A sample of triblock copoly(oxyethylene/oxypropylene/oxyethylene) Synperonic F127 was purified. The micellisation and gelation properties of aqueous solutions of purified and unpurified copolymers were investigated by surface tension measurement, static and dynamic light scattering, differential scanning calorimetry and NMR spectroscopy. Generally, the results obtained for the two samples were similar: an exception was the surface tension. Endothermic standard enthalpies of micellisation were obtained over a wide concentration range, with corresponding endothermic standard enthalpies of gelation in the high concentration range. Considered on an equivalent basis, i.e. kJ mol-'(chains), gelation was found to be an almost athermal process compared to micellisation. Based on the presented evidence, particularly that from DSC, and considering other recent studies, it was concluded that the thermal gelation of F127 (i.e. gelation on raising the temperature) resulted essentially from the packing of spherical micelles. A small thermal event at the gelation point was ascribed to a disorder-order discontinuity.Block copolyethers composed of hydrophobic poly(oxypr0-pylene) (POP) and hydrophilic poly(oxyethy1ene) (POE) are non-ionic surface-active agents with a wide range of application. The most used commercial copolymers are triblocks : i.e. H[OCH,CH,],[OCH2CH(CH3)]n[OCH2CH2]mHor E,P,E, Variation of the ratio of oxyethylene to oxypropylene (rn : n) and the number of units in each block (i.e. the overall chain length, x = 2m + n) allows the properties of the block copolymers to be varied in a controlled way.The association properties of triblock copolymer F 127 in aqueous solution have attracted much research interest, not least because of the interesting thermally reversible gelation of its concentrated solutions. 'J According to the published grid,' F127 has the formula E1,$&1,6, where E represents an oxyethylene unit and P an oxypropylene unit. The micellisation of F127 in dilute aqueous solution has been studied p r e v i o~s l y ,~-~ as have the solubilisation properties of its micellar solutions.' The gelation properties of concentrated solutions of F127 have been studied more ~f t e n , ' ,~,~,~-'~ particularly with regard to application in controlled-drug-release systems. Detailed studies of micellisation and micellar solutions by Attwood et ~1 . ~7~ and by Wanka et a[.' reveal some divergence of quoted results: e.g. at 25 "C ref. 3, 4 ref. 5 critical micelle concentration aggregation number ca. 15 ca. 30 (c.m.c.)/g dm-1 0.04In part, these differences reflect a different choice of experimental methods and interpretation of results. A significant consideration, pointed out by Attwood et aI.,12 is the variability of the properties of different batches of F127 (and related copolymers) resulting from variation in their molecular composition. Apart from the natural width of the composition distribution, triblock copolyethers may contain diblock copolymers originating from the transfer reaction in the anionic polymerisat...

A phase diagram is presented for aqueous solutions of oxyethylene/oxypropylene (E/B) block copolymer E41B8. The concentration range covered is 5−70 wt %. The range of techniques used (tube inversion, polarized-light microscopy, rheometry, and differential scanning calorimetry) enabled regions to be assigned to micellar sol, isotropic soft gel, isotropic cubic gel, and birefringent hexagonal gel. The soft gel is assigned to a fractal network formed from spherical micelles and highly swollen by the water phase.

Six diblock copoly(oxybutylene/oxyethylene)s (Eg2B7, E50B73, E4, B, , E50B4, E24B10 and E27B5, where E represents oxyethylene and B represents oxybutylene) have been prepared by sequential anionic copolymerisation and their micellisation in aqueous solution investigated. Surface tension, static and dynamic light scattering and gel permeation chromatography techniques were used to study solutions at temperatures in the range 20 to 50°C over a wide concentration range from dilute to 100 g dm-3. The micellar properties reported are critical micelle concentrations, micellar molar masses and radii. The thermodynamics of micellisation of E , B , diblock copolymers is discussed in relation to that of related triblock copolymers ( E, , . , B, E, and E , P , E , , where P represents oxypropylene).

The article deals with the association behaviour in dilute aqueous solution of block copoly(oxyalkylene)s in which hydrophilic poly(ethylene oxide) is combined with hydrophobic poly(propylene oxide), poly(1,2-butylene oxide) or poly(styrene oxide). Polymers with three simple architectures are considered, i.e. copolymers of type EmAn, EmAnEm and AnEmAn, where E denotes an oxyethylene unit, A denotes a hydrophobic oxyalkylene unit, and the subscripts m and n denote number-average block lengths in repeat units. The aim is to examine how composition, block length and block architecture govern two fundamental properties, critical micelle concentration (cmc) and micelle association number (N), for systems which are in dynamic equilibrium. Copolymers with properties known to be greatly affected by heterogeneity in composition are excluded from consideration. A uniform pattern of behaviour emerges when log(cmc) is plotted against reduced hydrophobic block length (x), consistent with the micellisation equilibrium changing from one between unimers and multimolecular micelles at low values of x, to one between unimolecular micelles and multimolecular micelles at high values of x. Support for this model is provided by the enthalpy of micellisation, values of which fall effectively to zero as x is increased. Values of the micelle association number are used to define a critical hydrophobic block length for micellisation (n(cr)) for each class of diblock copolymers, values of which apply equally well to the half-length of the central block of corresponding EmAnEm triblock copolymers. Given these values, and irrespective of block architecture, the overall scaling law for the weight-average association number of the micelles is shown to be Nw = n'(1.07)m(-0.63) where m is the length (or half-length) of the hydrophilic block, and n' is the effective length of the hydrophobic block, equal to its length (or half-length) minus the critical length, i.e. n' = n-n(cr).

Crystalline cyclic poly(oxyethylene)s with number-average molar masses (M n) of 4000, 6000, and 10000 g mol -1 were studied by wide-angle (WAXS) and small-angle (SAXS) X-ray scattering, highfrequency and low-frequency laser-Raman spectroscopy, and differential scanning calorimetry (DSC). The subcell of the crystalline cyclic polymers was the same as that of high-molar-mass poly(oxyethylene). Cyclic polymers of Mn ) 4000 or 6000 g mol -1 crystallized in their twice-folded conformation under the conditions investigated, but the cyclic polymer of Mn )10000 g mol -1 crystallized in a four-times-folded conformation when cooled from its melt and in a twice-folded conformation when crystallized slowly at high temperature. Comparison is made with the properties of corresponding linear poly(oxyethylene) dimethyl ethers.

Block copolymers were prepared by copolymerization of ethylene oxide and butylene oxide to have identical overall composition and chain length but to differ in their distributions of oxyethylene (E) block length by virtue of the sequence of polymerization of the two monomers:  ethylene oxide first to obtain copolymer E41B8, and butylene oxide first to obtain B8E41. Gel permeation chromatography was used to show that the chain length distributions were in accord with the prediction of the kinetic scheme of Weibull and Nycander. The effect of E-block-length distribution on the self-association (micellization) of the two copolymers in water was determined by means of surface tension and light scattering (dynamic and static) measurements. Compared with copolymer E41B8 under similar conditions, it was found that copolymer B8E41 micellized more readily and formed larger micelles. The effect of the difference in micellar properties on the gelation of moderately concentrated solutions of the two copolymers is described and discussed.

A preparation is described which affords good yields of cyclic poly(oxyethy1ene)s with narrow chain length distributions and number-average molar masses in the range 1000-20 000 g mol-1.

Thermoelastic measurements at constant volume are reported for a series of natural rubber samples. The energy component of the stress supported by the network is more or less independent of the network cure at a value of &/f= 0.1240.02. The energy component of the stress is independent of whether the measurements are made in the dry or in the swollen state, despite the fact that the dry rubbers have non-Gaussian equations of state and that the swollen rubbers approach Gaussian behaviour. Flory's analysis of rubber elasticity which includes hindered internal rotation in the main polymer chain, is compared with experimental results. To a first approximation it gives the correct order of magnitude for the energy component of stress. Measurements have also been made of the pressure coefficient of stress, from which the dilation coefficient of the rubber has been calculated as a function of strain. Flory's analysis does not appear to'predict this coefficient satisfactorily.