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ABSTRACT:Highly isotactic PMMAs with narrow molecular weight distribution (Mwl M. < 1.2) have been prepared by the polymerization of MMA in toluene at -78oC initiated by t-C 4 H 9 MgBr prepared in diethyl ether. The polymerization proceeded in a "living" manner, in which the initiation reaction was fast and quantitative whereas the propagation was slow. The ether solution of t-C4 H9MgBr used as the initiator contained almost equal amounts of MgBr2 produced by an Wurtz type coupling during the preparation. It has been found from 1 H NMR analyses that the excess amount of MgBr 2 contributes to form the initiating species of homogeneous activity and stereospecificity. Polymerizations of MMA by n-, iso-, and s-C4 H9 MgBr were also investigated in toluene at -78°C. With an increase in the bulkiness of the alkyl group the isotacticity of the polymer increased and the molecular weight distribution became narrower. The addition of MgBr 2 also .increased the isotacticity of the polymer. The results of block copolymerizations of MMA and MMA-d8 or ethyl methacrylate are also described.KEY WORDS Methyl Methacrylate I t-Butylmagnesium Bromide I Isotactic PMMA I Tacticity I Narrow Molecular Weight Distribution I Living Polymerization I Grignard Reagent I Schlenk Equilibrium I Block Copolymerization I 1 H and 13 C NMR I understanding of the reaction mechanism. Isotacti<:: poly(methyl methacrylate) (PMMA) is usually prepared by an anionic initiator such as alkyllithium or Grignard reagent in a nonpolar solvent. Such a polymerization system often involves multiple active species and side reactions, 1 -11 making the molecular weight distribution (MWD) of the resulting PMMA broad. For example, in the polymerization of alkyl methacrylate by n-C 4 H 9 Li 8 • 10 or CH 3 CH 2 CH 2 CD 2 Li 12 the initiator reacts with the carbonyl double bond during the initiation process, and this side reaction brings about the formation of propagating species of different tacticities and activities. Moreover, in the polymerization of methacrylate by Grignard reagent, Schlenk equilibrium also makes the reaction complex, 2 • 6 and these have prevented a clear In the previous communication, 13 we reported that t-C 4 H 9 MgBr prepared in diethyl ether caused no side reaction in the polymerization of MMA in toluene at -78°C and formed highly isotactic PMMA with narrow MWD. That is the first example of the direct preparation of highly isotactic PMMA with narrow MWD, although it was derived from the isotactic poly( triphenylmethyl methacrylate) prepared in THF with an organolithium compound. 14 • 15 In this work we studied the polymerization of MMA by t-C 4 H 9 MgBr under several reaction conditions and clarified the mechanism of formation of highly isotactic PMMA with narrow MWD. 1037

The treatment of deproteinized natural rubber (DPNR) latex with phospholipases A(2), B, C, and D decreased significantly the long-chain fatty acid ester contents in DPNR and also the molecular weight and Higgins' k' constant, except for phospholipase D treatment. This indicates the presence of phospholipid molecules in NR, which combine rubber molecules together. Transesterification of DPNR resulted in the decomposition of the functional group at the terminal chain-end (alpha-terminal), including phospholipids and formed linear rubber molecules. The addition of small amounts of ethanol into the DPNR solution reduced the molecular weight and shifted the molecular weight distribution (MWD) comparable to that of transesterified DPNR (TE-DPNR). The addition of diammonium hydrogen phosphate into DPNR-latex in order to remove Mg2+ ions yielded a slight decrease in molecular weight and a slight shift in MWD. The phospholipids are expected to link with mono- and diphosphate groups at the alpha-terminal by hydrogen bonding and/or ionic linkages. The decrease in the molecular weight and Huggins' k' constant of DPNR demonstrates the formation of linear molecules after decomposition of branch-points by this treatment, showing that phospholipids participate in the branching formation of NR. The branch-points formed at the alpha-terminus are postulated to originate predominantly by the association of phospholipids via micelle formation of long-chain fatty acid esters and hydrogen bonding between polar headgroups of phospholipids.

Several recent publications have been presented on the syntheses of syndiotactic poly(methyl methacrylate)s (PMMAs) of low polydispersity by alkyllithium in a polar solvent1 -4 and a group transfer reaction. 5 For these syntheses except for group transfer polymerization, alkyllithium having a bulky alkyl group was usually used as an initiator to avoid side reactions. However, to our knowledge, there has been no investigation on the preparation of highly isotactic PMMA with narrow molecular weight distribution. Isotactic PMMA is usually prepared by an anionic initiator in a nonpolar solvent. Such a polymerization system may involve multiple active species and side reactions, 6 -16 causing the molecular weight distribution to be broad. In the polymerization of MMA by C 2 H 5 MgBr or C4H 9 MgCl, the initiator reacted with both the carbonyl double bond of the monomer and vinyl double bond during the initiation process, and the resulting alkyl isopropenyl ketone was incorporated into the polymer chain, as evident by the totally deuterated monomer technique. 16 In this work, we found that tC4H9MgBr prepared in diethyl ether caused no side reaction and formed pure PMMA of narrow molecular weight distribution.MMA and MMA-d 8 were purified by distillation, and distilled twice over calcium dihydride under high vacuum just before use. tC4H9MgBr was prepared in diethyl ether from t-butyl bromide and magnesium. A solution of 12.3 g (90 mmol) of t-butyl bromide in 27 ml anhydrous diethyl ether was dropped slowly on the 3.3 g (135 mmol) of magnesium turnings covered with 54 ml of diethyl ether over a period of 1 h. Stirring was continued for one additional hour under reflux. The reaction mixture was allowed to stand overnight to precipitate the unreacted magnesium. The supernatant solution was separated from the precipitate with a hypodermic syringe and used as an initiator solution. The yield of talkylmagnesium bromide from the bromide and magnesium is generally low and depends on the form of magnesium and rate of addition of the halide solution. 17 · 18 The concentration of the t-C 4 H 9 Mg-group in the t-C 4 H 9 MgBr solution used in this work was determined as 0.289 N (28.9% yield from t-C 4 H 9 Br used) by hydrolysis with excess 0.1 N HCl and backtitration with 0.1 N NaOH using phenolphthalein as the indicator. However, the solution was found to contain 0.812M of Mg 2 + by chelatometric titration with EDT A using Eriochrome Black T as the indicator. The concentrations of t-C 4 H 9 MgBr shown in the 977

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Deproteinized natural rubber latex (DPNR-latex) was treated with lipase and phosphatase in order to analyze the structure of the chain-end group (alpha-terminal). The enzymatic treatment decreased the content of long-chain fatty acid ester groups in DPNR from about 6 to 2 mol per rubber molecule. The molecular weight and intrinsic viscosity were reduced to about one-third after treatment with lipase and phosphatase. The Huggins' k' constant of the enzyme-treated DPNR showed the formation of linear rubber molecules. The molecular weight distribution of DPNR changed apparently after treatment with lipase and phosphatase. (1)H NMR spectrum of rubber obtained from DPNR-latex showed small signals due to monophosphate, di-phosphate and phospholipids at the alpha-terminus. Treatment of DPNR-latex with lipase and phosphatase decreased the relative intensity of the (1)H NMR signals corresponding to phospholipids, whereas no change was observed for the signals due to mono- and diphosphates. The residual mono- and diphosphate signals as well as some phospholipid signals after lipase and phosphatase treatments indicate that mono- and diphosphate groups are directly linked at the alpha-terminus with the modified structure, expected by aggregation or linking with phospholipid molecules.

Stereoregular isotactic and syndiotactic poly(methyl methacrylate)s (it- and st-PMMAs) are known to form a multiple-stranded complementary helix, so-called stereocomplex (SC) through van der Waals interactions, which is a rare example of helical supramolecular structures formed by a commodity polymer. In this study, we prepared SCs by using uniform it- and st-PMMAs and those with a narrow molecular weight distribution having different molecular weights and investigated their structures in detail using high-resolution atomic force microscopy as a function of the molecular weight and molecular weight distribution of the component PMMAs. We found that complementary it- and st-PMMAs with the longer molecular length determine the total length of the SC, and molecules of the shorter component associate until they fill up or cover the longer component. These observations support a supramolecular triple-stranded helical structure of the SCs composed of a double-stranded helix of two intertwined it-PMMA chains included in a single helix of st-PMMA, and this triple-stranded helix model of the SCs appears to be applicable to the it- and st-PMMAs having a wide range of molecular weights we employed in this study. In homogeneous double-stranded helices of it-PMMA, it has been found that, in mixtures of two it-PMMAs with different molecular weights, chains of the same molecular weight selectively form a double-stranded it-PMMA helix, or recognize the molecular weights of each other ("molecular sorting"). We thus demonstrate that molecular weight recognition is possible, without any specific interaction between monomer units, through the formation of a topological multiple-stranded helical structure based upon van der Waals interaction.

J. Am. Chem. SOC. termediate in MTG chemistry, but the observation that 1 can form in HZSM-5 from a known MTG intermediate removes a major objection to mechanisms such as those in Scheme I. Furthermore, with the ability to generate significant quantities of 1 in HZSM-5, it should be possible to further explore these mechanisms.We report the observation of helix-sense reversal of linear chloral oligomers (degree of polymerization, DP = 4-6) in solution by NMR spectroscopy and determination of the inversion barrier, which has been found to be dependent on DP.Some synthetic polymers such as polychloral,* poly(triphenylmethyl metha~rylate),~ and poly(tert-butyl i~ocyanide)~ are known to show optical activity arising entirely from conformational asymmetry (macromolecular asymmetry) when the polymers are prepared by helix-sense selective polymerization. The helix of the optically active polymers seems to be rigid in s o l~t i o n~~~ or slowly undergoes racemization to a nearly 1:l mixture of the rightand left-handed helices.' The helical conformation of polyisocyanates is less stable, and consequently, right-and left-handed states exist In equilibrium.* Although the one-handed helicity