Hº = -690 kj/mol for ionization of n-propylene Hº = -757 kj/mol for ionization of isopropylene

Transcription

1 Prblem 56. (a) (b) re egative º values are a idicati f mre stable secies. The º is mst egative fr the i-ryl ad -butyl is, bth f which ctai a alkyl substituet bded t the iized carb. Thus it aears that catis are stabilized by alkyl substituets. This effect is als illustrated i art b, i which bth is are derived frm the same alkee. º -69 kj/ml fr iizati f -rylee º -757 kj/ml fr iizati f isrylee Thus º f rearragemet is -67 kj/ml. These umbers idicate that the rearragemet t i-ryl is is eergetically favred. (c) ( f, X ) f, f, X Fr -butee: ( f, X f, X f, X (.6 kj / ml) f, X f, f, ) f, kj / ml ( 68 kj / ml) Fr cis -butee: ( 5.8 kj / ml) f, X f, X f, f, 776. kj / ml ( 78 kj / ml) Fr rearragemet: kj / ml) ( ( f, f, 93. kj / ml 776. kj / ml) Rearragemet ges i the same directi as the ryl is ad is mre eergetically favred fr butyl is tha fr ryl is.

2 (d) Isbutee will have three electr sulyig alkyl substituets whe iized as shw belw, which will rvide a largely egative º as rved i art (a) Rearragemet is ulikely, give that it wuld be highly ufavred eergetically as rved i arts (b) ad (c). These argumets d surt the ti that isbutee uderges catiic lymerizati. Prblem 57. k a k P Pi ubr P K P Br ubr I i s Geerally fr a free radical lymerizati, k is arximately 3 - s -. Substitutig: k a 3 ( P 3.9 K 7.5 s 8 3 ) P 3.9 / K (.45 ) 5 s

3 Prblem 58. T c ly (eq 4.7.6) S R l ly eq 9 J / ml T c 4. J / mlk (8.34 J / mlk) l() T c 557 K 84 º This value suggests that iterferece frm equilibrati is a ssibility. Fr mre evidece fid the value f K ( / eq ) at rm temerature: 9 J / ml 98 K 4. J / mlk (8.34 J / mlk)l( ).4 K 7 The equilibrati cstat is small eugh that equilibrati wuld be a mir rblem i the lymerizati f Ply(L-lactide). The fllwig lts f T c vs. l ad l vs. /T (as shw i class) als illustrate this it. Equilibrati i Ply(L-Lactide) Plymerizati 8 Tc (K) l

4 Equilibrati i Ply(L-Lactide) Plymerizati 4 l /T (K^-) Bth the º ad S º values fr the lymerizati f L-lactide are cmarable t thse f the majrity f cyclic mmers reseted i hater 4, althugh there is a discreacy betwee the 6-membered alkae ad L-lactide. This may seem cuterituitive sice L-lactide is als a 6-membered rig, but the differece ca be exlaied by the resece f xyge heteratms i the lactide rig, which icrease the rig strai slightly. As a result, L-lactide behaves mre like the 5-membered alkae rigs tha cyclhexae.

5 Prblem 59. RT l eq ly T S ly eq e ly T S RT ly At 8º: e eq ( 9) (353)(4.) (8.34)(353) At º: e eq ( 9) (393)(4.) (8.34)(393) Prblem 6. The kietics f rig clsig are very slw fr high mlecular weight lymers (large umber f reeat uits wuld lead t very large rigs). Thus, i geeral, we d t eed t wrry abut its effect the lymerizati. Rig clsig is smewhat f a rblem as the lymer is grwig ad has very few reeat uits.

6 Prblem 6. acid S catiic * S S S aiic * S S

7 Prblem 6. * * * * 3 3 * * Prblem 63. Fr a ideal livig lymerizati the kietic chai legth varies liearly with cversi, ad the arriate mlecular weight distributi is the Piss distributi. Stated mathematically: I ν I ) ( ν ν w I I w

8 Fr a livig lymerizati, the extet f reacti varies with time as: k e I t Substitutig this it ur equati btaied abve fr will give us the umber average mlecular weight as a fucti f time: I k I t ( e ) The grahs belw shw these relatishis as cmared t bth free radical lymerizati with termiati by disrrtiati ad ste grwth lymerizati. f lymer frmed (g/ml) livig ste grwth radical ttal cversi f mmer

9 . PDI f lymer frmed livig ste grwth radical ttal cversi f mmer f lymer frmed (g/ml) livig ste grwth radical t (s)