Search

The bulk radical polymerization of three methacrylic monomers, butyl, dodecyl, and 3-[tris(trimethylsilyloxy)silyl] propyl methacrylate, were studied in the dark period after previous illumination by ultraviolet light at λ = 365 nm. An important postpolymerization process took place in all the polymerization reactions. This indicates that, even at low monomer conversions, a certain and nonnegligible radical concentration remains after switching off radical production. Monomer concentration measurements by FT-IR spectroscopy in the dark period showed that long-lived radicals continued the polymerization up to conversions that, in some cases, were higher than 70%. The half-lifetimes of these macroradicals ranged from 300 to 14000 s. Kinetic expressions were developed to determine the fraction of living and dead polymer during the course of the postpolymerization. The SEC traces of the resulting polymers showed bimodal molecular weight distributions and extremely high-molecular-weight polymers obtained in the post-effect period. By means of both kinetic results and molecular weight distribution, the values of the radical concentration in the dark period, the average termination rate coefficient of the macroradicals, and the transfer constant to the monomer were determined for the different polymerizations reactions carried out.

The effect of diffusion on linear, step-growth polymerizations has been quantified via “chain-by-chain” simulations of the polymerization process and a diffusion model consistent with reptation theories. The results show that diffusion limitations can narrow the molecular weight distribution and alter the way it evolves during polymerization; e.g., when diffusion is the limiting step, the polydispersity index (PDI1 = Mw/Mn) converges to a value of ~1.3 at complete conversion. Nevertheless, diffusion limitations have little effect on the time dependence of conversion. Consequently (for this type of polymerization), modeling of diffusion phenomena is important only when an accurate calculation of the MWD is needed. We also show that the numerical value of the Hatta number, at the point of entanglement (ϕ), can be used to determine whether diffusion limitations are likely to be important in a given system. Guidelines for the estimation of ϕ are given.

A series of methacrylic copolymers was prepared by radical polymerization of the monomers 2-ethoxyethyl methacrylate and 2-hydroxyethyl methacrylamide and a small quantity of a cross-linking agent ethylene glycol dimethacrylate. Water swelling of the membranes, mechanodynamical analysis, density measurements, and ATR-FTIR studies were performed on the copolymers. High vacuum pressure techniques were used to evaluate the flow of He, O2, N2, CO2, CH4, CH3CH3, and CH2CH2 through these membranes, and solubility, diffusivity, and permeability coefficients were determined. The effect of the increase of the amount of methacrylamide in the copolymer on transport properties, glass transition, fractional free volume, cohesive energy density, and specific interactions has been studied and is reported in this work.

An experimental study of the diffusion and permeability coefficients of helium, oxygen, and nitrogen in membranes prepared by solvent casting of commercial poly(vinyl chloride) (PVC) is reported. Transport parameters are very sensitive to the densification of PVC so that at 25 °C a sharp drop in the values of the permeability and solubility coefficients during the first week takes place. The variation of the transport parameters with aging time is nearly negligible after one month. Molecular dynamics methods were used to simulate a host matrix of poly(vinyl chloride) with density similar to that of the aged polymer. The application of the transition states approach to the simulation of the diffusion of gases in poly(vinyl chloride) gives values of the diffusion coefficient somewhat lower than the experimental ones for oxygen and nitrogen and higher for helium. Gas solution in poly(vinyl chloride) was simulated by means of a Monte Carlo cycle that inserts, with probability pin, or removes, with probability pre, particles of diffusant at randomly selected positions within the polymeric matrix. The values of the permeability coefficients calculated from the simulated diffusion and solubility coefficients are in very good agreement with the experimental results.

Two new monomers, cis-(2-phenyl-1,3-dioxan-5-yl) methacrylate (CPDM) and trans-(2-phenyl-1,3-dioxan-5-yl) methacrylate (TPDM), have been synthesized. The stereochemical configuration in both monomers was unequivocally assigned by correlation ¹H−¹³C NMR experiments. The radical polymerization reactions of both monomers were studied by ultraviolet spectroscopy and electron paramagnetic resonance spectroscopy to determine the polymerization rate parameter kp/kt^1/2 and the absolute propagation and termination rate constants (kp and kt) at different temperatures. The values of kp/kt^1/2 lie in the range 0.40−0.55 L^1/2/(mol^1/2 s^1/2) for CPDM and 0.29−0.37 L^1/2/(mol^1/2 s^1/2) for TPDM at temperatures between 45 and 70 °C, showing that the polymerization rate of the cis monomer with the substituents in equatorial−axial positions on the dioxane ring is higher than that of its trans counterpart with the phenyl and ester residue in equatorial positions on the dioxane ring. Using EPR measurements of the polymer radical concentrations, similar values for kp were obtained for both trans and cis monomers, whereas the termination rate constant of the trans monomer was about twice that of the cis monomer at the same temperature.

The temperature dependence of the α and β relaxations of poly(2-phenyl-5-acryloxymethyl-5-ethyl-1,3-dioxacyclohexane) is studied by broad-band dielectric spectroscopy. The strength of the α relaxation decreases with increasing temperature, pointing to an onset temperature (Δεα = 0) of ca. 97 °C. Seen from the high-temperature side, the α relaxation starts with zero intensity at the onset temperature and steeply increases with decreasing temperature until it levels off in the vicinity of Tg. Whereas in the glassy state the strength of the β relaxation is only slightly dependent on temperature, it undergoes a strong increase at temperatures above Tg. Arrhenius plots of both relaxations show that the β process remains operative at temperatures above the onset temperature of the α relaxation. The temperature dependence of the stretch exponent does not show a definite trend, most of the values obtained lying in the interval 0.3−0.5.

The diffusivity, permeability, and solubility coefficients of O2, N2, CO2, and CH4 have been measured in PVC and in four samples of PVC functionalized with mercapto pyridine groups up to 6.8, 11, 21, and 46 mol %. It has been found that the permeability of all four gases progressively increases by a factor of more than 4 because of a similar increase in the diffusion coefficients. In addition, permeability selectivity augments significantly for the gas pair O2/N2 and only slightly for the pair CO2/CH4. The structural changes in the modified samples have been monitored by means of density and Tg determinations and FFV calculations, which are a measure of interchain spacing and chain stiffness. An interpretation of the changes seen in the gas transport properties of modified PVC samples has been proposed in terms of the structural changes introduced by the progressive functionalization of the PVC chains.

The transport of argon in membranes of poly(bisphenol A carbonate-co-4,4‘-(3,3,5-trimethylcyclohexylidene)diphenol carbonate), under differences of pressure, Δp, lying in the interval 8−160 cmHg and in the temperature range 30−55 °C, is described. The experimental values of the permeability and diffusion coefficients at 30 °C and Δp = 76 cmHg are 4.5 barrers and 3.0 × 10^-8 cm² s^-1, respectively. The values of these parameters are nearly independent of the differences of pressure between the two faces of the membrane. The permeability and the diffusion coefficients obey Arrhenius behavior with activation energies of 3.7 and 6.7 kcal mol^-1, respectively. The permeation of argon in the membranes was simulated using the transition-state approach. Good agreement between simulated and experimental results is found by assuming that the polymer chains of the membrane fluctuate around equilibrium positions with a root-mean-square deviation Δ of 0.3 Å at 40 °C. Comparison of the experimental and simulated values for the diffusion and solubility coefficients suggests that the value of Δ increases with temperature at a rate of 0.005 Å K^-1.

Thermoelastic networks were prepared by end-linking hdroxyl-terminated poly(neopentylglycol hexafluoroglutarate) using tris(p-isocyanate phenyl) thiophosphate as cross-linking agent. The plot of birefringence versus stress exhibits negative deviations from linearity at elongation ratios larger than 1.9. The value of the optical configuration parameter Δa is 2.98 ų at 5 °C. Theoretical calculations carried out using the rotational isomeric state model give for this parameter the value of 2.24 ų, in fair agreement with the experimental results. The cause of the strong discrepancies between the theoretical and experimental results observed for the optical configuration parameter of polyesters containing phenyl groups in the acid residue is discussed.

This work reports the permeation of argon through membranes prepared from poly(pentaerythritoltribenzoate acrylate) (PPTBA) (IUPAC name poly[1-(3-benzoyloxy-2,2-dibenzoyloxymethylpropyloxy)-2-propen-1-one]). The permeation measurements were performed in the vicinity of the glass transition temperature of the membranes (48 °C). The permeation coefficient only shows a slight dependence on temperature in the glassy state, but it undergoes a sharp increase with temperature in the rubbery state. The results for the diffusion coefficient do not show a definite temperature dependence in the glass−rubber transition. As expected, the solubility of the gas in the membrane is higher in the rubbery state than in the glassy state. The diffusion coefficient was calculated theoretically by using the Transition-State Approach which assumes that the diffusant path is independent of the structural relaxations in the polymer matrix. Reasonably good agreement between the simulated and the experimental values of the diffusion coefficient was obtained in the range of temperatures from 40 to 60 °C in which the measurements were performed.

From a comparative study of the polarity of poly(neopentyl glycol hexafluoroglutarate) (PNFG) and its hydrogenated counterpart, poly(neopentyl glycol glutarate) (PNG), the influence of the presence of the fluorine atoms on the conformational characteristics of polyesters is investigated. At 30 °C, the experimental values of the mean-square dipole moment per repeating unit of PNG and PNFG chains, 〈μ²〉/x, are 5.25 and 9.16 D², respectively. A critical interpretation of the experimental results using the rotational isomeric state model suggests that the conformational energies associated with the gauche states about both the C^αH2−C*(O*) and C^βH2−C^αH2 bonds of the acid residue of PNG have, respectively, lower and higher energy than the alternative trans states. Similar conclusions are reached for the conformational energies associated with the skeletal bonds of the C^βF2−C^αF2−C*(O*) segment of the acid residue of PNFG chains. This study leads us to conclude that differences in the orientations of the dipoles associated with the ester groups, rather than differences in the rotational populations about the skeletal bonds of the chains, may be responsible for the significant higher polarity of the fluorinated polyesters.

The kinetic aspects of the radical polymerization of triethylene glycol monoacrylate are studied finding that the values of kp/kt^1/2 are in the range 0.17−0.40 L^1/2/mol^1/2 s^1/2 at temperatures between 50 and 65 °C. The values of the activation enthalpy, ΔH**, and activation entropy, ΔS**, of the global process amount of 11.0 kcal mol^-1 and −28.3 cal mol^-1 K^-1, within the range reported for other acrylate polymers. Mean-square dipole moments per repeating unit, 〈μ²〉/x, were determined from measurements of dielectric permittivities in dilute dioxane solutions. The results at 30 °C were 〈μ²〉/x = 7.97 D² and 10³ d ln 〈μ²〉/dT = 0.85 K^-1. Values of dipole moments associated with the conformations of the side groups range from 0.2 to 5 D, and hence a combination of standard matricial products and Monte Carlo techniques were used to evaluate by the rotational isomeric state model the dipolar correlation coefficient of the chains. Good agreement between theoretical and experimental results was found using the set of statistical weights utilized for other acrylate polymers with short side groups.

The synthesis and radical polymerization of 2,2-bis[4-(2-hydroxyethoxy)phenyl]propyl monoacrylate are described. The values found at 50 and 60 °C for the rate constants ratio, kp/kt^1/2, are similar to those reported for some acrylic polymers with short side groups at the same temperatures although conflicting results are obtained by comparison with the kinetic constants reported for other similar acrylic monomers. The experimental value of the mean-square dipole moment per repeating unit of the resulting polymer, poly{2,2-bis[4-(2-hydroxyethoxy)phenyl]propyl monoacrylate} was 7.24 D² at 30 °C. This result is very close to the value of 7.83 D² found, at the same temperature, for the model compound of the side group of the polymer, 2,2-bis[4-(2-hydroxyethoxy)phenyl]propyl monoacetate. Owing to the wide distribution of dipole moments associated with the side groups, the dipolar correlation coefficient of the chains was calculated by combining matricial products of the rotational isomeric state model and Monte Carlo techniques. The calculations suggest that the statistics of long side groups rather than the statistics of the main chain govern the dipolar correlation coefficient of atactic comblike polymers.