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Microblock copolymers as a result of transesterification catalyzing behavior of lipase CA in sequential ROP
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
2007 (English)In: Macromolecules, ISSN 0024-9297, E-ISSN 1520-5835, Vol. 40, no 13, 4464-4469 p.Article in journal (Refereed) Published
Abstract [en]

The copolymerization of epsilon-caprolactone (CL) and 1,5-dioxepan-2-one (DXO) was performed by sequential addition of monomers in lipase CA catalyzed ring-opening polymerization (ROP) at 60 degrees C in bulk. CL was first polymerized up to a monomer conversion of 95%, and then DXO was added to the reaction mixture. The polymerization was stopped when the DXO conversion reached a level of more than 95%. The molar feed ratio of CL and DXO was varied from 1.5 to 10, and the copolymer composition, as determined by H-1 NMR spectroscopy, agreed well with the feed. The block lengths of PCL and PDXO segments in the structure of these high molecular weight copolymers reduced significantly due to the occurrence of extensive transesterification during ROP. The enzyme, lipase CA, in addition to acting as the catalyst for ROP also promoted transesterification reactions. The increase in number-average molecular weight (M-n) after DXO polymerization in the second step illustrated that the terminal hydroxyl group of preformed PCL chains in the first step possibly initiated the DXO polymerization. A single glass transition, in between the glass transition temperatures of corresponding homopolymers of PDXO and PCL, was observed in the DSC thermograms of all the copolymers. A composition of 15-20% DXO gave optimal balance between strength and elasticity of the copolymers.

Place, publisher, year, edition, pages
2007. Vol. 40, no 13, 4464-4469 p.
Keyword [en]
Catalysis; Elasticity; Homopolymerization; Lipases; Molecular weight; Monomers; Nuclear magnetic resonance spectroscopy; Ring opening polymerization; DXO; Microblock copolymers; Molar feed ratio; Thermograms; Transesterification; Copolymers
National Category
Polymer Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-7009DOI: 10.1021/ma0701179ISI: 000247340700014Scopus ID: 2-s2.0-34547189110OAI: oai:DiVA.org:kth-7009DiVA: diva2:11883
Note
QC 20100818. Uppdaterad från Accepted till Published 20100818.Available from: 2007-04-20 Created: 2007-04-20 Last updated: 2010-08-18Bibliographically approved
In thesis
1. Aliphatic Polyesters for Soft Tissue Engineering: Development from Conventional Organometallic to Novel Enzymatic Catalysis
Open this publication in new window or tab >>Aliphatic Polyesters for Soft Tissue Engineering: Development from Conventional Organometallic to Novel Enzymatic Catalysis
2007 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

The development of macromolecules with defined structure and properties, aimed specifically for biomedical applications, has resulted in diverse biodegradable polymers with advanced architectures. Among them, aliphatic polyesters synthesized by ring-opening polymerization (ROP) of lactones and lactides have a leading position due to their good mechanical properties, hydrolyzability and biocompatibility. To achieve tailored properties and controlled architecture, the technique for ROP of lactones and lactides has been continuously refined in the past years. Enzyme-catalyzed ROP is one of the most promising tools, which avoids the use of toxic organometallic catalysts and brings a “green-chemistry” appeal with it. In the work described in this thesis, enzyme-catalyzed ROP of 1,5-dioxepan-2-one (DXO), ε-caprolactone (CL) and lactides (L-, D- and D,L-lactide) was performed in bulk using Lipases from different sources. The effects of enzyme concentration, polymerization temperature and reaction water content on the monomer conversion and the polymer molecular weight during DXO polymerization were studied, and the role of water as initiator was confirmed. Terminal functionalized, block, comb and star polymers were synthesized using different alcohols as initiator in the enzyme-catalyzed ROP of DXO, CL or lactides under strictly anhydrous conditions. The effect of simultaneous and sequential copolymerization of DXO and CL on the micro-block structure of the copolymers was studied and the reactivity ratios of DXO and CL were determined under Lipase catalysis. High molecular weight copolymers of DXO and CL thus obtained were fabricated into porous scaffolds for tissue implant applications. Enzymatic degradation and alkaline hydrolysis of lactides was performed to study the effect of molecular branches and the stereochemistry of the monomer on the degradation profile. In another approach, cross-linked films of DXO and CL were prepared using 2,2´-bis-(ε-caprolactone-4-yl) propane (BCP) as the cross-linking agent and Sn(Oct)2 as the catalyst. The networks obtained thereof were elastomeric materials, easy to cast and remove from the mould.

Place, publisher, year, edition, pages
Stockholm: KTH, 2007. 125 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2007:2
Keyword
aliphatic polyester, 1, 5-dioxepan-2-one, ε-caprolactone, L-lactide, D-lactide, D, L-lactide, enzyme, lipase CA, lipase PS
National Category
Polymer Chemistry
Identifiers
urn:nbn:se:kth:diva-4341 (URN)978-91-7178-595-4 (ISBN)
Public defence
2007-05-04, F3, KTH, Lindstedtsvägen 26, Stoclholm, 10:15
Opponent
Supervisors
Note
QC 20100818Available from: 2007-04-20 Created: 2007-04-20 Last updated: 2011-02-21Bibliographically approved

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