Configurational dependences of carbon‐13 and proton NMR spin‐lattice relaxation times of various polymethacrylates

ABSTRACT:The stereoregularity ofpoly(isobutyl vinyl ether) with a narrow molecular weight distribution obtained by the living cationic polymerization in toluene at + 40 -78oC was studied.As an initiating system, 1-(isobutoxy)ethyl acetate1EtAICI2 was used in the presence of methyl acetate or methyl pivalate as an added base, which can stabilize the propagating carbocation by the nucleophilic interaction. The stereostructure was determined as a diad fraction by 13 C NMR spectroscopy and compared with that of the non-living polymer obtained in the absence of added bases. The diad fraction and the temperature coefficient of ln (P miP,) for the living polymerization were equal to those for the non-living polymerization. The L1H.:; -L1H," was determined to be -900 cal mol-1 , indicating that meso-rich poly(isobutyl vinyl ether) was synthesized favorably at low temperature polymerization. A counteranion and an added base in the living cationic polymerization of IBVE did not affect obviously the stereostructure of polymers obtained. The stereo regularity of seven living poly( vinyl ethers) having various side groups was investigated. Benzyl vinyl ether (meso: 89%) and 2-benzoyloxyethyl vinyl ether (meso: 75%) gave meso-rich living polymers in the presence of ethyl acetate as an added base at ooc. On the other hand, the stereostructure of living poly(2-benzoyloxyethyl vinyl ether) obtained in the absence of added bases (meso: 58%) was quite different from that for the living polymerization in the presence of ethyl acetate. The ln(P ml P,) vs. IIT curve had a maximum at about + 20°C, and it decreased with decreasing the polymerization temperature and became constant at the lower temperature below ooc. The facts and the profile about polymerization rates suggested a stabilization of the propagating carbocation by the side ester group of the terminal unit through an intramolecular interaction.

mentioning

confidence: 99%

Stereoregularity of Poly(vinyl ether)s with a Narrow Molecular Weight Distribution Obtained by the Living Cationic Polymerization

Aoshima

Ito

Kobayashi

1993

“…Then the macromonomer uints in the copolymers tend to be isolated in styrene unit sequences. Since the values of 1/r2 ( = k 2 dk 22 ) correspond to the relative reactivity of the macromonomers to styrene toward styrene radical, the larger value of 1 /r 2 for the iso-PMMA macromonomer than that for the syn-one indicates the higher reactivity of iso-macromonomer; k 21 for the iso-macromonomer is 1.26 times as large as k21 for the syn-macromonomer. In the above discussion, only the reactivity in the propagation process should be concerned, and thus the higher mobility of iso-PMMA chain 21 than that of syn-PMMA chain may be related to the higher reactivity of the iso-macromonomer.…”

Section: Effect Of Tacticity Of Pmma Macromonomer On the Radical Polymentioning

confidence: 99%

“…19 • 20 The 13 C NMR spin-lattice relaxation times of the carbons in iso-PMMA are larger than those of the corresponding carbons in syn-PMMA, indicating that the iso-polymer chains have greater segmental mobility than the syn-ones. 21 Therefore, control of stereoregularity of PMMA macromonomer will provide another means for controlling the properties of graft …”

mentioning

confidence: 99%

Radical Polymerization of Highly Isotactic and Syndiotactic Poly(methyl methacrylate) Macromonomers

Masuda

Kishiro

Kitayama

et al. 1991

Self Cite

ABSTRACT:Highly isotactic (iso-) and syndiotactic (syn-) poly( methyl methacrylate) (PMMA) macromonomers having styrene end group were prepared by the reaction of the corresponding PMMA living anions withp-vinylbenzyl bromide and their polymerizations were studied in toluene using 2,2'-azobisisobutyronitrile as an initiator. The rate of polymerization (Rp) of iso-PMMA macromonomer was slightly higher than that of syn-macromonomer. A similar tacticity dependence of the reactivity was also observed in the radical copolymerization of the macromonomers with styrene. Propagation rate constant (kp) for the homopolymerization of macromonomers was estimated from R", termination rate constant (k,) determined by ESR spectroscopy [K. Hatada et al., Makromol. Chern., Rapid commun., 11, 101 (1990)] and initiator efficiency (f) determined from end group analysis of polymacromonomer by means of NMR spectroscopy [T. Kitayama et al., Polym. Bull., 25, 205 (1991)]. Both the k, and k" values were much smaller than those for styrene polymerization, and the decrease of k, of the macromonomer was much more evident than the decrease of k". The kv and k, values for iso-macromonomer were much larger than the corresponding values for the syn-one. The results suggest that the higher segmental mobility of iso-PMMA chain than that of syn-PMMA chain brings about the larger rate constants for propagation and termination reactions.KEY WORDS PMMA Macromonomer I Stereoregularity I Tacticity I Propagation I Termination I Monomer Reactivity Ratio I Initiator Efficiency I Many papers have been published on the syntheses and applications of macromonomers.1-5 Especially, macromonomers of high purity and narrow molecular weight distribution (MWD) have been desired for the syntheses of graft or comb-like polymers which have well-defined structures. Characteristic features of the radical polymerization of macromonomers have been studied by kinetic experiments. 6 -14 However, little attention has been paid to the tacticity of the macromonomers. 15 -17 Poly(methyl methacrylate) (PMMA) is one of the typical polymers whose tacticity can be widely varied by changing the reaction conditions and whose properties in bulk and in solution depend strongly on the tacticity.18·19 Glass transition temperature (Tg) of PMMA is much lower for the iso-PMMA than for the syn-PMMA. 19 • 20 The 13 C NMR spin-lattice relaxation times of the carbons in iso-PMMA are larger than those of the corresponding carbons in syn-PMMA, indicating that the iso-polymer chains have greater segmental mobility than the syn-ones. 21 Therefore, control of stereoregularity of PMMA macromonomer will provide another means for controlling the properties of graft

“…The methanol-soluble and -insoluble products are recovered by ordinary procedures.Z 2 -78°C. 29 The multiplicity of active species may be a general trend in the anionic polymerization of methacrylates even in a polar medium such as THF as well as toluene. A detailed report on these phenomena will be published elsewhere in the near future.…”

Section: Coexistence Of Multiple Active Speciesmentioning

confidence: 99%

Studies on the Mechanism of Polymerization of Ethyl Methacrylate with BuLi in Toluene Using Perdeuterated Monomer and Multiplicity of Active Species

Hatäda

Kitayama

Okahata

et al. 1982

Self Cite

ABSTRACT:Perdeuterated ethyl methacrylate was polymerized with BuLi in toluene at -78°C. The resulting product consisted of syndiotactic and isotactic polymers and oligomers, indicating the existence of multiple active species. The structure of each component was confirmed by 1 H NMR spectroscopy. Most of the oligomers had butyl isopropenyl ketone units at the chain ends. The isotactic polymer contained one ketone unit near the beginning of the chain, while the syndiotactic polymer had about two ketone units located near the beginning and interior sequence of the chain. The mechanism of polymerization is discussed in detail, and also the structures of active species are proposed from the standpoint of the association oflithium alkoxide formed in the system, that is, the syndiotactic active species are associated with the alkoxide while the isotactic species are not.KEY In the anionic polymerizations of some a-substituted acrylates with butyllithium (BuLi), it was confirmed that isotactic and syndiotactic polymers are formed independently in the same reaction system. 1 -3 This suggests the existence of multiple active species in the polymerization. The polymerization of ethyl methacrylate (EMA) with BuLi in toluene gives methanol-soluble and -insoluble fractions.3 The methanol-insoluble fraction was found to consist syndiotactic polymer, and the methanolsoluble fraction to contain the isotactic polymer and the oligomer. These two fractions are easily separated by pouring the polymerization mixture into methanol. No syndiotactic polymer was obtained when the polymerization temperature was above -20°C or 1,1-diphenylhexyllithium was used as an initiator instead of BuLi. These results were explained in terms of the multiplicity of active species.3 However, the difference in structure other than tacticity among the syndiotactic and isotactic polymers and oligomers was not clear.Recently we have developed a new method for studying the polymerization reaction, in which the perdeuterated monomer is polymerized with an undeuterated initiator and the product is analyzed by 1 H NMR spectroscopy. 4 -8 The study on the anionic polymerization of methyl methacrylate (MMA) with BuLi in toluene 4 and in tetrahydrofuran (THF) 5 by the perdeuterated monomer technique revealed that butyl isopropenyl ketone, formed through the attack of BuLi on the carbonyl double bond of MMA, was incorporated into the polymer and oligomer chains. The manner of incorporation of the ketone unit in the syndiotactic polymer formed in THF differed from the case of the isotactic polymer formed in toluene. These findings lead us to investigate the structural differences in the isotactic and syndiotactic polymers of EMA formed in toluene by the perdeuterated monomer method.In this study, perdeuterated EMA was synthesized and polymerized with BuLi in toluene at 971