Block Terpolymers Research Articles

Efficient biotransformation of biobased raw materials into novel polyesters/polyesteramides; comparative investigation of enzymatic synthesis of block and random copolymers and terpolymers

Within the context of paving the way for a sustainable bioeconomy, there is a strong emphasis on utilizing bio-based raw materials as substitutes for fossil fuels in the production of polymers. When designing the synthesis of novel polymeric materials from bio-based building blocks, a promising green approach consists in utilizing enzymes as biocatalysts. This aspect is particularly important when aiming to obtain products from the class of polyesters and polyesteramides with biocompatible and biodegradable properties, as enzymes facilitate the synthesis of polymers that align closely with biological systems. Lipases have been proven to be very effective in the synthesis of polymers, particularly in the ring-opening polymerization of ε-caprolactone. Considering the possibility of performing the copolymerization of ε-caprolactone for obtaining random and block structures, this is the first comparative study of the enzymatic polymer synthesis utilizing an innovative approach of combining ring-opening polymerization with polycondensation. Terpolymers derived from ε-caprolactone and dimethyl itaconate or dimethyl adipate with either 1,8-octanediol or 1,8-octanediamine were obtained at 85 °C in a solventless systems, yielding products with a copolymer content of >85 % and weight-average molecular weight (Mw) up to 40,000 Da. The thermal properties and biodegradation behavior of the synthetized terpolymers were assessed.

Cylinders-in-Undulating-Lamellae Morphology from ABC Bottlebrush Block Terpolymers.

Block polymer self-assembly affords a versatile bottom-up strategy to develop materials with the desired properties dictated by specific symmetries and dimensions. Owing to distinct properties compared with linear counterparts, bottlebrush block polymers with side chains densely grafted on a backbone have attracted extensive attention. However, the morphologies found in bottlebrush block polymers so far are limited, and only lamellar and cylindrical ordered phases have been reported in diblock bottlebrushes. The absence of complex morphologies, such as networks, might originate from the intrinsically stiff backbone architecture. We experimentally investigated the morphologies of nonfrustrated ABC bottlebrush block terpolymers, based on two chemistries, poly(ethylene-alt-propylene)-b-polystyrene-b-poly(dl-lactic acid) (PEP-PS-PLA) and PEP-b-PS-b-poly(ethylene oxide) (PEP-PS-PEO), synthesized by ring-opening metathesis polymerization of norbornene-terminated macromonomers. Structural characterization based on small-angle X-ray scattering and transmission electron microscopy measurements revealed an unprecedented cylinders-in-undulating-lamellae (CUL) morphology with p2 symmetry for both systems. Additionally, automated liquid chromatography was employed to fractionate the PEP-PS-PLA bottlebrush polymer, leading to fractions with a spectrum of morphologies, including the CUL. These findings underscore the significance of macromolecular dispersity in nominally narrow dispersity bottlebrush polymers while demonstrating the power of this fractionation technique.

Recent progress in the study of the self-assembly of ABC block terpolymers

Recent progress in the study of the self-assembly of ABC block terpolymers

Biodegradable Block Poly(ester amine)s with Pendant Hydroxyl Groups for Biomedical Applications.

The article presents the results of the synthesis and characteristics of the amphiphilic block terpolymers, built of a hydrophilic polyesteramine block, and hydrophobic blocks made of lactidyl and glycolidyl units. These terpolymers were obtained during the copolymerization of L-lactide with glycolide carried out in the presence of previously produced macroinitiators with protected amine and hydroxyl groups. The terpolymers were prepared to produce a biodegradable and biocompatible material containing active hydroxyl and/or amino groups, with strong antibacterial properties and high surface wettability by water. The control of the reaction course, the process of deprotection of functional groups, and the properties of the obtained terpolymers were made based on 1H NMR, FTIR, GPC, and DSC tests. Terpolymers differed in the content of amino and hydroxyl groups. The values of average molecular mass oscillated from about 5000 g/mol to less than 15,000 g/mol. Depending on the length of the hydrophilic block and its composition, the value of the contact angle ranged from 50° to 20°. The terpolymers containing amino groups, capable of forming strong intra- and intermolecular bonds, show a high degree of crystallinity. The endotherm responsible for the melting of L-lactidyl semicrystalline regions appeared in the range from about 90 °C to close to 170 °C, with a heat of fusion from about 15 J/mol to over 60 J/mol.

Degradable terpolyesters synthesized from a monomer mixture mediated by a heterometallic complex: Defined monomer- and stereo-sequences

Copolymers provide a feasible platform to extend the structures of polymeric material, and the control of architecture (such as monomer sequence and stereo sequence) plays a critical role in tailoring specific properties. Herein, a heterometallic (Salph Zn)2-Ho complex was screened out for the synthesis of architecture-defined block terpolymers from a monomer mixture of epoxide, cyclic anhydride and l-lactide (LLA). The polymerization in one-pot firstly underwent ring-opening copolymerization reaction producing completely alternating ester linkage, and then transformed to LLA polymerization with trace stereoerrors, forming block polyesters with a semicrystalline segment and an amorphous segment. The polymerization was “immortal” with the ability to synthesize sequence-defined multiblock polyesters by sequential monomer addition. Furthermore, DSC traces revealed that the obtained block polyesters exhibited distinct thermal properties stemming from each segment. The melting temperature of block terpolymer was increased to 207.6 °C facilitated by the stereocomplexes of PLA segment.

Core-Shell Gyroid in ABC Bottlebrush Block Terpolymers.

Block polymer self-assembly provides a versatile platform for creating useful materials endowed with three-dimensional periodic network morphologies that support orthogonal physical properties such as high ionic conductivity and a high elastic modulus. However, coil configurations limit conventional linear block polymers to finite ordered network dimensions, which are further restricted by slow self-assembly kinetics at high molecular weights. A bottlebrush architecture can circumvent both shortcomings owing to extended backbone configurations due to side chain crowding and molecular dynamics substantially free of chain entanglements. However, until now, network morphologies have not been reported in AB bottlebrush block copolymers, notwithstanding favorable mean-field predictions. We explored the phase behavior by small-angle X-ray scattering of 133 poly(ethylene-alt-propylene)-b-polystyrene (PEP-PS) diblock and PEP-PS-PEO triblock bottlebrush copolymers prepared by ring-opening metathesis polymerization (ROMP) of norbornene-functionalized poly(ethylene-alt-propylene) (PEP), poly(styrene) (PS), and poly(ethylene oxide) (PEO) macromonomers with total backbone degrees of polymerization Nbb between 20 and 40. The PEP-PS diblocks exhibited only cylindrical and lamellar morphologies over the composition range of ca. 30-70%. However, addition of variable-length bottlebrush PEO blocks to diblocks containing 30-50% PS led to the formation of a substantial core-shell double gyroid (GYR) phase window containing 20 bottlebrush triblock specimens, which is the focus of this report. Encouragingly, the GYR unit cell dimensions increased as d ∼ Nbb0.92, portending the ability to access larger network dimensions than previously obtained with linear AB or ABC block polymers. This work highlights extraordinary opportunities associated with applying facile ROMP chemistry to multiblock bottlebrush polymers.

One‐pot sequence‐selective synthesis of polylactone‐containing block terpolymers based on renewable terpenoid‐derived monomer and a simple organocatalyst

AbstractIn this work, we report the synthesis and polymerization performances of terpenoid‐derived camphoric anhydride (CA). Utilizing simple organo‐base tBuP2 as the catalyst, CA can polymerize with various epoxides by efficient and controlled ring‐opening alternating copolymerization (ROAC) to afford perfectly alternating poly(CA‐alt‐epoxide). Kinetic study shows that the polymerization proceeds following zero‐order dependence on the concentration of CA. The self‐switchable terpolymerization from the mixture of CA, propylene oxide (PO) and ε‐caprolactone (CL) is conducted under the catalysis of tBuP2. First, ROAC of CA and PO is carried out exclusively with benzyl alcohol as initiator. Then, block copolymer (BCP) poly(CA‐alt‐PO)‐b‐PCL is obtained via the sequential polymerizations after the complete consumption of CA. The followed ring‐opening polymerization (ROP) of CL is initiated by the terminal hydroxyl of the ROAC‐resulted poly(CA‐alt‐PO) polyester without external stimulus. During the process, the excess PO compound remains intact. The one‐pot synthesis displays distinct living nature and perfect chemoselectivity. The as‐prepared terpenoid‐derived alternating and BCP's exhibit elevated thermal properties.

NIPAm-Based Modification of Poly(L-lysine): A pH-Dependent LCST-Type Thermo-Responsive Biodegradable Polymer.

Polylysine is a biocompatible, biodegradable, water soluble polypeptide. Thanks to the pendant primary amines it bears, it is susceptible to modification reactions. In this work Poly(L-lysine) (PLL) was partially modified via the effortless free-catalysed aza-Michael addition reaction at room temperature by grafting N-isopropylacrylamide (NIPAm) moieties onto the amines. The resulting PLL-g-NIPAm exhibited LCST-type thermosensitivity. The LCST can be tuned by the NIPAm content incorporated in the macromolecules. Importantly, depending on the NIPAm content, LCST is highly dependent on pH and ionic strength due to ionization capability of the remaining free lysine residues. PLL-g-NIPAm constitutes a novel biodegradable LCST polymer that could be used as “smart” block in block copolymers and/or terpolymers, of any macromolecular architecture, to design pH/Temperature-responsive self-assemblies (nanocarriers and/or networks) for potential bio-applications.

Spontaneous Formation and Fusion of Raspberry Vesicle Self-Assembled from Star Block Terpolymers in Aqueous Solution.

The spontaneous formation and fusion of raspberry vesicles was studied using the dissipative particle dynamics (DPD) method. The vesicles were formed through the self-assembly of amphiphilic E12O6F2 star terpolymers in selective solvent. E and F blocks are solvophobic and the O block is solvophilic. The shortest F block plays a major role in the formation of raspberry vesicles. Distinct vesicle formation mechanisms were observed at different polymer concentrations. At higher concentrations, vesicles form via the bending and closure of an oblate F-bump-E bilayer. At lower concentrations, the formation pathway contains: the initial formation of a vesicle with a core, the combination of such vesicles into cylindrical micelles, and the bending of the cylindrical micelles to form a hollow vesicle. In addition, raspberry vesicle fusion is regulated by F bumps through the continuous coalescence of them from apposed vesicle membranes. The contact area bends, followed by the formation of a fusion pore and a tilted inner layer. As the pore sealed, the hemifusion structure appears, which further restructures to form a vesicle. Our results provide guidance on understanding the dynamic processes of complex vesicles and biological membrane fusion.

Simple and Precision Approach to Polythioimidocarbonates and Hybrid Block Copolymer Derivatives

The advancement of polymeric materials relies heavily on the innovation in polymerization reactions. In this study, we have discovered alternating copolymerization of isothiocyanate (ITC) and epoxide, which results in a nearly unexploited sulfur-containing polymer, polythioimidocarbonate (PTC). Provided with a simple two-component catalyst, i.e., a Lewis pair consisting of triethylborane (Et3B) and excess phosphazene base (PB), the copolymerization starts from an alcohol and proceeds in a strictly alternating and highly chemoselective manner, yielding PTC with controlled molar mass and low dispersity, free of cyclic byproducts and ether linkages. The method applies well to a variety of ITCs and epoxides. It is also found with great excitement that the reaction on ITC is fully inhibited when the catalyst composition is inverted to have Et3B in excess, while homopolymerization of epoxide occurs selectively in this case. Density functional theory (DFT) calculation reveals that Et3B-alkoxide complexation is the key to suppressing the back-biting reaction during the copolymerization ([Et3B] < [PB]) and inhibiting the copolymerization ([Et3B] > [PB]). This unique “biased” feature is harnessed to develop a catalyst switch strategy for one-pot block copolymerization from the mixture of ITC and epoxide with either copolymerization or homopolymerization conducted first, resulting in tailor-made PTC-polyether block copolymers with reversible sequence structures. On the other hand, sequence-selective terpolymerization occurs from a mixture of phthalic anhydride, ITC, and epoxide, allowing the one-step synthesis of polyester-PTC block terpolymer. These results have highlighted the versatility of the method for exploring this uncharted area of polymers.

Effect of branching architecture on the self-assembly of symmetric ABC-type block terpolymers

It has been well known that the phase boundaries of AB-type block copolymers can be largely deflected by designing their asymmetric architectures to regulate the stable regions of various ordered phases in a large range. One of the simplest asymmetric architecture is ABn miktoarm star, of which the spherical and cylindrical regions are significantly enlarged by the deflections of the phase boundaries toward large volume fraction of A-block. Accordingly, we design a symmetric ABC-type pentablock terpolymer by branching B-blocks, i.e. connecting one of the B-arms of a pair of miktoarm star copolymers AB2 and CB2 together. This symmetric pentablock terpolymer is composed of two equal A and C blocks tethered on a B-chain. We investigate the self-assembly behaviors of this terpolymer using self-consistent field theory, focusing on the control of the length ratio of the middle B-block to the total B-blocks on the regions of alternating spherical, cylindrical and gyroid phases. It is predicted that the three phase regions are successfully regulated in a large range by the architectural parameter, which are accompanied by a lot of interesting phase behaviors. For instance, an unusual order-order transition from the spherical phase to the gyroid phase with the absence of the cylindrical phase is determined. Our results reveal that these interesting phase behaviors result from three sophisticated effects including the branching effect on the spontaneous curvature, the released packing frustration from different B-blocks and the stretched bridging middle B-block.

Statistical and block conjugated polymers for bulk heterojunction solar cells: Molecular orientation, charge transfer dynamics and device performance

Two terpolymers based on fluorene, benzothiadiazole, and carbazole monomer units were investigated as electron donor materials in organic solar cells. Variation of the microstructure, either statistical or in block, significantly affected the polymers' optoelectronic properties. Both terpolymers presented a high open-circuit voltage in photovoltaic devices (ca. 0.8–0.95 V). Polymer solar cells assembled with the active layer composed of the statistical polymer combined with PCBM exhibited good photovoltaic performance, with power conversion efficiency (PCE) of 1.5% using chlorobenzene as the solvent and an annealing treatment of the active layer. In its turn, the block terpolymer showed the best result when the same solvent and the additive 1,8-diiodooctane (DIO) were used in the mixture. After introducing the additive in the preparation of the active layer, changing the solvent to dichlorobenzene, and varying the ratio of donor to acceptor, i.e., block polymer:PC60BM, the device showed PCE of 1.2% and 2.2%, with ratio 1:2 and 1:1 w/w, respectively. To better understand the different devices' performance, spectroscopic techniques were employed to gain information on the electronic structure, morphology, and dynamic processes of the polymeric films' charge transfer.

Multifaceted pH and Temperature Induced Self‐Assembly of P(DMAEMA‐co‐LMA)‐b‐POEGMA Terpolymers and Their Cationic Analogues in Aqueous Media

AbstractThis work focuses on the synthesis of novel amphiphilic block terpolymers of the type poly[(2‐(N,N‐dimethylamino) ethyl methacrylate)‐co‐(lauryl methacrylate)]‐b‐poly[(oligo ethylene glycol) methyl ether methacrylate] (P(DMAEMA‐co‐LMA)‐b‐POEGMA)) by reversible addition‐fragmentation chain transfer polymerization. The cationic amphiphilic polyelectrolyte analogs P(QDMAEMA‐co‐LMA)‐b‐POEGMA are obtained through quantitative quaternization of the DMAEMA segments. Molecular characterization by size exclusion chromatography, nuclear magnetic resonance, and Fourier Transform Infrared spectroscopies indicates the successful synthesis of these novel series of block terpolymers. The amine forms of the block copolymers respond to pH and temperature changes in aqueous solutions by forming unimolecular or multichain nanoaggregates of varying size, micropolarity, and internal structure, as indicated by light scattering and fluorescence spectroscopy techniques. At neutral and basic pH, the existence of micellar like nanoassemblies is observed in the solutions of P(DMAEMA‐co‐LMA)‐b‐POEGMA terpolymers, while aggregation into micellar‐like clusters take place at temperature values above room temperature due to the presence of the hydrophobic LMA segments. Unexpectedly, the cationic polyelectrolytes P(QDMAEMA‐co‐LMA)‐b‐POEGMA counterparts show temperature responsiveness as a consequence of the amphiphilicity of the polymeric system.

Cholesteric mesophase based 1D photonic materials from self-assembly of liquid crystalline block and random terpolymers containing chromonic molecules.

We describe the influence of competing self-organizing phenomena on the formation of cholesteric mesophase in liquid crystalline brush block terpolymers (LCBBTs) and liquid crystalline random brush terpolymers (LCRBTs) containing chromonic molecules. A library of LCBBTs and LCRBTs are synthesized using ring-opening metathesis polymerization (ROMP) of norbornene side-chain functionalized monomers comprising cholesteryl mesogen (NBCh9), chromonic xanthenone (NBXan), and poly(ethylene glycol) (NBMPEG). Compression molded films of LCRBTs containing chromonic molecules display multilevel hierarchical structure in which cholesteric mesophase co-exists with π–π stacking of the chromonic mesophase along with PEG microphase segregated domains. This is unexpected as conventional LCBCPs and LCBBCs that lack chromonic molecules do not form cholesteric mesophases. The presence of π–π interactions modifies the interface at the IMDS so that both chromonic and cholesteric mesophases coexist leading to the manifestation of cholesteric phase for the first time within block architecture and is very reminiscent of previously published LCRBCs without chromonic molecules. The key to the observed hierarchical assembly in these LCBBTs containing chromonic molecules lies in the interplay of LC order, chromonic π–π stacking, PEG side chain microphase segregation, and their supramolecular cooperative motion. This unique “single component” polymer scaffold transforms our capacity to attain nanoscale hierarchies and optical properties from block architecture similar to nanoscale mesophases resulting in random architecture.

Amphiphilic random and random block terpolymers with PEG, octadecyl, and oleyl pendants for controlled crystallization and microphase separation

Amphiphilic random and random block terpolymers bearing PEG chains, crystalline octadecyl groups, and amorphous oleyl groups were designed to control crystallization and microphase separation in the solid state.

Synthesis, aqueous solution behavior and self-assembly of a dual pH/thermo-responsive fluorinated diblock terpolymer

The synthesis of fluorinated dual-responsive block terpolymers via sequential reversible addition–fragmentation chain transfer (RAFT) polymerization is presented.

Synthesis of novel low bandgap random and block terpolymers with improved performance in organic solar cells

Novel conjugated random and block terpolymers composed of two electron-donating blocks - fluorene (Flo) and carbazole (Cz) - as well as one electron-accepting unit of thiophene-benzothiadiazole-thiophene (TBT) with the same (Flo:TBT:Cz) molar ratio of 0.5:1:0.5 were synthesized. The effects of their microstructure on physico-chemical properties and the performance of photovoltaic conversion were characterized. These conjugated terpolymers displayed two absorption peaks in UV–Vis analysis around 400 and 600 nm with a similar and narrow bandgap (1.9 eV, UV–Vis film), which is suitable to be applied as p-type semiconductors in an organic solar cell (OSC). Both synthesized terpolymers presented a high average molecular weight and degradation temperature above 400 °C. OSCs were assembled for determining the power conversion efficiency (PCE). Block terpolymer with a PCE of 1.3%, higher than that of 0.9% for the random terpolymer, was used as the electron donor in a conventional cell configuration. The device's optimization improved the photovoltaic parameters, mainly the short circuit current density, which allowed a PCE of 3.2% to be achieved. These results demonstrate that the synthesis of block terpolymers is a simple and practical approach for optimizing a conjugated polymer for an efficient OSC.

Zinc Amido-Oxazolinate Catalyzed Ring Opening Copolymerization and Terpolymerization of Maleic Anhydride and Epoxides.

Ring opening copolymerization (ROCOP) of epoxides and cyclic anhydrides has become an attractive approach for the synthesis of biodegradable polyesters with various compositions. Encouraged by the efficiency and versatility of a series of amido-oxazolinate zinc complexes, in this study they were shown to be active catalysts for the synthesis of unsaturated polyesters via ROCOP of maleic anhydride and various epoxides. The relative activity of epoxides in these reactions was observed to be styrene oxide > cyclohexene oxide > phenyl glycidyl ether, which could be correlated with the electronic and steric features of the substrate. To provide more structural possibilities for the polyesters, the difference in epoxide reactivity was exploited in an attempt to prepare block terpolymers from one anhydride and two epoxides. Terpolymerization was carried out in one or two steps in a single pot. The thermal characterization by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) techniques suggested that the resulting materials were mostly random terpolymers.

Temperature-induced self-assembly of amphiphilic triblock terpolymers to low cytotoxic spherical and cubic structures as curcumin carriers

In this study, self-assembly of amphiphilic thermo- and UV-sensitive block terpolymers, namely poly (methyl acrylate-b-[(7-(allyloxy)-2H-chromen-2-one)-co-(2-hydroxyethyl methacrylate(]-b-N-vinylpyrrolidone) P (MA-b-[AC-co-HEMA]-b-NVP) in water at different temperatures is studied. The synthesis of terpolymers, in three various block length for hydrophobic PMA block, is carried out by atom transfer radical polymerization (ATRP) and reversible addition-fragmentation chain-transfer (RAFT)/macromolecular design by interchange of xanthate (MADIX) polymerization. Three different critical micelle temperatures (CMT) of terpolymers are calculated via UV-VIS-NIR absorptions at 600 nm. Results of self-assembly behavior of terpolymers under CMT showed spherical micelle aggregation whereas cubic-like particles with larger particle size were self-assembled at the temperatures above CMT because of second aggregation phenomena. Additionally, UV light irradiation is used to photo-crosslinking of particles owing to presence of photo-responsive coumarin derivative of AC in the middle block. The self-assembled structures are loaded with curcumin (Cur) before and after photo-crosslinking and Cur-release behavior is investigated at different temperatures of 37 and 25 °C. Drug-release behavior of samples illustrated that cumulative Cur-release above the CMT of terpolymers is higher than under CMT due to squeezing of PVP coronas and expelling of drug molecules to outside. Moreover, cumulative release of photo-crosslinked self-assembled structures was lower than before crosslinking. The cytotoxicity of terpolymers and Cur-loaded micelles was examined through culturing on the MG-63 cells which showed high cell viability after 48 h.

Synthesis, structures, and thermal properties of terpolymers of propylene oxide, carbon dioxide, and cyclohexene oxide

High molecular weight block terpolymers with different contents of polypropylene carbonate and cyclohexene carbonate units in the polymer chain were synthesized by the copolymerization of carbon dioxide, propylene oxide, and cyclohexene oxide. Zinc adipate was used as a catalyst. The terpolymerization products were characterized by 1H and 13C NMR spectroscopy, IR spectroscopy, GPC, DSC, and DMA methods. The influence of the reaction conditions on the composition, microstructure, and molecular-weight and thermal characteristics was studied.