California Association of Chemistry Teachers
Nuclear Magnetic Resonance Studies
W. P. Slichter b'!i,.l.,:l, hlLtrr;::.
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of Molecular Motion in Polymers ~
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ninlrr~tl:~r mntim ~ ~ n d r r l i tr hs r p l ~ r n n n i r ~ ~of n nr111krr chstirity, povrrrls tllr visrous flow of n ~ r ~ l llmlymrrs. rt~ I clrtrrrninr.; tlw flrsildity of f i l ~ r n ~s ~ t rs~ ~ r t ~ ~ r r s . .\Inst of \ v l ~ : ~\lv r know : I ~ W I I I tlw ~ n ~ o l r r ~ t lprnrrssrs :~r in\~olvwI in s11rI1 p ~ q i r r t i wrotnrs f r n n ~~Iynnniirn i c rll:~t~ir:~l tnr:~.;~~rc*mrnt.;. strlclirs r r f clirlrrtrir rrl:~s:~tiim. :1n11mr:~siIrrmrntsOF sprrifir \w1111nr: I I I ~11r:lt ~ (.:lp:wity. I n ~ p n r t : ~ nnrw t inforn~:itinnis ncnv ~ I N W ~ ~11y ~ Y1111r1fw I n~:~gtwtir rrwn:inrr (nnlr) sprrtrnwiqy. T l ~ i sn ~ r t l ~ i n l r o t ~ ~ ~ h n rntlwr n t s kinds of mr:I.wrrnwnt, :din I I I : I I I ~ IYIW.; i t ;~flnnlstlw nwst (lirrrt virw at t l ~ rmolrrul:~r lrvrl of prorrssrs of n~otiont11:1t ~ ~ n ( l r r lni ir : ~ r r f w ~ i p i r prolwrtirs. l'liis rrvirw s l ~ o wrs:~mplrsof tlir wr of nnir in stit~lirsof 1no1rr11I:irmot inn in lnlynwrs, I n ~ t \vith no :~ttrnlpt : ~ t r o n ~ l ~ l r l r ~ ~ r\Inrf. s s . rstrtwivr infnrn1:1tion n11 tlw n ~ r t l ~ n:III~I i l its :~ppIi(.:~tit~n to p l y I'IIC nwrs m:~yh r f o ~ ~ nilld snnw r:~rlirrr r v i r w (I). prit~riplr.;of nmr :lrr (lisruwrl in wvrr:~lt r r t s ( 2 ) . General Principles
Volume 47, Number 3, Morch 1970
/ 193
Figure 1. Temperohm dependanre of h rpinloni~ereloxelion time rubber, polypmpylcne, polyilobvtylem, ond cir.polybutodicne, meawnd 01 0 radio-frequency of 30 MHz (Ref. I18)I. in nohlrol
In the next srctions we give es:~mplrsof t h r study of molrculnr motion in srvcr:~ltyprs nf ~n)lynirrs. ('ompnrisons nre mndr with o l l ~ r cl:~ssr.i r of iqwrinirnt :UNI rmph:~sis is given to the kinds of niwrurrmrnt for which nmr is part ieulsrly rlTrrti\.r. Relaxation in Some Elastomers
sl~in-spincoupling to thc mrthyl grnups (I?). T h r coupling withi~rthe spin systrm ix rffirirnt cornpnrrrl with t h r sl~in-lattice roupling of thc rnc.thyl gr~ul)s. *. I l u ~ x ,the mrthyl g r n u p rnnstitute "rinks" for the clissilx~tionof tlw energy of llw uuclrar spin systrm to t l i v rnvimnnirnl, nncl the n ~ t c c l r t r r n ~ i n iprncrss n is I I - t t i r r I : : t i o n I I n i l l ~ y rl o ~ Tl~r s ninpt~itudrof TI :it 1111. nlininum :~srrihnlto n ~ r t h y l r o t : t i ~thrrrfnrc ~ P ~ I P on I I ~the ~ cmwFntn~tion of ('113 i ~ n ~ t o in n stlw tol:il I H I I I I I ~ : L ~ ~ OofI Iprotms. i t ~ ~ ~ I y i s n l r u t y l rt h~ r~ r lo\vrr-trml~rctt~~rc , TI nii~~iniuni is 4 i f t n I to :I rrl:~tivrly high tmnpw:!turr, inrlirnling t h ~ tt h r n~otionis more hi~~clrrtvl t h n in rul~ln-r: ~ n d pnlypropylrur. With nic~t11yIgmups :ktt : ~ r l ~ ninl pnirs to : ~ l t r n l a t cr ~ r l m natonis in the rh:~in, polyiwln~tylrncprrsrnts :I strurturr in which thrrr is cousi~lrr:~l)le strric intrrfrrrnce :tmong the sul~stiturnts. i'owlrs (/.I) h:~s s11ggrstw1 th:11 sonw motinu of the elr:tin hncklmnr is ncwSrs:iry to frrc thc mrthyl groups iron^ l~inclr:u~ecto n k ~ t i o n . This intrrpretalior~ is Imrne out I I ~the ol)srrvati?n I . 1) tll;~t t h r 11'1 niinimum ssrril~etlto ('Ill rot:~tionoccurs :11 :I t m i p r n ~ turr not far 1)rlow thnt :~scrihnIto motion of tlw m:~in chain. Tlir l n w r T, niinin~uni is rrl:ltivrIy hro:~cl, suggesting th:~ttlw n ~ u t u i ~I~inrlr:u~c~ l :tniong t h r CIIr ~ ~ O I I wries ~ I S in drgrrr thmughout t l ~ solid, c clclwncling on t l ~ lowl c chniu cnnforn~:~tion. Temperature-Frequency Dependence of T,
N'v rsprct t h r s p r r t n m of motionx t o shift t o Iiighrr llolrculnr motion is i~nsicnllyinilmrt:u~tin rulhrrlikr frrqurnrirs ns the trml)rrnturr is r:~isnl ( 1 4 ) . This e o m l n ~ ~ u ~(rlnstomrrs) ds : I U ~ is rwlily srru I)? mnr. shift is rt~flrrtrdin t h r displnrrmrnt of t h TI miuin111n1. For rs:~mple.the t r n i p r n ~ t u r rclrl)rndrnrr of TI in four For rx:~mplr,in the s l ~ i ~ ~ - l : ~ lrcl:~s:~tiou ticr of ri.q-lmlyel:~.tonirrs is summ:~rianl in 1:igurv 1. 111 the dishutnclienc, me:~snrnl :it srvrr:d c~cliofrrclurncies, t l ~ c C I I S S ~ ~ inimnli:~trly II folloving, !vr ~ I I ~ I on I S t h r dc*t:~ilnl minim:^ : ~ r cfound to occur nt ~~mgrrrsivcly higl~rrternl)el~:~vior of t h r suhstiturnt mrtl~ylgrnups, whir11 :Ire Iwr:Iturw 81s thc frcqurncy is iucrcwnl (I:ig. 2) ((i). ohsrrvnI \vith grrnt cli~rity hy nnir. IIn\v~vrr,the , I hr prngrcsivo chr~ngrin the m:~guituclcof TI:tt the proprrties of polynwr soliA is the m t r r mrthyl gwup, wr r o n r l ~ d rt h t , t h r rorrwponclinpl TI minimum in I'\I\IA rrwlts f m n t h r rot:~tionof this m n p . Similnrly, in IY'y\I:\ t l w c is n mininwm nt intrrnmnlintr t r m p r r : ~ t u m ,rrsrmlrling thnt found in 1'11 \I.\, hnt t h r r r is no minirnnm : ~ tlow trmlwrnturw. I
