Novel SiO2‐Supported Chromocene and Vanadium Bimetallic Catalysts Producing Bimodal Polyethylene

Polyethylene (PE) with bimodal molecular weight distribution has intrigued researchers because of its significant processability and mechanical properties. Novel SiO₂‐supported chromocene (S‐9)/vanadium (V) bimetallic catalysts utilizing the different hydrogen response for producing bimodal PE are successfully synthesized and studied systematically. The catalysts are prepared through using the residual hydroxyl groups on the surface of SiO₂‐supported vanadium catalyst to introduce chromocene. Both of the low molecular weight (MW) fraction and the high MW fraction can be controlled through adjusting the loading of bimetallic active centers. The bimetallic catalysts also show good 1‐hexene incorporation ability in ethylene/1‐hexene copolymerization.     

Novel SiO2‐Supported Silyl‐Chromate(Cr)/Imido‐Vanadium(V) Bimetallic Catalysts Producing Polyethylene and Ethylene/1‐Hexene Copolymers with Bimodal Molecular‐Weight Distribution

Novel SiO₂‐supported silyl‐chromate(Cr)/imido‐vanadium(V) (Cr‐imidoV) bimetallic catalysts for ethylene and ethylene/α‐olefin polymerization are investigated. These catalysts are prepared using the residual surface hydroxyl groups in SiO₂‐supported imido‐vanadium catalysts to further support bis(triphenylsilyl) chromate (BC) in order to get the merits from both the SiO₂‐supported imido vanadium catalyst and the SiO₂‐supported silyl chromate S‐2 catalyst. By investigation of the polymerization behavior and the microstructures of their polymers, several vital factors such as the addition amount of imido vanadium active centers and the dosage of 1‐hexene in the ethylene homopolymerization and ethylene/1‐hexene copolymerization are systematically investigated. Compared with the traditional S‐2 catalyst and our previously reported SiO₂‐supported silyl‐chromate(Cr)/vanadium(V)‐oxide (Cr‐V) bimetallic catalyst, the novel Cr‐imidoV bimetallic catalysts show even higher activity and better 1‐hexene incorporation ability, together with higher molecular weight (MW) and bimodal molecular‐weight distribution (MWD).

     

New ester and lactone end‐functionalized N‐vinyl‐2‐pyrrolidinone oligomers

New oligomers of N‐vinyl‐2‐pyrrolidinone functionalized at one end with either ester or lactone functions were obtained by radical polymerization in the presence of different ester (methyl isobutyrate and methyl phenylacetate) and lactone (ε‐caprolactone, δ‐valerolactone and γ‐butyrolactone) compounds as chain transfer agents. The oligomeric samples obtained were characterized in terms of molecular weight and molecular weight distribution by means of analytical size exclusion chromatography (SEC), using purposely synthesized poly(N‐vinyl‐2‐pyrrolidinone) standards. The chain transfer constant C_T of either methyl isobutyrate, δ‐valerolactone, or γ‐butyrolactone towards N‐vinyl‐2‐pyrrolidinone were determined with the help of the known cumulative number‐average degree of polymerization X_n and monomer conversion Y_t of the samples during the reaction.     

Photoinduced Cu(0)‐Mediated Atom Transfer Radical Polymerization

Photoinduced Cu(0)‐mediated atom transfer radical polymerization (ATRP) of methyl methacrylate is investigated by using Cu(0)/N,N,N′,N″,N″‐pentamethyldiethylenetriamine as the catalyst, ethyl 2‐bromopropionate as the initiator, and dimethyl sulfoxide as the solvent. The effect of light on the conventional Cu(0)‐mediated ATRP and molecular weight characteristics of the obtained polymers are described. Although the polymerization can be achieved in the absence of light, low initiation efficiency of the process is observed. By introducing UV light and additional Cu(II) deactivator, not only the rate of polymerization is increased, but also well‐controlled polymers with narrow‐molecular‐weight distributions at ambient conditions are obtained. The chain extension study clearly confirms high end‐group fidelity of the polymer that is active in the further polymerization process.

     

Effects of Internal and External Donors on the Regio‐ and Stereoselectivity of Active Species in MgCl2‐Supported Catalysts for Propene Polymerization

Poly(propylene)s prepared using MgCl₂‐supported catalysts containing different electron donors have been characterized using temperature rising elution fractionation (TREF), gel permeation chromatography (GPC) and ¹³C NMR analysis. In addition, the regio‐ and stereochemical composition of oligomeric fractions present in selected polymers has been determined. The results indicate that catalysts in which the internal donor is a diether have a relatively narrow distribution of active species, for which the effects of regioselectivity on chain transfer with hydrogen are particularly prominent. The regio‐ and stereoselectivity of active species in catalysts in which the internal donor is diisobutyl phthalate is dependent on the nature of the alkoxysilane external donor used in polymerization. The effects of different alkoxysilanes on polymer tacticity and molecular weight distribution are interpreted in terms of lability of donor coordination in the vicinity of active species, a labile as opposed to a stable donor coordination giving rise to a higher proportion of defect‐rich sequences in the polymer chain. Such species will also give relatively low molecular weight as a result of an increased probability of chain transfer with decreasing regio‐ and stereoselectivity. A broad tacticity and molecular weight distribution in poly(propylene) prepared using monoesters as internal and external donors indicates that these systems may contain not only a significant proportion of labile active species, but also species that do not require the presence of an electron donor in their immediate vicinity for high selectivity.     

Pseudo‐Living Anionic Telomerization of Buta‐1,3‐diene

Low‐molecular‐weight liquid polybutadienes (1 000–2 000 g · mol^?1) consisting of 60 mol‐% poly(buta‐1,2‐diene) repeating units were synthesized via anionic telomerization. Maintaining the initiation and reaction temperature at less than 70 °C minimized chain transfer and enabled the polymerization to occur in a living fashion, which resulted in well‐controlled molecular weights and narrow polydispersity indices. MALDI‐TOF mass spectrometry confirmed that the end groups of liquid polybutadienes synthesized via anionic telomerization contained one benzyl end and one protonated end. In comparison, the end groups of liquid polybutadienes synthesized via living anionic polymerization contained one sec‐butyl or butyl end and one protonated end.

     

Synthesis of 3‐[tris(trimethylsilyloxy)silyl]propyl methacrylate macromers using catalytic chain transfer polymerization: a kinetic and mechanistic study

Macromers of 3‐[tris(trimethylsilyloxy)silyl]propyl methacrylate (TRIS) were synthesised using catalytic chain transfer polymerization, and the kinetic parameters governing the reaction were evaluated. A study on the radical solution polymerization of TRIS in the presence of the catalytic chain transfer agent bis[(difluoroboryl)dimethylglyoximato]cobalt(II) (COBF) at 60°C was conducted. Using appropriate Mark‐Houwink‐Kuhn‐Sakurada constants for polyTRIS, the chain transfer constant (C_S) for COBF was found to be ˜1 400 in toluene solution. This low C_S value, as compared to the value reported for methyl methacrylate polymerization (˜3.5·10⁴), is only partly explained by a diffusion‐controlled chain transfer reaction in the methacrylate series of monomers. A study on the influence of conversion on the molecular weight distribution indicated significant broadening and bimodality, consistent with reversible catalyst poisoning and chain transfer to the macromers. High oxygen solubility in TRIS is hypothesised to play a role in the reversible catalyst poisoning making it difficult to obtain a controlled reaction under normal free‐radical polymerization reaction conditions.     

Chain‐Growth Polycondensation in Solid‐Liquid Phase with Ammonium Salts for Well‐Defined Polyesters

Polycondensation of a potassium 4‐bromomethylbenzoate derivative dispersed in organic solvent was carried out with tetrabutylammonium iodide as a phase transfer catalyst (PTC) and a reactive benzyl bromide as an initiator to yield polyesters having a defined molecular weight and a narrow molecular weight distribution (M̄_w/M̄_n < 1.3). Polymerization involves the transfer of monomer to organic solvent layer with the PTC and the reaction of monomer with the initiator and the polymer end benzyl bromide moiety in a chain polymerization manner, as evidenced by polymerization behavior; increase of the molecular weight in proportion to monomer conversion and equal amount of the initiator unit and the end group in polymer irrespective of monomer conversion. Furthermore, the molecular weight increased in proportion to feed ratio ([monomer]₀/[initiator]₀), and the polydispersity index M̄_w/M̄_n stayed less than 1.3 over the whole range of feed ratio.     

A Study of Copolymerization of 1‐Hexene with 2,5‐Norbornadiene Using Metallocene Catalysts

Summary: Copolymerization of 1‐hexene with a symmetrical diene, namely 2,5‐norbornadiene was studied using four different metallocene catalysts. Copolymerization was found to occur exclusively through one of the two equally reactive endocyclic double bonds with all the four catalysts. Copolymerization results in low molecular weight oligomers with the number average molecular weight ( ) varying from 1 000–3 000. End group analysis of the co‐oligomers revealed that the β‐hydrogen transfer after 2,1 insertion also occurs in the presence of highly regiospecific catalysts. The regio errors were also found to depend on various reaction parameters such as polymerization time, Al/Zr mol ratio, metallocene concentration and polymerization temperature.

Plots of variation in end groups and NBD incorporation with time.     

Anionic synthesis of well‐defined,poly[(styrene)‐block‐(propylene oxide)] block copolymers

Well‐defined, narrow molecular weight distribution (M_w/M_n ≤ 1.1) poly[(styrene)‐block‐(propylene oxide)] block copolymers with relatively high molecular weight poly(propylene oxide) blocks [e. g. M_n (PPO) = 10 000–12 000 g/mol] have been prepared by anionic polymerization. The polystyrene block (M_n = 5 000; M_w/M_n = 1.1) was prepared by alkyllithium‐initiated polymerization of styrene followed by chain‐end functionalization with ethylene oxide and protonation with acidic methanol. The resulting ω‐hydroxyl‐functionalized polystyrene was converted to the corresponding alkali metal salts with alkali metals (Na/K alloy, Rb, Cs) and then used to initiate block polymerization of propylene oxide in tetrahydrofuran. The effects of crown ethers (18‐crown‐6 and dicyclohexano‐24‐crown‐8) and added dimethylsulfoxide were investigated. Chain transfer to the monomer resulted in significant amounts of poly(propylene oxide) formation (50%); however, the diblock molecular weight distributions were narrow. The highest molecular weight poly(propylene oxide) blocks (12 200 g/mol) were obtained in tetrahydrofuran with cesium as counterion without additives.     

cis‐Specific Living Polymerization of 1,3‐Butadiene with CoCl2 and Methylaluminoxane

The polymerization of 1,3‐butadiene was conducted by CoCl₂ combined with methylaluminoxane (MAO) as a cocatalyst at 0 and 18°C. The uni‐modal molecular weight distribution curves of the resulting polymers shifted toward higher molecular weight regions and became narrower when increasing the polymerization time. The number‐average molecular weight increased linearly with polymerization time, while the polymer yield increased exponentially in the initial stage. As a consequence, the number of polymer chains, calculated from the polymer yield and M̄_n, increased gradually with polymerization time to reach a plateau value. These phenomena was interpreted based on a slow initiation system without any termination and chain transfer reaction. The microstructure of the polymer was determined by ¹H NMR and ¹³C NMR spectroscopy to be a cis‐1,4 structure in a 98–99% purity.     

Ionic (Co)Organocatalyst with (Thio)Urea Anion and Tetra‑n‑butyl Ammonium Cation for the Polymerization of γ‐Butyrolactone

An effective ionic organocatalyst system is developed for the challenging ring‐opening polymerization (ROP) of γ‐butyrolactone (GBL) at low temperature. The catalysts are prepared by dehydration reaction between tetra‐n‐butyl ammonium hydroxide (TBAOH) and (thio)ureas at ambient temperature, and utilized with or without extra benzyl alcohol (BnOH) initiator. The solid‐state structure of TUA‐3 comprising thiourea anion is characterized by X‐ray diffraction analysis. Typically, a mixture of cyclic and linear poly(GBL) with low molecular weights (5000–1600 g mol^?1) and slightly narrow molecular distribution Ð (1.2–1.4) is obtained by single base with/without combination with (thio)ureas. Interestingly, solely linear high‐molecular‐weight poly(GBL) (10 400 g mol^?1) can be achieved by a synergistic effect of TBAOH/N,N′‐isopropylthiourea in the presence of BnOH. The obtained poly(GBL) is characterized with NMR spectroscopy and matrix‐assisted laser desorption/ionization time‐of‐flight mass spectroscopy (MALDI‐TOF MS). Mechanistic studies reveal different polymerization initiation steps in this reported catalyst system, which leads to poly(GBL) with divergent end groups.     

Preparation of Polyisobutene‐graft‐Poly(methyl methacrylate) and Polyisobutene‐graft‐Polystyrene with Different Compositions and Side Chain Architectures through Atom Transfer Radical Polymerization (ATRP)

Polyisobutene‐graft‐poly(methyl methacrylate) and polyisobutene‐graft‐polystyrene with controlled compositions and side chain architectures were prepared through atom transfer radical polymerization (ATRP). Poly[isobutene‐co‐(p‐methylstyrene)‐co‐(p‐bromomethylstyrene)] (PIB) was used as a macroinitiator in the presence of CuCl or CuBr as a catalyst and dNbpy as a ligand. The compositions were controlled by the conversion of the monomer with polymerization time. The molecular weight distributions of the side chains were controlled through ATRP in the presence/absence of a halogen exchange reaction. DSC and DMA measurements showed that graft copolymers have two glass transition temperatures suggesting microphase separated behavior, which was also confirmed by SAXS measurements. The phase and dynamic mechanical behaviors were strongly affected by the compositions and/or the side chain architectures. The properties of the graft copolymers were controlled in a wide range leading to toughened glassy polymers or elastomers.     

Polymerization of Vinyl Acetate Initiated with Di‐tert‐butyl Perfumarate

The polymerization behavior of vinyl acetate ( 2 ) was studied in benzene using di‐tert‐butyl perfumarate ( 1 ) as an initiator. Low molecular weight polymer (M̄_n ≈ 3 000) is formed in the early stage of polymerization where 1 is substantially consumed by thermal decomposition, copolymerization with 2 , and chain transfer reactions through an addition‐substitution mechanism. As a result, the low molecular weight polymer formed in the early stage of polymerization contains five peroxy ester groups per polymer molecule. Then, the polymerization of 2 initiated with the low molecular weight polymer further proceeds to yield high molecular weight poly( 2 ) (M̄_n = 2.5–23×10⁴). Decomposition of the peroxy ester group of 1 in benzene was studied in the absence and in the presence of methyl methacrylate (MMA) or 2 . The activation energy of decomposition of the peroxy ester group of 1 is 118 kJ/mol in the absence of the monomers. The decomposition of the peroxy ester group of 1 is highly accelerated in the presence of MMA. The peroxy ester groups derived from 1 decompose in two stages in the presence of 2 . In the first stage, some of them are rapidly consumed mainly by the chain transfer reaction. In the second stage, the peroxy ester groups of copolymer from 1 and 2 decompose slowly.     

CrV Bimetallic Phillips Catalyst Prepared by Citric Acid‐Assisted Impregnation on Ethylene Polymerization

Three CrV bimetallic Phillips catalysts are developed by a citric acid‐assisted impregnation method and studied in ethylene homopolymerization and ethylene/1‐hexene copolymerization. The method benefits to the dispersion of bimetallic active sites, especially for the V ones. The electron binding energy shift of V 2p_3/2 in CrV‐1/2‐CA suggests the increased electron deficiency of V active center. The CrV‐1/2‐CA, CrV‐1/3‐CA catalysts present higher activity, broader molecular weight distribution, than the counterparts without CA‐assisted impregnation, suggesting more active sites involved in the reaction. The 1‐hexene is higher inserted in the polyethylene by CrV‐1/2 than the CrV‐1/2‐CA. But the results of temperature rising elution fractionation‐successive self‐nucleation and annealing (TREF‐SSA) show the thinner platelet thickness at the high molecular weight parts of high‐density polyethylene by CrV‐1/2‐CA, suggesting the higher insertion of 1‐hexene and higher tensile properties. The CrV‐1/2‐CA also shows the more hydrogen‐regulated response in the polymerization. The deconvolution of the gel permeation chromatography curves presents the higher fractions of high molecular weight polymer component.     

Well‐Defined High‐Molecular‐Weight Polyacrylonitrile Formation via Visible‐Light‐Induced Metal‐Free Radical Polymerization

Polyacrylonitrile (PAN) with high molecular weight and low dispersity is successfully synthesized by visible‐light‐induced metal‐free radical polymerization at room temperature. This polymerization technique uses organic dye Eosin Y as photocatalyst and benzenediazonium tetrafluoroborates as initiator. Gel permeation chromatography‐multiangle laser light scattering shows the absolute molar weight of the PAN more than 1.50 × 10⁵ g mol⁻¹ with a polydispersity index < 1.3 while MALDI‐TOF MS and ¹⁹F NMR spectroscopy indicate the F‐chain‐end process. The first‐order kinetic behavior, molecular weight distributions shifting, and “ON/OFF” experiment results suggest this reaction may follow the atom‐transfer‐like radical polymerization mechanism. In addition, this new approach allows for the efficient synthesis of well‐defined random copolymers.

     

Ni‐Catalyzed Polymerization of Poly(3‐alkoxythiophene)s

The Ni‐catalyzed polymerization of P3AOTs was studied and compared with the controlled chain‐growth polymerization of P3ATs. By varying the ratio of the initial monomer concentration to the initiator concentration, no linear dependence of the molar mass was observed, revealing that the polymerization does not proceed via a controlled mechanism. This was also confirmed by analyzing the end‐groups of the polymer with MALDI‐TOF mass spectrometry. To acquire more information on the polymerization mechanism, the formation of the actual monomer and the polymerization reaction were studied into more detail. These experiments proved that the polymerization proceeds via a chain‐growth mechanism, although not in a controlled way.

     

Visible Light Controlled Polymerization of Azide‐Derived Monomers: A Facile,Metal‐Free PET‐ATRP Route to Construct Azide Polymers

Well‐defined azide polymers are successfully synthesized by visible‐light‐induced metal‐free electron transfer–atom transfer radical polymerization (PET‐ATRP) at room temperature. This technique uses Eosin Y/Et₃N as the reductive quenching photocatalyst system, which can effectively prevent the destruction of the azide group in polymerization. Four kinds of azide‐derived monomers participate well in this reaction and obtain satisfactory results. The kinetic behavior, “ON/OFF” experiment, and chain‐extension experiment confirm the living feature of this visible light controlled polymerization. Moreover, random copolymers obtained by this protocol can be used as surface modifier which further demonstrates the utility and reliability of this method.     

Temporally Controlled Ultrasonication‐Mediated Atom Transfer Radical Polymerization in Miniemulsion

Due to the increasing requirement for more environmentally and industrially relevant approaches in macromolecules synthesis, ultrasonication‐mediated atom transfer radical polymerization (sono‐ATRP) in miniemulsion media is applied for the first time to obtain precisely defined poly(n‐butyl acrylate) (PBA) and poly(methyl methacrylate) (PMMA) homopolymers, and poly(n‐butyl acrylate)‐block‐poly(tert‐butyl acrylate) (PBA‐b‐PtBA) and poly(n‐butyl acrylate)‐block‐poly(butyl acrylate) (PBA‐b‐PBA) copolymers. It is demonstrated in the reaction setup with strongly hydrophilic catalyst copper(II) bromide/tris(2‐pyridylmethyl)amine (Cu^IIBr₂/TPMA) responsible for two principal mechanisms – interfacial and ion‐pair catalysis reflecting single‐catalyst approach. This solution turns out to be an excellent tool in controlled preparation of well‐defined polymers with narrow molecular weight distribution (up to Ð = 1.28) and preserves chain‐end functionality (DCF = 0.02% to 0.32%). Temporal control over the polymer chain growth is successfully conducted by turning the ultrasonication on/off. Taking into consideration long OFF stage (92.5 h) during ultrasonication‐induced polymerization in miniemulsion, synthesis is efficiently reinitiated without any influence on controlled characteristics maintaining the precise structure of received PBA homopolymers, confirmed by narrow molecular weight distribution (Ð = 1.26) and high retention of chain‐end functionality (DCF = 0.01%). This procedure constitutes an excellent simple and eco‐friendly approach in preparation of functional polymeric materials.     

Polythioethers with Controlled α,ω‐End Groups Prepared by Visible Light Induced Thiol–Ene Click Polymerization of Dithiol and Divinyl Ether with 4‐(N,N‐diphenylamino)benzaldehyde as Organocatalyst

This study reports a step‐growth click‐polymerization of 1,4‐benzenedimethane (BDMT) and diethylene glycol divinyl ether (DEGVE) with 4‐(N,N‐diphenylamino)‐benzaldehyde (DPAB) as a photoredox catalyst under irradiation of visible light. DPAB exhibits a strong UV–vis absorption at 350 nm and a strong fluorescence emission at 480 nm in anisole. There is a strong fluorescence quenching between BDMT and DPAB. The molecular weight of the polythiolether can be controlled by reaction time and monomer feed ratios. More importantly, α,ω‐dithiol and α,ω‐divinyl telechelic polythiolether oligomers are successfully synthesized by simply changing the molar ratios of BDMT to DEGVE. ¹H NMR and MALDI‐TOF MS spectra demonstrate that the oligomers have high end group fidelity. In addition, strong fluorescence is observed when the α,ω‐dithiol terminated polythiolether adds with N‐(1‐pyrenyl) maleimide, indicating that the as‐prepared polythiolether bears reactive thiol end groups. Furthermore, high molecular weight polythiolether are prepared by chain extension with reactive polythiolether oligomers as macro‐monomers. For example, α,ω‐divinyl oligomer (M_n = 2000 g mol^?1) could further react with α,ω‐dithiol oligomer (M_n = 2400 g mol^?1) to form high molecular weight polythiolether (M_n = 6000 g mol^?1).