Chain Segment Length Research Articles

A unified kinetic analysis for the hyperbranched polymerization with ABg type monomers

The unified analytical expressions of the size distribution function and the degree of branching for the hyperbranched polymerization with ABg type monomers are developed by kinetic theory of polymerization, based on the ABg + ABh + Bf model. The effect of the reactant parameters, the monomers branching degree g and h, the monomers feed ratio r, the functionality f and feed ratio α of the core molecule Bf, on the molecular parameters of the products formed was investigated. Compared with the general polycondensation of ABg monomer or copolycondensation of ABg and AB monomer without core molecule, the presence of multifunctional core molecules makes the polydispersity index of the products go down fast when the reaction approaches completion. At the end of the reaction, the polydispersity index increases with increasing g, and decreases with increasing α and f. For the ABg + AB + B3 polycondensation system, within the range of the feed ratio of ABg monomer less than 0.3, the average chain segment length significantly decreases with the increasing r, and then the change becomes moderate with its further increase. For g > 2, the average chain segment length shows a shallow minimum with increasing r. The degree of branching, fractions of terminal and branching units also show maximum value with the change of monomer feed ratio r. The information obtained in this work can help people understand the structure of ABg type hyperbranched polymers and carry out molecular design.

Hyperstretching in elongational flow of densely grafted comb and branch-on-branch model polystyrenes

Strain hardening of long-chain branched polymers in elongational flow occurs due to the stretch of the backbone chain between branch points. With an increasing number of side arms, the length of the backbone chain segment between two branch points of a comb decreases. Of particular interest is the case when the number Nb of arms per entanglement length of the polymer is larger than one. This leads not only to larger strain hardening but also to hyperstretching, i.e., the elongational stress growth shows an enhanced increase with strain. We consider elongational data reported by Abbasi et al. [Macromolecules 50(15), 5964–5977 (2017)] and Faust et al. [Macromol. Chem. Phys. 224(1), 2200214 (2023)] on a series of comb and branch-on-branch polystyrene (PS) melts with the average number Nb of branches per entanglement segment of the backbone ranging from Nb = 0.2 to Nb = 9.5. In addition, we present measurements of the elongational viscosity of two PS combs with Nb = 4.7 as well as of blends consisting of 5 to 50 wt. % of a PS comb and a monodisperse linear PS. Analysis by the hierarchical multimode molecular stress function model shows that while backbone chains of loosely grafted combs with Nb < 1 are stretched affinely in elongational flow, backbone chains of more densely grafted combs with Nb > 1 show increasing hyperstretching with increasing Nb. The elongational data of the comb/linear blends confirm that hyperstretching is an intrinsic property of the comb macromolecule with Nb > 1, independent of its concentration in the blend. While this is of considerable interest from a modeling point of view, hyperstretching causing an enhanced increase of the elongational stress growth can also have a significant impact on the processability of polymers, and quantification of this effect is, therefore, important.

A New Self-Healing Degradable Copolymer Based on Polylactide and Poly(p-dioxanone).

In this paper, the copolymerization of poly (p-dioxanone) (PPDO) and polylactide (PLA) was carried out via a Diels-Alder reaction to obtain a new biodegradable copolymer with self-healing abilities. By altering the molecular weights of PPDO and PLA precursors, a series of copolymers (DA2300, DA3200, DA4700 and DA5500) with various chain segment lengths were created. After verifying the structure and molecular weight by 1H NMR, FT-IR and GPC, the crystallization behavior, self-healing properties and degradation properties of the copolymers were evaluated by DSC, POM, XRD, rheological measurements and enzymatic degradation. The results show that copolymerization based on the DA reaction effectively avoids the phase separation of PPDO and PLA. Among the products, DA4700 showed a better crystallization performance than PLA, and the half-crystallization time was 2.8 min. Compared to PPDO, the heat resistance of the DA copolymers was improved and the Tm increased from 93 °C to 103 °C. Significantly, the rheological data also confirmed that the copolymer was self-healing and showed obvious self-repairing properties after simple tempering. In addition, an enzyme degradation experiment showed that the DA copolymer can be degraded by a certain amount, with the degradation rate lying between those of PPDO and PLA.

Initial Crystallization Effects in Coarse-Grained Polyethylene Systems After Uni- and Biaxial Stretching in Blow-Molding Cooling Scenarios

This study investigates the initial stage of the thermo-mechanical crystallization behavior for uni- and biaxially stretched polyethylene. The models are based on a mesoscale molecular dynamics approach. We take constraints that occur in real-life polymer processing into account, especially with respect to the blowing stage of the extrusion blow-molding process. For this purpose, we deform our systems using a wide range of stretching levels before they are quenched. We discuss the effects of the stretching procedures on the micro-mechanical state of the systems, characterized by entanglement behavior and nematic ordering of chain segments. For the cooling stage, we use two different approaches which allow for free or hindered shrinkage, respectively. During cooling, crystallization kinetics are monitored: We precisely evaluate how the interplay of chain length, temperature, local entanglements and orientation of chain segments influence crystallization behavior. Our models reveal that the main stretching direction dominates microscopic states of the different systems. We are able to show that crystallization mainly depends on the (dis-)entanglement behavior. Nematic ordering plays a secondary role.

Effect of aliphatic segment length and content on crystallization and biodegradation properties of aliphatic-aromatic co-polyesters

In this work, dimethyl terephthalate (DMT), 1,4-butanediol (BDO) and different diacids were introduced to investigate the effects of variations in aliphatic chain length and component content in aliphatic aromatic terpolymers on the basic thermal properties, crystalline morphology, mechanical properties and biodegradability of the polyesters. The experimental results from nuclear magnetic resonance (NMR), Fourier-transform infrared spectroscopy (FT-IR) and Gel permeation chromatography (GPC) indicate the successful synthesis of the anticipated aliphatic aromatic co-polyesters. The variation of melting and crystallization temperatures with aliphatic chain segment length and content were analyzed by differential scanning calorimetry (DSC). The Wide-angle X-ray diffraction (WAXD) results suggest that the coexistence of both crystals formed by rigid and flexible chain segments can be achieved by varying the length and component content of the aliphatic chain segments in the co-polyesters. The scanning electron microscopy (SEM) and composting experiment results indicate that the type of crystals formed with the more flexible chain segments and the lower degree of crystallinity have a positive effect on the biodegradability.

Impact of Chemically Specific Interactions between Anions and Weak Polyacids on Chain Ionization, Conformations, and Solution Energetics

The presence of salts in a solution containing weak polyelectrolytes is known to modify both their titration behavior and conformations due to electrostatic screening. Instead, little is currently known about the changes induced by chemically specific interactions (e.g., charged hydrogen bonds, c-H-bonds). To investigate this aspect, we simulated the titration of weak polyacids with a primitive model and Monte Carlo methods in the presence of monovalent salts whose anions are capable of forming c-H-bonds with associated acid groups. The interaction between anions and weak polyacids (e.g., poly(acrylic acid)) substantially hampers ionization at low pH despite the somewhat limited number of coordinated anions, whereas it has a limited impact once pH > pKa + 2 due to a progressive anion decoordination. Importantly, the suppression of ionization appears extremely local in nature, with different chain segments differing in pKa by up to 1.3 units. As for chain conformations, c-H-bonds reduce the average sizes of polyacids independently of their structure as a consequence of multidentate binding or multiarm coordination in starlike species. Analyzing the length of chain segments with all monomers coordinated or uncoordinated has also evidenced that anion binding is extremely local in nature. The energetic analysis of c-H-bond formation suggests that polyacid chemical potential may be strongly lowered (up to −0.7 kcal/mol per monomer), the impact of such results on a few phenomena relevant for the physical chemistry of polyacid-containing solutions being analyzed in some detail.

Olefin polymerization cocatalysts: Development, applications, and prospects

<p indent="0mm">The annual global production of polyolefin products exceeds 100 million tons, and they are widely used in various fields. In contrast to heterogeneous polymerization that produces polyolefins with broad dispersity, single-site transition-metal-catalyzed homogeneous olefin polymerization enables the synthesis of polyolefins with narrow molecular weight distribution, controllable chain segment length, and uniform insertion ratio. It can flexibly tune the molecular structure of polyolefins to provide polyolefin materials with the required properties, which can be applied to high-end applications such as medical packaging and medical equipment. It is important to choose a suitable combination of a catalyst and cocatalyst to obtain tailor-made polyolefins through high-efficiency homogeneous polymerization. The main function of the cocatalyst is to react with the catalyst precursor to generate and stabilize active metal cations, the latter being the center of catalyzing olefin polymerizations. This review summarizes the most important work regarding cocatalysts in the past two decades, including novel structures: Mono/dinuclear boron-, aluminum-, and polymer-based promoters. This review illustrates the importance of the weakly coordinative nature of the counter anion, providing the design principle for the development of a highly efficient cocatalyst. Activation mechanism: The use of an industrial catalysis-related pyridylamido hafnium complex is an example that showcases the complicated reactions of this catalyst with different cocatalysts, shedding light on the importance of choosing the pair of catalyst and cocatalyst. Applications in polymerization: Binuclear cocatalysts and the cocatalysts combined with coordination chain transfer polymerizations are used to synthesize novel structural polyolefins, indicating that the cocatalyst plays a crucial role in alternating polyolefin structures. Cocatalyst-involved catalyst deactivation reactions: This part emphasizes the reaction pathways of cocatalysts that lead to catalyst deactivation, including the replacement of metal and ligand. Further, this review proposes the possible future development of cocatalysts by investigating the reported compounds with high Lewis acidity and the development of novel functionalized cocatalysts. For instance, the development of external stimuli-responsive cocatalyst structures may be one of the future development directions. Combining cocatalysts with existing catalytic methods, such as the coordinative chain transfer polymerization for synthesizing polyolefins with a novel structure, may be the second development direction in the future. With the advancement of computer hardware and algorithms together with experimental data, computational chemistry helps understand the effect of cocatalysts on polymerization. Predicting the structure of new and efficient cocatalysts through big data and artificial intelligence is the third possible future development direction.

Investigation of Crystallization and Relaxation Effects in Coarse-Grained Polyethylene Systems after Uniaxial Stretching.

In this study, we investigate the thermo-mechanical relaxation and crystallization behavior of polyethylene using mesoscale molecular dynamics simulations. Our models specifically mimic constraints that occur in real-life polymer processing: After strong uniaxial stretching of the melt, we quench and release the polymer chains at different loading conditions. These conditions allow for free or hindered shrinkage, respectively. We present the shrinkage and swelling behavior as well as the crystallization kinetics over up to 600 ns simulation time. We are able to precisely evaluate how the interplay of chain length, temperature, local entanglements and orientation of chain segments influences crystallization and relaxation behavior. From our models, we determine the temperature dependent crystallization rate of polyethylene, including crystallization onset temperature.

Tuning the length of aliphatic chain segments in aromatic poly(arylene ether sulfone) to tailor the micro-structure of anion-exchange membrane for improved proton blocking performance

Proton blocking anion exchange membrane (AEMs) can be used to treat various of acidic wastewater (i.e., enrich the recovered acid from acidic wastewater). In this work, four AEMs based on aliphatic chain segment imbedding poly(arylene ether sulfone)s bearing salt-terminated side-chains have been prepared for acid enrichment by electrodialysis (ED). In particular, the length of flexible aliphatic chain segments (methylenes of –(CH2)3–), –(CH2)6–, –(CH2)9–, and –(CH2)12–) in aromatic poly(arylene ether sulfone) was tuned to tailor the micro-structure. Our investigation demonstrates that the AEM with aliphatic chain segments of –(CH2)12– shows the strongest surface hydrophobicity (water contact angle: 107°) and has the smallest ion clusters (0.75 nm, relative to the other three AEMs with 0.78 nm, 0.80 nm, and 0.81 nm). In ED process, at the current densities of 10 mA cm−2, the maximum concentration of H+ enriched by the AEM is 2.06 M (initial concentration: 1.0 M). The investigations demonstrate that the optimized AEM with stronger hydrophobicity and smaller ion clusters shows the superior capacity of acid concentration relative to commercial AEM (AMX, Astom Japan). This work should be certain guiding significance for designing advanced proton blocking AEMs.

Free Volumes and Grüneisen Parameters in Mixed‐Tacticity Polyhydroxybutyrates

AbstractRecently, nonlinear progressions of mechanical and thermal properties of mixed‐tacticity polyhydroxybutyrates have been discovered with their fraction of meso diads . Characteristic is traced by a measure of polymer chain segment length disturbance, due to the inclusion of S enantiomers in chains consisting otherwise of R monomers. In this article, the material compositions' thermal expansion coefficients are reported on as determined by X‐ray diffraction and connect the qualitative to their free volume fractions. Further, it is demonstrate that the previously determined Einstein oscillator modes correlate to Grüneisen parameters determined for a range of mixed‐tacticity polyhydroxybutyrates.

Impact of Macrodiols on the Morphological Behavior of H12MDI/HDO-Based Polyurethane Elastomer.

In this study, we evaluated the morphological behavior of polyurethane elastomers (PUEs) by modifying the soft segment chain length. This was achieved by increasing the soft segment molecular weight (Mn = 400–4000 gmol−1). In this regard, polycaprolactone diol (PCL) was selected as the soft segment, and 4,4′-cyclohexamethylene diisocyanate (H12MDI) and 1,6-hexanediol (HDO) were chosen as the hard segments. The films were prepared by curing polymer on Teflon surfaces. Fourier transform infrared spectroscopy (FTIR) was utilized for functional group identification in the prepared elastomers. FTIR peaks indicated the disappearance of −NCO and −OH groups and the formation of urethane (NHCOO) groups. The morphological behavior of the synthesized polymer samples was also elucidated using scanning electron microscopy (SEM) and atomic force microscopy (AFM) techniques. The AFM and SEM results indicated that the extent of microphase separation was enhanced by an increase in the molecular weight of PCL. The phase separation and degree of crystallinity of the soft and hard segments were described using X-ray diffraction (XRD). It was observed that the degree of crystallinity of the synthesized polymers increased with an increase in the soft segment’s chain length. To evaluate hydrophilicity/hydrophobicity, the contact angle was measured. A gradual increase in the contact angle with distilled water and diiodomethane (38.6°–54.9°) test liquids was observed. Moreover, the decrease in surface energy (46.95–24.45 mN/m) was also found to be inconsistent by increasing the molecular weight of polyols.

Molecular dynamics simulations of solvent evaporation-induced repolymerization of covalent adaptable networks

Covalent adaptable networks (CANs) can be decomposed in suitable solvents via bond exchange reactions. Repolymerization can occur by heating the decomposed solution and evaporating the solvent. This solvent-assisted decomposition and repolymerization approach can be used to recycle CANs. In this study, the solvent evaporation from decomposed CAN solutions along with the repolymerization of decomposed chain segments are investigated using molecular dynamics simulations. The evolution of density profiles and chain segment lengths are presented to characterize the solvent evaporation and network repolymerization. The effects of solvent molecule size and evaporation rate on the evaporation and repolymerization processes are analyzed. Our results show that a polymer-rich layer at the solution surface quickly forms when evaporating into a vacuum. The polymer-rich layer significantly inhibits the evaporation of solvent molecules with larger size. Molecules have sufficient time to diffuse when evaporating at a slow rate, thus a more homogenous density distribution can be achieved.

Rational design of phosphonate/quaternary amine block polymer as an high-efficiency antibacterial coating for metallic substrates

Developing advanced technologies to address the bacterial associated infections is an urgent requirement for metallic implants and devices. Here, we report a novel phosphonate/quaternary amine block polymer as the high-efficiency antibacterial coating for metallic substrates. Three pDEMMP-b-pTMAEMA block polymers that bearing identical phosphonate segments (repeat units of 15) but varied cationic segments (repeat units of 8, 45, and 70) were precisely prepared. Stable cationic polymer coatings were constructed on TC4 substrates based on the strong covalent binding between phosphonate group and metallic substrate. Robust relationship between the segment chain length of the polymer coating and the antibacterial property endowed to the substrates have been established based on quantitative and qualitative evaluations. Results showed that the antibacterial rate of the modified TC4 surface were 95.8 % of S. aureus and 92.9 % of E. coli cells attached. Interestingly, unlike the cationic free polymer or cationic hydrogels, the surface anchored cationic polymers do compromise the viability of the attached C2C12 cells but without significant cytotoxicity. In addition, the phosphonate/quaternary amine block polymers can be easily constructed on titanium, stainless steel, and Ni/Cr alloy with significantly improved antibacterial property, indicating the generality of the block polymer for surface antibacterial modification of bio-metals.

Polymer Labelling with a Conjugated Polymer-Based Luminescence Probe for Recycling in the Circular Economy.

In this paper, we present the use of a disubstituted polyacetylene with high thermal stability and quantum yield as a fluorescence label for the identification, tracing, recycling, and eventually anti-counterfeiting applications of thermoplastics. A new method was developed for the dispersion of poly[1-phenyl-2-[p-(trimethylsilyl)phenyl]acetylene] (PTMSDPA) into polymer blends. For such purposes, four representative commodity plastics were selected, i.e., polypropylene, low-density polyethylene, poly(methyl methacrylate), and polylactide. Polymer recycling was mimicked by two reprocessing cycles of the material, which imparted intensive luminescence to the labelled polymer blends when excited by proper illumination. The concentration of the labelling polymer in the matrices was approximately a few tens ppm by weight. Luminescence was visible to the naked eye and survived the simulated recycling successfully. In addition, luminescence emission maxima were correlated with polymer polarity and glass transition temperature, showing a marked blueshift in luminescence emission maxima with the increase in processing temperature and time. This blueshift results from the dispersion of the labelling polymer into the labelled polymer matrix. During processing, the polyacetylene chains disentangled, thereby suppressing their intermolecular interactions. Moreover, shear forces imposed during viscous polymer melt mixing enforced conformational changes, which shortened the average conjugation length of PTMSDPA chain segments. Combined, these two mechanisms shift the luminescence of the probe from a solid- to a more solution-like state. Thus, PTMSDPA can be used as a luminescent probe for dispersion quality, polymer blend homogeneity, and processing history, in addition to the identification, tracing, and recycling of thermoplastics.

A multiscale chemomechanics theory for the solvent – Assisted recycling of covalent adaptable network polymers

Thermosetting polymers are hard to be recycled using conventional methods due to their permanently crosslinked networks. It was recently reported that covalent adaptable network (CAN) polymers could be fully decomposed in organic solvents utilizing bond-exchange reactions (BERs). Re-polymerization occurs by heating the decomposed solution to evaporate the solvent. This prominent feature of CANs provides exciting opportunities to enable the green and sustainable recycling of thermosets. In this paper, we develop a multiscale chemomechanics theory to study the re-polymerization process of CANs, where the soluble chain segments connect at the tails via BERs. At the macromolecular level, the chemical reaction rates are formulated by considering the distance and diffusivity of reactive species, which determine the average chain segment length and network degree of curing (DoC). The evolution rule of DoC is then fed into the continuum-level multi-branched model to capture the thermomechanical properties of CANs at different curing states. The established theory can predict the conversion ratio of functional groups, solution viscosity, volume shrinkage, and glass transition behaviors of re-polymerizing CANs. It also reveals the influencing mechanisms of various material and processing conditions, which paves the road for the immediate engineering applications of the green and sustainable recycling approach for thermosets and their composites.

Preparation of three-dimensional palygorskite based carrier

Palygorskite is a kind of crystalline hydrated magnesium aluminum silicate mineral with micro-fibrous morphology. Due to the large specific surface area, moderate cationic exchange capacity and pronounced adsorption properties, it has been widely used in many fields. In order to enhance the loading capacity and adjust the microstructure of palygorskite (Pal) crystal, series of three-dimensional palygorskite carriers (3D Pal) with different pore size were fabricated through grafting from or grafting onto method. Due to the functional and cross-linked molecules act as upholder reagents, the specific surface of individual palygorskite is fully utilized and the load capacity is greatly improved. The porosity and pore size of 3D palygorskite based carrier also can be regulated by the length of organic molecular chain segments. The successful preparation of 3D Pal-based carrier provides a new way for surface grafting, modification or preparing 3D carrier of palygorskite and other minerals.•The developed method allows fabricating three-dimensional palygorskite based carriers by covalent bonding method.•The pore size of the as-prepared carriers can be conveniently adjusted by length of the bonded molecular chain.

Characterization and solubility effects of the distribution of carboxymethyl substituents along the carboxymethyl cellulose molecular chain

Sodium carboxymethyl cellulose (CMC) is a major cellulosic derivative that has a wide variety of applications. The solubility of CMC is affected by the degree of substitution (DS) of carboxymethyl groups and their distribution along the CMC molecular chain. In this study, an enzymatic hydrolysis technique was used to determine the distribution of carboxymethyl substituents. Two key parameters, namely the average length of the molecular chain segments not susceptible to enzymatic hydrolysis by cellulases (L ̅Sn, including chains fully substituted or containing single unsubstituted unit) and the average length for the molecular chain segments susceptible to enzymatic hydrolysis (L ̅Gn, unsubstituted chains segments), were obtained. This approach was subsequently applied to characterize four CMC samples having similar DS values (~0.80). The distributions of carboxymethyl substituents along the CMC molecular chain were found to be drastically different. The L ̅Sn varied from 9.6 to 49.5, while the L ̅Gn was almost constant (from 4.5 to 5.4). This information was correlated to the CMC solubility. The swelling ratio and the dynamic contact angle revealed that the CMC samples with higher L ̅Sn exhibited stronger swelling and wettability than those with lower L ̅Sn. The dissolving time of the CMC molecule decreased substantially with the increase in L ̅Sn.

Effect of chain segment length on crystallization behaviors of poly(l-lactide-b-ethylene glycol-b-l-lactide) triblock copolymer

The poly(l-lactide-b-ethylene glycol-b-l-lactide) (PLLA-PEG-PLLA) triblock copolymers with different chain segment length are fabricated by ring-opening polymerization. The structure, molecular weight, and crystallization behaviors of the triblock copolymers are characterized by Fourier transform infrared, nuclear magnetic resonance spectroscopy, gel permeation in chromatography, X-ray diffraction, differential scanning calorimetry, and polarizing optical microscopy (POM). The results show that the increase of block length is beneficial to improve its crystallization. In addition, the triblock copolymer exhibits a double crystallization phenomenon. The POM results indicate that PEG and PLLA chains of the copolymer crystallize in their respective crystallization temperature regions. The growth rate of the PLLA spherocrystal decreases and the dendritic spherocrystals appear with increasing the PEG chain length when the PLLA chain of the copolymer is isothermal crystallized at 80°C and PLLA chain length is constant. The growth rate of the PEG spherocrystal decreases and the spherocrystal morphology changes little with increasing PLLA chain length when the PEG chain is isothermal crystallized at 25°C and the length of PEG chain remained unchanged.

Mechanical and Thermal Properties of Mixed-Tacticity Polyhydroxybutyrates and Their Association with Iso- and Atactic Chain Segment Length Distributions

We investigated the effect of including S enantiomers on the mechanical and thermal properties of predominantly (R)-β-polyhydroxybutyrate (PHB). From tensile testing, we determined resulting ratios of meso to racemo diads, for which elastic modulus, strength, and fracture strain combine to provide maximized fracture energies. We found that these coincide with an inversion of the respective elastic moduli of the amorphous and crystalline phases. From thermocalorimetric analyses, we determined the glass-transition temperatures and enthalpic relaxations, the heat capacities of the materials and their constituent phases, the directional crystallization rates and melting points, as well as the melting enthalpies for the α-PHB phase as functions of tacticity. We present a unifying characteristic, accounting for tacticity mismatches, based on the previously determined random polymerization action of the catalyst ethylzinc β-diketiminate and 4-methoxybenzyl alcohol. This characteristic provides a qualitative indication of the transition points in nonlinear correlations encountered between the ratios of meso to racemo diads and mixed-tacticity polyhydroxybutyrates’ fracture energies, amorphous and crystalline phase elastic moduli, melting enthalpies, and lattice vibrational frequencies.

Surfactant selection as a strategy for tailoring the structure and properties of UCT manganese oxides

Mesoporous manganese oxides were synthesized using the UCT inverse micelle templating method with four different Pluronic surfactants to investigate the effects on the morphology, microstructure and desulfurization behavior of these materials. All of the as-synthesized samples exhibited similar hierarchical microstructures, but the size and shape of the primary nanoparticles for each sample was different. The primary nanoparticle sizes for these samples vary between 2.3 and 7.0 nm. Most of the samples are crystalline and are composed of a mixture of Mn3O4 and Mn5O8 phases. The adsorption behavior of these samples was tested using a fixed bed reactor at a temperature of 200 °C. Microstructural analysis of the samples after the desulfurization tests revealed a transformation of the mesoporous manganese oxide to a dense manganese sulfide phase; this involves a volumetric expansion of the crystal, leading to densification and a rapid decay in the sorption capacity after the breakthrough point. The variation in the structure and properties of these materials is related to ratio of the PEO and PPO chain segment lengths in the Pluronic surfactants used. This indicates that the ratio must dictate the volume, shape and assembly of the inverse micelles in the UCT synthesis.