Cover Picture: Macromol. Biosci. 1/2005

Abstract

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.

Thermomechanical properties of stereoblock poly(lactic acid)s with different PLLA/PDLA block compositions

“…As a way to improve the sc formation, block copolymers of PLLA and PDLA, i.e., stereoblock poly(lactic acid)s (sb-PLAs), have been developed [5][6][7][8][9][10][11]. The placement of the enantiomric segments of PLLA and PDLA in the neighborhood can effectively promote the sc formation [12]. The sb-PLA thus developed, however, could not be processed into fibers and films because of their relatively low molecular weight, not exceeding 100 kg/mol.…”

Enhanced Stereocomplexation by Enantiomer Adjustment for Stereo Diblock Polylactides with Non‐Equivalent D/L Ratios

“…[4][5][6][7][8][9][10] In fact, we have recently synthesized stereo multiblock sb-PLAs (multi-sb-PLA) consisting of relatively short enantiomeric sequences by solid-state polycondensation (SSP) of mixtures of PLLA and PDLA having medium molecular weight to ensure the easier sc crystallization of the multi-sb-PLA without hc crystal formation. [11][12][13][14] We have also synthesized stereo diblock polylactides (di-sb-PLA: PLLA-b-PDLA) by two-step ring-opening polymerization (ROP) of L-and D-lactides by which exclusive sc formation is possible even at PLLA-or PDLA-rich compositions. Their preferential sc formation is attributed to the neighboring interaction between the enantiomeric sequences.…”

Relatively Short Poly(D‐lactide) Segments as Intra‐Crystallization‐Accelerating Moieties in Stereo Diblock Poly(lactide)s

“…[16][17][18] On the other hand, since SC formation readily occurs in stereo diblock (SDB) and multiblock poly(lactide) (PLA) composed of PLLA and PDLA segments, compared with PLLA/PDLA polymer blends when the molecular weights of polymers are higher than 1 Â 10 5 g mol À1 , synthesis of a wide variety of stereoblock copolymers of PLLA and PDLA has been carried out. [19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35] Equimolar SDB-PLAs with different molecular weights of 3.3 Â 10 3 -1.1 Â 10 4 g mol À1 [32] and equimolar stereo multiblock PLAs having molecular weight of about 1 Â 10 4 g mol À1 and different stereoblock lengths of 5-20 lactyl units [33][34][35] were synthesized and their SC crystallization behavior was investigated in detail.Although there has been numerous reports regarding the crystallizationaccelerating effects of incorporated PDLA polymer in PLLA polymer on PLLA homo-crystallization, [10][11][12][13][14][15][16][17][18] to the best of our knowledge, the effectiveness of a relatively short PDLA segment, which is linked to a relatively long PLLA segment and can form SC crystallites, on the acceleration of homo-crystallization of the PLLA segment, has not been reported so far. Thus, SDB-PLAs with total numberaverage molecular weight (M n ) ¼ 1 Â 10 5 g mol À1 with relatively short PDLA segments (M n ¼ 2.0-7.7 Â 10 3 g mol À1 ) were synthesized, together with PLLA having M n ¼ 1 Â 10 5 g mol À1 , and the effectiveness of a relatively short PDLA segment on the acceleration of homo-crystallization of PLLA segments is reported.…”