Propylene polymerization by C1‐symmetric {ONNO′}‐type salan zirconium complexes

The activities of C₁‐symmetric dibenzyl zirconium complexes of Salan ligands that bear a halo‐substituted phenolate ring and an alkyl‐substituted phenolate ring in propylene polymerization with methylaluminoxane as cocatalyst were studied. These {ONNO′}ZrBn₂‐type catalysts exhibited moderate‐to‐high activities and yielded polypropylene of low molecular weight. The degree of tacticity was found to depend on the steric bulk of the substituents on both phenolate rings and ranged from practically atactic to substantially isotactic (74–78% [mmmm] for polymerizations at room temperature by Lig⁵ZrBn₂). Hemi‐isotactic polypropylene was not obtained, despite the diastereotopicity of the two positions. The pattern of stereo errors was consistent with the enantiomorphic site control of propylene insertion typically observed for C₂‐symmetric catalysts and implied a facile site‐averaging mechanism. A regular 1,2‐insertion and a β‐H transfer to an incoming monomer correspond to the main propagation and termination processes, respectively. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

The relationship between catalyst precursors and chain end groups in homogeneous propene polymerization catalysis

The chain transfer to monomer reactions promoted by primary and secondary growing chains in the propene polymerization promoted by ansa‐zirconocenes and postmetallocene precursors are studied by using DFT methods. From the theoretical results it comes out that the prevalence of propene insertion over β‐hydrogen transfer to the monomer decreases drastically in the presence of a secondary chain. Furthermore, we explained the reason why C₂‐symmetric metallocene catalysts promote the selective formation of cis but‐2‐enyls end group after a 2,1 inserted unit whereas for octahedral bis(phenoxy‐imine)titanium‐based catalysts, chain release promotes exclusively the formation of allyl terminated chain end. These results might be useful to design ligand precursors able to obtain not only high M_n PP polymers but also tuned chain end groups to build new polymer architectures. Overall, a more general picture of the enantioselectivity of the chain transfer to monomer processes is reported. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 699–708, 2010     

Hydrogen effects in propylene polymerization reactions with titanium‐based Ziegler–Natta catalysts. I. Chemical mechanism of catalyst activation

The hydrogen activation effect in propylene polymerization reactions with Ti‐based Ziegler–Natta catalysts is usually explained by hydrogenolysis of dormant active centers formed after secondary insertion of a propylene molecule into the growing polymer chain. This article proposes a different mechanism for the hydrogen activation effect due to hydrogenolysis of the Ti? iso‐C₃H₇ group. This group can be formed in two reactions: (1) after secondary propylene insertion into the Ti? H bond (which is generated after β‐hydrogen elimination in the growing polymer chain or after chain transfer with hydrogen), and (2) in the chain transfer with propylene if a propylene molecule is coordinated to the Ti atom in the secondary orientation. The Ti? CH(CH₃)₂ species is relatively stable, possibly because of the β‐agostic interaction between the H atom of one of its CH₃ groups and the Ti atom. The validity of this mechanism was demonstrated in a gas chromatography study of oligomers formed in ethylene/α‐olefin copolymerization reactions with δ‐TiCl₃/AlEt₃ and TiCl₄/dibutyl phthalate/MgCl₂–AlEt₃ catalysts. A quantitative analysis of gas chromatography data for ethylene/propylene co‐oligomers showed that the probability of secondary propylene insertion into the Ti? H bond was only 3–4 times lower than the probability of primary insertion. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1353–1365, 2002     

Simultaneous Chain‐Growth and Step‐Growth Polymerization of Methoxystyrenes by Rare‐Earth Catalysts

The simultaneous chain‐growth and step‐growth polymerization of a monomer is of great interest and importance because it can produce unique macromolecules which are difficult to prepare by other means. However, such a transformation is usually difficult to achieve in one polymerization system because chain‐growth polymerization and step‐growth polymerization proceed by different reaction mechanisms. Reported here is the simultaneous chain‐growth and step‐growth polymerization of para‐ and meta‐methoxystyrenes catalyzed by half‐sandwich rare‐earth alkyl complexes, and the step‐growth polymerization proceeds by the C?H polyaddition of anisyl units to vinyl groups. This unprecedented transformation affords a new family of macromolecules containing unique alternating anisole‐ethylene sequences. In contrast to para‐ and meta‐methoxystyrenes, ortho‐methoxystyrene exclusively undergo syndiospecific, living chain‐growth polymerization by continuous C=C bond insertion to give perfect syndiotactic poly(ortho‐methoxystyrene) with high molecular weight and narrow polydispersity (rrrr >99 %, M_n up to 280 kg mol^?1, M_w/M_n <1.10).     

Catalytic synthesis of styryl‐capped isotactic polypropylenes

Bis‐styrenic molecules, 1,4‐divinylbenzene (DVB) and 1,2‐bis(4‐vinylphenyl)ethane (BVPE), were successfully combined with hydrogen (H₂) to form consecutive chain transfer complexes in propylene polymerization mediated by an isospecific metallocene catalyst (i.e., rac‐dimethylsilylbis(2‐methyl‐4‐phenylindenyl)zirconium dichloride, I ) activated with methylaluminoxane (MAO), rendering a catalytic access to styryl‐capped isotactic polypropylenes (i‐PP). The chain transfer reaction took place in a unique way where prior to the ultimate chain transfer DVB/H₂ or BVPE/H₂ caused a copolymerization‐like reaction leading to the formation of main chain benzene rings. A preemptive polymer chain reinsertion was deduced after the consecutive actions of DVB/H₂ or BVPE/H₂, which gave the styryl‐terminated polymer chain alongside a metal‐hydride active species. It was confirmed that the chain reinsertion occurred in a regio‐irregular 1,2‐fashion, which contrasted with a normal 2,1‐insertion of styrene monomer and ensured subsequent continuous propylene insertions, directing the polymerization to repeated DVB or BVPE incorporations inside polymer chain. Only as a competitive reaction, the insertion of propylene into metal‐hydride site broke the chain propagation resumption process while completed the chain transfer process by releasing the styryl‐terminated polymer chain. BVPE was found with much higher chain transfer efficiency than DVB, which was attributed to its non‐conjugated structure with much divided styrene moieties resulting in higher polymerization reactivity but lower chain reinsertion tendency. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3709–3713, 2010     

Titanium complexes of dialkanolamine ligands as initiators for living ring‐opening polymerization of ε‐caprolactone

The titanium complexes with one ( 1a , 1b , 1c ) and two ( 2a , 2b ) dialkanolamine ligands were used as initiators in the ring‐opening polymerization (ROP) of ε‐caprolactone. Titanocanes 1a and 1b initiated living ROP of ε‐caprolactone affording polymers whose number‐average molecular weights (M_n) increased in direct proportion to monomer conversion (M_n ≤ 30,000 g mol^?1) in agreement with calculated values, and were inversely proportional to initiator concentration, while the molecular weight distribution stayed narrow throughout the polymerization (M_w/M_n ≤ 1.2 up to 80% monomer conversion). ¹H‐NMR and MALDI‐TOF‐MS studies of the obtained poly(ε‐caprolactone)s revealed the presence of an isopropoxy group originated from the initiator at the polymer termini, indicating that the polymerization takes place exclusively at the Ti–OⁱPr bond of the catalyst. The higher molecular weight polymers (M_n ≤ 70,000 g mol^?1) with reasonable MWD (M_w/M_n ≤ 1.6) were synthesized by living ROP of ε‐caprolactone using spirobititanocanes ( 2a , 2b ) and titanocane 1c as initiators. The latter catalysts, according MALDI‐TOF‐MS data, afford poly(ε‐caprolactone)s with almost equal content of α,ω‐dihydroxyl‐ and α‐hydroxyl‐ω(carboxylic acid)‐terminated chains arising due to monomer insertion into “Ti–O” bond of dialkanolamine ligand and from initiation via traces of water, respectively. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1230–1240, 2010     

Living copolymerization of ethylene with norbornene mediated by heteroligated (Salicylaldiminato)(β‐enaminoketonato)titanium catalysts

Three heteroligated (salicylaldiminato)(β‐enaminoketonato)titanium complexes [3‐Bu^t‐2‐OC₆H₃CH?N(C₆F₅)][(p‐XC₆H₄)N?C(Bu^t)CHC(CF₃)O]TiCl₂ ( 3a : X = F, 3b : X = Cl, 3c : X = Br) were synthesized and investigated as the catalysts for ethylene polymerization and ethylene/norbornene copolymerization. In the presence of modified methylaluminoxane as a cocatalyst, these unsymmetric catalysts exhibited high activities toward ethylene polymerization, similar to their parallel parent catalysts. Furthermore, they also displayed favorable ability to efficiently incorporate norbornene into the polymer chains and produce high molecular weight copolymers under the mild conditions, though the copolymerization of ethylene with norbornene leads to relatively lower activities. The sterically open structure of the β‐enaminoketonato ligand is responsible for the high norbornene incorporation. The norbornene concentration in the polymerization medium had a profound influence on the molecular weight distribution of the resulting copolymer. When the norbornene concentration in the feed is higher than 0.4 mol/L, the heteroligated catalysts mediated the living copolymerization of ethylene with norbornene to form narrow molecular weight distribution copolymers (M_w/M_n < 1.20), which suggested that chain termination or transfer reaction could be efficiently suppressed via the addition of norbornene into the reaction medium. Polymer yields, catalytic activity, molecular weight, and norbornene incorporation can be controlled within a wide range by the variation of the reaction parameters such as comonomer content in the feed, reaction time, and temperature. ©2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6072–6082, 2009     

Demonstration of isospecific free radical polymerization of acrylate controlled by conformation and chirality of monomer

Radical polymerization of lactic acid‐based chiral and achiral methylene dioxolanones, a model for conformationally s‐cis locked acrylate, was carried out with AIBN to demonstrate an isospecific free radical polymerization controlled by chirality and conformation of monomer. Polymerization of the dioxolanones proceeded smoothly without ring opening to give a polymer with moderate molecular weight and 100% of maximum isotacticity. ESR spectrum indicated a twisted conformation of the growing poly(methylene dioxolanone) radical in contrast to an acyclic analogous radical, suggesting a restriction of the free rotation around main chain C_α? C_β bond of the growing radical center. Chirality as well as the polarity and bulkiness of monomer affected the polymer tacticity, and chiral alkyl substituent would afford a high isotactic polymer, in which higher the enantiomeric excess of the monomer was, higher the isotacticity of the polymer was. While, achiral or polar substituents including dibenzyl and trichloromethyl groups would afford an atactic polymer. In addition, glass transition temperature (T_g) of the resulting polymers was significantly high, ranging from 172.2 to 229.8 °C, and even for an isotactic polymer T_g was as high as 206.8 °C. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2007–2016     

Well‐controlled ring‐opening polymerization of cyclic esters catalyzed by aluminum amido complexes: Kinetics and mechanism

A series of aluminum dimethyl complexes 1 – 6 bearing N‐[2‐(pyrrolidinyl)benzyl]anilido ligands were synthesized and well characterized. The molecular structure of complex 1 determined by an X‐ray diffraction study indicates the bidentate chelating mode of the pyrrolidinyl‐anilido ligand. In the absence of a coinitiator, these complexes exhibited excellent control toward the polymerizations of ε‐caprolactone and rac‐lactide, affording polyesters with quite narrow molecular weight distributions (M_w/M_n = 1.04–1.26). The end group analysis of ε?CL oligomer via ¹H NMR and ESI‐TOF MS methods gave strong support to the hypothesis that the polymerization catalyzed by these aluminum complexes proceeds via a coordination‐insertion mechanism involving a unique Al? N (amido) bond initiation. Via ¹H NMR scale oligomerization studies, it is suggested that the insertion of the first lactide monomer into Al? N bond of the complex is much easier than the insertion of lactide monomer into the newly formed Al? O (lactate) bond and might also be easier than the insertion of the first ε?CL monomer into Al? N bond. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 3096–3106     

Titanium complexes based on aminodiol ligands for the ring‐opening polymerization of ε‐caprolactone,rac‐β‐butyrolactone,and trimethylene carbonate

Several titanium complexes based on aminodiol ligands were tested as initiators for the ring‐opening polymerization (ROP) of ε‐caprolactone under solution and bulk conditions. All complexes were found to be efficient under both conditions. For bulk polymerization at 70 °C, high activities were observed (113.3–156.2 g_poly mmol_cat^?1 h^?1) together with controlled molar mass distribution. Kinetic studies revealed controlled polymerization, and the chain propagation was first order with respect to monomer conversion. One complex was also tested for the ROP of rac‐β‐butyrolactone and the end‐group analysis suggested that ring opening occurs through acyl‐oxygen bond cleavage via coordination–insertion mechanism. The microstructure analysis of polymer by ¹³C NMR indicates atactic polymer. Another complex was also found to be efficient initiator for the ROP of trimethylene carbonate under solution and bulk conditions. Again, end‐group analysis suggests coordination–insertion mechanism. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Influence of the catalyst on monomer insertion in the syndiospecific copolymerization of styrene and para‐methylstyrene

The effect of the kind of transition‐metal catalyst on the extent of comonomer insertion in the syndiospecific complex‐coordinative copolymerization of styrene and para‐methylstyrene has been investigated. The results for the influence of the polymerization conditions have shown that there is no real difference between solution copolymerization in toluene and solvent‐free styrene copolymerization in bulk, with respect to the reactivity ratio for para‐methylstyrene (r₂), under comparable conditions in the presence of methylaluminoxane and triisobutylaluminum and at low polymerization conversions. All the investigated catalysts lead to a preferred incorporation of para‐methylstyrene into the polymer chain in comparison with styrene and over the whole range of monomer compositions. The increasing capability of the different catalysts to provide copolymers with enhanced para‐methylstyrene concentrations can be summarized by the increasing r₂ values for the copolymerization in bulk as follows: η⁵‐pentamethylcyclopentadienyl titanium trichloride < η⁵‐octahydrofluorenyl titanium trimethoxide < η⁵‐octahydrofluorenyl titanium tristrifluoroacetate < η⁵‐cyclopentadienyl titanium(N,N‐dicyclohexylamido)dichloride < η⁵‐cyclopentadienyl titanium trichloride. For a correlation between the catalyst structure and the comonomer insertion, the catalysts can be described by electronic effects (electrostatic charge of the transition‐metal atom) and steric effects (minimum structural cone angle). The results show that the steric properties of the transition‐metal complexes have the most important effect on the insertion of para‐methylstyrene into the copolymer. If the minimum structural cone angle of the ligand of the transition‐metal catalyst decreases, the incorporation of the comonomer para‐methylstyrene increases significantly. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2061–2067, 2005     

Stereoselective and regioselective propylene polymerization with group 4 bisphenolate ether complexes

Octahedral group 4 bisphenolate ether complexes, activated by methylaluminoxane, were tested in propylene polymerization in the presence and absence of diethyl zinc. The resulting polypropylenes were analyzed thoroughly by means of differential scanning calorimetry and ¹³C NMR techniques. Despite structural similarity of the Hf and Zr complexes, the performance in propylene polymerization differs significantly in terms of productivity, isospecificity, and propensity to incorporate specific regioerrors. These catalysts are capable of generating high‐molecular weight polypropylene (M_n = 130,000–360,000 g/mol) with isotacticities [mmmm] up to 97% and melting points as high as 165 °C when very bulky ligands are used. ¹³C NMR analysis revealed that the type and the number of regioerrors being incorporated into the polymer chain highly depend on the ligand and the metal. Polymerizations in the presence of diethyl zinc generate saturated low‐molecular weight polypropylenes (M_n = 1700–9900 g/mol) and facilitated an end‐group analysis, which revealed the presence of isobutyl and 2‐methylbutyl groups. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Control of molecular weight in polymerization of vinyl chloride with Cp*Ti(OPh)3/MAO catalyst

Polymerization of vinyl chloride (VC) with titanium complexes containing Ti‐OPh bond in combination with methylaluminoxane (MAO) catalysts was investigated. Among the titanium complexes examined, Cp*Ti(OPh)₃/MAO catalyst (Cp*; pentamethylcyclopentadienyl, Ph; C₆H₅) gave the highest activity for the polymerization of VC, but the polymerization rate was slow. From the kinetic study on the polymerization of VC with Cp*Ti(OPh)₃/MAO catalyst, the relationship between the M_n of the polymer and the polymer yields gave a straight line, and the line passed through the origin. The M_w/M_n values of the polymer gradually decrease as a function of polymer yields, but the M_w/M_n values were somewhat broad. This may be explained by a slow initiation in the polymerization of VC with Cp*Ti(OPh)₃/MAO catalyst. The results obtained in this study demonstrate that the molecular weight control of the polymers is possible in the polymerization of VC with the Cp*Ti(OPh)₃/MAO catalyst. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3872–3876, 2007     

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     

Schiff base as a novel kind of catalyst for reversible complexation‐mediated radical polymerization of methyl methacrylate

Two kinds of Schiff base, N,N′‐dibenzylidene‐1,2‐diaminoethane (NDBE) and N,N′‐disalicylidene‐1,2‐diaminoethane, have been found as efficient organic catalyst for reversible complexation‐mediated radical polymerization (RCMP) of methyl methacrylate (MMA) for the first time. The polymerization results show obvious features of “living”/controlled radical polymerization. Well‐defined and low‐polydispersity polymers (M_w/M_n = 1.20–1.40) are obtained in RCMP of MMA catalyzed by Schiff base at mild temperature (65–80°C). Moreover, Schiff base also exhibits a particularly high reactivity for RCMP of MMA with in situ formed alkyl iodide initiator. The polymer molecular weight and its polydispersity (M_w/M_n is around 1.20) are well controlled even with high monomer conversion. Notably, when the dosage of azo initiator is same as the dosage of iodine, the polymerization could also be realized in the presence of NDBE. The living feature of synthesized polymer is confirmed through the chain extension experiment. In short, Schiff base is a kind of high‐efficient catalyst for RCMP and reverse RCMP of MMA, which can be one of the most powerful and robust techniques for polymer synthesis. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1653–1663     

Polymerization of 4‐methylpentene and vinylcyclohexane by amine bis(phenolate) titanium and zirconium complexes

The polymerization of the substituted olefins 4‐methylpentene and vinylcyclohexane by dibenzyl titanium and zirconium complexes of three amine bis(phenolate) ligands is reported. The ligands featured a dimethylamino side‐arm donor and either electron‐withdrawing (Cl and Br) or methyl phenolate substituents. After activation with B(C₆F₅)₃, the zirconium catalysts exhibited a higher activity than the titanium catalysts toward these bulky olefins. Very high weight‐average molecular weight poly(4‐methylpentene) was obtained with the zirconium catalysts. The zirconium catalysts were employed in 1‐hexene polymerization, and their activity was found to be the highest ever reported for catalysts of the amine bis(phenolate) family. The catalysts featuring methyl phenolate substituents showed a higher activity toward these substituted olefins than the electron‐poor catalysts; this trend was opposite to their activity toward 1‐hexene. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1136–1146, 2006     

Facile one‐pot/one‐step technique for preparation of side‐chain functionalized polymers: Combination of SET‐RAFT polymerization of azide vinyl monomer and click chemistry

An azido‐containing functional monomer, 11‐azido‐undecanoyl methacrylate, was successfully polymerized via ambient temperature single electron transfer initiation and propagation through the reversible addition–fragmentation chain transfer (SET‐RAFT) method. The polymerization behavior possessed the characteristics of “living”/controlled radical polymerization. The kinetic plot was first order, and the molecular weight of the polymer increased linearly with the monomer conversion while keeping the relatively narrow molecular weight distribution (M_w/M_n ≤ 1.22). The complete retention of azido group of the resulting polymer was confirmed by ¹H NMR and FTIR analysis. Retention of chain functionality was confirmed by chain extension with methyl methacrylate to yield a diblock copolymer. Furthermore, the side‐chain functionalized polymer could be prepared by one‐pot/one‐step technique, which is combination of SET‐RAFT and “click chemistry” methods. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Polymerization of β‐pinene with Schiff‐base nickel complexes catalyst: Synthesis of relatively high molecular weight poly(β‐pinene) at high temperature with high productivity

A series of easily accessible and stable Schiff‐base nickel complexes (complex 1 – 4 ) in conjunction with methylaluminoxane (MAO) were employed for the synthesis of relatively high molecular weight β‐pinene polymers at high temperature with high productivity. The ligand structure of the complex had a substantial effect on the polymerization in terms of the productivity and the molecular weight. With complex 4 in the presence of MAO, high molecular weight polymers of β‐pinene (M_n ～ 10,900) were obtained at 40 °C with an extremely high productivity up to 1.25 × 10⁷ g polyβ‐pinene/mol of Ni. ¹H NMR analyses showed that the obtained β‐pinene polymer was structurally identical to that formed by conventional cationic Lewis acid initiators. The polymerization was presumably initiated by the nickel cation formed by the reaction of the schiff‐base nickel complex and MAO, while the propagation proceeded in a manner typical for a conventional carbocationic polymerization process. Direct evidence for the carbocationic polymerization was offered by the fact that quenching of the polymerization with methanol at a low monomer conversion resulted in incorporation of a methoxyl end group into the polymer chain. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3739–3746, 2007     

Polymerization of styrene in alcohol/water mediated by a macro‐RAFT agent of poly(N‐isopropylacrylamide) trithiocarbonate: From homogeneous to heterogeneous RAFT polymerization

The reversible addition fragmentation chain transfer (RAFT) polymerization of styrene in alcohol/water mixture mediated with the poly(N‐isopropylacrylamide) trithiocarbonate macro‐RAFT agent (PNIPAM‐TTC) is studied and compared with the general RAFT dispersion polymerization in the presence of a small molecular RAFT agent. Both the homogeneous/quasi‐homogeneous polymerization before particle nucleation and the heterogeneous polymerization after particle nucleation are involved in the PNIPAM‐TTC‐mediated RAFT polymerization, and the two‐stage increase in the molecular weight (M_n) and nanoparticle size of the synthesized block copolymer is found. In the initial homogeneous/quasi‐homogeneous polymerization, the M_n and nanoparticle size slowly increase with monomer conversion, whereas the M_n and particle size quickly increase in the subsequent heterogeneous RAFT polymerization, which is much different from those in the general RAFT dispersion polymerization. Besides, the PNIPAM‐TTC‐mediated RAFT polymerization runs much faster than the general RAFT dispersion polymerization. This study is anticipated to be helpful to understand the polymer chain extension through RAFT polymerization under dispersion conditions. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Ring‐opening polymerization of β‐butyrolactone catalyzed by efficient magnesium and zinc complexes derived from tridentate anilido‐aldimine ligand

Magnesium (Mg) and zinc (Zn) complexes incorporating tridentate anilido‐aldimine ligand, (E)‐2, 6‐diisopropyl‐N‐(2‐((2‐(piperidin‐1‐yl)ethylimino)methyl)phenyl)aniline ( AA ^Pip ‐H, 1 ), were synthesized and structurally characterized. The reaction of AA ^Pip ‐H ( 1 ) with MgⁿBu₂ or ZnEt₂ in equivalent proportions afforded the monomeric complex [( AA ^Pip )MgⁿBu] ( 2 ) or [( AA ^Pip )ZnEt] ( 3 ), respectively. The coordination modes of these complexes differ in the solid state: Mg complex 2 shows a four‐coordinated and distorted tetrahedral geometry, whereas Zn complex 3 adopts a trigonal planar geometry with a three‐coordinated Zn center. Complexes 2 and 3 are efficient catalysts for the ring‐opening polymerization of β‐butyrolactone (β‐BL) in the presence of 9‐anthracenemethanol (9‐AnOH). The polymerization of β‐BL with the Zn catalyst system is demonstrated in a living fashion with a narrow polydispersity index, PDI = 1.01–1.10. The number‐averaged molecular weight (M_n) of the produced poly(3‐hydroxybutyrate) (PHB) is quite close to the expected M_n over diverse molar ratios of monomer to 9‐AnOH. A greater ratio of monomer to alcohol catalyzed by Zn complex 3 served to form PHB with a large molecular weight (M_n > 60000). An effective method to prepare PHB‐b‐PCL and PEG‐b‐PHB by the ring‐opening copolymerization of β‐BL catalyzed by zinc complex 3 is reported. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010