High‐pressure synthesis of cyclic mesitylacetylene oligomer

Reaction of mesitylacetylene was carried out by annealing under high pressure (0.13 and 0.52 GPa). The products obtained were classified into soluble and insoluble products in chloroform. The insoluble product reacted under 0.13 GPa was the mesitylacetylene polymer. The soluble product reacted under 0.13 GPa was classified as the monomer and the oligomer [number‐average molecular weight (M̄_n): 390, weight‐average molecular weight (M̄_w): 453, Oligomer yield (O_y): 36%]. The oligomer yield was accelerated by pressure [pressure: 0.13–0.52 GPa, M̄_n: 390–315, M̄_w: 453–968, O_y: 36–98%]. Field desorption mass spectrum showed that the oligomer had cyclic structure. The result of the elementary analysis revealed that the insoluble product reacted under 0.52 GPa was a polycyclic aromatic compound. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 1539–1542, 1999     

Molecular weight averages and distributions of unsaturated polyesters: Their effect on the properties of styrene-crosslinked networks

Unsaturated polyesters have been synthesised and modified to determine the effect of number-average molecular weight (M̄_n) and molecular weight distribution (MWD) on the following properties of the polyesters after crosslinking with styrene: (i) water absorption, (ii) initial mechanical properties and (iii) property retention after immersion The most important factor was found to be the very low molecular weight ‘tail’ which adversely affected behaviour in several respects. Above a certain M̄_n, initial mechanical properties were insensitive to the variables mentioned, but mechanical property retention after immersion closely reflected the water absorption behaviour by its dependence on the average chain length and the low molecular weight constituents. The importance of removing such constituents is apparent.     

Butyllithium-initiated anionic synthesis of well-defined poly(styrene-block-ethylene oxide) block copolymers with potassium salt additives

Poly(styrene-block-ethylene oxide) (PS–PEO) diblock copolymers have been synthesized with predictable block molecular weights and narrow molecular weight distributions. sec-Butyllithium-initiated polymerization of styrene was effected in benzene solution followed by ω-end-group functionalization with ethylene oxide to form the corresponding polymeric lithium alkoxide (PSOLi). Block copolymerization of ethylene oxide initiated by the unreactive PSOLi was promoted by addition of dimethylsulfoxide and either potassium t-butoxide, potassium t-amyloxide or potassium 2,6-di-t-butylphenoxide. Although the PS–PEO block copolymer product contained some poly(ethylene oxide) homopolymer, the poly(ethylene oxide) block M̄_n was in good agreement with the calculated value and the molecular weight distribution of the final block was generally narrow (M̄_w/M̄_n ≤ 1.1). The amount of PEO homopolymer was minimized using potassium 2,6-di-t-butylphenoxide rather than potassium t-alkoxides.     

Structure and viscoelastic properties of epoxy resins prepared from four-nuclei novolacs

The relation between the structure and the viscoelastic properties of seven kinds of epoxy resins was studied. Seven tetraglycidylethers were synthesized from four-nuclei novolacs in which the positions of methylene linkage or number of kind of substituents were different. These epoxy compounds were cured with diaminodiphenylmethane as a hardener. From the viscoelastic properties of the fully cured resins with the hardener, characteristic properties such as glass transition temperature (T_g), average molecular weight between crosslinking points (M̄_c), and front factor (ϕ) were obtained. It was concluded that higher linearity in the main chain of epoxy resins gave a cured resin with a higher T_g, a smaller M̄_c, and a larger ϕ.     

Synthesis and thermoanalysis of emulsion terpolymers of N‐phenylmaleimide,styrene, and acrylonitrile

Terpolymers of N‐phenylmaleimide (PMI), styrene, and acrylonitrile (AN) were synthesized by emulsion polymerization. The thermal properties of terpolymers at different PMI and AN feed contents were investigated by differential scanning calorimetry, torsional braid analysis, thermogravimetric analysis, and a Vicat softening point test. The results showed the glass‐transition temperature and decomposition temperature of the terpolymers increased with increasing PMI feed content. Furthermore, the Vicat softening point of the terpolymers rose with PMI feed content. The weight‐ and number‐average molecular weights (M̄_w and M̄_n) of the terpolymers were also determined by gel permeation chromatography. The results showed that the M̄_w and M̄_n of the terpolymers decreased with increasing PMI feed content and increased with increasing AN feed content. The mechanical properties (tensile strength and impact strength) of the terpolymers decreased with increasing PMI feed content and increased with increasing AN feed content. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1067–1073, 2001     

Copolymerization of 4-chlorophenyl acrylate with methyl acrylate: synthesis,characterization, reactivity ratios,and their applications in the leather industry

4-Chlorophenyl acrylate (CPA) was prepared by reacting 4-chlorophenol and acryloyl chloride in the presence of triethylamine in ethyl acetate solution. Poly(4-chlorophenyl acrylate) and copoly(4-chlorophenyl acrylate–methyl acrylate) were synthesized by the free radical polymerization in ethyl acetate at 70°C. All the polymers were characterized by infrared (IR) and nuclear magnetic resonance (NMR) spectroscopic techniques. The composition of the copolymers was determined by the ¹H-NMR spectroscopic technique, that is, by integrating the aromatic peaks corresponding to the 4-chlorophenyl acrylate unit against the carbomethoxy group in the methyl acrylate unit. The reactivity ratios were calculated by Fineman–Ross, Kelen–Tudos (K–T), and the extended Kelen–Tudos methods. The values of r₁ and r₂ obtained by these methods were in close agreement with each other; that is, r₁(CPA) = 0.64 and r₂(MA) = 0.13 by the K–T method. The number-average molecular weight (M̄_n = 1.55 × 10³), the weight-average molecular weight (M̄_w = 8.39 × 10³), and the polydispersity index (M̄_w/M̄_n = 5.42) of poly(CPA) were determined by gel permeation chromatography (GPC). Thermal properties of the polymers were studied in a nitrogen atmosphere using thermogravimetric analysis (TGA). As the CPA increases in the copolymer, thermal stability of the copolymer increases (e.g., 90% weight loss occurs at 480°C for 20 mol % CPA, whereas the same weight loss occurs at 571°C for 80 mol % CPA). Acrylic binders, based on the CPA–MA–BA terpolymer, of different glass transition temperatures were prepared for applications in leather industry as top coat and base coat materials. These acrylic emulsions were cast into thin films, and their characteristics were tested for physical properties. These acrylic emulsions were applied as a base coat on leather, and the compositions having T_g values of 1.08 and 9.25°C were found to have excellent properties as base coats for leather when compared with commercial samples. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1153–1160, 1999     

Chain extension of recycled poly(ethylene terephthalate) with 2,2′‐(1,4‐phenylene)bis(2‐oxazoline)

The present work provides improved recycled high molecular weight poly(ethylene terephthalate) (PET) by chain extension using 2,2′‐(1,4‐phenylene)bis(2‐oxazoline) (PBO) as the chain extender. PBO is a very reactive compound toward macromolecules containing carboxyl end groups but not hydroxyl end groups. In the case of PET, where both species are present, for even better results, phthalic anhydride (PA) was added in the initial sample, before the addition of PBO. With this technique, we succeeded in increasing the carboxyl groups by reacting PA with the hydroxyl terminals of the starting polymer. From this modification of the initial PET sample, PBO was proved an even more effective chain extender. So, starting from a recycled PET with intrinsic viscosity [η] = 0.78, which would be [η] = 0.69 after the aforementioned treatment without a chain extender or M̄_n = 19,800, we prepared a PET grade having [η] = 0.85 or M̄_n = 25,600 within about 5 min. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2206–2211, 2000     

Long Chain Branched Polypropene Prepared by Means of Propene Copolymerization with 1,7‐Octadiene Using MAO‐Activated rac‐Me2Si(2‐Me‐4‐Phenyl‐Ind)2ZrCl2

Small amounts of 1,7‐octadiene (OD) comonomer, ranging from 0.5–5.0 mol‐%, were added during propene polymerization, catalyzed with methylalumoxane (MAO) activated rac‐Me₂Si(2‐Me‐4‐phenyl‐Ind)₂ZrCl₂ (MPI), in order to incorporate long chain branches and small amounts of high molecular mass polypropene (PP), thus improving melt processability of isotactic metallocene‐polypropene. As a function of the OD content the PP melting temperatures varied from 120 to 160°C. The presence of long chain branches was reflected by increased zero shear viscosities combined with pronounced shear thinning behavior in the case of propene/OD copolymers with molecular mass distribution of M̄_w/M̄_n < 4. Rheological measurements clearly revealed crosslinking occurring at high OD content. OD addition impaired catalyst activities. However, in the presence of trace amounts of ethene, catalyst activities increased significantly even in the presence of high OD content.     

The Effect of the Density and Nature of Spatial Network in Elastomers on Their Viscoelastic Characteristics

Abstract

We have studied the effect of the density of the networks formed by fluctuating entanglements and chemical crosslinking on the relationships between the circular frequency ω and the storage and loss moduli, G' and G”, for polybutadienes of narrow and wide molecular weight distributions (the ratio M_w/M_n varied from 1.1 to 3.35) and different microstructure. Polybutadienes were crosslinked by thermal, radiation, and sulphur vulcanization. With increasing density v of a network of chemical crosslinks, which is characterized by the average molecular weight of a chain length (M_e ), pseudo-equilibrium plateau extends to the side of low frequencies with a certain small increase of its level. This increase becomes noticeable when M_e is approximately equal to the average molecular weight M_e of the chain length between the fluctuating entanglements of an uncrosslinked elastomer. At the same time the maxima on the curves of G”(ω) are smoothed out and the losses reduce to negligibly small values with decreasing frequency.     

Dielectric investigation of molecular dynamics of blends: III. Effect of molecular weight in TMPC/PS blends

Dielectric and calorimetric measurements have been carried out for tetramethyl polycarbonate/polystyrene (TMPC/PS) blends with different compositions. The effect of varying the molecular weight of the weakly polar component (PS) on the molecular dynamics of the polar segments of TMPC has been thoroughly studied over wide ranges of frequency (10⁻²−10⁵ Hz), temperature (50–220°C) and number average molecular weight, M̄_n, (6500–560 000 g mol⁻¹). All blends were found to be compatible regardless of the composition ratio and the molecular weight of PS. Some new and interesting experimental findings have been observed concerning the effect of molecular weight on the glass temperature and on the broadness of the glass transition and relaxation. Neither the kinetics nor the distribution of relaxation times of the local process observed in pure TMPC was affected by blending with PS, regardless of the composition ratio or the molecular weight of PS. It has been concluded that the mixing of the polymeric components to form a homogeneous single phase (compatible blend) does not take place on a segmental level but on a structural one. The size of this structural level has been suggested to have the same volume as the cooperative dipoles, which is assumed to be the minimum volume responsible for a uniform glass transition (10–15 nm). The molecular weight dependence of the relaxation characteristics of the glass process and temperature could be attributed to the variation in the size and packing of the structural units.     

Organic/inorganic support for immobilizing (n‐BuCp)2ZrCl2/TiCl3 hybrid catalyst for use in the preparation of polymer blends

Reactor blends of ultrahigh‐molecular‐weight polyethylene (UHMWPE) and low‐molecular‐weight polyethylene (LMWPE) were synthesized by two‐step polymerization using a hybrid catalyst. To prepare the hybrid catalyst, styrene acrylic copolymer (PSA) was first coated onto SiO₂/MgCl₂‐supported TiCl₃; then, (n‐BuCp)₂ZrCl₂ was immobilized onto the exterior PSA. UHMWPE was produced in the first polymerization stage with the presence of 1‐hexene and modified methylaluminoxane (MMAO), and the LMWPE was prepared with the presence of hydrogen and triethylaluminium in the second polymerization stage. The activity of the hybrid catalyst was considerable (6.5 × 10⁶ g PE (mol Zr)^?1 h^?1), and was maintained for longer than 8 h during the two‐step polymerization. The barrier property of PSA to the co‐catalyst was verified using ethylene polymerization experiments. The appearance of a lag phase in the kinetic curve during the first‐stage polymerization implied that the exterior catalyst ((n‐BuCp)₂ZrCl₂) could be activated prior to the interior catalyst (M‐1). Furthermore, the melting temperature, crystallinity, degree of branching, molecular weight and molecular‐weight distribution of polyethylene obtained at various polymerization times showed that the M‐1 catalyst began to be activated by MMAO after 40 min of the reaction. The activation of M‐1 catalyst led to a decrease in the molecular weight of UHMWPE. Finally, the thermal behaviors of polyethylene blends were investigated using differential scanning calorimetry. Copyright © 2011 Society of Chemical Industry     

Simple 13C-NMR methods for quantitative determinations of polyflavonoid tannin characteristics

A simple ¹³C-NMR method for the quantitative determination of polyflavonoid tannin characteristics was developed. The system is effective for use on concentrated (25–50%) solutions of natural and modified tannins. It allows the determination of the average degree of polymerization (DP _n) of the polyflavonoid, resorcinol vs. phloroglucinol proportion of the A-ring and catechol vs. pyrogallol proportion of the B-ring. The results obtained are consistent with existing data determined by other techniques. The method was also tried with tannin extract that was modified to form thermosetting adhesive intermediates, and with tannin modified by sulfonation, a common commercial modification for these materials. The results were again consistent with what was expected. The method affords the possibility to follow by a simple technique the variations in DP _n and MM?_n (number-average molecular weight) induced by chemical modifications of polyflavonoid tannin extracts and thus to correlate them with relevant structural modifications affecting these parameters. The method is not capable of distinguishing the relative proportions of the four important flavonoid units present in commercial polymeric tannin extract. It can only distinguish the relative proportions of (i) (procyanidins + prodelphinidins) vs. (profisetinidins + prorobinetinidins) and (ii) (prorobinetinidins + prodelphinidins) vs. (profisetinidins + procyanidins). © 1995 John Wiley & Sons, Inc.     

Molecular weight and molecular weight distribution from dynamic measurements of polymer melts

A method for determining the molecular weight distribution (MWD) of a polymer melt has been developed using the dynamic elastic modulus (G'), plateau modulus (G), and zero shear complex viscosity (η). The cumulative MWD was found to be proportional to a plot of (G'/G)^0.5 vs. measurement frequency (ω). Frequency (ω) was found to be inversely proportional to (MW)^3.4, as expected. Results were scaled to absolute values using the empirical relationship η ∝ (M?_w)^3.4, where M?_w is the weight-average MW. M?_w, M?_n (number-average MW) and M?_w/M?_n calculated from melt measurements were found to agree with size exclusion chromatography usually well within 10 percent for broad and bimodal distribution samples. M?_w/M?_n tended to be approximately 20 percent higher for narrow distribution samples (M?_w/M?_n < 1.2) because we did not account for a finite distribution of relaxation times from a collection of monodisperse polymer chains. We also did not account for the plasticizing effect of short chains mixed with long ones which caused peak positions to be closer together for Theological vs, size exclusive chromatography (SEC) determinations of MW for bimodal distribution blends.     

Molecular weight distribution of commercial PVC

The molecular weight distribution (MWD) of commercial suspension grade poly(vinyl chloride) (PVC) resins with K values from 50 to 93 and mass grade PVC resins with K values from 58 to 68 has been determined by size exclusion chromatography (SEC), using literature Mark‐Houwink coefficients. The MWD is characterized by the number average molecular weight (M_n), the weight average molecular weight (M_w) and the polydispersity (M_w/M_n). Our results for M_w are consistent with recently published data, but we find different results for M_n and consequently for M_w/M_n. The polydispersity of PVC increases with increasing K value. This effect can be explained by two mechanisms. The first mechanism is a reduced terminating reaction rate between two growing polymer chains (disproportionation) at higher molecular weight owing to the reduced mobility of the polymer chains. The second mechanism is long‐chain branching of molecules with high molecular weight which lets the molecules grow at two ends. For two examples graphs of the measured MWD are compared with the theoretically expected MWD.     

Engineering plastics from lignin. XVII. Effect of molecular weight on polyurethane film properties

A series of five fractions with number average molecular weights (M?_n) between 1500 and 10,000 daltons were isolated from a Kraft hydroxypropyl lignin (HPL). From ¹H-NMR and UV analysis the chemical properties of the HPLs were found to vary slightly with molecular weight. The hydroxyl content decreased while the glass transition temperature (T_g) increased as the HPL molecular weight increased. The Fox-Flory equation adequately described the M?_n vs. T_g relationship. The HPL fractions were used as polyols for the preparation of solvent-cast polyurethane networks (PU) in film form. The T_g of the PUs increased from 40° to 120°C as the M?_n of the polyol rose from 1500 to 10,000 daltons. The molecular weight between crosslinks (M?_c) of the networks was determined by swelling. An observed decrease in M?_c with an increase in M?_n was related to the functionality of the system. The strength properties of films prepared from fractionated HPLs were superior to those prepared from nonfractionated HPLs.     

Influence of mixing procedures and curing time on molecular and topological structures of NR/BR vulcanizate

A rubber compound containing butadiene rubber (BR), natural rubber (NR), and carbon black was investigated by thermomechanical analysis (TMA). A difference in dynamics of the formation of molecular and topological structures of a vulcanizate were found to be dependent on the mixing technology and curing time. Separation of the topological structure of cured rubber into two blocks with differing transition temperatures was visible after 20 min of vulcanization, when a share of a low‐temperature block is minimal and M̄_n(n) reaches a stable value of about 2400. A low‐temperature block had a predominant concentration of covalent branching junctions, independent of the mixing procedures, whereas the high‐temperature block had covalent and topological junctions in concentrations that were dependent on the mixing method. For curing times longer than 20 min, the characteristic changes in values of M̄_n(n) are dependent on the procedure of rubber compound mixing. After additional homogenization of compounds and vulcanization, the rubbers are characterized by a diblock structure with the same qualitative structure of the branching junctions as for nonhomogenized ones. In some cases, the homogenization increases the relative concentration of the covalent junctions in the high‐temperature block. When a preblend of BR and carbon black was prepared first, and then mixed with NR, this technology makes rubber compounds less sensitive to additional homogenization during further processing. A mechanism of creation and transformation of rubber–carbon black junctions during compounding and vulcanization of rubber compounds with two raw rubbers that differed in adsorption ability was proposed. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 660–669, 2000     

Living carbocationic polymerization of isobutylene by tert-amyl alcohol/BCl3/1-methyl-2-pyrrolidinone initiating system

1-Methyl-2-pyrrolidinone has been investigated, for the first time, as an efficient electronpair donor in conjunction with tert-amyl alcohol and BCl₃ in CH₂Cl₂ diluent at ?40°C for the living polymerization of isobutylene. The use of this new monofunctional initiator -trans fer (minifer) system has led to the synthesis of low molecular weight, living (near-monodisperse) polyisobutylenes carrying “ethyl” head group and “tert-chloro” end group (asymmetric telechelic polyisobutylenes). The nature of these groups was confirmed by ¹H-NMR spectroscopy. The living nature of the α-ethyl-ω-(tert-chloro)polyisobutylenes has been demonstrated by a linear plot, passing through the origin, of number-average molecular weight (M?_n) vs. the amount of polymer formed (W_p) and a horizontal N (number of polyisobutylene molecules) vs. W_p plot. These results are further substantiated by gel permeation chromatography data of these polymers, and the molecular weight distributions of these polymers are narrow (low M?_w/M?_n = 1.1–1.2). The initiating efficiencies (I_eff) are close to 100% with this system. Dehydrochlorination of the prepolymer has yielded an isopropylidene (exo-olefin) end group. Structure of the end group in the resulting polymer, α-ethyl-ω-(isopropenyl)polyisobutylene, was confirmed by FTIR spectroscopy.     

Synthesis of end-group functionalized poly(octadecyl vinyl ether)

The cationic polymerization of octadecyl vinyl ether (ODVE) initiated by trimethylsilyl iodide and 1,1-diethoxyethane in the presence of ZnI₂ in toluene at 0°C and 10°C has been investigated. For molecular weights lower than 6000, a linearity of M̄_n with conversion was observed, but for higher molecular weights a strong deviation from calculated values, assuming a living mechanism, was found. Kinetic analysis of the polymerization and the variation of molecular weight as a function of conversion was in agreement with a transfer to monomer with k_tr/k_p ≌ 0.006 at 10°C. Analysis of the polymers obtained by termination with methanol provided evidence that the alkenyl ether end-groups formed by the transfer reaction lead to the same acetal end-groups as the active species. As a consequence, it is possible to prepare functionalized polyODVE polymers by end-capping with alcohols. This was confirmed by the synthesis of polyODVE macromonomers by end-capping with 2-hydroxyethyl methacrylate.     

Study of ion solvation and ion association in polymer gel electrolyte with polyethylene oxide-co-polypropylene oxide as a plasticizer

Using a molal conductance method, ion solvation and ion association in polytriethylene glycol dimethacrylate (PTREGD)–LiClO₄ gel electrolytes with amorphous ethylene oxide-co-propylene oxide (EO-co-PO, M̄_n = 1750) as the plasticizer were investigated. It was found that the fraction of solute existing as single ions (α_i) and ion pairs (α_p) decreases, while that of triple ions (α_t) increases linearly with increasing salt concentration. The dependence of these fractions on molecular weight of plasticizer was also examined. It was shown that α_i and α_t increase and α_p decreases with increasing molecular weight. The result of temperature dependence of these fractions was very interesting: when the temperature is lower than 55°C, α_i increases while α_p and α_t decrease with increasing temperature; however, when the temperature is higher than 55°C, the reverse is true.     

Reversible addition–fragmentation chain transfer polymerization of styrene with benzoimidazole dithiocarbamate as a reversible addition–fragmentation chain transfer agent

Two novel dithiocarbamates [2‐Y‐benzoimidazole‐1‐carbodithioic acid benzyl esters: Y = methyl (1b) or phenyl (1c)] were synthesized and successfully used in the reversible addition–fragmentation chain transfer (RAFT) polymerization of styrene in bulk with thermal initiation. The effects of the temperatures and concentration ratios of the styrene and RAFT agents on the polymerization were investigated. The results showed that the polymerization of styrene could be well controlled in the presence of 1b or 1c. The linear relationships between ln([M]₀/[M]) and the polymerization time (where [M]₀ is the initial monomer concentration and [M] is the monomer concentration) indicated that the polymerizations were first‐order reactions with respect to the monomer concentration. The molecular weights increased linearly with the monomer conversion and were close to the theoretical values. The molecular weight distributions [weight‐average molecular weight/number‐average molecular weight (M_w/M_n)] were very narrow from 5.3% conversion up to 94% conversion (M_w/M_n < 1.3). © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 560–564, 2006