Block and random copolymerization of ε‐caprolactone, L‐, and rac‐lactide using titanium complex derived from aminodiol ligand

Abstract

A series of di‐ and triblock copolymers [poly(L‐lactide‐b‐ε‐caprolactone), poly(D,L‐lactide‐b‐ε‐caprolactone), poly(ε‐caprolactone‐b‐L‐lactide), and poly(ε‐caprolactone‐b‐L‐lactide‐b‐ε‐caprolactone)] have been synthesized successfully by sequential ring‐opening polymerization of ε‐caprolactone (ε‐CL) and lactide (LA) either by initiating PCL block growth with living PLA chain end or vice versa using titanium complexes supported by aminodiol ligands as initiators. Poly(trimethylene carbonate‐b‐ε‐caprolactone) was also prepared. A series of random copolymers with different comonomer composition were also synthesized in solution and bulk of ε‐CL and D,L‐lactide. The chemical composition and microstructure of the copolymers suggest a random distribution with short average sequence length of both the LA and ε‐CL. Transesterification reactions played a key role in the redistribution of monomer sequence and the chain microstructures. Differential scanning calorimetry analysis of the copolymer also evidenced the random structure of the copolymer with a unique Tg. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

Mixed Allyl Rare‐Earth Borohydride Complexes: Synthesis, Structure, and Application in (Co‐)Polymerization Catalysis of Cyclic Esters

“…The [LA]/[CL] feed monomer ratio was set to 100:100 and to 100:200, and the reactions were carried out in toluene at 70 °C, either in the absence or the presence of BnOH as CTA (Table ). The composition of the copolymers and the microstructural magnitudes were determined by NMR spectroscopy as reported ,. For an equimolar feed ratio and in the absence of a CTA (Table , entries 33–37), the conversion was found to be almost complete for l ‐LA whereas the conversion of ϵ‐CL was limited in comparison (up to 39 %; Table , entry 34).…”

“…This resulted in copolymers containing 7.6 (Table , entry 33, Sc initiator) to 28.6 % (Table , entry 34, Y initiator) ϵ‐CL incorporated. Apart from a few exceptions, the results are in agreement with what is generally obtained in LA/ϵ‐CL copolymerization attempts under smooth experimental conditions (i.e., solution, low temperature): even though ϵ‐CL is more easily homopolymerized than LA, the competition between these two monomers is clearly in favor of the conversion of LA, with a difficulty to enchain two CL monomers successively. In terms of the microstructure, the l CL value was found to be close to 1 (1.1 to 1.5), which indicates homogeneous dispersion of the CL single units into the PLA backbone, as confirmed by the randomness factor R about the value of 1 (0.77–1.16).…”

“…11 B NMR values were calibrated against BF 3 ⋅ Et 2 O. Elemental analyses were performed on a Carlo Erba 1108 Elemental Analyzer instrument at the London Metropolitan University. In the case of polymers analyses, the conversion as well as the composition of the copolymers and the microstructural magnitudes were determined as reported by mean of 1 H and 13 C NMR spectroscopy, after deconvolution by using the Topspin 3.2 software. Size exclusion chromatography (SEC) of the samples was performed in THF as an eluent at 40 °C (1 mL min −1 ) with a Waters SIS HPLC pump, a Waters 410 refractometer, and Waters Styragel columns (HR2, HR3, HR4, and HR5E) calibrated with polystyrene standards, with the correction M n (SEC)= M n (PS)×0.56(PCL), and M n (SEC)= M n (PS)×0.58 PLA) .…”

Synthesis of lactide/ɛ‐caprolactone quasi‐random copolymer by using rationally designed mononuclear aluminum complexes with modified β‐ketiminato ligand

“…Their substantially distinct reactivity ratios usually result in block‐like copolymers or gradient copolymers, whose degradation behavior and drug permeability are very different from those of random counterparts . Although the transesterification side reaction can gradually convert the blocky or gradient copolymers into tendentially random ones in some case, it is hard to precisely control the distribution of LA or CL repeat units along the polymer chain …”

Synthesis of trimethylene carbonate/ϵ -caprolactone copolymers initiated with zinc alkoxide: influence of copolymer chain microstructure on thermal and mechanical properties

“…The often prolonged degradation time significantly limits the application of poly(CL) to drug delivery devices or commercial sutures . However, one can modify its properties by copolymerization with other monomers . Through copolymerization of TMC with CL, materials can be obtained characterized by high flexibility, which due to their specific properties are promising materials for forming three‐dimensional scaffolds in tissue engineering, carriers for sustained drug release and various implants for surgery or neurosurgery …”