Geneviève Delmas

Effect of solvent on the polymorphism of poly(4-methylpentene-1): 2. Crystallization in semi-dilute solutions

Abstract The structure of poly(4-methylpentene-1) (P4MP1) crystallized in semi-dilute solutions (polymer volume fraction between 0.02 and 0.08) in linear and branched alkanes, cycloalkanes, alkane-like compounds, aromatics, carbon tetrachloride and carbon disulphide is reported. As much as five different modifications can be recovered, depending on the solvent and the thermal history of the solution. The results are consistent with the existence of a wide variety of polymer conformations in solution, made accessible by the P4MP1 solubility over a large temperature range. From the observed effects of solvent and thermal history, the main parameter which determines the resulting polymer structure, appears to be the crystallization temperature. The four possible structures prepared in the lower cycloalkanes, as well as crystallizing from tetraalkyltins, structures often unexpected with regard to the correlation with the crystallization temperature, suggest that specific solvent effects, involving shape and size factors, could also affect the resulting polymer conformation at low temperature.

Effect of solvent on the polymorphism of poly(4-methylpentene-1): 1. Solution-grown single crystals

Abstract The morphology and structure of poly 4-methylpentene-1 single crystals grown in a variety of solvent systems is studied by electron microscopy, electron and X-ray diffraction. Depending on the solvent, two different crystalline structures are identified. The usual modification I is formed in a xylene-amylacetate mixture. Modification III is grown in decalin and in a xylene-cyclohexane mixture. In a slowly cooled xylene solution, a mixture of single crystals of both structures is obtained. These results confirm earlier work and show that there is a definite dependence of the structure of the solution-grown polymer crystals on the crystallization temperature. Finally, a refined characterization of modification III single crystals is presented.

Thermodynamic properties of polyolefin solutions at high temperature: 1. Lower critical solubility temperatures of polyethylene, polypropylene and ethylene-propylene copolymers in hydrocarbon solvents

Abstract Lower critical solubility temperatures (LCST) of linear polyethylene (PE), isotactic polypropylene (PP) and of five random ethylene-propylene (EP) copolymers of different composition have been measured in (i) five linear alkanes (n-C5 to n-C9); (ii) sixteen branched alkanes and (iii) four cycloalkanes. The effect of correlations of molecular orientations (CMO) on the LCST was investigated. The main results of this work are the following: (1) the LCST for PE are much lower than those for PP although the expansion coefficients of the two polymers are similar. Calculations using the van der Waals model for a liquid would predict them 10° to 20° apart while the experimental difference can reach 90°. (2) In PE solutions, the linear alkanes are much better solvents than those which are branched. This constitutes a rare example in non-polar solutions in which the magnitude of the equation of state term is not sufficient to predict or even to compare the LCST. The importance on x of polymer-segment and solvent shapes even above the boiling point of the solvent is to be noted. (3) The LCST of the five copolymer samples are almost a linear function of their composition over all the composition range. (4) These results can be understood if the existence of CMO between the (CH2Ch2) sequences is assumed in the pure PE melt and in the copolymers but not between the CH(CH3)CH2 sequences. CMO in solution between the polymeric chains and the linear alkanes make the linear alkanes better solvents than the branched ones. From LCST data in n-C7 and its isomers, the temperature to which CMO in PE disappear can be estimated to be above 170°C, a value which is consistent with those found for long linear alkanes. (5) Branched volatile alkanes such as 2,2-dimethylpentane appear to be a good choice for dosage of the ethylene content of an EP copolymer because of the large interval of LCST between PP and PE in such solvents. LCST measurements could become a sensitive and routine analytical tool for polymer and copolymer characterization for some polymers in well-chosen solvents.

“Modification V” of poly 4-methylpentene-1 from cyclopentane solutions and gels

A new crystalline structure of poly 4-methylpentene-1 (P4MP1), modiification named modification V, is obtained from cyclopentane solutions and gels, for polymer volume fractions between 0.01 and 0.10. The effect of the thermal history imparted to the solution is analyzed. The relation between gelation, polymorphism and existence of helical conformations of P4MP1 in solution is discussed. Modification V is tentatively indexed on the basis of an hexagonal unit cell with dimensions a = 22.17 ± 0.14 Å and c = 6.69 ±0.02 Å. The crystal transforms into modification I at 130 ± 5°C, the heat of transition being + 15 ±2 J.g−1.

Thermodynamic properties of polyolefin solutions at high temperature: 2. Lower critical solubility temperatures for polybutene-1, polypentene-1 and poly(4-methylpentene-1) in hydrocarbon solvents and determination of the polymer-solvent interaction parameter for PB1 and one ethylene-propylene copolymer

Abstract Lower critical solubility temperature (LCST) for 3 polyolefins, polybutene-1 (PB1), polypentene-1 (PP1) and poly(4-methylpentene-1) (P4MP1), and the x interaction parameter in concentrated solutions for PB1 and the 33% ethylene ethylene-propylene copolymer have been measured in linear, branched, cyclic alkanes and some other solvents. Effects on x of the equation of state term, of correlations of molecular orientations (CMO) and of the solvent steric hindrance were investigated. The solvent density ds is found to be a good empirical parameter to characterize the equation of state term and to correlate the LCST. The parameter d s d p (where dp is the polymer density) affords an excellent correlation for the LCST of all polyolefins in normal and branched alkanes (polyethylene (PE) excepted). In dilute solution (at the LCST) the effect of CMO and solvent steric hindrance could not be distinguished from equation of state effects. However, values of x, found to be higher in branched than in linear alkanes in solutions of the linear polymer (PE) but not with the branched PB1 and the copolymer, are indicative of the importance in concentrated solutions of CMO even at high temperatures (100°–135°C). Furthermore, the lowering of x from linear PE to the branched PE and to the ethylene-propylene copolymers, following the expected diminution of CMO in the corresponding melts, is another indication of the persistance of CMO at high temperature. Solvent steric hindrance is seen to lower x (measured here by gas-liquid chromatography).

Orientational order in non-alkane chain molecules. Heats of mixing of tetralauryltin, dioctyl ether, trans- and cis-dec-5-ene with linear and branched alkanes

Heats of mixing at 25°C have been measured for the following 24 systems: Sn(C12H25)4 with five linear and three branched alkanes, dioctyl ether with the same alkanes (except C5), cis-dec-5-ene with trans-dec-5-ene, cis- and trans-decene with n-C12, n-C16, br-C6, br-C16. Orientational order in long chain non-alkane molecules was investigated. It was found to be present between the chains of Sn(C12H25)4. Compounds in which the C—C sequence of an alkane is interrupted by C—O—C (dioctyl ether) appear to retain part of the orientational order, but interruption by a double bond (dec-5-ene) destroys the order. The heat of mixing profile of a given compound with the linear alkane series and that of the branched alkane gives information on the orientational order of this compound in the pure liquid state. Correlation of the heats or of the calculated X12 parameter with the Bothorel J orientational order parameter is made.

Upper and lower critical solution temperatures in polybutadiene-alkane systems: Effect of the surface-to-volume ratio of the polymer

Abstract Cloud point curves (CPC) have been measured for 1–4 cis polybutadiene (M r = 40,000–830,000) in n-hexane, 2-methyl-hexane, 2,2,3 trimethylbutane and 2,2,4 trimethylpentane. These four systems show upper and lower critical solubility temperatures which approach one another as the molecular weight increases. An hourglass-shaped CPC is found for two systems. The CPC are found to be much more dependent on polymer concentration than is usual. Calculated (Prigogine, Patterson, Flory theories) and experimental critical temperatures, critical volumes and shapes of the CPC are in much better agreement for these systems than for other systems involving polystyrene, polyisobutylene or polybutene-1. Analysis of these results with those for other systems in the literature indicates the importance of the surface-to-volume ratio s of the polymers. A small value of s = s 2 / s 1 (0·5–0·8) for thick polymer chains improves the calculated value of the critical temperature while s = 1 is quite good for thin polymer chains such as polybutadiene and polyethylene.

A Study of the Deformation, Network, and Aging of Polyethylene Oxide Films by Infrared Spectroscopy and Calorimetric Measurements

The calorimetric and infrared (IR) spectroscopy measurements of polyethylene oxide (PEO) are used to evaluate the deformation and relaxation that films experience during a temperature cycle (30°C–90°C–30°C). After melting, the intensity of some bands decreases by 10 to 70%. During the temperature cycle, the C–O band in the 1100 cm−1 region and the C–C–O deformation bands at 650 and 500 cm−1 show some new features. A network of cooperative oxygen-hydrogen interactions between the PEO chains form in films with special history, namely, in thermally treated films, in thin films prepared from gel forming solutions, and in thick films after aging. The interchain interaction network is suggested from the IR absorption bands in the 1200 and 900 cm−1 region and also from small bands at 1144 and 956 cm−1. The network seems absent or reduced in thin films. IR spectroscopy appears a sensitive technique to study chain conformations in PEO films and in other materials where order, disorder, and the formation of intermolecular interactions coexist.

Thermodynamic properties of mixtures of linear and branched alkanes with 1,2-dibromoethane and tetrahydronaphthalene. Part 1.—Enthalpies of mixing

Enthalpies of mixing of dibromoethane (DBE) and tetrahydronaphthalene (THN) were measured with branched and linear alkanes at 298 K. These were three highly branched alkanes 2,2,4-trimethylpentane, 2,2,4,6,6-pentamethylheptane, 2,2,4,4,6,8,8-heptamethylnonane and five linear alkanes from C6 to C16. Enthalpies of mixing at 308, 318 and 328 K for DBE with branched and linear hexadecane and at 328 K for THN with branched hexadecane are also presented. With THN, the maxima in the enthalpies of mixing at 298 K are generally <700 J mol–1 and, surprisingly the differences between the mixtures with normal and branched alkanes as the second component are only tens of J mol–1 and are either positive or negative although THN might have been expected to act as an order-breaker. HE values with THN may be explained either by the existence of some order in THN and/or by an exothermic contribution from the condensation effect. With the DBE mixtures, a disordering contribution to the enthalpies of mixing can be discerned, although the total enthalpies are large (2000 J mol–1). The HEdisorder whose values are respectively 367, 208 and 128 J mol–1 at 298 K disorder for n-C16, n-C12 and n-C8, agree with those found for other order-breaker molecules and diminish with temperature, as does the orientational order of the long-chain alkanes. The origin of the large enthalpies for DBE with the alkanes is discussed in terms of an unfavourable interaction of the bromine atom with the CH2 groups, a change in the trans–gauche equilibrium of DBE in going from the pure state to the solution and the effect of non-central forces in DBE.

Heats of mixing of atactic polybutene-1 and of a model molecule with normal alkanes-order in long alkanes

Abstract Heats of mixing at infinite dilution of atactic polybutene-1 in the alkanes have been measured at 25° with a Calvet microcalorimeter. Heats for a model molecule, the 3,5-dimethylheptane, in the same alkanes were obtained also. The enthalpy parameter XH was found to be very close for the two sets of systems. Fitting the experimental data with the calculated free volume term of the heats, the parameter X12 (as expressed in the Flory theory) is found to go through a minimum with chain length. This feature is explained thus: for longer alkanes, the large heat is thought to be due to loss of order in the chain solvent. For the short alkanes, X12 is found large to compensate an overestimation of the free volume term.