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A study of the efficiency of plasticizers in polyvinylchloride by the nuclear magnetic resonance method
A STUDY OF THE EFFICIENCY OF PLASTICIZERS IN POLYVINYLCHLORIDE BY THE NUCLEAR MAGNETIC RESONANCE METHOD* A. I . C H E R N I T S Y N ,
A. I. M A K L A K O V , V. A. ar_d Y E . M. 0 R L O V A
VOSKRESENSKII
V. I. U l ' y a n o v - L e n i n State University, K a z a n K a z a n Structural Engineering I n s t i t u t e
(Received 24 February, 1964) I T IS w e l l k n o w n t h a t t h e e f f i c i e n c y o f p l a s t i c i z e r s i n p o l y m e r s c a n b e a s s e s s e d b y v a r i o u s m e t h o d s , f o r e x a m p l e b y t h e r e d u c t i o n in g l a s s t e m p e r a t u r e , Tg, [1, 2], t h e c h a n g e i n p h y s i c o m e c h a n i c a l c h a r a c t e r i s t i c s [3] etc. O n t h e e x a m p l e o f p h t h a lutes and sebacates as plasticizers for polyvinylehloridc (PVC) it has been shown t h a t t h e e f f i c i e n c y o f t h e p l a s t i c i z e r s is d e p e n d e n t o n t h e i r c h e m i c a l s t r u c t u r e [2, 4]. It seemed of interest to examine the possibility of determining tile efficiency o f p l a s t r i e i z c r s f o r tiffs p r e v i o u s l y s t u d i e d p o l y m e r , P V C , b y t h e n u c l e a r m a g n e t i c r e s o n a n c e ( N M R ) m e t h o d , b y m e a s u r i n g t h e s p i n - s p i n (T2) a n d s p i n - l a t t i c e (T1) r e l a x a t i o n t i m e s . T h i s is t h e s u b j e c t o f t h e p r e s e n t c o m m u n i c a t i o n . EXPERIMENTAL The test specimens were in the form of fihns, 0-25 0.30 m m thick, made b y milling on rollers. The plastieizers examined wore: a ) p h t h a l a t o esters -- dimethyl p h t h a l a t e (DMP), diethyl p h t h a l a t e (DEP), dibutyl phthalate (DBP), dioetyl p h t h a l a t e (DOP) and dinonyl p h t h a l a t e (DNP); b) sebacate esters -- dibutyl sebacate (DBS) and dioctyl sebacate (DOS); e) trierosyl phosphate (TCP). The plasticizer content of the specimens varied between 9 and 43% b y weight. Most of the measurcments wer~ made on specimens containing 39o/0 of plastieize.r. The specimens were stabilized by the addition of small quantities of ca.leimn stearate. The relaxation times T 2 and T 1 wore measured on hydrogen nuclei at a frequency of 16.6 Mc/s b y the impulse NMR (spin echo) m e t h o d in a production-line NMR relaxometor manufactured b y the K a z a n Mathematical Machine Plant. F o r measurement of T~ times of the order of 10-5-10 -2 sec the method of H a h n [2] was used with successive impulses at 90 and 180 °. The length of the 90 ° impulse was 8 msec. ]?he inhomogeneity of the magnetic field of the a p p a r a t u s is such t h a t self diffusion does not affect the measurement of T~ up to 20 msec. F o r measurement of larger values of T 2 the method of Carr and Purcell [6] was used. Spin--spin relaxation times shorter t h a n 10 msec were determined from the width of the NMR line recorded as the derivative of the absorption curve from an ordinary NMR spectrometer operating at 17 Me/s, b y means of the formula T2 ~ (2/V'3)(1/y. SH) where * Vysokomo]. soyed. 6: No. 12, 2185-2188, 1964. 2419
2420
A . I . CHERNITSYt~
et
al.
? is the proton gyromagnetic ratio and 5H is the distance between the points of maximal slope of the curve [7]. T 1 was measured by means of the series of impulses 90-180, 90 and 180°. The measurements were made at room temperature. T h e d e r i v a t i v e of t h e N M R a b s o r p t i o n c u r v e of unplasticized P V C is a b r o a d line w i t h 5 H ~ 9 oersteds a n d T 2 ~ 5/~sec, in a g r e e m e n t w i t h p u b l i s h e d results [8]. W i t h t h e a d d i t i o n of plasticizers c o n t a i n i n g h y d r o g e n a t o m s t h e a b s o r p t i o n c u r v e b e c o m e s a t w o - c o m p o n e n t c u r v e w i t h a n a r r o w a n d a b r o a d section. As t h e plasticizer c o n t e n t of t h e s p e c i m e n increases t h e i n t e n s i t y of the n a r r o w p o r t i o n increases. T h e T 2 t i m e s of t h e p r o t o n s c o r r e s p o n d i n g t o t h e n a r r o w c o m p o n e n t , m e a s u r e d b y t h e spin echo m e t h o d , for P V C specimens c o n t a i n i n g plasticizers of different chemical s t r u c t u r e , are s h o w n in t h e table. T h e T 2 t i m e s of t h e p u r e plasticizers lie b e t w e e n 100 a n d 140 msec, d e p e n d ing on t h e i r chemical s t r u c t u r e . T h e d e p e n d e n c e of T 2 a n d T 1 on t h e plasticizer c o n t e n t of t h e s p e c i m e n is s h o w n in t h e d i a g r a m (for D B P ) . A t a plasticizer c o n t e n t of 30-40 ~ b y w e i g h t t h e r e is a s h a r p increase in T~ a n d a fall in T r T h e values of T e a n d T 1 differ DEPENDENCE
OF T 2 A N D
TI, A N D OF T H E EFFICIENCY N U M B E R , E, [2],IN PLASTICIZED P V C O N
THE NATURE OF THE PLASTICIZER
(Specimens contained 39~ by weight of plasticizer) Plasticizer DMP DEP DBP DOP
T2,
TI~
(~see)
(sec)
120 300 590 850
Plasticizer
9"8 10"6 11"9
0"12 0"10
DNP DBS DOS TCP
T2,
T1,
E,
(asec)
(see)~
(°C)
0-07
13.8 15.1 9.4
830 1580 1730 390
c o n s i d e r a b l y for t h e s a m e specimen. A r o u g h e s t i m a t i o n of t h e f r a c t i o n s of protons c o r r e s p o n d i n g t o t h e n a r r o w a n d b r o a d c o m p o n e n t s of t h e s p e c t r u m was m a d e b y t h e use of Wilson a n d P a k e ' s m e t h o d of s e p a r a t i o n of t w o - c o m p o n e n t T2,~sec I000
Tl,sec
20060Qi o,~x~80.1 10
30
wf.%
50
Dependence of T= and T z on eontent of DBP in PVC.
Efficiermy of plasticizers in polyvinylchloride
2421
NMI~ curves [8]. Ill specimens containing v,aq'V~oof DBP and 61 ~/o of PVC it was found t h a t 0.30-0.35 ~ of all the protons are in the free state and the remainder are relatively retarded. This suggests (the proportion of hydrogen atoms in the DBP molecule and PVC repeatirtg unit being approximately the same) t h a t the narrow component of the NMR absorption and the Te times measured by the spin echo method characterize the protons of the plasticizer. The protons of the PVC molecules are responsible for the broad portion of the spectrum. I t is very difficult to estimate 5H and T 2 for these. DISCUSSION
Judging by the known characteristics of the plastieizers studied in this work t h e y function as intra-bundle plasticizers [9], which means t h a t polyhaer-plasticizer interaction must be strong. This is confirmed by the results of measurement of T 2. As is well know, T 2 increases with increase in the mobility of the molecules and vice versa. When a plasticizer with a spiu-spin relaxation time in the pure state of a hundred milliseconds is added T, falls by 2-3 orders of magnirude (to hundreds of microseconds), indicating retardation of the motion of the plasticizer molecules and consequently t h a t there is strong interaction between the plasticizer molecules and the rigid PVC molecules. It is seen from the diagram t h a t with increase in the plasticizer content of the specimen T 2 increases, indicating increase in the mobility of the plasticizer molecules, and evidently of the PVC molecules at the same time. These results are in good agreement with the f~ll in Tg with increase in plasticizer content [4]. The sharp rise in the curve of the det)endence of T 2 on plasticizer content in the region of 35 ~ indicates "freeing" of the plasticizer molecules from ~he binding action of the PVC molecules. We shall now consider the problem of the effect of the nature of the plasticizer on T 2. According to reference [2] its effect can be represented by the efficiency number, E, which is the fall in Tg brought, about by the addition of 1 mole of the given plasticizer to the polymer. The values of E obtained in reference [2] are given in the table, from which it is seen t h a t with increase in size of the terminal Miphatic group of the plasticizer up to octyl the value of Tg falls. Then beginning with a plasticizer containing nonyl radicals Tg rises. A similar relationship has been found in other polymer-plasticizer systems [10]. By eomparison of the plasticizing efficiency of phthalate and sebaeate esters with the same alcohol radical it is easy to see t h a t the sebacates are the more efficient plasti('izers for t)VC. Study of the relatiollship between T 2 and the chemical structure of the plasticizers leads to similar conclusions. I t is seen from the table t h a t T 2 increases with increase in the number of CH 2 groups in the alcohol radicals. For DNP there is a slight fall in T 2 and at the same time it is a slightly poorer plasticizer for PVC. The specimens with the best plasticizers, DBS and DOS, have the highest T,, values. Moreover, TCP and DEP, which differ markedly in chemical
2422
A.I. CHERNITSYNet al.
structure b u t have almost the same values of E have similar spin-spin relaxation times, T 2. Compositions with the more efficient plasticizers have lower T 2 relaxation times. Reduction in the value of T 1 occurs with increase in the plasticizer content of the specimen (see diagram). The observed variation in T 2 can obviously be explained in the following way. In the case of intra-bundle plasticization the plasticizer molecules penetrate between the polymer molecules. When a small quantity of plasticizer has been introduced the molecules of the latter strongly bind the polymer molecules as a result of the strong polymer-plasticizer interaction occurring in our specimens, thus causing loss of mobility of the polymer molecules, i.e. a decrease in T 2. Increase in the plasticizer content leads to greater freedom of its molecules, i.e. to increase in T2. Simultaneously ~dth this there must be an increase in the mobility of the PVC molecules and a fall in Tg. The molecules of the sebacates, having an aliphatic middle section, have a wide choice of distribution i.e. when incorporated into PVC they can arrange themselves in a large number of ways among the polymer molecules. The phthalates, having the more rigid benzene ring in addition to the aliphatic portion, have a narrow choice of distribution in the polymer. This explains the larger values of T 2 for DBS and DBP, and for DOS and DOP. In conclusion it is evident that the mobilities of the PVC and plasticizer molecules are closely related. W~ith increase in mobility of the polymer molecules, as indicated b y decrease in Tg, the mobility of the plasticizer molecules also increases, i.e. b y study of the mobility of the latter it is possible also to consider its plasticizing effect. CONCLUSION
A study has been made of the spin-spin and spin-lattice relaxation times in plasticized PVC, in relation to the quantity and chemical structure of the plasticizer. It is shown that relaxation times T2> 100 zsec, measured b y the spin echo method, characterize the state of the plasticizer molecules. In the case of intra-bundle plasticization of PVC there is strong interaction between the polymer and plasticizer molecules. I t has been established that the efficiency of plasticizers for PVC can be judged b y the value of T~. Translated by E. O. PHILLIPS
REFERENCES 1. S. N. Z H U R K O V , Dissertation, Leningrad, 1948 2. Sh. M. LEL'CHUK and V. I. SEDLIS, Zh. prikl, khim. 30: 412, 1957; 31: 887, 1958 3. V. A. VOSKRESENSKII and S. S. SHAKIRZYANOVA, Zh. prikl, khirn., 35: 217, 1962 4. A. A. TAGER, Fiziko-khimiya polimerov. (The Physical Chemistry of Polymers.) Goskhimizdat, Moscow, 1963
Crystallization of polyurethanes
2423
5. 6. 7. 8. 9.
E. L. HAHN, Phys. Rev. 80: 580, 1950 H. G. CARR and E. M. PURCELL, Phys. Rev. 94: 630, 1954 G. G. POWLES, Polymer 1: 219, 1960 I. Ya. SLONIM, Uspekhi khimii 31: 609, 1962 V. A. KARGIN, P. V. KOZLOV, R. I. ASIMOVA and L. I. ANANYEVA, Dokl. Akad. Nauk SSSg 135: 357, 1960 10. A. A. TAGER, A. I. SUVOROVA, L. N. GOLDYREV, V. I. YESAFOV and L. L. TOPINA, Vysokomol. soyed. 4: 809, 1962
T H E E F F E C T OF T E M P E R A T U R E
ON T H E N A T U R E OF T H E
C R Y S T A L L I Z A T I O N OF P O L Y U R E T H A N E S *
J~. V. VASILYEV and O. G. TAgAKANOV Vladimirsk Scientific-Research Institu?~oof Synthetic Resins
(Received 26 February 1964) THE polyurethanes are a comparatively new class of polymers t h a t have found considerable industrial application in the last t h i r t y years. Whereas the chemistry and technology of polyurethanes is developing fairly rapidly the study of their fundamental properties and structure is lagging behind to a considerable extent. Of the large number of knoval polyurethane compounds sufficiently detailed structural studies have been carried out on only one polymer, based on 1,4butanediol and 1,6-hexamethylene di-isoeyanate [1-7]. The first descriptions of the structure of a polyurethane were given by Brill [8] and later by Zahn and Winter [9]. They ascribe a triclinic lattice to polyurethanes. The latter is built up from a "two-dimensional network" in which neighbouring molecules are connected by H-bridges through regularly alternating segments. The "two-dimensional networks", lying one over another, form a three-dimensional lattice in which the bond between the grids is formed by van der Waals forces. Thus a polyurethane has the layer lattice type of packing. The main valence bonds lie in the direction of the chains (b axis) and hydrogen bonds act in the "two-dimensional network" (a axis). Between the "two-dimensional networks" (c axis) the bonds are formed by van der Waals forces. A crystal lattice constructed by translations in these directions represents an ideal crystal. In crystallizable polymers a perfect lattice can be obtained by slow evaporation of dilute solutions or by slow cooling of the molten polymer. * Vysokomol. soyed. 6: ~o. 12~ 2189-2192, 1964.
A. I. M A K L A K O V , V. A. ar_d Y E . M. 0 R L O V A
VOSKRESENSKII
V. I. U l ' y a n o v - L e n i n State University, K a z a n K a z a n Structural Engineering I n s t i t u t e
(Received 24 February, 1964) I T IS w e l l k n o w n t h a t t h e e f f i c i e n c y o f p l a s t i c i z e r s i n p o l y m e r s c a n b e a s s e s s e d b y v a r i o u s m e t h o d s , f o r e x a m p l e b y t h e r e d u c t i o n in g l a s s t e m p e r a t u r e , Tg, [1, 2], t h e c h a n g e i n p h y s i c o m e c h a n i c a l c h a r a c t e r i s t i c s [3] etc. O n t h e e x a m p l e o f p h t h a lutes and sebacates as plasticizers for polyvinylehloridc (PVC) it has been shown t h a t t h e e f f i c i e n c y o f t h e p l a s t i c i z e r s is d e p e n d e n t o n t h e i r c h e m i c a l s t r u c t u r e [2, 4]. It seemed of interest to examine the possibility of determining tile efficiency o f p l a s t r i e i z c r s f o r tiffs p r e v i o u s l y s t u d i e d p o l y m e r , P V C , b y t h e n u c l e a r m a g n e t i c r e s o n a n c e ( N M R ) m e t h o d , b y m e a s u r i n g t h e s p i n - s p i n (T2) a n d s p i n - l a t t i c e (T1) r e l a x a t i o n t i m e s . T h i s is t h e s u b j e c t o f t h e p r e s e n t c o m m u n i c a t i o n . EXPERIMENTAL The test specimens were in the form of fihns, 0-25 0.30 m m thick, made b y milling on rollers. The plastieizers examined wore: a ) p h t h a l a t o esters -- dimethyl p h t h a l a t e (DMP), diethyl p h t h a l a t e (DEP), dibutyl phthalate (DBP), dioetyl p h t h a l a t e (DOP) and dinonyl p h t h a l a t e (DNP); b) sebacate esters -- dibutyl sebacate (DBS) and dioctyl sebacate (DOS); e) trierosyl phosphate (TCP). The plasticizer content of the specimens varied between 9 and 43% b y weight. Most of the measurcments wer~ made on specimens containing 39o/0 of plastieize.r. The specimens were stabilized by the addition of small quantities of ca.leimn stearate. The relaxation times T 2 and T 1 wore measured on hydrogen nuclei at a frequency of 16.6 Mc/s b y the impulse NMR (spin echo) m e t h o d in a production-line NMR relaxometor manufactured b y the K a z a n Mathematical Machine Plant. F o r measurement of T~ times of the order of 10-5-10 -2 sec the method of H a h n [2] was used with successive impulses at 90 and 180 °. The length of the 90 ° impulse was 8 msec. ]?he inhomogeneity of the magnetic field of the a p p a r a t u s is such t h a t self diffusion does not affect the measurement of T~ up to 20 msec. F o r measurement of larger values of T 2 the method of Carr and Purcell [6] was used. Spin--spin relaxation times shorter t h a n 10 msec were determined from the width of the NMR line recorded as the derivative of the absorption curve from an ordinary NMR spectrometer operating at 17 Me/s, b y means of the formula T2 ~ (2/V'3)(1/y. SH) where * Vysokomo]. soyed. 6: No. 12, 2185-2188, 1964. 2419
2420
A . I . CHERNITSYt~
et
al.
? is the proton gyromagnetic ratio and 5H is the distance between the points of maximal slope of the curve [7]. T 1 was measured by means of the series of impulses 90-180, 90 and 180°. The measurements were made at room temperature. T h e d e r i v a t i v e of t h e N M R a b s o r p t i o n c u r v e of unplasticized P V C is a b r o a d line w i t h 5 H ~ 9 oersteds a n d T 2 ~ 5/~sec, in a g r e e m e n t w i t h p u b l i s h e d results [8]. W i t h t h e a d d i t i o n of plasticizers c o n t a i n i n g h y d r o g e n a t o m s t h e a b s o r p t i o n c u r v e b e c o m e s a t w o - c o m p o n e n t c u r v e w i t h a n a r r o w a n d a b r o a d section. As t h e plasticizer c o n t e n t of t h e s p e c i m e n increases t h e i n t e n s i t y of the n a r r o w p o r t i o n increases. T h e T 2 t i m e s of t h e p r o t o n s c o r r e s p o n d i n g t o t h e n a r r o w c o m p o n e n t , m e a s u r e d b y t h e spin echo m e t h o d , for P V C specimens c o n t a i n i n g plasticizers of different chemical s t r u c t u r e , are s h o w n in t h e table. T h e T 2 t i m e s of t h e p u r e plasticizers lie b e t w e e n 100 a n d 140 msec, d e p e n d ing on t h e i r chemical s t r u c t u r e . T h e d e p e n d e n c e of T 2 a n d T 1 on t h e plasticizer c o n t e n t of t h e s p e c i m e n is s h o w n in t h e d i a g r a m (for D B P ) . A t a plasticizer c o n t e n t of 30-40 ~ b y w e i g h t t h e r e is a s h a r p increase in T~ a n d a fall in T r T h e values of T e a n d T 1 differ DEPENDENCE
OF T 2 A N D
TI, A N D OF T H E EFFICIENCY N U M B E R , E, [2],IN PLASTICIZED P V C O N
THE NATURE OF THE PLASTICIZER
(Specimens contained 39~ by weight of plasticizer) Plasticizer DMP DEP DBP DOP
T2,
TI~
(~see)
(sec)
120 300 590 850
Plasticizer
9"8 10"6 11"9
0"12 0"10
DNP DBS DOS TCP
T2,
T1,
E,
(asec)
(see)~
(°C)
0-07
13.8 15.1 9.4
830 1580 1730 390
c o n s i d e r a b l y for t h e s a m e specimen. A r o u g h e s t i m a t i o n of t h e f r a c t i o n s of protons c o r r e s p o n d i n g t o t h e n a r r o w a n d b r o a d c o m p o n e n t s of t h e s p e c t r u m was m a d e b y t h e use of Wilson a n d P a k e ' s m e t h o d of s e p a r a t i o n of t w o - c o m p o n e n t T2,~sec I000
Tl,sec
20060Qi o,~x~80.1 10
30
wf.%
50
Dependence of T= and T z on eontent of DBP in PVC.
Efficiermy of plasticizers in polyvinylchloride
2421
NMI~ curves [8]. Ill specimens containing v,aq'V~oof DBP and 61 ~/o of PVC it was found t h a t 0.30-0.35 ~ of all the protons are in the free state and the remainder are relatively retarded. This suggests (the proportion of hydrogen atoms in the DBP molecule and PVC repeatirtg unit being approximately the same) t h a t the narrow component of the NMR absorption and the Te times measured by the spin echo method characterize the protons of the plasticizer. The protons of the PVC molecules are responsible for the broad portion of the spectrum. I t is very difficult to estimate 5H and T 2 for these. DISCUSSION
Judging by the known characteristics of the plastieizers studied in this work t h e y function as intra-bundle plasticizers [9], which means t h a t polyhaer-plasticizer interaction must be strong. This is confirmed by the results of measurement of T 2. As is well know, T 2 increases with increase in the mobility of the molecules and vice versa. When a plasticizer with a spiu-spin relaxation time in the pure state of a hundred milliseconds is added T, falls by 2-3 orders of magnirude (to hundreds of microseconds), indicating retardation of the motion of the plasticizer molecules and consequently t h a t there is strong interaction between the plasticizer molecules and the rigid PVC molecules. It is seen from the diagram t h a t with increase in the plasticizer content of the specimen T 2 increases, indicating increase in the mobility of the plasticizer molecules, and evidently of the PVC molecules at the same time. These results are in good agreement with the f~ll in Tg with increase in plasticizer content [4]. The sharp rise in the curve of the det)endence of T 2 on plasticizer content in the region of 35 ~ indicates "freeing" of the plasticizer molecules from ~he binding action of the PVC molecules. We shall now consider the problem of the effect of the nature of the plasticizer on T 2. According to reference [2] its effect can be represented by the efficiency number, E, which is the fall in Tg brought, about by the addition of 1 mole of the given plasticizer to the polymer. The values of E obtained in reference [2] are given in the table, from which it is seen t h a t with increase in size of the terminal Miphatic group of the plasticizer up to octyl the value of Tg falls. Then beginning with a plasticizer containing nonyl radicals Tg rises. A similar relationship has been found in other polymer-plasticizer systems [10]. By eomparison of the plasticizing efficiency of phthalate and sebaeate esters with the same alcohol radical it is easy to see t h a t the sebacates are the more efficient plasti('izers for t)VC. Study of the relatiollship between T 2 and the chemical structure of the plasticizers leads to similar conclusions. I t is seen from the table t h a t T 2 increases with increase in the number of CH 2 groups in the alcohol radicals. For DNP there is a slight fall in T 2 and at the same time it is a slightly poorer plasticizer for PVC. The specimens with the best plasticizers, DBS and DOS, have the highest T,, values. Moreover, TCP and DEP, which differ markedly in chemical
2422
A.I. CHERNITSYNet al.
structure b u t have almost the same values of E have similar spin-spin relaxation times, T 2. Compositions with the more efficient plasticizers have lower T 2 relaxation times. Reduction in the value of T 1 occurs with increase in the plasticizer content of the specimen (see diagram). The observed variation in T 2 can obviously be explained in the following way. In the case of intra-bundle plasticization the plasticizer molecules penetrate between the polymer molecules. When a small quantity of plasticizer has been introduced the molecules of the latter strongly bind the polymer molecules as a result of the strong polymer-plasticizer interaction occurring in our specimens, thus causing loss of mobility of the polymer molecules, i.e. a decrease in T 2. Increase in the plasticizer content leads to greater freedom of its molecules, i.e. to increase in T2. Simultaneously ~dth this there must be an increase in the mobility of the PVC molecules and a fall in Tg. The molecules of the sebacates, having an aliphatic middle section, have a wide choice of distribution i.e. when incorporated into PVC they can arrange themselves in a large number of ways among the polymer molecules. The phthalates, having the more rigid benzene ring in addition to the aliphatic portion, have a narrow choice of distribution in the polymer. This explains the larger values of T 2 for DBS and DBP, and for DOS and DOP. In conclusion it is evident that the mobilities of the PVC and plasticizer molecules are closely related. W~ith increase in mobility of the polymer molecules, as indicated b y decrease in Tg, the mobility of the plasticizer molecules also increases, i.e. b y study of the mobility of the latter it is possible also to consider its plasticizing effect. CONCLUSION
A study has been made of the spin-spin and spin-lattice relaxation times in plasticized PVC, in relation to the quantity and chemical structure of the plasticizer. It is shown that relaxation times T2> 100 zsec, measured b y the spin echo method, characterize the state of the plasticizer molecules. In the case of intra-bundle plasticization of PVC there is strong interaction between the polymer and plasticizer molecules. I t has been established that the efficiency of plasticizers for PVC can be judged b y the value of T~. Translated by E. O. PHILLIPS
REFERENCES 1. S. N. Z H U R K O V , Dissertation, Leningrad, 1948 2. Sh. M. LEL'CHUK and V. I. SEDLIS, Zh. prikl, khim. 30: 412, 1957; 31: 887, 1958 3. V. A. VOSKRESENSKII and S. S. SHAKIRZYANOVA, Zh. prikl, khirn., 35: 217, 1962 4. A. A. TAGER, Fiziko-khimiya polimerov. (The Physical Chemistry of Polymers.) Goskhimizdat, Moscow, 1963
Crystallization of polyurethanes
2423
5. 6. 7. 8. 9.
E. L. HAHN, Phys. Rev. 80: 580, 1950 H. G. CARR and E. M. PURCELL, Phys. Rev. 94: 630, 1954 G. G. POWLES, Polymer 1: 219, 1960 I. Ya. SLONIM, Uspekhi khimii 31: 609, 1962 V. A. KARGIN, P. V. KOZLOV, R. I. ASIMOVA and L. I. ANANYEVA, Dokl. Akad. Nauk SSSg 135: 357, 1960 10. A. A. TAGER, A. I. SUVOROVA, L. N. GOLDYREV, V. I. YESAFOV and L. L. TOPINA, Vysokomol. soyed. 4: 809, 1962
T H E E F F E C T OF T E M P E R A T U R E
ON T H E N A T U R E OF T H E
C R Y S T A L L I Z A T I O N OF P O L Y U R E T H A N E S *
J~. V. VASILYEV and O. G. TAgAKANOV Vladimirsk Scientific-Research Institu?~oof Synthetic Resins
(Received 26 February 1964) THE polyurethanes are a comparatively new class of polymers t h a t have found considerable industrial application in the last t h i r t y years. Whereas the chemistry and technology of polyurethanes is developing fairly rapidly the study of their fundamental properties and structure is lagging behind to a considerable extent. Of the large number of knoval polyurethane compounds sufficiently detailed structural studies have been carried out on only one polymer, based on 1,4butanediol and 1,6-hexamethylene di-isoeyanate [1-7]. The first descriptions of the structure of a polyurethane were given by Brill [8] and later by Zahn and Winter [9]. They ascribe a triclinic lattice to polyurethanes. The latter is built up from a "two-dimensional network" in which neighbouring molecules are connected by H-bridges through regularly alternating segments. The "two-dimensional networks", lying one over another, form a three-dimensional lattice in which the bond between the grids is formed by van der Waals forces. Thus a polyurethane has the layer lattice type of packing. The main valence bonds lie in the direction of the chains (b axis) and hydrogen bonds act in the "two-dimensional network" (a axis). Between the "two-dimensional networks" (c axis) the bonds are formed by van der Waals forces. A crystal lattice constructed by translations in these directions represents an ideal crystal. In crystallizable polymers a perfect lattice can be obtained by slow evaporation of dilute solutions or by slow cooling of the molten polymer. * Vysokomol. soyed. 6: ~o. 12~ 2189-2192, 1964.