Gérard Charlet

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.

Solid cholesteric films cast from aqueous (hydroxypropyl)cellulose

Influence des conditions de coulee; processus irreversible; proprietes cholesteriques metastables; proprietes optiques en fonction de la temperature, entre 25 et 200°C

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).

Solution properties and characterization of polyisoprenes at a lower critical solution temperature (LCST)

Abstract This paper reports two investigations on polyisoprene. One consists of obtaining the molecular weight distribution (MWD) of cis -polyisoprene (PIP) standards by a new method using the turbidity at a lower critical solution temperature (LCST). Advantage is taken for this analysis of the fact that the MW dependence of the critical temperature is greater for systems with a narrow solubility gap, i.e. for systems whose LCST and upper critical solution temperature (UCST) are not too far apart. Typically, in n-pentane, a narrow MW standard phase-separates over 25 K. When the solution is heated by temperature increments of 2 K, 15 fractions can be identified, without physical separation. The relative amount of each phase is analysed by turbidity and the average MW of the phases by the temperature at which they phase separate. The MW s recalculated with two constants for the standards are in excellent agreement with gel permeation chromatography (g.p.c.) data. Possible effects leading to a higher polydispersity found by the LCST are discussed. Application to rubber analysis is feasible. The second investigation consists of reporting and analysing the temperatures of phase separation of medium MWD cis - and trans -PIP samples in a series of linear and branched alkanes. The occurrence of correlations of molecular orientations (CMO) in the melt, similar to those found from thermodynamic analysis of PE solutions, was considered. Trans -PIP has a LCST about 25 K lower than cis -PIP in alkanes. Linear solvents are better solvents than branched ones. The low LCSTs (100°C in n-pentane) support CMO or order in polyisoprene melt or concentrated solutions.