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Solid-state postpolymerization of l-lactide was studied by two different ways with 0.1 mol % of stannous 2-ethyl hexanoate as the catalyst. In a two-step method, the ordinary melt polymerization of l-lactide was first performed at temperatures higher than the crystallization temperature (T c) of poly(l-lactide) (PLLA), and then the postpolymerization was continued around the T c of PLLA. As PLLA crystallized in the second stage (e.g., when the temperature was changed from 140 to 120 °C), the monomer consumption was found to reach 100% because the monomer and catalyst could be concentrated in the amorphous part. Without the crystallization of PLLA occurring in the postpolymerization, a homogeneous supercooling state was formed to have a remaining monomer ratio exceeding 5 wt %. In the alternative one-step method where the polymerization was continued around the T c of PLLA, the polymer crystallization was induced during the polymerization to promote the monomer consumption to reach 100%. The kinetic analysis of this polymerization revealed that the rate of monomer consumption is inversely proportional to the square of the amorphous ratio of PLLA, which is opposite to the crystal ratio. However, the molecular weight did not increase with the monomer consumption. This should be because various oligomers are formed in the postpolymerization stage by the ester interchange reaction.

Cover: The cover depicts the novel synthetic scheme for the stereoblock poly(lactic acid) (sb-PLA) by solid-state polycondensation of a stereocomplexed mixture of poly(L-lactic acid) (PLLA), and poly(D-lactic acid) (PDLA), having medium molecular weight. First, meltpolycondensation of L-and D-lactic acids is conducted to obtain the PLLA and PDLA, respectively. In the second step, these polymers are melt-blended to form the stereocomplex. Then, the solid-state polycondensation of the melt-blend affords the sb-PLA with high molecular weight and high melting temperature without formation of single polymer crystals of PLLA or PDLA.Further details can be found in the Full Paper by K. Fukushima, Y. Furuhashi, K. Sogo, S. Miura, and Y. Kimura* on page 21.

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Bio-based polymers are made from bio-originated feedstocks. Among those developed thus far, polylactides (PLA) stand at the forefront of practical use and are now manufactured on a commercial scale. However, the application of PLAs has been rather limited because of their higher cost, inferior thermal and mechanical properties, and worse processability as compared to the conventional oil-based polymers. Much effort has therefore been made to address it. Our major approach is to develop a direct polycondensation method to synthesize PLA and to use stereoblock-type PLA (sb-PLA) consisting of enantiomeric poly(L-lactide) (PLLA) and poly(D-lactide) (PDLA) because it can easily form stereocomplex (sc) showing a high melting temperature. Other specialty bio-based polymers are also synthesized for application to high-value fields. Particularly, with amphiphilic copolymers consisting of PLA and poly(oxyethylene) (PEG), new morphology change and sol-gel process have been disclosed. New bio-based polymers consisting of bio-derived monomeric units have also been synthesized to demonstrate their special functions. In addition, molecular and material design has been done with other biobased polymers such as poly(butylene succinate) (PBS) and poly(3-hydroxyalkanoate)s (PHA).

The discovery of Ideonella sakaiensis, a plastic‐degrading bacterium, creates possibilities for a sustainable “bioeconomy” for recycling plastic waste.

An aliphatic/aromatic copolyester, poly(butylene succinate‐co‐terephthalate) (PBST), was prepared to investigate the effect of the aromatic units on the enzymatic degradation of the poly(butylene succinate) (PBS) derivatives in the presence of a lipase originated from Pseudomonas cepacia (Lipase PS®). The degradability of PBST was found to increase with increasing BS content. The degradation products were analyzed in detail by liquid chromatograph mass spectrometry (LC‐MS). A hexamer containing one terephthalate unit was the largest fragment among the diverse fragments detected, while a pentamer was the largest one consisting only of succinate units. The oligomeric fragments cut out from the polymer chain were involved in the secondary hydrolysis into 4‐hydroxybutyl succinate (BSH) and terephthalate (BTH). The trimeric fragments tetramethyl disuccinate (SBSH) and succinate terephthalate (SBTH), having both carboxyl end groups, were slowly hydrolyzed by a nonspecific mechanism. Based on these data, the overall mechanism of the enzymatic hydrolysis of this aliphatic/aromatic copolyester is proposed, in which PBST undergoes endo hydrolysis.A plausible mechanism of enzymatic hydrolysis of PBST with Lipase PS®.magnified imageA plausible mechanism of enzymatic hydrolysis of PBST with Lipase PS®.