13C NMR Study of Poly(Propylene Oxide)S Prepared with Organotin-Alkyl Phosphate Condensates of Various Degrees of Condensation

Polymer Journal, Vol. 25, No. 7, pp 685~696 (1993)

13C NMR Study of Poly(propylene oxide)s Prepared with Organotin-Alkyl Phosphate Condensates of Various Degrees of Condensation

Katsuhito MIURA,t Tatsuki KITAYAMA, Koichi HATADA,tt and Tetsuya NAKATA*

Department of Chemistry, Faculty of Engineering Science, Osaka University, Toyonaka, Osaka 560, Japan * Research Laboratories, Daiso Co., Ltd., Amagasaki, Hyogo 660, Japan

(Received November 24, 1992)

ABSTRACT: Polymerizations of (S)- and (RS)-propylene oxides were carried out with various organotin-alkyl phosphate condensates derived from dibutyltin oxide (Bu2SnO) and tributyl phosphate (Bu 3PO4 ) as initiators. Regioirregularity of poly((S)-( - )-propylene oxide) was studied by 13C NMR spectroscopy based on revised peak assignments. The results suggest the presence of alternating irregular units as well as isolated ones, in contrast with poly((S)-( - ) propylene oxide)s formed with ZnEt2-H2 O and A!Et3-H20--(acetylacetone), in which only isolated irregular units exist. The benzene-hexane insoluble fraction of poly((RS)-propylene oxide) initiated with Bu 2 Sn0--Bu 3PO4 (I : 2) condensate, which was insoluble in a variety of organic solvents, had isotactic diad of 94% and isotactic triad of 91 %. The reactivity of

Bu 2 Sn0--Bu 3PO4 (I : 2) condensate was higher than that of Bu2 Sn0--Bu3PO4 (1 : 4) condensate or Bu 2 SnO-Bu3PO4 (I: I) condensate. Among the Bu 2 Sn0--Bu3 PO4 (I: 2) condensates, high molecular weight condensate showed higher reactivity than the low molecular weight one. KEY WORDS Propylene Oxide / Organotin-Alkyl Phosphate Condensate / Irregular Linkage / Tacticity / 13C NMR /

Organozinc and organoaluminum com of the monomer) is effective for rapid po pounds are known as highly reactive initiators lymerization of various oxirane compounds. in ring opening polymerization of oxirane Polymerization with these initiators in aliphatic compounds. The structural analyses of the hydrocarbons proceeds in slurry. For the polymers with those initiators have been pre polymerization of ethylene oxide by organotin viously reported. 1 - 10 Recently, we reported alkyl phosphate condensates, a bimetallic that organotin-alkyl phosphate condensates mechanism shown in Scheme 1 has been also functioned as efficient initiators for the suggested by one of the present authors. 11 As polymerization of oxirane compounds, 11 • 12 one of the possible mechanisms, it seems that and these have been used for the industrial such structures would be effective for steric production of epichlorohydrin-ethylene oxide control in propagation step in the polymeriza rubber. 13 tion of substituted oxiranes. The organotin-alkyl phosphate condensates In this work, the stereochemical structure exhibit excellent stability and can be stored of poly((RS)-propylene oxide) and the regio under air for a long period. A very small irregularity of optically active poly((S)-( - ) amount of the initiators (0.01---0.5% by weight propylene oxide)prepared with dibutyltin oxide

t On leave from Daiso Co., Ltd. tt To whom correspondence should be addressed.

685 K. MIURA et al. ½)\ 0 '

Sn /; L1 \~: t O 0 \ I I \ /, \ ?i p p P ,O-t-CH-CHz-O-t-P- /~ ,-+;\ / \ / ' I \ o. r o 0 :' CH3 ~..._ I \ / Sn Sn j D 0 Sn I 0 \ 0 \ I \ 11 p o-t-CH-CHz-O-t-P- / \o\ / bn3 I Sn

Scheme 1. Proposed mechanism of initiation and propagation.

(Bu2 SnO)-tributyl phosphate (Bu3PO4 ) con Measurements densates were studied by means of 13C NMR 13C NMR spectra of the polymers were spectroscopy, Effects of Bu 2 SnO/Bu 3PO4 ratio measured in benzene-d6 at 50°C on a JEOL on the tacticity of poly((RS)-propylene oxide) JNM-GX 500 spectrometer at 125 MHz, are also discussed, Chemical shifts were referred to the central

peak of benzene-d6 at 128,0 ppm, Gel permea EXPERIMENTAL tion chromatography (GPC) was performed using a Waters model 150-C instrument Materials equipped with a differential refractometer, Racemic propylene oxide was refluxed over Tetrahydrofuran was used as an eluent at a a mixture of potassium hydroxide and cal flow rate of 1 ml min - 1 , The chromatograms cium dihydride, and then fractionally distilled were calibrated against standard polystyrene under nitrogen atmosphere, (S)-( - )-Propylene samples, The weight average molecular weight oxide was obtained from Aldrich Chemical of the polymers were determined by viscom

Company, Inc; [c,:Jf/ = - 7,2° (c= 1, CHC1 3), etry in benzene at 25°C using the following 98,8% e,e, The optical purity of (S)-( - ) equation; [11]=0,81 x 10- 4 Mw 0 ·85 , 15 The propylene oxide was measured by complexa number average molecular weight of the tion gas chromatography, 14 Solvents were initiator was determined by vapor pressure purified by conventional methods and distilled osmometry (VPO) in benzene at 40°C using a just before use, Corona-114 osmometer, Optical rotation of polymers derived from (S)-propylene oxide was measured in benzene at a concentration

686 Polym. J,, VoL 25, No, 7, 1993 13C NMR Study of PPO Prepared with Bu 2 Sn0-Bu3PO4 of I g dl- 1 at 20°C on a JASCO polarimeter Bu O 0 I II II model DIP-181. Melting point of polymers +sn-O-P-O-P-O+ X=Bu I I I were measured on a Perkin-Elmer differential X OBu OBu scanning calorimeter model DSC-4 at a heat ing rate of l0°C min - 1 . 0 II or +O-P-O+ I Preparation of Bu2 Sn0-Bu3 P04 Condensates OBu Organotin-alkyl phosphate condensates can be prepared from various combinations of or branched or crosslinked structure ganotin compounds such as Bu2SnO, tributyl tin chloride (Bu3 SnCl), and triphenyltin chlo Polymerizations of Propylene Oxide ride (Ph3 SnCl), with alkyl phosphates such Polymerization of propylene oxide in ben as Bu 3PO4 , dibutyl phosphate (Bu2PHO4 ), zene was carried out in the following manner. 11 13 and triethyl phosphate (Et3PO4 ). • In the Insoluble Bu 2 SnO-Bu3PO 4 (1: 2) condensate present work, condensates of Bu2 SnO and was dried in a glass ampoule at l 50°C for 1 h Bu3PO4 prepared in the following manner in vacuo. After cooling, benzene and racemic were used as initiators. or optically active propylene oxide were added The mixture of Bu2 SnO and Bu3PO4 was subsequently into the ampoule under dry stirred and heated at 250°C for 20--30 min nitrogen atmosphere. Polymerizations were under dry nitrogen. In the condensation reac carried out at 5°C for 3 or 8 h, and then tion, butane, butene, 1-butanol, and dibutyl terminated by adding methanol. The polym ether were distilled out. The condensates erization mixture was diluted with benzene formed in the early stage of the reaction and the insoluble initiator residue was removed were soluble in a variety of organic solvents, by centrifugation. The polymers were re but they became insoluble as the degree of covered from the benzene solution by evapo condensation increased because of the forma rating the solvent. Benzene-hexane (1 : 2) in tion of network structure. The molecular soluble fraction of the polymer was isolated by weights and elemental analyses of various centrifugation. Benzene-hexane soluble frac Bu2 SnO-Bu3 PO4 condensates used in the tion of the polymer was obtained by evapo present work are listed in Table I. These rating the solvents. Polymerization in bulk condensates were assumed to have the follow was carried out in a similar manner at 30°C ing structure 11 : for 2.5 or 5 h. After the solvent was evapo rated, the residual polymer was dried under

Table I., The molecular weights and elemental analyses of various Bu 2 SnO--Bu 3 PO4 condensates

Sn p C H Bu 2 SnO-Bu3PO4 condensates % % % %

Bu 2 SnO-Bu3 PO4 (I: 2)" 24.5 12.7 29.9 5.7 Bu 2 SnO-Bu3 PO4 (I: 2) 11700 24.2 12.4 30.8 6.1

Bu2 SnO-Bu3 PO4 (I: 2) 8300 24.1 12.1 32.7 6.4 Bu2 Sn0-Bu3P04 (I: 2) 3000 20.1 10.2 33.1 6.4 Bu2 SnO-Bu3PO4 (I: 4) 4500 12.9 13.9 31.5 6.3 Bu 2Sn0-Bu3PO4 (I: I) 5600 28.2 8.0 34.9 6.9

• Determined by VPO. b The condensate was insoluble in a variety of organic solvents such as benzene, chloroform, and tetrahydrofuran.

Polym. J., Vol. 25, No. 7, 1993 687 K. MIURA et a/. high vacuum. lowing four types of triad are distinguishable Polymerizations with diethylzinc (ZnEt2) by NMR spectroscopy: H2O (1: 1) and triethylaluminium(AlEt3)• H20-acetylacetone(AcAc) (1 : 0.5: 0.5) were AAA(BBB) carried out according to the methods of -CH2-CH-O-CH2-CH-O-CH2-CH-0- Oguni6 ·9 and Vandenberg, 1 respectively. 1 I I CH 3 CH 3 CH 3 RESULTS AND DISCUSSION AAB(BBA)

-CH2-CH-O-CH2-CH-O-CH-CH2-0- Polymerization of racemic or optically active I I I propylene oxide was carried out with an CH 3 CH 3 CH 3 insoluble Bu2SnO-Bu3 PO4 (1: 2) condensate ABA(BAB) in benzene. The results are shown in Table II. -CH2-CH-O-CH-CH2-0-CH2-CH-0- The polymers obtained were fractionated into 1 I I benzene-hexane (1 : 2, v/v) soluble and in CH 3 CH 3 CH 3 The insoluble fractions soluble fractions. BAA(ABB) showed melting points but not the soluble ones. ·The specific optical rotation of the soluble -CH-CH 2-0-CH2-CH-O-CH2-CH-O- I I I fraction of poly((S)-( - )-propylene oxide) was CH 3 CH 3 CH 3 much lower than that of the insoluble one. It should be noted that the spectrum of the Although the M w values of the soluble frac optically active polymer does not involve tions are lower than the insoluble ones, the stereoisomerism and can be analyzed in terms difference is not so remarkable to explain the of the above four types of triads. differences in these physical properties. Figure 1 shows the 13C NMR spectra of Poly(propylene oxide) may have irregular benzene-hexane soluble and insoluble fraction enchainments (head-to-head and tail-to-tail) as of the poly((S)-(-)-propylene oxide) prepared well as regular head-to-tail sequence due to ring with Bu SnO-Bu PO (1 : 2) condensate. Sig opening reactions in both a- and p-positions: 2 3 4 nals of each carbon consisted mainly four CH 2-CH-CH3 groups of resonance. The assignments of the 13C NMR spectra of poly((R)-( + )-propylene /"cf~ oxide) and poly((RS)-propylene oxide) have p ti. been reported by Oguni et al. 9 and Schilling et al., 16 respectively. The absence of melting point and lower optical The assignment of AAA triad can be made rotation of the soluble fraction of poly((S) easily from Figure lA. The assignments of ( - )-propylene oxide) are due to the regio other peaks due to irregular units at triad level irregularity in the polymer chains as described shown in Figure 1 were made by 13C-1 H in the followings. COSY experiment. 1 7 Some of the peaks, methyl resonances in particular, showed fur Regioirregularity ther splittings, which were ascribed to longer For poly((S)-( - )-propylene oxide), eight sequence distribution of regioirregular en isomeric triads are possible· AAA AAB chainment but not to stereosequence distribu ABA, BAA, ABB, BAB, BBA, and BBB'. tion in the irregular triads, since the spectrum where A is -CH CH(CH 3)0- (P-cleavage) 2 of poly((RS)-propylene oxide) that should and B -CH(CH )CH 0- (a-cleavage) accord 3 2 contain various stereosequences showed much ing to Oguni's definition. 9 However, the fol-

688 Polym. J., Vol. 25, No. 7, 1993 "C 0 j ".... < ?-- ;"Iv z ? Table II. Polymerization of racemic or (S)-( - )-propylene oxide in benzene with different initiators __, \0 Time Temp. Yield mp \0- Propylene w Initiator Fraction' [1X]f,O Mwc Mw/M." oxide oc oc n h % z

Bu2SnO-Bu3PO4 Insoluble 4 68 J.5 X 105 3.8 :,:, (RS)- 3 5 [.ll (I : 2)" Soluble 4 8.8 X 104 5.6 c= Bu SnO-Bu PO4 Insoluble 11.3 J.4 X 105 3.0 0. 2 3 69 +31.5° '< (S)-( - )- 8 5 4 (I : 2)b Soluble 5.2 + 19.2° 5.8 X [0 5.1 ....,0 "C "C ZnEt2-H2O 0 (RS)- 36 40 Whole 61 57 2.3 X 105 55.2 (I: I) (in situ)' ...,"C ZnEt2-H2O 'O" (S)-( - )- 24 40 Whole 52 60 +29.4° 2.6 X 105 44.2 !))..., (I: I) (in situ)' "0. AJEt3-H 2O-AcAc (RS)- 40 Whole 76 63 3.2 X [0 5 2.5 (I : o.5: o.5t 36 ;.~- AIEt3-H20--AcAc 0:, (S)-( - )- 18 40 Whole 62 64 + 17.2° l.8x 105 3.2 ...,= (I: o.5: o.5t [.ll ::,

• Monomer 68 mmol, initiator 200 mg, benzene 26 ml. ?0:, b Monomer 34mmol, initiator 100mg, benzene 13ml. ;,= ' Monomer 34mmol, initiator 100mg, benzene 3ml. ..0 d Monomer 34 mmol, initiator 50 mg, benzene 3 ml. AcAc; acetylacetone. ' Benzene-hexane insoluble or souble fraction. f Determined by viscometry (25°C in benzene). • Determined by GPC.

°'\000 K. MIURA et al.

-CH-

(A)

AAA AAA AAA ABA ABA

ABA AAB AAB AAB BAA BAA BAA l PPM 76. 5 75. 5 74. 0 73. 0 19. 0 18. 0

Figure 1. 125 MHz 13C NMR spectra of poly(S)-( - )-(propylene oxide) prepared with insoluble

Bu 2 SnO-Bu3PO4 (1 : 2) condensate measured in benzene-d6 at 50°C. (A) Benzene-hexane (! : 2) insoluble fraction. (B) Benzene-hexane (I : 2) soluble fraction. complicated signals (Figure 2). The present RIS model is not applicable to the present assignments differ from those reported by case. Oguni9 and by Schilling. 16 The assignments 13C NMR spectra of poly((S)-( - )-propyl by Oguni are based on magnetic shielding ene oxide) prepared with ZnEt2-H2 O (1: 1) effects from the neighboring units, while those and AIEt3-H2O-AcAc (I : 0.5: 0.5) were also by Schilling were made from calculation of the analyzed similarly and the results are included chemical shifts based on y-gauche effect and in Table III. If an irregular enchainment B rotational isomeric (RIS) model. However, if (-CH(CH3)-CH2-0-) occurs infrequently to the assignments by these authors were adopted give isolated B unit in A sequence (-AABAA-), to the present spectra, the intensity of AAB the fractions of ABA, AAB, and BAA triads triad signal would be twice as large as that of are equal to each other. This is the case for the

BAA signal. AAB and BAA triads should polymers obtained with ZnEt2-H2 O (I: 1) and have statistically equal proportion regardless A1EtrH2 0--AcAc (1: 0.5: 0.5) (Table III). of propagation mechanism. The present as However, the fraction of ABA triad in the signments shown in Table III satisfy this polymer formed with Bu 2 SnO-Bu3PO4 con requirement. The results indicate that chemical densate is almost twice as large as those of shift prediction from simple shielding effect or AAB and BAA triads (Table III). The distri more elaborated combination of y-effect and bution of triad sequences in regard of regio-

690 Polym. J., Vol. 25, No. 7, 1993 13 C NMR Study of PPO Prepared with Bu2 Sn0-Bu3P04

-CH-

(Al

mm m

rr r

ABA AAB

PPM PPM 76. 5 75. 5 74. 0 73 0 19. 0 18. 0

Figure 2. 125 MHz 13C NMR spectra of poly((RS)-propylene oxide) prepared with insoluble Bu 2 Sn0-

Bu3P04 (I: 2) condensate measured in benzene-d6 at 50°C. (A) Benzene-hexane (I: 2) insoluble fraction. (B) Benzene-hexane (I : 2) soluble fraction. irregularity in this polymer is quite charac larger ABA triad fraction. Assuming that teristic, even though the total of irregular irregular units exist either in an isolated manner triad fractions (AAB + ABA + BAA) is close (-AABAA-) or an alternate manner (-AABA to those for the polymers prepared with BAA-), the fractions of the most probable three

ZnEt2-H2 0 and AIEt3-H2 0-AcAc. There tetrads were calculated as shown in Table IV. fore, other types of irregular enchainment On the other hand, similar calculations for than isolated B unit (-AABAA-) should be the polymers formed with ZnEt2-H2 0 and taken into consideration. AIEt3-H20-AcAc confirmed that the poly If there exist contiguous irregular units in mers scarcely contain alternating irregular the chain (-ABBA-), the fractions of AAB and units (-AABABAA-) but isolated ones (-AAB BAA triads are equal but the fraction of ABA AA-) (Table IV). The results mean that propa triad should be sma11er than the former. When gating anion with irregular chain end [BJ the irregular units B exist alternately in regular formed through o:-cleavage of propylene oxide A sequence (-AABABAA-), the fraction of attacks the next coming propylene oxide in ABA triad is three times as large as that of /]-cleavage fashion to reproduce a regular AAB or BAA triad. Thus the presence of polymer chain end [A]; alternate sequence -ABAB- may contribute to

Polym. J., Vol. 25, No. 7, 1993 691 °' '°N

Table III. Relative abundances(%) of regular and irregular triads in poly((S)-( - )-propylene oxide) prepared with several initiators•

CH CH2 CH3 Initiator AAA ABA AAB BAA AAA ABA AAB BAA AAA ABA AAB BAA (75.92) (76.21) (75.85) (75.51) (73.92) (73.16) (74.33) (73.62) (17 .80) (18.71) (18.85) (17.67)

Bu2SnO-Bu3PO4 (I : 2) 3:: Whole sampJeb 79 10 6 5 81 9 5 5 79 II 5 5 :,,2 Insoluble part' 90 4 3 3 93 3 2 2 90 4 3 3 > Soluble part' 54 23 12 11 56 22 11 II 54 25 II 10

ZnEt2-H 2O (I: I) 85 5 5 5 86 5 4 5 85 5 5 5 AIEt3-H 20-AcAc (I: 0.5: 0.5)d 76 8 8 8 75 9 8 8 76 8 8 8

• Chemical shift value for each triad signal is shown in parentheses. b Determined from the ratio of soluble and insoluble parts. ' Benzene-hexane (I: 2, v/v). d AcAc, acetylacetone. d'

? ,..... < ?-- N .'-" z ? _-__, '°..., 13C NMR Study of PPO Prepared with Bu2 Sn0-Bu3PO4

--O-CH2-CH-O---CH-CH2O- + __J ------. -O-CH2---CH-O-CH-CH 2--0-CH2-CH-O- + __J ______. I I \7 I I I "'-_I CH3 CH3 0 CH3 CH3 CH3 0 [AJ [BJ [AJ [BJ [AJ

--0-CH 2-CH-0---CH---CH 2-0-CH2---CH-0- -O---CH 2-CH-O---CH-CH2--0-CH2---CH-O-CH-CH2-O- 1 I I 1 I I I CH3 CH3 CH3 CH3 CH3 CH3 CH3 [AJ [BJ [AJ [AJ [BJ [AJ [BJ (1) (3) which propagates further in a regular manner. The ratio of frequencies for the propagation

-O-CH2-CH-O-CH-CH2-0---CH 2---CH-O-CH 2---CH-O- (2) and the propagation (3) is 50: 50 for the I I I I CH3 CH3 CH3 CH3 soluble fraction and 86: 14 for the insoluble [AJ [BJ [AJ [AJ fraction, while the propagation (3) did not (2) occur in the polymerization with ZnEt2-H2O (1: 1) and AlEt3-H2 O-AcAc (1: 0.5: 0.5). The Contrastingly, in the polymerization with reason for this peculiar control of regioregu larity in the polymerization with Bu SnO Bu2SnO-Bu3PO4 (1: 2) condensate, a part of 2 the reproduced regular chain ends (1) attack Bu3PO4 is not clear at present. However, if propylene oxide in a a-cleavage manner to the bimetallic catalyst site model (Scheme 1) produce the irregular chain end again; is adopted for the polymerization, the active site "Sn" is switched in each propagation step and thus irregular enchainment may occur alternately.

Table IV. Fraction of tetrad in regard of regioregularity in poly((S)-( - )-propylene oxide) prepared with several initiators

Tetrad Enchainment•

Initiators -ABAA- -ABAB- -AAAA- ABA-,ABAA ABA-+ABAB

% % % % %

Bu2 SnO-Bu3PO4 (!: 2) Whole sample 3.3 2.3 94.4 59 41 Insoluble part 2.5 0.4 97.1 86 14 Soluble part 5.5 5.5 89.0 50 50

Et2Zn-H2 O (!: 1) 5.0 0 95.0 100 0 AIEt 3-H20-AcAc 8.0 0 92.0 100 0 (! : 0.5: 0.5)

• Relative frequency of occurrence of ABAA and ABAB tetrad after ABA triad.

Polym. J., Vol. 25, No. 7, 1993 693 K. MIURA et a/.

Table V. Polymerization of racemic propylene oxide with various

Bu 2 SnO-Bu3 PO4 condensates in bulk at 30°C•

Tacticity/%

Time Yield M w C Bu 2 SnO-Bu 3PO 4 M/ Dyad (-CH2-) Triad (-CH-) h % X 10 5 m r mm mr rr

(1: 2t 2.5 98 5.3 71 29 63 18 19 (I: 2) 11700 2.5 72 3.9 68 32 61 15 17 (I: 2) 8300 2.5 46 3.0 66 34 57 21 22 (1 : 2) 3000 5 26 2.8 59 41 46 27 27 (1 : 4) 4500 5 12 1.9 72 28 59 26 15 ( 1 :1) 5600 5 no polymer

a Monomer 200 mmol, initiator 0.12 mg atom of Sn. b Determined by VPO in benzene at 40°C. ' Determined by viscometry using following equations: [17] =0.81 x 10- 4 M~· 85 in benzene at 25°C. d The condensate was insoluble in a variety of organic solvents such as benzene, chloroform and tetrahydrofuran.

(RS)-Propylene oxide was polymerized with (1: 1) condensates. The reactivity of Bu2SnO the insoluble Bu 2 Sn0-Bu3PO4 (I : 2) conden Bu3PO4 (1 : 2) condensate as well as the iso sate and the polymer formed was fractionated tacticity of the polymer formed increased as into benzene-hexane soluble and insoluble molecular weight of the condensate increased. fractions. Figure 2 shows 13C NMR spectra of Bu2SnO-Bu3PO4 (I : 2) condensate of Mn the both fractions, which are informative con 3000 exhibited higher reactivity than Bu2SnO cerning the stereoregularity of the polymer. 5 Bu3PO4 (1: 4) condensate of Mn 4500. How The distributions of diad and triad sequences ever, Bu2 SnO-Bu3PO4 (1: 4) condensate of were estimated from the signals in methylene Mn 4500 gave the polymer with higher iso and methine carbon regions. Signals due to tacticity than the Bu2 SnO-Bu3PO4 (1 : 2) con irregular linkages were assigned from the densate. Bu2 SnO-Bu3PO4 (1: 1) condensate comparison with the 13 C NMR spectra of of Mn 5600 gave no polymer. From these poly((S)-( - )-propylene oxide) (Figure 1). results, higher molecular weight and higher

proportion of Bu 3 PO 4 of Bu 2 Sn0-Bu3PO 4 Stereoregularity condensates are the important factors for the Polymerization of (RS)-propylene oxide higher reactivity as well as higher stereo was also carried out with various Bu 2 SnO specificity. Bu3PO4 condensates in bulk at 30°C for 2.5 Stereoregularity of poly((RS)-propylene ox or 5 h. The molar ratio of tin atom in Bu2 Sn0- ide) prepared with several initiators is shown Bu3PO4 condensates against the monomer in Table VI. Benzene-hexane insoluble frac was set to be constant in every polymerization. tion of poly((RS)-propylene oxide) formed The results of the polymerization are shown with Bu2 SnO-Bu3PO4 (I : 2) condensate was in Table V. The activity of the initiator, the found to be highly isotactic. (RS)-Propylene molecular weight and the stereoregularity of oxide can be polymerized by a wide variety of the polymers are affected by the molecular initiators (anionic, cationic, and ionic co weight of the initiator. Bu2 Sn0-Bu3PO4 (I: 2) ordination initiators). Generally, the ionic condensate exhibited higher reactivity than coordination initiators such as ZnEt2-H2 O, Bu2 SnO-Bu3PO4 (1: 4) and Bu2 SnO-Bu3PO4 ZnEt2-ROH, and AlEt3-H2 0-AcAc afford

694 Polym. J., Vol. 25, No. 7, 1993 13C NMR Study of PPO Prepared with Bu 2 Sn0- Bu 3P04

Table VI. Stereoregularity of poly((RS)-propylene oxide)s prepared with different initiators

Tacticity/%

Initiators Dyad (-CH2-) Triad (-CH-) References

m r mm mr rr

Bu2 Sn0-Bu3 P04 (!: 2)" Whole sample 76 24 67 16 17 This work Insoluble partb 94 6 91 6 3 This work Soluble partb 63 37 52 24 24 This work

Et2 Zn--MeOH (I : 1.65) 71 29 54 31 15 ref 7

Et2 Zn-MeOH (1 : 2) 66 34 47 33 20 ref 8

Et2 Zn-H2 0 (]:!) (in situ) 66 34 51 33 16 This work

AIEt3-H2 0-AcAc (1: 0.5: 0.5)' 72 28 58 30 12 This work KOH 50 50 27 47 26 ref 7 'BuOK 50 50 25 50 25 ref 5

• The condensate was insoluble in common organic solvents. b Benzene-hexane (I: 2, v/v). ' AcAc, acetylacetone. the polymers with high molecular weight as than the zinc or aluminum initiator as well as well as with high stereoregularity.6 - 10 On the the peculiar regioirregular enchainment. contrary, the anionic initiators such as potas sium hydroxide and potassium butoxide give REFERENCES regular head-to-tail polymers with low molec ular weight and random distribution of con I. E. J. Vandenberg, J. Polym. Sci., A-1, 7, 525 (1969). 2. K. E. Steller, Am. Chem. Soc. Symp. Ser., 6, 136 figuration in the chain. 5 • 7 Cationic initiators (1975). such as A!Et -H 0 and (PhCHOCH )+ - 3 2 3 3. A. Dworak, Makromol. Chem., Rapid Commun., 6, (SbCl6 )- lead to polymers having irregular 665 (1985). enchainments due to ring-opening reactions 4. H. N. Cheng and D. A. Smith, J. Appl. Polym. Sci., at both a- and fl-positions of propylene 34, 909 (1987). 5. N. Oguni, K. Lee, and H. Tani, Macromolecules, 5, oxide. 5 • 18 Ionic coordination mechanism has 819 (1972). 8 19 been well established for the ZnEt2-H20, • 6. N. Oguni, S. Watanabe, M. Maki, and H. Tani, 1 ZnEt2-MeOH,20•21 and AIEt3-H2 0-AcAc Macromolecules, 6, 195 (1973). 7. T. Uryu, H. Shimazu, and K. Matsuzaki, J. Polym. initiated polymerizations. Bu 2 Sn0-Bu3 P04 Sci., condensates exhibit very similar catalytic 11, 275 (1973). 8. M. Ishimori, K. Tsukigawa, T. Nakada, and T. activity to those of the zinc and aluminum Tsuruta, J. Macromol. Sci., Chem., 11, 379 (1977). initiators, that is, high regioselectivity and 9. N. Oguni, S. Shinohara, and K. Lee, Polym. J., 11, stereospecificity, although the sequence dis 755 (1979). 10. H. C. W. M. Buys, H. G. J. Overmas, and J. G. tribution of irregular enchainment existed in Naltes, "Coordination Polymerization," C. C. Price small amounts was quite different. The fact and E. J. Vanderberg, Ed., Plenum Publishing suggests that ionic coordination mechanism is Corporation, New York, N.Y., 1983, pp 75-93. also predominant for the polymerization of 1 I. T. Nakata, "Coordination Polymerization," C. C. Price and E. Vandenberg, Ed., Plenum Publishing propylene oxide with Bu Sn0-Bu P0 con J. 2 3 4 Corporation, New York, N.Y., 1983, pp 55-74. densates. The present studies indicate the 12. K. Miura, T. Kitayama, K. Hatada, and T. Nakata, higher isotactic specificity of Bu2 Sn0-Bu3 P04 Polym. J., 22, 671 (1990).

Polym. J., Vol. 25, No. 7, 1993 695 K. MIURA et al.

13. T. Nakata and K. Kawamata, Osaka Soda Co., Polym. J., 25, 697 (1993). Ltd., U.S. Patent 3,773,694 (Nov. 20, 1973). 18. T. Iijima, Y. Sakamoto, and H. Kakiuchi, J. Polym. 14. V. Schurig, J. Chromatogr., 441, 135 (1988). Sci., Polym. Chem., 26, 3189 (1988). 15. E. J. Vandenberg, "Kirk-Othmer: Encyclopedia of 19. M. Ishimori, 0. Nakasugi, N. Takeda, and T. Chemical Technology," Vol. 8, 3rd ed, 1979, pp Tsuruta, Makromol. Chem., 115, 103 (1968). 568-582. 20. S. Inoue, T. Tsuruta, and J. Furukawa, Makromol. 16. F. C. Schilling and A. E. Tonelli, Macromolecules, Chem., 79, 34 (1964). 19, 1337 (1986). 21. S. Inoue, I. Tsukuma, M. Kawaguchi, and J. 17. K. Miura, T. Kitayama, K. Hatada, and T. Nakata, Furukawa, Makromol. Chem., 103, 151 (1967).

696 Polym. J., Vol. 25, No. 7, 1993