PRECISE SYNTHESIS OF OLEFIN BLOCK COPOLYMERS USING A SYNDIOSPECIFIC LIVING POLYMERIZATION SYSTEM

This feature article summarizes the synthesis of novel olefin block copolymers using fast syndiospecific living homo- and copolymerization of propylene, higher 1-alkene, and norbornene with ansa-fluorenylamidodimethyltitanium- based catalyst according to the authors＇ recent results. The catalytic synthesis of monodisperse polyolefin and olefin block copolymer was also described using this living system.

Enantiomer-selective Living Polymerization of rac-Phenyl Isocyanide Using Chiral Palladium Catalyst

We report the polymerization of phenyl isocyanides with the chiral palladium（II） initiating system. The resulting polymers with optically active properties were obtained by polymerization of the racemic isocyanide monomer （rac-1）, and enantiomerically unbalanced polymerization of the monomer was found, providing substantial evidence for the enantiomer-selective polymerization of rac- 1 mediated through chiral catalyst. A comparison between the enantiomerically pure monomers, 4-isocyanobenzoyl-L-alanine decyl ester （1 s） and 4-isocyanobenzoyl-D-alanine decyl ester （1 r）, revealed a drastic discrepancy in the reactivity ratio of their homopolymerizations. It turned out that the monomer reactivity ratio of ls was higher than that of lr with chiral ligands. The results clearly demonstrated the inclination for incorporation of the ls enantiomer during the polymerization process and thus resulted in the enantiomer-selective polymerization in this system. The effects of the catalyst chirality on the optically active properties of polymerization were investigated, and it was concluded that the formation of higher-ordered conformation with a handed helicity might be attributed to the chiral induction of chiral palladium（II） catalyst. Moreover, the polymers obtained through the enantiomer-selective polymerization of the enantiomerically pure monomer were with a significant improvement of the optical activity if the chirality of the monomer and the catalyst matched with each other.

Living Polymerization of 1,3-Butadiene Catalyzed by Half-titanocene Complex Bearing Dibenzhydryl-substituted Aryloxide Ligand

Half-titanocene complexes bearing dibenzhydryl-substituted aryloxide ligands （2a-2d） were prepared. Among them, 2e adopted a three-legged distorted tetrahedral geometry evidenced by X-ray crystallography. The poly-1,3-butadiene with high molecular weight and narrow molecular weight distribution was obtained by using these complexes as the catalysts activated with methylaluminoxane （MAO）. The catalytic activities of the complexes depended on their structures. The Ti-- O--C bond in the complexes with large angle afforded them with higher activity, while Cp＊-based complexes exhibited lower activities than the Cp-based analogues. The activity of complex increased with increasing the polymerization temperature while the selectivity remained no change, indicating the high thermal stability. Furthermore, the polymerization of 1,3-butadiene catalyzed by 2a/MAO at 0 ℃ has been found in a living fashion.

Studies on the Self-condensing Vinyl Living Radical Polymerization of a Novel Acrylate Inimer

A novel acrylate inimer, 2-（2-chloroacetyloxy） ethyl acrylate, was prepared by the reaction of 2-hydroxyethyl acrylate with chloroacetyl chloride in the presence of triethylamine. The self-condensing vinyl living radical polymerization of the inimer was studied and the hyperbranched macromolecules containing ester linkages on their backbone were prepared. All the polymerization products were characterized by 1H NMR. The polymerization degree and the branching parameter were calculated based on the 1H NMR spectra. It has been shown that this inimer exhibits a very distinctive polymerization behavior. Similar to step-growth polymerization, the polymerization degree of the products formed increased exponentially during the early stage of the polymerization, and then the increasing rate slowed down. However, the inimer remained present throughout the polymerization consistent with conventional free radical polymerization. Also, if much longer polymerization time was used, the polymerization system would become gel due to the crosslinking reaction derived from radical-radical recombination. As a result of the unequal reactivity of -CH2Cl and >CHCl, an almost linear product was obtained at a molar ratio of bipy to inimer=0.05, while a relatively high ratio of bipy to inimer 1 favored the formation of the branched structure. The macromolecules formed at a high ratio of bipy to inimer 1 exhibited an excellent solubility in organic solvents such as acetone.

SYNTHESIS OF BLOCK COPOLYMER BY INTEGRATED LIVING ANIONIC POLYMERIZATION-ATOM TRANSFER RADICAL POLYMERIZATION(ATRP)

Alpha-trichloroacetoxy terminated polystyrene oligomer (PS-CH2CH2OCOCCl3) and poly-(styrene-b-butadiene) oligomer [P(S-b-B)-CH2CH2OCOCCl3)] were synthesized by living anionic polymeri-zation using n-butyllithium as initiator. Then the PS-CH2CH2OCOCCl3 (PS-Cl-3) or P(S-b-B)-CH2CH2O-COCCl3 (PSB-Cl-3) was used as the macroinitiator in the polymerization of(meth)acrylates in the presence of CuX/bpy. AB diblock and ABC triblock copolymers were prepared by the integrated living anionic polymerization (LAP)-atom transfer radical polymerization (ATRP). The structures of the PSB-Cl-3 and the P(S-b-MMA) were identified by FTIR and H-1-NMR spectrum, respectively. A new way to design block copolymers (the combination of LAP and ATRP) was developed.

Impact of Molecular Shape on Supramolecular Copolymer Synthesis in Seeded Living Polymerization of Perylene Bisimides

Supramolecular polymerization properties have been studied for a series of perylene bisimide(PBI)dyes containing identical hydrogen-bonding amide groups in imide positions but variable number or size of alkoxy substituents in bay-positions.

Chemoselective and Living/Controlled Polymerization of Alkenyl Methacrylates by the Phosphonium Ylide/Organoaluminum Lewis Pairs

Chemoselective,living/controlled polymerizations of allyl methacrylate(AMA) and vinyl methacrylate(VMA) with/without methyl methacrylate(MMA) by using the phosphonium ylide/organoaluminum based Lewis pairs(LPs) have been realized.The P-ylide-2/AIMe(BHT)_(2)(Pylide-2=Ph_(3)P=CHMe and BHT=2,6-iBu_(2)-4-MeC_(6)H_(2)O) was demonstrated to be superior by which homopolymers PAMAs(M_(n)=27.6-111.5kg/mol and ■=1.14-1.25) and PVMAs(M_(n)=28.4-78.4 kg/mol and ■=1.12-1.18) and block copolymers PMMA-b-PAMA,PAMA-b-PVMA,PAMA-bPMMA,PMMA-b-PAMA-b-PMMA,PAMA-b-PMMA-b-PAMA,and PAMA-b-PVMA-b-PAMA were synthesized.In the polymerizations,all of the monomers were reacted by the conjugated ester vinyl groups leaving intactly the nonconjugated acryloxy groups.The pendant acryloxy groups attached to the main chain enable further to post-functionalization by the AIBN-induced radical "thiol-ene" reaction using PhCH_(2)SH.The thiolether side group-containing polymers PAMA-SCH_(2)Ph and PAMA-SCH_(2)Ph-b-PMMA-b-PAMA-SCH_(2)Ph were thus prepared.

GROUP TRANSFER POLYMERIZATION OF ETHYL ACRYLATE WITH LEWIS ACID CATALYST

This paper reports the kinetics of group transfer polymerization (GTP)of ethyl acrylate (EA)with zinc iodide catalyst in 1,2-dichloroethane using dimethyl ketene methyl trimethylsilyl acetal (MTS) as initiator at 0℃ and above 0℃. The amount of catalyst used was studied. When zinc iodide catalyst used is more than 10mol% relative to monomer, the rate of polymerization is proportional to the concentration of monomer, whereas zinc iodide catalyst used is less than 10 mol% of the monomer, the rate of polymerization is independent of the monomer concentration.In the GTP of EA an induction period was observed when the zinc iodide contents are less than l0mol%. If the reaction temperature is over 0℃, living species become unstable and diminish, leading to incomplete monomer conversion. The reaction curves equations are obtained. The polymers have narrow molecular weight distributions which are not changed as decreasing zinc iodide contents. The polydispersity is about 1.2.

AMPHIPHILIC STAR-BLOCK COPOLYMERS BY IODIDE-MEDIATED RADICAL POLYMERIZATION

Amphiphilic star-block copolymers composed of polystyrene and poly（acrylic acid） were synthesized by iodide- mediated radical polymerization. Firstly, free radical polymerization of styrene was carried out with AIBN as initiator and 1,1,1-trimethyolpropane tri（2-iodoisobutyrate） as chain transfer agent, giving iodine atom ended star-shaped polystyrene with three arm chains, R（polystyrene）3. Secondly, tert-butyl acrylate was polymerization using polystyrene obtained as macro-chain transfer agent, and star-block copolymer, R（polystyrene-b-poly（tert-butyl acrylate））3 with controlled molecular weight was obtained. Finally, amphiphilic star-block copolymer, R（polystyrene-b-poly（acrylic acid））3 was obtained by hydrolysis of R（polystyrene-b-poly（tert-butyl acrylate））3 under acidic condition.

Synthesis of α-Bromine-Terminated Polystyrene Macroinitiator and Its Initiation of MMA Polymerization by ATRP

In the present paper the synthesis of block copolymers via the transformation from living anionic polymerization (LAP) to atom transfer radical polymerization (ATRP) was described. α-Bromine-terminated polystyrenes(PStBr) in the LAP step was prepared by using n-BuLi as initiator, tetrahydrofuran (THF) as the activator, α-methylstyrene (α-MeSt) as the capping group and liquid bromine (Br_2) as the bromating agent. The effects of reaction conditions such as the amounts of α-MeSt, THF, and Br_2 as well as molecular weight of polystyrene on the bromating efficiency (BE) and coupling extent (CE) were examined. The present results show that the yield of PStBr obtained was more than 93. 8% and the coupling reaction was substantially absent. PStBr was further used as the macroinitiator in the polymerization of methyl-methacrylate (MMA) in the presence of copper (I ) halogen and 2, 2' -bipyridine (bpy) complexes. It was found that the molecular weight of the resulted PSt-b-PMMA increased linearly with the increase of the conversion of MMA and the polydispersity was 1. 2-1.6. The structures of PStBr and P(St-b-MMA) were characterized by ~1H NMR spectra.

Effect of solvent on the initiation mechanism of living anionic polymerization of styrene:A computational study

For living anionic polymerization(LAP),solvent has a great influence on both reaction mechanism and kinetics.In this work,by using the classical butyl lithium-styrene polymerization as a model system,the effect of solvent on the mechanism and kinetics of LAP was revealed through a strategy combining density functional theory(DFT)calculations and kinetic modeling.In terms of mechanism,it is found that the stronger the solvent polarity,the more electrons transfer from initiator to solvent through detailed energy decomposition analysis of electrostatic interactions between initiator and solvent molecules.Furthermore,we also found that the stronger the solvent polarity,the higher the monomer initiation energy barrier and the smaller the initiation rate coefficient.Counterintuitively,initiation is more favorable at lower temperatures based on the calculated results ofΔG_(TS).Finally,the kinetic characteristics in different solvents were further examined by kinetic modeling.It is found that in benzene and n-pentane,the polymerization rate exhibits first-order kinetics.While,slow initiation and fast propagation were observed in tetrahydrofuran(THF)due to the slow free ion formation rate,leading to a deviation from first-order kinetics.

SYNTHESIS AND POLYMERIZATION OF α-METHACRYLYOXYLETHYLOXYCARBONYLMETHYL-ω-(N,N-DIETHYLDITHIOCARBAMYL)POLYSTYRENE MACROMONOMERS

Polystyrene macromonomers with different molecular weight were prepared by radical polymerization of styrene(St) in benzene using β-methacryloxylethyl 2-N,N-diethyldithiocarbamylacetate (MAEDCA) as a monomer-iniferter.Characterization of the macromonomer by ~1H-NMR showed that the end groups were α-methacrylyoxylethyloxycarbonyl-methyl and ω-(N,N-diethyldithiocarbamyl). The macromonomer was difficult to homopolymerize, but it was easilycopolymerized with methyl methacrylate (MMA) initiated by AIBN to form graft copolymers (PMMA-g-PSt) with PStbranches randomly distributed along the PMMA backbone. Copolymerization reaction and the structure of the graft copolymers were strongly affected by M_n and concentration of the macromonomer. The composition and M_n of the purified graft copolymer were determined by ~1H-NMR and GPC analysis.

LIVING/CONTROLLED GRAFTING FROM POLYMER MICROSPHERES

A review is given of grafting-from methods using living polymerizations, with emphasis on grafting from polymermicrospheres using ATRP.

A NOVEL PHOTO-INITIATING SYSTEM FOR ATOM TRANSFER RADICAL POLYMERIZATION OF STYRENE

A novel photo-induced initiating system, 2,2-dimethoxy-2-phenylacetophenone (DMPA)/ferric tri(NN-diethyldithiocarbamate) [Fe(DC)(3)], was developed and used for the atom transfer radical polymerization (ATRP) of styrene in toluene. The polymerization proceeds with DMPA as photo-initiator, Fe(DC)(3) as catalyst and DC as a reversible transfer group, while the halogen and ligands are free. Well-defined PSt was prepared and the polymerization mechanism revealed by end group analysis belongs to a reverse ATRP. Block copolymer was prepared by using thus obtained PSt as macroinitiator and Fe(DC)(2) as catalyst under UV light irradiation via a conventional ATRP process.

Studies on Rate Enhancement of Polymerization in NMRP

In NMRP, the polymerization of MMA, the polymerization of St and the copolymerization of MMA with St were distinctly accelerated by the addition of a small amount of MN. The polymerization proceeds in a living fashion as indicated by the increase in molecular weight with the increase of time and conversion and a relatively low polydispersity. It has been found that the addition of MN results in a nearly one hundred times higher rate of the polymerization of MMA, a nearly twenty times higher rate of the polymerization of St and a nearly fifteen times higher rate of the copolymerization of St and MMA.

Research progress in the living/controlled polymerization of(meth)acrylate monomers by Lewis pair

Lewis pair polymerization(LPP)has demonstrated its unique advantages,such as high activity,high stability,and adjustable variability,towards the polymerization of(meth)acrylate monomers in comparison with the other polymerization techniques.The combination of Lewis acid(LA)and Lewis base(LB)to construct Lewis pairs(LPs)with appropriate Lewis basicity,Lewis acidity,and steric effects would significantly impact the polymerization process,including chain initiation,propagation,termination and chain transfer reaction,as well as polymerization manner of monomers.In this feature article,we briefly review recent progress made by our research group towards the living/controlled polymerization of(meth)acrylate monomers,which were accomplished by a series of newly designed LPs,including monofunctional LPs,dual-initiating LPs and intramolecular tethered trifunctional LP.This article is divided into three parts:(1)the development of monofunctional living/controlled LP polymerization system;(2)the design and preparation of dual-initiating LPs in synthesizing thermoplastic elastomers;(3)the application of intramolecular trifunctional LP to the synthesis of cyclic polymers.These developed LPPs have demonstrated their powerful capability in precise control over the molecular weight,molecular weight distribution,and monomer sequence as well as the topology of polymers.This review will serve as a good resource or guideline for researchers currently working in the area of LPP and for those who are interested in synthesizing new materials by LPP.

Real-time Monitoring of Living Cationic Ring-opening Polymerization of THF and Direct Prediction of Equilibrium Molecular Weight of Poly THF

A convenient real-time monitoring of monomer concentration during living cationic ring-opening polymerizations of tetrahydrofuran（THF） initiated with methyl triflate（Me OTf） has been developed for kinetic investigation and determination of equilibrium monomer concentration（[M]e） via in situ FTIR spectroscopy in combination with a diamond tipped attenuated total reflectance（ATR） immersion probe. The polymerization rate was first order with respect to monomer concentration and initiator concentration from the linear slope of ln（[M]0-[M]e）/（[M]-[M]e） versus polymerization time at different temperatures in various solvents. [M]e decreased linearly with initial monomer concentration while increased exponentially with increasing polymerization temperature. The equilibrium also strongly depends on solvent polarity and its interaction with monomer. The equilibrium polymerization time（te） decreased with increasing solvent polarity and decreased linearly with increasing [M]0 in three solvents with different slopes to the same point of bulk polymerization in the absence of solvent. Equation of Mn,e = 72.1/（0.14–0.04[M]e） has been established to provide a simple and effective approach for the prediction for the number-average molecular weight of poly THFs at equilibrium state（Mn,e） in the equilibrium living cationic ring-opening polymerization of THF at 0 °C.

Super-Grignard reagents(R_(2)Mg·LiCl)mediated covalent-anionic-radical polymerization capable of low?and reactive hydrogen compatibility

The precise synthesis of polymer with narrow molecular weight distribution(?)and well-defined architectures is very essential to exploring the functions and properties of polymer materials.Here,a universal polymerization method capable of low?and reactive hydrogen compatibility is reported by introducing super-Grignard reagents(R_(2)Mg?Li Cl)into polymer chemistry.Under mild conditions,various monomers,including nonpolar polystyrene and 4-methoxystyrene that cannot be initiated by Grignard reagents,and polar methacrylate,are successfully polymerized with full monomer conversion and low?.This approach is amenable to wide varieties of initiators,polymerization temperature,and feed ratio,which makes it attractive for applications in polymer synthesis.By adding methanol and water during the polymerization process,the reactive hydrogen compatibility of this method is confirmed,which makes this method avoid the rigorous restriction on polymerization conditions of anionic polymerization.Moreover,chain extension polymerization and block copolymerization are achieved and demonstrate the livingness of chain propagation,enabling the facile synthesis of well-defined macromolecular architectures.This work therefore expands the methodology libraries of living polymerization,which may cause inspirations to polymer science.

Synthesis of Glutathione Imprinted Polymer Particles via Controlled Living Radical Precipitation Polymerization

A general protocol was described for fabricating uniform molecularly imprinted polymer （MIP） particles via controlled living radical precipitation polymerization at ambient temperature. By adopting glutathione as model template, benzyl dithiocarbamate as iniferter agent, 4-vinylpyridine as monomer, and ethylene glycol dimethacrylate as cross-linker, it is demonstrated that the polymerization parameters including the iniferter concentration, monomer loading and molar ratio of cross-linker to functional monomer have profound effect on the final particle size and recognition property of the MIP particles. The batch static binding experiments were carried out to estimate the adsorption kinetics, adsorption isotherms and selective recognition of the MIP particles. The adsorption behavior followed the pseudo-second order kinetic model, revealing that the process was chemically carried out. Two adsorption isotherm models were applied to analyze equilibrium data, obtaining the best description by Langmuir isotherm model. In addition, the MIP particles also could selectively recognize glutathione over similar analogs, indicating the possibility for the separation and enrichment of the template from complicated matrices.

Synthesis of Star-like Polybutadienes by a Combination of Living Anionic Polymerization and “Click” Coupling Method

Three-arm and four-arm star-like polybutadienes （PBds） were synthesized via the combination of living anionic polymerization and the click coupling method. Kinetic study showed that the click reaction between the azido group terminated PBd-t-N3 and the alkyne-containing multifunctional linking reagent was fast and highly efficient. All coupling reactions were fully accomplished within 40 min at 50 ℃ in toluene in the presence of the reducing agent Cu（0）, proven by 1H-NMR, FTIR and GPC measurements. For the coupling reactions between the PBd-t-N3 polymer and dialkyne-containing compound, the final conversion of the coupled PBd-PBd polymer was ca. 97.0%. When a PBd-t-N3 polymer was reacted with trialkyne-containing or tetraalkyne-containing compound, the conversion of three-arm or four-arm PBd was around 95.5% or 87.0%, respectively. Several factors influencing the coupling efficiency were studied, including the molecular weight of the initial PBd-t-N3, arm numbers and the molar ratio of the azido group to the alkynyl group. The results indicated that the conversion of the target products would be promoted when the molecular weight of the PBd-t-N3 was low and the molar ratio of the azido to alkynyl groups was close to 1.