Light-scattering and viscometric results are presented from micellar solutions of (PI)2PS (I2S) and (PS)2PI (S2I) three-miktoarm stars and a PSPI (SI) diblock copolymer in n-decane. The influence of architecture on the micellization properties of simple graft copolymers is investigated by keeping the overall molecular weights and compositions of the samples constant. All samples formed spherical micelles in n-decane, a selective solvent for polyisoprene. Aggregation numbers were found to increase in the order I2S < S2I < SI. Hydrodynamic radii of the micelles increased in the same order. The thickness of the corona is determined by the length of the soluble blocks, which they were found to be stretched to almost the same extent in all cases. The area of the core−corona interface per copolymer chain, A c, depends on the architecture of the molecule, and it is larger in the case of I2S micelles. In the case of S2I, larger A c values were found compared to the SI reference sample, indicating that the PS arms are arranged in different ways in the two kinds of micelles. The presence of only one grafted chain per molecule can change considerably the micellar characteristics of complex block copolymers. A simple scaling theory is developed taking into account the free energy contributions from the core, the corona, and the interfacial region of the micelle in the different cases. Theoretical predictions agree qualitatively with the experimental results.

Controlled polymerization of hexamethylcyclotrisiloxane was achieved by carrying out the polymerization first at room temperature to about 50% conversion and then at -20 °C until complete conversion in order to avoid side reactions. The poly(dimethylsiloxane)s produced show narrow molecular weight distributions (M w/Mn e 1.1). Using this approach, a model linear triblock copolymer PS-b-PDMSb-PS, as well as 3-miktoarm star co-and terpolymers of the (PDMS)(PS)2 and (PDMS)(PS)(PI) type, where PS is polystyrene, PI is polyisoprene, and PDMS is poly(dimethylsiloxane), have been prepared.

The phase state of 25 poly(ethylene oxide-b-isoprene) (PEO-PI) diblock copolymers spanning the composition range 0.05 < f PEO < 0.8 has been studied using small-angle X-ray scattering and rheology. In addition, the thermal and thermodynamic properties have been obtained from differential scanning calorimetry and pressure-volume-temperature measurements. Twenty of the diblocks exhibit at least one order-to-order transition, and two show four ordered phases. The phase diagram consists of four equilibrium phases in the melt; lamellar (Lam), hexagonally packed cylinders (Hex), spheres packed in a body centered cubic lattice (bcc) and a bicontinuous cubic phase with the Ia3 hd space group symmetry known as the gyroid phase. The latter is formed for the range of compositions 0.4 < f PEO < 0.45 which are the highest ever reported for a stable gyroid phase. The high asymmetry in the present phase diagram is attributed to the high conformational asymmetry of the PEO and PI ( ) 2.72). At low temperatures, upon PEO crystallization, all phases revert to the crystalline lamellar structure (Lc). Within the composition range 0.66 < fPEO < 0.7 another intermediate phase is formed known as perforated layers (PL) which is clearly not an equilibrium phase. The thermal expansion coefficient was found to be a sensitive probe of the ordered microstructures.

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Much is known about the structure and order-disorder transitions of linear block copolymers.1-3 Detailed information about the kinds of microphase domain morphologies that can be found in block polymers, the composition of copolymer that display each structure, and the conditions for the transitions between these morphologies, as well as into a disordered state, is available. For graft polymers, there has been only one theoretical treatment

We have investigated the influence of composition gradients on the microdomain structure and viscoelastic properties of tapered block copolymers by (i) varying the amount of interfacial material and (ii) the block sequence. Normal tapered and inverse tapered triblock copolymers of polystyrene and polyisoperne with a tapered midblock have been synthesized via anionic polymerization with a nearly symmetric composition and compared with the corresponding diblock copolymers. We found that increasing the amount of tapered material within the interface systematically increases the compatibility. Block sequencing is found to be an important factor controlling compatibility. Inverse tapered block copolymers are much more compatible than the corresponding normal tapered block copolymers. Results presented here could be used as a guideline for preparing copolymers with controlled compatibility at the synthesis level.

In this paper, we exploit the stochastic slip-spring model to quantitatively predict the stress relaxation dynamics of star/linear blends with well-separated longest relaxation times and we analyze the results to assess the validity limits of the two main models describing the corresponding relaxation mechanisms within the framework of the tube picture (Doi’s tube dilation and Viovy’s constraint release by Rouse motions of the tube). Our main objective is to understand and model the stress relaxation function of the star component in the blend. To this end, we divide its relaxation function into three zones, each of them corresponding to a different dominating relaxation mechanism. After the initial fast Rouse motions, relaxation of the star is dominated at intermediate times by the “skinny” tube (made by all topological constraints) followed by exploration of the “fat” tube (made by long-lived obstacles only). At longer times, the tube dilation picture provides the right shape for the relaxation of the stars. However, the effect of short linear chains results in time-shift factors that have never been described before. On the basis of the analysis of the different friction coefficients involved in the relaxation of the star chains, we propose an equation predicting these time-shift factors. This allows us to develop an analytical equation combining all relaxation zones, which is verified by comparison with simulation results.

The static and kinetic aspects of the order-disorder transition (ODT) in newly synthesized model 3-miktoarm star copolymer (simple graft) of SI2 type, (polystyrenexpolyisoprenek, and a 3-miktoarm star terpolymer of SIB type, (polystyrene)fpolyisoprene)(polybutadiene), have been studied using smallangle X-ray scattering (SAXS) and rheology. The morphology and the order-disorder transition temperature (TODT) have been identified from the two-dimensional SAXS patterns with shear-oriented samples. Hexagonally ordered cylindrical microdomains aligned along the direction of shear and with TODT = 379 K have been formed for both samples studied. The SAXS profiles at temperatures well above the Tom have been fitted to the mean-field theory (MFT) for graft copolymers. Near the ODT deviations from the theory have been observed and the SAXS data provide unambiguous evidence for the existence of fluctuations. The Tom obtained from rheology is in excellent agreement with the one from SAXS.Discontinuities in the SAXS peak intensity and m the storage modulus near the Tom are more pronounced in these systems as compared to linear diblwks. The ordering kinetics have been studied with rheology and complementary with SAXS. The width of the kinetically accessible metastable region is enlarged as compared to linear diblocks. For shallow quenthes the ordering proceeds by heterogeneous nucleation and growth of three-dimensional grains with cylindrical microstructure. Our kinetic studies probe the metastable states near but below the Tom.