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Smart polymeric materials have received extensive attention for various applications. Here, we reported a facile and efficient approach to prepare a class of pegylated polypeptoids by a combination of ring-opening polymerization (ROP) and post-modification strategy. Three different initiators were involved to mediate the polymerization of the monomers. Unlike the previously reported pegylated polypeptoids, the obtained polypeptoids show completely reversible thermoresponsive behaviors in aqueous solution after 8 heating and cooling cycles. In addition, the phase transition of the polypeptoid solutions can be very sharp (ΔT < 5 °C), which is comparable to poly( N -isopropylacrylamide) (PNIPAM). The influence of temperature on solution properties of the polypeptoids has been systematically studied. The clouding points (CPs) of the polypeptoids are highly tunable depending on the degree of polymerization (DP), the side-chain length, and the polymer concentration. We demonstrate that the thermoresponsive property of the polypeptoid may possibly arise from the incorporation of thioether groups and the branched molecular architecure of side chains. These features enable the pegylated polypeptoids potential candidates for next generation of smart polymeric materials. [ABSTRACT FROM AUTHOR]

Phosphate-binding particles are clinically used to reduce the phosphate level in patients with chronic kidney diseases. However, the binding efficiency of the current amino-functional polymers is low, resulting in high pill burden and low patient adherence. Here, we used polylysine nanogels with amino- and guanidinium-functional groups (PLL nanogel and GPLL nanogel), respectively, and experimentally proved that guanidinium is a much more efficient phosphate-binding group than the amino group at all the tested conditions. The phosphate binding amount of the GPLL nanogel is 60% higher than that of the PLL nanogel at pH 7, 55% higher at pH 2, and 30% higher in the presence of 150 mM NaCl. This guanidination strategy should also be applicable to non-polypeptide systems for anion sequestration. Though the difference of amino and guanidinium functional groups interacting with phosphate ions had been known in the literature, this is the first experimental study to directly compare their phosphate binding performance in clinically relevant conditions (e.g., crosslinked particle forms with all the other parameters controlled to be the same). Therefore, guanidinium functionalized polymers have the potential to become the new generation therapeutics. [ABSTRACT FROM AUTHOR]

Four poly( N -methacryloyl- l -alanine) homopolymers containing different tertiary amine moieties, dimethylaminoethyl, dimethylaminopropyl, diethylaminoethyl, and diethylaminopropyl, were prepared by reversible addition-fragmentation chain transfer (RAFT) polymerization in an effort to use natural amino acids as building blocks to design stimuli-responsive polymers that display pH-tunable lower critical solution temperature (LCST) transitions in the basic pH range. Monomer structure was found to be critical for the corresponding polymer to exhibit desired stimuli-responsive properties in water. While all four polymethacrylamides showed thermosensitive property in water, only poly( N -methacryloyl- l -alanine 2-(diethylamino)ethylamide) (PMAEE) exhibited LCST behavior in a wide pH range, from 9.0 to 13.0. Other polymers' thermoresponsive properties were found either at very high pH values (e.g., ≥13.0) or in a rather narrow pH range. The effects of pH, polymer molecular weight, polymer concentration, presence of NaCl, and end groups on cloud point of PMAEE in water were investigated; the cloud point decreased with the increase of solution pH and polymer concentration, the addition of NaCl, and the introduction of a more hydrophobic end group but varied little with polymer molecular weight. The incorporation of tertiary amine moieties endowed the polymers with a CO 2 -responsive property; we demonstrated that the thermosensitive property of PMAEE can be reversibly tuned by bubbling its solution alternately with CO 2 and N 2 gases. [ABSTRACT FROM AUTHOR]

Abstract: Four kinds of well defined poly(N-methacryloyl-L-amino acid)s were prepared via reversible addition fragmentation chain transfer polymerization. The effects of molecular structure, molecular weight, and end-group on their responsive properties in water were investigated. We found that the monomer structure is critical for the polymer to exhibit stimuli-responsive properties in water; only polymers derived from aspartic acid showed defined dual thermo- and pH-responsive properties. To study the effects of molecular weight and end group on the lower critical solution temperature behavior of poly(N-methacryloyl-L-β-isopropyl aspartic acid) (PMAIPAC), a series of PMAIPAC homopolymers with controlled molecular weights and narrow polydispersities were prepared and treated with excess radical initiators to give defined end groups. The cloud point of PMAIPAC was found to increase with the increase of solution pH, due to the ionization of carboxylic acid groups, and decrease with the increase of molecular weight. The structure of end groups also affects the cloud point of PMAIPAC particularly for low molecular weight samples at low pH. [Copyright &y& Elsevier]

Tensile deformation behavior of bimodal polyethylene (PE) was investigated by employing coarse-grained (CG) molecular dynamics simulations based on a united atom model. The bimodal PE was modeled by blending two linear polyethylene chains with different molecular weights. The mechanical response and corresponding conformational behaviors of the polymer melt during stretching were recorded as a function of strain under both high and low strain rates. We find that the tensile toughness was enhanced in an additive fashion by increasing the fraction of polymers with high molecular weight in bimodal PE. During elongation, the polymer chain extends and orients itself along the loading direction. Surprisingly, varying the bimodal distribution and the strain rates, the disentanglement does not synergistically follow the tendency of chain expansion and ordering along the tensile direction as the strain is gradually raised, implying that multiple deformation modes might exist during the plastic flow process. The molecular origin of this unique development of the entanglement network in bimodal PE is discussed in detail. Image 1 • Tensile mechanical response of bimodal PE melts is elastomer-like. • Bimodal distribution and strain rate both influence degree of orientational order. • Disentanglement is strongly coupled with intermolecular non-bond energy. [ABSTRACT FROM AUTHOR]

The properties and applications of silicone elastomers depended on the molecular structure and composition of polysiloxane precursors, which were the most technologically important silicon-based polymers. Preparation of perfect diphenyl silicone elastomers was challenging due to the unexpected branches formed during the ring-opening copolymerization (ROCP) of phenylcyclosiloxane monomer. In this contribution, diphenyl silicone elastomer precursors with controlled structure were successfully prepared by cyclic trimeric phosphazene base (CTPB) catalyzed ROCP of octamethylcyclotetrasiloxane (D 4), octaphenylcyclotetrasiloxane (D 4 8Ph), and 2,4,6,8-tetravinyl-2,4,6,8-tetramethylcyclotetrasiloxane (D 4 Vi) with high molecular weight up to 551.0 kg/mol and dispersity (Đ) ≤ 2.50. 29Si NMR characterization verified the random microstructures of the resulting diphenyl containing polysiloxanes without chain branching. Moreover, the silica-filled elastomer prepared from poly(dimethylsiloxane- co -vinylmethylsiloxane) (PMVS) and poly(dimethylsiloxane- co -diphenylsiloxane- co -vinylmethylsiloxane) (PMPVS) precursors exhibited very high elasticity, which can be stretched to 1043% with a high tensile strength of 7.7 MPa. Thermal oxidation aging test proved the excellent thermal aging resistance of the phenyl-containing silicone elastomers. This work demonstrated facile method to prepare high quality diphenyl containing polysiloxane precursor toward robust silicone elastomers. [Display omitted] • Diphenyl silicone elastomer precursors with controlled structure were successfully prepared by CTPB catalyzed ROCP. • Silica-filled elastomer prepared from PMVS and PMPVS precursors exhibited very high elasticity. • Thermal oxidation aging test proved the excellent thermal aging resistance of the phenyl-containing silicone elastomers. [ABSTRACT FROM AUTHOR]

Tough and transparent poly(L-lactic acid)/poly(D-lactide)-b-poly(butadiene)-b-poly(D-lactide) (PLLA/PDLA-PB-PDLA) film with balanced strength was obtained. The PDLA-PB-PDLA triblock copolymer was firstly synthesized by ring-opening polymerization (ROP) of D-lactide using bihydroyl-terminated polybutadiene as macroinitiator, and then the obtained triblock copolymer was mixed with PLLA in solution. The blended films kept in good transparence even when the loading of PDLA-PB-PDLA reached to 15 wt%. Meanwhile, the elongation at break of the PLLA/PDLA-PB-PDLA film increased by ∼10 times without a significant reduction in tensile strength as compared with that of pure PLLA. The mechanical property was ascribed to the synergetic effect of the flexible PB chains and the stereocomplex crystals formed between PLLA matrix and PDLA chains. "Salami-like" dispersed-phase with nanometer scales was observed, which would contribute to the transparency of the blended film. The tensile fractured morphologies indicated that shear yield of the matrix and cavitation might be the major toughening mechanism of PLLA/PDLA-PB-PDLA film. We prepared tough and transparent poly(L-lactic acid) film with balanced tensile strength by blending with poly(D-lactide)-b-poly(butadiene)-b-poly(D-lactide) triblock copolymer. [Display omitted] • Tough and transparent poly(L-lactic acid)/poly(D-lactide)-b-poly(butadiene)-b-poly(D-lactide) film with balanced strength. • The mechanical properties were ascribed to the synergetic effect of the flexible PB chains and the stereocomplex crystals. • "Salami-like" dispersed-phase with nanometer scales would contribute to the transparency of the blended film. • Shear yield of the matrix and cavitation might be the major toughening mechanism of PLLA/PDLA-PB-PDLA film. [ABSTRACT FROM AUTHOR]

Smart protein-mimetic materials have received increasing interest for many applications. Here, we reported a facile and efficient approach to prepare a class of dual-responsive copoly( l -glutamate)s by ring-opening polymerization (ROP) and post-modification strategy. Both the oligo(ethylene glycol) (OEG) and glutamic acid residues were incorporated to offer thermal- and pH-responsive property simultaneously. We present a systematic study of the influence of both temperature and pH on the solution properties of the copolypeptides. The copolypeptides show entirely reversible pH-dependent thermal-responsive behaviors with tunable phase transition temperatures. It is demonstrated that the sequence of the polymer units can also influence the solution behavior. The α-helix conformation appears to be the dominant secondary conformation, which shows the pH dependence, but generally irrespective of the temperature. We further verify that the reduced circular dichroism (CD) signal upon heating above the clouding point (CP) is entirely due to the aggregation of the polymer chains. All these features make the obtained polypeptides potential candidates for next generation of smart protein-mimetic materials. [ABSTRACT FROM AUTHOR]

Abstract: Herein, we present a concept of combining host–guest chemistry with block copolymer self-assembly to fabricate an inner cross-linking block copolymer aggregate with photo-responsive switches on the basis of the reversible interaction between azobenzene and β-cyclodextrin, which can serve as a controllable supramolecular container to load and release guest molecules reversibly. The inner cross-link makes the block copolymer aggregates exhibit good stability, and the aggregates can keep their spherical morphologies during photo-irradiation treatment. When the switches are in on-state, cyclodextrins can bind with hydrophobic pyrene molecules; and when the switches are in off-state, pyrene molecules will get away from the cyclodextrins. The photo-controllable switches embedded in the aggregates endow this new supramolecular container with the capability to load and release guest molecules reversibly without structure disruption. It is anticipated that this line of work may open an avenue for fabricating new polymeric containers which can be used for controllable molecular transfer and catalysis. [Copyright &y& Elsevier]

A new polystyrene supported cyclic trimeric phosphazene base (PS-CTPB) was designed and synthesized. It was demonstrated that hypotoxic poly (ε -caprolactone) (PCL) can be directly prepared via ring-opening polymerization (ROP) by using PS-CTPB as catalyst. The PS-CTPB catalyst was prepared via immobilization of cyclic trimeric phosphazene base (CTPB) moiety on polystyrene microspheres to obtain a heterogeneous organocatalyst. The composition and chemical structure of the heterogeneous PS-CTPB was systematically characterized using solid-state 13C and 31P MAS NMR, FTIR, SEM and element analysis. It was found that immobilization of CTPB on PS microsphere maintained its excellent catalytic activity for ROP of ε -CL, δ -valerolactone (δ -VL), rac -lactide (rac -LA). Moreover, the heterogeneous PS-CTPB could be easily separated or recycled via simple filtration. Given that, the obtained polyesters contained negligible catalyst residual, so the obtained PCL samples have low cytotoxicity indicated from MTT assay. It was worth noting that the recycled PS-CTPB catalyst could be reused for another six consecutive cycles without significant decrease of catalytic activity. Image 1 • PS-CTPB is prepared via immobilization of cyclic trimeric phosphazene base moiety on polystyrene microspheres. • PS-CTPB exhibits highly efficient for ring-opening polymerization of cyclic esters. • PS-CTPB is easily recovered and reusable for six consecutive cycles without obvious deactivation. • The PCLs without catalyst-residue have been facilely synthesized using PS-CTPB by simple filtration. • MTT assay indicates that the resulting PCLs have low cytotoxicity. [ABSTRACT FROM AUTHOR]