A density functional theory computational study of the role of ligand on the stability of CuI and CuII species associated with ATRP and SET‐LRP

Atom transfer radical polymerization (ATRP) and single electron‐transfer living radical polymerization (SET‐LRP) both utilize copper complexes of various oxidation states with N‐ligands to perform their respective activation and deactivation steps. Herein, we utilize DFT (B3YLP) methods to determine the preferred ligand‐binding geometries for Cu/N‐ligand complexes related to ATRP and SET‐LRP. We find that those ligands capable of achieving tetrahedral complexes with Cu^I and trigonal bipyramidal with axial halide complexes with [Cu^IIX]⁺ have higher energies of stabilization. We were able to correlate calculated preferential stabilization of [Cu^IIX]⁺ with those ligands that perform best in SET‐LRP. A crude calculation of energy of disproportionation revealed that the same preferential binding of [Cu^IIX]⁺ results in increased propensity for disproportionation. Finally, by examining the relative energies of the basic steps of ATRP and SET‐LRP, we were able to rationalize the transition from the ATRP mechanism to the SET‐LRP mechanism as we transition from typical nonpolar ATRP solvents to polar SET‐LRP solvents. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4950–4964, 2007     

Synthesis of poly(vinyl chloride)‐b‐poly(n‐butyl acrylate)‐b‐poly(vinyl chloride) by the competitive single‐electron‐transfer/degenerative‐chain‐transfer‐mediated living radical polymerization in water

The synthesis of a block copolymer poly(vinyl chloride)‐b‐poly(n‐butyl acrylate)‐b‐poly(vinyl chloride) is reported. This new material was synthesized by single‐electron‐transfer/degenerative‐chain‐transfer‐mediated living radical polymerization (SET‐DTLRP) in two steps. First, a bifunctional macroinitiator of α,ω‐di(iodo)poly (butyl acrylate) [α,ω‐di(iodo)PBA] was synthesized by SET‐DTLRP in water at 25 °C. The macroinitiator was further reinitiated by SET‐DTLRP, leading to the formation of the desired product. This ABA block copolymer was synthesized with high initiator efficiency. The kinetics of the copolymerization reaction was studied for two PBA macroinitiators with number–average molecular weight of 10 k and 20 k. The relationship between the conversion and the number–average molecular weight was found to be linear. The dynamic mechanical thermal analysis suggests just one phase, indicating that copolymer behaves as a single material with no phase separation. This methodology provides the access to several block copolymers and other complex architectures that result from combinations of thermoplastics (PVC) and elastomers (PBA). From industrial standpoint, this process is attractive, because of easy experimental setup and the environmental friendly reaction medium. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3001–3008, 2006     

Single electron transfer–degenerative chain transfer living radical polymerization of N‐butyl acrylate catalyzed by Na2S2O4 in water media

Living radical polymerization of n‐butyl acrylate was achieved by single electron transfer/degenerative‐chain transfer mediated living radical polymerization in water catalyzed by sodium dithionate. The plots of number–average molecular weight versus conversion and ln[M]₀/[M] versus time are linear, indicating a controlled polymerization. This methodology leads to the preparation of α,ω‐di(iodo) poly (butyl acrylate) (α,ω‐di(iodo)PBA) macroinitiators. The influence of polymerization degree ([monomer]/[initiator]), amount of catalyst, concentration of suspending agents and temperature were studied. The molecular weight distributions were determined using a combination of three detectors (TriSEC): right‐angle light scattering (RALLS), a differential viscometer (DV), and refractive index (RI). The methodology studied in this work represents a possible route to prepare well‐tailored macromolecules made of butyl acrylate in an environmental friendly reaction medium. Moreover, such materials can be subsequently functionalized leading to the formation of different block copolymers of composition ABA. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2809–2825, 2006     

Intramolecular charge transfer complexes. 16. Copolymers of N,N-dimethyl-p-aminobenzyl methacrylate with acryloyl- and methacryloyl-β-hydroxyethyl-3,5-dinitrobenzoate

A new electronodonor monomer, N,N-dimethyl-p-aminobenzyl methacrylate (DMABM), was synthesized and radical copolymerized with two electronoacceptor monomers, acryloyl- (DNBA) and methacryloyl-(DNBM) β-hydroxyethyl-3,5-dinitrobenzoate, in order to obtain intramolecular charge-transfer-complex copolymers. Also, the small-molecular models of poly(DMABM), poly(DNBA), and poly(DNBM), the respective acetates, were synthesized and used to measure the values of ionization potential I_p of the donor and the electronic affinity E_a of the acceptor. They are I_p = 7.15 eV and E_a = 1.41 eV. The lower value of I_p as compared with that of carbazole derivatives is taken as evidence of a nonterminal mechanism of copolymerization. Also, from the ¹H-NMR and electronic spectra, the intramolecular complexation is discussed in terms of total transfer of the electron from donor to acceptor structural units.     

Phase transfer catalyzed polymerization of 4-bromo-2,6-dimethylphenol in the presence of either 2,4,6-trimethylphenol or 4-tert-butyl-2,6-dimethylphenol

The synthesis of poly(2,6-dimethyl-1,4-phenylene oxide) with one 2,6-dimethylphenol chain end (PPO–OH) and with well-defined molecular weight by phase transfer catalyzed polymerization of 4-bromo-2,6-dimethylphenol ( 20 ) in the presence of either 2,4,6-trimethylphenol ( 1 ) or 4-t-butyl-2,6-dimethylphenol ( 1 ′) as chain initiators is described. The range of controllable molecular weights and the mechanism of molecular weight control are discussed based on the differences between the reactivities of 20 , 1 , and 1 ′ and of the corresponding reactive species. The PPO–OH synthesized from 20 / 1 ′ has structural units derived from 1 ′ attached only at the chain end. PPO–OH synthesized from 20 / 1 contains structural units derived from 1 both internally and at the chain ends. Structural units derived from side reactions were identified by ¹H-NMR spectroscopy. A reaction mechanism is proposed to account for their formation.     

Living polymerization of aryl substituted acetylenes by MoCl5 and WCl6 based initiators: The ortho phenyl substituent effect

The polymerization of phenylacetylene initiated by MoCl₅ and WCl₆ based initiators was monitored directly in the NMR sample tube and demonstrated the presence of backbiting and intramolecular cyclization reactions. It was shown that the ratio of cis to trans structural units obtained by isomerization prior to double bond formation dictates the degree of backbiting and intramolecular cyclization reactions. This cis–trans ratio determines the length of cis–transoidal sequences present in the polymer backbone which are available for both backbiting and intrachain cyclization reactions. The cyclic trimers obtained in the metathesis polymerization of phenylacetylene are formed only through the cis–cisoidal-induced backbiting and/or intramolecular reactions. The o-trimethylsilylphenylacetylene follows a living mechanism of polymerization. This is due to the fact that the size of the ortho substituent suppresses the cis–transoidal to cis–cisoidal isomerization reactions and therefore eliminates the backbiting reactions. The steric hindrance provided by the size of the ortho substituent also eliminates interchain and intrachain reactions.     

Synthesis and anticonvulsant activity of 3H-imidazo[4,5-c]-pyridazine, 1H-imidazo[4,5-d]pyridazine and 1H-benzimidazole analogues of 9-(2-fluorobenzyl)-6-methylamino-9H-purine

The 3H-imidazo[4,5-c]pyridazine, 1H-imidazo[4,5-d]pyridazine, and 1H-benzimidazole analogues of the potent anticonvulsant purine 9-(2-fluorobenzyl)-6-methylamino-9H-purine (1, 78U79) were synthesized and tested for anticonvulsant activity. The 3H-imidazo[4,5-c]pyridazines 8 and 9 were prepared in five stages from 3,4,5-trichloropyridazine (2) . The 1H-imidazolo[4,5-d]pyridazine 15 was synthesized in four stages from 5-[(benzyloxy)methyl]-1,5-dihydro-4H-imidazo[4,5-d] pyridazin-4-one (10a) . The benz-imidazole analogues 18 and 20 were prepared from 2,6-dinitroaniline in three stages. These compounds were one-tenth or less as active as 1 in protecting rats against maximal electroshock-induced seizures.     

Etude sur le comportement thermique de quelques polymeres ignifugeants contenant du phosphore et des halogenes

The thermal behaviour a series of polyphosphonates was studied by thermogravimetry (TG) and differential thermal analysis (DTA). The obtained data permitted the calculation of activation energies and reaction orders on decomposition zones by the Coats — Redfern method.     

Single‐electron‐transfer/degenerative‐chain‐transfer mediated living radical polymerization of vinyl chloride catalyzed by thiourea dioxide/octyl viologen in water/tetrahydrofuran at 25 °C

The single‐electron‐transfer/degenerative‐chain‐transfer mediated living radical polymerization (SET–DTLRP) of vinyl chloride (VC) in H₂O/tetrahydrofuran at 25 °C catalyzed by thiourea dioxide [(NH₂)₂C?SO₂] is reported. This polymerization occurs only in the presence of a basic sodium bicarbonate (NaHCO₃) buffer and the electron‐transfer cocatalyst octyl viologen. The resulting poly(vinyl chloride) (PVC) has a number‐average molecular weight of 1500–7000 and a weight‐average molecular weight/number‐average molecular weight ratio of 1.5. This PVC does not contain detectable amounts of structural defects and has both active chloroiodomethyl and inactive chloromethyl chain ends. Because of possible side reactions caused by the primary sulfoxylate anion (SO), the catalytic activity of (NH₂)₂C?SO₂ in the SET–DTLRP of VC is lower than that of the single‐electron‐transfer agent sodium dithionite. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 287–295, 2005     

Synthesis and characterization of liquid crystalline polymethacrylates,polyacrylates, and polysiloxanes containing 4-methoxy-4′-hydroxy-α-methylstilbene-based mesogenic groups

The synthesis and characterization of polymethacrylates and polyacrylates containing 4-methoxy-4′-hydroxy-α-methylstilbene side groups attached either directly or through flexible spacers containing eleven, eight, six, three, and respectively two methylenic units, and of the polysiloxanes containing the same mesogenic group connected through flexible spacers containing eleven, eight, six, and respectively three methylenic units are described. All polymers exhibit thermotropic liquid crystallinity. The nature of the mesophase is determined by the spacer length. However, the nature of the polymer backbone determines the thermal stability of the mesophase. That is, for the same spacer length and similar polymer molecular weight, the most flexible polymer backbone leads to the highest isotropization temperature.