Cooperativity length evolution during crystallization of poly(lactic acid)
(2414-2423) European Polymer Journal 47  #12 (2011)
Delpouve, Saiter and Dargent of the Université de Roue, France, found that for each PLA, the cold crystallization leads to the appearance of a less perfect crystalline phase and to an important rigid amorphous fraction RAF content (35%), although only 10% of RAF is generated after crystallization from the melt.  Temperature Modulated Differential Scanning Calorimetry is used to determine the Cooperative Rearranging Regions (CRR) size at the glass transition temperature in the mobile amorphous phase MAP.  It is shown that the CRR size in the MAP is not modified by the appearance and the spherulite growth.  For the intra-spherulite MAP, a confining effect is evidenced, causing an amorphous phase thickness decrease during crystallization, and inducing a drastic CRR size reduction.  (RDC 11/16/2011)

Access to new carbohydrate-functionalized polylactides via organocatalyzed ring-opening polymerization
(5018-5026) Polymer 52 #22 (2011)
Miao et al, France, studied the 4-dimethylaminopyridine (DMAP) catalyzed ring-opening polymerization of lactide using various carbohydrate initiators for the functionalization of polylactide. According to the solubility of the carbohydrate derivative, the polymerizations were conducted in chlorinated solvents and in the bulk. Relatively narrow distributions are obtained in high yields in the absence of side reactions, affording a 100% functionalization efficiency. The catalytic synthesis of new carbohydrate link-functionalized polylactides and carbohydrate core star polylactides is reported.  (RDC 10/13/2011)

Highly Enhanced Nucleating Effect of Melt-Recrystallized Stereocomplex Crystallites on Poly(L-lactic acid) Crystallization
(887–893)Macromolecular Materials and Engineering 296 #10 (2011)
Narita, Katagiri and Tsuji of Mitsui and Toyohashi University of Technology, Japan, showed that poly(L-lactic acid) (PLLA) articles (210–240 °C), PLLA/poly(D-lactic acid) (PDLA) stereocomplex (SC) crystallites melted just above the endset temperature of SC melting (228–238 °C) and recrystallized during cooling.  These crystalliteswere the most effective nucleating agents for enhancing the crystallization of PLLA compared to partially melted SC crystallites (211–227 °C) or those melted far above the endset temperature of SC melting (240 and 250 °C) and recrystallized during cooling. The high nucleating effect of the SC crystallites melted in the temperature range of 228–238 °C was found to be caused by their smaller sizes or the larger number of SC crystallites per unit mass. The incorporation of such SC crystallites facilitates the processing of PLLA articles having high crystallinity and, therefore, high heat-resistance in a shorter period to reduce the production cost.  (RDC 10/13/2011)

Titanium complexes based on aminodiol ligands for the ring opening polymerization of l- and d,l-lactide
(4686-4693) Polymer 52 #21 (2011)
Deivasagayam and Peruch of the University of Bordeaux, France, prepared a series of new titanium isopropoxide complexes (1-4-Ti(OiPr)2 based on enantiopure (1-H2), racemic (2-H2), meso (3-H2) and diastereomeric (4-H2) aminodiol ligands and tested as initiators for the ring opening polymerization (ROP) of l/rac-lactide in solution and in bulk conditions.  All complexes were shown to have significant activity in solution at 70 °C and higher activity in bulk at 130 °C with a good control over the molar mass distribution and molecular weights.  The complex derived from the racemic-aminodiol ligand gave partially heterotactic polylactide in ROP of rac-lactide and afforded atactic polylactide in the bulk, whereas all other complexes yielded atactic polylactides both in solution and in bulk.  Ligand variation (chirality) in the complexes has little effect on either the activity or selectivity of the initiators.  The polymerization kinetics using (1-Ti(OiPr)2) as an initiator indicated a first order reaction with respect to the monomer concentration.  (RDC 10/6/2011)

 Mesophase formation and its thermal transition in the stretched glassy polylactide revealed by infrared spectroscopy
(4979-4984) Polymer 52 #21 (2011)
Lv et al of the East China Institute of Technology and Tianjin University, China, studied the structural development in the glassy polylactide during stretching and subsequent heating by Fourier transform infrared spectroscopy.  Only when molecular chains in the amorphous phase approach their finite extensibility beyond a critical strain of about 1, accompanied by remarkable conformational ordering, can cohesive mesophase with certain molecular ordering be brought out to trigger strain-induced crystallization.  Upon heating cohesive mesophase endures melting during glass transition region where an endothermic peak is observed, and the extent of melting relies on its initial thermal stability and is in particular affected by the subsequent advent of strain-induced crystallization.  (RDC 10/6/2011)

Decoupling the effects of crystallinity and orientation on the shear piezoelectricity of polylactic acid
(1555–1562)Journal of Polymer Science B: Polymer Physics 49, #21 (2011)
Lovell, Fitz-Gerald and Park of the University of Virginia, Virgina, fabricated polylactic acid (PLA) samples by a dual drawing/annealing process to expand the investigation into the relationship between crystallinity, orientation, and shear piezoelectricity.  The results of this study show for the first time that PLA shear piezoelectricity possesses a stronger relationship with the product of crystallinity and orientation than either of these parameters individually.  However, this research also shows that processing of PLA for shear piezoelectric applications should focus only on achieving large degrees of orientation, which will inherently lead to increases in crystallinity as well. This approach will optimize PLA's shear sensing capabilities while avoiding certain detrimental effects, specifically embrittlement and a reversal of polymer chain orientation, which can occur during annealing.  (RDC 10/4/2011)

Preparation and Properties of Water and Glycerol-plasticized Sugar Beet Pulp Plastics
(559-567) Journal of Polymers and the Environment 19 #3 (2011)
Chen, Li and Ren of Tongji University, China, prepared stereocomplex poly(lactic acid) (SC-PLA) based on poly(l-lactic acid) (PLLA) and poly(d-lactic acid) (PDLA) prepolymers. PLLA and PDLA by direct melt polycondensation of lactic acid (DMP). Combined with the dual catalyst system, PLA prepolymers with Mw more than 20,000 were prepared by DMP. PLLA was mixed by powder blending or melt blended with PDLA. It is revealed that melt-point and spherulite growth rate of SC-PLA is strongly dependent on the perfection of SC structure.  The melt point of PLA can be increased by nearly 50 °C because of the particular strong intermolecular interaction between PLLA and PDLA chains.  Solid-state polycondensation (SSP) is an efficient method to increase the molecular weight of SC-PLA, but it can have a negative effect on the regularity of linear chains of SC-PLA. (RDC 8/23/2011)

Enhanced Stereocomplex Crystallization of Biodegradable Enantiomeric Poly(lactic acid)s by Repeated Casting
(583–589)Macromolecular Materials and Engineering 296 #7 (2011)
Tsuji and Yamamoto of Toyohashi University of Technology, Japan, showed that for all solvents, the crystallinities of stereocomplex crystallites and homocrystallites increased and decreased, respectively, with increasing number of castings, indicating that repeated casting is a promising method to enhance stereocomplex crystallization.  (RDC 7/14/2011)