Dielectric dispersion studies of poly(vinyl alcohol) in aqueous solutions

The dielectric constant ε′ and loss factor ε″ of deionized water and poly(vinyl alcohol) in aqueous solutions are measured in the frequency region 200 MHz to 20 GHz at four different temperatures (25, 35, 45 and 55 °C). Complex plane plots (ie ε″ vs ε′) are drawn to obtain the static dielectric constant ε₀, high frequency dielectric constant ε_∞, distribution parameter α and average relaxation time τ₀. The variations of dielectric constants with increasing solvent concentration and temperature are discussed in terms of solute–solvent and solute–solute interactions. The average relaxation time τ₀ of poly(vinyl alcohol) aqueous solutions is found to the very short. It is also observed that the relaxation time is almost independent of the viscosity of the solution. The effect of water concentration on macromolecular size, shape and flexibility of the molecular chain are discussed using the observed values of dielectric relaxation times at different temperatures. The possibility of multiple dielectric dispersion is also discussed with concentration variation. © 2000 Society of Chemical Industry     

Glass transition of poly(oxymethylene)

Heat capacity data of semicrystalline poly(oxymethylene) samples. Delrin and Celcon, are analysed in order to discuss the glass transition behaviour of this polymer. There are two types of non-crystalline poly(oxymetheylene). the mobile and rigid amorphous parts. The glass transition of the former occurs in a rather wider range of temperature: it starts at 180 K and could end at 265 K. The latter, under restraint due to the crystallites, remains frozen up to the melting temperature.     

Dielectric,mechanical and thermal properties of some chlorinated poly (p-phenylene oxide)s in the solid state

The dielectric, mechanical and thermal properties were investigated for poly(2,6-dichloro-1,4-phenylene oxide) (PDCPO), poly(2-chloro-6-methyl-1,4-phenylene oxide) (PCMPO) and poly(2,6-dimethyl-1,4-phenylene oxide) (PDMPO). PDCPO exhibited two dielectric secondary relaxations designated as β and γ processes around 160 and 100K, respectively. The γ process was assigned to the motion of a trace of chloroform included in the PDCPO film. A blend film PDMPO/PCMPO ($\text{9}\text{1}$ mixing ratio) exhibited dielectric relaxation around 330K and the process was assigned to the rotation of phenyl group with respect to oxygen-phenyl-oxygen axis. No dielectric relaxation was observed for the PDMPO film dried carefully, while the PDMPO film kept under an atmosphere of water vapour exhibited dielectric relaxation due to the motion of the water molecules at about 180K. Tensile stress at break measured on PDCPO prepared by Stamatoff's method was 38 MPa and was much higher than that for PDCPO prepared by the method reported by Blanchard et al. Temperature dependence of the dynamic Young's modulus for PDCPO measured at 110 Hz exhibited no appreciable loss peak in the range below 480K. Glass transition temperatures for PDCPO, PCMPO and PDMPO were determined to be 490, 445 and 500K, respectively, by differential scanning calorimetry.     

Dielectric relaxation spectroscopy of poly(ethylene terephthalate)

Contour maps of dielectric loss tangent within the ranges 0.1 Hz to 3 MHz and ?175 °C to +190 °C are presented for a commercial poly(ethylene terephthalate) (PET) in two initial states of crystallinity. Individual absorption regions resemble those for poly(butylene terephthalate) and are attributed to carbonyl‐driven α‐ and β‐relaxation processes and to Maxwell–Wagner–Sillars polarizations. Possible causes are considered for the asymmetry and structure apparent in the α‐peak of partially crystalline PET. © 2001 Society of Chemical Industry     

Molecular motions in poly(vinyl acetate) revisited. A thermally stimulated current study

The dipolar relaxation mechanisms in poly(vinyl acetate) have been studied in detail using the technique of thermally stimulated currents. The papers published in the literature about this subject are very contradictory, particularly with respect to the assignment of the observed discharges to the corresponding motions at the molecular level. This work aims at clarifying these problems. We detected and characterised three different relaxation mechanisms: (1) a low temperature one (around ?140°C) which was attributed to local internal rotations in the acetate side-groups; (2) a relaxation whose maximum occurs at 42°C, which corresponds to the glass transition relaxation, and shows a compensation behaviour; (3) an upper glass transition relaxation whose maximum appears at 87°C and was attributed to a liquid-liquid transition. These assignments have been made on the basis of the analysis of the behaviour of the samples when submitted to different thermal and electrical treatments.     

Amorphous-smectic glassy main chain LCPs. II. Dielectric study of the glass transition

The analysis of the dielectric relaxations of two main chain liquid crystalline polymers, derived from hydroxybibenzoic acid and (R,S)- and (R)-2-methyl-1,3-propanediol, is reported. These polymers can be obtained in their glassy amorphous, glassy liquid crystalline or in the crystalline state depending on their thermal history. The effect of the morphology of the sample on the dielectric spectra is analyzed. Particular interest has been paid to the characteristics of the dynamic glass transition of the different glassy states. It has been observed that the glass transition of the liquid crystalline SmC_alt phase occurs at lower temperatures and involves a smaller free volume than the glass transition of the amorphous fraction. The glass transition of the semicrystalline material follows the classical tendency of semicrystalline polymers.     

Delayed action heat seal adhesives. I: Dielectric relaxation studies of mixtures of dicyclohexyl phthalate with poly(vinyl acetate) and polystyrene

The design of delayed action heat seal adhesives depends on the physical properties of the polymer, plasticiser and their resultant mixtures. This paper explores the relationships between various molecular interactions and the performance of the adhesives. Dielectric relaxation measurements of mixtures of poly(vinyl acetate) or polystyrene and a plasticiser, dicyclohexyl phthalate, were performed to characterise the molecular dynamics of the system. Binary mixtures over the entire composition range were examined from 244 to 408 K and over a frequency range from 10^?1 to 6 × 10⁴ Hz, and allowed the nature of the interaction between plasticiser and polymer to be quantified. Dielectric studies are compared with measurements of the glass transition temperature obtained using thermal and mechanical analysis, and indicate that over certain composition ranges segregation of the components occurs at a molecular level. These observations are discussed in relation to the design of a delayed action heat seal formulation.     

Dielectric properties of low molecular weight poly(ethylene glycol)s

This paper reports the measured values of dielectric permittivity ε′ and dielectric loss ε″ of ethylene glycol, diethylene glycol and poly(ethylene glycol)s of average molecular weight 200, 300, 400 and 600 g mol⁻¹ in the pure liquid state. The measurements have been carried out in the frequency range 200 MHz to 20 GHz at four different temperatures of 25, 35, 45 and 55 °C. The complex plane plots (ε″ versus ε′) of these molecules are Cole–Cole arcs. The static dielectric constant ε₀, high‐frequency limiting dielectric constant ε_∞, average relaxation time τ₀ and distribution parameter α have been determined from these plots. The value of the Kirkwood correlation factor g and the dielectric rate free energy of activation ΔF have also been evaluated. The dependence of relaxation time on molecular size and viscosity has been discussed. A comparison has also been made with the dielectric behaviour of these molecules in dilute solutions of non‐polar solvents, which were carried out earlier in this laboratory. The influences of intermolecular hydrogen bonding and molecular chain coiling on the dielectric relaxation of these molecules have been recognized. © 2000 Society of Chemical Industry     

Ester exchange reactions in polyarylate/poly(ethylene terephthalate) blends

Blends coagulated by a solution/precipitation procedure of a polyarylate (PAr) based on bisphenol A and tere/isophthalates with poly(ethylene terephthalate) (PET) have been studied by a variety of experimental methods. Differential scanning calorimetry experiments have shown that in blends containing more than 30% PET, conditioning of the blends at high temperatures required for calorimetric measurements resulted in progressive ester exchange reactions. The 10% and 20% PET mixtures, in which this extreme conditioning was not required, showed a single glass transition, contrary to the behaviour of the other PET compositions. These differences may be attributed to the shape of the spinodal curve, which has been simulated according to the McMaster model for polymer mixtures. The progression of the interchange reactions has been followed by solvent extraction of the resulting products and subsequent Fourier transform infra-red spectroscopy analysis. A parallel decrease in the PET heat and temperature of fusion in the insoluble fractions was observed. In our opinion this was due to the incorporation of PAr units in the PET chains, which caused a decrease in their crystallizable segment length.     

Glass transition and physical ageing in plasticized poly(vinyl chloride)

Several samples of poly(vinyl chloride) both unplasticized and plasticized with dioctyl phthalate, have been examined by differential scanning calorimetry. It was observed that, while the glass transition temperature T_g decreased as expected with increasing plasticizer content, a small portion of the sample appeared to be resistant to the plasticizer. This was manifest in the appearance of a second T_g corresponding to the unplasticized sample which remained unaffected by addition of plasticizer. The ageing behaviour of the samples was also examined using enthalpy relaxation measurements and it was observed that the presence of plasticizer accelerates the ageing process, probably due to the fact that there is greater mobility of the chains in the plasticized samples.     

非晶态粉体玻璃化转变温度的测量方法与装置

为了研究非晶态高分子粉体玻璃化转变与结块特性,需要建立一种实用有效的玻璃化转变温度的测定方法。基于非晶态高分子粉体的体膨胀系数在玻璃化转变时发生突变的原理,采用热膨胀计技术,提出了一种用膨胀计测量非晶态高分子粉体玻璃化转变温度的新方法——膨胀计法,并建立了相应的测量装置。以聚苯乙烯为例,详细介绍了用该方法进行测量及数据处理的过程,并考察了测量结果的有效性。以谷物及含水淀粉体为例,考察了该方法在食品粉体玻璃化转变温度测量中的应用。结果表明,膨胀计法测量非晶态高分子粉体玻璃化转变温度,实用、有效,为非晶态高分子粉体的玻璃化转变温度测量提供了一种新途径。     

Dielectric and viscoelastic relaxations in poly(dicyclohexyl itaconate)

The relaxation spectrum of poly(dicyclohexyl itaconate) (PDCHI) was studied by dynamic mechanical, DC dielectric and thermally stimulated current measurements. Four relaxations, α, β, γ and δ, were obtained. The only method by which all four peaks were observed is that of dynamic dielectric measurements because of the broad range of frequencies employed. The β, γ and δ relaxations were characterized by the activation energy in a relaxation map. A tentative explanation of the molecular origin of each absorption is proposed. In the case of the α relaxation we have used two transformations, one from the permittivity to polarizability and the second from compliance to deformability in order to make evident the existence of this relaxation.     

The glass transition temperature of poly(N-vinyl pyrrolidone) by differential scanning calorimetry

Previously a wide range of values have been reported for the glass transition temperature, T_g, of poly(N-vinyl pyrrolidone), PVP, and it was suggested that lower values are due to variable uptakes of water caused by the hygroscopic nature of the polymer. Now it has been found that there are large variations in T_g, even in carefully dried specimens of PVP. Other factors found to influence T_g are residual monomer and the molecular weight of PVP. Polymers prepared by bulk polymerization, either by γ-irradiation or by heating with 2-azobisisobutyronitrile, have much lower values of T_g than dried ones prepared containing 30% water. The difference is mainly due to depression of T_g by residual monomer which, in the absence of water during polymerization, fails to react completely because of conversion to a glassy state. An unexplained observation is that even when all residual monomer has been removed, polymers prepared by bulk polymerization still have a lower T_g than would be expected from their molecular weight.     

Deuteron n.m.r. in relation to the glass transition in polymers

²H n.m.r. is introduced as a tool for investigating slow molecular motion in the glass transition region of amorphous polymers. In particular, we compare ²H spin alignment echo spectra of chain deuterated polystyrene with models for restricted rotational Brownian motion. Molecular motion in the polystyrene-toluene system has been investigated by analysing ²H n.m.r. of partially deuterated polystyrene and toluene, respectively. The diluent mobility in the mixed glass has been decomposed into ‘solid’ and ‘liquid’ components where the respective average correlation times differ by more than 5 decades.     

On the Splitting of d.c. Contribution to the Dielectric Loss. Case of Poly(monocyclohexylitaconate)

Abstract

The splitting of the d.c. conductivity on the low frequency side of the dielectric loss has been performed by using the complex dielectric polarizability α, instead of the permittivity. Data dealing with the dielectric loss for poly(monocyclohexylitaconate) have been used to compare both methods. The dielectric relaxation peaks in M″ and α″, are in general in good qualitative agreement. There is a small shift which is attributed to the fact that M is a modulus and α a compliance.     

Dielectric investigation of the molecular dynamics in blends: polymers with similar molecular architecture (TMPC/PC blend)

Broad band dielectric spectroscopy was used in the investigation of the molecular dynamics and compatibility of tetramethyl polycarbonate/polycarbonate (TMPC/PC) blends. Frequency scan measurements in the range 10^?2?10^?5 Hz were carried out in the temperature range 50–220°C for several blends with different compositions, namely, 0, 12.5, 25, 50, 75, 87.5 and 100 wt% of TMPC. The results obtained show that these two polymers are ideally compatible over the entire composition range. The blends reveal only one common glass process. The dielectric relaxation strength and the common glass transition temperature, T_g, were found to vary linearly with composition. Moreover, it was found, surprisingly, that blending has no effect on the distribution of relaxation times of the common glass process of the blends. Furthermore, neither the kinetics (relaxation frequency at a certain temperature) nor the distribution of relaxation times of the local process were influenced by blending. It is concluded that the polymeric chains of the different components are not miscible on a segmental level although the blend exhibits only one glass transition temperature.     

Dielectric properties of poly(vinyl chloride) in tetrahydrofuran and cyclohexanone

The dielectric absorption and dispersion of poly(vinyl chloride), M M_v = 49 000, in THF and in cyclohexanone have been studied over a frequency range of 120 kHz to 11·0 MHz, at temperatures from ?22·5 to 35°C, and at concentrations ranging from 4 to 12·0(w/v)% PVC/THF and from 2 to 8·0(w/v)% PVC/cyclohexanone. The viscosities of the two systems have also been measured at temperatures from 20 to 50°C. A single relaxation time was found (β = 0·8–1·0), which indicates that relaxation occurs by segmental rotation. The dielectric and viscous activation energies have been calculated. The dipole moment associated with the relaxation process has also been calculated. The relaxation time, dielectric and viscous activation energies and the dipole moment were found to be dependent on the type of solvent. The dipole moment also showed a molecular weight dependence. The influence of the concentration and temperature on the apparent dipole moment and on the relaxation time is discussed.     

Multiple transitions in poly(allylbenzene): 2. Dielectric relaxations: relationship between structure and properties

The relaxations associated with the phase transitions observed in poly(allylbenzene) have been investigated by dielectric spectroscopy. A morphological model is proposed to describe the fine structure of glass and liquid-liquid transitions and a correlation is established between the polymer structure and several of its properties.     

Quantitative evaluation of the Gibbs—DiMarzio theory of the glass transition

The applicability of the Gibbs—DiMarzio (G—DM) theory of the glass transition (T_g) is quantitatively evaluated for PS, PVC, PαMS and PMMA. The analysis was conducted under the assumption that both the inter-/intramolecular energy ratio (r) and the effective chain segment density (n) remain constant while the fractional free volume at T_g(V₀) varies as a function of the reciprocal degree of polymerization ($\text{10}{}^3\text{P}\text{?}$). Based upon reduced parametric plots of $\text{T}{}_{\mathrm{<mtext>g</mtext>}}\text{T}{}_{\mathrm{<mtext>g\infty </mtext>}}$versus$\text{10}{}^3\text{P}\text{?}$, the results showed that the G-DM equations were satisfactory for PS and PVC but unsuccessful in the cases of PαMS and PMMA. For the former cases the analysis indicated that when 0.015 ? V₀ ? 0.045 optimum agreement occurred at n=1.80, r=10.5 and n=1.36, r=0.95, respectively. Although potential n, r values were obtained for PαMS when the allowable V₀ range was expanded to 0.010–0.050, none of these combinations satisfied all of the analytical requirements. No agreement for the PMMA data sets could be obtained even when this less stringent V₀ criterion was adopted. Attempts to improve this situation by incorporating ‘beads’ and ‘flexes’ into the statistical mechanical equations are also considered.