Polylactide glass transition temperatures

Passerini, N. Craig, D.Q.M. An investigation into the effects of residual water on the glass transition temperature of polylactide microspheres using modulated temperature DSC. J. Control. Release 2001, 73(1), 111-115. 

SMP based on miscible blends of semicrystalline polymer/amorphous polymer was reported by the Mather research group, which included semicrystalline polymer/amorphous polymer such as polylactide (PLA)/poly vinylacetate (PVAc) blend [21,22], poly(vinylidene fluoride) (PVDF)/PVAc blend [23], and PVDF/polymethyl methacrylate (PMMA) blend [23]. These polymer blends are completely miscible at all compositions with a single, sharp glass transition temperature, while crystallization of PLA or PVDF is partially maintained and the degree of crystallinity, which controls the rubbery stiffness and the elasticity, can be tuned by the blend ratios. Tg of the blends are the critical temperatures for triggering shape recovery, while the crystalline phase of the semicrystalline PLA and PVDF serves well as a physical cross-linking site for elastic deformation above Tg, while still below T ,. 

Figure 11.28. Glass transition temperature, Tg, and crystallization temperature, T, of polylactide plasticized with variable amounts of epoxidized polypropylene glycol having molecular weight of 640 daltons. [Data from McCarthy S Song X, Antec 2001.Conference proceedings, Dallas, Texas, 6th-10th May, 2001, paper 363.]...

L-PL is a ciy stalline, biodegradable polymer having a melting point (T ,) of approximately 175°C and a glass transition temperature (Tg) of approximately 65° C (Schindler et al., 1977). Fisher, et al. (1973) has reported a calculated value for the heat of fusion of 100% crystalline PL as 93.7 J/gram, while the heat of fusion for commercial products has been reported as low as 30 J/gram (PURAC 1996). The empirical formula of the polylactides is (C3H402)r,. 

Copolymerization is the one way to synthesize polymeric materials with desired properties and functions. The cyclic carbonate monomers are successfully copolymerized with various cyclic monomers, such as cyclic carbonates, lactones with/without substituents, lactide, and cyclic phosphates. TMC was copolymerized with lactide by PPL to produce poly(lactide-co-TMC)s having carbonate contents from 0 to 100% and having molecular weights of up to 21000. The glass transition temperature (Tg) of the copolymer was dependent on the carbonate content, and the Tg values linearly decreased from 35° (polylactide) to - 8° [poly(TMC)] [47]. TMC was also copolymerized with medium to large ring-sized lactones. As an example, TMC was copolymerized with PDL in toluene by lipase CA at 70 °C to yield random copolymers [135]. All the poly(PDL-TMC)s were highly crystalline, even those with an equimolar comonomer content and close-to-random distribution. Thermal stability improves with randomization of the comonomer distribution [136]. 

The optically pure polylactides L-PLA (or PLLA) and D-PLA (or PDLA) are semicrystalline polymers with glass transition and melting temperatures of about 60 °C and 180 °C, respectively. In contrast, DL-PLA (or PDLLA) is an amorphous polymer that consists of racemic lactate units and is crystalline only when the D and L unit sequence is completely alternating such a polymer is termed poly (meso-lactide) [44]. The blending of PLAs can result in new materials that present with unexpected synergisms, such as those observed in the equimolar blends between the optically pure polylactides, PLLA and PDLA. 

---