Tg) ~ the temperature beginning the segmental motion ~ polymeric materials undergo a marked change in properties associated with the virtual cessation of local molecular motion Melting Temperature(Tm) ~ the temperature of disappearance of the last traces of polymer crystalline phase ~ material becomes a viscous liquid with discontinuous changes in density, refractive index, heat capacity, transparency and other properties

16 Melting vs. Glass Transition Temp. What factors affect T m and T g? Both T m and T g increase with increasing chain stiffness hain stiffness increased by 1. Bulky side groups 2. Polar groups or side groups 3. Double bonds or aromatic chain groups Regularity (tacticity) affects T m only

17 Polymer lassification: Terminology While we have chosen an applications perspective on polymer classification, many alternate schemes are widely used. These are usually composition/property specific, as opposed to applications oriented.

18 Polymer lassification: hemical lass A popular classification scheme amongst chemists is based on polymer functionality. Polyesters: poly(ethylene terephthalate) - Dacron Polyamides: poly(caprolactam) - nylon 6 O N O O Urethanes: carbamate linkages through reaction of diisocyanates and diols. N O O Another (!) classification scheme, again favored by chemists is based on differences between the polymer and constituent monomer(s). ondensation polymers: synthesis involves elimination of some small molecule ( 2 O in the preparation of nylon) Addition polymer: formed without loss of a small molecule i.e. ethylene polymerization to generate poly(ethylene)

19 Addition Polymerization Free radical polymerization (addition polymerization) R + R initiation free radical monomer (ethylene) R + R propagation dimer Initiator: example - benzoyl peroxide O O 2 O = 2 R

20 ondensation Polymerization Water is ondensed out during polymerization of Nylon Some of the original monomer s materials are shed (condensed out) during polymerization process Process is conducted in the presence of a catalyst Water, O 2 are commonly condensed out but other compounds can be emitted including N or other acids

21 엔지니어링플라스틱 (engineering plastics, EP) 구조용및기계부재에적합한고성능플라스틱으로서주로금속대체를목표로함 자동차부품이나, 기계부품, 전기, 전자부품과같은공업적용도에사용되는플라스틱 500 kgf/cm2(49mpa) 이상의인장강도, 100 o 이상의내열성을갖음 내열성이더욱높아 150 o 이상의고온에서도장기간사용할수있는것을슈퍼엔지니어링플라스틱 (super engineering plastics) 이라고함 엔지니어링플라스틱은범용엔지니어링플라스틱과슈퍼엔지니어링플라스틱으로분류됨 범용엔지니어링플라스틱중폴리아마이드 (PA), 폴리아세탈 (POM), 폴리카보네이트 (P), 폴리페닐렌옥사이드 (M-PPO), 폴리부틸렌테레프탈레이크 (PBT) 등 5 가지플라스틱을 5 대엔지니어링플라스틱이라부름 슈퍼엔지니어링플라스틱에는폴리이미드 (PI), 폴리설폰 (PSF), 폴리페닐렌설파이드 (PPS), 폴리아마이드이미드 (PAI), 폴리에테르설폰 (PES), 폴리에테르에테르케톤 (PEEK), 폴리에테르이미드 (PEI), 액정폴리에스테르 (LP), 폴리에테르케톤 (PEK) 등이있음

23 범용엔지니어링플라스틱의특징 수지장점단점 결정성수지 NYLON 강인성, 내약품성 내유성, 내마찰마모성 POM 내피로성, 강성내마찰마모성 PBT 내약품성, 내마모성 전기적특성, 내열성 비결정성수지 P 내충격성, 투명성 치수안정성 MPPO 성형성, 내충격성치수안정성, 내수성 흡습시치수변화성형시치수안정성 성형시치수안정성난연화곤란 GF 강화시이방성성형시치수안정성 내약품성내 Stress rack 성 내약품성내유성, 내열성

25 Additive lassification ( 첨가제분류 ): It is relatively rare for an article to be made from polymer alone. Most are polymer compounds, consisting of a mixture of polymer and various additives. These include:

26 1) 가소제 (plasticizer) non-volatile solvents added to improve flexibility 고분자물질에유동성을주어 plastic flow 를유발시켜가공을쉽게하고, 고분자의딱딱한정도를감소시켜유연성을증가시킴 (Tg 를낮춤 ) 첨가제수요의가장큰부분을차지함 가소제의요구조건 1 고분자물질과잘섞여서균일한상을이루어야함 2 유리전이온도가낮아야함 3 확산에의해고분자밖으로배출되지않아야함 4 가공시휘발을억제하기위해비점이 300 o 이상이되어야함 Dialkyl phthalates in poly(vinylchloride), Dioctyl phthalate (DOP) MW : 390, bp : 384 o, mp : -50 o, 용해도지수 (δ) : 7.9 저렴하면서가소성이좋기때문에유연한 PV 를제조하는데널리사용됨 Nylon, acryl 계고분자 물이가소제 가소제첨가에따른기계적물성유리전이온도 ( ), 용융점 ( ), 인장강도 ( ), 탄성율 ( ), 연신율 ( ), 충격강도 ( )

27 2) Fillers: solid additives used to modify physical properties. 기계적강도, 치수안정성, 열변형온도, 견고도등의물리적성질을증가시키거나, 수지의가격을낮추고, 가공성을향상시키기위하여첨가하는물질 1 충전제 (filler) : 기계적강도를크게감소하지않고비용감소를목적으로하는경우 2 강화제 (reinforcement) : 기계적성질 ( 탄성율, 인장강도등 ) 및다른물리적성질의보강을주목적으로하는경우 사용예 흑연, 카본블랙, 금속류등 : 성형수축을감소시키거나정전기를최소화하기위함 카본블랙, 실리카 : 강도, 마모저항성등과같은기계적물성을향상시키기위함 Dilution - talc Reinforcing - carbon black in tires Toughening - rubber in ABS plastic 충전제와고분자 matrix 간의계면접착은좋은충전효과를위하여매우중요함

28 섬유강화수지 (Fiber Reinforced Plastics, FRP) 섬유를보강재로사용하여강도를향상시킨수지 밀도가낮음 비강도 (specific strength) 가높음 응용분야 : fishing rods, tennis racket, skis, aircraft fiber 로사용하는물질 : glass, graphite, boron, Kevla 등수지로사용하는물질 : 불포화폴리에스터, PBT, Nylon66, polycarbonate 등 복합재료 (composite materials) FRP 의경우보다섬유의사용량을 60~70 % 까지증가시킴으로써수지와섬유간의물성들이복합적으로결합되어보다개선된물성을갖도록가공된소재

29 3) Light Stabilizer ( 광안정제 ): prevent plastics from discoloration and degradation due to be exposed to sunshine and UV light 자외선안정제 자외선은 200~300 nm 의파장을지닌광선으로, 고분자사슬의공유결합을깨뜨리기에충분하므로, 자유라디칼반응을일으켜고분자를분해시킴 이를방지하기위하여자외선을흡수하는유기화합물 (benzophenone 등 ) 이사용됨 벤조페논은 UV 영역에서높은흡광계수를가지며, 흡수된방사에너지를화학적인변화없이열로전환시킴 4) Antioxidants( 산화방지제 ): compounds that reduce polymer degradation through intervention in free radical reactions 성형공정이나사용중에열또는다른물리적자극에의하여분해되어생성된자유라디칼의산화반응을억제하기위하여사용되는첨가제 5) 열안정제열에의한분해반응을억제하기위하여첨가되는물질 ( 납, barium, cadmium, 유기인화합물등이사용됨 )

30 6) Flame Retardant ( 난연제 ): keep safety from fire accident 대부분의고분자는탈때많은유해한물질을배출하므로고분자에난연성을부여하는것이요구됨 (TV, 라디오, 카펫, 커튼등 ) 예 ) 유기염화물, 유기브로민화합물, 유기인산, 안티모니산화물, 보론화합물등 7) ompatibilizer ( 상용화제 ) 계면접착력과상용성을향상시키기위하여첨가되는물질 많은고분자들은서로불용성이기떄문에가공중에상분리를일으킴 이러한불용성블렌드는분산상과매트릭스사이의취약한계면결합력으로기계적물성이떨어짐 8)Antistatic agent( 대전방지제 ): dust attraction free, discharge from damage the electronic chips and spark discharge from danger of fire and explosions 9) Lubricants( 윤활제 ): beneficial effect on dispersion of filler, mold release property 10)olorants: additives used to change product aesthetics Pigments - soluble colorants Dyestuffs - insoluble additives

POLYMER STRUCTURES ISSUES TO ADDRESS...

POLYMER STRUCTURES ISSUES TO ADDRESS... POLYMER STRUTURES ISSUES TO ADDRESS... What are the basic microstructural features? ow are polymer properties effected by molecular weight? ow do polymeric crystals accommodate the polymer chain? Melting