Poly stereocomplex

Iso tactic poly(methyl methacrylate) (it-PMMA) can form a stereocomplex with st-PMMA. Recent X-ray studies 179) of this material indicate that the two polymer chains probably interact to form a double helical structure. The it-PMMA chain forms the inner helix and is surrounded by the st-PMMA helical chain which winds around it. If subsequent work confirms this model, this material would constitute a most unusual inclusion compound involving only one monomeric substance. 

Usual PLAs have two enatiomeric forms, PLLA and poly(D-lactide) (PDLA), which are synthesized from LLA and the D,D-isomer of lactide (DLA), respectively. It is well known that 1 1 mixture of PLLA and PDLA can form a stable stereocomplex (SC), which has a higher Tm and higher mechanical strength than either of homopolymers [261], We reported on the utility of SC formation to enhance the stability of nanogels. Monodisperse SC nanogels were obtained through the self-assembly of an equimolar mixture of Dex-g-OLLA and Dex-g-ODLA in a dilute aqueous solution. 

Poly(lactic acid)-based Stereocomplex formation pH [21-25]... 

Watanabe J, Eriguchi T, Ishihara K (2002) Stereocomplex formation by enantiomeric poly (lactic acid) graft-type phospholipid polymers for tissue engineering. Biomacromolecules 3 1109-1114... 

Poly(lactic acid) (PLA) has also been added to poly(SA) via melt polycondensation to produce the triblock copolymers poly(lactic acid-Wock-sebacic acid-Wock-lactic acid) (P(LA-block-SA-block-LA)) by Slivniak and Domb (2002). The PLA (d-, l-, and dl-) was incorporated by acetylation and addition to the PSA synthesis. They showed the formation of stable stereocomplexed particles with increased melting points and reduced solubility, and studied the degradation and drug release characteristics of the same (Slivniak and Domb, 2002). The stereocomplexes self-assemble as a consequence of the chirality in the PLA portions of the chains (Slivniak and Domb, 2002). 

Acknowledgement Special thanks to Urs J. Haenggi (Biomer) for information about biotechnological PHB synthesis and literature on stereocomplex formation of poly(lactide). We are also grateful to Dr. Carly Anderson and Dr. Sergei Vagin for their help with this article, as well as Benedikt Simon Soller and Simon Meister for their extensive help with the literature research. 

Many radical polymerization systems were examined hy Challa at a/. A number of papers were devoted to polymerization of methyl methacrylate, MM, in the presence of poly(methyl methacrylate). The role of tacticity of template was stressed. Isotactic PMM forms stereocomplex with syndiotactic PMM. Polymerizations of MM in the presence of isotactic PMM were carried out and the product (template + daughter polymer) was analyzed by NMR. When MM is polymerized in the polar solvent in the presence... 

The tacticity of PLA influences the physical properties of the polymer, including the degree of crystallinity which impacts both thermo-mechanical performance and degradation properties. Heterotactic PLA is amorphous, whereas isotactic PLA (poly(AA-lactide) or poly (55-lac tide)) is crystalline with a melting point of 170-180°C [26]. The co-crystallization of poly (RR-lactide) and poly(55-lactide) results in the formation of a stereocomplex of PLA, which actually shows an elevated, and highly desirable, melting point at 220-230°C. Another interesting possibility is the formation of stereoblock PLA, by polymerization of rac-lactide, which can show enhanced properties compared to isotactic PLA and is more easily prepared than stereocomplex PLA [21]. 

Ryan and Fleischer, Jr. (21) found that if isotactic and syndiotactic poly (methyl methacrylate) (PMMA) are mixed, they form a stereocomplex. It might have been supposed that the course of polymerization of methyl methacrylate in the presence of preformed stereoisomers of... 

Fig. 36. Composition of the stereocomplex in the system of isotactic poly-(methyl methacrylate) (iso-PMAA) and syndiotacticPMMA (synd-PMMA)376). Time after mixing O 1 h, 4h,A 8h...

Even relatively weak van der Waals and dipole-dipole interactions very often prove sufficient for maintaining the stabilization of some macromolecular associates in solution4965. This may be exemplified by the stereocomplexes or the associates of the right- or left-handed helices of poly (y-methyl-L(or -d)-glutamate) in organic solvents4975. 

Stereocomplexes, e.g. complexes between stereoisomers of poly(methyl methacrylates) caused by van der Waals interactions23. ... 

In bulk we may not forget the so called stereocomplexes between stereoregular polymers. In 1961 Watanabe reported that mixing syndiotactic poIy(methylmetha-crylate) (j-PMMA) and isotactic poly(methylmethacrylate) (/t-PMMA) leads to the... 

Figure 16 (a) Morphology of solution-grown poly(lactide) stereocomplexes and (b) the... 

T. Serizawa, K. Hamada, T. Kitayama, N. Fujimoto, K. Hatada, M. Akashi, Stepwise Stereocomplex Assembly of Stereoregular Poly(Methyl Methacrylate)s on a Substrate , J. Am. Chem. Soc., 122, 1891 (2000)... 

One of the cases of such complementarity may be the atactic polymer which can be considered as a copolymer of isotactic and syndiotactic links. Indeed, the composition and properties of the polyccanplex depend on the chain stereoregularity, for example in the case of poly(methyl methacrylate) stereocomplexes and poly(ethylene glycol) with isotactic or atactic PAA complexes ... 

Ute, K. Niimi, R. Matsunaga, M. Hatada, K. Kitayama, T. On-line SEC-NMR analysis of the stereocomplex of uniform isotactic and uniform syndiotactic poly(methyl methacrylate)s. Macromol. Chem. Phys. 2001, 202, 3081-3086. 

Table 2. Mechanical properties of isotactic, syndiotactic poly(MMA) and the stereocomplex...

Recently Purac [223] has developed a PLA compound with heat stability and impact strength comparable to poly(acetonitrile butadiene styrene) (ABS) in injection moulding apphcations based on the stereocomplex technology. 

In toluene solution, syndiotactic block copolymers of methyl methacrylate (PMMA) and allyl methacrylate were formed using triphenylphosphine and triethylaluminum as initiator [76]. In acetone solution, syndiotactic poly(methyl methacrylate) forms a stereocomplex with other syndiotactic polymers. The complex formed with syndiotactic poly(allyl methacrylate), upon separation from the reaction mixture and drying had a melting point of 141.5°C by DSC thermogram. From X-ray powder patterns of this and related complexes of PMMA with other polymethacrylates, the authors postulate that a double-stranded helix may represent a model of the structure of these complexes [77]. 

T.im DW, Choi SH, Park TG. A new class of biodegradable hydrogels stereocomplexed by enantiomeric ohgo(lactide) side chains of poly(HEMA-g-OLA)s. Macromol Rapid Comm 2000 21 464- 71. 

Li SM, Vert M. Synthesis, characterization, and stereocomplex-induced gelation of block copolymers prepared by ringopening polymerization of L(d)-lactide in the presence of poly(-ethylene glycol). Macromolecules 2003 36 8008-8014. 

Zhang, J., Sato, H., Tsuji, H., Noda, I. Ozaki, Y. (2005). Differences in the CH3"0=C interactions among poly(L-lactide), poly(L-lactide)/poly(D-lactide) stereocomplex, and poly(3-hydroxybutyrate) studied by infrared spectroscopy. Journal of Molecular Structure. Vol. 735-736, No. 14, pp. 249-257... 

Ishii D, Lee WK, Kasuya KI, Iwata T (2007) Fine structure and enzymatic degradation of poly[(R)-3-hydroxybutyrate] and stereocomplexed poly(lactide) nanofibers. 1 Biotechnol 132 318-324... 

Gallos et al. [6] synthesized stereocomplexed polylactide using reactive extrusion process. The stereocomplexed PLA obtained in a two-step polymerization of L-lactide and D-lactide process to yield poly-L,D-lactic acid multiblocks. In the first step, DSM Micro 15... 

Furthermore for the formation of a stereocomplex which blends of poly(L-lactide) and poly (D-lactide) could be found the interesting phenomena. The PLA stereocomplex was found to possess a racemic crystalline structure, where PDLA and PLLA chains were packed side hy side with a D monomer unit to L monomer unit... 

On the other hand, stereocomplexes and solvatophobic bonds are specific to macromolecular multimerization. Certain polymers with mutually complementary stereostructures form what are called stereocomplexes whose stoichiometry is dependent on the stereosequence length. Examples of such stereocomplexing are provided by the pairs poly(7-benzyl-D-glutamate) with poly(7-benzyl-L-glutamate) and isotactic with syndiotactic poly(methyl methacrylates) (PMMA). The specific enthalpy of stereocomplex formation with it- and st-PMMA is, for example, a linear function of the syndiotactic diad mass fraction, with a maximum at Wst = 0.58 (Figure 6-11). If, however. 

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