Copolymerization of ethylene with 5‐vinyl‐2‐norbornene in the presence of the Ph2C(Flu)(Cp)ZrCl2 /MAO catalyst

Cycloolefin copolymer, poly[(ethylene)‐co‐(5‐vinyl‐2‐norbornene)], was synthetized using the MAO activated ansa‐metallocene Ph₂C(Flu)(Cp)ZrCl₂ as a catalyst. Formation of mostly isolated 5‐vinyl‐2‐norbornene sequences was confirmed by NMR analysis. Comonomer incorporated selectively via cyclic double bond. No selectivity towards the reactivity of the particular isomer of 5‐vinyl‐2‐norbornene (5‐endo : 5‐exo) was observed. The molar mass was found to decrease when the comonomer concentration in product increased. At low comonomer incorporation levels copolymers were insoluble, cross‐linked elastomers. With high comonomer concentration in reaction medium copolymers were amorphous determined by means of DSC and X‐ray diffraction and the vinyl group of the comonomer remained unreacted for further modification.     

On the 1,4‐cis‐Polymerization of Butadiene with the Highly Active Catalyst Systems Nd(C3H5)2Cl·1.5 THF/Hexaisobutylaluminoxane (HIBAO), Nd(C3H5)Cl2· 2 THF/HIBAO and Nd(C3H5)Cl2·2 THF/Methyl‐aluminoxane (MAO) – Degree of Polymerization,Polydispersity, Kinetics and Catalyst Formation

The allylneodymium chloride complexes Nd(C₃H₅)₂Cl·1.5 THF and Nd(C₃H₅)Cl₂·2 THF can be activated by adding hexaisobutylaluminoxane (HIBAO) or methylaluminoxane (MAO) in a ratio of Al/Nd = 30 for the catalysis of butadiene 1,4‐cis‐polymerization. A turnover frequency (TOF) of about 20 000 mol butadiene/(mol Nd·h) and cis‐selectivity of 95–97% are achieved under standard conditions ([BD]₀ = 2 m, 35°C, toluene). Molecular weight determinations indicate a low polydispersity (M̄_w (LS)/M̄_n (LS) = 1–1.5), the formation of only one polymer chain per neodymium and the linear increase of the degree of polymerization (DP) with the butadiene conversion, as observed for living polymerizations. First indications of chain‐transfer reaction occur only at the highest conversion or degree of polymerization. The rate law r_P = k_P[Nd][C₄H₆]^1.8 is derived for the catalyst system Nd(C₃H₅)₂Cl·1.5 THF/HIBAO and for the system Nd(C₃H₅)Cl₂·2 THF/MAO the rate law r_P = k_P[Nd] [C₄H₆]² with k_P = 3.24 L²/(mol²·s) (at 35°C). Taking into account the Lewis acidity of the alkylaluminoxanes and the characteristic coordination number of 8 for Nd(III) in allyl complexes the formation of an η³‐butenyl‐bis(η⁴‐butadiene)neodymium(III) complex of the composition [Nd(η³‐RC₃H₄)(η⁴‐C₄H₆)₂(X‐{AlOR}_n)₂] is assumed to be a single‐site catalyst for the chain propagation by reaction of the coordinated butadiene via the π‐allyl insertion mechanism and the anti‐cis and syn‐trans correlation to explain the experimental results.     

Influence of polymerization conditions on the copolymerization of styrene with ethylene using Me2Si(Me4Cp)(N-tert-butyl)TiCl2/methylaluminoxane Ziegler-Natta catalysts

Styrene was copolymerized with ethylene using Me₂Si(Me₄Cp)(N-tert-butyl)TiCl₂/methylaluminoxane (Me = methyl, Cp = cyclopentadienyl) varying monomer concentration, styrene/ethylene molar ratio and polymerization temperature. Increasing styrene or decreasing ethylene concentration, respectively, in the monomer feed lowered both activity of the catalyst system and molecular weight of the copolymer. Only at low styrene content, a linear correlation of styrene concentration in the monomer feed and styrene incorporation in the copolymer was found. From copolymerizations at various temperatures the activation energy of the insertion step was calculated to be 56 kJ/mol. According to Fineman-Ross plot, the copolymerization parameters are r_E = 23,4 for ethylene and r_S = 0,015 for styrene. Investigation of the thermal properties by means of differential scanning calorimetry and dynamic mechanical analysis revealed pronounced decrease of melting temperature and increase of glass transition temperature with increasing styrene content.     

Syndiospecific Living Polymerization of Silyl‐Protected Hydroxystyrene Derivatives and Preparation of Syndiotactic Poly(4‐hydroxystyrene) with Narrow Molecular Weight Distribution

At –25°C, the polymerizations of hydroxystyrene, the phenolic —OH of which was protected with trialkylsilyl compounds, were investigated by using a syndiospecific living polymerization catalyst system composed of (trimethyl)pentamethylcyclopentadienyltitanium (Cp*TiMe₃), trioctylaluminium (AlOct₃) and tris(pentafluorophenyl)borane (B(C₆F₅)₃). The use of bulky trialkylsilyl protective groups was effective to control a stereoregularity and a molecular weight distribution (MWD) of polymer. In the case of 4‐(tert‐butyldimethylsilyloxy)styrene (TBDMSS) monomer, the number‐average molecular weights (M̄_n's) of polymer produced increased proportionally with increasing of monomer conversion. The MWD of polymer stayed narrow (M̄_w /M̄_n = 1.05–1.15). It was concluded, thus, the polymerizations of TBDMSS with Cp*TiMe₃/B(C₆F₅)₃/AlOct₃ catalytic system proceeded under living fashion. The ¹³C NMR analysis clarified that the polymers obtained in this work had highly syndiotactic structure. By the deprotection reaction of silyl group with conc. hydrochloric acid (HCl), syndiotactic poly(4‐hydroxystyrene) (PHOST) with narrow MWD was prepared. The obtained syndiotactic PHOST had a good solubility for polar solvents and a high glass transition temperature (T_g) of 194°C.     

Syndiospecific Living Block Copolymerization of Styrenic Monomers Containing Functional Groups,and Preparation of Syndiotactic Poly{(4‐hydroxystyrene)‐block‐[(4‐methylstyrene)‐co‐(4‐hydroxystyrene)]}

At –25°C, the sequential block copolymerizations of 4‐(tert‐butyldimethylsilyloxy)styrene (TBDMSS) and 4‐methylstyrene (4MS) were investigated by using a syndiospecific living polymerization catalyst system composed of (trimethyl)pentamethylcyclopentadienyltitanium (Cp*TiMe₃), trioctylaluminum (AlOct₃) and tris(pentafluorophenyl)borane (B(C₆F₅)₃). The number‐average molecular weight (M̄_n) of the poly(TBDMSS)s increased linearly with increasing the polymer yield up to almost 100 wt.‐% consumption of TBDMSS used as 1^st monomer. The M̄_n value of the polymer after the second monomer (4MS) addition continued to increase proportionally to the polymer yield. The molecular weight distributions (MWDs) of the polymers remained constant at around 1.05–1.18 over the entire course of block copolymerization. It was concluded that the block copolymerizations of TBDMSS and 4MS with the Cp*TiMe₃ /B(C₆F₅)₃ /AlOct₃ catalytic system proceeded with a high block efficiency. The ¹³C NMR analysis clarified that the block copolymers obtained in this work had highly syndiotactic structure. By the deprotection reaction of silyl group with conc. hydrochloric acid (HCl), syndiotactic poly{(4‐hydroxystyrene)‐block‐[(4‐methylstyrene)‐co‐(4‐hydroxystyrene)]} (poly[HOST‐b‐(4MS‐co‐HOST)]) was successfully prepared.     

Propylene polymerization with Ph2C(3-RCp)(Flu)ZrCl2 [R = Me,i-Pr,PhCH2, Me3Si] catalysts activated with MAO and Me2PhNH·B(C6F5)4/i-Bu3Al

Propylene polymerization was conducted with Ph₂C(R-Cp)(Flu)ZrCl₂ [R = Me, i-Pr, PhCH₂, Me₃Si] catalysts in combination with methylaluminoxane (MAO) and dimethylanilinium tetrakis(pentafluorophenyl)borate (Me₂PhNH·B(C₆F₅)₄) as cocatalyst; the dependence of the stereoregularity of poly(propylene) on cocatalysts and bulkiness of the substituents in β-position of the cyclopentadienyl ligand was studied. Methyl and i-propyl substituted metallocene catalysts produce hemi-isotactic poly(propylene). These results are in good agreement with the results of the isopropylidene bridged metallocene analogue. The benzyl substituted metallocene catalyst produces syndiotactic poly(propylene) regardless of the cocatalyst. This means that this substituent group does not affect migration insertion of propylene. Stereoregularity of poly(propylene) obtained with diphenylmethylidene(3-trimethylsilylcyclopentadienyl)(fluorenyl)zirconium dichloride (Ph₂C(Me₃SiCp)(Flu)ZrCl₂) as a catalyst was significantly influenced by the cocatalyst. Me₂PhNH· B(C₆F₅)₄/triisobutylaluminium(i-Bu₃Al) produces poly(propylene) with 65% racemic and 23% meso pentads at 40°C, whereas the MAO activated catalyst produces isotactic rich poly(propylene). Fractionation experiments indicated that Me₂PhNH·B(C₆F₅)₄/i-Bu₃Al forms two active sites, one of them being the same as that of the MAO activated catalyst, the other one producing syndiotactic rich poly(propylene).     

Copolymerization of Ethylene and Butylene‐1 with Monotitanocene/Methylaluminoxane as the Catalyst

Ethylene and butylene‐1 were homo‐ and co‐ polymerized using monotitanocene catalysts composed of η⁵‐pentamethylcyclopentadienyl tribenzyloxytitanium [Cp*Ti(OBz)₃] and two kinds of solid modified methylaluminoxane (mMAO) containing different amounts of residual trimethylaluminium (TMA). The mMAO1 with lower TMA content to activate Cp*Ti(OBz)₃ for homo‐ and co‐ polymerization of ethylene and butylene‐1 showed higher activity and more butylene‐1 incorporation in their copolymers than mMAO2 with higher TMA content. Influences of copolymerization conditions including ethylene/butylene‐1 ratio in the feed, polymerization temperature and Al/Ti molar ratio on activity, butylene‐1 content in copolymers, molecular weight and molecular weight distribution, the triad and tetrad sequence distributions and butylene‐1 content in the copolymers. The monomer reactivity ratios r_E and r_B (E = ethylene, B = butylene‐1) for ethylene/butylene‐1 copolymerizations were estimated from the ¹³C NMR spectra. The Cp*Ti(OBz)₃/mMAO catalyst gave rise to r_Er_B lower than 1. A correlation between the reactivity ratios and mMAO composition was also made. The thermal properties of copolymers determined by DSC are mainly dependent on the butylene‐1 content in the copolymers.     

Blends of Syndiotactic Polystyrene and Isotactic Polypropene Prepared Using a Ziegler‐Natta Catalyst Containing a Novel Donor

Blends of syndiotactic polystyrene (sPS) and isotactic polypropene (iPP) have been prepared using TiCl₄/MgCl₂/β‐diketone activated with methylaluminoxane (MAO). The influences of the Al/Ti ratio and the polymerization temperature on the catalyst activity and the blend composition have been investigated. It is shown that the polymerization temperature is an important factor in determining catalyst activity and the blend composition. Through controlling the polymerization conditions, blends containing a wide composition range of styrene/propene molar fractions can be prepared. The supported catalyst shows a good activity of about 1.5×10⁵ (g blend)·(mol Ti)^–1·h^–1. ¹³C NMR analysis allows the composition of the blends to be calculated. Dynamic mechanical analysis (DMA) reveals that the blends of sPS/iPP prepared this way are partially compatible; the two glass transition temperatures (T_g's) of the components shift towards each other. The values of T_g, as well as the peaks of sPS intensity, increase with an increasing molar fraction of styrene in the blend. When the sPS content is in the range of 59–80 wt.‐%, dual phase continuity occurs in the blends. The morphology found by microscopic observation is consistent with the DMA results.     

Chlorolanthanocene‐dialkylmagnesium systems for styrene bulk polymerization and styrene‐ethylene block copolymerization

The bulk polymerization of styrene has been investigated at 105°C in the presence of exclusively dialkylmagnesium or combination of chlorolanthanocene and dialkylmagnesium. In the presence of butylethylmagnesium or n,s‐dibutylmagnesium, styrene polymerization proceeds via thermal self‐initiation, but is accompanied by a reversible transfer to dialkylmagnesiums to yield in turn oligostyrylmagnesium species; the latter are finally hydrolysed to oligostyrenes with M_n = 500–1 500 and M_w/M_n = 2.0–2.8. The analysis of the oligostyrenes by MALDI‐TOF mass spectrometry establishes the presence of ethyl and butyl headgroups, consistent with the transfer process. When the dialkylmagnesium is combined with a lanthanocene such as (C₅Me₅)₂NdCl₂Li(OEt₂)₂ ( 1 ), an increase in activity is obtained which is ascribed to additional styrene polymerization initiated by in situ generated alkyl(hydride)lanthanocene species. The influence of various reaction parameters on the performance of this system has been investigated. The oligostyrenes (M_n = 500–9 000) produced under optimum conditions have a relatively narrow molar mass distribution (M_w/M_n = 1.20–1.40) which can be explained in terms of an efficient transfer between the chain‐growing lanthanide and the oligostyrylmagnesium species. The MALDI‐TOF mass spectra of the oligostyrenes produced with various dialkylmagnesium‐lanthanocene combinations gives an insight into the initiation mechanism. Finally, the combination of butylethylmagnesium and Cp*₂NdCl₂Li(OEt₂)₂ has been used to achieve (styrene‐co‐ethylene) block copolymers.     

Synthesis of Block Graft Copolymer with Syndiospecific Living Polymerization of Styrene Derivatives by (Trimethyl)pentamethylcyclopentadienyltitanium/Tris(pentafluorophenyl)borane/Trioctylaluminium Catalytic System

Two kinds of syndiotactic AB type block copolymers were prepared, which were (1) poly(4‐methylstyrene)‐block‐polystyrene {Poly(4MS‐b‐S), (A: poly(4MS), B: polystyrene (S))}, (2) poly(4‐methylstyrene)‐block‐poly(styrene‐co‐3‐methylstyrene) {poly[4MS‐b‐(S‐co‐3MS)] (A: poly(4MS), B: styrene/3‐methylstyrene (3MS) copolymer)}. For the syntheses of these diblock copolymers, the living polymerization catalytic system composed of (trimethyl)pentamethylcyclopentadienyltitanium (Cp*TiMe₃) premixed with trioctylaluminium (AlOct₃), and tris(pentafluorophenyl)borane (B(C₆F₅)₃) was used at –25°C. Chlorination of the methyl groups of poly[4MS‐b‐(S‐co‐3MS)] was conducted by aqueous sodium hypochlorite (NaOCl) and phase‐transfer catalyst such as tetrabutylammonium hydrogensulfate (TBAHS). The novel tapered densely grafted diblock copolymer was synthesized with by coupling reaction of living poly(2‐vinyl pyridine)lithium (Poly(2VP)Li) with the partly chloromethylated poly[4MS‐b‐(S‐co‐3MS)].     

Synthesis of Ethylene‐co‐Norbornene Polymers Promoted by MAO Free Catalysts Based on Group 4 Dicarbollide Complexes

Ethylene‐co‐norbornene polymers [P(E‐co‐N)s] have been synthesized with the dicarbollide catalysts (η⁵‐C₂B₉H₁₁)M(NEt₂)₂(NHEt₂) [M = Ti ( 1 ), Zr ( 2 )] activated with methylaluminoxane (MAO) or alkylaluminium compounds, as AlMe₃ (TMA), Al(ⁱBu)₃ (TIBA), AlH(ⁱBu)₂ (DIBALH), AlEt₂Cl (DEAC). Polymerization results by 1 ‐TIBA, 2 ‐TIBA, 1 ‐MAO and 2 ‐MAO catalysts have been preliminary compared with those of cyclopentadienyl derivatives of the group 4 metals, (η⁵‐C₅R₅)TiX₃ [R = H, X = Cl ( 3 ); R = Me, X = Cl ( 4 ), Me( 5 )], (η⁵‐C₅H₅)ZrCl₃ ( 6 ), ethylenebis(1‐indenyl) zirconium dichloride ( 7 ) and “Cp‐free” compounds M(NEt₂)₄ [M = Ti ( 8 ), Zr ( 9 )] precursors of the dicarbollide compounds 1 – 2 , under the same conditions (T_p = 50°C, [M] = 1×10^–3 M ; P_E = 1 atm; [N] = 1.75 M ). The 1 ‐TIBA and 2 ‐TIBA catalysts exhibit productivity values greater than the corresponding MAO activated system and incorporate high concentration of the cyclic monomer in the copolymer products (N mol‐% = 38–45). Crystalline blocks of isotactic alternating NENE sequences were identified in the P(E‐co‐N)s copolymers produced by these catalysts by means of ¹³C NMR and DSC analysis. The dicarbollide derivatives 1 and 2 were also efficiently activated with the alkyl aluminium compounds TMA, DIBALH and DEAC at very low Al/M molar ratio (Al/M = 10); the titanium and zirconium cyclopentadienyl derivatives 3 , 4 , 6 , 7 are inactive under these conditions.     

Copolymerization of ethylene and styrene with a MgCl2‐supported CpTiCl3 catalyst

Copolymerization of ethylene and styrene was carried out with CpTiCl₃/MgCl₂‐PMAO as a catalyst at various temperatures and comonomer concentrations. The present catalyst system produces a pseudorandom copolymer of ethylene and styrene beside syndiotactic poly(styrene) (sPS) and poly(ethylene) (PE). The copolymers were obtained at temperature ⪈60°C, indicating the active species promoting the copolymerization being formed at elevated temperatures. On the other hand, styrene incorporation in the copolymer increases progressively with the increase of styrene concentration.     

Radical Copolymerization Behavior of 2,2‐Dimethyl‐5‐methylene‐1,3‐dioxolan‐4‐one with Common Monomers

Radical copolymerization of 2,2‐dimethyl‐1,3‐dioxolan‐4‐one (DMDO) consisting of a hybrid structure of acrylate and vinyl ether moieties with styrene, methyl methacrylate, and vinyl acetate was examined. The radical copolymerization was carried out without a solvent or in chlorobenzene in the presence of 3 mol‐% of 2,2′‐azoisobutyronitrile at 60°C for 20 h to obtain the copolymers with number‐average molecular weights of 1 400‐700 000 in 27–86% yields. No ring‐opening occurred but vinyl polymerization of DMDO selectively proceeded in the copolymerization. The monomer reactivity ratios were evaluated as r₁ = 6.42, r₂ = 0.08 (M₁, DMDO; M₂, styrene) by the Fineman‐Ross method. The Alfrey‐Price Q‐ and e‐values of DMDO were calculated as 5.97 and –0.13, respectively. Ab initio molecular orbital calculations were carried out to compare the reactivity of DMDO with methyl α‐methoxyacrylate and vinyl ether.     

EPDM Synthesis by the Ziegler Catalyst Cp*TiMe3/B(C6F5)3

The utilization of the Ziegler catalyst Cp*TiMe₃/B(C₆F₅)₃ for the terpolymerization of ethylene, propylene and 5‐ethylidene‐2‐norbornene to give EPDM is investigated, and the major factors affecting yields, molecular weights, molecular weight distributions and compositional distributions of the EPDM polymers are assessed. High molecular weight polymers with narrow molecular weight distributions are obtained at ˜18°C.     

Use of Original ω‐Perfluorinated Dithioesters for the Synthesis of Well‐Controlled Polymers by Reversible Addition‐Fragmentation Chain Transfer (RAFT)

A series of five fluorinated dithioesters PhC(S)SRCH₂C_nF_2n+1 (where R represents an activating spacer and n = 6 or 8) was obtained in fair to high yields (57–88%). These transfer agents were successfully used in reversible addition‐fragmentation transfer (RAFT) of styrene (S), methyl methacrylate (MMA), ethyl acrylate (EA) and 1,3‐butadiene. Well‐chosen fluorinated dithioesters were able to lead to a good control of the radical polymerization of these monomers (i.e., molar masses of the produced polymers increased linearly with the monomer conversion and the polydispersity indexes ranging between 1.1 and 1.6 remained low). The relationship between the structures of the dithioesters and the living behavior of the radical polymerization of these above monomers is discussed and it is shown that the nature of the R group influences the living behavior from different contributions to radical stabilization. Furthermore, the RAFT process also yielded PMMA‐b‐PS and PEA‐b‐PS block copolymers bearing a fluorinated moiety.     

Detailed Kinetics of 1‐Hexene Oligomerization Reaction with (n‐Bu‐Cp)2ZrCl2–MAO Catalyst

The paper describes a kinetic study of 1‐hexene oligomerization reaction with the (n‐Bu‐Cp)₂ZrCl₂–MAO catalyst system at 70 °C. GC analysis of the monomer/oligomer mixtures at different reaction times in the course of a 5‐h reaction, provided information on the formation rates of individual oligomer molecules, from the 1‐hexene dimer, C₁₂H₂₄, to the tetradecamer, C₈₄H₁₆₈. Kinetic modeling of the oligomerization kinetics strongly supports the principal premise of polymerization kinetics, that the value of the propagation rate constant of the chain growth reaction does not depend on the number of monomer units in the growing polymer chain. The only exception from this rule is the insertion of a 1‐hexene molecule into the Zr⁺? C bond in the active center bearing a single monomer unit, (n‐Bu‐Cp)₂Zr⁺? CH₂? CH₂? C₄H₉. The rate constant of this reaction in one order of magnitude is higher than the rate constant of 1‐hexene insertion into active centers which are β‐branched with respect to the Zr atom, (n‐Bu‐Cp)₂Zr⁺? [CH₂? CH(C₄H₉)]_n? CH₂? CH₂? C₄H₉.

     

Trägerkatalysatoren aus C12-allylnickel(II)-komplexen [Ni(C12H19)]X (X = SbF6, O3SCF3) und amorphem aluminiumfluorid in toluol als modell-katalysatoren für das technische katalysatorsystem Ni(octanoat)2/BF3·OEt2/AlEt3 zur 1,4-cis-polymerisation des butadiens

The η³, η², η²-dodeca-2(E), 6(E), 10(Z)-trien-1-yl-nickel(II) complexes [Ni(C₁₂H₁₉)]X (X = SbF₆, O₃SCF₃) were treated in toluene with amorphous aluminium trifluoride (which was prepared from AlEt₃ and BF₃ · OEt₂) in a mole ratio 1 : 10 to 20, forming a highly active catalyst for the 1,4-cis polymerization of butadiene. This catalyst is comparable in its activity and selectivity, and in the molar mass distribution of the polybutadiene, with the technical nickel catalyst Ni(O₂CR)₂/BF₃?OEt₂/AlE₃ developed by Bridgestone Tire Company thirty years ago. The existence of the C₁₂-allynickel(II) cation [Ni(C₁₂H₁₉)]⁺ on the AlF₃ support could be proved by FAB mass spectroscopic measurements. In agreement with our reaction model for the allyl nickel complex catalyzed butadiene polymerization, it is concluded that the technical nickel catalyst in its effective structure can be described as a polybutadienylnickel(II) complex co-ordinated to a polymeric fluoroaluminate anion via a fluoride bridge.     

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.     

Syndiospecific Homopolymerisation of Higher 1‐Alkenes with Two Different Bridged [(RPh)2C(Cp)(2,7‐tert‐BuFlu)]ZrCl2 Catalysts

Summary: Syndiotactic polymers of 1‐pentene, 1‐hexene and 1‐octene were obtained with the C_S‐symmetric metallocene catalysts [Ph₂C(Cp)(2,7‐tert‐Bu₂Flu]ZrCl₂ and [(4‐MePh)₂C(Cp)(2,7‐tert‐Bu₂Flu)]ZrCl₂, which have already been proven to give high molar masses and excellent tacticities in propene polymerisation. The monomers were polymerised in bulk and in solution processes at temperatures between 0 and 60 °C using methylaluminoxane as a cocatalyst. The effects on catalyst activity as well as on polymer microstructure and molar mass were determined. Polymers with high syndiotacticities and molar masses (up to 550 000 g · mol^?1 in the 1‐octene polymerisation) compared to other metallocenes were obtained.

     

Synthesis and Thermosensitive Properties of Poly[(N‐vinylamide)‐co‐(vinyl acetate)]s and Their Hydrogels

Free radical copolymerization of water‐soluble N‐vinylamides such as N‐vinylacetamide (NVA) and N‐vinylformamide (NVF) with hydrophobic vinyl acetate (VAc) gave amphiphilic copolymers. The monomer reactivity ratios were determined as r₁ = 5.8 and r₂ = 0.68 (M₁ = NVA, M₂ = VAc) and r₁ = 6.2 and r₂ = 0.37 (M₁ = NVF, M₂ = VAc), respectively. The growing radical of the terminals of N‐vinylamides propagates more favorably for N‐vinylamide monomers than for VAc monomer, resulting in the possible formation of blocky copolymers. It is found that aqueous solutions of these amphiphilic copolymers exhibited a lower critical solution temperature (LCST), depending on their chemical composition, followed by coacervate formation above the LCST. Furthermore, thermosensitive hydrogels could be prepared by the free radical copolymerization of N‐vinylamide and VAc in the presence of the crosslinker butylenebis(N‐vinylacetamide) (Bis‐NVA). The swelling ratios of these hydrogels decreased with an immediate increase in temperature from 20 to 80 °C, and then reversibly increased with decreasing temperature. These hydrogels showed the same thermosensitive properties as linear copolymers of NVF and VAc.

Relationship between LCST and vinyl acetate content in poly(N‐vinylamide‐co‐VAc)s.