Multi‐arm star block copolymers based on ε‐caprolactone with hyperbranched polyglycerol core

Multi‐arm star block copolymers based on ε‐caprolactone have been prepared by a core‐first approach using propoxylated hyperbranched polyglycerol P(G₅₂PO₃) as a polyfunctional initiator. Various monomer/initiator ratios were employed in the Sn‐catalyzed polymerization in order to vary the length of the caprolactone arms (DP_n(arm) = 10 to 50). The molecular weights of the block copolymers were in good aggreement with the calculated values. Careful NMR analysis revealed that the monomer/initiator ratio not only controls the arm length, but also influences the degree of functionalization. Poly(ε‐CL) stars with 52 arms and absolute molecular weights between 69 200 and 360 400 g/mol have been prepared. SEC measurements showed that the narrow polydispersity of the core molecule (M_w/M_n = 1.24) could be maintained upon block copolymerization. The resulting star polymers exhibited polydispersities between 1.21 and 1.33.     

Synthesis and Micellization Properties of Novel Symmetrical Poly(ε‐caprolactone‐b‐[R,S] β‐malic acid‐b‐ε‐caprolactone) Triblock Copolymers

Summary: A four‐step strategy to synthesize well‐defined amphiphilic poly(ε‐caprolactone‐b‐[R,S] β‐malic acid‐b‐ε‐caprolactone) triblock copolymers [P(CL‐b‐MLA‐b‐CL)], which combines the anionic polymerization of [R,S] benzyl β‐malolactonate (MLABz), and the coordination‐insertion ring‐opening polymerization (ROP) of ε‐caprolactone (CL), followed by the selective removal of benzyloxy protective groups of the central poly(malolactonate) block is described. The first step involves MLABz initiated by potassium 11‐hydroxydodecanoate in the presence of 18‐crown‐6 ether. This step was carried out at 0 °C with an initial monomer concentration of 0.2 mol · L^?1 in order to limit the occurrence of undesirable transfer and termination reactions by proton abstraction. After selective reduction of the carboxylic acid end‐group of the resulting α‐hydroxy, ω‐carboxylic poly([R,S] benzyl β‐malolactonate) leading to an α,ω‐dihydroxy PMLABz, the polymerization of CL was initiated by each hydroxyl end‐groups previously activated by AlEt₃. Finally, after catalytic hydrogenation of the benzyl ester functions, the P(CL‐b‐MLA‐b‐CL) triblock copolymer was recovered and the amphiphilic character evidenced by UV spectroscopy. As demonstrated, the CMC of these new P(CL‐b‐MLA‐b‐CL) triblock copolymer is higher by one order of magnitude than that of a P(MLA‐b‐CL) diblock copolymer of similar composition.

Concentration dependence of pyrene I₃₃₈/I₃₃₅ intensitiy ratio for P(MLA‐b‐CL) diblock and P(CL‐b‐MLA‐b‐CL) triblock copolymers in water.     

Synthesis and Characterization of Functionalized Crosslinkable Poly(ε‐caprolactone)

Summary: A new and rather simple method to obtain randomly crosslinked PCL is reported. PCL was previously functionalized through radical grafting of MA and GMA in the melt, using a Brabender‐like apparatus. GMA was added in order to obtain higher grafting efficiency. The structure of PCL‐g‐MAGMA was elucidated by ¹H NMR spectroscopy, and the content of grafted MA was determined by FT‐IR spectroscopy. PCL‐g‐MAGMA was successively crosslinked through reaction with HMDI. The degree of crosslinking was determined by solvent extractions with chloroform. Thermal and dynamic mechanical analysis and tensile tests were performed on plain PCL, on PCL‐g‐MAGMA and on crosslinked PCL samples.

Schematic representation of PCL‐g‐MAGMA structure.     

Polymerization of Lactides and Lactones, 8. Study on the Ring‐Opening Polymerization of 3‐Phenyl‐ε‐caprolactone and 5‐Phenyl‐ε‐caprolactone

Ring‐opening polymerization of 3‐phenyl‐ε‐caprolactone (3‐ph‐CL) and 5‐phenyl‐ε‐caprolactone (5‐ph‐CL) by tin(II) salt, Al(OⁱPr)₃ and CpNa has been studied; 3‐ph‐CL cannot be initiated by Al(OⁱPr)₃. Polymerization of 5‐ph‐CL initiated with Al(OⁱPr)₃ in toluene at 15°C yielded a polymer of a predictable molecular weight and a narrow molecular weight distribution. 3‐ph‐CL and 5‐ph‐CL can be polymerized by initiating with tin(II) salt, and CpNa. In CpNa‐based polymerization, high molecular weight P(3‐ph‐CL) and P(5‐ph‐CL) were obtained. DSC studies indicate that P(5‐ph‐CL) is an amorphous material, exhibiting a rubber state at room temperature. Compared with PCL, the glass transition temperature of P(3‐ph‐CL) and P(5‐ph‐CL) is higher (–60°C), in contrast to the melting temperature, which is higher for PCL. These new monomers give a route to novel aliphatic polyesters.     

Molecular Motions in the Supramolecular Complexes between Poly(ε‐caprolactone)‐Poly(ethylene oxide)‐Poly(ε‐caprolactone) and α‐ and γ‐Cyclodextrins

The structure and molecular motions of the triblock copolymer PCL‐PEO‐PCL and its inclusion complexes with α‐ and γ‐cyclodextrins (α‐ and γ‐CDs) have been studied by solid‐state NMR. Different cross‐polarization dynamics have been observed for the guest polymer and host CDs. Guest–host magnetization exchange has been observed by proton spin lattice relaxation T₁, proton spin lattice frame relaxation T_1ρ and 2D heteronuclear correlation experiments. A homogeneous phase has been observed for these complexes. Conventional relaxation experiments and 2D wide‐line separation NMR with windowless isotropic mixing have been used to measure the chain dynamics. The results show that for localized molecular motion in the megahertz regime, the included PCL block chains are much more mobile than the crystalline PCL blocks in the bulk triblock copolymer. However, the mobility of the included PEO block chains is not very different from the amorphous PEO blocks of the bulk sample. The cooperative, long chain motions in the mid‐kilohertz regime for pairs of PCL‐PEO‐PCL chains in their γ‐CD channels seem more restricted than for the single PCL‐PEO‐PCL chains in the α‐CD channels, however, they are not influencing the more localized, higher frequency megahertz motions.     

Microwave‐Assisted Synthesis and Characterization of Poly(ε‐caprolactone)/Montmorillonite Nanocomposites

Poly(ε‐caprolactone) (PCL)/montmorillonite (MMT) nanocomposites were prepared by in situ ring‐opening polymerization of ε‐caprolactone in the presence of MMT modified by hydroxyl‐group containing alkylammonium cation (Cloisite®30B) in a single mode microwave oven. For the polymerization mixtures, plateaus or exothermal peaks were observed in their temperature‐time profiles and can be attributed to the heat‐generating nature of the ring‐opening polymerization. The morphologies of the nanocomposites showed a predominantly exfoliated structure. The mechanical properties of the nanocomposites were evaluated via dynamic mechanical analysis. Compared with that of the recovered PCL matrix, the mechanical properties of the PCL/Cloisite®30B nanocomposites showed obvious improvement.

     

Synthesis of a Novel Chitin Derivative Having Oligo(ε‐caprolactone) Side Chains in Aqueous Reaction Media

A chitin‐based graft copolymer, chitin‐graft‐oligo(ε‐caprolactone) ( 2 ), was synthesized via ring‐opening graft polymerization of (ε‐caprolactone (ε‐CL) to ca. 50% partially deacetylated chitin 1 catalyzed by tin(II) 2‐ethylhexanoate in the presence of water as a swelling agent. The graft copolymer with ca. 40 wt.‐% poly(ε‐CL) content was obtained by the reaction using the catalyst of 0.17 mol‐% and water of 130 mol‐%, respectively, to the ε‐CL monomer at 100°C for 20 h. The chemical structure of 2 was characterized by IR, ¹H and ¹³C NMR spectroscopies. The poly(ε‐CL) contents by IR were in accordance with those determined by ¹H NMR analysis. T₁ measurements of an aqueous solution of 2 suggested that the molecular motion of the hydrophobic poly(ε‐CL) side chains is restricted to some extent. On the other hand, it was demonstrated by ¹³C CP/MAS NMR that the mobility of the chitin skeleton of 2 in the solid‐state is higher than that of the partially deacetylated chitin. X‐ray diffraction diagrams showed that 2 is amorphous, indicating that the crystallinity due to the chitin main chain was reduced by introducing the oligo(ε‐CL) side chains.     

Studies on Poly[acrylamide‐co‐(ε‐caprolactone)]: Synthesis,Characterization and Biodegradability

The synthesis, characterization, hydrolysis and biodegradation of a copoly(ester amide), poly[acrylamide‐co‐(ε‐caprolactone)], are described. The hydrogen transfer copolymerization of acrylamide (AA) with ε‐caprolactone (CLN) in the presence of butyllithium or calcium hydride as initiators has been investigated. The calcium hydride was effective for the synthesis of the copoly(ester amide) in a wide range of polymer composition (AA/CLN =  10 : 90 to 90 : 10). The copoly(ester amide) was readily hydrolyzed in the presence of hydrochloric acid (0.1 n) at 125°C in an autoclave (e. g. AA/CLN =  59 : 41, degradation 93%). Furthermore, the copoly(ester amide) was hydrolyzed enzymatically by lipase from Rhizopus arrhizus. The behavior of the enzymatic hydrolysis differed to the non‐enzymatic hydrolysis. The enzymatic hydrolyzability was remarkable in the range of the AA repeating unit (β‐alanine unit) from 10 to 40 mol‐% (e. g. AA/CLN =  27 : 73, degradation 44%), while, the degradability for the non‐enzymatic hydrolysis rose with increasing AA repeating unit content. The biodegradation of the copoly(ester amide) was evaluated using a standard activated sludge (e. g. AA/CLN =  27 : 73 biodegradation 45%). The relationship between the biodegradation and the polymer composition was similar for the standard activated sludge and the enzymatic hydrolysis.     

Fullerene End‐Capped Biodegradable Poly(ε‐caprolactone)

Fullerene capped poly(ε‐caprolactone)s (PCLs), namely single‐ and double‐fullerene end‐capped PCLs with different fullerene content, were successfully synthesized. The effect of the fullerene end on the crystallization behavior and mechanical properties of the PCL was studied. The aggregation behavior of the fullerene moieties at the end of the PCL chain was also studied. It was found that the aggregated fullerenes have two kinds of effect on the crystallization behavior of the PCL i.e., confinement effect and nucleating effect. The fullerene content shows a certain balance between the confinement effect and the nucleating effect on the crystallization rate of PCL. It was also found that the mechanical properties of the fullerene end‐capped PCLs are strongly related to the content of fullerene and the mode of end‐capping style: either single or double end‐capping.

     

Reorganization of Lamellar Diblock Copolymer Poly(ε‐caprolactone)‐block‐poly(4‐vinylpyridine) in the Melting Temperature Range

The reorganization kinetics of the “original” lamellar diblock copolymer poly(ε‐caprolactone)‐block‐poly(4‐vinylpyridine) crystals formed at 260 K is studied in the melting region from 270 K (10 K below the onset of the melting peak of original crystals) to 310 K (the melting peak temperature) on the time scale starting from 10^?4 to 10² s by ultrafast differential scanning calorimetry. Different reorganization pathways are observed in this temperature range. Annealing at temperatures below 295 K leads to further stabilization of original crystals by secondary crystallization. At annealing temperatures higher than 295 K, crystals partially melt and the reorganization occurs via the melting–recrystallization. For even higher temperature, such as 310 K, the melting is completed within a few milliseconds and recrystallization starts from the nuclei formation. The sigmoidal recrystallization kinetics is analyzed by the Avrami equation. It is found that the copolymer experiences about one order of magnitude slower recrystallization rate and has higher melting peak temperatures of crystals formed after recrystallization than the homopolymer. The slower recrystallization kinetics in the copolymer is discussed from the viewpoint of the nanoscale spatial constraint and the intermediate state prior to the recrystallization.

     

Synthesis and Characterization of Comb‐Like Copolymers Based on Poly(ε‐caprolactone) and Poly(α‐olefin)

Comb‐like copolymers based on a polyolefin backbone of poly(10‐undecene‐1‐ol) (PUol) with poly(ε‐caprolactone) (PCL) side chains are synthesized in two steps. After synthesis of PUol by metallocene‐catalyzed polymerization, the side‐chain hydroxyl functionalities of this polar polyolefin are used as an initiator for the ring‐opening polymerization (ROP) of ε‐caprolactone (CL). In this context, copolymers with different lengths of PCL grafts are prepared. The chemical structure and the composition of the synthesized copolymers are characterized by ¹H and ¹³C NMR spectroscopy. It is shown that the hydroxyl end groups of PUol act effectively as initiating sites for the CL ROP. Size‐exclusion chromatography (SEC) measurements confirm the absence of non‐attached PCL and the expected increase in molar mass after grafting. The thermal and decomposition behaviors are investigated by DSC and thermogravimetric analysis (TGA). The effect of the length of the PCL grafts on the crystallization behavior of the comb‐like copolymers is investigated by DSC and wide‐angle X‐ray scattering (WAXS).

     

Synthesis of hydroxytelechelic ε‐caprolactone/poly(ethylene terephthalate) co‐oligomers, 1

In the presence of ethylene glycol, poly(ethylene terephthalate) (PET) undergoes chain scissions with the formation of α,ω‐hydroxyl oligomers, through classical transesterification by alcoholysis. ε‐Caprolactone was subsequently added on the hydroxyl end groups of PET oligomers by ring‐opening polymerization at different molar ratios of ε‐caprolactone to PET oligomers. The chemical structure of the products was investigated by size exclusion chromatography, ¹H NMR spectroscopy, and differential scanning calorimetry. A large majority of these products are soluble in common organic solvents. The thermal and ¹H NMR analyses reveal that the transesterification between base units of PET oligomers and ε‐caprolactone during the synthesis is always present whatever the reaction conditions. This phenomenon leads to copolymers having thermal properties different from those of PET. However, some co‐oligomers present the interest of keeping properties close to those of PET. The main purpose of this study was the synthesis of PET co‐oligomers that are soluble in some organic solvents that would make their use easier, and so that they can be used further as hard segment precursers for polycondensation reactions.

Ring‐opening polymerization of ε‐caprolactone onto hydroxytelechelic oligomers of PET.     

Synthesis of Functional Poly(ε‐caprolactone)s via Living Ring‐Opening Polymerization of ε‐Caprolactone Using Functionalized Aluminum Alkoxides as Initiators

The new aluminum compounds 1–3 modified by unsaturated alcohol, Me_3−n Al(O(CH₂)₄OCHCH₂)_n (n = 1 ( 1 ), 2 ( 2 ), 3 ( 3 )), are synthesized and investigated by multinuclear (¹H, ¹³C, ²⁷Al) NMR spectroscopy. The compounds 1 – 3 initiate living ring‐opening polymerization of ε‐caprolactone in bulk at 40–80 °C to afford polyesters with controlled molecular weight (M _n up to 35 000 g mol⁻¹) and relatively narrow molecular weight distribution (M _w/M _n < 1.8). Among initiators studied here, aluminum trialkoxide shows the highest activity, whereas aluminum dialkoxide is a less active. In all cases, the fragment of unsaturated alcohol is transferred to the end of the polymeric chain with high degree of functionality (>85%) yielding macromonomers. These macromonomers are copolymerized with maleic anhydride to give poly(vinyl ether‐co‐maleic anhydride)‐g‐poly(ε‐caprolactone) graft copolymers.

     

Synthesis and Micellization of Star‐Shaped Poly(ethylene glycol)‐block‐Poly(ε‐caprolactone)

Summary: The relationship between the architecture of block copolymers and their micellar properties was investigated. Diblock, 3‐arm star‐shaped and 4‐arm star‐shaped block copolymers based on poly(ethylene glycol) and poly(ε‐caprolactone) were synthesized. Micelles of star‐shaped block copolymer in an aqueous solution were then prepared by a solvent evaporation method. The critical micelle concentration and the size of the micelles were measured by the steady‐state pyrene fluorescence method and dynamic light scattering, respectively. The CMC decreased in the order di‐, 3‐arm star‐shaped and 4‐arm star‐shaped block copolymer. The size of the micelles increased in the same order as the CMC. Theory also predicts that the formation of micelles becomes easier for 4‐arm star‐shaped block copolymers than for di‐ and 3‐arm star‐shaped block copolymers, which qualitatively agrees with the experiments.

     

Well‐Defined Miktocycle Eight‐Shaped Copolymers Composed of Polystyrene and Poly(ε‐caprolactone): Synthesis and Characterization

A series of well‐defined miktocycle number‐eight‐shaped copolymers composed of cyclic polystyrene (PS) and cyclic poly(ε‐caprolactone) (PCL) have been successfully synthesized by a combination of atom transfer radical polymerization (ATRP), ring‐opening polymerization (ROP), and “click” reaction. The synthesis involves three steps: 1) preparation of tetrafunctional initiator with two acetylene groups, one hydroxyl group and a bromo group; 2) preparation of two azide‐terminated block copolymers, N₃‐PCL‐(CH?C)₂‐PS‐N₃, with two acetylene groups anchored at the junction; and 3) intramolecular cyclization of the block copolymer through “click” reaction under high dilution. The ¹H NMR, FT‐IR, and gel permeation chromatography (GPC) techniques are applied to characterize the chemical structures of the resulting intermediates and the target polymers. Their thermal behavior is investigated by differential scanning calorimeter (DSC). The decrease in chain mobility of eight‐shaped copolymers restricts the crystallization of PCL.

     

Synthesis of Saccharide‐Terminated Poly(ε‐caprolactone) via Michael Addition and ‘Click’ Chemistry

Maleimido‐terminated PCL (M‐PCL) and alkyne‐terminated PCL (A‐PCL) are prepared by the ring‐opening polymerization of ε‐caprolactone with N‐hydroxyethyl maleimide and 4‐pentyn‐1‐ol as initiators catalyzed by tin(II ) trifluoromethane sulfonate at 25 °C, respectively. A series of saccharide‐terminated PCLs have also been synthesized under mild conditions by two chemical strategies: 1). Michael addition of M‐PCL and amino‐containing maltose, and 2). a ‘click’ reaction of A‐PCL and azide‐containing saccharide. The amphiphilic nature of these maltose‐terminated PCLs make self‐assembly into aggregates in water possible. These aggregates have been characterized by transmission electron microscopy and dynamic light scattering measurements.

     

Branched Polytetrahydrofuran and Poly(tetrahydrofuran‐co‐ε‐caprolactone) Synthesized by Janus Polymerization: A Novel Self‐Healing Material

The Janus polymerization combines cationic and anionic polymerizations into growing chains with two different chain ends. This provides a novel pathway to produce topologically interesting polymers. Here this polymerization is applied to allow the synthesis of branched polytetrahydrofuran (bPTHF) and poly(tetrahydrofuran‐co‐ε‐caprolactone) (bPTC). Rare earth triflates [RE(OTf)₃] (RE = Lu, Sc, and Y) are used as catalyst, and small amounts (0.10–0.15 mol%) of ethylene glycol diglycidyl ether act as both initiator and comonomer due to the different reactivities of the two epoxide groups. The poly(ε‐caprolactone) block in bPTC provides crystalline domains and potential degradation under acidic conditions. The products of bPTHF show unusual tensile properties with a high strain at break of 1070% differing greatly from linear PTHF. Due to the large number of terminal hydroxyl groups and their strong hydrogen bonding, bPTHF has self‐healing properties with potentially promising applications.

     

Surface Patterning of Poly(ε‐caprolactone): Epitaxial Crystallization and Enzymatic Degradation

Surface patterning was carried out by the epitaxial crystallization of biodegradable PCL on a HOPG, and the surface morphologies were observed by atomic force microscopy. Edge‐on view lamellae were aligned along the HOPG lattice to display stripe patterns in the threefold symmetry. The intervals of stripe patterns composed of ridges and valleys increased with an increase in the crystallization temperature. Enzymatic degradation of the PCL nanopattern allowed the different depth profiles of the fringed structure. The persistence length of the nanopattern could be tuned by the molecular weight of PCL.

     

Polyhedral Oligomeric Silsesquioxane‐ and Fullerene‐End‐Capped Poly(ε‐caprolactone)

Novel fullerene‐ and polyhedral oligomeric silsesquioxane‐ (POSS) double end‐capped poly(ε‐caprolactone) (PCL) were successfully synthesized. The crystallization behavior of the fullerene‐ and POSS‐ double end‐capped PCL and the effect of aggregation of the POSS and fullerene moieties on the crystallization of PCL were thoroughly studied. The aggregation of the fullerene moieties has much larger confinement effect on the crystallization of PCL than that of POSS. The successful incorporation of two nano‐sized objects, that is, fullerene and POSS, into the PCL matrix may introduce their merits, so that PCL can attain multi‐functional properties.

     

Star‐shaped poly[(trimethylene carbonate)‐co‐(ε‐capro‐lactone)] and its block copolymers with lactide/glycolide: synthesis,characterization and properties

Linear and star‐shaped copolymers of trimethylene carbonate/ε‐caprolactone were synthesized using different polyol initiators and catalysts. Unexpectedly, when dipentaerythritol was used as an initiator cross‐linked rubbers were obtained, that swell in chloroform. This network formation can be understood by ‘in situ’ generation of cross‐linker molecules from trimethylene carbonate and initiator. SEC analysis showed that with D‐sorbitol star‐shaped copolymers are synthesized with an average functionality between 4 and 6. These low molecular weight rubbers were used as a macro‐initiator for the subsequent lactide/glycolide polymerization. Star‐shaped lactide/glycolide block copolymers with a poly[(trimethylene carbonate)‐co‐(ε‐caprolactone)] rubber core based on D ‐sorbitol show good mechanical properties. At relatively low rubber content ductile tensile behavior was observed indicating extensive toughening.