A novel group transfer polymerization of 1-trimethylsiloxy-benzocyclobutene via hetero Diels-Alder reaction

A novel group transfer polymerization via hetero-Diels-Alder reaction is described. When 1-trimethylsiloxybenzocyclobutene ( 1 ) was treated with a catalytic amount of p-anisaldehyde (4-methoxybenzaldehyde) and TASF (tris(dimethylamino)sulfonium difluorotrimethylsilanide) at room temperature for 0.5 h, poly[1,2-phenylene-1-(trimethylsiloxy)ethylene] was obtained quantitatively. The number-average molecular weight of the polymer was M̄_n = 2000 and the molecular weight distribution was narrow (ratio of weight-to number-average molecular weights M̄_w/M̄_n = 1.18). Structural characteristics suggested a polymerization mechanism involving isomerization of 1 to o-quinodimethane and successive hetero-Diels-Alder reaction leading to poly[1,2-phenylene-1-trimethylsiloxy ethylene]. The living-like nature of the polymerization was supported by a monomer addition experiment in which the molecular weight increased according to the increase of the added monomer.     

Modelling free-radical copolymerization kinetics—evaluation of the pseudo-kinetic rate constant method, 1. Molecular weight calculations for linear copolymers

The moment equations for binary copolymerization in the context of the terminal model have been solved numerically for a batch reactor operating over a wide range of conditions. Calculated number- and weight-average molecular weights were compared with those found using pseudo-kinetic rate constants with the method of moments and with the instantaneous property method for homopolymerization. With the pseudo-kinetic rate constant method under polymerization conditions where number-average molecular weights (M̄_n) are below about 10³ the error in calculating M̄_n exceeds 5%. The error increases rapidly with decrease in molecular weight for M̄_n < 10³. M̄_n measured experimentally for polymer chains (homo- and copolymers) have error limits of greater than ±5% at the 95% confidence level. Therefore, for all practical purposes, the pseudo-kinetic rate constant method is valid for M̄_n greater than 10³. Errors in calculating weight-average molecular weights (M̄_w) or higher averages are always smaller than those for M̄_n when applying the pseudo-kinetic rate constant method. The assumptions involved in molecular weight modelling using the pseudo-kinetic rate constant approach are thus proven to be valid, and therefore it is recommended that the pseudo-kinetic rate constant method be employed with the instantaneous property method to calculate the full molecular weight distribution and averages for linear chains synthesized by multicomponent chain growth polymerization.     

Polymerization of ϵ-caprolactone using heterobimetallic lanthanocene complexes

The chiral heterobimetallic complexes Li[Ln(η⁵ : η¹-C₅R₄¹SiMe₂NCH₂CH₂R²)₂] (Ln = Y, Lu; C₅R₄¹ = C₅Me₄, C₅H₄, 3-C₅H₃ t Bu; R² = OMe, NMe₂; Me: methyl; tBu: tert-butyl) have been found to polymerize ϵ-caprolactone to give a polymer of high molecular weight (M̄_n < 20 000) and moderate polydispersity (M̄_w/M̄_n < 2.0). Failure to observe a correlation between monomer/initiator ratio and molecular weight suggests a polymerization mechanism different from a pseudo-anionic mechanism.     

Free-radical polymerization of a reducing vinyl sugar ester in dimethylformamide and water

To develop a new synthetic polymer containing sugar branches, radical polymerization of the reducing vinyl sugar ester 6-O-vinyladipoyl-D -glucose ( 1 ) was performed in an organic solvent or in water. The polymers obtained with several azoinitiators in dimethylformamide (DMF) showed comparatively low average molecular weight (M̄_n ≈ 4500). In contrast, the use of a redox initiator (FeSO₄ and H₂O₂) in water gave polymers of higher average molecular weight (M̄_n ≈ 33000) in higher yield (90%), followed by crosslinking at high conversions.     

Copolymerization of β-butyrolactone and β-benzyl malolactone with aluminoxane catalysts

Poly (β-hydroxylbutyrate-co-benzyl β-malolactonate), (P-HB-co-BML) copolymers, were prepared by the ring-opening copolymerizations of β-butyrolactone (BL) and benzyl β-malolactone (BML) with several alkyl aluminoxane catalysts, including ethylaluminoxane (EAO), methylaluminoxane (MAO), and isobutylaluminoxane (IBAO). The copolymers had very broad molecular weight distributions with weight average molecular weights, M̄_w, greater than 200,000. The products were fractionated by solubility into acetone-soluble and insoluble copolymers. The former were random, atactic copolymers while the latter were stereoblock copolymers. Random, atactic copolyesters of these two monomers were also obtained with the diethylzinc-water, ZnEt₂-H₂O (0.6:1), and the (5,10,15,20-tetraphenylporphinato)aluminium chloride, TPPAlCl, catalysts. The copolymerization reactions with the latter two catalysts gave much higher yields (up to 98%) and better control of both the copolymer compositions and the molecular weight distributions, but these copolymers had M̄_w values of only 20,000 or less. The copolymer tacticities and comonomer sequences were determined by ¹³C NMR spectroscopy.     

The grafting of acrylamide onto poly(ε‐caprolactone) and poly(1,5‐dioxepan‐2‐one) using electron beam preirradiation. II. An in vitro degradation study on grafted poly(ε‐caprolactone)

Acrylamide was graft polymerized onto the surface of a biodegradable semicrystalline polyester, poly(ε‐caprolactone). Electron beam irradiation at a dose of 5 Mrad was used to generate initiating species in the polyester. The degradation in vitro at pH 7.4 and 37°C in a phosphate buffer solution was studied for untreated, irradiated and acrylamide‐grafted polymers. In the case of poly(ε‐caprolactone), all materials showed similar behavior in terms of weight loss. No significant decrease in weight was observed up to 40 weeks, after which the loss of weight accelerated. The main differences in degradation behavior were found for the average molecular weights, M̄_n and M̄_w. Virgin poly(ε‐caprolactone) maintained M̄_n and M̄_w up to about 40 weeks, whereas the irradiated and grafted poly(ε‐caprolactone) showed similar continuous declines in M̄_n and M̄_w throughout the degradation period. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1651–1657, 1999     

Polymerization of ethene initiated with a mixture of siloxane-bridged mono- and dinuclear zirconocenes

In the polymerization of ethene cocatalyzed with modified methylaluminoxane, the catalyst activities of the siloxane-bridged dinuclear zirconocenes, tetramethyldisiloxanediylbis(cyclopentadienylindenylzirconium dichloride) ( 3 ) and hexamethyltrisiloxanediylbis(cyclopentadienylindenylzirconium dichloride) ( 4 ) were lower than that obtained with the siloxane-bridged mononuclear zirconocene, tetramethyldisiloxanediyldicyclopentadienyldimethylzirconium ( 1 ). On the other hand, weight-average molecular weight M̄_w and ratio of weight- to number-average molecular weights M̄_w/M̄_n of polyethene (PE) obtained with 3 or 4 were higher than those of PE obtained with 1. For a binary mixture of 1/3 or 1/4 , it was found that the obtained PE exhibits a bimodal molecular weight distribution for an appropriate composition of the mixed zirconocenes. M̄_w/M̄_n of PE could be adjusted by changing the relative concentrations of the two zirconocenes.     

Modelling free-radical copolymerization kinetics—evaluation of the pseudo-kinetic rate constant method, 2. Molecular weight calculations for copolymers with long chain branching

The full moment equations and equations using pseudo-kinetic rate constants for binary copolymerization with chain transfer to polymer in the context of the terminal model have been developed and solved numerically for a batch reactor operating over a wide range of conditions. Calculated number- and weight-average molecular weights (M̄_n and M̄_w) were compared with those found using the pseudo-kinetic rate constant method (PKRCM). The results show that the weight-average molecular weights calculated using PKRCM are in agreement with those found using the method of full moments for binary copolymerization when polymeric radical fractions φ₁^˙ and φ₂^˙ of type 1 and 2 (radical centers are on monomer types 1 and 2 for a binary copolymerization) are calculated accounting for chain transfer to small molecules and polymer reactions in addition to propagation reactions. Errors in calculating M̄_w using PKRCM are not always negligible when polymer radical fractions are calculated neglecting chain transfer to small molecules and polymer. In this case, the relative error in M̄_w by PKRCM increases with increase in monomer conversion, extent of copolymer compositional drift and chain transfer to polymer rates. The errors in calculating M̄_w, however, vanish over the entire monomer conversion range for all polymerization conditions when chain transfer reactions are properly taken into account. It is theoretically proven that the pseudo-kinetic rate constant for chain transfer to polymer is valid for copolymerizations. One can therefore conclude that the pseudo-kinetic rate constant method is a valid method for molecular weight modelling for binary and multicomponent polymerizations.     

Anionic synthesis of in-chain 3° amine-functionalized polybutadienes

Anionic copolymerizations of butadiene (M₁) with excess 1-(4-dimethylaminophenyl)-1-phenylethylene (M₂) were conducted in benzene at room temperature for 24–48h using sec-butyllithium as initiator. Anisole, triethylamine and t-butyl methyl ether were added in ratios of [B]/[RLi] = 60, 20, 30, respectively, to promote copolymerization. Narrow molecular weight distribution copolymers with M̄n = 14 × 10³ to 32 × 10³ g/mol (M̄_w/M̄n =1.02–1.03) and 8,12 and 30 amine groups per chain for anisole, triethylamine and t-butyl methyl ether, respectively, were obtained. The butadiene monomer reactivity ratios (r1) were 42, 33 and 14 for anisole, triethylamine and t-butyl methyl ether, respectively.     

Cationic 1,2-vinyl addition polymerization of cyclic ketene acetals initiated by conventional acids

Pure 1,2-addition polymers, poly(2-methylene-1,3-dioxolane), 1b , poly(2-methylene-1,3-dioxane), 2b , and poly(2-methylene-5,5-dimethyl-1,3-dioxane), 3b , were prepared using the cationic initiators H₂SO₄, TiCl₄, BF₃, and also Ru(PPh₃)₃Cl₂. Small ester carbonyl bands in the IR spectra of 1b and 2b were observed when the polymerizations were performed at 80°C ( 1b ) and both 67 and 138°C ( 2b ) using Ru(PPh₃)₃Cl₂. The poly(cyclic ketene acetals) were stable if they were not exposed to acid and water. They were quite thermally stable and did not decompose until 290°C ( 1b ), 240°C ( 2b ), and 294°C ( 3b ). Different chemical shifts for axial and equatorial H and CH₃ on the ketal rings were found in the ¹H NMR spectrum of 3b at room temperature. High molecular weight 3b (M̄_n = 8.68 × 10⁴, M̄_w = 1.31 × 10⁵, M̄_z = 1.57 × 10⁵) was obtained upon cationic initiation by H₂SO₄. Poly(2-methylene-1,3-dioxane), 2b , underwent partial hydrolysis when Ru(PPh₃)₃Cl₂ and water were present in the polymer. The hydrolyzed products were 1,3-propanediol and a polymer containing both poly(2-methylene-1,3-dioxane) and polyketene units. The percentages of these two units in the hydrolyzed polymer were about 32% polyketene and 68% poly(2-methylene-1,3-dioxane). No crosslinked or aromatic structures were observed in the hydrolyzed products. The molecular weight of hydrolyzed polymer was M̄_n = 5740, M̄_w = 7260, and M̄_z = 9060. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3707–3716, 1997     

Effect of the mixture t - BuCl/SnCl4 on the cationic polymerization of isobutylene

The polymerizations of isobutylene initiated with the system tert-butyl chloride (t-BuCl)/SnCl₄ and carried out in CH₂Cl₂ at −20°C and −78°C were investigated. The results obtained demonstrate that the presence of t-BuCl in the polymerizing system gives rise to a PIB product with a distinctly bimodal MWD. The higher-molecular weight (HMW) PIB, M̄_n = 20000, I=M̄_w/M̄_n ∼ 2.5, is the result of existence of the protogenic initiation with residual water in the reaction system. The lower-molecular weight (LMW) PIB, M̄_n < 600, M̄_w/M̄_n ≤ 1.4, is the product of polymerization initiated presumably with a complex t-BuCl-SnCl₄-H₂O. To elucidate the reaction mechanism of the polymerization initiated with the complex, a series of similar isobutylene polymerizations using the initiation system 2,5-dichloro-2,5-dimethylhexane (DDH)/SnCl₄ was run and the oily LMW PIB samples were investigated by ¹H-NMR. A new polymerization mechanism describing the role of DDH and t-BuCl is suggested.     

Well defined columnar liquid crystalline polydiethylsiloxane

The kinetics of the anionic ring opening polymerization of hexaethylcyclotrisiloxane (D₃^Et) with the cryptate Li⁺/[211] as counterion have been studied by means of ¹³C NMR spectroscopy. The propagation reaction was found to be of first order in monomer as well as living end concentration. It proceeds by two decades slower than the corresponding reaction with hexamethylcyclotrisiloxane (D₃^Me) as monomer. The Li⁺/[211] system could be used to synthesize well defined polydiethylsiloxane (PDES) samples (M̄_w/M̄_n <1.2). However, when the polymerization was aimed at high molecular weights (≥ 600 000 g/mol), the obtained molecular weights were lower than expected, and the molecular weight distributions became broader. All PDES samples were capable of forming a columnar mesophase. The temperature range in which this phase exists was found to be strongly molecular weight dependent. Initiation of the D₃^Et polymerization with polybutadienyllithium and coupling of the living chain ends yielded a PB-PDES-PB triblock copolymer, which could be crosslinked, resulting in a mesomorphic network.     

Liquid crystalline,highly luminescent poly(2,5-dialkoxy-p-phenyleneethynylene)

A high-molecular-weight poly(2,5-dialkoxy-p-phenyleneethynylene) derivative has been prepared by the Heck reaction of 1,4-bis(2-ethylhexyloxy)-2,5-diiodobenzene and 1,4-diethynyl-2,5-dioctyloxybenzene. The highly luminescent polymer exhibits excellent solubility and can readily be processed into high-optical-quality films. The weight-average molecular weight M̄_w was 240000 g · mol⁻¹, with a polydispersity index of 2.9. Thermal analysis revealed a glass transition around 90°C, and an onset of chemical crosslinking at 130°C. The high M̄_w and the remarkable solubility enabled the preparation of liquid crystalline solutions of the new PPE.     

Semicontinuous Emulsion Copolymerization of Vinyl Acetate and Butyl Acrylate Using Different Initiators and Different Chain Length Emulsifiers

The semicontinuous emulsion copolymerization of vinyl acetate and butyl acrylate (VAc/BuA) (85:15) initiated by thermal initiators ammonium persulfate (APS) and potassium persulfate (PPS) at 70°C in the presence of nonylphenol ethoxylates of varying chain lengths (NP-n) and acrylamide partially polymerized (Amol) was investigated. VAc-BuA copolymer latexes were synthesized as two different series in the glass reactor, in the first serie was initiated by APS and PPS was used as initiator in the second serie. The influence of the counterions or initiators and chain lenghts of non-ionic emulsifier on the properties of VAc-BuA copolymer latexes were determined by measuring Brookfield viscosities, weight average molecular weights (M̄_w), number average molecular weights (M̄_w), molecular weight distribution and surface tension of latexes to air. The results of copolymer latexes indicated that their physicochemical properties increased with the increasing chain length of nonionic emulsifier for two initiators.     

Novel Polymer Clusters with a Uniform Chain Density

The thermal decomposition of polystyrene clusters prepared by using 4‐methacryloyloxy‐2,2,6,6‐tetramethylpiperidine‐N‐oxyl as a branching agent was studied. The weight‐average molar mass (M̄_w) and the radius of gyration (R_g) of the resultant clusters can be scaled as M̄_w ∝︁ R_g^{3.0 ± 0.1}, revealing that these clusters have a uniform chain density. Moreover, the dynamic properties of such clusters converge unexpectedly faster than the static properties as the molar mass decreases.     

Reverse atom transfer radical polymerization of methyl acrylate using AIBN as the initiator under heterogeneous conditions

Reverse atom transfer radical polymerization of methyl acrylate in the presence of a conventional radical initiator (2,2′-azoisobutyronitrile, AIBN) in bulk was successfully implemented via a new polymerization procedure. The system first reacts at 65–70°C for ten hours, then polymerizes at 100°C. Various mole ratios of AIBN to Cu^IICl₂ were used in this work, all of which result in a well-controlled radical polymerization with high initiation efficiency and narrow molecular weight distribution, i.e., the polydispersity is as low as M̄_w/M̄_n = 1.36.     

Controlled polymerization of ϵ-caprolactone -from macromolecules to microspheres

Pseudoanionic polymerization of ϵ-caprolactone (CL), initiated with dialkylaluminum alkoxides, was used for the tailored synthesis of poly(CL) with M̄_n ≤ 100 000 and M̄_w /M̄_n < 1. 20. Macromolecules with functional groups at one or at both ends were obtained in this way. Controlled polymerization of CL allowed to prepare poly(dodecyl acrylate)-g-poly(ϵ-caprolactone) (poly(DAC)-g-poly(CL)) with well defined poly(CL) grafts. These copolymers were used as the surface active agents for the direct synthesis of poly(CL) microspheres. The number average diameter (D̄_n ) of poly(CL) microspheres varied from 0.628 μm to 0.94 μm and the diameter polydispersity (D̄_v /D̄_n ) varied from 1.038 to 1.26, depending on the composition of poly(DAC)-g-poly(CL). Human serum albumin (HSA) and human gamma globulins (_γ G) were attached to the poly(CL) microspheres. The maximal surface concentrations of HSA and _γ G adsorbed onto the microspheres were equal to 9·10⁻⁴ g/m² and 2.0·10⁻³ g/m² respectively.     

Polymerization of N-phenylmaleimide with rare earth coordination catalysts

A highly active rare earth coordination catalyst composed of neodymium acetylacetonate, dibutylmagnesium, and hexamethylphosphoramide (mole ratio 1:7:14) for the polymerization of N-phenylmaleimide (N-PMI) was developed. The resulting poly(N-PMI) has high molecular weight (M̄_n = 9.0 × 10⁴) and shows excellent thermal stability.     

A new method for the polymerization of methyl methacrylate

Dialkyl iodomethylmalonates in the presence of tetrabutylammonium iodide initiate the polymerization of methyl methacrylate, but not of methyl acrylate or acrylonitrile. Typically, at 60°C in 1,3-dimethyltetrahydro-2-1H-pyrimidone (DMPU) as the solvent, poly(methyl methacrylate (PMMA)) is obtained in the number-average molecular weight range of 2 000 to 8 000, the molecular weight distribution being fairly narrow (ratio of weight- to number-average molecular weights M̄_w/M̄_n 1.2–1.3).     

Synthesis and mesomorphic behavior of poly(dipropylsilylenemethylene)

Based on the reaction of trichloro(chloromethyl)silane ( 1 ) with 2 equivalent amounts of the respective Grignard-reagent and subsequent cyclization, 1,1,3,3-tetrapropyldisilacyclobutane ( 3 ) has been prepared. Catalytic polymerization with H₂PtCl₆ was employed to prepare the corresponding poly(dipropylsilylenemethylene) (PDPSM, 4 ) with strictly alternating SiR₂/CH₂ backbone structure. A high-molecular-weight fraction of the material (weight-average molecular weight M̄_w = 166 500 and number-average molecular weight M̄_n = 115 200) obtained by fractionating precipitation was investigated with respect to glass transition and formation of conformationally disordered mesomorphic phases. The glass transition temperature T_g = 232 K of PDPSM evidenced lower backbone flexibility than observed for the analogous poly(dipropylsiloxane), (PDPS). PDPSM exhibited mesomorphic behavior. In contrast to poly(dipropylsiloxane), PDPSM showed a surprisingly narrow mesomorphic regime between 355 K and 365 K. Based on polarizing microscopy and ²⁹Si-MAS (magic angle spinning) solid-state NMR the mesophase is described as a conformationally disordered state, which is most probably columnar in analogy to PDPS.