| 1. |
- Ryner, M., et al.
(författare)
-
Mechanism of ring-opening polymerization of 1,5-dioxepan-2-one and L-lactide with stannous 2-ethylhexanoate. A theoretical study
- 2001
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 34:12, s. 3877-3881
-
Tidskriftsartikel (refereegranskat)abstract
- A theoretical study of the ring-opening polymerization (ROP) mechanism of 1,5-dioxepana-2-one (DXO) and (L)-lactide (LLA) with stannous(IE) a-ethylhexanoate (Sn(Oct)(2)) is presented. The B3LYP density functional method has been used for the quantum chemical calculations. Our results support a coordination-insertion mechanism initiated by a tin-alkoxide species formed prior to the ROP. The rate-determining step in the ROP was the nucleophilic attack of the alkoxide on the carbonyl carbon of the monomer. The activation energy for the ROP of DXO with Sn(Oct ')(2) has been determined to be 19.8 kcal/mol and for L-lactide 20.6 kcal/mol. At normal reaction temperatures, a ligand may dissociate as Oct 'H during propagation. An excess of carboxylic acid hinders the coordination of monomer to the initiating/propagating complex.
|
|
| 2. |
- von Schenck, H., et al.
(författare)
-
Ring-opening polymerization of lactones and lactides with Sn(IV) and Al(III) initiators
- 2002
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 35:5, s. 1556-1562
-
Tidskriftsartikel (refereegranskat)abstract
- A theoretical study is presented of the ring-opening polymerization (ROP) mechanism of 1,5-dioxepan-2-one (DXO) and glycolide with Sn(II) and Al(III) alkoxide initiators (SnMe3MeO, SnMe2-(MeO)(2), and AlMe2MeO). The B3LYP density functional method has been used to perform the quantum chemical calculations. A coordination-insertion mechanism is presented with two principal reaction steps. First, the alkoxide of the initiator performs a nucleophilic attack on the carbonyl carbon, and the carbonyl bond is broken. An intermediate is formed at this point, where the former carbonyl oxygen of the monomer is coordinated to tin via an alkoxide bond, while the carbonyl carbon assumes a sp(3) bonding geometry. The second step involves the acyl-oxygen cleavage of the monomer. For all three initiators it was found that the transition state involving the breaking of the carbonyl double bond (TS1) represented the highest point on the potential energy surface for DXO. For glycolide, however, the transition state of the acyl-oxygen cleavage (TS2) was the least stable structure. The reaction barriers were calculated to 17.1 kcal/mol for DXO/SnMe3MeO, 18.7 kcal/mol for glycolide/SnMe3MeO, 14.3 kcal/mol for DXO/SnMe2(MeO)(2), 14.5 kcal/mol for glycolide/SnMe2(MeO)(2), 13.6 kcal/mol for DXO/AlMe2MeO, and 9.3 kcal/mol for glycolide/AlMe2MeO. Both electronic and steric properties of the monomer affect the reaction barriers. It was found that the more electrophilic initiators polymerized cyclic esters faster.
|
|
| 3. |
- Finne Wistrand, Anna, et al.
(författare)
-
Degradable polymers : Design, synthesis and testing
- 2003
-
Ingår i: Macromolecular Symposia. - : Wiley. - 1022-1360 .- 1521-3900. ; 195, s. 241-246
-
Tidskriftsartikel (refereegranskat)abstract
- The object for our research is to mimic Nature's perfectly designed resorbable materials to obtain important materials, which are biocompatible and degradable. We have therefore synthesized different architectures and copolymers of aliphatic polyesters with ring-opening polymerization. The first studies of these materials properties show that properties like hydrophilicity and tensile properties can be controlled.
|
|
| 4. |
- Ryner, M., et al.
(författare)
-
Resorbable and highly elastic block copolymers from 1,5-dioxepan-2-one and L-lactide with controlled tensile properties and hydrophilicity
- 2002
-
Ingår i: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; 3:3, s. 601-608
-
Tidskriftsartikel (refereegranskat)abstract
- New resorbable and elastomeric ABA tri- and multiblock copolymers have been successfully synthesized by combining ring-opening polymerization with ring-opening polycondensation. Five different Poly(L-lactide-b-1,5-dioxepan-2-one-b-L-lactide) triblock copolymers and one new Poly(L-lactide-b-1,5-dioxepan-2-one) multiblock copolymer have been synthesized. The triblock copolymers were obtained by ring-opening polymerization of 1,5-dioxepan-2-one (DXO) and L-lactide (LLA) with a cyclic tin initiator. The new multiblock copolymer was prepared by ring-opening polycondensation of a low molecular weight triblock copolymer with succinyl chloride. The molecular weight and the composition of the final copolymers were easily controlled by adjusting the monomer feed ratio, and all of the polymers obtained had a narrow molecular weight distribution. It was possible to tailor the hydrophilicity of the materials by changing the DXO content. Copolymers with a high DXO content had a more hydrophilic surface than those with a low DXO content, The receding contact angle varied from 27 to 44degrees. The tensile proper-ties of the copolymers were controlled by altering the PDXO block length. The tensile, testing showed that all the polymers were very elastic and had very high elongations-at-break (epsilon(b)). The copolymers retained very good mechanical properties (epsilon(b) approximate to 600-800% and sigma(b) approximate to 8-20 MPa) throughout the in vitro degradation study (59 days).
|
|
| 5. |
- Ryner, M., et al.
(författare)
-
Star-shaped and photocrosslinked poly(1,5-dioxepan-2-one) : Synthesis and characterization
- 2002
-
Ingår i: Journal of Polymer Science Part A. - : Wiley. - 0887-624X .- 1099-0518. ; 40:12, s. 2049-2054
-
Tidskriftsartikel (refereegranskat)abstract
- New star-shaped and photocrosslinked poly(1,5-dioxepan-2-one) (PDXO) has been synthesized through ring-opening polymerization initiated by SnOct(2)/pentaerythritol. The star-shaped PDXO was end-functionalized by acrolyol chloride to form acrylate end groups. The end-functionalized PDXO was photocrosslinked initiated by 2,2-dimethoxy-2-phenylacetophenone. The gel content ranged from 80 to 99%, indicating a high degree of crosslinking. The thermal properties of the star-shaped PDXO and the photocrosslinked PDXO were analyzed by differential scanning calorimetry. The glass-transition temperature was determined to approximately -32 degreesC for the crosslinked PDXO. The viscosity numbers were determined for star-shaped PDXO, with reference to linear homologues. The star-shaped PDXO had lower viscosity numbers than the linear counterparts, The crosslinked PDXO showed a rather hydrophilic surface as compared with other resorbable polyesters. The advancing contact angle was 64 +/- 2, and the receding angle was 57 +/- 4.
|
|
| 6. |
- Ryner, M., et al.
(författare)
-
Tailored mechanical properties and degradability of polyesters by controlled molecular architecture
- 2001
-
Ingår i: Macromolecular Symposia. - 1022-1360 .- 1521-3900. ; 175, s. 11-18
-
Tidskriftsartikel (refereegranskat)abstract
- Advanced molecular architectures have been used as a toot for tailoring the mechanical properties and the degradation process of polymers for specific applications. Crosslinked poly(1,5-dioxepan-2-one), random poly(1,5-dioxepan-2-one-co-L-lactide), triblock poly(L-lactide-b-1,5-dioxepan-2-one-b-L-lactide) and triblock poly(epsilon -caprolactone-b-1,5-dioxepan-2-one-b-epsilon -caprolactone) have been synthesized and their thermal and mechanical properties as well as degradation times and degradation products have been characterized and compared. The stress at break of the synthesized polymers ranged from 4 MPa to 55 MPa and the elongation at break from 25% to 1200%. The degradation time varied from 70 days up to 360 days. These polymers are suitable as films or microspheres for controlled drug delivery or as temporary tissue replacements e.g. for tendons or nerve guides.
|
|
| 7. |
- Stridsberg, K., et al.
(författare)
-
Dihydroxy-terminated poly(L-lactide) obtained by controlled ring-opening polymerization : Investigation of the polymerization mechanism
- 2000
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 33:8, s. 2862-2869
-
Tidskriftsartikel (refereegranskat)abstract
- Hydroxy telechelic poly(L-lactide)s of different molecular weight have been synthesized by controlled ring-opening polymerization using cyclic tin alkoxides. NMR analysis showed that the propagation proceeded through an insertion mechanism. No free hydroxyl or carboxyl end groups were detected in the polymerization mixture. Complete reaction of the initiator was observed over the entire range of compositions studied. Both tin-oxygen bonds were reactive and participated in the propagation reaction. Peak assignments were obtained by H-1, C-13, distortionless enhancement polarization transfer (DEPT), and heteronuclear multiple quantum coherence-gradient selected (hmqc-gs) nuclear magnetic resonance spectroscopy. The kinetics of the solution polymerization of L-lactide has been investigated and showed a first order in monomer. The external order in initiator has been determined to be 3/4 for initiator concentrations above 5 mmol/L and to 2 below 2 mmol/L. The molecular weight could easily be adjusted by the monomer-to-initiator ratio, and the molecular weight distribution remained narrow even at high molecular weight(MWD < 1.15). The polymerization products were characterized by size exclusion chomatography (SEC) as well as H-1 and C-13 NMR.
|
|
