Microencapsulation by Coacervation of Poly(lactide-co-glycolide)-II:Encapsulation of a Dispersed Aqueous Phase

in polymer International (1993), 32

This paper is related to the phase separation of different copolyesters of lactides and glycolide solutions induced by the addition of silicone oil in order to promote microencapsulation of proteins. This ... [more ▼]

This paper is related to the phase separation of different copolyesters of lactides and glycolide solutions induced by the addition of silicone oil in order to promote microencapsulation of proteins. This coating process can be divided in three successive steps: phase separation of the coating polymer; adsorption of the coacervate droplets around the drugs phase, and microcapsule solidification. This paper focuses on the physico-chemical analysis of the second step. The knowledge of the interfacial tensions between the three liquid phases allows understanding of the microscopic evolution of the phase separation medium. [less ▲]

Macromolecular engineering of polylactones and polylactides. 8. Ring-opening polymerization of ε-caprolactone initiated by primary amines and trialkylaluminum

in Macromolecules (1992), 25

Whenever added with triethylaluminum, primary amines have been found to be effective initiators for epsilon-caprolactone polymerization in both toluene and THF at 40°C. The IR and NMR analysis of the ... [more ▼]

Whenever added with triethylaluminum, primary amines have been found to be effective initiators for epsilon-caprolactone polymerization in both toluene and THF at 40°C. The IR and NMR analysis of the polyester has supported a polymerization mechanism proceeding through a "coordination-insertion" pathway and the selective rupture of the acyl-oxygen bond of the monomer. The alkylaluminum activates the carbonyl group of the monomer and accordingly favors the nucleophilic addition of the amine, which is the actual initiation step. Propagation is typically a living process, and the molecular weight distribution is controlled by both AlEt3/amine molar ratio and solvent As an extension of that mechanism, diethylaluminum omega-amino alkoxide has been prepared on purpose and successfully used as an initiator for the synthesis of α,ω-dihydroxypoly(ε-caprolactone). [less ▲]

Microencapsulation by coacervation of poly(lactide co glycolide) : morphology of the microstructures in relationship with the physico chemical characteristics of the phase separated systems.

Conference (1992, September 13)

Living (co)polymerization of adipic anhydride and selective end functionalization of the parent polymer

in Macromolecules (1992), 25(14), 3820-3824

Coacervation of copolymers of lactic and glycolic acids. Part A : physico chemical characteristics of the phase separation process.

Poster (1992, April 01)

Macromolecular engineering of polylactones and polylactides. 7. Structural analysis of copolyesters of epsilon-caprolactone and L- of D,L-lactide initated by Al(OiPr)3

in Macromolecules (1992), 25(1), 37-44

Copolymerization of mixtures of epsilon-caprolactone (epsilon-CL) and D,L- or L-lactide has been initiated by aluminum isopropoxide. On the basis of the monomer reactivity ratios and assuming that no side ... [more ▼]

Copolymerization of mixtures of epsilon-caprolactone (epsilon-CL) and D,L- or L-lactide has been initiated by aluminum isopropoxide. On the basis of the monomer reactivity ratios and assuming that no side reaction occurs, tapered copolymers should be formed particularly when D,L-lactide is the comonomer rather than L-lactide. The sequential distribution of the comonomers has been analyzed by an original method based on the quantitative measurement of the carbonyl C-13 signals. Comparison of the experimental and the theoretical distributions clearly shows that transesterification reactions occur during copolymerization through both intra- and intermolecular mechanisms. Gel permeation chromatography and differential scanning calorimetry data support that conclusion. The D,L-lactide-based copolymers have however a more blocky structure than those containing L-lactide, and they are also less sensitive to transesterification reactions. [less ▲]

Synthetic biomedical polymers

Poster (1991, November 28)

Dielectric properties of a model cationic ionomer

in Macromolecules (1991), 24(24), 6439-6442

An alpha,omega-bis(dimethylamino)polyisoprene (M(n)BAR = 5000) has been quaternized by alpha,alpha'-dibromo-p-xylene with formation of a model cationic ionomer. Dielectric spectroscopy has shown an alpha ... [more ▼]

An alpha,omega-bis(dimethylamino)polyisoprene (M(n)BAR = 5000) has been quaternized by alpha,alpha'-dibromo-p-xylene with formation of a model cationic ionomer. Dielectric spectroscopy has shown an alpha-relaxation which corresponds to the micro-Brownian motion of chain segments directly attached to the quaternary ammonium dipoles. A shoulder on the low-temperature side of the alpha-relaxation has been assigned to the contribution of the polymer segments, the mobility of which is not restricted by the multiplets. That situation is in full agreement with the multiplet-cluster concept recently revisited by Eisenberg et al. [less ▲]

Synthetic Biomedical Polymers (Part B)

Poster (1991, May 31)

Macromolecular engineering of polylactones and polylactides. 5. Synthesis and characterization of diblock copolymers based on poly-ε-caprolactone and poly(L,L or D,L)lactide by aluminum alkoxides

in Macromolecules (1991), 24(11), 3027-3034

Aluminum isopropoxide is known to be an effective initiator for the ring-opening polymerization of lactides (D,L and L,L) and epsilon-caprolactone (epsilon-CL). For a question of mutual reactivity, the ... [more ▼]

Aluminum isopropoxide is known to be an effective initiator for the ring-opening polymerization of lactides (D,L and L,L) and epsilon-caprolactone (epsilon-CL). For a question of mutual reactivity, the sequential polymerization of these two comonomers can only be achieved when epsilon-CL is first polymerized followed by the lactide. Formation of a large amount of homo PLA is however observed and has been attributed to a great difference in the mean degree of association of aluminum alkoxides in toluene in the presence of epsilon-CL and LA. In toluene, the mean number (n) of active sites per Al(O(i)Pr)3 molecule jumps from 1 to 3 when epsilon-CL is substituted by LA. The addition of a small amount of an alcohol, like 2-propanol, is effective in preventing the aluminum alkoxide from associating, and n is then 3 whatever the monomer used. 2-Propanol participates in the polymerization of epsilon-CL and LA as supported by a decrease in the molecular weight of the final polymer in relation to the molar amount of added alcohol. This means that the alcohol molecules are rapidly exchanged with the alkoxide groups on Al. Under such conditions, the formation of pure diblock copolymers P(epsilon-CL-b-LA) is reported. Another successful strategy for the synthesis of the diblock copolymer consists in using an Al derivative that bears only one alkoxide group to initiate the polymerization of the two cyclic esters. In this regard, a diethylaluminum alkoxide is of great value, particularly the ethoxide one. A third, conceptually similar, approach to the synthesis of P(epsilon-CL-b-LA) copolymers relates to the reaction of a performed hydroxy-terminated PCL with triethylaluminum and the use of that macroinitiator in the ring-opening polymerization of the lactide. [less ▲]