Triblock copolymers of poly(N‐isopropylacrylamide)‐block‐poly(N,N‐dimethylacrylamide)‐block‐poly(N‐isopropylacrylamide) were synthesised via RAFT polymerisation using a symmetrical bistrithiocarbonate. Keeping the block length of the permanently hydrophilic middle block constant, the length of the poly(N‐isopropylacrylamide) block was varied broadly. The thermoresponsive aggregation of the polymers in water was studied by 1H NMR, turbidimetry, and dynamic light scattering. The complex aggregation behaviour was block length dependent and occurred under kinetic control. Importantly, different information on the hydrophilic‐hydrophobic transition of the poly(N‐isopropylacrylamide) block was obtained using the various analytical methods and could not be directly correlated.
Polymerization of NVPI was carried out by a RAFT process using five xanthate‐type, a dithiocarbamate‐type, and a dithioester‐type CTA. The xanthate‐type [O‐ethyl‐S‐(1‐ethoxy carbonyl) ethyl dithiocarbonate and O‐ethyl‐S‐(1‐ethoxycarbonyl‐1‐methyl)ethyl dithiocarbonate] and the dithiocarbamate‐type CTA (benzyl‐1‐pyrrolecarbodithioate) were the most efficient to obtain poly(NVPI) with controlled molecular weights ( = 4 100–13 000) and low polydispersities ( = 1.29–1.38). The effects of parameters such as solvent, temperature, and CTA‐to‐initiator molar ratio, were examined in order to determine the conditions leading to optimal control of the polymerization.
A nonconjugated N‐vinyl monomer, N‐vinylphthalimide (NVPI), was copolymerized with various comonomers via reversible addition‐fragmentation chain transfer (RAFT) process. Two different chain transfer agents (CTAs), O‐ethyl‐S‐(1‐ethoxycarbonyl) ethyldithiocarbonate (CTA 1) and benzyl 1‐pyrrolecarbodithioate (CTA 2), were compared for these copolymerizations with 2,2′‐azobis(isobutyronitrile) as an initiator. The effects of the nature of CTA, the comonomer structure, and solvent on the copolymerization were investigated in terms of the controlled character of the copolymerization and alternating structure. The copolymerization of NVPI and N‐isopropylacrylamide using CTA 2 in DMF or MeOH afforded well‐defined copolymers with predominantly alternating structure, controlled molecular weights, and low molecular mass distributions.
Amino acid‐based amphiphilic block copolymers involving poly(N‐acryloyl‐L ‐alanine), poly(A‐Ala‐OH), which exhibits a characteristic chiroptical property and pH‐dependent solubility, have been synthesized by reversible addition‐fragmentation chain transfer (RAFT) polymerization. The direct polymerization of A‐Ala‐OH without any protecting chemistry using the dithiocarbamate‐terminated polystyrene or poly(N‐acryloyl‐L ‐phenylalanine methyl ester) as a macrochain transfer agent produced well‐defined amphiphilic block copolymers. The self‐assembly behaviors and chiroptical properties of these amphiphilic block copolymers in selective solvents were investigated by dynamic light scattering, circular dichroism, and UV–Vis spectroscopic methods.
Linear and branched poly(lactide)s and poly(lactide‐co‐glycolide)s are synthesized using stannous (II) 2‐ethylhexanoate and alcoholic co‐initators resulting in polymers with 1, 2, 25, or 51 arms. 1‐dodecanol is used to produce the 1‐arm polymer, poly(ethylene glycol) is used for the 2‐arm polymers, and poly(glycidol)s of appropriate molecular weights are used to initiate the 25‐ and 51‐arm branched polyesters. The polymers are evaluated by melt rheology and dynamic mechanical analysis. In vitro degradation is investigated in phosphate buffer pH 7.4 at 37 °C for 28 d for moisture uptake and mass loss. Degraded samples are analyzed by gravimetry, differential scanning calorimetry, dilute solution viscometry (Cannon‐Fenske), and gel‐permeation chromatography.
New polyhydrazides and poly(amidehydrazide)s bearing redox‐active carbazole and triphenylamine units were prepared. The resulting poly(1,3,4‐oxdiazole)s and poly(amide‐1,3,4‐oxadiazole)s had high glass‐transition temperatures (288–330 °C) and high thermal stability. The dilute solutions of all the hydrazide and oxadiazole polymers showed a weak–medium photoluminescence with emission maxima around 474–506 nm. The polymer films revealed two well‐defined and reversible redox couples upon electrochemical oxidation, together with interesting electrochromic behaviors. They showed enhanced redox‐stability and electrochromic performance. CV of the oxadiazole polymers also showed reduction processes due to the formation of radical anions of the oxadiazole units.
Six new bifunctional bis(trithiocarbonate)s were explored as RAFT agents for synthesizing amphiphilic triblock copolymers ABA and BAB, with hydrophilic “A” blocks made from N‐isopropylacrylamide and hydrophobic “B” blocks made from styrene. Whereas the extension of poly(N‐isopropylacrylamide) by styrene was not effective, polystyrene macroRAFT agents provided the block copolymers efficiently. End group analysis by 1H NMR spectroscopy supported molar mass analysis and revealed an unexpected side reaction for certain bis(trithiocarbonate)s, namely a fragmentation to simple trithiocarbonates while extruding ethylenetrithiocarbonate. The amphiphilic block copolymers with short polystyrene blocks are directly soluble in water and self‐organize into thermoresponsive micellar aggregates.
Clickable poly(ethylene glycol) (PEG) derivatives are used with two sequential aqueous two‐phase systems to produce microsphere‐based scaffolds for cell encapsulation. In the first step, sodium sulfate causes phase separation of the clickable PEG precursors and is followed by rapid geleation to form microspheres in the absence of organic solvent or surfactant. The microspheres are washed and then deswollen in dextran solutions in the presence of cells, producing tightly packed scaffolds that can be easily handled while also maintaining porosity. Endothelial cells included during microsphere scaffold formation show high viability. The clickable PEG‐microsphere‐based cell scaffolds open up new avenues for manipulating scaffold architecture as compared with simple bulk hydrogels.
Amino acid‐based block copolymers containing poly(A‐Pro‐OMe) have been synthesized by RAFT polymerization using the dithioester‐terminated poly(DMA) as a macro‐CTA. An amphiphilic block copolymer composed of polystyrene as a hydrophobic segment and poly(A‐Pro‐OMe) as a hydrophilic segment was also prepared using polystyrene as the macro‐CTA. The chiroptical properties of the block copolymer, poly(DMA)‐block‐poly(A‐Pro‐OMe), was evaluated by specific rotation, CD, and UV‐vis spectroscopy. The assembled structure of the block copolymer on a mica surface was characterized by SFM. Thermally induced phase separations of the random and block copolymers were also studied in aqueous solution.
Amphiphilic ABCBA pentablock copolymers based on PVP, PS, and PDMS were synthesized using a combination of ATRP and RAFT polymerizations. The PVP‐block‐PS‐block‐PDMS‐block‐PS‐block‐PVP pentablock copolymer was characterized using a variety of chromatography and spectroscopic methods which showed that a high degree of end group and molecular weight control can be achieved. Preliminary analysis of the aqueous solution behavior of the pentablock copolymer showed that it self‐assembles in water in order to shield the PDMS and PS segments from the water.
Well‐defined β‐CD‐terminated poly(N‐isopropylacrylamide) (β‐CD‐PNIPAM) was synthesized via a combination of atom transfer radical polymerization (ATRP) and click chemistry. Moreover, adamantyl‐terminated poly(2‐(diethylamino)ethyl methacrylate) (Ad‐PDEA) was synthesized by ATRP using an adamantane‐containing initiator. Host‐guest inclusion complexation between β‐CD and adamantyl moieties drives the formation of supramolecular double hydrophilic block copolymers (DHBC) from β‐CD‐PNIPAM and Ad‐PDEA. The obtained supramolecular PNIPAM‐b‐PDEA diblock copolymer exhibits intriguing multi‐responsive and reversible micelle‐to‐vesicle transition behavior in aqueous solution by dually playing with solution pH and temperatures.
A well‐defined, high‐density poly(N‐isopropylacrylamide) (PNIPAM) brush was fabricated through a novel and reliable strategy by the combination of the self‐assembly of a monolayer of dendritic photoinitiator and surface‐initiated photopolymerization. The whole fabrication process of the PNIPAM brush was followed by water contact angles, X‐ray photoelectron spectroscopy, and atomic force microscopy. Characterization of the PNIPAM brush, such as molecular weight and thickness determination, were measured by gel permeation chromatography, and ellipsometry, and the graft density was estimated. The temperature response of the PNIPAM brush was further investigated and the result verified the coil‐to‐globule transition of the PNIPAM chains in water from low to high temperature.
A novel, easy and high‐efficient method is described for transferring hydrophobic magnetic Fe3O4 nanoparticles from organic to aqueous solution by wrapping a thermo‐responsive and photocrosslinkable poly(N‐isopropylacrylamide) (PNIPAm) terpolymer around the particles. The wrapping procedure is introduced by the co‐nonsolvent transition of PNIPAm in the mixing solvent and the polymer can dissolve in water carrying Fe3O4 nanoparticles by noncovalent interaction. The temperature‐dependant and magnetic properties of the water‐soluble particles are characterized in this paper.
The binary phase diagram of amphiphilic poly(ethylene oxide)‐block‐poly(γ‐methyl‐ε‐caprolactone) block copolymers in water is examined for four polymers having the same hydrophilic block length but different hydrophobic block lengths across the whole concentration range. The bulk polymers show no ordered morphology. With increasing water concentration the polymers undergo transitions from lamellar phases to packed vesicles and subsequently all polymers self‐assemble into vesicles in dilute aqueous solutions. Additionally, the largest polymer forms an inverse hexagonal phase, and the smallest polymer self‐aggregates into rod‐like micelles and showed a hexagonal phase.
A simple and efficient approach for the preparation of rod‐coil block copolymers comprising oligo‐ and polythiophenes blocks together with PMMA or PS blocks is described. The block copolymers were prepared using a two‐step procedure. α,ω‐dicarboxy‐terminated oligothiophenes and carboxy terminated poly(3‐hexylthiophene) were first prepared. These were then reacted with P4S10 in a second step to generate the α,ω‐thioester terminated oligothiophenes and poly(3‐hexylthiophene)s which were subsequently used in a one‐pot reaction as RAFT polymerization agents with methylmethacrylate and styrene. The di‐ and tri‐block copolymers hence obtained were fully characterized, both in solution and as thin films.
During characterization of a temperature‐responsive poly(N‐isopropylacrylamide) (PIPAAm) layer grafted onto a Si(100) substrate, atomic force microscopy (AFM) is able to probe the interactions between the microscope tip and the polymer. The modification of the AFM tip surface with octadecyltrichlorosilane (OTS) changes the interaction between the PIPAAm surface and the tip. Although a repulsive interaction is observed between a commercially available Si tip and the PIPAAm surface, a strong attractive interaction between the OTS‐modified Si tip and the surface is observed. Adhesion‐force analysis shows changes in the hydrophilic/hydrophobic character of ultrathin PIPAAm surfaces immediately after a change in temperature. The PIPAAm surface becomes hydrophobic less than 30 min after temperature increase, but requires 120 min to become hydrophilic after temperature reduction.
A series of well‐defined poly(methyl methacrylate)‐block‐poly(butyl acrylate) 3‐arm star block copolymers have been synthesized by ATRP. The incorporation of polar hard segment of PMMA was made possible with the aid of halogen exchange technique. Phase‐separated morphology of cylindrical PMMA domains hexagonally arranged in the pBA matrix was observed by small angle X‐ray scattering in all studied materials. The mechanical and thermal properties of the PBA–PMMA 3‐arm star block copolymers have been thoroughly characterized and their thermoplastic elastomer behavior was studied. It was found that the tensile properties of these materials are comparable with those of their linear ABA type block copolymer counterparts with similar compositions.
The synthesis of two random copolymers bearing pendant mixed‐ligand orthometallated terpyridine‐based cationic iridium (III) complexes, as well as their uses as single‐layered electrophosphorescent emitters in polymer light‐emitting diodes is described. Both solution‐processable iridium metallopolymers are prepared by copolymerization of styrene with a complex‐substituted styrene by nitroxide mediated polymerization. Results on devices based on metallopolymers used as dopant of poly(N‐vinylcarbazole) or alone as single layers are presented.
Well‐defined diblock poly(L ‐lactide)‐block‐poly(dimethylamino‐2‐ethyl methacrylate) (PLLA‐b‐PDMAEMA) copolymers were synthesized by combining ROP of LLA and ATRP of DMAEMA, from a dual‐initiator 2‐hydroxylethyl 2‐bromoisobutyrate. The molecular characterization of these diblock copolymers was performed using 1H NMR, FT‐IR, and GPC‐MALLS analysis. The responsive behavior of these diblock copolymers in aqueous solutions at different pH and temperatures were investigated using DLS. Results show that both higher pH and temperature result in a higher degree of neutralization, weaker hydrogen bonding, and micellar aggregation. As observed by TEM, changes in micellar morphology are in accordance with DLS results.
The self‐assembling properties of hydrophobically modified (N‐isopropylacrylamide) have been investigated by dynamic light scattering and rheological measurements. Size of the globules and transmission of the solutions vary strongly in the same range of temperature. The presence of hydrophobic groups leads to contraction of the globules' size compared to poly(N‐isopropylacrylamide) (PNIPAM). The viscoelastic properties of the samples in aqueous solution have been investigated as a function of copolymer concentration, structure of the hydrophobic group (dodecyl or adamantyl group), substitution level (1–5%) and over a temperature range covering the lower critical solution temperature (LCST). At high concentration and high level of adamantyl substitution, gelation is observed several degrees before the phase transition. A physical network is formed due to the strong hydrophobic interactions, and this physical gel undergoes phase transition without macroscopic phase separation.
