PCL-b-PLLA

Fig. 24 X-ray diffraction patterns of as-synthesized (a) and coalesced (b) PCL-b-PLLA melt-pressed films observed following various enzymatic degradation times [20]...

The spin-lattice relaxation time Ti provides information on the molecular dynamics of polymer chains in the high-frequency megahertz regime. The Tic parameter, measured in seconds, is used to characterize this motion and is usually sensitive to the cooperative polymer-polymer interactions common in bulk semicrystalline polymers. In bulk PCL-b-PLLA, double exponential-decay relaxation times have been observed. This confirms the semicrystalline (crystalline and amorphous) morphology of the diblock copolymer. The longer Tic values observed are due to slower motions and represent the rigid crystalline phase of the copolymer, whereas the shorter Tic values, that is, faster motions, describe the dynamics of the amorphous chains which are above their glass transition temperature Tg. 

Figure 1. CP-MAS spectra of (a) bulk diblock PCL-b-PLLA copolymer,...

When coalesced from its a-CD-lC, the structure and properties of the biodegradable-bioabsorbable di-block copolymer (PCL-b-PLLA) are found to be significantly different from the as-synthesized sample, as can be seen in Table 11.1. Note, for example, that both the levels of block phase segregation and crystallinity are substantially reduced in the coalesced di-block. This results in a much more rapid biodegradation of the coalesced di-block, compared with the as-synthesized sample, which is critical to several of its potential applications. 

The phase segregation and crystallinity of block copolymers may not be reduced only via the formation of and coalescence from their CD-ICs, as mentioned above for PCL-b-PLLA, but may actually be controlled through the formation of ICs using CDs which incorporate only some or all of the constituent blocks. For example, the phase segregation and crystallinity of... 

Table 77.7 Thermal properties of as-synthesized and coalesced PCL-b-PLLA di-block copolymer (melting and crystallization temperatures T, T o, melting enthalpy AH, and % crystallinity)...

PCL-b-PLLA di-block copolymer coalesced from its 1C with a-CD remains more homogeneous, amorphous, and less phase segregated than an as-... 

Fig. 13.12. Schematic representation of chain folding and domain spacing of the amorphous PCL block (top), amorphous PLLA block (middle) and crystalline PLLA block (bottom) for (a) PLLA-6-PCL (high l / ) and (b) PLLA-6-PCL (low M ) at 110" C and 140°C. Taken from [29]...

A-B-C structures are another possibility to develop new properties of polymeric nanocarriers for drug release. This approach was examined for instance by Kim ef a/. [ 310 ], with PEO-PPO-PCL triblock copolymers, by Deng et al. [ 108] with PEG-b-PLLA-b-PLGA and by Gadzinowski etal. [311] with PEO-b-poly(glycidol)-b-PLLA. 

Figure 2.9 Scanning electron microscopy images of fracture surfaces of (a) PLLA, (b) PLLA/PCL 80/20, (c) PLLA/PCL 60/20, and (d) PLLA/PCL 20/80.

Fig. 20 X-ray diffractograms of pure PCL (a) and PLLA (b) and PCL/PLLA blends obtained by casting from dioxane solution (c) and hot water coalescence from PCL/PLLA-a-CD-IC (d) [12]...

Scheme Chemical structures of poly(e-caprolactone)-b-poly(y-benzyl-L-glutamate) (PCL-PBLG) and poly(L-lactic acid)-b-poly(y-benzyl-L-glutamate) (PLLA-PBLG)...

Fig. 13.8. Polarized Optical Micrographs taken during isothermal crystallization (a) homo-PLLA, after 8 min at 122°C (b) homo-PCL, after 10 min at 42 C (c) after 30 min at 122""C (d) Ls2 Cea after 15 min at 42°C. Taken from [34]...

The formation and properties of inclusion compounds of cyclodextrin with double crystalline PLLA-b-PCL diblock copolymers has been extensively discussed in a series of contributions by Tonelli et al. [64-67], where they highlight the changes that can be introduced in the structure and properties of the copolymers when they form these peculiar inclusion complexes. 

Figure 3.12 Left Peak ciystallization and melting temperatures for the PLLA and PCL block for a wide range of PLLA-A-PCL diblock copolymers versus PLLA content Right PLOM micrographs for a) L32 C6s after 30 min. at 122 °C, b) the same sample after 15 min. additional time at 42 °C (modified from Ref. 107).

Cardoso, G.B.C., 2011. Initial study of electrospinning PCL/PLLA blends. Advances in Materials Physics and Chemistry 01 (03), 94—98. 

Scanning electron micrographs of typical electrospun fibres fabricated from (A) polyglycolic acid, (B) PLGA, (C) PLA, (D) PLGA, (E) PLLA, and (F) PCL. Scale bars = 10 pm. 

Figure 5.16 (a) CrystaUizalion and melting temperatures (obtained from the data reported in Ref. [211]) for PLLA and PCL blends as a function of PLLA content, (b) Photomicrograph obtained by PLOM for the 32/68 PLLA/PCL blend. Castillo et al. [212]. Reproduced with... 

Goonoo N, Bhaw-Luximon A, Rodrignez lA, Wesner D, Schbnherr H, Bowlin GL, Jhurry D. Poly(ester-ether)s III. assessment of cell behaviour on nanofibrous scaffolds of PCL, PLLA and PDX blended with amorphous PMeDX. J Mater Chem B 2015 3 673-687. 

Homo-PCL and PCL Block within the PLLA-b-PCL Diblock Copolymers The overall crystallization rate, expressed as r for homo-PCL and for the PCL block within the PLLA-b-PCL diblock copolymers are shown in Figure 11.14. It is important to note that the isothermal crystallization of the PCL block was performed after crystallizing the PLLA block until saturation. At this condition, the PCL block chains are nucleated by the PLLA block crystals where the PCL peak crystallization temperature (T pcl) shifted to higher values. 

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