Vesiculation and Stability: Oligomer of Conjugated Linoleate Acids Prepared by High Internal Phase Self-emulsion Polymerization†

doi:10.7503/cjcu20190084

Abstract

Abstract:

High internal phase O/W emulsion of conjugated linoleic acids(CLA) was prepared by self-emulsifying technology, and oligomer of CLA(oligo-CLA) was obtained by thermal self-emulsion polymerization(SEP) of the above emulsion. Furthermore, fatty acid vesicles(FAV) self-assemble by the oligo-CLA showing 10—30 nm diameter at pH=8.6—13 that was revealed by both transmission electron microscopy and dynamic light scattering, which has theoretical significance for FAV stable at a broader pH range. The experimental results show that free-surfactant emulsion polymerization was completed in the high internal phase emulsion of 75.3%(mass fraction) CLA according to the unique self-emulsification/thermal oligomerization strategy, achieving 33% total self-crosslinking degree and the target oligo-CLA with an average polymerization degree of 6, which is instructive for scaling up oligo-CLA and FAV preparation. The oligo-CLA has better low temperature solubility in comparison with CLA itself, and the FAV self-assembling by it has stronger resistance to acidic and calcium conditions and shows calcium responsive size-tunable features. Moreover, the hybrid vesicles of oligo-CLA with a small amount of Span 40 or AEO₂ additives show even broader pH windows for vesiculation. Therefore the FAV self-assembling by oligo-CLA should have a wider application prospect in drug delivery systems, daily chemical products, and household detergents and personal care products.

Key words: Conjugated linoleic acid, Oligomer, Fatty acid vesicle, Vesicle stability, Self-emulsion polymerization

CLC Number:

O648

TrendMD:

FAN Ye,LIU Tingting,FANG Yun,XIA Yongmei. Vesiculation and Stability: Oligomer of Conjugated Linoleate Acids Prepared by High Internal Phase Self-emulsion Polymerization^†[J]. Chem. J. Chinese Universities, 2019, 40(6): 1193.

Figures/Tables 8

Fig.1 Phase diagram of the CLA-NaOH-H2O system

Fig.2 Effect of reaction conditions on oligomerization of CLA by thermal polymerization (A) Dosage of CLA(APS: 3%, SCL: 16.6%); (B) dosage of SCL(APS: 3%, CLA: 60%); (C) dosage of initiator based on CLA(SCL: 16.6%, CLA: 60%). All reactions were initiated by APS for 20 h at 80 ℃, and initial dose of CLA was 4 g.

Fig.3 UV spectra of the oligomerization products of CLA at 80 ℃ for 20 h a. Pre-initiated by APS(3%); b. post-initiated by APS(3%); c. post-initiated by APS(1.5% + 1.5%).

Fig.4 SI-pH curve of oligo-CLA

Fig.5 TEM images(A1—A4), size distribution(B1—B4) and DLS(C1—C4) of FAV pH: (A1—C1) 8.6; (A2—C2) 10.0; (A3—C3) 11.5; (A4—C4) 13.0.

Fig.6 Vesicle stability of the FAV assembling by 3 mmol/L oligo-CLA (A) Acid resistance. a. Pre-oligomerization; b. post-oligomerization. The digital photographs of post-oligomerization(B) and preoligomerization(C) at different concentrations of SDS. c(SDS)/(g·L-1): (B1) 0.01(cloudy); (B2) 0.02(cloudy); (B3) 0.04(clear); (B4) 0.06(clear); (C1) 0.06(precipitation); (C2) 0.10(cloudy); (C3) 0.18(cloudy); (C4) 0.25(semitransparent).

Fig.7 Size distribution(A) and the corresponding TEM images(B—E) of FAV assembling by oligo-CLA(3 mmol/L, pH=13) with total crosslinking degree of 33% (A) c(Ca2+)/(mmol·L-1): a. 0, b. 0.3, d. 0.6, d. 0.9, e. 1.2; (B) c(Ca2+)=0.3 mmol/L; (C) c(Ca2+)=0.6 mmol/L; (D) c(Ca2+)=0.9 mmol/L; (E) c(Ca2+)=1.2 mmol/L.

Fig.8 SI-pH curves(A, B) of composite systems(cCLA=3 mmol/L), TEM images of hybrid vesicles of oligo-CLA/Span 40(x=0.05,pH=5.2)(C) and oligo-CLA/AEO2(x=0.09, pH=5.6)(D) (A) a. CLA/Span 40, x=0.05; b. oligo-CLA/Span 40, x=0.05; c. oligo-CLA. (B) a. CLA/AEO2, x=0.09; b. oligo-CLA/AEO2, x=0.09; c. oligo-CLA.

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