可控自由基聚合与其它活性聚合方法结合制备嵌段共聚物

可控自由基聚合与其它聚合方法结合,可以制备多种类型的嵌段共聚物,因此得到了广泛关注。本文着重介绍可控自由基聚合与离子开环聚合、阴离子聚合、烯类单体的阳离子聚合及其它活性聚合方法结合制备嵌段共聚物的研究现状和进展。     

Controlled Positioning of Activated Ester Moieties on Well‐Defined Linear Polymer Chains

The successful sequence‐controlled installation of an activated ester using a newly designed monomer pentafluorophenyl 4‐maleimidobenzoate is demonstrated. Pentafluorophenyl 4‐maleimidobenzoate is kinetically installed at different stages of a nitroxide‐mediated polymerization, namely, near the α‐chain end and in the middle of a PS chain. In addition, successful installation of apolar and polar functional groups is achieved via post‐polymerization functionalization, which demonstrated the versatility of the synthesis of a universal precursor for locally functionalized polymers.     

Orthogonal Cationic and Radical RAFT Polymerizations to Prepare Bottlebrush Polymers

An orthogonal combination of cationic and radical RAFT polymerizations is used to synthesize bottlebrush polymers using two distinct RAFT agents. Selective consumption of the first RAFT agent is used to control the cationic RAFT polymerization of a vinyl ether monomer bearing a secondary dormant RAFT agent, which subsequently allows side‐chain polymers to be grafted from the pendant RAFT agent by a radical‐mediated RAFT polymerization of a different monomer, thus completing the synthesis of bottlebrush polymers. The high efficiency and selectivity of the cationic and radical RAFT polymerizations allow both polymerizations to be conducted in one‐pot tandem without intermediate purification.     

End‐Functionalized Palladium SCS Pincer Polymers via Controlled Radical Polymerizations

A direct and facile route toward semitelechelic polymers, end‐functionalized with palladated sulfur–carbon–sulfur pincer (Pd^II‐pincer) complexes is reported that avoids any post‐polymerization step. Key to our methodology is the combination of reversible addition‐fragmentation chain‐transfer (RAFT) polymerization with functionalized chain‐transfer agents. This strategy yields Pd end‐group‐functionalized materials with monomodal molar mass dispersities (Đ ) of 1.18–1.44. The RAFT polymerization is investigated using a Pd^II‐pincer chain‐transfer agent for three classes of monomers: styrene, tert‐butyl acrylate, and N‐isopropylacrylamide. The ensuing Pd^II‐pincer end‐functionalized polymers are analyzed using ¹H NMR spectroscopy, gel‐permeation chromatography, and elemental analysis. The RAFT polymerization methodology provides a direct pathway for the fabrication of Pd^II‐pincer functionalized polymers with complete end‐group functionalization.

     

Stereogradient Polymers Formed by Controlled/Living Radical Polymerization of Bulky Methacrylate Monomers

Life RAFT : A bulky methacrylate monomer, triphenylmethyl methacrylate (TrMA), was polymerized with reversible addition–fragmentation chain transfer (RAFT) agents. Stereogradient polymers in which the isospecificity increased spontaneously as the monomer concentration decreased were formed by a polymerization–depolymerization equilibrium that can convert a less stable growing polymer terminal into a more stable form (see picture).

     

稀土有机化合物在催化聚合反应中的应用

本文综述了稀土有机化合物作为单组份催化剂用于聚合反应的进展。它包括：烯烃和α－烯烃聚合、甲基丙烯酸酯类的均聚合及共聚合、乙与人烯酸酯及含官能团烯的共聚合、内醌的开环均聚合及共聚合等。茂基稀土氢化物是乙烯聚合的高活性催化剂，对茂基结构作一定调节，可催化α－烯烃的规整聚合。这类氢化物、茂基稀土甲基化合物和二价稀土配合物都是人烯酸酯类及内酯聚合的有效催化剂，并显示活性聚合特点给出高分子量、窄分子量分布的     

连续流离子聚合

微流场技术因其良好的传质传热性能应用于各种机理的聚合反应中,引起了学术界和工业界的广泛关注。本文聚焦于高度放热的离子聚合,总结了近年来不同单体连续流阴/阳离子聚合的研究进展。微反应器在改善离子聚合苛刻的反应条件、精确地控制聚合产物分子量及其分布、调控共聚物结构等方面显示出釜式反应器无法比拟的优势。此外,本文对连续流离子聚合的工业化应用前景进行了探讨和展望。     

Data Reconciliation and Control in Styrene-Butadiene Emulsion Polymerizations

Summary: A nonlinear model-based predictive control (NLMPC) method was developed using a First Principles model of an emulsion copolymerization of carboxylated styrene butadiene rubber (XSBR). Copolymer composition, conversion and average molecular weights of the copolymer were chosen as the controlled variables due to their influence on the final product properties and quality. These properties, however, are rarely measured in-line due to the operational difficulties associated with their measurement. For this reason a soft-sensor using reaction calorimetry techniques was developed and used to infer reaction conditions, rates, species concentrations and polymer properties in a industrial scale emulsion polymerization reactor.     

Mechanistic Transformations Involving Radical and Cationic Polymerizations

Mechanistic transformation approach has been widely applied in polymer synthesis due to its unique feature combining structurally different polymers prepared by different polymerization mechanisms.Reported methods for the formation of block and graft copolymers through mechanistic transformation involve almost all polymerizations modes.However,certain polymerization processes require extensive purification processes,which can be time-consuming and problematic.Recent developments on controlled/living polymerizations involving radical and cationic mechanisms with the ability to control molecular weight and functionality led to new pathways for mechanistic transformations.In this mini-review,we systematically discussed relevant advances in the field through three main titles namely(i)from radical to cationic mechanism,(ii)from cationic to radical mechanism,and(iii)application of specific catalyst systems for both radical and cationic polymerizations.     

Zirconium Allyl Complexes as Participants in Zirconocene‐Catalyzed α‐Olefin Polymerizations

In a search for the hitherto elusive catalyst resting state(s) of zirconocene‐based olefin polymerization catalysts, a combination of UV/Vis and NMR spectrometric methods reveals that polymer‐carrying cationic Zr allyl complexes make up about 90 % of the total catalyst concentration. Other catalyst species that take part in the polymerization process have to be generated from this allyl pool into which they appear to relapse rather frequently.     

Solvent Influence on Propagation Kinetics in Radical Polymerizations Studied by Pulsed Laser Initiated Polymerizations

The influence of the reaction medium (organic solvents, water, ionic liquids, supercritical CO₂) on the propagation rate in radical polymerizations has very different causes, e.g., hindered rotational modes, hydrogen bonding or electron pair donor/acceptor interactions. Depending on the origin of the solvent influence propagation rate coefficients, k_p, may be enhanced by up to an order of magnitude associated with changes in the pre‐exponential or the activation energy of k_p. In contrast, non‐specific interactions, size and steric effects lead to rather small changes in the vicinity of the radical chain end and are reflected by modest variations in k_p.

     

Enhancing Temporal Control and Enabling Chain‐End Modification in Photoregulated Cationic Polymerizations by Using Iridium‐Based Catalysts

Gaining temporal control over chain growth is a key challenge in the enhancement of controlled living polymerizations. Though research on photocontrolled polymerizations is still in its infancy, it has already proven useful in the development of previously inaccessible materials. Photocontrol has now been extended to cationic polymerizations using 2,4,6‐triarylpyrylium salts as photocatalysts. Despite the ability to stop polymerization for a short time, monomer conversion was observed over long dark periods. Improved catalyst systems based on Ir complexes give optimal temporal control over chain growth. The excellent stability of these complexes and the ability to tune the excited and ground state redox potentials to regulate the number of monomer additions per cation formed allows polymerization to be halted for more than 20 hours. The excellent stability of these iridium catalysts in the presence of more nucleophilic species enables chain‐end functionalization of these polymers.     

Click polymerization: The aurora of polymer synthetic methodology

As an emerged efficient polymerization methodology, the click polymerization plays a significant role in the area of polymer and materials sciences. Similar to the click reaction, the click polymerization enjoys the advantages of high efficiency, mild reaction conditions, and high regio- and stereo-selectivity etc. In this highlight, we summarize the recent progress on click polymerizations, with focus on the alkyne-based ones. The challenges and opportunities in this area are also briefly discussed. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 616–621     

pH‐Regulated Selectivity in Supramolecular Polymerizations: Switching between Co‐ and Homopolymers

A strategy is presented to regulate the selectivity in aqueous supramolecular polymerizations by changes in pH. In neutral buffered conditions, oppositely charged phenylalanine‐based dendritic peptide amphiphiles self‐assemble into (A?B)_n alternating copolymers of low polydispersity when mixed in a 1:1 comonomer feed ratio. Via pH switch of the glutamic acid and lysine side chains, attractive Coulomb interactions in the coassembled materials are screened and selective polymerization occurs to form (A)_n homopolymers of the acidic comonomer at low pH and (B)_n homopolymers of the basic comonomer at high pH, while the complementary comonomer is released during the transition. Reversible switching is demonstrated between these three different polymeric states, which were characterized by CD and fluorescence spectroscopy, using a peptide based minimalistic fluorophore/quencher pair, and transmission electron microscopy.     

Vanadium(V) complexes containing tetradentate amine trihydroxy ligands as catalysts for copolymerization of cyclic olefins

A series of vanadium(V) complexes bearing tetradentate amine trihydroxy ligands [NOOO], which differ in the steric and electronic properties, have been synthesized and characterized. Single crystal X‐ray analysis showed that these complexes are five or six coordinated around the vanadium center in the solid state. Their coordination geometries are octahedral or trigonal bipyramidal. In the presence of Et₂AlCl, these complexes have been investigated as the efficient catalysts for ethylene polymerization and ethylene/norbornene copolymerization at elevated reaction temperature and produced the polymers with unimodal molecular weight distributions (MWDs), indicating the single site behaviors of these catalysts. Both the steric hindrance and electronic effect of the groups on the tetradentate ligands directly influenced catalytic activity and the molecular weights of the resultant (co)polymers. Other reaction parameters that influenced the polymerization behavior, such as reaction temperature, ethylene pressure, and comonomer concentration, are also examined in detail. Furthermore, high catalytic activities of up to 3.30 kg polymer/mmol_V·h were also observed when these complexes were applied to catalyze the copolymerization of ethylene and 5‐norbornene‐2‐methanol, producing the high‐molecular‐weight copolymers (M_w = 157–400 kg/mol) with unimodal MWDs (M_w/M_n = 2.5–3.0) and high polar comonomer incorporations (up to 12.3 mol %). © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1122–1132, 2010     

Controlled anionic synthesis of star‐shaped polystyrene by the incremental addition of divinylbenzene

Star polystyrenes were synthesized from polystyryllithium with an incremental procedure in which equally divided portions of divinylbenzene (DVB) were added periodically. When the addition of DVB was repeated, the content of the unreacted polystyryllithium dramatically decreased, and complete conversion was readily achieved. In the conventional linking reaction, however, in which all the required amounts of DVB were added at once, there was an incomplete conversion of the arm polymer. The arm number of star polymers also continuously increased upon the subsequent addition of DVB. The incremental‐addition method effectively synthesized star polystyrene, minimizing uncoupled polystyrene and reproducibly controlling the arm number of star polystyrene without the formation of gel polymers. The intrinsic viscosity of star polystyrene was measured to determine the highly branched structure of star polystyrene prepared by incremental or one‐shot addition. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 870–878, 2005