Molecular Organization of Polylactides Immobilized on a Flat Surface: Observation of Single Crystal Arrays of Homochiral and Stereocomplexed Polylactides

Abstract

Formation of single crystal arrays of polylactides (PLA) was found on a flat surface immobilized with poly(D-lactide) (PDLA) having different chain lengths. Monoalkoxydimethylsilyl-terminated PDLAs were synthesized by hydrosilylation of (allyloxy)ethyl-terminated PDLAs and covalently immobilized onto silicon surfaces by a silicone coupling reaction in which the immobilization took place homogeneously through a single Si−O−Si bond. Atomic force microscopy (AMF) of the immobilized surfaces revealed that PDLA chains having M n = 2400−7000 formed many projections (dots) on the surface of the polymer layers, each having a diameter of 30 nm and a height less than 1.0 nm with a narrow size distribution. When these surfaces were treated with free PDLAs and enantiomeric poly(L-lactide)s (PLLA) having similar chain lengths, nano-ordered arrangement of single crystallites arrays of homochiral (hc) and stereocomplexed (sc) PLAs were formed with ordering by the deposition of PDLA and PLLA chains on the surface-immobilized PDLA chains, respectively.

Nano-Ordered Surface Morphologies by Stereocomplexation of the Enantiomeric Polylactide Chains: Specific Interactions of Surface-Immobilized Poly(d-lactide) and Poly(ethylene glycol)-Poly(l-lactide) Block Copolymers

“…4.5 kDa (the first deposit) for surface immobilization of PDLA chains by siloxane bond formation with the surface silanol groups as reported previously. 12,13 Figure 1a shows a typical AFM image of the resultant PDLA-immobilized surface of the first deposit, exhibiting a homogeneous scattering of particulate deposits of PDLA chains. The average thickness of the deposit layer was 3.7 nm with bumpiness less than 0.7 nm.…”

“…This surface morphology, formed by the aggregation of the terminally anchored PDLA chains, was identical to that reported in our previous study. 13 This surface-modified silicon wafer was then submerged into a CH 2 Cl 2 solution of each of PLLA-PEG (4.6k-5.2k in the block sequence) and PLLA-PEG-PLLA (4.0k-3.2k-4.0k in the block sequence) (the second deposit). The AFM images of the surfaces obtained after the second deposition are shown in Figure 1b spaces ranging from 35 to 60 nm as shown by white bidirectional arrows.…”

“…Very recently, we reported that a monofunctional ethoxydimethylsilyl-terminated PDLA (Si-PDLA: shown by the chemical structure below) can homogeneously be immobilized on a plasma-treated surface of silicon wafer through single Si−O−Si bond 12 and that the surface-immobilized PDLA chains can bind free PLLA and PDLA molecules to form specific surface morphologies with homochiral (hc) and stereocomplex (sc) crystallizations, respectively. 13 Particularly, the formation of a single crystal array of the PDLA/PLLA complex strongly suggested a possibility of biding various PLLA block copolymers, and by which the copolymerized macromolecular chains can readily be immobilized on the surface for modification.…”

Macromolecular design of specialty polylactides by means of controlled copolymerization and stereocomplexation

“…Slager and Domb observed the morphology of sc and hetero‐sc formation behavior of PLLA and a peptide l ‐leuprolide, respectively, onto immobilized PDLA on a silicon surface . Our groups reported the direct surface immobilization of PLLA on a silicon surface treated with silyl‐terminated PDLA . As shown in Scheme , two types of silyl‐terminated PDLAs ((MeO) 3 ‐Si‐PDLA and EtO‐Si‐PDLA) having trimethoxysilyl and monoethoxydimethylsilyl terminals were synthesized and immobilized onto silicon surfaces.…”

Dip- and spin-assisted stereocomplexation-driven LbL self-assembly involving homochiral PVA-g-OLLA and PVA-g-ODLA copolymers

“…41,42 By the way, Nakajima et al, reported on the deposition of one layer of PLLA-containing diand triblock (conjugated to poly-(ethylene glycol)) onto PDLA chains pre-immobilized on a at silicon surface. 43,44 They evidenced the formation of stereocomplexes on the surface, leading to bumpy surface structures but they focused their work on the deposition of only one copolymer layer, without constructing multilayers. To summarize, stereocomplexation-driven LbL assembled lms including PLA-containing (co)polymers, such as gra copolymers have never been reported so far in literature.…”