Structural Effects of Terminal Groups on Nonenzymatic and Enzymatic Degradations of End-Capped Poly(l-lactide)

Abstract

Poly(L-lactide) (PLLA) with various alkyl ester chain end groups were synthesized by ring-opening polymerization of L-lactide in the presence of zinc alkoxide as a catalyst. The structural effect of chain end groups on the rate of enzymatic and nonenzymatic degradations for amorphous films of PLLA were investigated at 37 degrees C in a Tris-HCl buffer solution (pH 8.6) with proteinase K and at 60 degrees C in a phosphate buffer solution (pH 7.4), respectively. The rate of enzymatic degradation for PLLA films was dependent on the carbon numbers of alkyl ester chain end groups, and the rates of PLLA samples with dodecyl (C12), tridecyl (C13), and tetracocyl (C14) ester end groups were much lower than those of the other samples. The surface morphologies of PLLA films after enzymatic degradation were characterized by scanning electron microscopy. After the enzymatic degradation, non-end-capped PLLA, PLLA with methyl (C1) and hexyl (C6) ester chain ends, were degraded homogeneously by proteinase K and the film surface was very smooth. In contrast, the PLLA with alkyl ester chain ends of carbon numbers over 12 were degraded heterogeneously by the enzyme, and the sponge-like network structure was formed on the film surface. These results indicated that the long alkyl ester groups at the chain ends of PLLA molecules aggregated in the amorphous films and the erosion rate was depressed due to the coverage of the aggregated terminal groups on the film surface. For the nonenzymatic degradation, the molecular weight of non-end-capped PLLA was remarkably decreased with progress of degradation. In contrast, the molecular weight of the end-capped PLLA gradually reduced at the initial stage of degradation and then the rate of degradation was accelerated. The decreases of molecular weight of PLLA by autocatalyzed degradation were retarded by the capping of carboxyl chain ends.

Amphiphilic PHA–mPEG copolymeric nanocontainers for drug delivery: Preparation, characterization and in vitro evaluation

“…A plausible explanation for the slower degradation rate of all mPEGylated systems was due to the coverage of the enzymatically inactive mPEG segment on the surface of enzymatically active PHA copolymer core. A similar effect on the surface barrier was found in the degradation of hydrocarbon (C12-C14) end-capped poly(l-lactide) film by proteinase K (Kurokawa et al, 2008). They suggested that the slower degradation, compared to non-end-capped polymer film, must be due to the coverage of the hydrocarbon end groups on the surface.…”

Organic acids catalyzed polymerization of ε‐caprolactone: Synthesis and characterization

“…The calculated molecular weight ( M n (calc.) ) of the obtained samples was estimated from the monomer/initiator ([CL] 0 /[ threo ‐9.10‐dihydroxyoctadecanoic acid] 0 ) ratio and the polymer yield 62. These values differ from that obtained by GPC and from calculated by 1 H‐NMR spectra (Table II).…”

The synthesis of copolymers, blends and composites based on poly(butylene succinate)

“…[1][2][3][4][5][6][7][8][9] Among aliphatic biodegradable polyesters, poly(butylene succinate) (PBS) is considered to be a promising material in many fields because it has excellent biodegradability, melt processibility and chemical resistance. However, PBS has limited applications because of its poor thermal stability and mechanical properties.…”