Molecular Weight Dependence of the Poly(l-lactide)/Poly(d-lactide) Stereocomplex at the Air−Water Interface

Abstract

The molecular weight dependence of poly(L-lactide)/poly(D-lactide) (PLLA/PDLA) stereocomplex behavior at the air-water interface was studied by surface pressure-area (pi-A) isotherms and atomic force microscopy (AFM). It was found that the compression-induced sterecomplexation of a PDLA/PLLA equimolar blend with high molecular weight (M(w) = 1 x 10(6) and 9.8 x 10(5), respectively) could occur at the air-water interface. This result is in marked contrast with the stereocomplexation of PDLA/PLLA blends in the bulk from the melt or in solutions, where the homocrystallites of either PLLA or PDLA rather than stereocomplex crystallites will be formed preferentially when the molecular weights of both polymers are higher than 1 x 10(5). Unexpectedly, the Langmuir-Blodgett behavior of the PDLA/PLLA blend with lower molecular weight (M(w) = 4 x 10(3) and 3.2 x 10(3), respectively), which should be favored in the stereocomplex, was distinct from that of other higher molecular weight blends. AFM images clearly disclosed for the first time the morphological changes of the equimolar blends of PLLA and PDLA at the air-water interface induced by increasing the surface pressure of the monolayer. Of particular note, the bilayer mechanism for the plateau in the isotherm was directly verified by the AFM height images.

Single Lipid Bilayers Constructed on Polymer Cushion Studied by Sum Frequency Generation Vibrational Spectroscopy

“…14–16 In addition, PLLA is an inert polymer that does not present any antigenic activity. PLLA is stable enough to investigate the interactions between the lipid bilayers and biological molecules.…”

Stereocomplex formation between poly(L‐lactic acid) and poly(D‐lactic acid) with disproportionately low and high molecular weights from the melt

“…On the other hand, crystallization and spherulite growth behavior of PLLA/PDLA SC crystallites with wide ranges of molecular or segmental weights have been intensively investigated 16–20, 27–29. From the melt, the radial growth rates of spherulites ( G ) for blends of PLLA and PDLA with low weight‐average molecular weight ( M w ) values of 4.0 × 10 3 –2.2 × 10 4 g mol −1 were much higher than those for neat PLLA or PDLA,30, 31 whereas the G values for the blend of PLLA and PDLA with intermediate number‐average molecular weight ( M n ) values of 5.9 × 10 4 and 3.2 × 10 4 g mol −1 were similar to those for neat PLLA and PDLA 32.…”

Synthesis and stereocomplex formation of enantiomeric alternating copolymers with two types of chiral centers, poly(lactic acid-alt-2-hydroxybutanoic acid)s

“…[12][13][14][15][16][17][18][19][20][21][22][23] Various parameters affect SC formation. Such parameters include the types, concentrations and sequence of monomer units, 13,14,18,[24][25][26][27][28][29] thermal history, 13,18,30,31 external forces, 13,18,[32][33][34][35][36] the types and concentrations of solvents for casting, 18,[37][38][39] the types and concentrations of third polymers and additives. 18,[40][41][42][43][44][45][46][47] Recently, the symmetry between PLLA and PDLA or their alternating packing was found to be retained in the SC crystal lattice, 48,49 whereas PDLA and PLLA chains were reported to be contained in the SC crystal lattice with a wide PLLA fractions from 30 to 70%.…”