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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

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.

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.