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1.
Yohann Guillaneuf Davy‐Louis Versace Denis Bertin Jacques Laleve Didier Gigmes Jean‐Pierre Fouassier 《Macromolecular rapid communications》2010,31(21):1909-1913
New photosensitive alkoxyamines have been designed using molecular orbital calculations to improve the selective C O versus N O cleavage. The targeted light‐sensitive alkoxyamine is synthesized in one step and its reactivity under UV has been investigated using both ESR and LFP. The ability of this alkoxyamine to control the photopolymerization of n‐butyl acrylate is evidenced through a process called nitroxide‐mediated photopolymerization NMP2. The selected alkoxyamine is finally used to prepare covalently bonded multilayered micropatterns. This original application highlights the high potential of this technique for some specific applications that require spatial control.
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This review article describes the preparation of polymer brushes by nitroxide‐mediated radical polymerization using either the ‘grafting to’ or the ‘grafting from’ approach. The use of TEMPO as a classical initiator is intensively described. More sophisticated nitroxides are also included in the discussion. Brush formation on flat surfaces such as wafers and also on particles is reported. Finally, some applications of polymer brushes are presented.
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Moon Suk Kim Kwang Su Seo Gilson Khang Hai Bang Lee 《Macromolecular rapid communications》2005,26(8):643-648
Summary: The polymerization of ε‐caprolactone (CL) in the presence of HCl · Et2O by an activated monomer mechanism was performed to synthesize diblock or triblock copolymers composed of poly(ethylene glycol) (PEG) and poly(ε‐caprolactone) (PCL). The obtained PCLs had molecular weights close to the theoretical values calculated from the CL to PEG molar ratios and exibited monomodal GPC curves. We successfully prepared PEG and PCL block copolymers by a metal‐free method.
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Jun‐Ting Xu Yan‐Qin Zhao Qi Wang Zhi‐Qiang Fan 《Macromolecular rapid communications》2005,26(8):620-625
Summary: Exfoliated and intercalated polyethylene/montmorillonite (PE/MMT) nanocomposites with high MMT content were prepared by in situ polymerization. The isothermal crystallization kinetics of the nanocomposites were analyzed with Lauritzen–Hoffman regime theory. Regime III crystallization, which is difficult to observe in linear polyethylene, appears in the PE/MMT nanocomposites. The broader temperature range of regime III crystallization in PE/MMT nanocomposites shows that the mobility and reptation ability of the PE chains are greatly reduced by the MMT, especially in the intercalated nanocomposite.
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Michael J. Bojdys Nikolai Severin Jürgen P. Rabe Andrew I. Cooper Arne Thomas Markus Antonietti 《Macromolecular rapid communications》2013,34(10):850-854
The carbon nitride poly(triazine imide) with intercalated bromide ions is a layered, graphitic material of 2D covalently bonded molecular sheets with an exceptionally large gallery height of 3.52 Å due to the intercalated bromide anions. The material can be cleaved both mechanically and chemically into thin sheets and scrolls analogous to the carbon‐only systems graphite and graphene.
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1,5‐Hydrogen transfer reactions in methyl acrylate and butyl acrylate free‐radical polymerization are studied using quantum chemistry and transition state theory to estimate the kinetic parameters (ktr, Ea, and A) with tetrameric radicals, requiring a number of atoms that ranks among the largest polymeric mimics to date. A two‐step transformation accounted for the overall reaction: rotation from an extended conformation to a coiled conformation and abstraction of the fifth hydrogen atom by the end‐chain radical. UB3LYP/6‐31G(d) was used for geometry optimization, validation of the transition states, and calculation of frequencies that were used to obtain thermodynamic properties. The more computationally demanding level of theory, MPWB1K/6‐31G(d,p), was used for calculation of the electronic energy.
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Summary: Novel alternating polyketone‐based polymers bearing pendant saccharide units that are accessible by polymerization catalysis are presented. The materials were synthesized by polymerization of carbon monoxide and α‐olefins containing protected glucose or N‐acetyl glucosamine residues. The dicationic PdII bis(phoshine) complex [Pd(dppp)(NCCH3)2](BF4)2 was used as a catalyst precursor. An O‐deacetylation of the copolymers afforded materials with amphiphilic character.
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Summary: Nanocomposites were formulated by curing a sonicated mixture of epoxy resin, C18 clay, and acrylic rubber dispersants. At 5.5 phr (parts per hundred) organoclay loading and a rubber concentration of 15 phr, the tensile‐failure strain of the nanocomposite was found to be higher than that of epoxy nanocomposite, rubber‐dispersed epoxy, and pristine epoxy. A plausible mechanism for improvement of the failure strain of nanocomposites is proposed.
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David Briers Lieven De Cremer Guy Koeckelberghs Stijn Foerier Thierry Verbiest Celest Samyn 《Macromolecular rapid communications》2007,28(8):942-947
A new chromophore, C1 , based on a similar DπA‐structure as in the FTC ‐chromophore but with a hydroxyalkyl spacer perpendicular to the direction of the dipole moment was synthesized. Both chromophores and the CLD ‐chromophore were used to prepare high Tg nonlinear optical vinyl polymers. The influence of the position of the spacer on the DπA‐system on the NLO response of the resulting polymers was investigated.
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Junpei Wakamatsu Masahiro Kawasaki Per B. Zetterlund Masayoshi Okubo 《Macromolecular rapid communications》2007,28(24):2346-2353
Nitroxide‐mediated polymerizations of styrene in microemulsion have been carried out at 125 °C using the cationic surfactant tetradecyltrimethylammonium bromide and the nitroxides 2,2,6,6‐tetramethylpiperidinyl‐1‐oxy (TEMPO) and N‐tert‐butyl‐N‐[1‐diethylphosphono‐(2,2‐dimethylpropyl)] nitroxide (SG1). TEMPO‐mediated polymerizations were extremely slow, with large particles (dn = 39–129 nm) and broad molecular weight distributions (MWDs). The origin of the broad MWDs was likely significant alkoxyamine decomposition and differing diffusion rates of monomer and low MW alkoxyamines (and nitroxide) between monomer‐swollen micelles and polymer particles. SG1‐mediated polymerizations proceeded at higher rates, resulting in nanoparticles (dn = 21–37 nm) and lower than for TEMPO.
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Jiaxi Cui Omar Azzaroni Arnzazu del Campo 《Macromolecular rapid communications》2011,32(21):1699-1703
Photolabile polymer brushes with tailored length containing a photoremovable protecting group (NVOC) are prepared via the SI‐ATRP method. Upon light irradiation, the NVOC group is removed to generate controlled densities of free amine groups (PAMA) randomly distributed along the brush. The presence of the ionizable groups induces a photo‐triggered swelling response. The swelling degree can be tuned by the irradiation dose. A dual (light and pH), tunable response is demonstrated.
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Summary: A novel method combining RAFT polymerization with pulsed‐laser initiation for determining chain‐length dependent termination rate coefficients, kt, is presented. Degenerative chain‐transfer in RAFT enables single‐pulse pulsed‐laser polymerization (SP‐PLP) traces to be measured on systems with a narrow radical distribution that remains essentially unchanged during the experiment. SP‐PLP‐RAFT experiments at different polymerization times allow for determining kt as a function of chain length via classical kinetics assuming chain‐length independent kt.
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Helena Bergenudd Mats Jonsson Eva Malmstrm 《Macromolecular theory and simulations》2011,20(9):814-825
Kinetic simulations are reported, where the ATRP equilibrium constant KATRP is varied and the rates and degree of control in different ATRP systems are evaluated. The apparent rate constant kapp increases with increasing KATRP, but a maximum is reached. The limit of control is passed before the maximum, i.e. when KATRP is increased further, apparent first‐order kinetics and well‐controlled molecular weights will no longer be obtained. The equilibrium constant at which the limit of control is reached varies linearly with the propagation rate constant. This enables the design of well controlled ATRP systems. The influence of the conversion and chain length dependence of the termination rate constant on the simulation results is discussed.
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Summary: A novel experimental set‐up has been devised to measure simultaneously, in real time, the conversion and shrinkage of multi‐acrylates during photopolymerization. The data show that the current practice of assigning the excess volume entirely as excess free volume is inappropriate as this leads to an increasing fractional free volume with conversion. We propose to partition the excess volume into free and occupied volume components. The new model produces satisfactory results.
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Tough networks are prepared by photo‐crosslinking high‐molecular‐weight DLLA and TMC macromers. These amorphous networks exhibit tunable thermal and mechanical properties and have excellent shape‐memory features. Variation of the monomer ratio allows adjustment of Tg between approximately ?13 and +51 °C. The elastic moduli at room temperature can be varied between 4.5 and 2730 MPa. The crosslinks allow the networks to return to their original shape after deformation. 60:40 DLLA:TMC networks have Tg values between room temperature and body temperature, with mechanical properties at body temperature close to soft tissues. Several medical devices are prepared from these networks.
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Mn(salen)Cl was applied as a low‐cost catalyst for the formation of alkoxyamines from nitroxides and substituted styrenes. These “unimolecular initiators” for nitroxide‐mediated radical polymerization (NMRP) were synthesized using 2,2,6,6‐tetramethyl‐1‐piperidine‐1‐oxyl and 2,2,5‐trimethyl‐4‐phenyl‐3‐azahexane‐3‐oxyl. Functionalized alkoxyamines were obtained from 4‐vinylbenzyl chloride and 4‐vinylbenzyl alcohol. The divinyl compound 1,2‐bis(4‐vinylphenyl)ethane was converted to an alkoxyamine monomer and to bisaminooxy compounds, which can be used as “biradical initiators” for NMRP.
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Harald Kirsebom Bo Mattiasson Igor Yu. Galaev 《Macromolecular rapid communications》2010,31(12):1095-1100
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.