Poly /polylactide semicrystalline

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 ,. 

In summary, the key feature of these approaches is the deconvolution of the spectrum of interest, which is sensitive to the presence of the different phases, into spectra corresponding to each component. Although the above discussion focused on semicrystalline polyethylene, detailed discussion of crystallinity measurements by NMR for other selected polymers can be foimd in the following references poly(vinyl chloride) (69), polypropylene (70), and polylactides (71). 

The commercial forms of PLA are the homopolymer poly(L-Lactide) (L-PLA or PLLA) and the copolymer poly(D,L-Lactide) (D,L-PLA or PDLLA), which are produced from L-lactide and D,L-lactide, respectively. The L-isomer constitutes the main fraction of PLA derived from renewable sources, since the majority of lactic acid from biological sources exists in this form [43]. Polylactides (PLAs) exhibit different properties depending on the D/L unit radio and sequence distribution. Generally, the crystallinity of PLLA and PDLA decreases with increasing racemic content. PLA polymers with an L-content >90% tend to be semicrystalline, while those with a lower optical purity are generally amorphous [43-45]. 

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. 

Polylactide is a kind of biodegradable polyester that possesses many desirable properties such as non-toxicity, hydrolyzability and biocompatibility for use for varied biomedical purposes such as sutures, fracture fixation, oral implant and drug delivery microspheres.It is popularly synthesized by the ringopening polymerization of lactide monomers which are the cyclic dimers of lactic acid. Polymerization of racemic D,L-lactide typically results in atactic, amorphous polymers named poly(D,L-lactide) (rg 60 °C), whereas polymerization of L-lactide or D-lactide results in isotactic, semicrystalline polymers called poly(L-lactide) or poly(D-lactide) (7" 180 PLA fractures... 

---