Bicomponent Transparent Polyester Networks with Shape Memory Effect

Mechanical response of composite materials prepared with polyurethane elastomers and polyvinyl chloride films

This study describes a new method for the preparation of composite materials using polyvinyl chloride (PVC) films and polyurethane (PU) foam elastomers. This new preparation method was applied to composite materials used for sound and thermal insulation in the automotive and aerospace industries, and it was found to be effective in reducing debonding and fracture defects. This feature was achieved via the formation of through-holes in the surface material and the substrate prior to lamination, which led to the increase in the flow of air and adhesive and allowed for better compatibility between the material layers. The composite material shows a tensile strength of up to 37.6 Kg⋅cm-2 and can achieve a tensile fracture strength of up to 281.3 N, if woven or biomaterials are used. This can be useful in solving challenges in the aerospace and automotive industries and may also act as a potential coating material for other applications in the future.

Synthesis and Post-Functionalization of Poly(conjugated ester)s Based on 3-Methylene-1,5-dioxepan-2-one

Poly(α-methylene ester)s are an attractive type of functional aliphatic polyesters that represent a platform for the fabrication of various biodegradable and biomedical polymers. Herein, we report the controlled ring-opening polymerization (ROP) of a seven-membered α-methylene lactone (3-methylene-1,5-dioxepan-2-one, MDXO) that was synthesized based on the Baylis-Hillman reaction. The chemoselective ROP of MDXO was catalyzed by diphenyl phosphate (DPP) at 60 °C or stannous octoate (Sn(Oct)₂) at 130 °C, generating α-methylene-containing polyester (PMDXO) with a linear structure and easily tunable molar mass. The ring-opening copolymerization of MDXO with ε-caprolactone or 1,5-dioxepan-2-one was also performed under the catalysis of DPP or Sn(Oct)₂ to afford copolymers with different compositions and sequence structures that are influenced by the kinds of monomers and catalysts. PMDXO is a slowly crystallizable polymer with a glass transition temperature of ca. -33 °C, and its melting temperature and enthalpy are significantly influenced by the thermal history. The thermal properties of the copolymers are dependent on their composition and sequence structure. Finally, the post-modification of PMDXO based on the thiol-Michael addition reaction was briefly explored using triethylamine as a catalyst. Given the optimized condition, PMDXO could be dually modified to afford biodegradable polyesters with different functionalities.

Shape memory polymer/graphene nanocomposites: State-of-the-art

Graphene is one of most exceptional type of nanocarbon. It is a two-dimensional, one atom thick, nanosheet of sp2 hybridized carbon atoms. Graphene has been employed as nanofiller for shape memory polymeric nanocomposites due to outstanding electrical conductivity, mechanical strength, flexibility, and thermal stability characteristics. Consequently, graphene nanostructures have been reinforced in the polymer matrices to attain superior structural, physical, and shape recovery properties. This review basically addresses the important class of shape memory polymer (SMP)/graphene nanocomposites. This assessment is revolutionary to portray the scientific development and advancement in the field of polymer and graphene-based shape memory nanocomposites. In SMP/graphene nanocomposites, polymer shape has been fixed at above transition temperature and then converted to memorized shape through desired external stimuli. Presence of graphene has caused fast switching of temporary shape to original shape in polymer/graphene nanocomposites. In this regard, better graphene dispersion, interactions between matrix-nanofiller, and well-matched interface formation leading to high performance stimuli-responsive graphene derived nanocomposites, have been described. Incidentally, the fabrication, properties, actuation ways, and relevance of the SMP/graphene nanocomposite have been discussed here. The potential applications of these materials have been perceived for the aerospace/automotive components, self-healing nanocomposites, textiles, civil engineering, and biomaterials.

Solvent-Free One-Shot Synthesis of Thermoplastic Polyurethane Based on Bio-Poly(1,3-propylene succinate) Glycol with Temperature-Sensitive Shape Memory Behavior

In this work, a new family of fully biobased thermoplastic polyurethanes (TPUs) with thermo-induced shape memory is developed. First, a series of TPUs were successfully synthesized by the one-shot solvent-free bulk polymerization of bio-poly(1,3-propylene succinate) glycol (PPS) with various molecular weights (M _n = 1000, 2000, 3000, and 4000), 1,4-butanediol (BDO), and 4,4'-methylene diphenyl diisocyanate (MDI). These polyurethanes (PUs) are denoted as PPS-x-TPUs (x = 1000, 2000, 3000, and 4000), where x represents the M _n of PPS in the polymers. To determine the effect of the molecular weight of the soft segment of PU, all PPS-TPUs were formed with the same hard segment content (32.5 wt %). The soft segment with high molecular weight in PPS-4000-TPU caused a high degree of soft segment entanglement and formed many secondary bonds. PPS-4000-TPU exhibited better mechanical (tensile strength: 64.13 MPa and hardness: 90A) and thermomechanical properties (maximum loading: 2.95 MPa and maximum strain: 144%) than PPS-1000-TPU. At an appropriate shape memory programming temperature, all synthesized PPS-x-TPUs exhibited excellent shape memory behaviors with a fixed shape rate of >99% and a shape recovery rate of >86% in the first round and 95% in the following rounds. Therefore, these bio-TPUs with shape memory have potential for use in smart fabrics.

Depolymerization of proanthocyanidins and application exploration in the field of preparation of flexible materials

A heat-induced flexible shape memory material was prepared.

Functional Polymers and Polymeric Materials From Renewable Alpha-Unsaturated Gamma-Butyrolactones

Sustainable chemistry requires application of green processes and often starting materials originate from renewable resources. Biomass-derived monomers based on five-membered γ-butyrolactone ring represent suitable candidates to replace sources of fossil origin. α-Methylene-γ-butyrolactone, β-hydroxy-α-methylene-γ-butyrolactone, and β- and γ-methyl-α-methylene-γ-butyrolactones bearing exocyclic double bond are available directly by isolation from plants or derived from itaconic or levulinic acids available from biomass feedstock. Exocyclic double bond with structural similarity with methacrylates is highly reactive in chain-growth polymerization. Reaction involves the linking of monomer molecules through vinyl double bonds in the presence of initiators typical for radical, anionic, zwitterionic, group-transfer, organocatalytic, and coordination polymerizations. The formed polymers containing pendant ring are characterized by high glass transition temperature (T g > 195°C) and render decent heat, weathering, scratch, and solvent resistance. The monomers can also be hydrolyzed to open the lactone ring and form water-soluble monomers. Subsequent radical copolymerization in the presence of cross-linker can yield to hydrogels with superior degree of swelling and highly tunable characteristics, depending on the external stimuli. The five-membered lactone ring allows copolymerization of these compounds by ring opening polymerization to provide polyesters with preserved methylene functionality. In addition, both the lactone ring and the methylene double bond can be attacked by amines. Polyaddition with di- or multi-amines leads to functional poly(amidoamines) with properties tunable by structure of the amines. In this mini-review, we summarize the synthetic procedures for preparation of polymeric materials with interesting properties, including thermoplastic elastomers, acrylic latexes, stimuli-sensitive superabsorbent hydrogels, functional biocompatible polyesters, and poly(amidoamines).

Functional biodegradable polymers via ring-opening polymerization of monomers without protective groups

Biodegradable polymers are of current interest and chemical functionality in such materials is often demanded in advanced biomedical applications. Functional groups often are not tolerated in the polymerization process of ring-opening polymerization (ROP) and therefore protective groups need to be applied. Advantageously, several orthogonally reactive functions are available, which do not demand protection during ROP. We give an insight into available, orthogonally reactive cyclic monomers and the corresponding functional synthetic and biodegradable polymers, obtained from ROP. Functionalities in the monomer are reviewed, which are tolerated by ROP without further protection and allow further post-modification of the corresponding chemically functional polymers after polymerization. Synthetic concepts to these monomers are summarized in detail, preferably using precursor molecules. Post-modification strategies for the reported functionalities are presented and selected applications highlighted.

Fabrication of Liquid Crystalline Polyurethane Networks with a Pendant Azobenzene Group to Access Thermal/Photoresponsive Shape-Memory Effects

Herein, we report a novel thermal/photoresponsive shape-memory polyurethane network with a pendant azobenzene group by utilizing its anisotropic-isotropic phase transitions and photoresponsive feature concurrently. To achieve this goal, the side-chain liquid crystalline polyurethane networks based on the pendant azobenzene group [SCLCPU(AZO)-Ns] were developed in a well-defined architecture. The smectic C nature of an LC phase in the polyurethane networks was confirmed by differential scanning calorimetry, polarized optical microscopy, and one-dimensional and two-dimensional wide-angle X-ray diffraction. The well-defined architecture-made SCLCPU(AZO)-N displays two distinct transition temperatures (T_trans) (T_g and T_cl), with a difference of about 40 °C. Consequently, the excellent triple-shape-memory effect in this network was demonstrated by cyclic thermomechanical analysis. By making full use of the trans-cis photoisomerization of azobenzene, the reversible bending and unbending behaviors were realized under the light irradiation with wavelengths of 450 and 550 nm, respectively.

Heat and solvent responsive polytriazole: shape recovery properties in different solvents

Shape memory polytriazole actuatable by both heat and solvents is presented. Hydrogen bonding solvents exhibit strong influence on shape recovery.

Facile fabrication of a well-defined poly(p-dioxanone) dynamic network from metallosupramolecular interactions to obtain an excellent shape-memory effect

A novel poly(p-dioxanone) dynamic network was fabricated from metallosupramolecular interactions via an elaborate synthetic strategy which shows excellent shape-memory performance.

Self-healing dynamic bond-based rubbers: understanding the mechanisms in ionomeric elastomer model systems

Systematic structure-property investigations on the time-dependent mechanical properties of an ionomer model system with variation of the ionic fraction and the counter ion as obtained from SAXS, dynamic oscillatory rheology and tensile tests, deliver the prerequisites and tools for property adjustment and optimization of their self-healing efficiency.

Aliphatic polyester block polymers: renewable, degradable, and sustainable

Nearly all polymers are derived from nonrenewable fossil resources, and their disposal at their end of use presents significant environmental problems. Nonetheless, polymers are ubiquitous, key components in myriad technologies and are simply indispensible for modern society. An important overarching goal in contemporary polymer research is to develop sustainable alternatives to "petro-polymers" that have competitive performance properties and price, are derived from renewable resources, and may be easily and safely recycled or degraded. Aliphatic polyesters are particularly attractive targets that may be prepared in highly controlled fashion by ring-opening polymerization of bioderived lactones. However, property profiles of polyesters derived from single monomers (homopolymers) can limit their applications, thus demanding alternative strategies. One such strategy is to link distinct polymeric segments in an A-B-A fashion, with A and B chosen to be thermodynamically incompatible so that they can self-organize on a nanometer-length scale and adopt morphologies that endow them with tunable properties. For example, such triblock copolymers can be useful as thermoplastic elastomers, in pressure sensitive adhesive formulations, and as toughening modifiers. Inspired by the tremendous utility of petroleum-derived styrenic triblock copolymers, we aimed to develop syntheses and understand the structure-property profiles of sustainable alternatives, focusing on all renewable and all readily degradable aliphatic polyester triblocks as targets. Building upon oxidation chemistry reported more than a century ago, a constituent of the peppermint plant, (-)-menthol, was converted to the ε-caprolactone derivative menthide. Using a diol initiator and controlled catalysis, menthide was polymerized to yield a low glass transition temperature telechelic polymer (PM) that was then further functionalized using the biomass-derived monomer lactide (LA) to yield fully renewable PLA-PM-PLA triblock copolymers. These new materials were microphase-separated and could be fashioned as high-performing thermoplastic elastomers, with properties comparable to commercial styrenic triblock copolymers. Examination of their hydrolytic degradation (pH 7.4, 37 °C) revealed retention of properties over a significant period, indicating potential utility in biomedical devices. In addition, they were shown to be useful in pressure-sensitive adhesives formulations and as nucleating agents for crystallization of commercially relevant PLA. More recently, new triblocks have been prepared through variation of each of the segments. The natural product α-methylene-γ-butyrolactone (MBL) was used to prepare triblocks with poly(α-methylene-γ-butyrolactone) (PMBL) end blocks, PMBL-PM-PMBL. These materials exibited impressive mechanical properties that were largely retained at 100 °C, thus offering application advantages over triblock copolymers comprising poly(styrene) end blocks. In addition, replacements for PM were explored, including the polymer derived from 6-methyl caprolactone (MCL). In sum, success in the synthesis of fully renewable and degradable ABA triblock copolymers with useful properties was realized. This approach has great promise for the development of new, sustainable polymeric materials as viable alternatives to nonrenewable petroleum-derived polymers in numerous applications.

Thermoplastic elastomers derived from menthide and tulipalin A

Renewable ABA triblock copolymers were prepared by sequential polymerization of the plant-based monomers menthide and α-methylene-γ-butyrolactone (MBL or tulipalin A). Ring-opening transesterification polymerization of menthide using diethylene glycol as an initiator gave α,ω-dihydroxy poly(menthide) (HO-PM-OH), which was converted to α,ω-dibromo end-functionalized poly(menthide) (Br-PM-Br) by esterification with excess 2-bromoisobutyryl bromide. The resulting 100 kg mol(-1) Br-PM-Br macroinitiator was used for the atom transfer radical polymerization of MBL. Four poly(α-methylene-γ-butyrolactone)-b-poly(menthide)-b-poly(α-methylene-γ-butyrolactone) (PMBL-PM-PMBL) triblock copolymers were prepared containing 6-20 wt % PMBL, as determined by NMR spectroscopy. Small-angle X-ray scattering, differential scanning calorimetry, and atomic force microscopy experiments supported microphase separation in the four samples. The mechanical behavior of the triblocks was investigated by tensile and elastic recovery experiments. The tensile properties at both ambient and elevated temperature show that these materials are useful candidates for high-performance and renewable thermoplastic elastomer materials.

Thermoresponsive semicrystalline poly(ε-caprolactone) networks: exploiting cross-linking with cinnamoyl moieties to design polymers with tunable shape memory

The overall goal of this study was to synthesize semicrystalline poly(ε-caprolactone) (PCL) copolymer networks with stimuli-responsive shape memory behavior. Herein, we investigate the influence of a cinnamoyl moiety to design shape memory polymer networks with tunable transition temperatures. The effect of various copolymer architectures (random or ABA triblock), the molecular weight of the crystalline domains, PCL diol, (M(w) 1250 or 2000 g mol(-1)) and its composition in the triblock (50 or 80 mol %) were also investigated. The polymer microstructures were confirmed by NMR, DSC, WAXS and UV-vis spectroscopic techniques. The thermal and mechanical properties and the cross-linking density of the networks were characterized by DSC, tensile testing and solvent swelling, respectively. Detailed thermomechanical investigations conducted using DMA showed that shape memory behavior was obtained only in the ABA triblock copolymers. The best shape memory fixity, R(f) of ~99% and shape recovery, R(r) of ~99% was obtained when PCL diol with M(w) 2000 g mol(-1) was incorporated in the triblock copolymer at a concentration of 50 mol %. The series of triblock copolymers with PCL at 50 mol % also showed mechanical properties with tunable shape memory transition temperatures, ranging from 54 °C to close to body temperature. Our work establishes a general design concept for inducing a shape memory effect into any semicrystalline polyester network. More specifically, it can be applied to systems which have the highest transition temperature closest to the application temperature. An advantage of our novel copolymers is their ability to be cross-linked with UV radiation without any initiator or chemical cross-linker. Possible applications are envisioned in the area of endovascular treatment of ischemic stroke and cerebrovascular aneurysms, and for femoral stents.

Formation of epoxide-amine oligo-adducts as OH-functionalized initiators for the ring-opening polymerization of ε-caprolactone

Epoxide-amine oligo-adducts were synthesized via a one-pot microwave assisted heterogeneous catalytic transfer hydrogenation. Accordingly, 4-nitroanisole was reduced under microwave conditions to give 4-aminoanisole which reacted immediately with the diglycidyl ether of bisphenol A in an addition polymerization reaction to yield oligo(amino alcohol)s. The hydroxy groups of the new formed oligomers were used as the initiator for the ring-opening polymerization of ε-caprolactone to produce a graft copolymer.