Atom Transfer Radical Self-condensing Vinyl Research Articles

Effect of branching architecture on glass transition behavior of hyperbranched copolystyrenes: the experiment and simulation studies

By controlling the feed ratio of CMS/styrene and the polymerization time, a series of hyperbranched copolystyrenes (HBCPS) were synthesized with comparable weight-averaged molecular weights (M w) but different degree of branching (DB) through atom transfer radical self-condensing vinyl copolymerization (ATR-SCVCP) with CuBr/2,2′-bipyridyl as the catalyst. The resulting HBCPS samples were used to investigate the effect of branching architecture on their glass transition behavior. With the DB increased, the glass transition temperatures (T g) of HBCPS samples measured by DMA and DSC both decreased. Their spin-lattice relaxation times (1H T 1r) of protons displayed the same downtrend with increasing DB. Besides, a correlation between the T gs and the DB was well established by all-atom molecular dynamics (MD) simulations. The values of MD-determined T gs are little higher than the corresponding experimental ones. However, the dependence of T gs on DB is in good agreement with the experimental results, i.e., T g decreases both in experiments and simulations with increasing DB.

Tuning the Solubility of Copper Complex in Atom Transfer Radical Self-Condensing Vinyl Polymerizations to Control Polymer Topology via One-Pot to the Synthesis of Hyperbranched Core Star Polymers

In this paper, we propose a simple one-pot methodology for proceeding from atom transfer reaction-induced conventional free radical polymerization (AT-FRP) to atom transfer self-condensing vinyl polymerization (AT-SCVP) through manipulation of the catalyst phase homogeneity (i.e., CuBr/2,2'-bipyridine (CuBr/Bpy)) in a mixture of styrene (St), 4-vinyl benzyl chloride (VBC), and ethyl 2-bromoisobutyrate. Tests of the solubilities of CuBr/Bpy and CuBr2/Bpy under various conditions revealed that both temperature and solvent polarity were factors affecting the solubility of these copper complexes. Accordingly, we obtained different polymer topologies when performing AT-SCVP in different single solvents. We investigated two different strategies to control the polymer topology in one-pot: varying temperature and varying solvent polarity. In both cases, different fractions of branching revealed the efficacy of varying the polymer topology. To diversify the functionality of the peripheral space, we performed chain extensions of the resulting hyperbranched poly(St-co-VBC) macroinitiator (name as: hbPSt MI) with either St or tBA (tert-butyl acrylate). The resulting hyperbranched core star polymer had high molecular weights (hbPSt-g-PSt: Mn = 25,000, Đ = 1.77; hbPSt-g-PtBA: Mn = 27,000, Đ = 1.98); hydrolysis of the tert-butyl groups of the later provided a hyperbranched core star polymer featuring hydrophilic poly(acrylic acid) segments.

Controlling Polymer Topology by Atom Transfer Radical Self-Condensing Vinyl Polymerization of p-(2-Bromoisobutyloylmethyl)styrene

A new unsymmetrical AB* inimer, p-(2-bromoisobutyloylmethyl)styrene (BiBMS), was applied to the atom transfer radical polymerization (ATRP) to prepare a family of polymers with the topologies ranging from linear to branched. The catalyst system was Cu/CuBr2 coupled with 2,2′-bipyridine (Bipy) or N,N-bis(2-pyridylmethyl)octylamine (BPMOA) as a ligand in toluene or anisole at different temperatures, which ensured a very low catalyst (CuBr) concentration throughout the polymerization by a slow reduction process. First, BiBMS was polymerized in anisole at 0 °C using Cu/CuBr2/BPMOA as a catalyst system; at this temperature, the initiating activity of the formed A* was frozen and the polymerization was a step-growth polymerization, resulting in the formation of a linear polymer (LP1) whose main chain was linked by ester bonds. Second, BiBMS was polymerized in toluene at 20 °C using Cu/CuBr2/Bipy as a catalyst system. Under this condition, initiation from the B* of BiBMS was slow, followed by a fast radical poly...

Amphiphilic Hyperbranched Fluoropolymers as Nanoscopic 19F Magnetic Resonance Imaging Agent Assemblies

Three hyperbranched fluoropolymers were synthesized and their micelles were constructed as potential (19)F MRI agents. A hyperbranched star-like core was first synthesized via atom transfer radical self-condensing vinyl (co)polymerization (ATR-SCVCP) of 4-chloromethyl styrene (CMS), lauryl acrylate (LA), and 1,1,1-tris(4'-(2''-bromoisobutyryloxy)phenyl)ethane (TBBPE). The polymerization gave a small core with M n of 5.5 kDa with PDI of 1.6, which served as a macroinitiator. Trifluoroethyl methacrylate (TFEMA) and tert-butyl acrylate (tBA) in different ratios were then "grafted" from the core to give three polymers with M(n) of about 120 kDa and PDI values of about 1.6-1.8. After acidolysis of the tert-butyl ester groups, amphiphilic, hyperbranched star-like polymers with M(n) of about 100 kDa were obtained. These structures were subjected to micelle formation in aqueous solution to give micelles having TEM-measured diameters ranging from 3-8 nm and DLS-measured hydrodynamic diameters from 20-30 nm. These micelles gave a narrow, single resonance by (19)F NMR spectroscopy, with a half-width of approximately 130 Hz. The T1/T2 parameters were about 500 and 50 ms, respectively, and were not significantly affected by the composition and sizes of the micelles. (19)F MRI phantom images of these fluorinated micelles were acquired, which demonstrated that these fluorinated micelles maybe useful as novel (19)F MRI agents for a variety of biomedical studies.

Complex Amphiphilic Hyperbranched Fluoropolymers by Atom Transfer Radical Self-Condensing Vinyl (Co)polymerization

Amphiphilic hyperbranched fluorohomopolymer (M(n) = 9.06 kDa, M(w)/M(n)= 1.90) and fluorocopolymer (M(n) = 17.2 kDa, M(w)/M(n)= 2.50) with tri(ethylene glycol) units incorporated at the molecular level were synthesized by atom transfer radical self-condensing vinyl homopolymerization of an inimer, 4-[oxy(tri(ethylene glycol))bromoisobutyryl]-2,3,5,6-tetrafluorostyrene, and copolymerization of the inimer with 2,3,4,5,6-pentafluorostyrene (1:3, inimer:monomer), using 2,2'-bipyridine together with CuCl/CuCl(2) as the ligand/catalyst/deactivator system. The structure and composition of the fluoropolymers were characterized by (1)H, (13)C, and (19)F NMR spectroscopies. As detected by thermogravimetric analyses, the homopolymer and the copolymer had thermal stability up to 175 °C and 210 °C, respectively. Differential scanning calorimetry revealed a glass transition temperature of -19 °C for the homopolymer and 20 °C for the copolymer. Solubility tests indicated that both polymers were soluble in a broad range of organic solvents, and the presence of tri(ethylene glycol) units resulted in the formation of water dispersible micelles from each of the polymers.