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     

Unconstrained geometry complexes: Ethylene/α‐olefin copolymerizations with a tetramethyldisilyl‐bridged Cp‐amido titanium complex

A new disilyl‐bridged complex, [(N‐tert‐butylamido)(3‐indenyl)tetramethyldisilyl]titanium dichloride ( 3 ), was synthesized and activated with methylaluminoxane (MAO) for propylene homopolymerization and ethylene/propylene and ethylene/1‐hexene copolymerizations. A polypropylene with a slight isotactic enrichment was obtained. The number of regioerrors present in the polypropylene was somewhat smaller than that found in most polypropylenes made from monosilyl‐bridged [(N‐tert‐butylamido)(3‐indenyl)dimethylsilyl]titanium dichloride. The regioerrors detected in the copolymers obtained from 3 /MAO were on the order of the amounts observed in polymers made with the monosilyl‐bridged constrained geometry catalysts. Ethylene copolymers of propylene and 1‐hexene had random sequence distributions and showed significant comonomer incorporation. Because of the presence of regioerrors, a modified method for determining the monomer composition and sequence distribution was developed from the direct measurement of the monomer content from the number of methylene and methine carbons per polymer chain, regardless of propylene inversion. An estimate of the error in the copolymerization reactivity ratio determination for regioirregular ethylene/α‐olefin copolymers was obtained by the calculation of the reactivity ratios from monomer dyad sequences, with consideration given to the contribution of major regioirregular sequences. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3840–3851, 2005     

Syndiotactic‐specific radical polymerization of N,N‐dimethylacrylamide in the presence of tartrates: A proposed mechanism for the polymerization

Radical polymerization of N,N‐dimethylacrylamide (DMAAm) was investigated in the presence of tartrates, such as diethyl L ‐tartrate, diisopropyl L ‐tartrate, and di‐n‐butyl L ‐tartrate, in toluene at low temperatures. Syndiotactic polymers were obtained in the presence of tartrates, whereas isotactic polymers were obtained in the absence of tartrates. The syndiotactic‐specificity increased with increasing amount of tartrates and with decreasing polymerization temperature. NMR analysis suggested that DMAAm and tartrates formed a 1:1 complex through double hydrogen bonding. A mechanism for the syndiotactic‐specific radical polymerization of DMAAm is proposed. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1192–1203, 2009     

The effect of the N‐substituent s‐trans to the carbonyl group of N‐methylacrylamide derivatives on the stereospecificity of radical polymerizations

Radical polymerization of N‐methylacrylamide (NMAAm), N,N‐dimethylacrylamide (DMAAm), and N‐methyl‐N‐phenylacrylamide (MPhAAm) was investigated in toluene at low temperatures. Atactic, isotactic, and syndiotactic polymers were obtained by the polymerization of NMAAm, DMAAm, and MPhAAm, respectively, indicating that the stereospecificity of the radical polymerization of acrylamide derivatives depended on the N‐substituents of the monomer used. From the viewpoint of monomer structure, the origin of the stereospecificity of radical polymerization of NMAAm derivatives is discussed. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6534–6539, 2009     

Inelastic neutron scattering from isotactic polypropylene

We used inelastic neutron scattering to probe the low‐energy excitations in semicrystalline isotactic polypropylenes with different degrees of crystallinity. The contributions from the amorphous and crystalline regions to the total scattering intensity were extracted under the assumption of a weighted linear contribution of the two regions in a simplified two‐phase system. The resulting intensity from the amorphous region showed a peak at 1.2 meV that was in good agreement with the previously determined boson peak characteristic of atactic polypropylene. The possibility of a contribution to the boson peak region by longitudinal acoustic mode modes that are characteristic of semicrystalline polymers and appear in the same low‐frequency region is discussed. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2852–2859, 2001     

Melt amination of polypropylenes

Amine (primary and secondary) functional polypropylenes were prepared by the melt blending of maleated polypropylenes with small diamines, including hexamethylenediamine (primary–primary diamine), p‐xylylenediamine (primary–primary diamine), and N‐hexylethylenediamine (primary–secondary diamine), at various diamine/anhydride molar ratios in a batch mixer and a twin‐screw extruder. The experimental conversion data by Fourier transform infrared nearly agreed with the assumption of a complete reaction between the primary amine and anhydride. Chain extensions of the maleated polypropylenes by the diamines were monitored by the torques during mixing and further evaluated by rheological (dynamic shear rheometry) and mechanical measurements. We show that these amino polypropylenes are very effective adhesion promoters and compatibilizers of thermoplastic polyurethanes with polypropylene. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4217–4232, 2005     

Synthesis of hydrophilic isotactic polypropylenes promoted by metallocene catalysts

In this paper, the synthesis of isotactic polypropylenes (i‐PP) modified with ? OH groups in sides (iPP‐OH), by combination of polyinsertion ansa‐metallocene catalysis and ring opening of propene oxide (PO), is described. i‐PP sequences interrupted by isolated ethylene/p‐methylstyrene units forms the backbone. This enchainment is obtained by controlled copolymerization of propene with ethylene and p‐methylstyrene comonomers in the presence of rac‐ethylenebis(1‐indenyl)zirconiumdichloride/methylalumoxane system. The metallation reaction of the p‐methyl group with sec‐BuLi generates an anionic center that can be reacted with PO. The iPP‐OH is the result of the monoaddition reaction of PO followed by hydrolysis with acidified methanol. By changing experimental conditions in the backbone synthesis, a tuned number of the functionalizable sites as well as polypropylene sequence lengths can be obtained. As a consequence, iPP samples with a different number of ? OH groups for the backbone can be synthesized after the PO monoaddition reaction. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 7008–7013, 2006     

Synthesis of a [60] fullerene—Functionalized isotactic polypropylene derivative

The covalent attachment of [60] fullerene (C₆₀) to isotactic polypropylene (i‐PP) is achieved by direct reaction in 1,2,4‐trichlorobenzene (TCB) solution in the presence of dicumyl peroxide (DCP). The chemically modified pendant C₆₀/i‐PP polymers are soluble in chlorinated solvents and have been characterized by ultraviolet–visible and fourier transform infrared spectroscopy, scanning electron microscopy, X‐ray diffraction, differential scanning calorimetry, cyclic voltametry, and thermogravimetric analysis. From the results it can be concluded that the modification of i‐PP by grafting via a free‐radical reaction competes with the possibility of chain scission of i‐PP due to the presence of DCP. The functionalized polymers crystallize in the monoclinic crystal modification, and have high crystallinity. The incorporation of C₆₀ significantly enhances the thermal stability of the i‐PP. Electrochemical measurements demonstrate good electron acceptor properties of the fullerenated i‐PP samples. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6722–6733, 2008     

Molecular orientation and mechanical anisotropy of polypropylene sheet containing N,N′‐dicyclohexyl‐2,6‐naphthalenedicarboxamide

Effect of mixing and processing conditions at T‐die extrusion on the structure and mechanical properties is studied for isotactic polypropylene (PP) containing a small amount of β‐form nucleating agent, N,N′‐dicyclohexyl‐2,6‐naphthalenedicarboxamide. It is found that trigonal β crystals are predominantly formed in the extruded samples containing the nucleating agent irrespective of the mixing and processing conditions, leading to the marked mechanical toughness. On the contrary, the molecular orientation is significantly affected by the mixing and processing conditions. In particular, it should be noted that PP molecules in the extruded sheet which was mixed at high temperature (260 °C) and extruded at low temperature (200 °C) orient perpendicular to the applied flow direction. As a result, the sheet shows anomalous mechanical anisotropy. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 424–433, 2009     

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     

Near‐infrared electrochromic poly(aryl ether)s based on isolated electroactive tetraphenyl‐p‐phenylenediamine moieties

A series of near‐infrared (NIR) electrochromic aromatic poly(aryl ether)s containing N,N,N′,N′‐tetraphenyl‐p‐phenylenediamine (TPPA) moieties in the backbone were prepared from the high‐temperature polycondensation reactions of a biphenol monomer, 2,5‐bis(diphenylamino)hydroquinone, with difluoro compounds. The obtained polymers were readily soluble in many organic solvents and showed useful levels of thermal stability associated with high glass‐transition temperatures (182–205 °C) and high char yields (higher than 40% at 800 °C in nitrogen). The polymer films showed reversible electrochemical oxidation with high contrast ratio both in the visible range and NIR region, and also exhibited high coloration efficiency (CE), low switching time, and stability for electrochromic operation. The polyether TPPA‐a thin film revealed good CE in visible (CE = 217 cm²/C) and NIR (CE = 192 cm²/C) region with reversible electroactive stability (over 500 times within 5% loss relative to its initial injected charge). © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5378–5385, 2009     

Synthesis of well‐defined azide‐terminated poly(vinyl alcohol) and their subsequent modification via click chemistry

A new azide‐functionalized xanthate, S‐(4‐azidomethylbenzyl) O‐(2‐methoxyethyl) xanthate, was synthesized and used to mediate the reversible addition fragmentation chain transfer polymerization of vinyl acetate. The polymerization was demonstrated to be controlled, and well‐defined PVAc with α‐azide, ω‐xanthate groups were obtained, the xanthate groups of which were further removed by radical‐induced reduction with lauroyl peroxide in the presence of excess 2‐propanol. Hydrolysis of α‐azide‐terminated PVAc (N₃‐PVAc) led to the formation of the corresponding α‐azide‐terminated PVA (N₃‐PVA). Finally, end‐modification of N₃‐PVA by click chemistry with alkyne‐end‐capped poly(caprolactone) (A‐PCL), alkynyl‐mannose, and alkynyl‐pyrene was carried out to obtain a new block copolymer PCL‐b‐PVA, and two PVA with mannose or pyrene as the end functional groups. The polymers were characterized by gel permeation chromatography, ¹H NMR spectroscopy, and FTIR. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4494–4504, 2009     

Rheological behavior of polypropylene/octavinyl polyhedral oligomeric silsesquioxane composites

The reactive blending composites of isotactic polypropylene (PP)/octavinyl polyhedral oligomeric silsesquioxane (POSS) were prepared in the presence of dicumyl peroxide. Comparison of the rheological behavior of physical and reactive blending composites was made by oscillatory rheological measurements. It was found that the viscosity of physical blending composites drops at lower POSS content (0.5–1 wt %) and thereafter increases with increasing POSS content; that of reactive blending composites increases with increasing POSS content and displays a solid‐like rheological behavior at low frequency region when POSS content is higher than 1 wt %. The deviation of reactive blending composites from the scaling log G′–log G″ of linear polymer in Han plot, upturning at high viscosity in Cole–Cole plot, and from van Gurp–Palmen plot are related to the gelation behavior reactively. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 526–533, 2008     

Isothermal crystallization behavior of exfoliated‐PP/IMMT nanocomposites via in situ polymerization

Highly exfoliated isotactic‐polypropylene/alkyl‐imidazolium modified montmorillonite (PP/IMMT) nanocomposites have been prepared via in situ intercalative polymerization. TEM and XRD results indicated that the obtained composites were highly exfoliated PP/IMMT nanocomposites and the average thickness of IMMT in PP matrix was less than 10 nm, and the distance between adjacent IMMT particles was in the range of 20–200 nm. The isothermal crystallization kinetics of highly exfoliated PP/IMMT nanocomposites were investigated by using differential scanning calorimeter(DSC) and polarized optical microscope (POM). The crystallization half‐time t_1/2, crystallization peak time t_max, and the Avrami crystallization rate constant K_n showed that the nanosilicate layers accelerate the overall crystallization rate greatly due to the nucleation effect, and the crystallization rate was increased with the increase in MMT content. Meanwhile, the crystallinity of PP in nanocomposites decreased with the increase in clay content which indicated the PP chains were confined by the nanosilicate layers during the crystallization process. Although the well‐dispersed silicate layers did not have much influence on spherulites growth rate, the nucleation rate and the nuclei density increased significantly. Accordingly, the spherulite size decreased with the increase in MMT content. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2215–2225, 2009     

Crystalline Isotactic Polar Polypropylene from the Palladium‐Catalyzed Copolymerization of Propylene and Polar Monomers

Moderately isospecific homopolymerization of propylene and the copolymerization of propylene and polar monomers have been achieved with palladium complexes bearing a phosphine‐sulfonate ligand. Optimization of substituents on the phosphorus atom of the ligand revealed that the presence of bulky alkyl groups (e.g. menthyl) is crucial for the generation of high‐molecular‐weight polypropylenes (M_w≈10⁴), and the substituent at the ortho‐position relative to the sulfonate group influences the molecular weight and isotactic regularity of the obtained polypropylenes. Statistical analysis suggested that the introduction of substituents at the ortho‐position relative to the sulfonate group favors enantiomorphic site control over chain end control in the chain propagation step. The triad isotacticity could be increased to mm=0.55–0.59, with formation of crystalline polar polypropylenes, as supported by the presence of melting points and sharp peaks in the corresponding X‐ray diffraction patterns.     

Star polymers with POSS via azide–alkyne click reaction

Azidopropyl‐heptaisobutyl‐substituted polyhedral oligomeric silsesquioxane (POSS‐N₃) was reacted with 1,1,1‐tris[4‐(2‐propynyloxy)phenyl]‐ethane ( 1 ) and poly(ethylene glycol) (PEG)‐b‐poly(methyl methacrylate) (PMMA) copolymer with alkyne at its center (PEG‐PMMA‐alkyne) affording the first time synthesis of 3‐arm star POSS and PEG‐PMMA‐POSS 3‐miktoarm star terpolymer, respectively, in the presence of CuBr/N,N,N′,N″,N″‐pentamethyldiethylenetriamine as catalyst and N,N‐dimethylformamide/tetrahydrofuran as solvent at room temperature. The precursors and the target star polymers were characterized comprehensively by ¹H NMR, GPC, and DSC. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5947–5953, 2009     

Synthesis of highly isotactic poly(N,N‐diethylacrylamide) by anionic polymerization with grignard reagents and diethylzinc

N,N‐Dimethylacrylamide (DMA) and N,N‐diethylacrylamide (DEA) were polymerized with various Grignard reagents in tetrahydrofuran at −78 °C in the presence of diethylzinc (Et₂Zn). Highly isotactic poly(DEA) was produced in quantitative yield with tert‐butylmagnesium bromide and Et₂Zn, whereas atactic poly(DEA) was generated in the absence of Et₂Zn. No stereospecific polymerization of DMA proceeded with Grignard reagent in the presence of Et₂Zn. The highly isotactic poly(DEA) obtained was soluble in water and showed the characteristic coil–globule transition phenomenon. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4677–4685, 2000     

Copolymerization of propylene with 1,3‐butadiene using isospecific zirconocene catalysts

Poly(propylene‐ran‐1,3‐butadiene) was synthesized using isospecific zirconocene catalysts and converted to telechelic isotactic polypropylene by metathesis degradation with ethylene. The copolymers obtained with isospecific C₂‐symmetric zirconocene catalysts activated with modified methylaluminoxane (MMAO) had 1,4‐inserted butadiene units ( 1,4‐BD ) and 1,2‐inserted units ( 1,2‐BD ) in the isotactic polypropylene chain. The selectivity of butadiene towards 1,4‐BD incorporation was high up to 95% using rac‐dimethylsilylbis(1‐indenyl)zirconium dichloride (Cat‐A)/MMAO. The molar ratio of propylene to butadiene in the feed regulated the number‐average molecular weight (M_n) and the butadiene contents of the polymer produced. Metathesis degradations of the copolymer with ethylene were conducted with a WCI₆/SnMe₄/propyl acetate catalyst system. The ¹H NMR spectra before and after the degradation indicated that the polymers degraded by ethylene had vinyl groups at both chain ends in high selectivity. The analysis of the chain scission products clarified the chain end structures of the poly(propylene‐ran‐1,3‐butadiene). © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5731–5740, 2007     

Synthesis and characterizations of new isotactic homopolyesters,statistical and block copolyesters derived of poly((S)‐3,3‐dimethylmalic acid) via the lactone route

This article presents the synthesis of a new family of synthetic isotactic polyesters derived from poly((S)‐3,3‐dimethylmalic acid) (PDMMLA). These polyesters are prepared via the lactone route bearing functionalized groups in its main or side chain. The aim of this work is twofold: metabolism and stereochemistry. First, the synthesis of these new polyesters is chosen to provide biodegradable polyesters biocompatible and bioassimilable by the human body. Next, the molecular chain of this family contains a stereogenic center in the aim to provide 100% isotactic homopolymers and copolymers (statistical and block). Finally, these polymers have been characterized by several analytical techniques: FTIR, ¹H and ¹³C NMR, SEC, DSC, and TGA. The greatest importance will be given to the ¹³C NMR and DSC to principally confirm the stereoregularity and crystallinity of these stereopolyesters. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1495–1507     

Morphology development during isothermal crystallization. I. Isotactic and atactic polypropylene blends

Morphology development during isothermal crystallization in equal molecular weight isotactic polypropylene (iPP) and atactic polypropylene (aPP) blends was studied with time‐resolved simultaneous small‐angle X‐ray scattering (SAXS) and wide‐angle X‐ray scattering methods with synchrotron radiation. The final long period obtained after crystallization at 115 °C was nearly independent of blend composition up to 50 wt % aPP but showed an increase in the 80 wt % aPP blend. At a high crystallization temperature (137.5 °C), the increase in the final long period with aPP content was significant, and the evolution of iPP crystallinity was also affected. However, at low crystallization temperatures, the additive decrease of the crystallinity and the constant melting point with increasing aPP content suggest that the crystallizability and crystal morphology of iPP is not a strong function of aPP. The iPP/aPP blends showed a strong low‐angle SAXS upturn as a function of composition, which suggests the segregation of aPP on size scales larger than the lamellar spacing. A detailed analysis of the SAXS patterns indicates that aPP disrupts the ordering within the lamellar stacking. The results are generally consistent with predominantly interfibrillar incorporation of the aPP diluent within the microstructure, with only modest interlamellar incorporation dependent on the crystallization temperature. The findings can be attributed to the partial miscibility/mixing of the aPP and iPP components in the blend before crystallization, depending on the crystallization undercooling. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2580–2590, 2000