结构与性能12_273909919

1.2 Configuration of Macromolecules Topic 1 • Configurational Isomerism • Fischer Projection • R/S Nomenclature for Configurational Isomers • Tacticity • Characterization of Tacticity in Real Polymers Average Tacticity Average Sequence Length To raise two questions ? Isotactic or syndiotactic ? C R H C CO O R H R H C O R H C C C R H R H C R H C CC C R H C R H C C C R HR H R H R H R H Isotactic or syndiotactic ? What does configuration mean ?? Configuration means different types of atoms or atomic groups in their steric relationship for a certain constitution For a certain constitution means for a certain chemical composition a certain linking sequence and a certain linking type Steric relationship means: C = C HH CH3 CH3 C =C H CH3 CH3 H cis trans C Cl H3C H C2 H5 C Cl H5C2 H CH3 counterclockwise clockwise not their position Configurational Isomerism double bond origin asymmetric center chiral molecule propadiene derivative phenylbenzene derivative H Cl C C CH Cl C C C H Cl H Cl COOH COOH NO2 NO2 COOH NO2 COOH NO2 phenylbenzene derivative Note：a, the internal rotation round the single bond can not take b, the two rings are perpendicular each other c, no symmetry elements exist in this kind of molecules Can we use Fischer Projection to describe the configuration of macromolecules ?? Fischer Projection Rules for 1 C* molecule ClH CH3 C2H5 CH3 C2H5 HCl a, the cross curve replaces the tetrahedron b, the cross point replaces the asymmetric carbon c, the horizontal line replaces the two bonds pointing forward d, the vertical line replaces the two bonds pointing backward e, the vertical line also replaces a carbon chain C Fischer Projection Rules for 2 C* molecule C1* C2* H OH H COOH COOH OH COOH COOH OH OH H H a, the C* projection should be taken one by one b, while taking the C1* projection, put COOH and C2* on the vertical line c, while taking the C2* projection, put COOH and C1* on the vertical line Pointing forward Pointing backward Fischer Projection Rules for 3 C* molecule H CH2OH OHC3* C1* H OH CHO HHO C2* CHO CH2OH OH OH OH H H H CHO CH2OH OH H OH H HO H stereo scheme Fischer projection direct projection a, while projecting C1*, put the light in front of this paper b, while projecting C2*, put the light on the back of this paper c, while projecting C3*, put the light in front of this paper again Fischer Projection can describe the configuration quite clear, but not for macromolecules Can we use R/S system to describe the configuration of macromolecules ?? R/S System Rule A, Number the atoms or groups linked with C* from 1 to 4 based on the atomic number of the atom bonded with C* a, “1” the lowest atomic number, “4” the highest one b, based on the atomic number of the second atom linked with C* indirectly c, consider C=A as , C B as A C A B C B B B, Circling and naming based on the serial number : a, Put the “1” atom far away from the observer b, Circling from “4” to “2” : clockwise R, counterclockwise S HHO CH3 CH2 CH3 ② ①④ ③ HHO CH3 C2H5 R HHO C2H5 CH3 S R/S System for 1C* R/S System for 2C* meso 2R,3S -m- tartaric acid S S C1* C2* HO H H COOH COOH OH COOH COOH H OH HO H racemic (－) 2S,3S (－) tartaric acid COOH COOH OH OH H H C1* C2* H OH H COOH COOH OH R S R R C1* C2* H OH HO COOH COOH H COOH COOH OH H H HO racemic (＋) 2R,3R (+) tartaric acid R/S system can describe the configuration of organic compound, but not for macromolecules. Why ? Reason 1: too many configurational isomers a a b d a a b b d d a a b b d d b d a a b b d d b d b d d d d d d d d d d d d b b b b b b b b b b b Pseudo asymmetric carbon atom R R R R R S S SS S S Reason 2: reversal of configuration What kind of method can describe the configuration of macromolecules ? No method ! Why ? For organic molecules, the subject of configuration means: to distinguish their configurational isomers, to name each of the isomers, to separate them one another. Because different configurational isomer has different property and different use. For macromolecules, people can not distinguish their configurational isomers, can not name them, can not separate them, there are no relationships between properties and isomers, there are relationships between properties and tacticity. Therefor, the subject of configuration for polymer means: to determine the types of ideal tactic configurations, to characterize the configurational tacticity in real polymers. Relationship between properties and tacticity of macromolecules polymer crystallinity Tm (℃) Tg (℃) ρ 103(kg/m3) at-PMMA it-PMMA st-PMMA － ＋ ＋ ╱ 160 200 104 45 115 1.188 1.220 1.190 at-PS it-PS － ＋ ╱ 230 90~100 100 1.052 1.127 Softening point (℃) at-PP it-PP － ＋ 75 160 0.85 0.92 at-PB[1] it-PB[1] － ＋ 65 128 0.87 0.91 h, if sign sequence is …(＋)(－)(－)(＋)(＋)(－)(－)(＋)… “ s t “ g, if sign sequence is …(＋)(－)(＋)(－)(＋)(－)(＋)(－)… “ i t ” Corradini Method + - + - + - + - + - R H R H R H R H R H b, observe all of atoms in the molecule at the same time c, front chain > R > r ( front chain > R > H ) d, circling from r to R to front chain e, if clockwise, mark the near bond with “＋”, far bond with “－” f, if counterclockwise, mark the near bond with “－”, far bond with “＋” a, fix the observation point Ideal Holotactic & Monotactic Polymers Holotactic(全规)----100% tactic Monotactic（单中心等规）----one asymmetric center / base unit R H R H C R H C CC C R H C C R H C C C R HR H R H R H R H poly(ethylidene) 聚乙叉 或 聚亚乙基 one asymmetric central atom / chain link i t or st ? sign sequence:(+) (－) (－) (+)(+) (－) (－) (+) (+) (－ ) (－) (+) (+) (－) (－) (+) + － － － － －+ + + + R＝CH3 +－ +－ +－ +－ +－ poly(propylene oxide) 聚氧化丙烯 one asymmetric central atom / three chain links i t or st ? Sign sequence: :(+) (－) (+) (－) (+) (－) (+) (－) C R H C CO O H R R H C O H R C C C+ － + － + － + － R＝CH3 C R H C CO O R H R H C O R H C C C+ － + － +－ +－ R＝CH3 Sign sequence: :(+) (－) (－) (+)(+) (－) (－) (+) Ideal Holotactic & Ditactic Polymers “ditactic”----two different kinds of asymmetric centers / base unit CH CH CH3 C2H5 －( )n－CH CH CH3 C2H5 n Poly[(1-ethyl)-(2-methyl)ethylene CH CH CH3 C2H5 － －C C C2H5 HCH3 H n － －C C HHCH3 C2H5 －C C C2H5 HCH3 H －C C C2H5 HCH3 H －C C C2H5 HCH3 H － HCH3H C2H5 C C －C C HHCH3 C2H5 －C C HHCH3 C2H5 －C C HHCH3 C2H5 － C2H5 CH3H H C C r H H R C r H C CC C H R C C H R C C C H RH R r H r H r H H H H H r R r R sign sequence－ r： (+) (－) (+) (－) (+) (－) (+) (－) (+) (－ ) (+) (－) R：(+) (－) (+) (－) (+) (－) (+) (－) (+) (－ ) (+) (－) erythro-diisotactic (eit) (赤型) 叠同双全同立构 r H R H C r H C CC C R H C C R H C C C R HR H r H r H r H sign sequence－ r： (+) (－) (+) (－) (+) (－) (+) (－) (+) (－ ) (+) (－) R：(－) (+) (－) (+) (－) (+) (－) (+) (－ ) (+) (－) (+) threo-diisotactic (tit) (苏型) 对映双全同立构 H R H R r H r H H r R H C r H C CC C H R C C R H C C C H RR H H r r H r H H H r R r R H H erythro-disyndiotactic (est) (赤型) 叠同双间同立构 threo-disyndiotactic (tst) (苏型) 对映双间同立构 sign sequence－ r： (+) (－) (－) (+) (+) (－) (－) (+) (+) (－ ) (－) (+) R：(+) (－) (－) (+) (+) (－) (－) (+) (+) (－ ) (－) (+) sign sequence－ r： (+) (－) (－) (+) (+) (－) (－) (+) (+) (－ ) (－)(+) R：(－) (+) (+) (－) (－) (+) (+) (－) (－ ) (+) (+) (－) H R r H r H H R H r H R C r H C CC C R H C C H R C C C R HH R H r r H r H Characterization of Tacticity in Real Polymers ideal holotactic structure holotactic & isotactic polymer holotactic & sydiotactic polymer tactic structure in real polymers isotactic in the main sydiotactic in the main less tacticity How to characterize the configuration in real polymers ? 1. average tacticity 2. average sequence length Using two parameters Average Tacticity m r i t s t m ---- meso r ---- racemic Diads xi + xs≡1 xi----mole fraction of diads “it” xs----mole fraction of diads “st” I + S ≡1 I ---- isotacticity of diads S ---- syndiotacticity of diads i t ---- isotactic diads st ---- syndiotactic diads NMR of PMMA Fr Fm Fmm Fr r Fm r I=Fm /(Fm+Fr) S=Fr /(Fm+Fr) I = S = 0.5 I = S= 0.5 Illustrate with PMMA C* C C* CH3 CH3Ha Hb C=O C=O OCH3 OCH3 C* C C* CH3 CH3 Ha Hb C=OC=O OCH3 OCH3 r C* C C* CH3 CH3Ha Hb C=O C=O OCH3 OCH3 m s t i t In st-PMMA, two methylene proton Ha and Hb are in a chemically equivalent environment. In it-PMMA, two methylene proton Ha and Hb are in a chemically nonequivalent environment. This leads to a single proton resonance signal, i.e. a single peak. In addition, spin of Ha coulpe with spin of Hb, it leads to two double peaks. (Ha和Hb互相自旋偶合而分裂为2个双重峰) C* CH3 C=O OCH3 C H H C* CH3 C=O OCH3 C H H C* CH3 C=O OCH3 m m C* CH3 C=O OCH3 C* CH3 C=O OCH3 C H H C H H C* CH3 C=O OCH3 r r C* CH3 C=O OCH3 C H H C H H C* CH3 C=O OCH3 C* CH3 C=O OCH3 m r Triads i i ---- isotactic triads ss ---- syndiotactic triads i s ---- heterotactic triads xii + xis+xss≡1 Ⅰ*+H*+S*≡1 I* =Fmm /(Fmm+Fmr+Frr) H*=Fmr /(Fmm+Fmr+Frr) S* =Fr r /(Fmm+Fmr+Frr) xi = xi i +0.5xi s xs = xss +0.5xi s I* = S* = 0 , H* = 1I* = S* = 0.5 , H* = 0 Average Sequence Length i i i i i i i i i i i i i i i ii i i i i s s s s s s number of monomeric units sequence length (LI)j number of sequence (NI)j number of including diads (NI)j 3 4 7 2 3 6 3 3 1 6 9 6 7 2 1∑ Tactic sequence consists of at least one tactic linkage, i.e. at least two monomeric units. The number of successive linkages of a like nature is defined as the sequence length, LI or LS . The transition from i to s or from s to i tactic sequence involves a hetertactic triad, “i -s” or “s -i ”. Number average sequence length of syndiotactic sequence (LS)n = 2xs / xis , (LS)n = 2S / H* Number average sequence length of isotactic sequence (LI)n = [∑j(NI)j(LI)j] / ∑(NI)j = 2Ni d/Nht = 2xi/xis (LI)n = 2I / H* Number average sequence length of all tactic sequence (L)n = 1 / xis , (L)n = 1 / H* Example (LI)n = (6 + 9 + 6 ) / 7 = 3 = 2 (6 + 9 + 6 ) / (12 +2) = 3