Rapid synthesis of functional poly(ester amide)s through thiol-ene chemistry

Poly(ester amide)s (PEAs) bearing various side chains were synthesized by post-polymerization modification of PA-1, a vinylidene containing PEA. The thiols 1-dodecanethiol (1A-SH), 2-phenylethanethiol (1B-SH), 2-mercaptoethanol (1C-SH), thioglycolic acid (1D-SH), furfuryl mercaptan (1E-SH) and sodium-2-mercaptoethanesulfonate (1F-SH) were reacted with PA-1 to form PEAs PA-1A through PA-1F respectively. PEAs containing non-polar thiol side chains (PA-1A, PA-1B, PA-1E), showed little change in solubility compared to PA-1, while PEAs with more polar side chains improved solubility in more polar solvents. PA-1F, functionalized with sodium-2-mercaptoethanesulfonate, became water-soluble. The introduction of pendant functional groups impacted the thermal behaviors of PEAs in a wide range. The PEAs were thermally stable up to 368 °C, with glass transition temperatures (T_g) measured between 117 to 152 °C. Moreover, to demonstrate the versatility of the PEAs, thermal reprocessable networks and polyurethanes were successfully fabricated by reacting with a bismaleimide (1,6-bis(maleimido)hexane, 1,6-BMH) and a diisocyanate (4,4'-diphenylmethane diisocyanate, 4,4'-MDI), respectively. This study paves the way for the facile synthesis of functional poly(ester amide)s with great potential in many fields.

Composite Corelated Molecular Orbital Theory Calculations of Ring Strain for Use in Predicting Polymerization Reactions

Strained ring systems play an important role in synthesis and can be characterized by the ring strain energy (RSE). The RSE of 3, 4, 5, and 6 membered saturated and unsaturated ring systems containing N, O, P, and S heteroatoms and H, F, Si(CH 3 ) 3 , and SO 2 (CH 3 ) substituents were calculated at the G3(MP2) composite correlated molecular orbital theory level using up to 5 models to predict the RSE. Generally, the RSE decreased as ring size increased with a substantial decrease from 4 to 5 membered rings. Replacement of a ring CH 2 with P or S reduced the RSE, consistent with less angle strain. The RSE for unsaturated systems were generally greater than for saturated systems due to increased angle strain. No general trends were found with respect to substituent effects. The RSE values suggest that 3-pyrroline and 2-pyrroline may be able to support ring opening metathesis polymerization and warrant further study.

In-Depth Analysis of the Effect of Fragmentation on the Crystallization-Driven Self-Assembly Growth Kinetics of 1D Micelles Studied by Seed Trapping

Studying the growth of 1D structures formed by the self-assembly of crystalline-coil block copolymers in solution at elevated temperatures is a challenging task. Like most 1D fibril structures, they fragment and dissolve when the solution is heated, creating a mixture of surviving crystallites and free polymer chains. However, unlike protein fibrils, no new nuclei are formed upon cooling and only the surviving crystallites regrow. Here, we report how trapping these crystallites at elevated temperatures allowed us to study their growth kinetics at different annealing times and for different amounts of unimer added. We developed a model describing the growth kinetics of these crystallites that accounts for fragmentation accompanying the 1D growth process. We show that the growth kinetics follow a stretched exponential law that may be due to polymer fractionation. In addition, by evaluating the micelle growth rate as a function of the concentration of unimer present in solution, we could conclude that the micelle growth occurred in the mononucleation regime.

Activated Monomer Polymerization of an N-Sulfonylazetidine

Previously, N-(methanesulfonyl)azetidine (MsAzet) was found to polymerize anionically via ring-opening at temperatures >100 °C to form p(MsAzet) in the presence of an anionic initiator. In the current report, potassium(azetidin-1-ylsulfonyl) methanide (KMsAzet), formed from deprotonation of the methanesulfonyl group of MsAzet by KHMDS, is shown to undergo spontaneous AROP at room temperature to form p(N-K-MsAzet). The structure of p(N-K-MsAzet) differs from that of p(MsAzet), as the sulfonyl groups are incorporated into the polymer backbone of p(N-K-MsAzet). Reaction of p(N-K-MsAzet) with MeOH produces p(N-H-MsAzet), a semicrystalline polymer with a structure like that of polyamides, but with sulfonylamides in place of the carboxamides found in polyamides. Reaction of p(N-K-MsAzet) with benzyl bromide results in the formation of amorphous p(N-Bn-MsAzet). P(N-K-MsAzet) is hypothesized to form via an activated monomer anionic polymerization; this is supported by polymerization kinetic data and structural characterization of the resulting polymers.

Aziridines and azetidines: building blocks for polyamines by anionic and cationic ring-opening polymerization

The synthesis of aziridine and azetidine monomers and their ring-opening polymerization via different mechanisms is reviewed.

Anionic Ring-Opening Polymerization of N-(tolylsulfonyl)azetidines To Produce Linear Poly(trimethylenimine) and Closed-System Block Copolymers

The anionic ring-opening copolymerization of N-( p-tolylsulfonyl)azetidine ( pTsAzet) and N-( o-tolylsulfonyl)azetidine ( oTsAzet) produces poly( pTsAzet- co- oTsAzet) as a statistical copolymer. The pTsAzet/ oTsAzet copolymerization is living and allows for the synthesis of poly(sulfonylazetidine) of target molecular weights with narrow dispersities. ¹H NMR spectroscopy was used to monitor the kinetics of the polymerization and estimate the monomer reactivity ratios. It was found that the reactivity ratios for oTsAzet and pTsAzet at 180 °C are 1.66 and 0.60, respectively. The tosyl groups of p( pTsAzet- co- oTsAzet) were reductively removed to produce linear poly(trimethylenimine) (LPTMI). This represents the first route to LPTMI of controlled molecular weight and low dispersity. Finally, the slow kinetics of the sulfonylazetidine polymerization facilitated the synthesis of a block copolymer without requiring the sequential addition of monomer. Specifically, pTsAzet, oTsAzet, and ( N- p-toluenesulfonyl-2-methylaziridine) ( pTsMAz) were combined in solution. pTsMAz selectively polymerizes to form the first block at moderate temperature. After consumption of pTsMAz, the temperature was increased to copolymerize pTsAzet and oTsAzet and produce the block copolymer p( pTsMAz)- b-p( pTsAzet- co- oTsAzet).

The anionic ring-opening polymerization ofN-(methanesulfonyl)azetidine

The first anionic ring-opening polymerization of an activated azetidine is reported.

Living Anionic Copolymerization of 1-(Alkylsulfonyl)aziridines to Form Poly(sulfonylaziridine) and Linear Poly(ethylenimine)

The anionic ring-opening copolymerization of 1-(methylsulfonyl)aziridine (MsAz) and 1-(sec-butylsulfonyl)aziridine (^sBsAz) produces a soluble random copolymer P(MsAz-r-^sBsAz), which can subsequently be converted to linear poly(ethylenimine) (lPEI). The copolymerization of MsAz and ^sBsAz is living and allows for the synthesis of copolymers with low molecular weight distributions. Sequential anionic polymerization of MsAz and ^sBsAz with 2-methyl-1-(methylsulfonyl)aziridine (MsMAz) creates P(MsAz-r-^sBsAz)-b-P(MeMsAz). Removal of the sulfonyl groups from P(MsAz-r-^sBsAz)-b-P(MsMAz) gives lPEI-b-poly(propylenimine). For the first time, lPEI can be synthesized by a controlled anionic polymerization.

Chemical Methods for the Separation of Copper Oxide Nanoparticles From Colloidal Suspension in Dodecane

Several chemical methods for the separation of nanoparticles from a colloidal mixture in a phase change material (PCM) have been developed and systematically investigated. The phase changing property of the colloidal mixture is used in energy storage applications and the mixture is labeled as the nanostructure enhanced phase change materials (NEPCM). The objective is to investigate viable methods for the separation and reclamation of the nanoparticles from the NEPCM before its disposal after its useful life. The goal is to find, design, test, and evaluate separation methods which are simple, safe, effective, and economical. The specific NEPCM considered in this study is a colloidal mixture of dodecane (C12H26) and CuO nanoparticles of 1–5% mass fraction and 5–15 nm size distribution. The nanoparticles are coated with a surfactant to maintain colloidal stability. Various methods for separating the nanoparticles from the NEPCM are explored. The identified methods are: (i) chemical destabilization of nanoparticle surfactants to facilitate gravitational precipitation, (ii) silica column chromatography, and (iii) adsorption on silica particle surface. These different methods have been pursued, tested, and analyzed; and the results are presented in this article. These methods are found to be highly efficient, simple, safe, and economical.

Dimensional control of block copolymer nanofibers with a π-conjugated core: crystallization-driven solution self-assembly of amphiphilic poly(3-hexylthiophene)-b-poly(2-vinylpyridine)

With the aim of accessing colloidally stable, fiberlike, π-conjugated nanostructures of controlled length, we have studied the solution self-assembly of two asymmetric crystalline-coil, regioregular poly(3-hexylthiophene)-b-poly(2-vinylpyridine) (P3HT-b-P2VP) diblock copolymers, P3HT23-b-P2VP115 (block ratio=1:5) and P3HT44-b-P2VP115 (block ratio=ca. 1:3). The self-assembly studies were performed under a variety of solvent conditions that were selective for the P2VP block. The block copolymers were prepared by using Cu-catalyzed azide-alkyne cycloaddition reactions of azide-terminated P2VP and alkyne end-functionalized P3HT homopolymers. When the block copolymers were self-assembled in a solution of a 50% (v/v) mixture of THF (a good solvent for both blocks) and an alcohol (a selective solvent for the P2VP block) by means of the slow evaporation of the common solvent; fiberlike micelles with a P3HT core and a P2VP corona were observed by transmission electron microscopy (TEM). The average lengths of the micelles were found to increase as the length of the hydrocarbon chain increased in the P2VP-selective alcoholic solvent (MeOH<iPrOH<nBuOH). Very long (>3 μm) fiberlike micelles were prepared by the dialysis of solutions of the block copolymers in THF against iPrOH. Furthermore the widths of the fibers were dependent on the degree of polymerization of the chain-extended P3HT blocks. The crystallinity and π-conjugated nature of the P3HT core in the fiberlike micelles was confirmed by a combination of UV/Vis spectroscopy, photoluminescence (PL) measurements, and wide-angle X-ray scattering (WAXS). Intense sonication (iPrOH, 1 h, 0 °C) of the fiberlike micelles formed by P3HT23-b-P2VP115 resulted in small (ca. 25 nm long) stublike fragments that were subsequently used as initiators in seeded growth experiments. Addition of P3HT23-b-P2VP115 unimers to the seeds allowed the preparation of fiberlike micelles with narrow length distributions (L(w)/L(n) < 1.11) and lengths from about 100-300 nm, that were dependent on the unimer-to-seed micelle ratio.

Self-seeding in one dimension: a route to uniform fiber-like nanostructures from block copolymers with a crystallizable core-forming block

One-dimensional micelles formed by the self-assembly of crystalline-coil poly(ferrocenyldimethylsilane) (PFS) block copolymers exhibit self-seeding behavior when solutions of short micelle fragments are heated above a certain temperature and then cooled back to room temperature. In this process, a fraction of the fragments (the least crystalline fragments) dissolves at elevated temperature, but the dissolved polymer crystallizes onto the ends of the remaining seed fragments upon cooling. This process yields longer nanostructures (up to 1 μm) with uniform width (ca. 15 nm) and a narrow length distribution. In this paper, we describe a systematic investigation of factors that affect the self-seeding behavior of PFS block copolymer micelle fragments. For PI(1000)-PFS(50) (the subscripts refer to the number average degree of polymerization) in decane, these factors include the presence of a good solvent (THF) for PFS and the effect of annealing the fragments prior to the self-seeding experiments. THF promoted the dissolution of the micelle fragments, while preannealing improved their stability. We also extended our experiments to other PFS block copolymers with different corona-forming blocks. These included PI(637)-PFS(53) in decane, PFS(60)-PDMS(660) in decane (PDMS = polydimethylsiloxane), and PFS(30)-P2VP(300) in 2-propanol (P2VP = poly(2-vinylpyridine)). The most remarkable result of these experiments is our finding that the corona-forming chain plays an important role in affecting how the PFS chains crystallize in the core of the micelles and, subsequently, the range of temperatures over which the micelle fragments dissolve. Our results also show that self-seeding is a versatile approach to generate uniform PFS fiber-like nanostructures, and in principle, the method should be extendable to a wide variety of crystalline-coil block copolymers.

Reversible cross-linking of polyisoprene coronas in micelles, block comicelles, and hierarchical micelle architectures using Pt(0)-olefin coordination

Previous work has established that polyisoprene (PI) coronas in cylindrical block copolymer micelles with a poly(ferrocenyldimethylsilane) (PFS) core can be irreversibly cross-linked by hydrosilylation using (HSiMe(2))(2)O in the presence of Karstedt's catalyst. We now show that treatment of cylindrical PI-b-PFS micelles with Karstedt's catalyst alone, in the absence of any silanes, leads to PI coronal cross-linking through Pt(0)-olefin coordination. The cross-linking can be reversed through the addition of 2-bis(diphenylphosphino)ethane (dppe), a strong bidentate ligand, which removes the platinum from the PI to form Pt(dppe)(2). The Pt(0) cross-linking of PI was studied with self-assembled cylindrical PI-b-PFS block copolymer micelles, where the cross-linking was found to dramatically increase the stability of the micellar structures. The Pt(0)-alkene coordination-induced cross-linking can be used to provide transmission electron microscopy contrast between PI and poly(dimethylsiloxane) (PDMS) corona domains in block comicelles as the process selectively increases the electron density of the PI regions. Moreover, following the assembly of a hierarchical scarf-shaped comicelle consisting of a PFS-b-PDMS platelet template with PI-b-PFS tassels, Pt(0)-induced cross-linking of the PI coronal regions allowed for the selective removal of the PFS-b-PDMS center, leaving behind an unprecedented hollowed-out scarf structure. The addition of Karstedt's catalyst to PI or polybutadiene homopolymer toluene/xylene solutions resulted in the formation of polymer gels which underwent de-gelation upon the addition of dppe.

The reactivity of an anionic gallium N-heterocyclic carbene analogue with a solution stable digermene

The reaction of the anionic gallium(I) N-heterocyclic carbene (NHC) analogue 3 with the solution stable digermene 5 results in the formation of the gallium NHC – germylene complex 8. The gallium NHC – germylene complex 8 was derivatized with CH3I and (CH3)3SiCl.Key words: digermene, carbene analogue, germylene, gallium(I).