Unsaturated polyesters are synthesized via ring‐opening copolymerization of α‐methylene‐δ‐valerolactone and δ‐valerolactone. These polyesters 4a–c are mixed with ethyl methacrylate (EMA), 2‐hydroxyethyl methacrylate (HEMA), and α‐methylene‐δ‐valerolactone (α‐MVL), respectively. Then, crosslinking is carried out by free radical polymerization initiated by an azo‐initiator. A second glass transition is found with incorporation of HEMA and α‐MVL. These findings indicate the formation of phase‐separated polyester blocks crosslinked with the poly(meth)‐acrylic‐segments, respectively poly(α‐methylene‐δ‐valerolactone) segments.
The homo‐ and copolymerizations of 1,3‐butadiene and isoprene are examined by using neodymium isopropoxide [Nd(Oi‐Pr)3] as a catalyst, in combination with a methylaluminoxane (MAO) cocatalyst. In the homopolymerization of 1,3‐butadiene, the binary Nd(Oi‐Pr)3/MAO catalyst works quite effectively, to afford polymers with high molecular weight ( ≈ 105 g mol‐1), narrow molecular‐weight distribution (MWD) (/ = 1.4–1.6), and cis‐1,4‐rich structure (87–96%). Ternary catalysts that further contain chlorine sources enhance both catalytic activity and cis‐1,4 selectivity. In the copolymerization of 1,3‐butadiene and isoprene, the copolymers feature high , unimodal gel‐permeation chromatography (GPC) profiles, and narrow MWD. Most importantly, the ternary Nd(Oi‐Pr)3/MAO/t‐BuCl catalyst affords a copolymer with high cis‐1,4 content in both monomer units (>95%).
Novel branched polyoxymethylene copolymers are synthesized by cationic copolymerization of 1,3,5‐trioxane (TOX) with 3‐(alkoxymethyl)‐3‐ethyloxetane (ROX) using BF3·Et2O as an initiator. Four oxetane derivatives with different side‐chain lengths (from 1 to 6 carbons) are tested for copolymerization. The copolymer composition is controlled by the feed ratio of ROX, and influenced by the chain length of alkyl group on ROX. The incorporation ratio and side‐chain length of the ROX unit have great influence on the thermomechanical properties and crystallinity of the copolymers.
Copolymerization of ethylene with 4‐penten‐1‐ol (4P1O) is conducted by using a half‐titanocene catalyst. The incorporation of 4P1O is high as approximately 10 mol%. The assignments of the 13C NMR spectrum and the analysis of the sequence distribution show the existence of not only the alternative structure but also the repeated 4P1O units. The product of the reactive ratios is calculated as ca. 2.
N‐vinylcaprolactam (NVCL) is modified via alkylation at the α‐position. The α‐substituents are ethyl (3‐ethyl‐1‐vinylcaprolactam), dodecyl (3‐dodecyl‐1‐vinylcaprolactam), octadecyl (3‐octadecyl‐1‐vinylcaprolactam), 1‐propanol (3‐(3‐hydroxy‐propyl)‐1‐vinylcaprolactam), and PEG3 bromide (3‐PEG3‐bromide‐1‐vinylcaprolactam). These monomers are homo‐ and copolymerized with N‐(4‐methylphenyl)maleimide by the free radical mechanism. The structures of the obtained polymers are characterized by means of 1H NMR and IR spectroscopy, gel permeation chromatography (GPC), and by use of differential scanning calorimetry (DSC) (Tg).
The synthesis of high‐aspect‐ratio (AR) CdSe (NRs) nanorods and their ordered assembly over large areas are reported. Long‐range ordering of hexagonal arrays of high‐AR NRs is achieved by a combination of controlled solvent evaporation and the use of an applied electric field. Vertically oriented assemblies of CdSe NRs functionalized with oligo‐ and polythiophene are also obtained. Aligned and oriented polythiophene CdSe NRs have potential applications in organic–inorganic hybrid bulk‐heterojunction photovoltaic devices.
Lamellar bending habits, as influenced by molecular‐chain chirality, in packing into dendritic spherulites with specific optical patterns are discussed using two model polymers of opposite chirality that are blended with a common polymer as examples: i) poly(l ‐lactic acid)/poly(butylene adipate) (PLLA/PBA) and ii) poly(d ‐lactic acid)/PBA (PDLA/PBA) blends. The bending habits in the spherulites of PLLA or PDLA blended with PBA are dictated by the chirality, specifically the counterclockwise and clockwise directions for the PLLA/PBA (50:50) and PDLA/PBA (50:50) blends, respectively. Straight lamellae in spiral lozenge crystals are packed with crystal aggregates of PLLA on top of the flat‐on lamellae plates acting as a basal plane during crystallization at Tc; spiral lozenge‐crystal frameworks are surrounded by needle‐like crystals resembling PBA crystals.
Dithiobenzoates are among the most popular agents for reversible addition‐fragmentation chain transfer (RAFT) polymerization. This is attributed to the better control over molecular weight and end‐group fidelity found in RAFT polymerization of methacrylates and methacrylamides. However, in polymerization of styrenes, acrylates, and acrylamides, their use has diminished, mainly in favour of trithiocarbonates, because of issues with retardation, as well as hydrolytic and thermal instability. This paper critically assesses developments in understanding the mechanism and kinetics of dithiobenzoate‐mediated RAFT polymerization from 2006 to 2013, with specific reference to the choice of reagents, polymerization conditions, side reactions, and factors leading to retardation.
A novel spacer‐free liquid crystalline polyrotaxane (LCPR) is synthesized by directly grafting 4‐phenylazobenzoyl chloride onto the hydroxyl of threaded α‐cyclodextrin (α‐CD) as the side‐chain. It is found that LCPR can form nematic LC phase above 180 °C or under the concentration of 5–0.2 wt% in dimethyl sulfoxide (DMSO) solution. The mechanisms of formation of thermotropic and lyotropic LC phase are proposed, respectively, which show the mobility of both threaded α‐CDs and substituted azo‐mesogens is responsible for the formation of LC phase. This mechanism is further demonstrated by the formation of crystalline phase under UV radiation, which is characterized by polarizing optical microphotograph and UV measurements.
An oxacyclophane framework is modified to include π‐conjugated segments positioned so as to allow an optimized face‐to‐face π‐stacking interaction between them. This unique architecture is first employed for the preparation of model compounds with defined interaction between two small molecular organic chromophores. The interaction allows facile through‐space energy transfer between the chromophores when they are held in the appropriate geometry. The oxacyclophane is thus employed in a polymer with consecutive short stretches of phenylene ethynylene such that polymer chain conjugation requires through‐space interaction between segments rather than the through‐bond π‐conjugation that typifies traditional conjugated polymers. The extent of the through‐space interactions along the polymer backbone is explored through photophysical measurements, calculations, X‐ray diffraction, and comparison with a variety of model and control materials.
An N‐vinylimidazole‐based monomer carrying an adamantyl group, (1‐vinyl‐2‐yl)methyladamantan‐1‐ylcarbamate ( 3 ), is synthesized. The terpolymerization with N‐vinylimidazole ( 4 ) and 1‐vinyl‐2‐(hydroxymethyl)imidazole ( 2 ) yields terpolymers ( 5a–b ) with high upper critical solution temperature (UCST)‐type transitions in water. The solubility can be influenced by the addition of various amounts of randomly methylated β‐cyclodextrin (RAMEB‐CD). It is found that supramolecular host/guest interaction clearly controls the solution behavior.
Electron‐acceptor units, combined with bithiophene substituted with flexible chains end‐functionalized with cross‐linkable moieties, provide soluble donor‐acceptor‐donor (DAD) π‐conjugated oligomer‐type molecules with cross‐linking ability and broad absorption in the visible spectrum. A study on the cross‐linking conditions of the new oligomers to yield insoluble polymer networks is presented, including conditions for obtaining polymer films over poly(3,4‐ethylenedioxythiophene):polystyrene sulfonate‐covered substrates. The combination of the DAD molecular design and cross‐linking functionality opens prospects for applications in solution‐processed small‐molecule solar cells with morphologically‐stable organic layers.
In the current investigation, nanocomposites containing a β‐nucleated poly(propylene‐co‐ethylene) (PPR) matrix filled with untreated (SiO2) and methacrylate‐modified silica nanoparticles (SiO2‐MAA) are prepared. Transmission electron microscopy (TEM) reveals the improvement in the quality of dispersion due to the surface modification of the nanoparticles. Also, from differential scanning calorimetry (DSC) and X‐ray diffraction (XRD), it is found that the β‐nucleating agent and silica nanoparticles work synergistically in order to increase the relative β‐content in the nanocomposite samples. The thermal stability of each samples is evaluated by means of thermogravimetric analysis (TGA) and the enhancement of the thermal stability of the nanocomposites is attributed to the nanoconfinement of the macromolecular chains caused by the presence of the fillers.
A novel polymer membrane ( TPP‐M ) with strong light harvesting ability within the entire visible‐ light spectrum has been prepared, in which the meso‐tetrakis(4‐cyanophenyl) porphyrin ( TPP‐1 ) as a functional unit is highly crosslinked through an aromatic nitrile trimerization reaction. The designed triazine framework controls the size of the π‐conjugation and retains the excellent photophysical properties of monomeric porphyrin, such as strong absorption and high singlet oxygen quantum yield. Due to these excellent photophysical properties and low solubility in common organic solvents, polyporphyrin membranes, as efficient singlet oxygen (1O2) sensitizers, could be easily recycled and reused for the photo‐oxidation of 1,5‐dihydroxynaphthalene (DHN).
Various biobased copolyesters composed of l ‐lactic acid (LLA) and side‐chain‐substituted lactic acids (SLAs) with high molecular weight and LLA‐rich composition are synthesized by direct solution polycondensation. Glycolic acid, 2‐hydroxyisobutyric acid, (S)‐2‐hydroxy‐3‐methylbutanoic acid (LVOH), and (S)‐2‐hydroxy‐4‐methylpentanoic acid (LLOH) are chosen as SLAs. Wide‐angle X‐ray diffraction (WAXD) and small‐angle X‐ray scattering (SAXS) reveal that the substituent size of the SLAs determines whether or not SLA units are included in crystallites of the LLA sequences. Unlike poly(l ‐lactic acid), tensile necking is seen in the copolymers with 2 mol% LVOH and with 6 mol% LLOH. Enzymatic degradation is accelerated with increasing SLA content. Especially for 6 mol% LLOH, the SLA introduction improves both the mechanical properties and the enzymatic degradability.
Synthesis of a multiblock copolymer composed of cis‐1,4‐polybutadiene (PBd) segments and poly(3‐buten‐1‐ol) segments is performed via successive hydroboration and oxidation of cis‐1,4/syn‐1,2‐multiblock PBd. The ratio of functionalization can be controlled by changing the amount of the borane reagent. The obtained polymer shows two distinctive glass‐transition temperatures, which correspond to the cis‐1,4‐PBd block and the poly(3‐buten‐1‐ol) block. These thermal properties clearly show that the functionalization of the PBd proceeds keeping the elastic property derived from cis‐1,4 segment.
Truxene–acridine‐1,8‐dione derivatives ( Tr_AD ) are proposed as new photoinitiators of polymerization under very soft irradiation (by a household halogen lamp), as well as laser‐diode exposure at 405 nm. They exhibit a strong absorption around 380 nm. The Tr_AD /diphenyl iodonium salt/9‐vinylcarbazole combination is able to promote the ring‐opening polymerization of an epoxide, whereas the Tr_AD /alkyl halide/amine system is very efficient in initiating the radical photopolymerization of an acrylate. Excellent polymerization profiles are obtained. Acrylate/epoxide blends are also easily polymerized. These Tr_ADs in the three‐component systems behave as photocatalysts according to oxidative cycles. The mechanisms are discussed for the different multicomponent initiating systems.
New thiophene derivatives (THs) are prepared and proposed here as new photoinitiators in combination with an iodonium salt for the cationic polymerization of vinylethers. They contain electron donor and electron acceptor (D–A) moieties and exhibit red‐shifted absorption spectra. They allow the use of a long‐wavelength excitation at 532 nm using a laser diode. Irradiation from a green light‐emitting diode (LED) at 514 nm can also be used. The high reactivity upon irradiation from the low‐intensity green LED highlights the high reactivity of the proposed structures. Interesting polymerization profiles (with conversions up to 70%) are obtained. The initiation step mechanisms are analyzed by electron spin resonance (ESR), fluorescence measurements, steady‐state photolysis, and laser flash photolysis experiments.
Four‐arm poly(l ‐2‐hydroxybutanoic acid) [P(L‐2HB)]/poly(d ‐lactic acid) (PDLA) blends are phase‐separated to form P(L‐2HB)‐rich and PDLA‐rich domains. Hetero‐stereocomplex (HTSC) crystallization should occur at the interface of two types of domains. The crystallization temperature ranges, wherein HTSC crystallites, P(L‐2HB), and PDLA homocrystallites are crystallizable in the star‐shaped 4‐arm P(L‐2HB)/PDLA blends, are much narrower than those reported for linear 1‐arm P(L‐2HB)/PDLA blends, indicating that the star‐shaped architecture disturbs the isothermal crystallization of the blends. Exclusive HTSC crystallization is not observed for the star‐shaped 4‐arm blends during isothermal crystallization in marked contrast with the result reported for the linear 1‐arm blends.
Poly(methyl methacrylate)‐block‐poly(4‐vinylpyridine), polystyrene‐block‐poly(4‐vinyl pyridine), and poly(ethylene glycol)‐block‐poly(4‐vinylpyridine) block copolymers are synthesized by successive atom transfer radical polymerization (ATRP), single‐electron‐transfer nitroxide‐radical‐coupling (SET‐NRC) and nitroxide‐mediated polymerization (NMP). This paper demonstrates that this new approach offers an efficient method for the preparation of 4‐vinylpyridine‐containing copolymers.
下载免费PDF全文