Kinetic Modeling of Surface-Initiated Photoiniferter-Mediated Photopolymerization in Presence of Tetraethylthiuram Disulfide

A rate equation-based kinetic model is developed to investigate the effect of important reaction parameters on surface-initiated photoiniferter-mediated photopolymerization (SI-PMP) of methyl methacrylate. In particular, the effect of incident light intensity and concentration of added deactivating species, tetraethylthiuram disulfide (TED), on the growth kinetics of surface-tethered poly(methyl methacrylate) (PMMA) layers was studied in detail. In accord with experimental results, model predictions suggest that maximum rates of PMMA layer growth observed during initial stages of SI-PMP increase as TED concentration ([TED]) is decreased and as light intensity is increased. Conversely, the maximum thickness of the PMMA layers, which is defined as the thickness at which 99% of the surface-tethered polymer chains are irreversibly terminated, increases as [TED] increases and as light intensity decreases. As light intensity and added deactivator affect the number of propagating surface-tethered radicals, findings from this study delineate strategies for optimizing the formation of surface-tethered PMMA brushes by SI-PMP and creating block copolymer brushes

Solution Behavior of Polystyrene−Polyisoprene Miktoarm Block Copolymers in a Selective Solvent for Polyisoprene

The dynamics and self-assembly of polystyrene− (PS−) polyisoprene (PI) miktoarm (mixed-arm) block copolymers in n-hexane, a selective solvent for PI, are investigated. The miktoarms present a branched arrangement in the soluble block in the fashion of PI−(PI)2, where two PI blocks are connected by a common end point to a linear PS−PI diblock. It is found that these copolymers self-assemble into spherical micelles having cores composed of the insoluble PS blocks and coronas of the well-solvated PI−(PI)2 blocks. Micelles formed from the branched polymer amphiphiles are more compact, having smaller sizes than the micelles formed from a linear PS−PI diblock copolymer of similar molecular weight and composition. As the concentration is decreased, the micelles with large aggregation numbers remain stable, only showing changes in the aggregation number. The hydrodynamic sizes and aggregation numbers determined from the micelles formed from miktoarm copolymers differ from theoretical predictions for spherical micelles made of the equivalent linear amphiphilic diblock copolymers. These differences may arise from the arrangements of the branched blocks inside the micellar corona

Highly Tailorable Materials based on 2-Vinyl-4,4-dimethyl Azlactone: (Co)Polymerization, Synthetic Manipulation and Characterization

Through rigorous spectroscopic characterizations, including in situ, real-time monitoring, and size-exclusion chromatography (SEC) we describe the functionalization of polymers and copolymers based on vinyl dimethyl azlactone (VDMA), as well as modification of the VDMA monomer using efficient ring-opening strategies. Specifically, we demonstrate modification of VDMA-based materials by “pegylation”, base-catalyzed ring-opening hydrolysis, and nucleophilic addition of short alkyl chains, fluorescent markers, and motifs used to specifically bind proteins. All of these functionalizations take advantage of the susceptibility of the pendant azlactone ring of VDMA to undergo nucleophilic attack. Polymers as well as copolymers incorporating vinyl pyrrolidone were synthesized by conventional free radical polymerization and thoroughly characterized by FTIR, 1H NMR, 13C NMR, SEC, thermogravimetric analysis and differential scanning calorimetry prior to modification. The variety of conjugations and ease of transformations enabled by use of the reactive yet hydrolytically stable VDMA-based materials inspires a broad range of applications for these soft materials

Role of Surface Reorganization on Preferential Adsorption of Macromolecular Ensembles at the Solid/Fluid Interface

The adsorption of micelles made from precisely synthesized branched block copolymers is investigated and analyzed using a model framework that incorporates the effects of mass transport and dynamic relaxation/reorganization events occurring at the solid/fluid interface. Both processes are required to represent adequately the adsorption profile over the entire progression to pseudoequilibrium. Insight into the relative importance of the two processes, the terminus of the diffusion-dominated regime, and differences between diffusion in free solution and in confinement is also provided. The results demonstrate commonality between adsorption of micelle-forming surfactant-like copolymers and biomimetic vesicles formed by small-molecule surfactants, both of which are systems dominated by rearrangements on the surface

In Situ Formation of Pyridyl-Functionalized Poly(3-hexylthiophene)s via Quenching of the Grignard Metathesis Polymerization: Toward Ligands for Semiconductor Quantum Dots

The synthesis of well-defined, end-functional poly­(3-hexylthiophene)­s (P3HTs) by in situ quenching of the Grignard metathesis (GRIM) polymerization is complicated by the extreme tendency to favor difunctional products in all but a few cases. A facile one-pot method for preparing 2-pyridyl and 3-pyridyl P3HTs with high abundance of monofunctional products is established via an examination of the kinetics of the end-functionalization quenching reaction with lithium chloride complexes of 2- and 3-pyridyl Grignard reagents. Density functional theory calculations guide the selection of pyridine as the end group, which provides the capacity to ligate cadmium selenide (CdSe) nanocrystals and arrests aggregation upon thermal annealing when dispersed in a P3HT matrix. The relative abundances of various end-functional products, as ascertained by high-resolution matrix assisted laser desorption ionization time-of-flight mass spectrometry, can be altered through the use of 1-pentene as an additive: GRIM polymerizations quenched with 3-pyridyl and 2-pyridyl Grignard reagents show 5% and 18% abundances of difunctional, pyridyl-capped P3HTs, respectively, when 1-pentene is present at 1000:1 relative to the nickel catalyst. This represents a significant improvement compared to quenching with aryl Grignard reagents, where difunctional products predominate. The ability to manipulate end group compositions coupled with the propensity of pyridyl-functionalized P3HTs to ligate semiconductor quantum dots (SQDs) opens new possibilities for tuning the morphology of conjugated polymer/SQD blends

Synthesis and Characterization of an ABC Miktoarm Star Terpolymer of Cyclohexadiene, Styrene, and 2-Vinylpyridine

Synthesis and Characterization of an ABC Miktoarm Star Terpolymer of Cyclohexadiene, Styrene, and 2-Vinylpyridin

DataSheet1_Architecture- and Composition-Controlled Self-Assembly of Block Copolymers and Binary Mixtures With Crosslinkable Components: Chain Exchange Between Block Copolymer Nanoparticles.pdf

Chain exchange behaviors in self-assembled block copolymer (BCP) nanoparticles (NPs) at room temperature are investigated through observations of structural differences between parent and binary systems of BCP NPs with and without crosslinked domains. Pairs of linear diblock or triblock, and branched star-like polystyrene-poly(2-vinylpyridine) (PS-PVP) copolymers that self-assemble in a PVP-selective mixed solvent into BCP NPs with definite differences in size and self-assembled morphology are combined by diverse mixing protocols and at different crosslinking densities to reveal the impact of chain exchange between BCP NPs. Clear structural evolution is observed by dynamic light scattering and AFM and TEM imaging, especially in a blend of triblock + star copolymer BCP NPs. The changes are ascribed to the chain motion inherent in the dynamic equilibrium, which drives the system to a new structure, even at room temperature. Chemical crosslinking of PVP corona blocks suppresses chain exchange between the BCP NPs and freezes the nanostructures at a copolymer crosslinking density (CLD) of ∼9%. This investigation of chain exchange behaviors in BCP NPs having architectural and compositional complexity and the ability to moderate chain motion through tailoring the CLD is expected to be valuable for understanding the dynamic nature of BCP self-assemblies and diversifying the self-assembled structures adopted by these systems. These efforts may guide the rational construction of novel polymer NPs for potential use, for example, as drug delivery platforms and nanoreactors.</p

Structure-Property Relations of Triblock Copolymer Thermoplastics with Interaction-Tuned Polymer Additives

Block copolymer (BCP) thermoplastics are used in a wide range of commercial products. It is well known that the mechanical performance of these materials depends on the BCP architecture and composition, and the introduction of non-covalent interactions via comonomers can be used to tune key properties. However, tailoring the mechanics of BCPs by blending with polymeric additives is rarely explored, as most BCP/polymer blends have limited miscibility. Here, we examine the structure, mechanics, and thermal stability of a commodity thermoplastic, poly(styrene-b-ethylene-co-butylene-b-styrene) (SEBS), with polymeric additives of either polystyrene (PS) or poly(methyl methacrylate-co-cyclohexyl methacrylate) (PrC, 70 mol % cyclohexyl methacrylate). PS and PrC are athermal and enthalpically compatible additives, respectively, for the PS end-blocks in SEBS. The SEBS/PS blends have a narrow miscibility window with respect to PS molecular weight and loading, where either an ordered lamellar morphology or a disordered morphology is observed. In contrast, the attractive interaction between PrC and PS end-blocks leads to complete miscibility of SEBS/PrC blends across the full range of PrC molecular weights (up to 63.8 kg/mol) and loadings (up to 40 vol %) that were studied, where an ordered lamellar morphology with continuity in the rubber phase was generally observed. Consequently, the PrC additives can increase the modulus and yield stress, as well as delay the onset of strain hardening, without loss of toughness. Additionally, PrC additives can elevate the glass transition temperature of the PS blocks and maintain a high modulus at elevated operating temperatures, expanding the service window for SEBS. The principles established in this research could be translated to other types of styrenic BCP thermoplastics

Versatile Synthesis of Amine-Reactive Microgels by Self-Assembly of Azlactone-Containing Block Copolymers

Relations between molecular design, chemical functionality, and stimulus-triggered response are important for a variety of applications of polymeric systems. Here, reactive amphiphilic block copolymers (BCPs) of poly­(2-vinylpyridine)-<i>block</i>-poly­(2-vinyl-4,4-dimethyl­azlactone) (PVP-<i>b</i>-PVDMA) were synthesized and assembled into microgels capable of incorporating functional amines. The composition of the PVP-<i>b</i>-PVDMA BCPs was varied to control the number of reactive sites in the spherical aggregates created by self-assembly of PVP-<i>b</i>-PVDMA BCPs in a 2-propanol/THF (v:v = 19:1) solvent mixture, which is selective for PVP. PVDMA and PVP segments were selectively cross-linked by 1,4-diaminobutane (DAB) or 1,4-diiodobutane (DIB) to fabricate core- and corona-cross-linked azlactone-containing microgels, respectively. Non-cross-linked aggregates of PVP-<i>b</i>-PVDMA and DIB-cross-linked microgels dissociate when exposed to THF, which is a good solvent for both blocks. However, the DAB-cross-linked BCP microgels swell in THF, suggesting the formation of a stable, three-dimensional network structure. Because of their ability to be reactively modified in ways that allows their stability or disassembly characteristics to be tailored, these azlactone-containing BCP microgels provide an attractive platform for applications in a wide range of fields, including catalysis, imaging, molecule separation, and guest loading for targeted delivery

Immobilization of Biomolecules on Poly(vinyldimethylazlactone)-Containing Surface Scaffolds

We describe the successful development of a procedure for the step-by-step formation of a reactive, multilayer polymer scaffold incorporating polymers based on 2-vinyl-4,4-dimethylazlactone (VDMA) on a silicon wafer and the characterization of these materials. Also discussed is the development of a procedure for the nonsite specific attachment of a biomolecule to a modified silicon wafer, including scaffolds modified via drop-on-demand (DOD) inkjet printing. VDMA-based polymers were used because of their hydrolytic stability and ability of the pendant azlactone rings to form stable covalent bonds with primary amines without byproducts via nucleophilic addition. This reaction proceeds without a catalyst and at room temperature, yielding a stable amide linkage, which adds to the ease of construction expected when using VDMA-based polymers. DOD inkjet printing was explored as an interesting method for creating surfaces with one or more patterns of biomolecules because of the flexibility and ease of pattern design