Takafumi Nishiura

Stability and Degradation of Polymethacrylates with Controlled Structure

Abstract Thermal degradation behaviors for homo- and copolymers of methacrylates prepared by stereospecific living polymerizations as well as radical polymerization were studied. Thermal stability of radically prepared PMMAs can be improved by careful control of end groups and by incorporation of methyl acrylate into the chain. The mechanism of the stabilization was elucidated. Tacticity dependence of thermal stability of PMMAs was examined using isotactic and syndiotactic PMMAs with molecular weights ( M n ) of 2,500–500,000 under nitrogen. Syndiotactic PMMAs showed higher degradation temperatures than the isotactic PMMAs of the same M n when the M n was lower than 25,000, and vice versa for the higher M n . A similar M n and tacticity dependence was observed in degradation in air, and the critical M n was found to be about 10,000. These phenomena are discussed in terms of zip length of degradation and the difference in flexibility between isotactic and syndiotactic PMMA chains. Thermal degradation behav...

PMMA-block-polyisobutylene-block-PMMA prepared with α,ω-dilithiated polyisobutylene and its characterization

SummaryA triblock copolymer of PMMA and polyisobutylene(PIB), PMMA-block-PIB-block-PMMA, was prepared by anionic polymerization of methyl methacrylate initiated with α, ω-dilithiated poly(isobutylene) diisobutylate in tetrahydrofuran at -60°C. The molecular weight distribution of the block copolymer was close to that of the starting PIB. The stereoregularity of PMMA block was predominantly syndiotactic. Proton spin-lattice relaxation time and solution viscosity of the block copolymer in acetone, which is non-solvent for PIB, indicate that the block copolymer forms rigid spherical particles. Stereocomplex formation with isotactic PMMA was also studied.

Preparation and solution properties of uniform three-arm star poly(methyl methacrylate)

Syndiotactic (st-) poly(methyl methacrylate) (PMMA) with a hydroxy group at the chain end (st-PMMA-OH) was prepared by st-living polymerization with t-C4H9Li/(n-C4H9)3Al in toluene at -78°C. The resulting st-PMMA-OH was fractionated into uniform polymers by means of supercritical fluid chromatography. Uniform st-PMMA-OH with degree of polymerization of 26 was reacted with 1,3,5-benzenetricarbonyl trichloride as a coupling agent and the three-arm star polymer uniform with respect to branch length was isolated from the reaction mixture by the aid of gel permeation chromatography (GPC). Viscometric property of the uniform star PMMA was studied in some detail by using a GPC-differential viscometer.

Preparation of stereoregular block copolymer comprising isotactic PMMA and polyisobutylene blocks and its characterization

SummaryA triblock copolymer of isotactic(it)-poly(methyl methacrylate) (PMMA) and polyisobutylene (PIB), it-PMMA-block-PIB-block-it-PMMA, was prepared by anionic polymerization of triphenylmethyl methacrylate initiated with α, ω-dilithiated PIB diisobutyrate in tetrahydrofuran at -78°C, and subsequntt hydrolysis and methylation with diazomethane. Molecular weight distribution of the triblock copolymer was narrow, and the stereoregularity of the PMMA block was highly isotactic. Proton spin-lattice relaxation times of the block copolymer in acetone-d6, which is non-solvent for PIB but dissolves the block copolymer, indicate the aggregation of the copolymer through PIB block. Stereocomplex formation between the it-block copolymer and syndiotactic(st)-PMMA-block-PIB-block-st-PMMA was also studied.

PREPARATION OF STAR-SHAPED POLYMER WITH STEREOREGULAR POLY(METHYL METHACRYLATE) ARMS

ABSTRACT Isotactic (it-) PMMA anions prepared with t-C4H9MgBr in toluene were reacted with ethylene glycol dimethacrylate (EGDMA) in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) to obtain a star shaped polymer. 1H NMR, SEC-LALLS and SEC-differential viscometric analyses of the polymer clearly indicated that the polymer is a highly branched star polymer with crosslinked dimethacrylate core; the number of arms was estimated to be 20–30. A similar reaction of syndiotactic (st-) PMMA anions formed with t-C4H9Li-(n-C4H9)3Al in toluene with EGDMA was unsuccessful. However, the use of butane-1,4-diol dimethacrylate instead of EGDMA resulted in the effective formation of star polymers having st-PMMA arms; the number of arms was estimated to be 139. As a result, two types of star -shaped polymethacrylates with it- and st-PMMA arms were obtained.

Comb-like triblock copolymers by Wurtz-Grignard coupling of syndiotactic PMMA anions to poly[(p-bromomethyl)styrene]-b-polyisobutylene-b-poly[(p-bromomethyl)styrene]

SummaryPoly[(p-bromomethyl)styrene]-b-polyisobutylene-b-poly[(p-bromomethyl)styrene]s prepared by sequential monomer addition technique of living cationic polymerization were connected with living syndiotactic (st)-poly(methyl methacrylate) macroanions via Wurtz-Grignard-type coupling. In nonpolar medium (toluene), the coupling resulted in the formation of chemically crosslinked network. In polar solvent (tetrahydrofuran), however, a comb-like triblock copolymer with properties of thermoplastic elastomer was obtained.

Preparation of highly syndiotactic block copolymers of methyl methacrylate and lauryl methacrylate and their characterization

SummaryHighly syndiotactic diblock and triblock copolymers comprising lauryl methacrylate (LMA) and methyl methacrylate (MMA) with narrow molecular weight distributions were prepared by the living anionic polymerization with t-C4H9Li/(C2H5)3Al in toluene at low temperature. The block copolymers were soluble in acetone which is a non-solvent for poly(lauryl methacrylate) (PLMA). 1HNMR and vapor pressure osmometric analyses of the block copolymers indicated the aggregation of the copolymer in acetone through the interaction between PLMA blocks. Stereocomplex formation between the triblock copolymer and isotactic poly(methyl methacrylate) (PMMA) took place more effectively in solution than in the solid state.

Revised patterns of reactivity scheme. VII. Revised patterns scheme and its relationship to carbon-13 NMR spectra

The electron density on a carbon atom determines the 13C chemical shift observed in the NMR spectrum. In a vinyl monomer, the same electron density must contribute strongly to polar effects involved in the addition of a radical to that monomer and possibly in the addition (to a double bond) of a radical terminated by a unit derived from that monomer. It is shown that the expected correlation exists when the polar effects in polymerization reactions are represented by the parameters of the revised patterns scheme.

Carbon-13 NMR Spectra of Stereoregular Copolymers of Methyl and Butyl Methacrylates

Abstract Highly isotactic and syndiotactic copolymers of methyl methacrylate (MMA) and butyl methacrylate (n-BuMA) with random monomer sequence distribution were prepared in toluene at -78°C with t-C4H9MgBr and t-C4H9Li/(C2H5)3Al, respectively. 13C NMR spectra of carbonyl region of the copolymers were measured in chlorobenzene-d 5 at 115°C and 125 MHz and analyzed in regard to both monomer sequence and configurational sequence distributions. 13C NMR spectra of radically prepared poly(MMA-ran-n-BuMA)s were also analyzed based on the assignments established by the analysis of the spectra of the stereoregular copolymers.

Highly efficient block copolymerization of methyl and t-butyl methacrylates by an incomplete and slow initiation system

SummaryBlock copolymerization of methyl methacrylate (MMA) with t-butyl methacrylate (t-BMA) was carried out in toluene at-78°C with triphenylphosphine (Ph3P)-triethylaluminum (Et3Al) initiating system. Polymerization of MMA with Ph3P-Et3Al under the same conditions gave highly syndiotactic PMMA living anion with low initiator efficiency. Even though a large part of the initiator remained unreacted, polymerization of t-BMA with the living anion of PMMA gave block copolymer without formation of poly(t-BMA), since t-BMA alone could not be polymerized under the same conditions due to the inability of initiation with Ph3P-Et3Al.