Preparation of syndiotactic polyolefins by using metallocene catalysts

Summary Polyolefins having syndiotactic structure were obtained by using 1-methyl-1-ethylidene-(cyclopentadienyl-1′-fluorenyl) zirconium dichloride and methylaluminoxane as a catalyst. 1-Butene and 4-methyl-1-pentene gave crystalline polymers having syndiotactic structure, while 1-pentene, 1-hexene and 1-octene gave noncrystalline polymers having syndiotactic structure. The identification of syndiotactic and isotactic polyolefins was made by ¹³C-NMR, X-ray diffraction, and differential scanning calorimetry.     

Preparation and properties of stereoregular poly(hydroxyethyl methacrylate) polymers and hydrogels

Linear poly(hydroxyethyl methacrylate) (PHEMA) has been synthesized in highly syndiotactic and highly isotactic configurations. The high syndiotactic PHEMA prepared by u.v. photolysis at ?40° C was found by ¹³C n.m.r. to have a tactic triad content of 84% syndio, 16% hetero and 0% iso. High isotactic PHEMA was prepared by anionic polymerization of benzoxyethyl methacrylate in toluene followed by selective hydrolysis of the benzoate ester, and was observed by ¹³C n.m.r. to have a 5% syndio, 15% hetero and 80% isotactic triad content. A linear PHEMA polymer formed by radical polymerization at 60°C in ethanol solvent was found to have a tactic triad content of 58% syndio, 42% hetero and 0% iso. These polymers have been crosslinked with hexamethylene diisocyanate and their water swelling properties determined as functions of temperature and crosslinker concentration. Isotactic PHEMA exhibited greater aqueous swelling below 30° C than the syndiotactic PHEMA samples. The stereochemistry of the polymer chain is shown to be a factor in determining the swelling behaviour of hydrophilic methacrylate gels.     

Stereocomplex formation between isotactic PMMA and syndiotactic polymethacrylates in bulk and in solution

Summary Blend of isotactic PMMA and syndiotactic poly(benzyl methacrylate) was found to form stereocomplex when annealed at 80°C. The blend showed endotherm in DSC thermogram due to the melting of the complex. The complex was also formed in toluene, which was evidenced by¹H NMR spectroscopy and thermal analysis. Several syndiotactic polymers of substituted benzyl methacrylates and aliphatic methacrylates having primary alkyl ester group with branching at -position, such as methallyl and cyclopropylmethyl methacrylates, were also found to form stereocomplexes with isotactic PMMA in bulk by annealing.     

Effect of polymer microstructure on methyl group torsional vibrations

Fundamental torsional frequencies of methyl groups have been measured with neutron incoherent inelastic scattering for isotactic poly(methyl methacrylate)-COOCD₃, and heterotactic, syndiotactic and head-to-head isomers of poly(α-methylstyrene). The measurements confirm that the spectrum of isotactic PMMA differs considerably from the syndiotactic polymer in the region of the fundamental vibration, but no difference is found for the two stereoregular forms of poly(α-methylstyrene). However, the torsional frequency of the methyl group in the head-to-head configuration of α-methylstyrene lies at lower wavenumbers than that observed in the head-to-tail.     

Measurement of the unperturbed dimensions of stereoregular poly(methyl methacrylate)

The results of measurements of unperturbed dimensions for a series of stereoregular poly(methyl methacrylates) are reported. The measurements were made by a recently developed method involving a gel permeation chromatograph coupled with an on-line low angle laser light scattering photometer. Measurements were performed in a thermodynamically good solvent, tetrahydrofuran at 25°C. The unperturbed dimensions were obtained by means of viscosity plots. Comparison of the results obtained by this method with those currently available in the literature, as well as with values predicted by statistical calculations, show good agreement. It was determined that a measurable difference occurs in the Mark-Houwink relationship between isotactic and syndiotactic poly(methyl methacrylate); isotactic poly(methyl methacrylate) is 30% more extended than syndiotactic poly(methyl methacrylate) in its unperturbed state; and isotactic poly(methyl methacrylate) exhibits a smaller degree of polymer solvent interaction than the syndiotactic form.     

Determination of tacticity in polypropylene by FTIR with multivariate calibration

A method for determination of tacticity in polypropylene (PP) using FTIR associated with multivariate analysis is presented. Blends of PP with known tacticity were prepared with isotactic, syndiotactic, and atactic polymer and analyzed by ¹³C‐NMR. The FTIR spectra were recorded and processed through principal components regression (PCR) and partial least‐squares regression (PLS), using information from several different portions of the spectra. The method was compared with the classical methods of tacticity determination by FTIR based on the intensities of the bands at 998 cm^?1 (isotactic), 868 cm^?1 (syndiotactic), and 975 cm^?1 (internal standard), which are known to be dependent on the crystallinity of the polymer and, thus, affected by temperature and sample preparation. The models obtained with multivariate calibration, both with PCR and PLS, gave prediction errors up to fivefold smaller than that of the classical methods, and were also shown not to be heavily dependent on the bands that are affected by the crystallinity of the polymer, but rather on the methyl and methylene bendings at 1375 and 1462 cm^?1. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 734–745, 2002     

Matrix tacticity controlled tuning of microstructure,constitutive behavior and rheological percolation effect of melt‐mixed amino‐functionalized MWCNT/PP nanocomposites

Amino‐functionalized multi walled nanotube (MWCNT‐NH₂) filled isotactic PP and isotactic‐syndiotactic (70:30) mixed PP based melt‐mixed nanocomposites have been comparatively evaluated with regard to morphological, rheological and thermo‐mechanical properties. The ratio of mean free space lengths (L_f) to infiltrated mean free space lengths (L_inf) between nanotubes in isotactic‐syndiotactic (70:30) blended matrix based nanocomposites increased relatively indicating a dispersed‐morphology. The rheological percolation threshold increased up to a higher extent of MWCNT‐NH₂ loading (from ø_c ～ 2.3 × 10^?4 in isotactic to ø_c ～ 11 × 10^?4 in iso‐syndio blend) accompanied with the formation of a mechanically responsive network structure. van‐GurpPalmen plot showed a transition in the rheological response as a consequence of network morphology getting shifted to higher concentration of MWCNT‐NH₂ in the isotactic‐syndiotactic mixed PP based nanocomposites than in the isotactic based one. Constitutive modeling of complex viscosity response of the nanocomposites led to functional correlation between the percolation and relaxation dynamics of polymer chains. POLYM. ENG. SCI., 58:1115–1126, 2018. © 2017 Society of Plastics Engineers     

1H- and 13C-NMR of tactic polymethallylalcohols and polymethallylurethanes

Summary The reduction of syndiotactic or isotactic polymethyl-methacrylate yields the tactic polymethallylalcohols. Degree of conversion and tacticity can be determined by ¹H-and ¹³C-NMR. The polymethallylalcohols are reacted with isocyanates to obtain the corresponding polymethallyl urethanes whose ¹³C-NMR spectra are also studied.     

Syndiotactic poly[(R,S)-β-hydroxybutyrate]isolated from methylaluminoxane-catalyzed polymerization

Summary Poly[(R,S)--hydroxybutyrate] was prepared via the methylaluminoxane-catalyzed polymerization of (R,S)--butyrolactone, fractionated, and characterized by ¹H and ¹³C nmr, gel permeation chromatography, differential scanning calorimetry, and x-ray diffraction. All the material isolated from these reactions was identified by nmr as poly(-hydroxybutyrate), but in each case, ¹³C nmr showed that a portion of the material contained more syndiotactic than isotactic diads. Although this new syndiotactic material was low in molecular weight, it showed crystallinity by differential scanning calorimetry and x-ray diffraction, with d-spacings different in value and relative intensity from those of the isotactic polymer.     

Irreversibility of stretching‐induced local conformational changes as verified through an FTIR dichroism study for PVC

The dichroic behaviour of 615 and 637 cm⁻¹ bands of the IR spectrum of poly(vinyl chloride) (PVC) has been analysed through FTIR measurements on PVC films stretched to various elongation ratios. By comparing the evolution both of the dichroic ratios and of the relative absorbance of those bands in the perpendicular direction to that of stretching, the occurrence of local chain orientation related to the conformational change GTTG⁻TT⇒ GTGTTT at mmr isotactic tetrads can be differentiated from the normal orientation of syndiotactic sequences, so confirming earlier proposals that the above conformational change takes place when stretching PVC. © 1999 Society of Chemical Industry     

Low-frequency thermomechanical spectrometry of polymeric materials: Tactic poly(methyl methacrylates)

A computerized and automated torsional pendulum has been used to characterize amorphous poly(methyl methacrylates) at about 1 Hz in the temperature sequence 473° → 93° → 473°K. The effects of thermal prehistory, temperature cycling, water content, and tacticity are demonstrated. In particular, a comparison of the out-of-phase shear modulus (G″) versus temperature for “syndiotactic,” “atactic,” and “isotactic” polymer specimens shows that the intensity of the glassy-state β loss peak decreases with increasing isotactic content while the temperature of its location remains the same. Extrapolation suggests that completely isotactic polymer would not display a β loss peak. The shape and location of the G″ data at low temperatures indicate that the basic mechanism of the β process is the same for the three polymer samples and support the validity of the extrapolation. The effect of tacticity is reflected also in the glass transition region; the isotactic sample has its T_g about 65°C lower with greater intensity than the syndiotactic polymer.     

NMR-study of structure and dynamics of associates of syndiotactic poly(methyl methacrylate) in toluene

Summary High-resolution ¹H NMR spectra (¹H HR-NMR) of solutions of isotactic (i) and syndiotactic (s) poly(methyl methacrylate) (PMMA) in toluene-d₈ were measured in the concentration range 0.2 to 10% w/v; for solutions of s-PMMA (10% w/v), ¹H NMR spectra with magic angle rotation (MAR-NMR) at various temperatures and ¹³C NMR spectra with strong proton decoupling were also measured. It was found that even in very dilute solutions of s-PMMA in toluene-d₈ a considerable portion (76%) of polymer segments are associated: association is of intramolecular origin and is due to interaction of long syndiotactic sequences. Prom NMR spectra the motion of associated segments appears as isotropic with and effective correlation frequency 10⁶ – 10⁷ Hz. A globular structure of the associates of s-PMMA is proposed.     

Relation between PVT measurements and linear viscosity in isotactic and syndiotactic polypropylenes

Pressure-Volume-Temperature (PVT) data of an isotactic and a syndiotactic PP are fitted to a modification of the Simha-Somcynsky equation of state (S-S), to calculate characteristic parameters, such as V^∗, T^∗, P^∗ and the solubility parameter δ. The hole fraction of the S-S model and the free volume are deduced from these parameters. The application of a modified Doolittle equation and a modified Berry-Fox equation to estimate viscosity, leads to extract novel conclusions on the differences between both types of PPs. An equation which accounts for the effect of temperature on the characteristic ratio of syndiotactic PP is presented.     

Preparation of PMMA macromers by o-vinylbenzylmagnesium chloride and their polymerization

Summary Polymerization of MMA with o-vinylbenzylmagnesium chloride was examined in toluene and in tetrahydrofuran (THF) at various temperatures. The polymer formed in toluene at –78°C was highly isotactic (mm=94%) and containing one vinylbenzyl group at the -end of the chain, although the methanol-soluble fraction concomitantly formed in an appreciable amount was less isotactic. The PMMAs formed in THF at –78 and –98°C were mostly methanol-soluble and highly syndiotactic (rr=88% at –78°C and 96% at –98°C), and also contained one vinylbenzyl group. The methanol-soluble, isotactic and syndiotactic PMMA macromers were polymerized or copolymerized with styrene by AIBN in toluene at 60°C. The isotactic macromer exhibited slightly higher reactivity than the syndiotactic one.     

Copolymerisation of 1,9-decadiene and propylene with binary and isolated metallocene systems

1,9-Decadiene/propylene copolymers were obtained with isolated metallocenes and with a binary metallocene catalyst system activated by methylaluminoxane. The metallocenes under investigation were syndiospecific diphenylmethyl(cyclopentadienyl)(9-fluorenyl)zirconium dichloride (1) and isospecific rac-dimethylsilylbis(4-tert-butyl-2-methyl-cyclopentadienyl)zirconium dichloride (2). A copolymer structure, in which 1,9-decadiene linked isotactic and syndiotactic polymer chains, was obtained when copolymerisation was started with catalyst 2 at 80 °C followed by injection of catalyst 1 and instantaneous lowering of polymerisation temperature to 40 °C after 15 min of polymerisation. The copolymer was also shown to work as a compatibiliser in a blend of syndiotactic and isotactic polypropylene. We propose that catalyst 2 incorporates 1,9-decadiene into the isotactic main chain without any significant crosslinking within the first 15 min of polymerisation at 80 °C and the produced isotactic macromonomers are further incorporated at 40 °C into the syndiotactic main chain in polymerisation with catalyst 1.     

Tactic poly(crown ether)s with pendant benzocrown ethers

Summary Tactic and atactic poly(crown ether)s, poly(methacryloyloxymethylbenzo-15-crown-5), were synthesized by polymer reaction of the respective poly(methacrylic acid) with chloromethylbenzo-15-crown-5 and radical polymerization of methacryloyloxymethylbenzo-15-crown-5. By solvent extraction of alkali metal picrates with these poly(crown ether)s, the isotactic poly(crown ether) was found to be a little more selective for K⁺ and Rb⁺ than the syndiotactic and atactic ones.     

Vibrational dynamics and heat capacity in syndiotactic poly(propylene) form II

Normal modes and their dispersion are obtained for planar-zigzag form II (tttt) of syndiotactic polypropylene (sPP) in the reduced zone scheme using Urey-Bradley force field and Wilson's GF matrix method as modified by Higgs. It is observed that this all trans backbone conformation can be characteristized by a band at 1233 cm⁻¹ (calculated at 1239 cm⁻¹). A comparison is made with the spectra of its isotactic and helical form. Characteristic features of the dispersion curves such as crossing, repulsion and von Hove type singularities (regions of high density-of-states) have been explained. Heat capacity obtained from the density-of-states agrees with the experimental data up to 250 K at which the glass transition sets in and the experimental curve exhibits a marked change in slope.     

Wettability and microstructure of polymer surfaces: stereochemical and conformational aspects

Stereoregular poly(methyl methacrylates) (PMMAs) solvent-cast in the form of films against a glass substrate were employed as model systems for a systematic study of the relationship between the molecular structure (as characterized by the stereochemistry and conformations of macromolecules), the functional-group composition, and the wettability of polymer surfaces. The water wettability of a syndiotactic surface was found to be highly sensitive to the polarity of the adjacent phase in the film-casting process, whereas the wettability of an isotactic surface was invariant to the polarity of the contacting medium. The tacticity-dependent wetting behavior arises from the difference in the extent of functional-group surface segregation or, in other words, from the different surface activity of the different tactic versions of the polymer. This difference, in turn, is associated with fundamental distinctions in the conformational structures energetically allowed for the isotactic and syndiotactic configurations of the polymer chain; the syndiotactic macromolecule is capable of adopting an amphiphilic surface conformation, whereas the energetically allowed conformational structures of the isotactic macromolecule do not possess amphiphilic character. In view of these findings, the isotactic surfaces can be regarded as 'ideal' model surfaces for research on the fundamentals of wetting phenomena. In addition, there is evidence for failure of the basic assumption of the Cassie approach, i.e. the assumption of macroscopic chemical heterogeneity, to describe adequately the wetting behavior of isotactic PMMA surfaces.     

The transport phenomena of some model solutes through postcrosslinked poly(2-hydroxyethyl methacrylate) membranes with different tactic precursors

Two series of membranes of various degree of hydration have been prepared by postcrosslinking highly syndiotactic and isotactic poly(2-hydroxyethyl methacrylate) [P(HEMA)] with various amounts of hexamethylene diisocyanate (HMDIC). The equilibrium water content, the partition coefficient, and the permeability of the model solutes such as urea, acetamide, NaCl, 2-propanol, and isobutanol for these membranes were measured. In addition, differential scanning calorimetry (DSC) study for the membranes was performed. The membranes of the isotactic precursor are more hydrated at 25°C compared to the ones of its syndiotactic counterpart. This may be due to the more hydrophobic nature of syndiotactic P(HEMA). The partition coefficient data show that the solutes of urea, acetamide, and NaCl are partitioned only into the water-containing region, whereas the alcohol solutes are preferentially sorbed on to polymer matrix. The permselectivity data of urea to NaCl reveal that the permselectivity of crosslinked isotactic P(HEMA), (ISO) membranes increases as the amount of HMDIC is increased from 2.5 to 10 mol %, while the trend is reversed for crosslinked syndiotactic P(HEMA), (SYN) membranes. The apparent diffusivity order of urea, acetamide, and NaCl is not the same in those two characteristic membranes: the order is urea > NaCl > acetamide for highly crosslinked ISO membranes, and NaCl > urea > acetamide for all SYN membranes, which was compared with the free diffusion data in aqueous solution and interpreted in terms of the water-structural orderlines within membranes.     

Synthesis of tellurium containing syndiotactic polymethyl methacrylate using diphenyl ditelluride as a novel initiator

The synthesis of syndiotactic polymethyl methacrylate containing tellurium by using diphenyl ditelluride in the dioxan at (60 ± 0.1)°C for 2 h has been carried out. The presence of tellurium in the polymer has been confirmed qualitatively as well as by induced coupled plasma mass spectroscopy (ICP‐MS). The electron spin resonance spectrum shows the presence of T?Ph, and value of gyromagnetic constant g has been calculated as 2.2203. The T_g of the polymer, measured by DSC, is 105°C. The syndiotactic nature has been confirmed by FTIR and NMR spectroscopy and DSC. The system follows ideal kinetics with activation energy 66 kJ mol^?1. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1017–1022, 2006