I Introduction 2.Write the name and structure of the monomers that are required to synthesize the following polymers.Please write the IUPAC name of each polymer. 3.Please discuss the importance of plastic recycling. (a) (b) (c) CN CH2CH2CH3 n CN (d) (e) 2) (h) References 1.J.Brandrup,E.H.Immergut,E.A.Grulke,A.Abe,D.R.Bloch,Polymer Handbook,4th edn. (Wiley,New York,2005) 2.R.W.Lenz,Organic Chemistry of Synthetic High Polymers.(Wiley-Interscience,New York, 1967) 3.M.P.Stevens,Polymer Chemistry,3rd edn.(Oxford University,Oxford,1999) 4.G.Odian,Principles of Polymerization,4th edn.(Wiley-Interscience,New York,2004)
2. Write the name and structure of the monomers that are required to synthesize the following polymers. Please write the IUPAC name of each polymer. 3. Please discuss the importance of plastic recycling. References 1. J. Brandrup, E.H. Immergut, E.A. Grulke, A. Abe, D.R. Bloch, Polymer Handbook, 4th edn. (Wiley, New York, 2005) 2. R.W. Lenz, Organic Chemistry of Synthetic High Polymers. (Wiley-Interscience, New York, 1967) 3. M.P. Stevens, Polymer Chemistry, 3rd edn. (Oxford University, Oxford, 1999) 4. G. Odian, Principles of Polymerization, 4th edn. (Wiley-Interscience, New York, 2004) 8 1 Introduction
Chapter 2 Polymer Size and Polymer Solutions The size of single polymer chain is dependent on its molecular weight and mor- phology.The morphology of a single polymer chain is determined by its chemical structure and its environment.The polymer chain can be fully extended in a very dilute solution when a good solvent is used to dissolve the polymer.However,the single polymer chain is usually in coil form in solution due to the balanced interactions with solvent and polymer itself.We will discuss the size of polymer first,and then go to the coil formation in the polymer solution. 2.1 The Molecular Weight of Polymer The molecular weight of polymer determines the mechanical properties of poly- mers.To have strong durable mechanical properties,the polymer has to have molecular weight much larger than 10,000 for structural applications.However, for thin film or other special application,low molecular weight polymer or oli- gomer sometime is adequate.As shown in Fig.2.1,above (A),strength increases rapidly with molecular weight until a critical point (B)is reached.Mechanical strength increases more slowly above (B)and eventually reaches a limiting value (C).High molecular weight polymer has high viscosity and poor processability. The control of molecular weight and molecular weight distribution (MWD)is often used to obtain and improve certain desired physical properties in a polymer product. Polymers,in their purest form,are mixtures of molecules of different molecular weights.The reason for the polydispersity of polymers lies in the statistical variations present in the polymerization processes.The above statement is true for common polymerization reaction such as free radical chain polymerization,step polymeri- zation,etc.However,cationic or anionic chain polymerization as so called living polymerization has small MWD.Low dispersity can also be obtained from emulsion polymerization,and new polymerization techniques such as living free radical polymerization including nitroxide-mediated polymerization(NMP),atom transfer radical polymerization (ATRP),and reversible addition-fragmentation chain W.-F.Su,Principles of Polymer Design and Synthesis, 9 Lecture Notes in Chemistry 82,DOI:10.1007/978-3-642-38730-2_2, Springer-Verlag Berlin Heidelberg 2013
Chapter 2 Polymer Size and Polymer Solutions The size of single polymer chain is dependent on its molecular weight and morphology. The morphology of a single polymer chain is determined by its chemical structure and its environment. The polymer chain can be fully extended in a very dilute solution when a good solvent is used to dissolve the polymer. However, the single polymer chain is usually in coil form in solution due to the balanced interactions with solvent and polymer itself. We will discuss the size of polymer first, and then go to the coil formation in the polymer solution. 2.1 The Molecular Weight of Polymer The molecular weight of polymer determines the mechanical properties of polymers. To have strong durable mechanical properties, the polymer has to have molecular weight much larger than 10,000 for structural applications. However, for thin film or other special application, low molecular weight polymer or oligomer sometime is adequate. As shown in Fig. 2.1, above (A), strength increases rapidly with molecular weight until a critical point (B) is reached. Mechanical strength increases more slowly above (B) and eventually reaches a limiting value (C). High molecular weight polymer has high viscosity and poor processability. The control of molecular weight and molecular weight distribution (MWD) is often used to obtain and improve certain desired physical properties in a polymer product. Polymers, in their purest form, are mixtures of molecules of different molecular weights. The reason for the polydispersity of polymers lies in the statistical variations present in the polymerization processes. The above statement is true for common polymerization reaction such as free radical chain polymerization, step polymerization, etc. However, cationic or anionic chain polymerization as so called living polymerization has small MWD. Low dispersity can also be obtained from emulsion polymerization, and new polymerization techniques such as living free radical polymerization including nitroxide-mediated polymerization (NMP), atom transfer radical polymerization (ATRP), and reversible addition–fragmentation chain W.-F. Su, Principles of Polymer Design and Synthesis, Lecture Notes in Chemistry 82, DOI: 10.1007/978-3-642-38730-2_2, Springer-Verlag Berlin Heidelberg 2013 9
0 2 Polymer Size and Polymer Solutions Fig.2.1 Dependence of mechanical strength on polymer molecular weight [1] A Molecular weight transfer polymerization(RAFT).The chemistry of different polymerization reac- tions will be discussed in detail in the subsequent chapters. Number-average molecular weight (M)is total weight (W)of all the molecules in a polymer sample divided by the total number of molecule present,as shown in Eq.2.1,where N is the number of molecules of size M,N,is number(mole) fraction of size Mx Mn=W/∑Nx=∑NxMr/∑Nx=∑NMr (2.1) Analytical methods used to determine Mn include (1)Mn<25,000 by vapor pressure osmometry,(2)Mn 50,000-2 million by membrane osmometry,and (3) M<50,000 by end group analysis,such as NMR for-C=C;titration for car- boxylic acid ending group of polyester.They measure the colligative properties of polymer solutions.The colligative properties are the same for small and large molecules when comparing solutions at the same mole fraction concentration. Therefore,the Mn is biased toward smaller sized molecules.The detailed mea- surement methods of molecular weight will be discussed in Sect.2.3.Weight- average molecular weight is defined as Eq.2.2,where Wx is the weight fraction of Mr molecules,Cr is the weight concentration of Mr molecules,and C is the total weight concentration of all of the polymer molecules,and defined by Egs.2.3-2.5. Mw=∑WMx=∑CxMx/∑Cx (2.2) Wx=Cx/C (2.3) Cx=N M (2.4) C=∑Cx=ΣNMx (2.5) Light scattering is an analytical method to determine the M in the range of 10,000-10,000,000.It unlike colligative properties shows a greater number for larger sized molecules than for small-sized molecules.Viscosity-average molec- ular weight (M)is defined as Eq.2.6,where a is a constant.The viscosity and
transfer polymerization (RAFT). The chemistry of different polymerization reactions will be discussed in detail in the subsequent chapters. Number-average molecular weight Mð Þn is total weight (W) of all the molecules in a polymer sample divided by the total number of molecule present, as shown in Eq. 2.1, where Nx is the number of molecules of size Mx, Nx is number (mole) fraction of size Mx M n ¼ W=RNx ¼ R NxMx=RNx ¼ R NxMx ð2:1Þ Analytical methods used to determine M n include (1) M n \25,000 by vapor pressure osmometry, (2) M n 50,000–2 million by membrane osmometry, and (3) M n \50,000 by end group analysis, such as NMR for –C=C; titration for carboxylic acid ending group of polyester. They measure the colligative properties of polymer solutions. The colligative properties are the same for small and large molecules when comparing solutions at the same mole fraction concentration. Therefore, the M n is biased toward smaller sized molecules. The detailed measurement methods of molecular weight will be discussed in Sect. 2.3. Weightaverage molecular weight is defined as Eq. 2.2, where Wx is the weight fraction of Mx molecules, Cx is the weight concentration of Mx molecules, and C is the total weight concentration of all of the polymer molecules, and defined by Eqs. 2.3–2.5. M w ¼ R WxMx ¼ R CxMx=RCx ð2:2Þ Wx ¼ Cx=C ð2:3Þ Cx ¼ NxMx ð2:4Þ C ¼ R Cx ¼ R NxMx ð2:5Þ Light scattering is an analytical method to determine the M w in the range of 10,000–10,000,000. It unlike colligative properties shows a greater number for larger sized molecules than for small-sized molecules. Viscosity-average molecular weight Mð Þv is defined as Eq. 2.6, where a is a constant. The viscosity and Fig. 2.1 Dependence of mechanical strength on polymer molecular weight [1] 10 2 Polymer Size and Polymer Solutions
2.1 The Molecular Weight of Polymer 11 weight average molecular weights are equal when a is unity.My is like M,it is greater for the larger sized polymer molecules than for smaller ones. M=[EMEW:]e=[EN.M+/EN.M.]a (2.6) A measure of the polydispersity in a polymer is defined as Mw divided over M (M/M).For a polydispersed polymer,Mw>M>M with the differences between the various average molecular weights increasing as the molecular-weight distribution (MWD)broadens,as shown in Fig.2.2. For example,consider a hypothetical mixture containing 95%by weight of molecules of molecular weight 10,000,and 5%of molecules of molecular weight 100.The M and Mw are calculated from Egs.2.1 and 2.2 as 1,680 and 9,505, respectively.The use of the M value of 1,680 gives an inaccurate indication of the properties of this polymer.The properties of the polymer are determined primarily by the molecules with a molecular weight of 10,000 that makes up 95 of the weight of the mixture.The highest fraction of molecular weight of molecule will contribute the most toward the bulk property.It is desirable to know the molecular weight distribution,then to predict the polymer properties.At present, the gel permeation chromatography (GPC)technique has been advanced to be able to easily measure MM,M,simultaneously and calculate PDI using only one sample.All the measurements of molecular weight of polymers are carried out using polymer solutions.Therefore,the accuracy of molecular weight measure- ment is dependent on the behavior of polymer solution.Usually,a calibration curve is established first using a specific polymer dissolving in a specific solvent. Polystyrene standard dissolved in tetrahydrofuran(THF)is the most popular cal- ibration curve used in GPC.If the measured polymer exhibits different behavior in THF from that of polystyrene,then a deviation from the actual molecular weight is occurred.For example,a conducting polymer,poly (phenylene vinylene),con- taining rigid rod molecular structure shows a higher molecular weight when the standard of coil structured polystyrene is used.More detailed discussion of GPC is in Sect.2.3. Fig.2.2 Distribution of molecular weights in a typical Mo polymer sample [1] M Molecular weight,M
weight average molecular weights are equal when a is unity. M v is like M w, it is greater for the larger sized polymer molecules than for smaller ones. M v ¼ R Ma xWx 1=a ¼ R NxMaþ1 x =RNxMx 1=a ð2:6Þ A measure of the polydispersity in a polymer is defined as M w divided over M n M w=M ð Þn . For a polydispersed polymer, M w [M v [M n with the differences between the various average molecular weights increasing as the molecular-weight distribution (MWD) broadens, as shown in Fig. 2.2. For example, consider a hypothetical mixture containing 95 % by weight of molecules of molecular weight 10,000, and 5 % of molecules of molecular weight 100. The M n and M w are calculated from Eqs. 2.1 and 2.2 as 1,680 and 9,505, respectively. The use of the M n value of 1,680 gives an inaccurate indication of the properties of this polymer. The properties of the polymer are determined primarily by the molecules with a molecular weight of 10,000 that makes up 95 % of the weight of the mixture. The highest % fraction of molecular weight of molecule will contribute the most toward the bulk property. It is desirable to know the molecular weight distribution, then to predict the polymer properties. At present, the gel permeation chromatography (GPC) technique has been advanced to be able to easily measure M n; M v; M w; simultaneously and calculate PDI using only one sample. All the measurements of molecular weight of polymers are carried out using polymer solutions. Therefore, the accuracy of molecular weight measurement is dependent on the behavior of polymer solution. Usually, a calibration curve is established first using a specific polymer dissolving in a specific solvent. Polystyrene standard dissolved in tetrahydrofuran (THF) is the most popular calibration curve used in GPC. If the measured polymer exhibits different behavior in THF from that of polystyrene, then a deviation from the actual molecular weight is occurred. For example, a conducting polymer, poly (phenylene vinylene), containing rigid rod molecular structure shows a higher molecular weight when the standard of coil structured polystyrene is used. More detailed discussion of GPC is in Sect. 2.3. Fig. 2.2 Distribution of molecular weights in a typical polymer sample [1] 2.1 The Molecular Weight of Polymer 11
12 2 Polymer Size and Polymer Solutions 2.2 Polymer Solutions Polymer solutions occur in two stages.Initially,the solvent molecules diffuse through the polymer matrix to form a swollen,solvated mass called a gel.In the second stage,the gel breaks up and the molecules are dispersed into a true solu- tion.Not all polymers can form true solution in solvent. Detailed studies of polymer solubility using thermodynamic principles have led to semi-empirical relationships for predicting the solubility [2].Any solution process is governed by the free-energy relationship of Eq.2.7: △G=△H-T△S (2.7) When a polymer dissolves spontaneously,the free energy of solution,AG,is negative.The entropy of solution,AS,has a positive value arising from increased conformational mobility of the polymer chains.Therefore,the magnitude of the enthalpy of solution,AH,determines the sign of AG.It has been proposed that the heat of mixing,AHmir,for a binary system is related to concentration and energy parameters by Eq.2.8: △Hnmt= )”-() (2.8) where Vmir is the total volume of the mixture,Vi and V2 are molar volumes (molecular weight/density)of the two components,0 and 02 are their volume fractions,and AE and AE2 are the energies of vaporization.The terms AE1/Vi and AE2/V2 are called the cohesive energy densities.If(AE/V)is replaced by the symbol the equation can be simplified into Eq.2.9: △Hmir=Vmr(61-62)）20102 (2.9) The interaction parameter between polymer and solvent can be estimated from △Hmix as: u-导画-r (2.10) The symbol 6 is called the solubility parameter.Clearly,for the polymer to dissolve (negative AG),AHmir must be small;therefore,(1-62)2must also be small.In other words,61 and 62 should be of about equal magnitude where 1=62,solubility is governed solely by entropy effects.Predictions of solubility are therefore based on finding solvents and polymers with similar solubility parameters,which requires a means of determining cohesive energy densities. Cohesive energy density is the energy needed to remove a molecule from its nearest neighbors,thus is analogous to the heat of vaporization per volume for a
2.2 Polymer Solutions Polymer solutions occur in two stages. Initially, the solvent molecules diffuse through the polymer matrix to form a swollen, solvated mass called a gel. In the second stage, the gel breaks up and the molecules are dispersed into a true solution. Not all polymers can form true solution in solvent. Detailed studies of polymer solubility using thermodynamic principles have led to semi-empirical relationships for predicting the solubility [2]. Any solution process is governed by the free-energy relationship of Eq. 2.7: DG ¼ DH TDS ð2:7Þ When a polymer dissolves spontaneously, the free energy of solution, DG, is negative. The entropy of solution, DS, has a positive value arising from increased conformational mobility of the polymer chains. Therefore, the magnitude of the enthalpy of solution, DH, determines the sign of DG. It has been proposed that the heat of mixing, DHmix, for a binary system is related to concentration and energy parameters by Eq. 2.8: DHmix ¼ Vmix DE1 V1 1=2 DE2 V2 1=2 " #2 ;1;2 ð2:8Þ where Vmix is the total volume of the mixture, V1 and V2 are molar volumes (molecular weight/density) of the two components, ;1 and ;2 are their volume fractions, and DE1 and DE2 are the energies of vaporization. The terms DE1=V1 and DE2=V2 are called the cohesive energy densities. If ðDE=VÞ 1=2 is replaced by the symbol d, the equation can be simplified into Eq. 2.9: DHmix ¼ Vmixðd1 d2Þ 2 ;1;2 ð2:9Þ The interaction parameter between polymer and solvent can be estimated from DHmix as: v12 ¼ V1 RT ðd1 d2Þ 2 ð2:10Þ The symbol d is called the solubility parameter. Clearly, for the polymer to dissolve (negative DG), DHmix must be small; therefore, ðd1 d2Þ 2 must also be small. In other words, d1 and d2 should be of about equal magnitude where d1 ¼ d2, solubility is governed solely by entropy effects. Predictions of solubility are therefore based on finding solvents and polymers with similar solubility parameters, which requires a means of determining cohesive energy densities. Cohesive energy density is the energy needed to remove a molecule from its nearest neighbors, thus is analogous to the heat of vaporization per volume for a 12 2 Polymer Size and Polymer Solutions