Graphene Enhances the Shape Memory of Poly (acrylamide‐co‐acrylic acid) Grafted on Graphene

Acrylamide and acrylic acid are grafted on graphene by free‐radical polymerization to produce a series of graphene–poly(acrylamide‐co‐acrylic acid) hybrid materials with different contents of graphene. The materials demonstrate shape memory effect and self‐healing ability when the content of graphene is in the range of 10%–30% even though poly(acrylamide‐co‐acrylic acid) itself had poor shape memory ability. The permanent shape of the materials can be recovered well after 20 cycles of cut and self‐healing. The result is attributed to the hard–soft design that can combine nonreversible “cross‐link” by grafting copolymer on graphene and reversible “cross‐link” utilizing the “zipper effect” of poly(acrylamide‐co‐acrylic acid) to form or dissociate the hydrogen‐bond network stimulated by external heating.

     

Reaction of Boranes with TMS Diazomethane and Dimethylsulfoxonium Methylide. Synthesis of Poly(methylidene‐co‐TMSmethylidene) Random Copolymers

Summary: Borane reacts with TDM by a sequence of insertion and disproportionation reactions to yield tris‐(trimethylsilylmethyl)borane. No further addition of TDM occurs. Triallylborane and tris‐(4‐methoxyphenylethyl)borane initiate the copolymerization of TDM and dimethylsulfoxonium methylide. The reactions afford TMS‐substituted polymethylene oligomers. The resultant poly(methylidene‐co‐TMSmethylidene) random copolymers arise from incorporation of TMSmethylidene (CHSiMe₃) and methylidene (CH₂) groups into the growing polymer chain one carbon at a time.

Trialkylborane‐catalyzed copolymerization of trimethylsilyl diazomethane and dimethylsulfoxonium methylide.     

Ultrafast Responsive Poly‐ (N‐isopropylacrylamide) Gel Produced by Cryostructuring of Self‐crosslinkable Polymer Microgels

A macroporous material composed of closely aggregated particles was prepared by cryo‐structuration of N‐isopropylacrylamide‐co‐N‐hydroxymethylacrylamide (NIPA‐co‐HMAm) particle suspensions. The formed structure was maintained by the formation of covalent bonds through self‐crosslinking between the particles while the system was in a semi‐frozen state thus avoiding the need to freeze‐dry the sample. This resulted in macroporous structure composed of closely aggregated thermoresponsive particles which exhibit an ultrafast temperature response. The response rate can be attributed both to the macroporous structure as well as the fast responsive properties of the individual particles.

     

Thermal Breakdown by the Retro Diels–Alder Reaction of Crosslinking in Poly[styrene‐co‐(furfuryl methacrylate)]

Crosslinked poly[styrene‐co‐(furfuryl methacrylate)] has been produced by the Diels–Alder (D‐A) reaction between the furan ring (within the copolymer) and the maleimide (MI) group (within the other reactant, bismaleimide). The retro D‐A reaction was followed by the analysis of MI groups produced at different times at five constant temperatures. The process was shown to follow first‐order kinetics, and the rate constants were determined. The findings are believed to be the first to provide quantitative information on the breakdown by a retro D‐A reaction of crosslinking in a polymer system. The D‐A and retro D‐A processes constitute a thermoreversible gelling system with respect to the formation and breakdown of crosslinks.

First‐order rate plot for the retro D‐A breakdown of crosslinked poly(ST‐co‐FM).     

Facile Fabrication of Multistimuli‐Responsive Metallo‐Supramolecular Core Cross‐Linked Block Copolymer Micelles

Metallo‐supramolecular core cross‐linked (CCL) micelles are fabricated from terpyridine‐functionalized double hydrophilic block copolymers, poly(2‐(2‐methoxyethoxy)ethyl methacrylate)‐b‐poly(2‐(diethylamino)ethyl methacrylate‐co‐4′‐(6‐methacryloxyhexyloxy)‐2,2′:6′,2″‐terpyridine) [PMEO₂MA‐b‐P(DEA‐co‐TPHMA)] via the formation of bis(terpyridine)ruthenium(II) complexes. These metallo‐supramolecular CCL micelles exhibit not only high structural integrity under different pH values and temperatures in aqueous solution, but multistimuli responsiveness including pH‐responsive cores, thermo‐responsive shells, and reversible dissociation of bis(terpyridine)ruthenium(II) complexes upon addition of competitive metal ion chelator, which allows for precisely controlled release of the encapsulated hydrophobic guest molecules via the combination of different stimuli.

     

Synthesis of Thermo‐Responsive Polymers With Both Tunable UCST and LCST

New water‐soluble block copolymers of 2‐(2‐methoxyethoxy)ethyl methacrylate (MEO₂MA), oligo(ethylene glycol) methacrylate (OEGMA), and N‐(3‐(dimethylamino) propyl) methacrylamide (DMAPMA) (poly(OEGMA‐co‐MEO₂MA)‐b‐poly(DMAPMA)) were prepared via sequential reversible addition‐fragmentation chain transfer (RAFT) polymerization. Selective quaternization of poly(DMAPMA) block gives poly(OEGMA‐co‐MEO₂MA)‐b‐poly((3‐[N‐(3‐methacrylamidopropyl)‐N,N‐dimethyl]ammoniopropane sulfonate)‐co‐N‐(3‐(dimethylamino) propyl) methacrylamide), such block copolymer exhibits double thermo‐responsive behavior in water, poly(MEO₂MA‐co‐OEGMA) block shows a lower critical solution temperature (LCST), and poly((3‐[N‐(3‐methacrylamidopropyl)‐N,N‐dimethyl]ammoniopropane sulfonate)‐co‐N‐(3‐(dimethylamino) propyl) methacrylamide) block shows a upper critical solution temperature (UCST). Both of LCST and UCST can be controlled: LCST could be tuned by the fraction of OEGMA units in poly(OEGMA‐co‐MEO₂MA), and UCST was found to be dependent on the degree of quaternization (DQ).

     

Synthesis of Strong Electrolyte Temperature‐Sensitive Hydrogels by Radiation Polymerization and Application in Protein Separation

Strong electrolyte temperature‐sensitive hydrogels were synthesized by radiation polymerization using N‐isopropylacrylamide and sodium 2‐acrylamido‐2‐methylpropanesulfonate. The influence of irradiation dose and mole ratio of the monomers was examined by swelling measurements in aqueous solution and organic solvents. The hydrogels without any pollution were applied in concentrating protein.

Effect of irradiation dose on swelling ratios of P(NIPA‐co‐NaAMPS) hydrogels.     

Effect of Microstructures on the Phase Transition Behavior of P(CL‐GL)‐PEG‐P(CL‐GL) Triblock Copolymer Aqueous Solutions

Amphiphilic poly[(ε‐caprolactone)‐co‐glycolide]‐block‐poly(ethylene glycol)‐block‐poly[(ε‐caprolactone)‐co‐glycolide) [P(CL‐GL)‐PEG‐P(CL‐GL)] triblock copolymers with different average lengths of caproyl sequences (L_CL) were synthesized by ring‐opening polymerization at different temperatures. A 25% aqueous solution of the copolymer with L_CL = 11.0 formed a gel, owing to strong crystallinity‐induced hydrophobicity at low temperature, and underwent a gel‐sol transition (UCST behavior) when the temperature was increased to 40 °C. In contrast, the solution of copolymer with L_CL = 6.7 underwent a sol‐gel transition (LCST behavior) due to micelle aggregation. However, a clear sol‐turbid sol phase transition was observed for the copolymer with more random microstructures (L_CL = 5.2).

     

Functionalization of Multi‐Walled Carbon Nanotubes by Thermo‐Grafting with α‐Methylstyrene‐Containing Copolymers

The present article reports on a strategy for the functionalization of multi‐walled carbon nanotubes (MWCNTs) by grafting with various polymer chains. Copolymers consisting of α‐methylstyrene (AMS) and a second monomer, that is glycidyl methacrylate (GMA) or styrene (St), were synthesized in advance. The copolymers were heated in the presence of MWCNTs in solution, decomposition of the AMS sequences occurred, providing macroradicals, which further attacked the double bonds on the MWCNT surfaces. Grafting of the copolymer chains onto the surface of the MWCNTs was thus achieved, as demonstrated by FT‐IR, XPS and Raman technologies. The resulting poly(AMS‐co‐GMA)‐g‐MWCNTs could be uniformly dispersed in N,N‐dimethylformamide (DMF) and acetone, and the poly(AMS‐co‐St)‐g‐MWCNTs also could be uniformly dispersed in DMF.

     

DMAP/Cr(III) Catalyst Ratio: The Decisive Factor for Poly(propylene carbonate) Formation in the Coupling of CO2 and Propylene Oxide

Highly efficient formation of poly(propylene carbonate) can be achieved in the coupling of CO₂ and propylene oxide assisted by 4‐(N,N‐dimethylamino)pyridine (DMAP) and catalyzed with salen chromium(III) chloride by using DMAP/Cr ratios of less than 2. Under these conditions a possible backbiting mechanism is suppressed, leading to only minor amounts of cyclic carbonate as a side product.

     

A Closed‐Loop Phase Diagram in a Weakly Interacting Polyolefin Copolymer Binary Blend System

Summary: The phase behavior of poly(ethylene‐co‐styrene) (PES) and poly(ethylene‐co‐butene) (PEB) blends has been studied. A closed‐loop phase diagram was clearly observed in this weakly interacting system as the styrene content in the PES decreased to about 1 mol‐%. At higher styrene contents, the phase loop starts to interplay with the crystallization transformation at lower temperatures.

Phase diagram of PEB/PES blends. Phase boundary line is only for easy demonstration.     

Reversibly Switchable Double‐Responsive Block Copolymer Brushes

Poly(2‐hydroxyethyl methacrylate)‐block‐poly(N‐isopropylacrylamide) (PHEMA‐b‐PNIPAM) was prepared by controlled surface‐initiated ATRP from silicon substrates, and the resulting block copolymers were successfully converted into the corresponding PSEMA‐b‐PNIPAM by esterification of the hydroxy groups on the PHEMA block using excess of succinic anhydride. The PSEMA‐b‐PNIPAM block copolymer brushes respond to both temperature and pH stimuli. The double‐responsive behavior of the block copolymer brushes in solution was investigated by height imaging and force–distance measurements of AFM. The results clearly show the responsive behavior of the smart block copolymer brushes.

     

Vapor‐Based Synthesis of Poly[(4‐formyl‐p‐xylylene)‐co‐(p‐xylylene)] and Its Use for Biomimetic Surface Modifications

Summary: The vapor‐based synthesis and characterization of a reactive polymer, poly[(4‐formyl‐p‐xylylene)‐co‐(p‐xylylene)] ( 1 ), have been reported. The reactive polymer coating enables the immobilization of oligosaccharides via the chemoselective aldehyde‐hydrazide coupling reaction.

     

Phase Transition Behaviors of Self‐Oscillating Polymer and Nano‐Gel Particles

Summary: Self‐oscillating polymers and nano‐gel particles consisting of N‐isopropylacrylamide and the ruthenium catalyst of the Belousov‐Zhabotinsky reaction have been prepared. In order to clarify the crosslinking effect on the self‐oscillating behavior, the phase transition behaviors were investigated by measuring the transmittance and the fluorescence intensity of the polymer solution and the gel bead suspension. Cooperative effects due to crosslinking will play an important role for the design of nanoactuators.

Chemical structure of poly(NIPAAm‐co‐Ru(bpy)₃).     

Novel pH‐ and Temperature‐Responsive Block Copolymers with Tunable pH‐Responsive Range

A series of novel pH‐ and temperature‐responsive diblock copolymers composed of poly(N‐isopropylacrylamide) (PNIPAM) and poly[(L ‐glutamic acid)‐co‐(γ‐benzyl L ‐glutamate)] [P(GA‐co‐BLG)] were prepared. The influence of hydrophobic benzyl groups on the phase transition of the copolymers was studied for the first time. With increasing BLG content in P(GA‐co‐BLG) block, the thermal phase transition of the diblock copolymer became sharper at a designated pH and the critical curve of phase diagram of the diblock copolymer shifted to a higher pH region. Notably, when the BLG content in P(GA‐co‐BLG) block was more than 30 mol.‐%, the diblock copolymer responded sharply to a narrow pH change in the region of pH 7.4–5.5.

     

ATRP of Silylated Glycerol Monomethacrylate in Organic Medium for Convenient Synthesis of Amphiphilic Copolymers

A synthetic method with broad spectrum of application in the preparation of self‐organizing amphiphilic copolymers having poly(glycerol monomethacrylate) (PG2MA) as a hydrophilic part is herein reported. The approach relies on the facile preparation of silylated glycerol monomethacrylate (G2MA‐TMS) monomer, and its controlled atom transfer radical polymerization (ATRP) in organic media, which produced well‐defined (co)polymers with predictable molar mass and low dispersity, followed by desilylation. The wide scope of such a strategy was demonstrated by the successful synthesis of original polycaprolactone‐b‐poly(glycerol monomethacrylate) (PCL‐b‐PG2MA) diblock copolymers with the ability to self‐assemble into ordered structures (micelles and vesicles) in an aqueous medium.

     

Controlled Dispersion of Silver Nanoparticles into the Bulk of Thermosensitive Polymer Microspheres: Tunable Plasmonic Coupling by Temperature Detected by Surface Enhanced Raman Scattering

By in situ reduction of Ag⁺ ions pre‐dispersed inside thermosensitive microspheres of poly[(N‐isopropylacrylamide)‐co‐(methacrylic acid)] (P(NIPAM‐co‐MAA)), a 3D copolymer‐supported network of silver nanoparticles is created and extensively characterized by surface‐enhanced Raman scattering (SERS). The effective dispersion and the suitable density of the silver nanoparticles in the composite microspheres are demonstrated by the thermal‐induced SERS signal and its high reproducibility during thermocycling. When the temperature of the system increases above 32 °C, spatial separation of the silver nanoparticles decreases and the numbers of Ag nanoparticles and P(NIPAM‐co‐MAA) microspheres under illumination spot increase as a result of the shrinkage of the P(NIPAM‐co‐MAA) chains, leading to the ramp of the SERS effect. By means of the high reversibility of the thermosensitive phase transition of the P(NIPAM‐co‐MAA) microspheres, SERS activity of the silver nanoparticle network embedded in the microsphere can be well controlled by thermal‐induced variation of special separation.

     

Encapsulation of a Single Metal Nanoparticle with Tunable Size in a Monodisperse Polymer Microcapsule

A versatile approach to fabricate monodisperse poly[styrene‐co‐(divinyl benzene)] (PS‐co‐DVB) microcapsules that contain a single gold nanoparticle (AuNP) has been demonstrated. Using the PS‐co‐DVB microcapsule as a microreactor, aqueous HAuCl₄ and NaBH₄ solutions are subsequently infiltrated. The size of the resulting AuNP inside of the PS‐co‐DVB microcapsules is easily tunable by controlling the repeated infiltration cycles of aqueous HAuCl₄ and NaBH₄. PS‐co‐DVB microcapsules that contain a single silver and palladium nanoparticle are also obtained by following a similar protocol.

     

Preparation of Monodisperse Polylactide Microspheres by Dispersion Polymerization Using a Polymeric Stabilizer with Hydroxy Groups

Monodisperse poly(D ,L ‐lactide) (PDLLA) microspheres have been prepared by dispersion polymerization of D ,L ‐lactide with a synthetic polymeric stabilizer. The polymerization is carried out in xylene/heptane (1:2, v/v) at 368 K for 3 h with poly[(dodecyl methacrylate)‐co‐(2‐hydroxyethyl methacrylate)] (P(DMA‐co‐HEMA)). P(DMA‐co‐HEMA) has hydroxy groups as an initiation group for pseudoanionic dispersion polymerization. The particle diameter and the coefficient of variation concerning the diameter distribution of the obtained PDLLA microspheres are 3.9 µm and 4.3%, respectively. In addition, from the results of dynamic light scattering measurements, it is found that P(DMA‐co‐HEMA) and the PDLLA‐grafted copolymer form a micellar structure in solution.