Structure and some physical properties of polyvinyl chloride polymerized at different temperatures

In discussing the structure of polyvinyl chloride as a function of the polymerization temperature, the effect of the stereoregularity and the branching should be principally taken into consideration. In the present work, in order to investigate the effect of the polymerization temperature on these two structural factors, both the degree of branching and the stereoregularity were determined on polyvinyl chloride samples polymerized at 90, 50, 20, ?15, and ?75°C., and these two factors were related to the physical properties such as density, crystallinity, glass transition temperature and melting temperature. It was found that, with decreasing polymerization temperature, the degree of branching decreased from 0.27 (CH₃/100 CH₂) for sample polymerized at 90°C. to zero (CH₃/100 CH₂) for sample polymerized at –75°C., whereas, the stereoregularity increased from 0.51 for sample polymerized at 90°C. to 0.77 for sample polymerized at –75°C. Density, crystallinity, glass transition temperature and melting temperature were increased as the polymerization temperature was lowered. It may be concluded that the syndiotacticity of the polymer, especially for samples polymerized at lower temperatures, may contribute principally to the physical properties of the polymer.     

Synthesis of high-molecular-weight poly(L-lactide) initiated with tin 2-ethylhexanoate

The bulk polymerization of L ,L -dilactide was studied as a function of polymerization temperature (T_p), time and concentration of catalyst (tin 2-ethylhexanoate). Poly(L -lactide) (PLLA), with the highest value of intrinsic viscosity ([η] = 13 dl · g^?1; M?_v ≈ 1 · 10⁶) and heat of fusion (ΔH_m = 64,7 J · g^?1), was synthesized at a low catalyst concentration (0,015 wt.-%) and at the lowest T_p studied (100°C), just above the melting point of L ,L -dilactide (98°C). The ceiling temperature of PLLA was found to be 275°C, as deduced from an M?_{v max.} ? T_p curve. The M?_w/M?_n ratios of as-polymerized PLLA samples ranged from 2 to 3. Fractions of PLLA with M?_{v max.} were already present at 50% conversion. The experimental results support a proposed nonionic insertion polymerization mechanism. Polymerization at 100–140°C resulted in early crystallization of PLLA leading to a rather untangled polymer and microporous (pores up to 100 nm) sample texture.     

Cationic polymerization of 4-ethyl-1,3-dioxolane

The bulk polymerization of 4-ethyl-1,3-dioxolane, ( 1 ), was investigated at temperatures ranging from ?48 to 0°C with boron trifluoride etherate and the perchloric acid/acetic anhydride binary system as initiators. At temperatures above ? 20°C, liquid oligomers were obtained in poor yield, while at lower temperatures viscous polymer consisting of alternating sequences of oxy-1-ethylethylene and oxymethylene units with number average molecular weights of several thousands was produced. ¹H NMR analysis of the acetal protons of the polymer on the basis of some model compounds disclosed that the bond cleavage of the monomer in the polymerization occurred nearly randomly at the two acetal C–-O bonds. This polymerization involves a monomer-polymer equilibrium. The thermodynamic parameters for the polymerization were determined from the temperature dependence of the equilibrium monomer concentrations: ΔH_1c = ?13,0±0,8 kJ mol^?1 (= ?3,1±0,2 kcal/mol) and ΔS_1c = ?59,4±3,8 J mol^?1 K^?1 (= ?14,2±0,9 cal/(mol K)). 4-Isopropyl-1,3-dioxolane, ( 2 ), was found very reluctant to polymerize above ? 78°C.     

Cationic polymerization of 2-methyl-1.3-dioxepane

2-Methyl-1.3-dioxepane was polymerized in 1.2-dichloroethane with triethyl oxonium tetrafluoroborate and boron trifluoride as initiators. This polymerization involves a monomer-polymer equilibrium and the polymer consists of regularly alternating tetrahydrofuran and acetaldehyde units. The thermodynamic parameters for the polymerization were determined from the temperature dependence of the equilibrium monomer concentration as follows: ΔH_SS = ?2.1 ± 0.3 kcal/mole and ΔS⁰_SS = ?8.9 ± 1.3 cal/mole deg. The ceiling temperature for the 1 mole/1. solution is ?37°C. The attempted polymerization of 2.2-dimethyl-1.3-dioxepane gave only a crystalline cyclic dimer.     

Continuous fractionation and solution properties of PVC, 6. Pressure dependence of the viscosity — influence of molecular weight and composition

Viscosities were measured as a function of pressure and temperature with solutions of PVC 75 000 in cyclohexanone (CHO) and polymer contents ranging from 0,6 to 12 wt.-%, by means of a Searle-type (≥3 wt.-%) and a rolling-ball viscometer (<3 wt.-%). Furthermore, the influence of molecular weight was determined with solutions of 8 wt.-% of PVC 20 000, PVC 37 000 and PVC 100 000. (The numbers in the codes of the PVC specimens are their approximate molecular weights.) For all concentrations and molecular weights, the viscosity increases in a more or less exponential manner with increasing pressure. The ratio f₁₀₀₀ of the viscosity of the solution at 1 000 and 1 bar can be varied by the change of the polymer content from 2,5 (the value of the pure solvent, index s) to 3,5 (12 wt.-% PVC 75 000) at t = 25°C and from 2,23 to 2,94 at t = 80°C. An increase of the molecular weight of the polymer raises f₁₀₀₀ in a similar manner as the polymer concentration. Using the reduced variables V^≠/V^≠ (ratio of the volumes of activation of the solution and the pure solvent) and c? (product of the polymer concentration and the intrinsic viscosity), all results obtained by variation of T, c and M_w can be represented by a master curve. This means that it is possible to calculate the pressure dependence of a given polymer solution of arbitrary polymer concentration from a mere measurement of the intrinsic viscosity at normal pressure. Criteria are presented which allow a forecast concerning the occurrence of minima in the concentration dependence of the energy of activation of the viscous flow E^≠ and V^≠.     

Acidolytic polymerization of N-methyldodecanelactam

The polymerization rate of 1-methylazacyclotridecan-2-one (N-methyldodecanelactam) ( 1 ) initiated with dodecanoic acid ( 2 ) can be described within the whole range of conversions in terms of the simple relation In ([ 1 ]₀/[ 1 ]) = k[ 2 ]₀t, in spite of the complexity of the overall reaction scheme. The rate constants (k) determined for 240, 260, and 280°C are 0,32, 1,21, and 3,4 kg · mol^?1 h^?1, respectively, and the constants of the Arrhenius equation are A = 6,6 · 10¹³kg · mol^?1 h^?1, E = 140 kJ · mol^?1. The resulting poly(N-methyldodecaneamide) ( 3 ) is a semicrystalline polymer (m.p. 65°C), soluble in polar organic solvents. The following constants of the Mark-Houwink equation were determined for solutions of this polyamide: for 5000 < M?_w < 150 000 g · mol^?1 at 25°C in THF (2-propanol), K = 0,124 (0,161) cm³ · g^?1, a = 0,59 (0,56); for 5 000 < M?_w < 80 000 g · mol^?1 at ?-temperature = 30,5°C in 1,4-dioxane, K = 0,215 cm³ · g^?1, a = 0,50. Analyses of molar masses, both theoretical and experimental (light-scattering, GPC, osmometry, end groups), indicate that at the polymerization temperature of 280°C side reactions already take place, reflected in random cleavage and in branching of chains.     

New hyperbranched poly(ether amide)s via nucleophilic ring opening of 2-oxazoline-containing monomers

An AB₂ monomer containing one oxazoline and two phenolic units was synthesized. The polymerization of the monomer 2-(3,5-dihydroxyphenyl)-1,3-oxazoline in N-methylcaprolactam resulted in a well-defined and fully soluble, high molar mass, hyperbranched polymer with etheramide structure. The hydrolysis of some oxazoline groups as side reaction limits the achieved molar mass when the polymerization is carried out in tetramethylene sulfone or in bulk. The polymers were characterized by one (1D) and two (2D) dimensional ¹H and ¹³C NMR spectroscopy which allowed to determine the degree of branching to be 50% as expected from statistics. DSC and TGA measurements revealed a glass transition temperature of 176°C and a decomposition onset of 330°C. The thermal ring-opening reaction was studied in situ by DSC measurements.     

Molecular weight distribution studies, 2. Radiation-induced polymerization of solid α-methylstyrene

The radiation-induced post - and “in-source” solid state polymerizations (the polymerizations occurred after and during the γ-irradiation, resp.) of α-methylstyrene were studied. Post-polymerizations studied at ?30°C, occurred only in pure and “dry” monomer. At a constant initial radiation dose of 2,5 Mrad (2,5.10⁴J/kg), the rate of polymerization increased, although slightly, with increasing conversion. With increasing initial radiation dose of up to 7,4 Mrad (7,4.10⁴J/kg) and post-polymerized for 8 h, resp., the percentage of polymer yield per unit radiation dose decreased with increasing conversion. The GPC chromatograms of the polymer samples obtained showed a peak at 27,4 elution counts resulting from ionic polymerization and a shoulder at 29,0 counts from free radical polymerization. In the case of the “in-source” polymerization, studied at ?30 and ?40°C, the “wet” monomer yielded rates of polymerization lower than those from “dry” monomer. GPC analysis of the polymer samples obtained at ?40°C from both “dry” and “wet” monomer showed bimodal distributions, the higher molecular weight peak resulting from ionic polymerization. At increased conversions, the positions of both GPC peaks remained unchanged, whereas the heights and hence the ionic and free radical polymerization contribution changed, the ionic contribution decreasing. At ?30°C polymerization temperature only one peak at 27,3 elution counts resulting from ionic polymerization was obtained.     

Calorimetric study of 5-trimethylsilyl-2-norbornene,of its polymerization process and of poly(5-trimethylsilyl-2-norbornene) from 5 to 600 K at standard pressure

Thermodynamic properties of 5-trimethylsilyl-2-norbornene (TMSNB) and poly(5-trimethyl-silyl-2-norbornene) (PTMSNB), viz. the temperature dependence of the isobaric heat capacity C^o_p of the monomer between 10 and 330 K and of the polymer from 7 to 600 K, were studied by adiabatic vacuum and differential dynamic calorimetry. Temperature and enthalpy of monomer melting as well as parameters of glass transition and glassy state of the monomer and the polymer were determined. From the experimental data, the thermodynamic functions H°(T)-H°(0), S°(T) and G°(T)-H°(0) were calculated for TMSNB in the range of 0 to 330 K and for PTMSNB from 0 to 380 K. In a differential automatic calorimeter, the enthalpy of polymerization of TMSNB to PTMSNB in toluene solution was measured at T = 301 K and p = 101,325 kPa. Under similar physical conditions and in the same calorimeter, enthalpies of dissolution for the monomer and the polymer were estimated. The results were used to calculate the enthalpy, entropy and Gibbs function of bulk polymerization of TMSNB in the range of 0 to 380 K at standard pressure. The ceiling temperature of the polymerization process was also evaluated.     

Effects of Chain Transfer Agent and Temperature on Branching and β‐Scission in Radical Polymerization of 2‐Ethylhexyl Acrylate

Poly(2‐ethylhexyl acrylate) is synthesized by conventional radical bulk polymerization both with and without 1‐dodecane thiol as chain transfer agent (CTA) at temperatures from 4 to 140 °C. Electrospray‐ionization mass spectrometry is used to analyze the polymer. This reveals the occurrence of significant β‐scission at high temperature and confirms the presence of CTA‐capped polymers at all temperatures, as well as combination products from 4 to 65 °C. Subsequent ¹³C melt‐state NMR analysis allows quantification of branching and β‐scission. Both are reduced when CTA is present, consistent with a “patching” effect. As expected, the amounts of β‐scission and branching increase with synthesis temperature, although β‐scission dominates at the highest temperature. The backbiting rate coefficient of 2‐ethylhexyl acrylate is determined from NMR results, taking β‐scission into account for the first time. Remarkable agreement with literature k_bb values is obtained, especially for activation energy. This strongly suggests family‐type behavior for acrylate k_bb.     

Studies of the metathesis polymerization and copolymerization of syn- and anti-7-methylnorbornene initiated by the tungsten-carbene complex

The tungsten-carbene complex was used to initiate the metathesis polymerization of syn-and anti-7-methylbicyclo [2.2.1] hept-2-ene (M_s and M_a). Two kinds of experiment were performed:(i) the reactions were followed at low monomer/initiator ratios by ¹H NMR spectroscopy at 220–250K; (ii) polymers and copolymers of M_s and M_a were prepared at room temperature and their microstructure analysed by ¹³C NMR spectroscopy. The propagating tungsten-carbene species derived from both M_a could be detected. Some rate constants were evaluated for various steps in the mechanism. A polymer of M_s was prepared for the first time, containing 90% trans double bonds and probably isotactic. After hydrogenation this polymer exhibits two first-order transitions, with DSC maxima at 179 and 230°C. Hydrogenated atactic polymers of M_a and of norbornene also exhibit first-order transitions. Conditions are described for the preparation of block and tapered block copolymers of M_a and M_s.     

Effects of aminoalcohol and alkoxyalcohol on the n-butyllithium-initiated polymerization of methyl methacrylate

The effects of the addition of aminoalcohols or alkoxyalcohols on the n-butyllithium initiated polymerization of methyl methacrylate in toluene were studied. Stereoregulating behavior in the polymerization was affected remarkably by these additives. The addition of 2-diethylaminoethanol, 2-ethoxyethanol or tetrahydrofurfurylalcohol favored formation of syndiotactic type polymer in the polymerization at ?78°C. On the other hand, isotactic type polymer was obtained by the addition of 3-diethylainino-1-propanol or 1-diethylamino-2-propanol. The influences of polymerization temperature and solvent were also investigated. In the polymerization with n-butyllithium-tetrahydrofurfurylalcohol system, these varibles affected scarcely on the stereoregularity of polymers, and considerably syndiotactic-rich polymer was prepared even at 0°C, both in toluene and in tetrahydrofuran. It is confirmed by gas-chromatographic analysis, electronic spectra, and the results of polymerization that the catalyst system consists of n-butyllithium and lithium alkoxide of aminoalcohols or of alkoxyalcohols.     

Propylene polymerization on titanium-magnesium catalysts determination of the number of active centers and propagation rate constants

By use of the quenching technique with ¹⁴CO and ¹⁴CO₂ the number of active centers and the propagation rate constants (k_p) were determined for the propylene polymerization on different titanium-magnesium catalysts in the presence and absence of an organoaluminium cocatalyst. The k_p values at 70°C were found to be 500–1000 1·mol^?1·s^?1, which were confirmed by independent data of molecular mass measurements of the isotatic polymer after a short polymerization time (5 s). Similar isotactic and atactic k_pvalues were found. The maximum number of active centers for supported titanium-magnesium catalysts can reach about 10% of the titanium content in the catalyst. The k_p values of ethylene polymerization on catalysts active without an organoaluminium cocatalyst were also determined (≈ 10⁴ l·mol^?1·s^?1 at 70°C).     

Synthesis and cationic ring-opening polymerization of 2-methylene-7-oxabicyclo[2.2.1]heptane

A new unsaturated bicyclic ether, 2-methylene-7-oxabicyclo[2.2.1]heptane ( 4 ) was synthesized by successive Diels-Alder addition of furan to acrylonitrile, hydrogenation of cyano compound 5 , and Hofmann degradation of the quaternary ammonium hydrate 7 derived from the amine 6 . Cationic polymerization of the monomer 4 was carried out in CH₂Cl₂ using BF₃ · OEt₂, PF₅, SbCl₅ and SnCl₄ as catalysts in the temperature range of ?20 to ?25°C. White or slightly yellow powdery polymers of low molecular weight were obtained with PF₅ and BF₃ · OEt₂ as catalysts, while no polymer was obtained with SbCl₅ and SnCl₄ as initiators. The IR, ¹H and ¹³C NMR spectra of the polymers indicated that they consist of three kinds of repeating units, that is, two unsaturated units caused by ring-opening polymerization and one addition unit. Using proton NMR data of the polymers, the distribution of repeating units was calculated. A polymerization mechanism is proposed. The thermal stability of the obtained polymers is discussed.     

Polymerization of bicyclic acetals, 5. Cationic polymerization of 6,8-dioxabicyclo[3.2.1]oct-3-ene

The polymerization of 6,8-dioxabicyclo[3.2.1]oct-3-ene ( 1 ) was carried out in methylene chloride at temperatures ranging from ?78 to 0°C. Boron trifluoride etherate, triethyloxonium tetrafluoroborate, and iodine were used as initiators. Completely or nearly completely soluble polymers were obtained at ?78°C in dilute monomer solution, whereas crosslinking occurred to an appreciable extent at higher temperatures or in concentrated monomer solution. ¹H NMR and ¹³C NMR analyses of the soluble polymer, together with its catalytic hydrogenation, disclosed that the cationic polymerization of 1 proceeded, without isomerization of its dihydropyran ring, through the selective cleavage of the C⁵? O⁶ bond to yield a polyacetal having a 5,6-dihydro-2H-pyran ring in the repeating unit.     

Syntheses and characterization of terminally functionalized polypropylenes

Functional polypropylenes having vinyl, phenyl or hydroxyl groups at the chain end were prepared by adding common monomers as butadiene, styrene and 1,2-epoxypropane, respectively, at ?78°C during the living coordination polymerization of propene with a soluble V(acac)₃/Al(C₂H₅)₂Cl catalyst. In addition, polypropylene with hydroxyl functions was prepared by an alternative method based on the hydrogenation of a polypropylene containing aldehyde functions with LiAlH₄. These new types of terminally functionalized polypropylenes were well-characterized by ¹H NMR analysis.     

Polymerization of lactams, 92. Non-activated anionic polymerization of ϵ-caprolactam initiated with the sodium salt of ϵ-caprolactam

The non-activated polymerization of ε-caprolactam initiated with the sodium salt of ε-caprolactam (CLNa), which was prepared in situ with sodium methoxide, was studied in the temperature range 170–230°C and at CLNa concentrations from 0.20 to 1.0 mol-%, and at 190°C in the presence of 2.0–10.0 mol-% CLNa. Apparent rate constants and values of apparent activation energy (E_a) were determined for the initial autoaccelerated stage of polymerization (E_a = 230 kJ·mol^–1) as well as for the stage characterized by a zero-order reaction with respect to the monomer (E_a = 120 kJ·mol^–1). Non-integral orders of the polyreaction with respect to the initiator indicate a highly complex polymerization mechanism. Degradation reactions accompany the polymerization at high polymer contents.     

Polymerization of 1,3‐Pentadiene Initiated by Aluminium Trichloride in Nonpolar Solvent: Pseudo‐Control is Explained by Continuous Grafting

Summary: The cationic polymerization of 1,3‐pentadiene initiated by AlCl₃ was studied in nonpolar solvent. It was previously shown that at room temperature the active species were long‐lived and that the number‐average molar mass of the polymer chains was increasing with the polymerization yield. In order to explain this apparent control, the macromolecules were labeled with a transfer agent, triphenylamine (NPh₃). The latter binds to active species by electrophilic aromatic substitution. The labeling of the polymer chains indicated that at 20 °C the polymer chains mainly contained one NPh₃ molecule per macromolecule while the NPh₃ content was higher for the high molar mass chains due to a “grafting from” polymer transfer mechanism. Thus, the pseudo‐control was assigned to the branching reactions. The labeling process by NPh₃ also succeeded at ?10 °C. Whereas at ?10 °C a dialkylation of NPh₃ was observed, a trialkylation at 20 °C was obtained. The analysis of the polymer microstructure at both temperatures highlighted an interaction between the active centers and NPh₃. This paper also describes a process to synthesize tri‐arm stars polymers by cationic polymerization.

RI SEC chromatograms of soluble polymers synthesized at 20 °C in the presence of NPh₃ with increasing reaction times (r = [NPh₃]/[AlCl₃] = 1); (a) t = 0.25 h, (b) t = 0.5 h, (c) t = 1 h, (d) t = 2 h, (e) t = 18 h, (f) t = 48 h; [AlCl₃] = 2.3 × 10^?2 mol · L^?1, [1,3‐pentadiene] = 1.6 mol · L^?1, pentane.     

Radiation-induced liquid state polymerization of some cyclic ethers

Cyclohexene α-oxide can be polymerized in the liquid state under the influence of Co⁶⁰ γ-radiation at room temperature. Several other oxiranes (including glycidyl ethers) and oxetanes were investigated at the same conditions but only cyclohexene α-oxide gives fairly high yields and rates of polymerization at the dose rate used, (2.21.10⁴ R/hr.). According to the IR spectra polymer does not contain carbonyl groups and has an identical spectra as the cationically polymerized product (BF₃ in CH₂Cl₂ solution at ?78°C.). Since cyclohexene α-oxide itself is very reactive toward cationic catalysts and rather stable in the presence of even strong bases a cationic mechanism of radiation induced polymerization is prefered.     

Hydrogenation of unsaturated polymers with diimide

We have studied the homogeneous hydrogenation of a series of unsaturated polymeric substrates with diimide formed from the thermal decomposition of p-toluenesulfonylhydrazide (TSH) at elevated temperatures (110 to 160°C) and in aromatic solvents. At a TSH/olefin ratio of 2.0, homopolymers of butadiene, polycyclohexadiene, and polyisoprene were quantitatively hydrogenated as were two styrene/butadiene copolymers. Alkyl branching at or near the residual polymer double bond, as in methyl rubber and poly-2.5-dimethyl-2.4-hexadiene, gave less than 50% hydrogenation. Polychloroprene was not hydrogenated by diimide (conversions less than 10%) which is in agreement with the behavior previously observed for low molecular weight olefins. The unsaturated polymers which were successfully hydrogenated were soluble and, hence, showed no excessive crosslinking. Polycyclohexadiene and polyisoprene, the only samples evaluated for molecular weight changes, exhibited no chain degradation. Some qualitative kinetic data were obtained using per cent conversion vs. time data. Under the conditions of toluene reflux and TSH/olefin ratios of 1.5, the relative rates of hydrogenation for cis, trans and vinyl butadiene units was k_cis ? k_trans < k_vinyl. Byproducts from the diimide generation resulted in the introduction of 0.2 to 1.0% of p-CH₃C₆H₄SO₂-groups into the polymer based upon 100% of the double bonds originally present.