Tunable Glass Transition Temperatures Research Articles

Chemically Recyclable, High Molar Mass Polyoxazolidinones via Ring-Opening Metathesis Polymerization.

The development of robust methods for the synthesis of chemically recyclable polymers with tunable properties is necessary for the design of next-generation materials. Polyoxazolidinones (POxa), polymers with five-membered urethanes in their backbones, are an attractive target because they are strongly polar and have high thermal stability, but existing step-growth syntheses limit molar masses and methods to chemically recycle POxa to monomer are rare. Herein, we report the synthesis of high molar mass POxa via ring-opening metathesis polymerization of oxazolidinone-fused cyclooctenes. These novel polymers show <5% mass loss up to 382-411 °C and have tunable glass transition temperatures (14-48 °C) controlled by the side chain structure. We demonstrate facile chemical recycling to monomer and repolymerization despite moderately high monomer ring-strain energies, which we hypothesize are facilitated by the conformational restriction introduced by the fused oxazolidinone ring. This method represents the first chain growth synthesis of POxa and provides a versatile platform for the study and application of this emerging subclass of polyurethanes.

Functional and Degradable Polyester-co-polyethers from CO2, Butadiene, and Epoxides.

Carbon dioxide (CO2), as a renewable and nontoxic C1 feedstock, has been recognized as an ideal comonomer to prepare sustainable materials. In this regard, substantial focus has been dedicated to the ring-opening copolymerization of CO2 and epoxides, which results in the creation of aliphatic polycarbonates in most cases. Here, we report an unprecedented strategy to synthesize functional and degradable polyester-co-polyethers from CO2, butadiene, and epoxides via a CO2/butadiene-derived δ-valerolactone intermediate (EVP). Utilizing a chromium salen complex as the catalyst, the copolymerization of EVP and epoxides was successfully achieved to produce CO2/butadiene/epoxide terpolymers. The obtained polyester-co-polyethers with varied 39-93 mol % EVP content (equal to 18-28 wt % CO2 incorporation) show high thermal stability, tunable glass-transition temperatures, on-demand functionality, and good chemical degradability. This method extends the potential to access functional CO2-based polymers.

Synthesis and Fabrication of Betulin-Derived Polysulfide and Polysulfoxide Electrospun Fibers for Fruit Preservation.

Plant-derived biocompounds play a crucial role in the field of renewable materials due to their sustainability as they can be converted into monomers for polymerization, comparable to numerous monomers obtained from petroleum. In this work, betulin, a triterpene derivative with antibacterial properties obtained from birch tree bark, was esterified to produce two varieties of α,ω-diene derivatives with different lengths of methylene spacers. These derivatives were then copolymerized with 2,2'-(ethylenedioxy)diethanethiol using thiol-ene photopolymerization. We optimized and confirmed the polymerization parameters such as solvents, catalysts, and monomer concentrations. These analyses allowed for the obtainment of polysulfides with a high molar mass of up to 38.9 kg/mol under the optimized conditions. Furthermore, the polysulfides were converted into polysulfoxides by using a dilute hydrogen peroxide solution. Thermal analysis of the obtained polymers revealed excellent thermal stability (up to 300 °C) and tunable glass transition temperatures depending on their molar mass and composition. We successfully produced fibers with a diameter of approximately 3.9 μm by using the electrospinning technique. The morphology and hydrophobicity of the fibers were analyzed by using scanning electron microscopy and water contact angle analysis. Plant-derived polymeric fibers exhibited good cellular biocompatibility and broad-spectrum antibacterial activity, making them promising candidates for applications in fruit preservation.

Strong and ultrafast stimulus-healable lignin-based composite elastomers with excellent adhesion properties

With the increased environmental issues, advanced high-performance and multifunctional polymeric materials derived from biomass have tremendous attention due to the great potential to replace their traditional petroleum-based counterparts. In this work, a series of lignin graft copolymers, lignin-graft-poly(n-butyl acrylate-co-acrylic acid) (Lig-g-P(BA-co-AA)), were rationally prepared via reversible addition-fragmentation chain transfer (RAFT) polymerization. These lignin-based copolymers demonstrate good thermal stability and tunable glass transition temperature (Tg) values. The mechanical performance, including tensile strength, extensibility, Young's modulus, and toughness can be facilely adjusted by the BA/AA feed ratio and lignin content during polymerization. Owing to the extraordinary photothermal conversion ability of lignin, the Lig-B550 copolymer, containing 11.8 wt% lignin content, shows excellent stimulus-healing behavior within 1 min with a 97.1 % healing efficiency under near-infrared (NIR) laser irradiation. Moreover, the Lig-g-P(BA-co-AA) copolymers exhibit remarkable adhesion property, broadening their potential applications in the adhesive area. This grafting strategy is versatile and efficient, conferring the resultant lignin-based composite elastomers with dramatically enhanced mechanical properties and unprecedented photothermal behavior, which can inspire the further development of strong lignin-based sustainable elastomers.

Biomass-Derived Degradable Polymers via Alternating Ring-Opening Metathesis Polymerization of Exo-Oxanorbornenes and Cyclic Enol Ethers.

Degradable polymers made via ring-opening metathesis polymerization (ROMP) hold tremendous promise as eco-friendly materials. However, most of the ROMP monomers are derived from petroleum resources, which are typically considered less sustainable compared to biomass. Herein, we present a synthetic strategy to degradable polymers by harnessing alternating ROMP of biomass-based cyclic olefin monomers including exo-oxanorbornenes and cyclic enol ethers. A library of well-defined poly(enol ether)s with modular structures, tunable glass transition temperatures, and controlled molecular weights was achieved, demonstrating the versatility of this approach. Most importantly, the resulting copolymers exhibit high degrees of alternation, rendering their backbones fully degradable under acidic conditions.

Amine-Functionalized Polybutadiene Synthesis by Tunable Postpolymerization Hydroaminoalkylation.

Early transition metal-catalyzed hydroaminoalkylation is a powerful single-step method to selectively add amines to polybutadienes, offering an efficient strategy to access amine-functionalized polyolefins. Aryl and alkyl secondary amines were used with a tantalum catalyst to functionalize both 28 wt% (PBD13) and 70 wt% (PBD50) 1,2-polybutadiene polymers. The degree of amination was controlled by modifying amine and catalyst loading in both small- and multigram-scale reactions. The vinyl groups of 1,2-polybutadiene were aminated with ease, and unexpectedly the hydroaminoalkylation of challenging internal alkenes of the 1,4-polybutadiene unit was observed. This unanticipated reactivity was proposed to be due to a directing group effect. This hypothesis was supported with small-molecule model substrates, which also showed directed internal alkene amination. Increasing degrees of amination resulted in materials with dramatically higher and tunable glass transition temperature (Tg) values, due to the dynamic cross-linking accessible to hydrogen-bonding, amine-containing materials. Primary amine-functionalized polybutadiene was also prepared, demonstrating that a broad new class of amine-containing polyolefins can be accessed by postpolymerization hydroaminoalkylation.

Multifunctional deoxybenzoins: Preparation of low heat release polymer networks by orthogonal crosslinking

Multifunctional epoxide monomers present opportunities to design cross-linked networks with conveniently tunable thermal and mechanical properties. This paper describes the synthesis of a novel, multifunctional deoxybenzoin monomer containing both epoxide and allyl groups, and its use in the preparation of epoxide networks. The orthogonal reactivity of these functional groups, operating via epoxide-amine and thiol-ene chemistry, facilitated the formation of networks with tunable glass transition temperatures and crosslink densities. Thermogravimetric analysis (TGA) and microscale combustion calorimetry (MCC) characterization revealed these networks to possess impressively low heat release properties (∼50% lower than conventional bisphenol A (BPA)-based networks) and very high char residues that reached ∼60%. Overall, introducing functional deoxybenzoin epoxide monomers into these types of network architectures imparts a method for combining low heat release structures with the advantageously tunable physical and mechanical properties of polymer networks.

Ultra-Tough Waterborne Polyurethane-Based Graft-Copolymerized Piezoresistive Composite Designed for Rehabilitation Training Monitoring Pressure Sensors.

Effective training is crucial for patients who need rehabilitation for achieving optimal recovery and reducing complications. Herein, a wireless rehabilitation training monitoring band with a highly sensitive pressure sensor is proposed and designed. It utilizes polyaniline@waterborne polyurethane (PANI@WPU) as a piezoresistive composite material, which is prepared via the in situ grafting polymerization of PANI on the WPU surface. WPU is designed and synthesized with tunable glass transition temperatures ranging from -60 to 0 °C. Dipentaerythritol (Di-PE) and ureidopyrimidinone (UPy) groups are introduced, endowing the material with good tensile strength (14.2MPa), toughness (62 MJ-1 m-3 ), and great elasticity (low permanent deformation: 2%). Di-PE and UPy enhance the mechanical properties of WPU by increasing the cross-linking density and crystallinity. Combining the toughness of WPU and the high-density microstructure derived by hot embossing technology, the pressure sensor exhibits high sensitivity (168.1 kPa-1 ), fast response time (32ms), and excellent stability (10 000 cycles with 3.5% decay). In addition, the rehabilitation training monitoring band is equipped with a wireless Bluetooth module, which can be easily applied to monitor the rehabilitation training effect of patients using an applet. Therefore, this work has the potential to significantly broaden the application of WPU-based pressure sensors for rehabilitation monitoring.

Synthesis and Fabrication of a Betulin-Containing Polyolefin Electrospun Fibrous Mat for Antibacterial Applications.

Biocompounds play a significant role in the area of renewable polymers in terms of sustainability, as they can be employed or converted into monomers for polymerization in a manner similar to many petroleum-derived monomers. In this work, betulin, a plant-derived triterpene with antibacterial and antiviral properties, was converted to two kinds of α,ω-diene derivatives with different methylene spacer lengths between the olefin and the ester group via an esterification reaction. Polyolefins were subsequently made by acyclic diene metathesis (ADMET) polymerization of betulin-based α,ω-diene. The polymer consists of rigid betulin and flexible unsaturated aliphatic segments, which was confirmed by NMR spectroscopy and gel permeation chromatography (GPC). The influence of different parameters including temperature, catalysts, and catalyst loading on ADMET polymerization was investigated. These polyolefins with high molar mass (up to 20.0 kg/mol) were obtained in an elevated yield (≥95%). Thermal analysis of these (co)polymers showed excellent thermal stability (up to 360 °C) and tunable glass transition temperatures depending on the nature of betulin and alkene segments. To evaluate the antimicrobial potential of betulin-containing polymers, the fabrication of polyolefin fibrous mats (ca. 400 nm diameter) via the electrospinning technique was successfully achieved. Their morphology and hydrophobicity were studied by scanning electron microscopy (SEM) and water contact angle analyses. The fibrous mats possessed broad-spectrum antibacterial property, providing a feasible strategy to design betulin-based polymeric fibers for many applications in the biomedical field.

Bio-Based Degradable Poly(ether-ester)s from Melt-Polymerization of Aromatic Ester and Ether Diols.

Vanillin, as a promising aromatic aldehyde, possesses worthy structural and bioactive properties useful in the design of novel sustainable polymeric materials. Its versatility and structural similarity to terephthalic acid (TPA) can lead to materials with properties similar to conventional poly(ethylene terephthalate) (PET). In this perspective, a symmetrical dimethylated dialkoxydivanillic diester monomer (DEMV) derived from vanillin was synthesized via a direct-coupling method. Then, a series of poly(ether-ester)s were synthesized via melt-polymerization incorporating mixtures of phenyl/phenyloxy diols (with hydroxyl side-chains in the 1,2-, 1,3- and 1,4-positions) and a cyclic diol, 1,4-cyclohexanedimethanol (CHDM). The polymers obtained had high molecular weights (Mw = 5.3–7.9 × 104 g.mol−1) and polydispersity index (Đ) values of 1.54–2.88. Thermal analysis showed the polymers are semi-crystalline materials with melting temperatures of 204–240 °C, and tunable glass transition temperatures (Tg) of 98–120 °C. Their 5% decomposition temperature (Td,5%) varied from 430–315 °C, which endows the polymers with a broad processing window, owing to their rigid phenyl rings and trans-CHDM groups. These poly(ether-ester)s displayed remarkable impact strength and satisfactory gas barrier properties, due to the insertion of the cyclic alkyl chain moieties. Ultimately, the synergistic influence of the ester and ether bonds provided better control over the behavior and mechanism of in vitro degradation under passive and enzymatic incubation for 90 days. Regarding the morphology, scanning electron microscopy (SEM) imaging confirmed considerable surface degradation in the polymer matrices of both polymer series, with weight losses reaching up to 35% in enzymatic degradation, which demonstrates the significant influence of ether bonds for biodegradation.

A novel bioderived AB2‐type monomer from castor oil derivative for the preparation of fully biobased hyperbranched polyesters

AbstractDesigning biobased hyperbranched polyesters from vegetable oil has been attracting considerable interests from academic industrial communities. Herein, a novel fully biobased hyperbranched polyester (HBPE) was prepared by self‐condensation of AB2‐type bioderived monomer based on methyl ricinoleate (MR), a castor oil‐derived renewable chemical. The reaction conditions were optimized to obtain the AB2‐type monomer in a high conversion ratio (up to 87%). The self‐condensation of AB2‐type monomers was carried out in the presence of two kinds of transesterification catalysts (Ti(OBu)4 versus Zn(Ac)2), among which Ti(OBu)4 was found to be more efficient one and yield higher molecular weights in the range of 5800~11,500 g/mol. The resulting HBPEs were characterized in terms of Fourier transform infrared spectroscopy, nuclear magnetic resonance, differential scanning calorimetry, and thermogravimetric analysis. The degree of branching was calculated to be 0.33~0.39. Thermal analysis revealed that the as‐prepared HBPEs were amorphous with tunable glass transition temperatures ranging from −44.8 to −24.6°C. All the prepared HBPEs exhibited good thermal stability with the maximum onset decomposition temperature (Tonset) up to 294.6°C. These structural features and properties of resulting biobased HBPEs enabled them to act as a potential ‘greener’ additive for polymers.

Tunable plasticization of sustainable ethyl cellulose toward thermoplastic elastomers through ATRP grafting

Thermoplastic elastomers (TPEs) derived from sustainable cellulose and its derivatives have attracted a great deal of attention, because of their abundance, renewable nature, rigid backbone and good mechanical properties. To fabricate TPEs with tunable performance, a series of sustainable ethyl cellulose (EC)-grafted poly(methyl methacrylate (MMA)) (EC-g-P(MMA)) and poly(MMA-co-butyl methacrylate (BMA)) (EC-g-P(MMA-co-BMA)) were fabricated by way of atom-transfer radical polymerization (ATRP). By tuning the molar ratio of MMA/BMA in the copolymer side chains, tunable performance of TPEs with tunable glass transition temperatures (118–47.8°C) was achieved. The chemical structures of EC-bromide and EC graft copolymers were identifiable by Fourier transform infrared spectroscopy and hydrogen-1 (1H) nuclear magnetic resonance spectroscopy. The EC graft copolymers exhibited a higher molecular weight and good thermal stability and mechanical properties. These results suggested that these tunable-performance copolymers with a sustainable cellulose backbone and an acrylate side chain were potential candidates for service as TPEs in some applications.

3D printing of polyurethane/nanocellulose shape memory composites with tunable glass transition temperature

Shape memory polyurethane (SMPU) has been widely recognized as promising potential smart materials. While, porous SMPU presented imperfect shape memory and mechanical properties. In this work, nanocellulose was incorporated in SMPU to improve the comprehensive properties of the porous SMPU by 3D printing prototyping. The shape fixation ratio (Rf) and the shape recovery rate (Rr) were improved to above 99.0%, with adding appropriate proportion of cellulose nanocrystals (CNCs) and ball milled nanocellulose (BMC). And the highest tensile strength of the 3D printed SMP composite was 12.05 MPa, which was 71% higher than pure PU (7.02 MPa), more importantly, these composites have tunable glass transition temperature (Tg), that is to say, when under the appropriate preparation, the composites with Tg close to human body temperature can be obtained, which enables the potential applications in smart biomaterials.

Ultra-stretchable chitin-based branched elastomers with enhanced mechanical properties via RAFT polymerization

In this work, a chitin-based macromolecular chain transfer agent (Chitin-CTA) was designed to graft polymers from chitin at the molecular level. Homogeneous reversible addition-fragmentation chain transfer (RAFT) polymerization was performed to prepare branched MA elastomers, chitin-graft-poly(methyl acrylate) (Chitin-g-PMA) copolymers, which were thermally stable and showed tunable glass transition temperatures. These ultra-stretchable branched MA elastomers exhibit unique strain-hardening behavior and significantly enhanced mechanical properties. Mechanical tests indicate that the chitin backbones in branched MA elastomers can act as cross-linking points to improve the tensile strength, toughness, and elasticity simultaneously. The macroscopic performance of branched MA elastomers c be further promoted by introducing hydrogen bonding as non-covalent interaction to form an additional reversible physical network. This robust and versatile grafting strategy can provide new opportunities to prepare chitin-based branched MA elastomers with extraordinary mechanical properties.

Investigation of the Long‐Term Storage Stability of Shape Memory Epoxy Prepolymer

Epoxy‐based shape memory polymers (ESMPs) are important types of thermoset shape memory polymers due to their unique thermomechanical properties, which have great potential in applications ranging from smart actuators to deformable structures. The long‐term storage stability is important for ESMPs, especially when pursuing the same batch of materials for alternatives. Stable storage of ESMP preplomyers in the long term and taking it out for curing when needed are of great benefit to engineering applications which highly require the same batch of materials for high production efficiency, such as in deployable space structures, semiconductor, and electronic packaging. However, this important storage stability of ESMP has not been studied so far. Herein, a series of ESMPs with tunable glass transition temperatures (Tgs) ranging from 100 to 170 °C is prepared. The effect of long‐term storage at low temperatures on rheological, thermal, thermomechanical, mechanical, and shape memory properties is systematically investigated. The ESMP after storage shows an improvement of crosslinking density, Tgs, and mechanical strength, while maintaining chemical structures and excellent shape memory properties. This feasible method of low‐temperature storage realizes overall long‐term stability and enhancement of strength in ESMPs, making it more promising for engineering applications.

Steric Hindrance Drives the Boron-Initiated Polymerization of Dienyltriphenylarsonium Ylides to Photoluminescent C5-Polymers.

A series of alkyl‐subsituted dienyltriphenylarsonium ylides were synthesized and used as monomers in borane‐initiated polymerization to obtain practically pure C5‐polymers (main‐chain grows by five carbon atoms at a time). The impact of triethylborane (Et3B), tributylborane (Bu3B), tri‐sec‐butylborane (s‐Bu3B), and triphenylborane (Ph3B) initiators on C5 polymerization was studied. Based on NMR and SEC results, we have shown that all synthesized polymers have C5 units with a unique unsaturated backbone where two conjugated double bonds are separated by one methylene. The synthesized C5‐polymers possess predictable molecular weights and narrow molecular weight distributions (M n,NMR=2.8 −11.9 kg mol−1, Ð=1.04–1.24). It has been found that increasing the steric hindrance of both the monomer and the initiator can facilitate the formation of more C5 repeating units, thus driving the polymerization to almost pure C5‐polymer (up to 95.8 %). The polymerization mechanism was studied by 11B NMR and confirmed by DFT calculations. The synthesized C5‐polymers are amorphous with tunable glass‐transition temperatures by adjusting the substituents of monomers, ranging from +30.1 °C to −38.4 °C. Furthermore, they possess blue photoluminescence that changes to yellow illuminating the polymers for 5 days with UV radiation of 365 nm (IIE, isomerization induced emission).

UV curable micro‐structured shape memory epoxy with tunable performance

AbstractMicro‐structured shape memory polymer (SMP) surfaces are indispensable in various applications. Epoxy polymer emerged as an ideal candidate for SMP surfaces due to its low curing shrinkage and superior thermo‐mechanical properties. In this study, we develop a UV curable epoxy system with tunable glass transition temperature and superior shape memory performance. The glass transition temperatures can widely range from 49 to 164°C by simply tuning the ratio of two comonomers. All samples possess excellent shape fixity, shape recovery ratios, and cycling stability. The synergy of the moldable liquid epoxy precursors and the spatiotemporal UV light allows shape memory epoxy with both surface microstructures and complex macro‐geometries. We anticipate this UV curable epoxy will expand the scopes of surface shape memory applications.

Non-isocyanate Polyurethanes from 1,1'-Carbonyldiimidazole: A Polycondensation Approach.

1,1'-Carbonyldiimidazole (CDI) provides a platform to generate high molecular weight polyurethanes from industrially relevant diols and diamines. CDI, which is described in the literature for its use in amidation and functionalization reactions, enables the production of well-defined and stable polyurethane precursors, thus eliminating the need for isocyanates. Herein, the functionalization of 1,4-butanediol with CDI yields an electrophilic biscarbamate, bis-carbonylimidazolide (BCI), which is suitable for further step-growth polymerization in the presence of amines. Elevated reaction temperatures enable the solvent-, catalyst-, and isocyanate-free polycondensation reaction between the BCI monomer and various diamines. The thermoplastic polyurethanes produced from this reaction demonstrate high thermal stability, tunable glass transition temperatures based on incorporation of flexible polyether segments, and mechanically ductile thin films. CDI functionalized diols will allow the preparation of diverse polyurethanes without the use of isocyanate-containing monomers.

Highly transparent and photopatternable spirobifluorene-based polythioethers with high refractive indices via thiol-ene click chemistry

A series of polythioethers with spirobifluorene skeletons was successfully synthesized by a thiol-ene reaction. A spirobifluorene-containing diacrylate (2,2′-diacryloyloxy-9,9′-spirobifluorene, DASF) was designed and reacted with dithiol components to prepare high-refractive-index polymers (1.7169–1.6690) with high transparency (>90% at 400 nm). The poly(phenylene thioether) obtained from DASF with 1,5-naphthalenedithiol exhibited the highest refractive index (1.7169) and a low Abbe number (14.3), while the polymer obtained with 1,3-benzenedithiol showed a high refractive index (1.7112) and a relatively high Abbe number (19.6). The resulting spirobifluorene-containing polythioethers exhibited tunable glass transition temperatures (Tg = 90–164 °C), and high thermal stabilities (Td5 = 297–353 °C). UV nanoimprinting lithography using rapid thiol-ene photopolymerization of DASF with 1,6-hexanedithiol enabled the successful formation of high-refractive-index polymer nanoimprinted patterns. The presented design strategy allows manipulation of the refractive index and Abbe number, as well as the ability to design molecular structures with suitable aromatic and aliphatic chains between the spirobifluorene units, thus helping to achieve high transparency, flexibility, and thermal stability, in addition to excellent light-induced processability for nano- and microfabrication.

A highly tough and ultralow friction resin nanocomposite with crosslinkable polymer-encapsulated nanoparticles

A resin nanocomposite embedded by encapsulated nanoparticles with exceptional mechanical and lubrication properties is reported. The functional encapsulated nanoparticles, synthesized by miniemulsion co-polymerization of methyl methacrylate with n-butyl acrylate, styrene and glycidyl methacrylate, had tunable glass transition temperatures and surface reactive glycidyl groups. The as-synthesized nanoparticles with controlled size, shell component and surface function, impacted a nanocomposite with the high toughness and strength as well as ultralow friction properties by their covalent crosslinking with the matrix and the formation of thin boundary lubricant film. Remarkably, the optimal toughness and strength of the nanocomposite with encapsulated nanoparticles achieved 3.8 and 1.5 times those of the counterpart with encapsulated microparticles, respectively. The nanocomposite incorporated with as-synthesized nanoparticles exhibited an ultralow coefficient of friction (COF) and a wear rate of 0.027 and 8.0 × 10−7 mm3/Nm, which were only 3.9% and 0.6% those of the matrix, respectively. The developed robust mechanical and ultralow friction resin nanocomposite from crosslinkable and flexible polymer-encapsulated nanoparticles is highly expected for engineering applications.