1384
A. E. WOODWARD, il. ODAJIMAAND J. A. SAUER
Vol. 65
PROTON MAGXETIC RESONANCE OF SOME POLY-(ALPHA-OLEFINS) AND ALPHA OLEFIN MONOMERS1 BY A. E. WOODWARD, A. ODAJIMAAND J. A. SAUER Department of Physics, Pennsylvania State University, Unzversity Park, Pa. Received March 4, 1981
Proton magnetic resonance spectra of a series of polyolefins: polypropylene, poly-(3,3',3''-trideuteriopropylene), PTDP, poly-(butene-l)! PB1, poly-(pentene-1), PP1, poly-(3-methylbutene-l), P3MB1, and poly-(4-methylpentene-l), P4MP1, have been ohtauled from 77 to 300°K. or higher. 'In addition spectra have been observed for the monomers: 3-methylbutene-1, pentene-1, and 4-methylpentene-1 from 77°K. to temperatures about 15°K. below the respective melting points. The line narrowiqg in the 77-150°K. region reported previously for polypropylene is not exhibited by PTDP which is further evidence that this process is a consequence of methyl group rotation. Both P3MB1 and P4MP1 show distinct line narrowing and second moment changes in the 77-130'K. region, this change being attributed to the onset of methyl group rotation. The second moment-temperatures curves for PPI and PI31 are similar to each other with no marked line narrowing processes occurring until temperatures of 260-300'K. are reached. However, by a comparison of experimental and calculated second moments it appears that considerable motion, presumably methyl rotation, is taking place in PB1 and PPI at 77°K. From '77-90"K., 4-methylpentene-1 undergoes an n.m.r. transition which takes place only 5-10'K. below that for the respective polymer and is attributed to methyl group rotation. PMethylpentene-1, 3-methylbutene-1 and pentene-1 exhibit abrupt n.m.r. transitions, possibly due to molecular tumbling, at temperatures 20-25°K. below the melting point. All polymers studied show line narrowing and second moment changes around room temperature which are believed to be due to reorientation motions associated with the glass transition. These n.m.r. motional narrowing processes occur in the order P P I 4 PB 1 'v PTDP < polypropylene < P4MP1 < P3MB1. Upon comparison of the proton resonance data for PB1, PPI, P3MBl and P4MPl with that from dynamic mechanical measurements on the same samples a t frequencies of 5002000 c.P.s., it is found that the transition regions are seen a t essentially the same temperatures by both types of measurements.
Introduction The use of the proton magnetic resonance technique, herein referred to as n.m.r., to investigate molecular motjion in the poly-(a-olefins) has been limited to date to the first two members of the series with aliphatic side chains projecting from alternate carbon atoms of the main chain. N.m.r. spectra have been obtained for crystalline and amorphous samples of p ~ l y p r o p y l e n e ~in- ~the 77400°K. temperature region. I n addition to marked changes in these spectra in the neighborhood of the glass transition all investigators have reported an 1i.m.r. line narrowing process, accompanied by a decrease in the second moment, in the 77-150'K. region. This effect has been attributed to the onset of methyl group rotation a t frequencies in the range detectable by this method. On the other hand, poly-(butene-1) does not exhibit a marked line narrowing: until temperatures in the vicinity of the glass transition are However, it has been suggested8 that a t the lowest temperature employed, 77O:K., the poly-(but,ene-1) molecules are riot completely rigid, as appears also to be the case for polypropylene. 2 * 3 One method which can be employed to give further information about the motional state of a given substance is to replace one or more of the hydrogen at,oms by an atom which does not absorb energy from t'he magnetic field under the conditions employed nor give effective magnetic dipole interactions with the protons. In order to have a com(1) Supported by the 5. e. Atomic Energy Commission under contract No. AT(30--1), 1958. (2) J. A. Sauer, H. A. Wall, N. Fuschillo and A . E. Woodward. J . A p p l . Phys., 29, 138; (1958). (3) K. P. Slichter and E. R. Mandell, J . Chem. PkUs.. 29, 232 (1958); J . A p p l . Phys., 29, .I138(1958). (4) A. Nhshioka, Y. Koike, hl. Owalii, T. Naraba and Y . Kato, J . Phys. Soc. Japan, 15,416 (1960). ( 5 ) R. L. Miller, Polymer 1, 135 (1960). (6) J. A. Sauer. A. E. Woodward and N. Fuschillo. J . A p p l . Phys., 30, 1488 (1959). ( i )W. P. Slichter. S. P. E. Journal, 1 6 , 3 0 3 (1959). (8) W . P. Slichter, Ann. N . Y . Acad. Sci., 83, 60 (1959).
pound with morphology as close to the parent substance as possible, atoms of similar size and which give bonds with carbon of similar polarity, such as deuterium in place of hydrogen, should be used. As described herein, a study of the proton resonance spectra of poly-(3,3',3"-trideuteriopropylene), PTDP, has been made and this study provides further evidence that the low temperature narrowing process in polypropylene is indeed a consequence of methyl group rotation. In order to obtain additional information concerning the effect of the length and size of the sidebranch on the motions occurring in polymers, the n.m.r. spectra of six compounds : polypentene-1, PP1, poly-(3-methylbutene-l), P3MB1, poly-(4methylpentene-1), P4MP1, and the respective crystalline monomers, in addition to poly-(butenel),PB1, have been obtained a t temperatures from 77OK. -4unique feature of this study is that the polymer specimens were taken from the sample rods used previouslyg in an investigation of the dynamic mechanical properties, and therefore a more detailed comparison than usual of the data from the two methods is possible.
Experimental The n.m.r. measurements were made using equipment purchased from Varian Associates, as described previously.lo Due to the small amount of sample of P T D P employed (0.3 9.) it was necessary to correct the derivative line shapes obtained for the measurable background signal of the polystyrene in the probe. However, these corrections only have a small effect on the second moment values. The PTDP was prepared from monomer (Merck and Co., Ltd.) with a minimum isotopic purity of 96 atom % D. The preparation of this polymer and of the polypropylene samples, on which data are reported herein, were kindly carried out by Dr. R. D. Lundberg of Union Carbide Chemicals Company using a procedure designed to give highly isotactic material. The polymerization charge per tube consisted of: 8.0 ml. of dry distilled heptane, 1.0 ml. of purple TiCls suspcnsion in heptane (7.3%), 1.0 ml. of Al(isobutyl)r (9) (a) A. E. Woodward, . I . A. Sauer and R. A. Wall. J . Chem. Phys., SO, 854 (1959): (b) .J. Polymer Sci., 60, 117 (1961). (10) A. Odajima, A. E. Woodward and 3. A. Sauer, J . PoZymer Sci.. in prew.
August, 1!361
PROTON &IbGNETIC
which was 1 &I in heptane and 28.45 mmoles of monomer. Catalyst and solvent were charged into glass tubes in a dry nitrogen atmosphere, then using high vacuum techniques, monomer waa added and the tubes sealed at liquid nitrogen temperature. The polymerizations were carried out for 16 hr. at 50". The contents of three tubes were combined and washed free of catalyst residues in 500 ml. of acidified (19; HCl) is0 ropy1 alcohol, then washed with an 80-20 waterisopropyralcohol mixture, and finally washed with isopropyl alcohol containing a small amount of 4,4thiobis-G-t-butyI-mcresol as oxidation inhibitor. The polymer then was dried overnight a t 50". In order to have the PTDP in chunk form, the precipitated polymer was heated to 440°K. and then cooled to 385°K. over a 45 minute period. Prior to the n.m.r. meamrements all aolvmer samales were heated in a vacuum oven for a t least' 46 hours, the temperature being 50" for PP1 and 100' for the other polymers. Samples of PBI, PP1, P3MB1 and P4MP1 were in the form df pieces, cut from specimens used for the dynamic mechanical investigations and having characteristics given previously.9 However, due to their use in previous tests, these specimens have been slow cooled from temperatures of 435, 400, 480 and 435"K., respectively. From a density value at 25" of 0.892 g./cc., the crystallinity of the PB1 sample was estimated as 30%, using the amorphous and crystalline specific volumes given by Danusso, Moraglio and Natta.11 Crystallinities at 300°K. of 60, 60, 30, 25 and 50% for aolwroavlene. PT'DP, PB1. PP1 and P4MPl were estimatid a technique involving a separation of the narrow and broad components of the derivative line shapes for the pure polymers (polypropylene, PTDP and PPl) or for the polymer swollen with tetrachloroethylene (PB1 and P4MPl). To effect the separation of the complex line into broad and narrow components, the low temperature line shape for the pure polymer (taken a t 149, 157, 197, 193 and 184'K., respectively, for the five polymers mentioned above) was assumed to be the correct line shape for the crystalline contribution a t 300°K. It was also assumed for the swollrn polymers that the solvent entered only into the amorphous regions and not the crystalline ones. It was found that the tails of the line sha.pes a t 300°K. for all five materials were the same as those for the line ehapes a t the lower tempera. tures cited above. The crystallinity for P3MR1 w~tsestimated as high. Samples of penkene-1 (Research grade b.p. 29.9'), 3methylbutene-1 (Research grade, 99.99% pure; b.p. 2s'); and 4-methylpentene-1 (99.77cT0 pure; b.p. 53') were kindly supplied by Dr. R. I). Lundberg of Union Carbide Chemicals Company and were used as received. The melting points of these compounds as given in the literatiire'* are -165.2. -168.5 and -l53.6', respectively.
Results In Fig. 1 are shown plots of the first derivative of the pro.ton absorption as a function of the applied magnetic field (one-half of the recorder trace being given) a t i"ioK. for all materials investigated except PBL. (The curve for this latter polvmer is given in Fig. 5.) Due to a change in the abscissa scale from one tci another of the absorption curves, changes in heights of maxima are not necessarily significant except for a given monomer-polymer pair. The peak-to-peak modulation width used in obtaining these line shapes was 2.2 gauss for P T D P and 1.1 gauss for all the other materials. At this temperature all the polymers except P4MP1 exhibit relativelv broad derivative shapes while for the monomers the shapes are generally sharper and narrower. 'The line shapes for P4MP1 and its monomer shlow greater similarities, although that for the latter is somewhat narrower, than those for the other two polymer-monomer pairs. (11) F. Daniisso, G. Moraglio and G. Natta, Ind. plostiques mod. 10, 40 11958). (12) F. D. Rossini, tmt a l . , "Selected Values of Physical and Thermodynamic Properties of IIydrocarbons and Related Compounds," A . P.I. Reaearcli Projwt 4.1. Carnngie Press. 1953,pp. 54-5.5, (pU?48),
RSSONASCE O F POLYOLEFINS
1383
PP-I p-1
, / e . ,
. I
: I -
3 M B I ---
'\\
P4MPl4 M P I ---
0
5 H-
IO
HO -GAUSS.
Fig. 1.-Derivative shapes of the proton resonance line absorption at 7i"K. for some poly-( a-olefins) and or-olefin monomers.
In addition, the line shape for P4MP1 exhibits two distinct components. It is found that oiily small changes in derivative line shape occur for P T D P in the 77-15OOK. region, while considerable changes are seen for polypropylene in this temperature region. At higher temperatures both exhibit a narrow and broad component, the presence of the two components being noticeable a t lower temperatures for PTDP than for polypropylene. The separation of the maximum and minimum of the derivative absorption line in gauss, referred to herein as line width, is given as a function of temperature for P T D P and polypropvlene in Fig. 2 . For polypropdene a narrowing of the line width in the 77-150°K. temperature region, observed by many investigators,2-6 is apparent, whereas for PTDP no such narrowing occurs. At higher temperatures for both polymer< a two component line shape with a relatively rapid narrowing of the narrow component is observed However, this narrowing process occurs at temperatures of 30-40°K. lower for the trideuterio compound. The dotted line in the figure connecting narrow component points for P T D P and broad component points for polypropylene indicates that in this region due to difficulty in separating the two components of the line the reproducibility is not
h.E. WOOD\$7ARD,
1386
1 cn m
values of 1.5-2 gauss2 less than those for ~ o l v propylene a t any given temperature from abo& 275 to .- 300°K. --The line widths as functions of temperature for the three monomers : pentene-1 , 3-methylbutene-1 and 4-methylpentene-1, are given in Fig. 4. At
1
2
3
a
6.01
W
I
'
\
-1
\
W
z
02
0O L t 100
I
I
I
I
150
200
250
300
TEMPERATURE -
350
O K
80
Fig. 2.-Line nidth vs. temperature for polypropylene (0) and poly-(3,3',3"-trideuteriopropylene) (e).
within the 3 ~ 3 %limit observed for the majority of values. A t two temperatures, 350 and 367"K., the line shape for polypropylene was found to be composed of three components with widths of 0.068, 0.164 and 8.0 and 0.045, 0.148 and 8.1 gauss, respectively. From plot:; of the second moment of the n.m.r. absorption us temperature in Fig. 3 it is found that I
"
"
i
0
100
200
TEMPERATURE
300 - O K
Fig. 3.--N.m.r. second moment us. temperature for polypropylene ( 0 ) and poly-(3,3',3"-trideuteriopropylene) (e).
the low tem:perature narrowing process for polypropylene is accompanied by a change of the second moment from 26 gauss2 a t 77°K. to 15.5 gauss2 a t 155('K., while for P T D P the second moment changes only from 18.0 to 17.3 gauss2 in this temperature region. In the 155 to 250°K. region the second moment is constant within experimental error for polypropylene and shows only about 1.5 gauss2decrease for PTDP. Commencing a t about 250'K. for P T D P and about 270°K. for polypropylene, the values of second moment drop quite sharply with the deuterated compound having
100
TEMPER A T URE
-OK.
Fig. 4.-Line width us. temperature for 3-methylbutene-1 (a),pentene-1 (o),and 4-methylpentene-1 ((3).
77°K. the widths are in the order 4MP1 7 P1 > 3MB1. Over part of the temperature range traversed, where the line width is 4-5 gauss or less, the shape of the line width vs. temperature curves are similar for the three monomers, the curve for pentene-1 being shifted about 4°K. to higher temperatures than that for 3-methylbutene-1 while that for 4-methylpentene-1 is shifted to temperatures about 15°K. higher. The line decreases from 4-5 gauss to 2 gauss over a 5OK. span, then abruptly drops to 0.3-0.4 gauss in a span of 1°K. or less a t temperatures 20-25OK. below the respective melting point and then decreases less abruptly a t higher temperatures. At low temperatures, 77-94"K., 4-methylpentene-1 shows a gradual decrease in line width from 9.5 to 4.4 gauss in contrast to the more abrupt decreases for the other two monomers. In Fig. 5 some derivative line shapes for P B l are shown. It can be seen that the shapes a t 105 and 191°K. are flat, making it difficult to obtain an accurate line width. The shapes for PP1 were found to be very similar to those for P B l a t any given temperature over the range studied (77300°K.). The complete data for PB1 and PPI are given herein only in terms of the second moment, due to the large errors involved in determining the line width from the typc of line shape exhibited over the 100-200°K. temperature region. The second moment behavior for PB1, recorded in Fig. 6, is in qualitative accord with that reported previ0usly.~~7As is the case with the line shapes, the second moment plots of PB1 and PP1 are the same within experimental error over the 77 to 260°K. range, with values decreasing from 21-22 to 1.5 gauss*. It is seen that the drop in the first 20°K. is of a slightly greater slope than that in the subsequent 140OK. Above 26OOK. the line width and second moment drop markedly for both polymers, with second moment values a t 300°K. of 10.0 and 5.0 gauss2 for PB1 and PP1, respectively.
PROTON MAGNETIC RESONANCE OF POLYOLEFISS
August, 196 1
13S7
Polv (butene - I ) vi cn 3
I k-
0
3 W
Z
E
I -0 \ h
I
v
w-
-0
TEMPERATURE
- O K
Fig. 7.-Line width us. temperature for polj"(3-methylbutene-1) (o),and poly-(4-methylpentene-l) (a).
280°K
5 IO H- HO -GAUSS.
0
Fig. 5.- -Derivative shapes af the proton resonance line absorption for poly-( butene-l).
p z
$10
1;
i
I I
I
0
w
I
cn 0
100
200
TEMPERATURE
300
-
OK.
Fig. 6.--N.m.r. second moment us. temperature for poly(butene-1) ()., poly-(pentene-1) ( 0 )and pentene-1 ( e ) .
As is readily seen by comparison of Fig. 3 and 6, in the 77 to 260°K. temperature region there is a marked difference in the data for PB1 and PP1 as compared to that for polypropylene, whereas above 260°K. the data for PB1 and polypropylene are essentially the same. Also included in Fig. 6 are second moment data for pentene-11 a t temperatures of 77 and 80°K.; upon comparison of the values for the monomer with those for the polymer, a difference of 6-7 gauss2 IS found a t these temperatures. At higher temper:itures the second moment falls sharply to values iirar zero.
In Fig. 7 the line width as a function of temperature is given for P3MB1 and P4MB1. Both polymers show a line narrowing process in the 77100°K. region which for P4hIP1 involves the disappearance of the broad component of the complex line shape. Both also show an additional line narrowing in the region above 300°K. For P4MP1 the data show that the narrow line width in the 1303OOOK. region is lower by 2-3 gauss and the transition starting around 3OOOK. occurs a t lower temperatures than for P31CIB1. ht temperatures above 300°K. a two component line shape was again discernible for P4MP1 but the two components were not separated easily and therefore only the widths of the narrow component in this temperature region are reported. The differences in behavior of the two polymers are not as striking in the second moment plots, given in Fig. 8, although it is again clear that the upper temperature transition for P4AIP1 occurs some 25°K. sooner. The second moment plot for P31IB1, showing a marked decrease in the 77-130°K. region, a nearflat portion from 130 to 30OOK. and a decrease of 10 gauss2 in the final 50"K., is sigxlar to that for polypropylene rather than that for PB1 and PP1. On the other hand, for P4MP1 a decrease of 2-3 gauss? in a second moment takes place over the temperature range between the low and high temperature transitions. The second moment for the monomer 4-methylpentene-l , given in Fig. 8, has values about 1-3 gauss2 lower than that for the respective polymer in the 77-90°K. region; above these temperatures a precipitous drop to a value near zero occurs. For 3-methylbdene-1 the second moment value a t 77°K. is 15 gauss,? 9 gauss? lower than that for P3MB1, and then approaches zero around 80°K. All the polymers studied herein except P T D P also have been investigated by dynamic mechanical and in all but the polypropylene case the same sample has been used in both sets of measurements. In all cases the higher temperature n.m.r. transition appears in the same temperature region as a peak in the internal friction, and a drop in the dynamic elastic storage moduluq, E', measured a t a frequency in the 500-2000 c.p.5.
A. E. WOODWARD, A. ODAJIMA AND J. A. SAUER
1388
Vol. 65
TABLE I CALCULATED SECOND MOMENTS FOR POLYMERS Polypropylene
Contributing: groups
CHa CHI (s.c.) CHs-CHz (s.c.) CHo-CH? (s.c.) CH&H (s.o.) CH (~.~.)-C132 (s.c.) main chain main chain-wide chain intermolecu1,ar total
...
CH-CH? (6.0.) main chain main chain-iside chain interrnolecu1,sr total
...
1.5
2
25-29 b. Methyl rotation .. 2.0 .. 2.7 .. 1.2
..
1.5 -
00
-
O
ti' T
k
-
-
15
-
0 W v )
5.0 -1-2 -3-4 15-17
..
-
0
...
13.3
6.6 2 -2-3 13-14
10-
z
...
..
-
0
...
..
...
-
-
15
-
-
-2.3 -5-8
-
-
w 2
5.0
..
I
z
...
13.3
6.6 5.2 5- 8
cn
I
...
..
cn 2 0 -
a w
...
..
N
3
2 7 I .7
..
...
... ... ... ...
CH&H ( s.c.)
.. ..
... ...
2.8
CHs CHs ( s.c.) C H r C H s (s.c.) CHz-CHt (s.c.)
a. Rigid lattice .. 8 2
11.0
__ 28-3 1
P B1
PTDP
P3MBl
PIMP1
13.1
...
10.9 1 8 0
4 -2-3 -5-8
1.4 0.6 4 -2-3 -5-8
1.2 0.5 3.3 -2-3 -5-8
24-28
26-30
PPI
6.5 4.1 1.4 0.8
...
...
1.0 4.4 0.9 0.8
... ...
4 -1-2 -3-4 15-17
... ...
3.3
... ...
...
25-29
3.7 1.8 0
...
..
0.9 0.6 4 -1-2 -3-4 13-15
0.8 0.5 3.3 -1-2 -2-3 12-14
component of the line, the second moment values for some simple motional cases, such as the rotation of side groups, can be estimated.'4 Usually, as is the case with the polymers and monomers under discussion here, the spatial arrangement of the atoms in the material is not known exactly and therefore certain contributions to the second moment can only be approximated. In Table I estimated values of second moments for the rigid lattice structure and also for the case of methyl rotation about the Ca axis are given for all six polymers studied. The separate contributions to the total second moment from protons on the same group or on different groups are also shown; in this table S.C.and m.c. signify the side chain and main chain, respectively. In calculations of the intramolecular contributions to the second moment the usual values for bond angles and lengths were used. The contributions due to proton-proton interactions on the chain backbone for all six polymers were calculated assuming these protons to occupy the positions given by Keedy, Power and Steinl3 obtained from the helical structure proposed by Katta and Corradini16 for polypropylene. Since it has been f ~ u n d l ~that . ' ~ the difference in values of second moment for helical and randomly coiled backbones is small, the use of the polyprop)*lene helix for PP1, P3RlBl and P4MP1 which have different
, , , 1 , , , , 1 , , , , 1 200
300
TEMPERATURE - OK, Fig. 8.--hr.m.r. second moment us. temperature for poly(3-methylbutene-1) (o), poly-(4-rnethylpentene-I) ),(. 3methylbutene-1 (8: and 4-methylpentene-1 ( 0 ) .
range. A detailed comparison of the line width, second moment, E', and & - I data for PB1, PP1, 1'3MB1 and P41MP1 shows that the onset of this transition occurEi a t 230°, 225-230°, 305-325" and 350°K., respecttively. The point of maximum slope (the peak in the case of Q-l) for the transition varies according: to what quantity is being discussed, with thle second moment and Q-' plots giving similar vrtlues of 285-290°, 290°, and 330345'K. for PB1, PP1 and P4MP1, respectively; the corresponding values from line width or modulus are 10-20'K. lower. Discussion When the proton positions in a solid are known, the equation given by Van Vleck13 can be used to calculate a value for the second moment of the rigid lattice structure; also, for the main central (13) J. A. Van Vleolc, Phys. Rev.. 74, 1164 (1948).
(14) J. G. Powles and H. S. Gutowsky, J . Chem. Phys., 21, 1695 (1953). (15) D.A. Keedy, J. Powers and R. S. Stein, J. Appl. Phys.. 31,1911 (1960). (16) G. Natta and P. Corradini, Attd. accad. nazl. Lincsi, [VIII] 4, 73(1955): Rend. aecad. nod. Lincei, [VIII]21, 365 (1956). (17) A. Odajima. J. Sohrna and M. Koike. J. Phgs. Soc. Japan, 12. 272 (1957). (18) A. Nishioka and Y. Kato, Report Prog. Polymer Phgsics Japan 8 , 128 (1960).
August, 1961.
PROTON MAGNETIC RESONANCE OF POLYOLEFINS
identity p e r i o d ~ ' ~should J~ not introduce appreciable error. The positions of the protons on the side chain with respect to those on the main chain of the same molecule for PB1, PP1, P3MB1 and P4MPl are not known and hence the contribution chosen is only an approximate one. I n calculations involving methyl-methylene, methyl-CH group and methylene-CH group proton interactions, an ethane-like configuration was assumed. The range of possible values for the intermolecular contribution to the second moment for all polymers except PTDP was taken as that given previouslyz for polypropylene. For PTDP this contribution was obtained by use of a molecular model based on the crystal structure given by Natta and Corradird16for polypropylene. It was assumed that rotation of the methyl group about the threefold axis reduced the contributions due to interactions of the protons on an individual methyl group with one another to the rigid lattice value while those contributions due to interactions of protons on a methyl group with protons on any other group were assumed to be reduced to '/% the rigid lattice values.10021 In the 77-160OK. region the observed second moment for polypropylene drops from a value a t 77OK. which is 2-5 gaussz lower than the estimated rigid lattice value to one at 160'K. which is about 2 gaussz higher than the estimated methyl rotation value. For P T D P in the 77-16O0K. region the experimental values are about 2 gauss2 greater than the calculated one. The presence of a more randoni orientation of the protons in the amorphous regions than in the crystal used as the model would be expected to lower the calculated second moments, an effect in the opposite direction to that observed. Reduction of the proton-proton distance on the pethylene group from the assumed value of J.78 A., based on a tetrahedral structure, to 1.75 A. will lead to increases in the calculated moment values of 1.8 and 0.9 gauss2for P T D P and polypropylene, respectively, if only the intragroup contribution is assumed to be affected. With these changes in spacing closer agreement between calculated and observed values for both polymers is found. It is concluded from all the evidence, including the absence of the low temperature motional narrowing process when the hydrogens on the methyl group are replaced by deuterons, that the results obtained support the hypothesis1J that the transition in the 1 7 7 to 150'K. region for polypropylene is ra consequence of the onset of methyl rotation. From a comparison of the second moments for PB1, PP1, P3MB1 and P4MP1 a t 77OK. with those calculated it appears that the rigid lattice state is not attained a t the lowest temperature employed, but that considerable motion, presumably methyl rotation, is taking place. The transition that is definitely present for P3MBl and P4MP1 and of which there is some indication for PB1 and PPI a t the lowest temperatures used, is therefore expected to extend to temperatures be(19) G. Natta. P. Corradini and I. W. Ba&, Rend. arrad. narl. Lineei, [VIII] 19, 404 (1955), ( 2 0 ) G . Natta, Angew. Chem , 6 8 , 393 (1956). (21) F.R.Andww, J . Chem. Phys., 18,607 (1950).
1389
low 77'K. At 140°K., a temperature above this transition region, the experimental second moments are higher by about 2 gauss2for P3MB1 and P4MP1 and about 3 gauss2 for PB1 and PP1 than the calculated methyl rotation values. These discrepancies are in the same direction and of comparable magnitude to those found for polypropylene and PTDP. Again a choice of a shorter proton-proton distance for the protons on the main chain methylene group would lead to calculated values in better agreement with the experimental ones. In addition to this, the averaging process of the magnetic dipolar fields brought about by the methyl group rotation might well lead to a reduction in second moment differing from the '/3 value assumed. However, the order of the second moments a t 140OK. for the six polymers studied is that expected if methyl group rotation is occurring in all cases. The relatively slow decrease in second moment with increasing temperature in the 130-240OK. region for PB1, PP1 and P4MP1 probably is due to side chain rotation involving CH and CH2groups in addition to CHI groups. This type of motion would not be expected to have much effect for P3MB1, in agreement with experiment. A number of alpha methyl group containing polymers exhibit n.m.r. transitions in the 77-300' K. range, attributed to the onset of methyl group rotation of the appropriate freauency. These include: poly-(1,1,2-trideuteriopropylene)22( 477 to 150°K.), natural r ~ b b e r ? ~( 4- 7~7~ to 150°K.), p01yisobutylene~~J~ ( L 7 7 to 200°K.), poly-(methyl m e t h a ~ r y l a t e ) ' ~ . ?(100 ~ J ~ to 200°K.), poly-(methacrylic acid)l0 (L77 to 200°K.), poly-(sodium methacry1ate)'O (L77 to 200°K.), and poly-(&methy1styrene)lO (120 to 260OK.). On the other hand, the methyl groups in poly-(dimethylsiloxane)z9-31 and the ester methyl groups in poly(methyl acrylate)?* and poly-( a-chloroacrylate) 27 are undergoing essentially complete rotation a t 77'K. Previous studies of polymers having side chains which contain aliphatic hydrocarbon parts larger than methyl have been confined to the poly-(methacrylate esters) z733 and include poly-(ethyl methacrylate) z7,28 and poly-(isobutyl methacrylate) .27 In contrast to the behavior of poly-(butene-1), in poly-(ethyl methacrylate) complete rotation of the ester ethyl and main chain methyl groups appears to be taking place a t temperatures of 200OK. and above, a transition being found in the 90 to 200OK. range.28 At 77'K., the second moment (22) W. P. Slichter, unpublished rpsults. (23) €1. S. Gutowsky and L. €1. Meyer, J . Chem. Phys., 21, 2122 (1953). (24) H. S. Gutowsky. H. Saika, M. Takeda and D. E. Woessner, ibid., 27. 534 (1957). (25) W.P. Slichter, Mncmmol. Chem., 34, 67 (1959). (26) J. G. Powles, Pvoc. Phys. SOC.(London), 69. 281 (1956). (27) W. P. Slichter and E. R. Mandell, J . A p p l . Phys., 30, 1473 (1 959). (28) K. M . Sinnott. J . Polymer Sei.. 42, 3 (ISGO). (29) E. G. Rochow and H. G. LeClair, J . Inorg. Nucl. Chem., 1, 92 (1955). (30) H. Kuaomoto, J. Lawrenson and H. S. Gutowsky, J . Chem. Phys., 32,724 (1960). (31) C . M. Huggins, L. E. St. Pierre and A. M. Bueohe, J. P h y s . Chem., 64, 1304 (1960).
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value for poly-(ethyl methacrylate) is about 5 gauss2 below the estimated rigid lattice value, indicating some rotation of the ester methyl group even a t this temperature. Since it is expected that the calculated rigid lattice and methyl rotation second moments for the three monomers studied would be within 1-3 gauss2 of those for the respective polymer, it appears from the data in Fig. 8 that methyl group rotation of comparable amount is taking place in 4-methylpentene-1 a t temperatures only -1OOK. lower than those for the polymer. This is in marked contrast to the resultslO for ar-methylstyrene and its polymer where complete methyl group rotation is believed to take place a t temperatures about 100°K. lower in the monomer than for the polymer. Removal of one of the methyl groups from 4-methylpentene-1 to give pentene-1 leads to a situation where considerably more motion is taking place a t 77°K. in the monomer than in the respective polymer. This effect is even more noticeable in the data for the branched isorner of pentene-1, 3-methylbutene1. The abrupt decrease of the second moment to values near zero, exhibited by all three monomers a t temperatures 25-3OOIC. below their respective melting points indicates the onset of motion other than side chain ]rotation, possibly involving tumbling of the individual monomers. This latter result is decidedly different from that obtainedlO for the monomers methyl methacrylate, methacrylic acid and a-methylstyrene, which have second moment values of 9-10, 7 and 10 gauss,%respectively, a t teimperatures not more than 8°K.
BERNARD L.WILLI.4MS
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below the melting point, indicating a much more rigid crystal structure for the latter three monomers. The second moment decreases taking place a t 260'K. or above for all polymers investigated is believed to be a consequence of side chain and main chain reorientations associated with the respective glass transitions. As reported p r e v i o u ~ l y ~ ~ ~ such reorientations are also believed to be the cause of the substantial changes found in the dynamic mechanical properties in the same temperature region for each polymer. On the other hand P31, PP1, P3MB1 and P4MP1 do not appear to exhibit marked line narrowing in or near the 150°K. region where a loss peak attributed to the motion of three or four segments in the amorphous regions of the polymer has been found.g The fact that the line narrowing process near room temperature occurs for PTDP before that for polypropylene prepared under the same conditions is not understood at this time. Acknowledgments.-We wish to express our thanks to Professor R. E. Click of Florida State University for frequent discussions during the formative stages of this work, to Professor R. S. Stein of University of Massachusetts and Dr. W. P. Slichter of Bell Telephone Laboratories for bringing to our attention their work prior to publication, to Mr. R. P. Gupta and Mr. R. A. Wall for preliminary n.m..r. measurements on some of these compounds, and to Drs. F. P. Reding and R. D. Lundberg of Union Carbide Chemicals Company for their aid and interest in this study.
THE TRAXSITIOX FROM TYPICAL POLYELECTROLYTE TO POLYSOAP. 111. LIGHT SCATTERING AND VISCOSITY STUDIES OF POLY-4VIXYLPYRIDINE DERIVATIVES1 BY ULRICHP. STRAUSS AND BERNARD L. WILLIAMS^ Ralph G. Wriyht Laboratory, School of Chemistry, Rutgers, The State University, N e w Brunswick, New Jersey Recetved March 3, 1961
One polyelectrolyte and four polysoaps were prepared from poly-4-vinylpyridine by quaternising 0, 4.8, 10.3, 16.3 and 34.1% of its pyridine groups with n-dodecyl bromide and the remainder with ethyl bromide. Light scattering studies in a solution of LiBr in iisopropyl alcohol gave results typical of normal polymers. The molecular weights were considerably lower than that of the parent polymer, indicating that degradation had occurred during quaternization. The mean-square end-to-end distance per unit chain length a t the theta point increased with increasing dodecyl group content, which was ascribed to steric hindrance. On the other hand, light scattering results obtained in 0.05, 0.1 and 0.2 M aqueous KBr solutions, while normal for the polyelectrolyte, indicated aggregate formation of the polysoap molecules. These aggregates are fairly stable to dilution at 25'; but the degree of aggregation decoreases with dilution if the diluted solutions are heated to 45" for a t least 24 hours before being allowed to equilibrate a t 25 . . With the latter type of procedure, one can obtain parameters characteristic of the individual polysoap moleculea a t infinite dilution. Flory's equation relating the rootmean-square end-to-end distance of random coils to the intrinsic viscosity is found to hold fairly well for all the samples except for the polysoap with the highest dodecyl group content. For the latter, only the assumption of a compact sphere model was consistent with both light scattering and viscosity results. Contrary to the behavior in isopropyl alcohol, the unperturbed molecular dimensions decreased with increasing dodecyl group content in the aqueous systems. Thus, in such systems, the previously postulated aggregation of dodecyl groups belonging to the same polysoap molecule is confirmed.
Introduction Several reports have appeared in recent years concerning the transitioii from polyelectrolyte to (1) This work was supported in part by the Officeof Naval Research. The paper is based on a. thesis presented by B. L. Williams in 1958 t o Rutgers University in ]partial fulfillment of the requirements for the Ph.D. degree. (2) Eestman Kodak Fellow, 1956-1957; Colgate-Palmolive Fellow, 1957-1958.
p ~ l y s o a p . ~ -The ~ studies were carried out with series of poly-4-vinylpyridine derivatives prepared by quateriiizing part (y%) of the pyridine groups with n-dodecyl bromide and the remainder with (3) U. P. Strauss and N. L. Gershfeld, J . Phys. Chem., 68, 747 (1954). (4) U. P. Strauss, X. L. Qeishfeld and E. H. Crooh, abzd., 60, 577 (1956). (5) D. \I oermann a n d 1;. T . FVall, %bid.,64, :8l (19bO).
