Chapter 1 Introduction

Transcription

1 hapter 1 Itroductio Sythetic polymers [1] are vital materials used i moder daily life from packagig, electroics, medical devices, clothig, vehicles, buildigs, etc., due to their ease of processig ad light weight. The first sythetic polymer, a pheol-formaldehyde resi, was iveted i the early 1900s by Leo Baekelad [2]. It was a commercial success ivetio although most of scietists had o clear cocept of polymer structure at that time. Wallace arothers iveted very importat polymers of eopree rubber ad Nylo i 1930s which shaped the leadership of DuPot i polymer idustry. Herma Staudiger developed theoretical explaatios of remarkable properties of polymers by ordiary itermolecular forces betwee molecules of very high molecular weight. He was awarded the Nobel Prize i hemistry i 1953 for this outstadig cotributio. World War II led to sigificat advaces i polymer chemistry with the developmet of sythetic rubber as atural rubber was ot accessible to the Allies. Karl Ziegler ad Giulio Natta wo the Nobel Prize i hemistry i 1963, joitly for the developmet of coordiatio polymerizatio to have cotrolled stereochemistry of polymers usig coordiatio catalysts. Their work has revolutioized the polymer idustry to sythesize stereoregular polymers that have mechaical properties superior tha that of o-stereoregular polymers. Equally sigificat work was doe by Paul Flory 1974, Nobel laureate o the quatitative ivestigatios of polymer behaviors i solutio or i bulk. Most of polymers are isulators, so they have passive fuctios ad used as a bulk material for structure or as thi layer for coatig barrier. I 1977, Ala Heeger, Ala MacDiarmid, ad Hideki Shirakawa reported high coductivity i iodie-doped polyacetylee. This research eared them the 2000 Nobel Prize i hemistry. Sice the, the applicatio of polymer has expaded ito active fuctioal area such as light emittig diode, sesor, solar cell, etc. Polymers ca be tailor made to meet the requiremets of specific applicatio through molecular desig ad sythesis. Therefore, they have become the material of choice to face the ever fast chagig world from electroics to medical applicatios. The physical properties of polymers are maily determied by their chemical structures. hemical structures of polymers affect their flow ad morphology that results i differet physical properties. The processability of polymers is cotrolled W.-F. Su, Priciples of Polymer Desig ad Sythesis, Lecture Notes i hemistry 82, DI: / _1, Ó Spriger-Verlag Berli Heidelberg

2 2 1 Itroductio Fig. 1.1 hemical structures of (a) moomers ad (b) their correspodig polymers by their flow characteristics i eat form or i solutio which affects by their molecular weight. Polymers are built up by likig together of large umber of moomers. Moomers are small molecules with fuctioal groups (orgaic compouds) ad they ca react with each other to form a large molecule. Figure 1.1 shows some commoly used polymers with their chemical structures of moomers ad their correspodig polymers. The polymers have to have molecular weight larger tha 10,000 to exhibit good mechaical properties for structural use. ligomer is a molecule that has molecular weight betwee 1,000 ad 10,000. The oligomer has bee widely used i coatig applicatios. Ed group is the chemical structure at the ed of the polymer chais. Whe the polymer is eded with a fuctioal group, such as H 2 [H 2 H 2 ] H=H 2, the polymer is called telechelic polymer. I the same way, reactive oligomer is oligomer that cotais ed groups ad capable to udergo polymerizatio. The size of polymer is determied by the degree of polymerizatio (DP). It is a total umber of structural uits, icludig ed groups, ad is related to both chai legth ad molecular weight. For example, the molecular weight of polymethacrylate with DP = 500 is 500 multiplyig by 74 (weight of uit) = 37,000. Because polymer chais withi a give polymer sample are always of varyig legths, we eed to use average value, such as umber-average molecular weight ðm Þ, weight-average molecular weight ðm w Þ, etc. The molecular weight distributio (PDI) is defied as dividig M w over M.

3 1.1 Types of Polymers 3 Fig. 1.2 Possible arragemets of repeatig uits to form differet type polymers 1.1 Types of Polymers There are may differet types of polymers that ca be differetiated from the arragemet of repeatig uits, ad the differet arragemets of molecular segmet [3]. A polymer prepared from oe kid of moomer is called homopolymer. A polymer prepared from more tha oe kid of moomer is called copolymer, icludig radom copolymer, alteratig copolymer, block copolymer, ad graft copolymer (Fig. 1.2). These homopolymer ad copolymers also ca be prepared ito polymers with differet arragemet of molecular segmet, such as star polymer, comb polymer, ladder polymer, dedrimer, ad so o. (Fig. 1.3). 1.2 Types of Polymerizatio The types of polymerizatios are geerally classified ito chai polymerizatio ad step polymerizatio accordig to chemical reactios i the polymerizatio [4]. The molecular weight of polymers ca be built either gradually by step reactios or simultaeously by chai reactio depedig o the chemical structure of the moomer. For the step polymerizatio, the moomers eed to have bifuctioal groups to lik 1 molecule at oe time. If the bifuctioal groups are the same such as ethylee glycol (H H 2 H 2 H), oe will eed differet type of bifuctioal moomer such as terephthalic acid (H 6 H 4 H) to sythesize polyester [ H 2 H 2 (=) 6 H 4 (=) ] at relative high temperature to remove water. This type of polymerizatio is also called polycodesatio polymerizatio due to the loss of molecule durig the polymerizatio. The moomers cotaiig double bod ca be polymerized by chai reactio. The polymerizatio proceeds by three steps of iitiatio, propagatio, ad termiatio. Depedig o the type of iitiatio, the chai polymerizatio ca be classified ito free radical chai polymerizatio, ioic chai polymerizatio, ad

4 4 1 Itroductio Fig. 1.3 Possible arragemets of molecular segmet to form differet type polymers: (a) liear polymer, (b) brached polymer, (c) crossliked polymer, (d) star polymer, (e) comb polymer, (f) ladder polymer, (g) polyrotaxae, (h) polycateae, (i) dedrimer coordiatig chai polymerizatio. Their priciples will be addressed i the subsequet chapters. opolymers are made from more tha oe kid of moomer to meet balaced properties required i may differet applicatios. The differeces i the reactivity of differet moomer ad growig polymer chai eed to be cosidered i the sythesis of copolymer. We will also discuss this subject i the later chapter. Rig opeig polymerizatio has bee extesively used i sythesis of polyether, polyamide, polysiloxae, ad the curig of the epoxy resi. The reactio mechaism of rig opeig polymerizatio is uique i its ow way which shows a combiatio behavior of step polymerizatio ad chai polymerizatio. The detailed reactio mechaism will be preset i the last chapter of this book. 1.3 Nomeclature of Polymers The omeclature of polymers [1, 3] is usually based o the source of moomer, for example, poly(viyl chloride) (H 2 Hl) is made from viyl chloride moomer, ad poly(e-caprolacto) [NH (H 2 ) 5 ], that is the same as poly (6-amiocaproic acid), is made from e-caprolacto. May polymers commoly are amed basis o their structures such as poly (hexamethylee sebacamide) [HN (H 2 ) 6 NH (H 2 ) 8 ], poly(ethylee terephthalate) [ H 2 H 2 6 H 5 ], ad poly(trimethylee ethylee urethae) [ H 2 H 2 H 2 NH H 2 H 2 NH ].

5 1.3 Nomeclature of Polymers 5 Table 1.1 ompariso betwee commo ame ad IUPA ame of polymers Structure ommo ame IUPA ame (H 2 H 2 ) polyethylee poly(methylee) (H( ) H 2 ) polypropylee poly(propylee) (H( 6 H 5 ) H 2 ) polystyree poly(1-pheyl ethylee) The Iteratioal Uio of Pure ad Applied hemistry (IUPA) polymer omeclature system is a more systematic approach. The basis of the IUPA polymer omeclature system is the selectio of a preferred RU (costitutioal repeatig uit), i.e., structural repeatig uit, as tabulated i Table 1.1. The ame is made accordig to the seiority amog the atoms or subuits makig up the RU. The steps icludig (1) RU is idetified, (2) substituet groups o the backboe are assiged the lowest possible umber, ad (3) the ame is placed i paretheses ad prefixed with poly. For the copolymers, they are amed accordig to the arragemets of the repeatig uits i copolymers. For example, for a copolymer that cosists of polystyree ad poly(methyl methacrylate), this copolymer ca be abbreviated as either poly[styree-co-(methyl methacrylate)] or copoly(styree/methyl methacrylate). For a alteratig copolymer, a abbreviatio of alt ca be placed betwee these two homopolymers, as poly[styree-alt-(methyl methacrylate)]. Therefore, the alt is replaced by block ad graft that ca represet the block copolymer [polystyree-block-poly(methyl methacrylate)] ad graft copolymer [polystyreegraft-poly(methyl methacrylate)], respectively. The source-based omeclature system is still oe of choices i the polymer commuity, although the importat referece sources such as hemical Abstracts ad Polymer Hadbook have adopted the IUPA system. Polymers used i busiess for log time usually have their ow trade ame, due to sometimes a polymer amed by IUPA ame is ot read easily ad too log to use Polycarboate H 3 H H 2 H H 2 H 2 HH 2 H 2 H H 2 Epoxy Resi Fig. 1.4 hemical structures of polycarboate ad epoxy resi

6 6 1 Itroductio Table 1.2 Represetative polymers used i moder society ommo ame Abbreviatio hemical structure Polyethylee PE Polypropylee PP H 2 H 2 H 2 H Poly(viyl chloride) Poly(ethylee terephthalate) Polystyree PV PET PS H 2 H l H 2 H 2 H 2 H Pheol formaldehyde oe H H 2 Polyisopree PI Polyacryloitrile PAN Poly(viyl acetate) PVA Poly(methyl methacrylate) PMMA Polycaprolactam Nylo 6 Polycarboate P Poly(3-hexyl thiophee) P3HT H 2 H 3 H 2 H H 2 H N H 2 H H 2 NH(H 2 ) 5 6 H 13 S

7 1.3 Nomeclature of Polymers 7 Table 1.3 Recyclig codes of plastics [3] Number Letters Plastic 1 PET Poly(ethylee terephthalate) 2 HDPE High desity polyethylee 3 V or PV Poly(viyl chloride) 4 LDPE Low desity polyethylee 5 PP Polypropylee 6 PS Polystyree 7 THER thers or mixed plastics coveietly. For example, IUPA ame for polycarboate is poly(oxy carboyl oxy -1,4-pheylee-isopropylidee -1,4-pheylee) ad the repeatig uit is [ 6 H 4 ( ) 2 6 H 4 ]. Bispheol A epoxy resi has a IUPA ame of 4,4 0 -dimethoxy oxirae -2,2-dipheyl propae. Figure 1.4 shows the chemical structures of polycarboate ad bispheol A epoxy resi. Table 1.2 orgaizes some represetative polymers i moder society with their commo ame, abbreviatio, ad chemical structure accordig to the amout of usage. Their sythesis ad properties will be discussed throughout this text book. The abbreviated ame of polymer has bee adapted for subsequet chapter for simplicity. 1.4 Polymer Recyclig Polymer recyclig [3] is a importat matter beig carried out worldwide to reduce pollutio ad coserve material. Poly(ethylee terephthalate) (PET) ad high desity polyethylee (HDPE) share more tha 70 % of the demad for recycled plastics. The recyclig idustry sometime ecouters ecoomic difficulties because most virgi plastics are ot oly of better quality tha their recycled couterparts, but are ofte less expesive. I Taiwa, the majority of used plastics are bured as fuel or pyrolyzed to make fuel. The Society of the Plastics Idustry (SPI) of USA has adopted plastic recyclig codes to be used iteratioally as show i Table 1.3, so the recycled polymers ca be sorted accordig to their code before they are used as raw materials for specific applicatios. 1.5 Problems 1. Write a cocise defiitio of each term listed below, usig examples as appropriate, (a) polymer, (b) moomer, (c) fuctioal group, (d) oligomer, (e) telechelic polymer, (f) degree of polymerizatio, (g) molecular weight distributio, (o) copolymer, (p) chai polymerizatio, (q) step polymerizatio.

8 8 1 Itroductio 2. Write the ame ad structure of the moomers that are required to sythesize the followig polymers. Please write the IUPA ame of each polymer. 3. Please discuss the importace of plastic recyclig. Refereces 1. J. Bradrup, E.H. Immergut, E.A. Grulke, A. Abe, D.R. Bloch, Polymer Hadbook, 4th ed. (Wiley, New York, 2005) 2. R.W. Lez, rgaic hemistry of Sythetic High Polymers. (Wiley-Itersciece, New York, 1967) 3. M.P. Steves, Polymer hemistry, 3rd ed. (xford Uiversity, xford, 1999) 4. G. dia, Priciples of Polymerizatio, 4th ed. (Wiley-Itersciece, New York, 2004)