Preparation and dispersibility of poly(L‐lactide)‐grafted silica nanoparticle

To improve dispersibility of silica nanoparticle in organic solvents, the grafting of poly(L ‐lactide) (PLLA) onto silica nanoparticle surface by ring‐opening polymerization of L‐lactide (LA) was investigated in the presence of an amidine base catalyst. The ring‐opening polymerization of LA successfully initiated in the presence of silica having amino groups (silica‐NH₂) and an amidine base catalyst to give PLLA‐grafted silica, but not in the presence of untreated silica (silica‐OH). In the absence of the amidine base catalyst no ring‐opening polymerization of LA even in the presence of silica‐NH₂ and no grafting of PLLA onto silica were observed. It became apparent that the amidine base catalyst acts as an effective catalyst for the ring‐opening graft polymerization of LA from the surface of silica‐NH₂. In addition, it was found that the percentage of PLLA grafting onto silica could be controlled according to the reaction conditions. The average particle size of PLLA‐grafted silica was smaller than that of silica‐NH₂. Therefore, it was considered that the aggregation structure of silica nanoparticles was considerably destroyed by grafting of PLLA onto the surface. The PLLA‐grafted silica gave a stable dispersion in polar solvents, which are good solvents for PLLA. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Synthesis of optically active lactide catalyzed by nanocrystals of La-Ti composite oxides

With sol-gel method, nanometer La-Ti composite oxides were prepared. By means of atomic force microscope, the surface pattern, particle size distribution and specific surface area were studied. The newly prepared nanocrystals of La-Ti composite oxides were used as the catalysts to catalyze the dehydration of external compensated lactic acid to lactide. The lactide product was measured by polarimeter and micropolariscope. The results demonstrate that the ratio between D-lactide and L-lactide will not be equal to 1：1 if nanocrystals of La-Ti composite oxides are used as the catalysts, which implies, that nanocrystals of La-Ti composite oxides may be potential catalysts with a good selectivity.     

常压CO2气流法制D,L-丙交酯

在ＣＯ２气流中用Ｄ,Ｌ－乳酸为原料,硫酸亚锡为催化剂,包括内外消旋体的粗丙交酯产率可达８２％,外消旋Ｄ,Ｌ－丙交酯约占其中的１／２。作为对比,用Ｎ２气流时的粗丙产酯产率为８３．２％,二者产率相差无几,可用ＣＯ２代替Ｎ２用于丙交酯的制备。     

Synthesis and properties of biodegradable supramolecular polymers based on polylactide‐block‐poly(δ‐valerolactone)‐block‐polylactide triblock copolymers

Biodegradable supramolecular polymers (SMPs) were synthesized by the end‐functionalization of polylactide‐block‐poly(δ‐valerolactone)‐block‐polylactide (PLA–PVL–PLA) triblock copolymers with 2‐ureido‐4[1H]‐pyrimidinone (UPy) self‐complementary quadruple hydrogen‐bonding units. The end‐functionalized PLA–PVL–PLA copolymers exhibit the typical characteristics of thermoplastic elastomers. Thermal properties, crystallization behavior, crystalline structure and other properties of SMPs can be adjusted by changing the length and stereostructure of PLA blocks. The UPy groups retard the crystallization of PLA and PVL blocks, and the crystallization of PVL blocks is also depressed with increasing PLA blocks. Tensile testing reveals that the prepared SMPs present excellent mechanical properties, and dynamic mechanical analysis indicates that the heat resistance of l ‐SMPs is better than that of d ,l ‐SMPs. Shape memory property of SMPs was also studied, and the recovery ratio of SMPs with PDLLA blocks can reach 100%. The recovery ratio of l ‐SMPs is depressed as the crystallizable PLLA blocks increase. This study has systemically investigated the effect of the composition, stereostructure and crystallizability of PLA blocks on the properties of SMPs, which would provide potential approaches for the synthesis of biodegradable SMPs with tunable properties. © 2017 Society of Chemical Industry