Masatoshi Miyamoto

Melt polycondensation of L‐lactic acid with Sn(II) catalysts activated by various proton acids: A direct manufacturing route to high molecular weight Poly(L‐lactic acid)

Poly(L-lactic acid) (PLLA) was produced by the melt polycondensation of L-lactic acid. For the optimization of the reaction conditions, various catalyst systems were examined at different temperature and reaction times. It was discovered that Sn(II) catalysts activated by various proton acids can produce high molecular weight PLLA [weight-average molecular weight (Mw ) ≥ 100,000] in a relatively short reaction time (≤15 h) compared with simple Sn(II)-based catalysts (SnO, SnCl2 · 2H2O), which produce PLLA with an Mw of less than 30,000 after 20 h. The new catalyst system is also superior to the conventional systems in regard to racemization and discoloration of the resultant polymer.

Chromatographic characterization of hydrophilic interaction liquid chromatography stationary phases: Hydrophilicity, charge effects, structural selectivity, and separation efficiency

Fourteen commercially available particle-packed columns and a monolithic column for hydrophilic interaction liquid chromatography (HILIC) were characterized in terms of the degree of hydrophilicity, the selectivity for hydrophilic-hydrophobic substituents, the selectivity for the regio and configurational differences in hydrophilic substituents, the selectivity for molecular shapes, the evaluation of electrostatic interactions, and the evaluation of the acidic-basic nature of the stationary phases using nucleoside derivatives, phenyl glucoside derivatives, xanthine derivatives, sodium p-toluenesulfonate, and trimethylphenylammonium chloride as a set of samples. Principal component analysis based on the data of retention factors could separate three clusters of the HILIC phases. The column efficiency and the peak asymmetry factors were also discussed. These data on the selectivity for partial structural differences were summarized as radar-shaped diagrams. This method of column characterization is helpful to classify HILIC stationary phases on the basis of their chromatographic properties, and to choose better columns for targets to be separated. Judging from the retention factor for uridine, these HILIC columns could be separated into two groups: strongly retentive and weakly retentive stationary phases. Among the strongly retentive stationary phases, zwitterionic and amide functionalities were found to be the most selective on the basis of partial structural differences. The hydroxyethyl-type stationary phase showed the highest retention factor, but with low separation efficiency. Weakly retentive stationary phases generally showed lower selectivity for partial structural differences.

Synthesis and characterization of hydroxy-terminated [RS]-poly(3-hydroxybutyrate) and its utilization to block copolymerization with L-lactide to obtain a biodegradable thermoplastic elastomer

Abstract A telechelic poly([RS]-3-hydroxybutyrate) ([RS]-PHB) was synthesized by the ring-opening polymerization of [RS]-β-butyrolactone (βBL) in the presence of 1,4-butanediol (BD) with distannoxane as the catalyst. This polymer was found to be terminated by secondary hydroxyl groups, having an (oxytetramethylen)oxy group in the main chain. It was subjected to block copolymerization with l -lactide by the catalysis of tin (II) octoate to obtain an A–B–A type triblock copolyester comprising poly( l -lactide) (A) and [RS]-PHB (B). In this block copolymerization, the molecular weight and the unit composition of the produced copolymer were successfully controlled by changing the l -lactide/[RS]-PHB ratio in feed. Its characterization revealed that this block copolymer has high potential for use as biodegradable thermoplastic elastomer.

Synthesis and Properties of High-Molecular-Weight Poly(L-Lactic Acid) by Melt/Solid Polycondensation under Different Reaction Conditions:

The melt/solid polycondensation of L-lactic acid (LA) was successfully conducted using a binary catalyst system comprising tin dichloride hydrate and p-toluenesulfonic acid (TSA). First, a thermal oligocondensate of LA with a degree of polymerization of eight was mixed with the binary catalyst and subjected to melt polycondensation at 180°C for 5 h to obtain a melt polycondensate with an average molecular weight of 13 000 Da. This melt polycondensate was then heat treated at 105°C for 2 h and subjected to solid-state polycondensation under various conditions to obtain a high-molecular-weight polymer of poly(L-lactic acid) (PLLA). In a typical case, the solid-state reaction was performed by raising the temperature from 130 to 155°C, or at a constant temperature of 140 or 150°C. In the former case the molecular weight of PLLA increased linearly with the temperature increase, while in the latter case the molecular weight increased above 500 000 Da in a relatively short reaction time. The crystallization of the polycondensate was a key step of this polycondensation and the crystallinity of the PLLA product was well correlated with the increase in the molecular weight. This method can be a direct industrial method for the manufacture of PLLA from LA, which may potentially be an alternative to the currently adopted lactide method.

Melt/solid polycondensation of glycolic acid to obtain high-molecular-weight poly(glycolic acid)

Bulk polycondensation of glycolic acid (GA) was studied to obtain high-molecular-weight poly(glycolic acid) (PGA). At first, a solid oligocondensate was prepared by melt-polycondensation of GA at 190°C, and then it was subjected to solid-state polycondensation at the same temperature to increase the molecular weight. After the catalyst screening, zinc acetate dihydrate was discovered to be the best catalyst. The weight-average molecular weight of PGA reached 91,000, which was at the same level with that of PGA prepared by the conventional ring-opening polymerization of glycolide. This process can afford a facile route to large-scale synthesis of PGA.

Intriguing morphology transformation due to the macromolecular rearrangement of poly(l-lactide)-block-poly(oxyethylene): from core–shell nanoparticles to band structures via fragments of unimolecular size

Abstract We report on anomalous structural organization from core–shell nanoparticles of a hydrophobic/hydrophilic diblock copolymer consisting of semi-crystalline poly( l -lactide) (PLLA) and poly(oxyethylene) (PEG). The copolymer was synthesized and suspended in an aqueous medium to prepare its core–shell particles. The resultant nanoparticles were spread on a germanium substrate to trace the particle aggregation by atomic force microscopy (AFM) and FT-IR spectroscopy. On the substrate surface, the core–shell particles were found to change their shape into disks, with the PLLA blocks being slightly crystallized. When heated to 60°C, these disk-like aggregations burst into small fragments and then turned to band structures. On the other hand, any ordered structure was not observed when a solution of PLLA-PEG was cast on the surface. In the freeze-dried sample of the suspension, it was found that a lamellar microphase-separated structure was created with crystallization of the PLLA blocks by annealing. The lamella thickness analyzed by the small- and wide-angle X-ray scatterings of this sample was reasonably correlated with the width of the band structures formed on the germanium surface. It is therefore concluded that the formation of the regular band structures can be guided by both the phase separation and crystallization behaviors of the semicrystalline block chains of PLLA-PEG.

Synthesis and properties of multiblock copolymers consisting of poly (L-lactic acid) and poly (oxypropylene-co-oxyethylene) prepared by direct polycondensation

A multiblock copoly(ester–ether) consisting of poly(l-lactic acid) (PLLA) and poly(oxypropylene-co-oxyethylene) (PN) was prepared and characterized. Preparation was done via the solution polycondensation of a thermal oligocondensate of l-lactic acid, a commercially available telechelic polyether (PN: Pluronic-F68), and dodecanedioic acid as a carboxyl/hydroxyl adjusting agent. When stannous oxide was used as the catalyst, the molecular weight of the resultant PLLA/PN block copolymers became very high (even with a high PN content) under optimized reaction conditions. The refluxing of diphenyl ether (solvent) at reduced pressure allowed the efficient removal of the condensed water from the reaction system and the feed-back of the intermediately formed l-lactide at the same time in order to successfully bring about a high degree of condensation. The copolymer films obtained by solution casting became more flexible with the increasing PN content as soft segments.

Preparing a Core-Sheath Bicomponent Fiber of Poly(butylene Terephthalate)/Poly(butylene Succinate-co-L-lactate)

A core-sheath bicomponent fiber is melt-spun by co-extrusion of poly(butylene tereph thalate) (PBT) as the core and poly(butylene succinate-co-L-lactate) (PBSL) as the sheath. The resulting melt-drawn fiber is continuously guided to cold-drawing at 80°C. The core/sheath ratio of the melt-drawn fiber increases with increasing melt-draw ratio at a constant extrusion of the two polymers, because the melt viscosity of PBT is much higher than that of PBSL. The tensile strength of the final drawn fiber increases with increasing melt-draw ratio. The highest strength is obtained at a core/sheath ratio of 65/35. Scanning electron micrographs of the cross-sectioned fibers reveal that the adhesion of both polymers at the interface is strong. The core-sheath fibers are then treated with alkali or a lipase solution for hydrolysis of the PBSL sheath at mild conditions where PBT receives no hydrolysis. The treated fibers, consisting only of PBT, show a very smooth surface. Their tensile strength and orientation are slightly lower than those of the original bicomponent fibers, maintaining a high level of quality as apparel material. These data suggest that conjugate fibers consisting of biodegradable and ordinary polyesters can be used for the environmentally friendly denier reduction treatment of polyester fibers.

Polymerizaton of Salts of 2-Alkenyl-2-Oxazolines and Their Homologs

Abstract The present paper describes a new type of polymerization of 2-vinyl-2-oxazoline and 2-vinyl-5,6-dihydro-4H-1,3-oxazine and their salts. When these two imino ether monomers are allowed to react with Meerwein reagents or super acid esters, N-alkylation takes place first, followed by polymerization through the opening of vinyl groups to give poly [(2-oxazolinium-2-yl)ethylene] and poly [(5,6-dihydro-4H-1,3-oxazinium-2-yl)ethylene], respectively. With the corresponding 2-isopropenyl homologs, 2-isopropenyl-2-oxazoline and 2-isopropenyl-5,6-dihydro-4H-1,3-oxazine, stable N-alkylated salts are obtained, which were subjected to radical and base-catalyzed polymerizations. From the above results the reactivities of the salts are considered in terms of their ring size and the substituents on the olefinic functions.

Ring-opening polymerization of six- and seven-membered cyclic pseudoureas

The cationic ring-opening polymerization of six-membered cyclic pseudoureas, 2-(1-pyrrolidinyl)- (2a) and 2-morpholino-5,6-dihydro-4H-1,3-oxazine (2b), was examined, which proceeded in two different ways, depending on the nature of initiator. The polymerization of 2 with methyl p-toluenesulfonate or trifluoromethanesulfonate (MeOTf) produced poly[(N-carbamoylimino)trimethylene], while that with benzyl chloride or bromide or methyl iodide gave a polymer consisting of 1,3-diazin-2-one-1,3-diylalkylene unit (the main component) and (N-carbamoylimino)trimethylene unit. The cationic ring-opening polymerization of seven-membered cyclic pseudourea, 2-(1-pyrrolidinyl)-4,5,6,7-tetrahydro-4H-1,3-oxazepine (3) was also examined. The polymerization of 3 with MeOTf as initiator gave poly{[N-(1-pyrrolidinycarbonyl)imino]tetra-methylene}. With benzyl chloride, on the other hand, no polymerization of 3 proceeded but, instead, the quantitative isomerization of 3 to 1,1′-carbonyldipyrrolidine took place. The polymerization mechanism of 2 and 3 as well as the isomerization mechanism of 3 were discussed with comparing them to the polymerization mechanism of five-membered pseudoureas.