In this study, liquid chromatography at critical conditions (LCCC) is used to determine the block lengths and molar masses of polydimethylsiloxane‐block‐polystyrene copolymers synthesized via atom transfer radical polymerization (ATRP) techniques. In addition, the analysis allows for the determination of the presence of homopolymers in the samples. LCCC at the critical point of polydimethylsiloxane (PDMS) on a reversed phase column allows for the determination of PDMS homopolymer and the length of the polystyrene (PS) block in the block copolymer which elutes in the size exclusion chromatography (SEC) regime under these conditions. The PDMS block length and PS homopolymer can be obtained under normal phase conditions. The results of LCCC are compared with data from conventional SEC.
Summary: The structure of polyacetal copolymers with respect to their end groups is investigated. Several techniques, such as liquid chromatography, MALDI‐TOF MS, IR and NMR spectroscopy, as well as combined techniques like 2D chromatography have been applied. Cyclic oligomers and polymers with formyl, hydroxy, and aliphatic end groups are identified. 2D chromatography shows that all the separated species are homogenously distributed with respect to their molar mass.
A self‐assembled lamellar‐within‐lamellar structure of a side chain liquid crystalline diblock copolymer was shear aligned to induce overall alignment and to direct the smectic layer orientation within the copolymer lamellae. The copolymer consisted of a polystyrene block and a poly(methyl methacrylate) block bearing cholesteryl mesogens with only short oxycarbonyloxyethyl spacers separating the mesogens from the backbone. Upon shearing, the copolymer lamellae exhibited uniaxial alignment whereas the smectic layers of the mesogens showed coexisting perpendicular and parallel orientations with respect to the copolymer lamellae. The fraction of the parallel oriented domains could be systematically increased by tuning the oscillation frequency and strain amplitude.
Summary: Novel block copolymers were synthesized in a controlled fashion by nitroxide‐mediated radical polymerization starting from a terpyridine‐modified alkoxyamine. An important feature for controlling the efficiency of the polymerization is the presence of excess nitroxide, responsible for the initial rate of deactivation, which eventually leads to a decrease of the polydispersity indices of the desired block copolymer. The materials obtained were characterized by means of 1H NMR, UV‐vis spectroscopy, and GPC. The complexation of the terpyridine ligands resulted in the formation of A‐B‐[Ru]‐C, A‐B‐[Ru]‐B‐A, and A‐B‐[Fe]‐B‐A metallo‐supramolecular block copolymers.
Telechelic polymers bearing a terpyridine end‐group at the α‐position and a nitroxide at the ω‐position were prepared in a living fashion by nitroxide‐mediated polymerization. 相似文献
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.
Two‐dimensional chromatographic methods were developed using LC‐CC in the first and SEC in the second dimension. These methods were applied for the investigation of PS‐b‐PI diblock copolymers synthesized by different approaches: sequential living anionic polymerization and coupling of living precursor blocks. The first dimension separates according to the individual block length of PS or PI blocks, whereas the second dimension separates with respect to the total molar masses of components. 2D‐LC analysis provides information on the purity of the reaction products, the presence of by‐products, the chemical compositions and the molar masses of all product components. The accuracy and selectivity of 2D‐LC is discussed.
Segmented block copolymers comprised of flexible PEO segments and monodisperse crystallizable bisestertetraamide segments have been synthesized. The influence of the terephthalic units in the soft phase on the transitions and the thermal mechanical and elastic properties are studied. The presence of terephthalic units in the copolymer increases the glass transition temperature of the soft phase by ≈5 °C. The low‐temperature flexibility of the copolymers is improved because of the lower crystallinity and melting temperature of PEO. With the use of terephthalic‐extended PEO segments, segmented block copolymers with low moduli (G' < 15 MPa) and good elastic properties could be obtained.
Summary: Cyclodi(ethylene succinate) (C2) easily reacts with poly(ethylene terephthalate) (PET) in the melt leading to the formation of high molar mass PET‐Poly(ethylene succinate) copolymers (PET‐PES). Copolyesters with a PET/C2 starting mass ratio of 90/10, 80/20, 70/30 and 50/50 were synthesized and characterized by 1H NMR and MALDI‐TOF MS. The 50/50 copolyester was almost random, while copolyesters with higher ethylene terephthalate contents exhibited some block copolymer character. MALDI‐TOF MS/SEC off‐line coupling was used to determine copolyester absolute average molar masses. The results indicate that the conventional SEC polystyrene calibration strongly overestimates copolyester molar masses. The melting temperatures and crystallinity of the 90/10, 80/20 and 70/30 copolyesters were significantly higher than those of comparable PET‐aliphatic polyester copolymers.
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.
PVP‐block‐PVAc block copolymers were synthesized by controlled radical polymerization applying a RAFT/MADIX system and were investigated by HPLC and by coupling of chromatography to FT‐IR spectroscopy and MALDI‐TOF MS. Chromatographic methods (LACCC and gradient techniques) were developed that allowed a separation of block copolymers according to their repeating units. The results of the spectroscopic and spectrometric analysis clearly showed transfer between radicals and process solvent. With the use of hyphenated techniques differences between main and side products were detected. In agreement with previously published results, obtained by NMR, SEC, static light scattering and MALDI‐TOF MS, our data proved a non‐ideal RAFT polymerization.
A liquid crystal (LC) ABA triblock copolymer with poly(styrene) (PS) A blocks and a main‐chain nematic LC polyester B block is synthesized by atom‐transfer radical polymerization of styrene with an LC polyester macro‐initiator. The nematic LC and PS amorphous phases are segregated from each other to form lamellae with a spacing of 27 nm. The 16 nm‐thick nematic LC lamellae are significantly smaller than the contour length of the LC segment (63 nm), and the nematic director is parallel to the lamellae. The central LC segment is primarily more extended in the lamellar direction, but folds so as to meander through the LC lamella and bridges adjacent PS domains. The lamellar microstructure exhibits a reversible spacing increase of up to 31 nm with increasing temperature, suggesting a corresponding increase in the probability of the chain folding.
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.
New degradable, transparent, and elastomeric materials based on PCL are reported in this work. These are block copolymers of PCL with a copolymer of MMA and MDO, i.e. P(MMA‐co‐MDO)‐b‐PCL‐b‐P(MMA‐co‐MDO). A PCL‐based macro‐azoinitiator is used for preparing the block copolymers by free‐radical chemistry. The free‐radical copolymerization of MDO with MMA provides CL units distributed randomly on the PMMA backbone of the second block. This provides the advantage of bringing degradability to the whole system. The detailed structural characterization of the new polymers, their properties evaluation like thermal and mechanical are also reported. The materials are degradable, transparent, and elastomeric depending upon the copolymer composition and block length.
Pressure‐volume‐temperature and surface tension behaviour were studied for random copolymers of styrene and acrylonitrile (SAN) and for poly(butylene terephthalate) (PBT). Results served to determine reduction parameters for the equation‐of‐states by Flory‐Orwoll‐Vrij and by Simha‐Somcynsky as well. Surface tension as a function of copolymer composition displays negative deviation from additivity. It indicates surface excess of styrene units. Similar behaviour with respect to copolymer composition was found for variation of interfacial tension between SAN and PBT. Thickness of surface region is around 1 nm and does not change with copolymer composition whereas extension of interfacial region between PBT and SAN copolymers varies strongly with copolymer composition between around 2 and 60 nm.
Summary: A novel double hydrophilic poly(N,N‐diethylacrylamide)‐poly(acrylic acid)‐poly(N,N‐diethylacrylamide) (PDEAAm‐PAA‐PDEAAm) triblock copolymer was synthesized by sequential anionic polymerization and modification of the poly(tert‐butyl acrylate) middle block by selective hydrolysis and neutralization to its ionic functions. Due to the pH‐sensitivity of the PAA central block and the thermo‐sensitivity of the PDEAAm end‐blocks, it exhibits responsive behavior in aqueous media. At low temperatures and high pH, it is molecularly dissolved while at temperatures above the LCST of the PDEAAm end‐blocks, a sol–gel transition was observed which should be ascribed to the formation of a three‐dimensional transient network comprising PDEAAm hydrophobic physical crosslinks interconnected by PAA negatively charged elastic chains. The sol–gel transition and the rheological properties of the physical gel are strongly influenced by the presence of salt.
Temperature induced sol–gel transition in PDEAAm‐PAA‐PDEAAm aqueous solutions. 相似文献
Poly(3‐hexylthiophene)‐block‐poly(2‐ethyl‐2‐oxazoline) amphiphilic rod–coil diblock copolymers have been synthesized by a combination of Grignard metathesis (GRIM) and ring‐opening cationic polymerization. Diblock copolymers containing 5, 15, and 30 mol‐% poly(2‐ethyl‐2‐oxazoline) have been synthesized and characterized. The synthesized rod–coil block copolymers display nanofibrillar morphology where the density of the nanofibrills is dependent on the concentration of the poly(2‐ethyl‐2‐oxazoline) coil segment. The conductivity of the diblock copolymers was lowered from 200 to 35 S · cm?1 with an increase in the content of the insulating poly(2‐ethyl‐2‐oxazoline) block. By contrast, the field‐effect mobility decreased by 2–3 orders of magnitude upon the incorporation of the poly(2‐ethyl‐2‐oxazoline) insulating segment.
Summary: A series of telechelic OH polysulfones (PSU) were converted to atom transfer radical polymerization (ATRP) macroinitiators by reaction with 2‐bromoisobutyryl bromide. Three macroinitiators with different chain lengths were extended with poly(butyl acrylate) (PBA) to form ABA triblock copolymers. The structure and dynamics of the ABA triblock copolymers with PSU central segments and various molecular weight PBA side chains were investigated by small‐angle X‐ray scattering and rheology. The block copolymers form micelles with a PSU core and PBA corona. The length of each block has an important effect on the structure and resulting dynamics of the copolymers. Dynamic mechanical measurements indicate three relaxation modes: (i) PBA segmental relaxation at high frequency; (ii) PBA relaxation of the corona block at intermediate frequency; (iii) an additional relaxation process related to structural rearrangement of the micelles at low frequency. The shear modulus plateau corresponding to a soft rubbery state extends over a very broad time or temperature range because of this slow additional relaxation.
Schematic illustration of the structural elements and the bulk supramolecular structure for a symmetric triblock copolymer with a stiff central segment strongly incompatible with the other constituent. 相似文献
Well‐defined sulfonated block copolymers were prepared by direct thermolysis with block copolymers of n‐butyl acrylate (nBA) and neopentyl styrene sulfonated (NSS), which were synthesized by Cu‐based living radical polymerization ( <1.20). A simple thermal process for 10 min at 150 °C completely deprotected the neopentyl groups in the poly(NSS) block segment to give fully sulfonated polystyrene backbone. SAXS profile of the block copolymer with 47 wt.‐% of poly(NSS) showed lamella structure, which appeared more clearly with long ranged order after sulfonation of the block copolymer.
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.
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.
