Tomomichi Itoh

Effects of polystyrene-b-poly(aminomethyl styrene)s as stabilizers on dispersion polymerization of styrene in alcoholic media.

The effects of polystyrene-b-poly(aminomethyl styrene) (PS(n)-b-PAMS(m)) stabilizers on the particle size (D(n)) and size distribution (PSD) in dispersion polymerization of styrene were investigated. The block copolymers, PS(n)-b-PAMS(m), were prepared as follows: (i) atom transfer radical polymerization (ATRP) of styrene (PS-Br), (ii) ATRP of vinylbenzylphthalimide with the PS-Br (PS-b-PVBP), and (iii) treatment of the PS-b-PVBP with hydrazine. When the dispersion polymerization of styrene proceeded at 60 degrees C in ethanol with PS(19)-b-PAMS(130) stabilizer, spherical polystyrene particles with D(n)=0.91 microm (PSD=1.01) were obtained. The particle size was strongly affected by the copolymer composition. With an increase in PAMS block length from m=54 to 100 in PS(17)-b-PAMS(m), particle diameter became smaller from 1.55 to 0.91 microm. On the other hand, an increase in the length from m=20 to 82 in PS(34)-b-PAMS(m)s caused an increase in particle size from 0.35 to 0.70 microm. Titration of the particles suggests that 14-81% of stabilizers used in the polymerization system were attached on the polystyrene particle surfaces, depending on the composition of the block copolymers. Thus, for the dispersion polymerization of styrene, PS(n)-b-PAMS(m) block copolymers have both functions as a stabilizer during polymerization and surface-modification sites of polystyrene particles.

Dispersion polymerization of styrene using a polystyrene/poly(L-glutamic acid) block copolymer as a stabilizer.

A block copolymer (PS-b-poly(L-Glu)) composed of polystyrene and poly(l-glutamic acid) was used as a stabilizer for dispersion polymerization of styrene. When dispersion polymerization of styrene was conducted at 70°C in 80% dimethylformamide-water with 0.5 wt% PS-b-poly(L-Glu), spherical polystyrene particles with D(n)=0.72 μm and narrow size distribution were obtained. Whereas AIBN concentration did not have any effects on particle size, molecular weight of the polystyrene particles was strongly dependent on the initiator concentration. As concentration of the PS-b-poly(L-Glu) increased from 0.2 to 1.0 wt%, particle size decreased from D(n)=0.91 to 0.69 μm with keeping surface area occupied by one poly(L-glutamic acid) chain about S=50 nm(2). On the other hand, an increase in initial concentration of styrene from 2 to 20 wt% caused an increase in particle size from D(n)=0.48 to 1.36 μm and a decrease in surface area per poly(L-glutamic acid) block from S=91 to 45 nm(2). Colloidal stability of the polystyrene particles in aqueous solution was responsive to pH due to the surface-grafted poly(L-glutamic acid). For dispersion polymerization of styrene, the PS-b-poly(L-Glu) functions as both a stabilizer and a surface modifier.

Side-Chain LC Block Copolymers with Well Defined Structures Prepared by Living Anionic Polymerization. 2: Effect of the Glass Transition Temperature of Amorphous Segments on the Phase Behaviour and Structure of the LC Segment

We have prepared two classes of LC diblock copolymers, OcSt-b-LC and MeStb-LC, by living anionic polymerization. These are composed of the side-chain LC polymer as one segment and two different amorphous polymers, poly(octyl styrene) (OcSt) and poly(α-methyl styrene) (MeSt), as the other segment. OcSt and MeSt segments have glass transition temperatures of −60 °C and 160 °C respectively, which are relatively lower and higher than the transition temperatures of crystal–SA (∼90 °C) and SA–isotropic (∼130 °C) in the LC segment. In OcSt-b-LC the lamellar domain size decreases gradually from that of the crystal phase to that of the isotropic phase, indicating that the global conformation of the backbone changes throughout the SA temperature region. In MeSt-b-LC, in contrast, no change in the lamellar size is observed and the crystallinity of the LC segment is reduced in comparison with that in OcSt-b-LC while the liquid crystal is well formed. Such a distinction between two copolymer systems, arising from an interplay between the LC and amorphous segments, shows that the global conformation of the backbone is significant for understanding the phase behaviour and structure of side-chain LC polymers.

Polymerization of alkyl diazoacetates initiated by the amidinate/Pd system: efficient synthesis of high molecular weight poly(alkoxycarbonylmethylene)s with moderate stereoregularity

The initiating ability of a new system, amidinate/Pd, for the polymerization of diazoacetates is described. The system is effective in affording relatively high number-average molecular weight (Mn) polymers from ethyl diazoacetate (EDA, e.g., Mn = 45 100, 44% yield) and methyl diazoacetate (MDA, e.g., Mn = 26 200, 56% yield) in moderate yield. The polymerization of n-hexyl diazoacetate (nHDA) and benzyl diazoacetate (BDA) by the amidinate/Pd system yields high Mn polymers (Mn = ca.100 000), although the yield was below 10%. The system is also effective in the copolymerization of EDA with nHDA, BDA, and cyclohexyldiazoacetate (cHDA), affording high Mn copolymers in moderate yield. NMR spectra of the products obtained with the system suggest that the polymerization proceeds with significantly higher stereoregularity compared to that with previously reported Pd-based initiating systems.