Broad Molecular Weight Distribution Research Articles

Selected Physicochemical and Pharmaceutical Properties of Poly-ε-caprolactone and Poly(d,l-lactide-co-ε-caprolactone) Conjugates of Lamivudine Synthesized via Ring-Opening Polymerization.

The modification of drug fate after administration may be achieved by the covalent coupling of active pharmaceutical ingredients with macromolecules. To prolong or delay the release, slowly degrading polymers such as polyesters may be applied for conjugation. The detachment of a covalently conjugated drug from the polymeric matrix relies mostly on the material degradation profile and barely on the weak interaction between the drug and macromolecules. In the present study, lamivudine was conjugated via ring-opening polymerization with poly-ε-caprolactone and poly(d,l-lactide-co-ε-caprolactone). The influence of the reaction parameters on the course of the polymerization and physicochemical properties of obtained conjugates were investigated. Subsequently, selected reaction products were formulated into submicron particles, and drug release profiles in physiological-like conditions were investigated. The course of the reaction was monitored via gel permeation chromatography. The structure and physicochemical properties of products were evaluated via spectroscopic, calorimetric, and diffractometric methods. The profile of the drug release from particles prepared by the slow evaporation of conjugate solution from o/w emulsion was monitored with high-performance liquid chromatography. Both an elevated reaction temperature and higher catalyst concentration increased the polymerization rate and simultaneously promoted the side reactions, resulting in a broad molecular weight distribution of products in the range from 1.30 to 2.15. The physicochemical properties of conjugates obtained in different conditions varied and had a direct influence on the drug release. The release curve of lamivudine from particles based on low molecular weight conjugates achieved a plateau between 18.9 and 22.2 μg per mg of conjugate within a month. Drug detachment from particles composed of high molecular weight conjugates exhibited a distinct delay period preceded by a drug burst release at a maximal level of 13.3 μg per mg of conjugate. Conjugate chemical composition and the degree of crystallinity were also found to influence the release.

Synthesis of molecular‐weight‐controlled polyfluorene with boronate at one end

ABSTRACTWe investigated the synthesis of polyfluorene with a pinacol boronate (PinB) moiety at one end and with controlled molecular weight by means of Suzuki–Miyaura coupling polymerization of pinacol (7‐bromo‐9,9‐dioctyl‐9H‐fluoren‐2‐yl)boronate (1) with a palladium(0) precatalyst in the presence of pinacol 4‐trifluoromethylphenylboronate (2) as a chain terminator and CsF/18‐crown‐6 as a base. When we used AmPhos Pd G2, which has a propensity for intramolecular catalyst transfer on a π‐electron face, polyfluorene with the PinB moiety at one end and PhCF3 (derived from 2) at the other end was obtained, and the molecular weight increased in proportion to the feed ratio of [1]0/[catalyst]0, though the molecular weight distribution was broad. Since the molecular weight also linearly increased with respect to the conversion of 1 until the middle stage of polymerization, the polymerization appears to involve chain‐growth polymerization through intramolecular catalyst transfer from the Pd catalyst inserted into the CBr bond of 1. The broad molecular weight distribution might be mainly due to slow initiation and slow termination with 2, rather than polymer–polymer coupling. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 2498–2504

Extensional flow dynamics of polystyrene melt

A linear polystyrene melt with broad molecular weight distribution (CAS 0993-53-6 from Aldrich) was characterized in extensional flow using a filament stretching rheometer. A series of measurements were performed, including (1) the startup of uniaxial extensional flow until steady state; (2) the strain controlled reversed (i.e., biaxial) flow following the startup of uniaxial flow; and (3) stress relaxation (i.e., keeping the strain unchanged) also following the startup of uniaxial flow. The measurements were compared with the model by Narimissa and Wagner [J. Rheol. 60, 625–636 (2016)]. Good agreements at low extension rates and low strain values were observed. Higher deviations were observed at high rates under steady state conditions as well as during stress relaxation and reversed flow.A linear polystyrene melt with broad molecular weight distribution (CAS 0993-53-6 from Aldrich) was characterized in extensional flow using a filament stretching rheometer. A series of measurements were performed, including (1) the startup of uniaxial extensional flow until steady state; (2) the strain controlled reversed (i.e., biaxial) flow following the startup of uniaxial flow; and (3) stress relaxation (i.e., keeping the strain unchanged) also following the startup of uniaxial flow. The measurements were compared with the model by Narimissa and Wagner [J. Rheol. 60, 625–636 (2016)]. Good agreements at low extension rates and low strain values were observed. Higher deviations were observed at high rates under steady state conditions as well as during stress relaxation and reversed flow.

Transcriptomic-proteomics-anticoagulant bioactivity integrated study of Pheretima guillemi

Ethnopharmacological relevanceEarthworms, a type of animal drugs from traditional Chinese medicine, have been used to treat coagulation for many years with less adverse effects and similar anticoagulant effects compared to the commonly used anticoagulants. There are four species of earthworms recorded in Chinese Pharmacopoeia, while few of them were studied and deficient information were involved in the NCBI and UniProt earthworm protein database. We have adopted a transcriptomic-proteomics-anticoagulant bioactivity integrated approach to investigate a seldom-studied Chinese Pharmacopoeia recorded species, Pheretima guillelmi. Aim of the studyIn the present study, we aimed to reveal the anticoagulant bioactivity of Pheretima guillelmi, and identify its functional proteins via LC-MS/MS-transcriptome cross identification. Methods and resultsWith the aid of fibrinogen-thrombin time assay, Pheretima guillelmi was found to possess strong anticoagulant activity, and the bioactivity was quite stable under 30–50 °C and near-neutral conditions. A comprehensive non-reference transcriptome assembly of P. guillelmi was first established to supplement the currently inadequate earthworm protein database and to illustrate the active proteins. Illumina RNA sequencing generated 25,931,175 of clean reads with over 97% high-quality clean reads (Q20) and assembled an average of 133,228 of transcript and 106,717 of unigenes. A total of 11,259 coding sequences were predicted via ESTScan (3.0.3). The P. guillelmi unigenes were searched and annotated against public database. The bioactive proteins in P. guillelmi were with broad distribution of molecular weight. With bottom-up proteomics analysis, ten proteins were identified against UniProt and NCBI earthworm database; and 31 proteins with high-confidence were matched against transcriptomic established P. guillelmi database. ConclusionThis study illuminated the therapeutic potency of P. guillelmi for antithrombus and provide a new strategy to investigate animal drugs of Chinese materia medica.

Preparation and characterization of high melt strength thermoplastic polyester elastomer with different topological structure using a two-step functional group reaction

Long-chain branched (LCB) thermoplastic polyester elastomer (TPEE) could be controllably prepared by the two-step reaction of the linear TPEE with triglycidyl isocyanurate (TGIC) and 2,2′-bis(2-oxazoline) (2,2′-BOZ) together in different sequences to improve their rheological properties and foaming ability. All of the modified TPEEs reacted with TGIC first and then with 2,2′-BOZ have more branching points and longer chains. These samples show a higher molecular weight, a broader molecular weight distribution. These samples also had a higher viscosity and modulus, a longer relaxation time, and a stronger strain-hardening effect. Moreover, the greater number of branching points accelerated the non-isothermal crystallization process. The foaming ability of the modified TPEEs was evaluated via a batch CO2-foaming process. The LCB structure improved the melt viscoelasticity and the foaming ability remarkably. The TPEE samples with more chain branching points and longer chains had the highest cellular densities and the largest expansion ratios, with average cell diameters of 4–13 μm, cell densities of 2.0 × 109–1.0 × 1011 cells/cm3, and expansion ratios of 2.5–14.1.

Oligomerization of Unsaturated Compounds in the Presence of Amorphous Mesoporous Aluminosilicates

High activity and selectivity of the samples of ASM amorphous mesoporous aluminosilicates in the synthesis of practically important oligomers of various unsaturated compounds (C5–C16 linear α-olefins, cyclooctene, norbornene, and α-methylstyrene) is found. The oligomerization products obtained in the presence of ASM have a broader molecular weight distribution in comparison with the oligomers synthesized over the H-Beta zeolite. The mesoporous structure of the ASM aluminosilicate provides the preparation of dimers of cyclooctene with high selectivity without cycle opening.

Characterization of the composition and the techno-functional properties of mannoproteins from Saccharomyces cerevisiae yeast cell walls

Broad molecular weight (MW) distribution and variability of mannan to protein ratio of purified mannoproteins (MP), isolated from yeast cell walls upon the enzymatic treatment, revealed their multiplicity. The main fraction of high-MW Agrimos®-MP1 and YCW-b-MP1′ contained mannoproteins with a mannan to protein ratio of 3.5 and 6.9, respectively. Low-MW YCW-b-MP2′ was mainly comprised of mannan, with a ratio of 181, whereas low-MW Agrimos®-MP2 was characterized by a ratio of 12.2. The solubility of MP1/MP2 was higher than that of MP1′/MP2′. Mannoproteins showed similar or lower solubility than mannan, and they exhibited a Newtonian behaviour. Sonication was the appropriate method for the formation of mannoproteins-based emulsions. Contrary to MP1/MP1′-based emulsions, MP2/MP2′-based ones showed higher affinity towards soybean oil than glyceryl-trioleate. pH affected the emulsifying ability of MP1/MP1′. MP1/MP1′ showed similar or slightly inferior emulsifying properties than lecithin. This study is expected to broaden the applications of mannoproteins as value-added ingredients.

Submaxillary Mucin: its Effect on Aroma Release from Acidic Drinks and New Insight into the Effect of Aroma Compounds on its Macromolecular Integrity

Submaxillary mucin is a major component that defines the makeup and functionality of saliva. Understanding its structure and function during food intake is key to designing appropriate strategies for enhancing the delivery of flavour. In the present study, the hydrodynamic integrity of bovine submaxillary mucin was characterised under physiological and acidic conditions and it was shown to have a broad molecular weight distribution with species ranging from 100 kDa to over 2000 kDa, and a random coil type of conformation. A decrease in the pH of mucin appeared to result in aggregation and a broader molecular weight distribution, which was shown to correlate with a release of flavour compounds. Our study also provides indications that p-cresol may have an effect on the macromolecular integrity of mucin.

Reaction: Size Distribution in Olefin Block Copolymers: Not Bad at All

Hongyu Chen completed his PhD in macromolecular science at Case Western Reserve University in 2010. He is a fellow of the Dow Chemical Company, where he focuses on developing new products. He is also a fellow of the American Physical Society and American Chemical Society. Valeriy Ginzburg completed his PhD in polymer physics at the Moscow Institute of Physics and Technology in 1992. He is a senior scientist at the Dow Chemical Company and a fellow of the American Physical Society.

Control of Dynamics in Polyelectrolyte Complexes by Temperature and Salt

The linear viscoelastic responses for a series of polyelectrolyte complexes, PECs, made from pairs of poly[3-(methacryloylamino)propyltrimethylammonium chloride], a polycation, and poly(sodium methacrylate), a polyanion, having various molecular weights were measured. Time–temperature superposition (TTS) for broad and narrow molecular weight distributions revealed entangled behavior at low salt concentration for the longer polyelectrolytes studied. All characteristic lifetimes were slowed by “sticky” dynamics of positive, Pol+ and negative, Pol–, pairing. Time–temperature–salt doping superposition (TTSS) was achieved by considering the dual effects of increasing salt concentration on PECs: the partner lifetimes of Pol+ and Pol– were inversely proportional to [NaCl], as was the population of Pol+Pol– pairs. Relaxation times for polymer partnering, entanglement, and reptation were measured directly on some systems. Whereas the intrinsic (in the absence of salt ions) lifetime for Pol+Pol– pairs was determine...

Chain structure comparison of two low density polyethylene resins fractionated by temperature rising elution fractionation and thermal fractionation

Two low-density polyethylene resins were fractionated into 11 fractions using the temperature rising elution fractionation technique. The resins were of injection molding grade with similar densities but different melt indexes and mechanical properties. High-temperature gel permeation chromatography (HT-GPC), 13C-nuclear magnetic resonance (13C-NMR) spectroscopy, differential scanning calorimetry (DSC), and successive self-nucleation/annealing (SSA) thermal fractionation were employed to characterize the original resins and their fractions. Resin A had a higher molecular weight and broader molecular weight distribution than resin B did. The highest contents were found for the 80 °C and 75 °C fractions of resins A and B, respectively. In addition, the highest molecular weights for resins A and B at 2.14 × 105 and 1.42 × 105 g/mol, respectively, were attained for the fractions eluted at 80 °C. According to the results of 13C-NMR, the total branching contents of resins A and B, including short- and long-chain branching, were 3.63 mol% and 4.89 mol%, respectively. DSC analysis revealed that the crystallinity of fractions 3–10 of resin A was lower than that of resin B. We noted the presence of approximately eight multiple melting peaks in the original sample and fractions from the results of SSA. These peaks indicated the inhomogeneity of the molecular chain. Lw and Ln of resin A were longer than those of resin B. Lastly, the relationship between chain structure and property was also discussed.

Two important factors of selecting lignin as efficient lubricating additives in poly (ethylene glycol): Hydrogen bond and molecular weight

Lignin, one of the most abundant natural polymers, has been successfully used as an effective lubricant additive with high value. The chemical structure of lignin is very diverse and strongly affected by both the source of lignin (i.e. plant species) and the lignin extraction process. In this work, a series of lignin from different biomass sources (hard or soft wood) and extraction process (organosolv with or without acid catalyst) has been successfully incorporated into poly(ethylene glycol) (PEG) and fortified lubricating properties were achieved. The effects of different lignin on the rheological, thermal and tribological properties of the lignin/EG lubricants were systematically investigated by different characterization techniques. Lignin in PEG significantly improves the lubricating property, where a wear reduction of 93.8% was observed. The thermal and lubrication properties of the PEG lubricants filled with different kinds of lignin are tightly related to the synergistic state of hydrogen bonding and molecular weight distribution. Lignin with broader molecular weight distribution and higher hydroxyl content shows better adhesion on metal surfaces and strengthened lubricating film, which could be used as the efficient lubricating additives. This work provides a criterion for selecting appropriate lignin as the efficient lubricant additive and accelerates the application of lignin.

Smectic–Smectic Phase Segregation Occurring in Binary Mixtures of Long and Short Rigid-Rod Helical Polysilanes

Small-angle X-ray scattering and atomic force microscopy were used to observe smectic–smectic phase segregation in binary mixtures of rigid-rod-like helical poly[n-decyl-(S)-2-methylbutylsilane] (PDMS) polymers with molecular-weight ratios of 4.82 and narrow molecular-weight distributions. Phase segregation is attributed to entropic effects as the homopolymers in the binary mixture differ only in molecular weight. Entropy-driven segregation in smectic phases was theoretically predicted in mixtures of rodlike particles with different lengths under high pressure. Binary mixtures of long and short PDMS with broader molecular-weight distributions, which do not form smectic phases, showed no such segregation, verifying that the driving force for segregation is the entropy gained through smectic-phase formation. The binary mixture of a long PDMS with a narrow molecular-weight distribution and a short PDMS with a broad molecular-weight distribution showed segregation of each component, indicating that the entrop...

Towards Unveiling the Exact Molecular Structure of Amorphous Red Phosphorus by Single-Molecule Studies.

Since the discovery of amorphous red phosphorus (a-red P) in 1847, many possible structures have been proposed. However, the exact molecular structure has not yet been determined because of its amorphous nature. Herein several methods are used to investigate basic properties of a-red P. Data from scanning tunneling microscopy (STM) and gel permeation chromatography (GPC) confirm that a-red P is a linear inorganic polymer with a broad molecular weight distribution. The theoretical single-molecule elasticities of the possible a-red P structures are obtained by quantum mechanical (QM) calculations. The experimental single-molecule elasticity of a-red P measured by single-molecule AFM matches with the theoretical result of the zig-zag ladder structure, indicating that a-red P may adopt this structure. Although this conclusion needs further validation, this fundamental study represents progress towards solving the structure of a-red P. It is expected that the strategy utilized in this work can be applied to study other inorganic polymers.

Towards Unveiling the Exact Molecular Structure of Amorphous Red Phosphorus by Single‐Molecule Studies

AbstractSince the discovery of amorphous red phosphorus (a‐red P) in 1847, many possible structures have been proposed. However, the exact molecular structure has not yet been determined because of its amorphous nature. Herein several methods are used to investigate basic properties of a‐red P. Data from scanning tunneling microscopy (STM) and gel permeation chromatography (GPC) confirm that a‐red P is a linear inorganic polymer with a broad molecular weight distribution. The theoretical single‐molecule elasticities of the possible a‐red P structures are obtained by quantum mechanical (QM) calculations. The experimental single‐molecule elasticity of a‐red P measured by single‐molecule AFM matches with the theoretical result of the zig‐zag ladder structure, indicating that a‐red P may adopt this structure. Although this conclusion needs further validation, this fundamental study represents progress towards solving the structure of a‐red P. It is expected that the strategy utilized in this work can be applied to study other inorganic polymers.

Nonlinear rheology of polydisperse blends of entangled linear polymers: Rolie-Double-Poly models

While there has been much success in modeling the linear and nonlinear rheology of monodisperse entangled linear polymers, progress in the constitutive modeling of polymeric materials continues to lag behind the needs of industry. Industrially sourced polymers are typically polydisperse (comprising a broad distribution of molecular weights), making their rheology more suitable for processing but also more difficult to predict. To date, there are no molecular-based constitutive models that are practically suitable for describing industrially relevant polymers in industrially relevant flows. In this article, we extend but strongly simplify the model of Read et al. [J. Rheol. 56, 823–873 (2012)], which is able to predict the linear and nonlinear rheology of bidisperse blends but is prohibitively complex for industrial use. We propose a pair of simplified tube models for polydisperse melts of entangled linear polymers that combine the success of the double reptation approximation [des Cloizeaux, Europhys. Lett. 5, 437–442 (1988)] in the linear regime with the success of the Rolie-Poly constitutive equation [Likhtman et al., J. Non Newtonian Fluid Mech. 114, 1–12 (2003)] in the nonlinear regime. We first review the key concepts of the double reptation approximation and the original (monodisperse) Rolie-Poly constitutive model. Subsequently, we provide the details of our approximate models for the particular case of a bidisperse blend and show that these models naturally identify the effects from couplings between constraint release and chain retraction (i.e., the so-called “enhanced stretch relaxation time”). Finally, we generalize to a multicomponent (polydisperse) model, based on the same underlying principles. Along the way, we also show that both of our models are in qualitative, and largely quantitative, agreement with experimental data for bidisperse and polydisperse melts of entangled linear polymers.

Silicon Photonic Microring Resonator Arrays for Mass Concentration Detection of Polymers in Isocratic Separations.

Molecular weight distribution (MWD) is often the most informative analytical parameter in polymer analysis, with gel permeation chromatography (GPC) being the most common approach for determining the MWD for polymer samples. Many industrially relevant polymers lack chromogenic or fluorogenic signatures, precluding use of spectroscopy-based detection. Universal detectors, such as evaporative light scattering and charged aerosol detectors, are nonlinear, limiting quantitative polymer analysis. Differential refractive index (dRI) detectors show linear mass concentration sensitivity but are limited for some analyses given that they are incompatible with gradient-based separations, have a limited dynamic range, and require extended thermal equilibration times. In this study, we investigated the utility of silicon photonic microring resonator arrays as a quantitative mass concentration detector for industrial polymer analysis. Microring resonators have optical properties that are sensitive to changes in refractive index, offer an extended dynamic range, have a broad solvent compatibility, and have a linear mass concentration detection for a range of molecular weights. Linear mass concentration detection for microrings was demonstrated through a series of isocratic GPC separations using narrow MWD polystyrene (PS) standards. This detection technology was then utilized in conjunction with conventional GPC detectors to analyze a series of broad MWD PS standards, with results in good agreement with dRI and UV/visible. These results demonstrate the potential of the microring resonator platform as a detector for industrial polymer analysis.

A comparative kinetic study of ethylene polymerization mediated by iron, cobalt and chromium catalysts bearing the same N,N,N-bis(imino)trihydroquinoline

The iron(II), cobalt(II) and chromium(III) chlorides, [2-{(2,4,6-Me3C6H2)NCMe}-8-{N(2,4,6-Me3C6H2)}C9H8N]MCln (n = 2, M = Fe LFeCl2, Co LCoCl2; n = 3, M = Cr LCrCl3), each bearing the same N,N,N-bis(imino)trihydroquinoline chelating ligand, have been employed as precatalysts for ethylene polymerization with modified methylaluminoxane (MMAO) as the co-catalyst. The kinetic profiles for these homogeneous polymerizations are reported in addition to the properties of the resultant polymers under comparable reaction conditions. All the experimental data indicate that the active metal center plays a key role on the catalytic performances of the complexes, especially the polymerization activity, thermal stability and lifetime of the active species. Under optimized conditions the iron catalyst displays the highest rate of polymerization but displays this for only a short period, while the chromium catalyst shows a lower maximum polymerization rate but sustains its performance over a longer period and at a higher temperature. In terms of the polymer properties, all three metal catalysts afford highly linear polymers with the metal center influencing the molecular weight and type of end group. Specifically, the cobalt and chromium catalysts produce narrowly dispersed low molecular weight polymers incorporating vinyl end groups, while the iron catalyst affords polymers of higher molecular weight displaying broad molecular weight distributions, with both fully saturated and unsaturated chain ends.

Synthesis of emulsion styrene butadiene rubber by reversible addition–fragmentation chain transfer polymerization and its properties

ABSTRACTEmulsion polymerization is generally used to synthesize styrene butadiene rubber (SBR), and the molecular weight of this rubber can be easily increased. However, the broad molecular weight distribution (MWD) of SBR increases energy loss and adversely affects the dynamic viscoelastic properties. To overcome this disadvantage, reversible addition–fragmentation chain transfer (RAFT) polymerization, which is a type of living polymerization, is applied to emulsion polymerization for preparing RAFT emulsion SBR (ESBR). The molecular weight and microstructure of RAFT ESBR are compared to those of commercially available ESBR 1502 by gel permeation chromatography and proton nuclear magnetic resonance spectroscopy. The aforementioned two polymers are used to prepare unfilled ESBR compounds, which are compared in terms of key physical properties (abrasion resistance, mechanical properties, and dynamic viscoelastic properties). It is confirmed that various physical properties of RAFT ESBR are improved due to its narrow MWD. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47069.

Synthesis of Well-Defined Pyrrolidone-Based Homopolymers and Stimulus-Responsive Diblock Copolymers via RAFT Aqueous Solution Polymerization of 2-(N-Acryloyloxy)ethylpyrrolidone.

Poly(N-vinylpyrrolidone) (PNVP) is a well-known, highly polar, nonionic water-soluble polymer. However, N-vinylpyrrolidone (NVP) usually exhibits strongly non-ideal behavior when copolymerized with methacrylic or styrenic monomers. Moreover, NVP is not particularly well-controlled under living radical polymerization conditions. For these reasons, alternative pyrrolidone-based monomers have been investigated. For example, the reversible addition–fragmentation chain transfer (RAFT) polymerization of 2-(N-methacryloyloxy)ethylpyrrolidone (NMEP) has been recently investigated using various polymerization formulations. However, PNMEP homopolymers are significantly less hydrophilic than PNVP and exhibit inverse temperature solubility in aqueous solution. In the present work, we studied the RAFT aqueous solution polymerization of 2-(N-acryloyloxy)ethylpyrrolidone (NAEP) using either AIBN at 70 °C or a low-temperature redox initiator at 30 °C. PNAEP homopolymers are obtained in high yield (>99%) with good control (Mw/Mn < 1.20) for target degrees of polymerization (DP) of up to 400 using the latter initiator, which produced relatively fast rates of polymerization. However, targeting DPs above 400 led to lower NAEP conversions and broader molecular weight distributions. 2-Hydroxyethyl acrylate (HEA) and oligo(ethylene glycol) methyl ether acrylate (OEGA) were chain-extended using a PNAEPx macro-CTA via RAFT aqueous solution polymerization, yielding double-hydrophilic acrylic diblock copolymers with high conversions (>99%) and good control (Mw/Mn < 1.31). In addition, a PNAEP95 macro-CTA was chain-extended via RAFT aqueous solution polymerization of N-isopropylacrylamide (NIPAM) at 22 °C. Dynamic light scattering (DLS) analysis indicated that heating above the lower critical solution temperature of PNIPAM led to so-called “anomalous micellization” at 35 °C and the formation of near-monodisperse spherical micelles at 40 °C. Finally, 2-(diethylamino)ethyl methacrylate (DEA) was polymerized using an N-morpholine-functionalized trithiocarbonate-based RAFT chain transfer agent and subsequently chain-extended using NAEP to form a novel pH-responsive diblock copolymer. Above the pKa of PDEA (∼7.3), DLS and 1H NMR studies indicated the formation of well-defined PDEA-core spherical micelles.