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Random introduction of degradable linkages into functional vinyl polymers by radical ring-opening polymerization, tailored for soft tissue engineering
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.ORCID iD: 0000-0001-6044-586X
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.ORCID iD: 0000-0002-1922-128X
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
2012 (English)In: Polymer Chemistry, ISSN 1759-9954, Vol. 3, no 5, 1260-1266 p.Article in journal (Refereed) Published
Abstract [en]

Vinyl polymers, e.g. polyvinyl acetate and polyvinyl alcohol, have properties which suit tissue engineering in many perspectives. A copolymer of 2-methylene-1,3-dioxepane (MDO) with vinyl acetate (VAc) should combine the desirable properties of vinyl polymers with the degradability of aliphatic polyesters. Our results and detailed kinetics information show that it is possible to vary the amount of MDO widely in the copolymer. Between 1 and 70% MDO was incorporated into the polymer when copolymerized with VAc at 60 degrees C using 2,2-azobisisobutyronitrile (AIBN) as an initiator. The amount of MDO in the copolymer was strictly controlled by the feed ratio, the copolymerization resulted in a high conversion, and the copolymers had high number average molar masses. The polymerization kinetics indicated that the ester units were added in a randomized manner to the vinyl backbone. This was a crucial point since the distribution of degradable bonds provides the opportunity to design the degradation profile of the polymer. The reactivity ratios for MDO and VAc were determined to be r(MDO) 0.93 and r(VAc) 1.71. The glass transition temperature and the number average molar masses increased with increasing amount of VAc in the feed. We confirmed that the copolymer degraded rapidly in alkali hydrolysis and less in enzymatic hydrolysis and it was apparent that it is possible to synthesize various degradable materials based on VAc and MDO with predetermined polymer compositions and high number average molar masses.

Place, publisher, year, edition, pages
2012. Vol. 3, no 5, 1260-1266 p.
National Category
Polymer Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-90825DOI: 10.1039/C2PY20034AISI: 000302315800021Scopus ID: 2-s2.0-84859742475OAI: oai:DiVA.org:kth-90825DiVA: diva2:506741
Note
QC 20120509Available from: 2012-02-29 Created: 2012-02-29 Last updated: 2014-05-14Bibliographically approved
In thesis
1. Synthesis of functional degradable polymers by radical ring-opening polymerization
Open this publication in new window or tab >>Synthesis of functional degradable polymers by radical ring-opening polymerization
2012 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The increased demand for understanding cell-material interactions and subsequently create personalized implants for tissue engineering has resulted in an increased interest in developing new monomers with functional groups. The focus of the work presented in this thesis has been on the synthesis of functional monomers and the polymerization of these into functional amorphous aliphatic polyesters.

The cyclic ketene acetal 2-methylene-1,3,6-trioxocane (MTC) was synthesized in a two-step reaction and subsequently polymerized at different temperatures using either 2,2’-azoisobutyronitrile (AIBN) or dicumyl peroxide as initiator. It was shown that the polymerization mechanism was not temperature-dependent and the polymerization proceeded with 100% ring-opening at all evaluated temperatures.

The polyester-ether was then successfully copolymerized with another cyclic ketene acetal 2-methylene-1,3-dioxepane (MDO) and a functional, hydrophilic and  amorphous copolymer was obtained. The feed ratios were varied between 90 to 25 mol% of MTC and it was shown that the proportion of MTC in the copolymers was in general higher than the proportion of MTC in the feed, confirming that the reactivity ratio was higher for MTC. A number average molecular weight of 6500 g/mol was obtained after 2 days at 70 °C in bulk. The high polydispersity index as well as the glass transition temperatures indicated a significant amount of branching.

MDO was also copolymerized with vinyl acetate (VAc). A series of copolymers with various combinations of MDO and VAc were synthesized by using AIBN as radical initiator. It was shown that the proportion of MDO in the copolymers was strictly controlled by the feed ratios and that the composition of the copolymers, the thermal properties and the molecular weights could be predetermined. The reactivity ratios for MDO and VAc were determined to be rMDO = 0.93 and rVAc = 1.71. The copolymerization resulted in a high degree of conversions and a high number average molecular weights, where both the molecular weight and the glass transition temperature increased with increased proportion of VAc in the feed. It was also confirmed that the copolymer were susceptible to both alkali and enzymatic hydrolysis and it was apparent that it is possible to synthesize various degradable materials based on VAc and MDO with predetermined polymer compositions and high number average molecular weights.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. 44 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2012:6
Keyword
tissue engineering, ring-opening polymerization, 2, 2´-azoisobutyronitrile, cyclic ketene acetals, 2-methylene- 1, 3, 6-trioxocane, 2-methylene- 1, 3-dioxepane, vinyl acetate, coopolymerization
National Category
Polymer Chemistry
Identifiers
urn:nbn:se:kth:diva-90826 (URN)978-91-7501-253-7 (ISBN)
Presentation
2012-03-09, K2, KTH, Teknikringen 28, Stockholm, 13:00 (English)
Opponent
Supervisors
Note
QC 20120229Available from: 2012-02-29 Created: 2012-02-29 Last updated: 2012-03-28Bibliographically approved
2. Functional Degradable Polymers by a Radical Chemistry approach
Open this publication in new window or tab >>Functional Degradable Polymers by a Radical Chemistry approach
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

One class of polymers that is inherently of great value for many applications is the aliphatic polyesters. Such polymers are very suitable for use as temporary guides, scaffolds, for tissue formation and other biomedical applications, due to their biocompatibility, degradability and appropriate mechanical properties. A prominent way to incorporate sites that allow alterations and modifications of the polymer backbone could be by copolymerization of functional monomers. The focus in this thesis is the development of new monomers and subsequent polymers bestowed with functional groups.

Radical ring-opening polymerization (RROP) of cyclic ketene acetals through a free-radical mechanism presents an alternative route to conventional ring-opening polymerization for the synthesis of aliphatic polyesters. By RROP, it is possible to incorporate ester functionality into the backbone of non-degradable polymers by copolymerize cyclic ketene acetals with vinyl monomers.

The possibility of creating materials with high degree of functionality is achieved by copolymerization with other and possible functional monomers. Three different copolymerizations including cyclic ketene acetals were performed. First, to increase hydrophilicity of a hydrophobic polymer by copolymerization of two cyclic ketene acetals, 2-methylene-1,3,6-trioxocane (MTC) and 2-methylene-1,3-dioxepane (MDO). Second, to introduce degradability into a non-degradable backbone by copolymerize MDO and vinyl acetal (VAc). Subsequently, the acetate side-group was hydrolyzed into the more hydrophilic alcohol group. Third, to introduce reactive functionalities into the degradable backbone of poly(2-methylene-1,3-dioxepane) (PMDO), by copolymerize MDO and glycidyl methacrylate (GMA). The epoxide side-groups, originating from GMA, were subsequently used in post-polymerization reactions by coupling with the bioactive molecule heparin.

The degradability of this class of copolymers was evaluated using the MDO/GMA-based material as model, showing that the materials degrade during 133 days without a rapid release of acidic degradation products or any substantial lowering of the pH. Methylthiazol tetrazolium (MTT) assays were also performed to confirm the innocuousness of the material. The results from the degradation study together with the MTT assays showed that these materials would be interesting for use in biomedical applications.

Finally, a combination of controlled radical polymerization with controlled ring-opening polymerization was performed. α-Bromo-γ-butyrolactone (αBrγBL) together with ε-caprolactone (εCL) or L-lactide (LLA) was successfully copolymerized to achieve copolymers with active and available grafting sites for single electron transfer living radical polymerization (SET-LRP). Different acrylates, ranging from the hydrophobic n-butyl acrylate and methyl methacrylate to the hydrophilic 2-hydroxyethyl methacrylate, were subsequently grafted via SET-LRP. All designated acrylate monomers were successfully grafted onto the polymer backbone, thereby emphasizing the versatility and ability of αBrγBL to act as a bridge between SET-LRP and ROP for a wide range of monomers.

Abstract [sv]

De alifatiska polyestrarna är en klass polymerer som är av stort intresse för många applikationer. Dessa polymerer är mycket lämpade att använda som temporära guider, scaffolds, för vävnadsregenerering och andra biomedicinska applikationer, på grund av sin biokompatibilitet, nedbrytbarhet och goda mekaniska egenskaper. Ett bra sätt att introducera funktionella grupper, som tillåter ändringar och modifikationer i polymerkedjan, kan vara att sampolymerisera med funktionella monomerer. I denna avhandling har därför fokus varit på att utveckla nya funktionella monomerer och polymerer.

Radikal ringöppningspolymerisation (RROP) av cykliska ketenacetaler har visat sig vara ett bra alternativ till att syntetisera alifatiska polyestrar jämfört med vanlig traditionell ringöppningspolymerisation. Med RROP är det möjligt att inkorporera esterfunktionalitet i polymerkedjan för icke nedbrytbara polymerer genom att sampolymerisera cykliska ketenacetaler med vinylmonomerer.

Möjligheten att skapa material med hög grad av funktionalitet uppnås genom att sampolymerisera med andra funktionella monomerer. Tre olika sampolymerer syntetiserades. Den första sampolymeren tillverkades för att introducera hydrofilicitet till en hydrofob polymer genom att sampolymerisera två ketenacetaler; 2-metyl-1,3,6-trioxocan (MTC) och 2-metyl-dioxepan (MDO). Därefter sampolymeriserades MDO med vinylacetat (VAc) för att tillföra nedbrytbarhet från MDO till ett, från huvudkedjan, onedbrytbart material. Acetatgruppen hydrolyserades därefter till den mer hydrofila alkoholgruppen. Som en sista sampolymerisation gjordes en med MDO med glycidylmetakrylat (GMA) för att införa funktionalitet till en nedbrytbar polymer. Epoxidgruppen tillhörande GMA, användes därefter för att kovalent koppla på den bioaktiva molekylen heparin på sampolymeren.

Nedbrytbarheten i denna klass av sampolymerer undersöktes med hjälp av att använda det MDO/GMA-baserade materialet som modell. Som resultat visade det sig att man, efter 133 dagar, varken kunde se en snabb frisättning av sura nedbrytningsprodukter eller en stor sänkning av pH. MTT-analyser utfördes för att visa att materialet inte var giftigt. Både resultaten från nedbrytningsstudien tillsammans med MTT-analyserna visade att dessa material är potentiella material för användning i biomedicinska applikationer.

Till sist kombinerades kontrollerad radikalpolymerisation med kontrollerad ringöppningspolymerisation. För att syntetisera funktionella makroinitiatorer sampolymeriserades monomeren α-brom-γ-butyrolakton (αBrγBL) med ε-kaprolakton (εCL) eller L-laktid (LLA). Dessa makroinitiatorer har aktiva grupper längs med huvudkedjan som kan användas för ympning av olika akrylater; från de hydrofoba n-butylakrylat och metylmetakrylat till den hydrofila 2-hydroxyetylmetakrylat med hjälp av en kontrollerad radikalpolymerisationsmetod som kallas för SET-LRP. Genom att lyckas ympa ett brett spektrum av monomer med olika egenskaper på polyester-makroinitiatorerna resulterade detta i att det gick att kombinera två olika polymerisationsmetoder på ett enkelt sätt.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2014. 74 p.
Series
TRITA-CHE-Report, ISSN 1654-1081 ; 2014:22
National Category
Polymer Technologies
Research subject
Fibre and Polymer Science
Identifiers
urn:nbn:se:kth:diva-145193 (URN)978-91-7595-126-3 (ISBN)
Public defence
2014-05-23, K2, Teknikringen 28, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20140514

Available from: 2014-05-14 Created: 2014-05-14 Last updated: 2014-05-14Bibliographically approved

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