Novel fluorinated block copolymer architectures fuelled by atom transfer radical polymerization

Block copolymers based on poly(pentafluorostyrene), PFS, in various numbers and of different lengths, and polystyrene are prepared by atom transfer radical polymerization (ATRP). Di- and triblock copolymers with varying amounts of PFS were synthesized employing either 1-phenylethylbromide or 1,4-dibromoxylene as initiators for ATRP. Diverse bromo(ester) (macro)initiators were also devised and involved in the formulation of fluorinated pentablock as well as amphiphilic triblock copolymers with a central polyether segment. Amphiphilic star-shaped fluoropolymers, hydrophobic fluorinated nanoparticles, or segmented fluorinated star-shaped block copolymers are further designed by use of different multifunctional initiators. The composition of the novel materials with PFS is determined by combination of SEC and ¹H NMR. Glass transition temperatures and thermal stabilities of the hydrophobic star-shaped PFSs on a six arm dipentaerythritol core are investigated in a wide range of molecular masses and further discussed.     

ATRP grafting of styrene from benzyl chloride functionalized polysiloxanes: An AFM and TGA study of the Cu(0)/bpy catalyst

Various combinations of Cu(0), CuCl, 2,2′-bipyridine (bpy) and 1,10-phenanthroline (phen) were used as catalysts for the grafting polymerizations of styrene from polysiloxane macroinitiators functionalized with benzyl chloride. While Cu(0)/bpy alone promotes the grafting, narrower polydispersities were obtained in the presence of CuCl. Analysis of the Cu(0) surface before and after polymerization by a combination of AFM, TGA and FTIR investigations reveals the formation of bpy or phen films on Cu(0). In the presence of CuCl, the ligand film appears decorated with CuCl particles which increase in size with increasing the CuCl concentration. The initial layer occurs most likely as a result of complexation between the ligands and the Cu(0) surface and acts as a support for the rest of the film. These observations are consistent with the film formation on Cu(0) from related nitrogen donors and indicate that the reactivity of the Cu surface may depend not only on its prior treatment but also on the deposition of ligands from the reaction mixture.     

硫代-Iniferters法活性自由基嵌段共聚合

自由基活性聚合近来发展很快,本文在概述了自由基活性聚合及其最新进展的基础上,对硫代－Ｉｎｉｆｅｒｔｅｒｓ法自由基活性聚合的机理,硫代－Ｉｎｉｆｅｒｔｅｒｓ法大分子引发剂的合成以及这些大分子引发剂在嵌段共聚物的制备等方面进行了综述。     

Synthesis of Boc protected block copolymers based on para-hydroxystyrene via NMRP

Nitroxide mediated free radical polymerization (NMRP) was used for the preparation of orthogonally protected block copolymers based on para-hydroxystyrene. The polymers have a low polydispersity and an active chain end. By a series of polymer analogous reactions, a partly deprotected block copolymer was synthesized consisting of a block with unprotected phenolic OH groups and a further block which is protected by the thermolabile Boc group.     

Novel regular polyimide‐graft‐(polymethacrylic acid) brushes: Synthesis and possible applications as nanocontainers of cyanoporphyrazine agents for photodynamic therapy

An approach to the synthesis of new regular graft‐copolymers polyimide (PI)‐graft‐polymethacrylic acid is elaborated, including (1) synthesis of multicenter PI macroinitiators, (2) controlled ATRP of tert‐butylmethacrylate on the prepared macroinitiators, and (3) protonolysis of tert‐butyl ester groups of side chains of the resulting PI‐graft‐poly(tert‐butylmethacrylate). Experimental conditions for attaining complete conversions of the first and the third stages of the process are determined by means of ¹H NMR and FTIR‐spectroscopy. Polymer products of the first and the second stages of the process, as well as poly(tert‐butylmethacrylate) side chains cleaved from the PI‐graft‐poly(tert‐butylmethacrylate) copolymers by complete decomposition of the PI backbone under alkaline hydrolysis conditions, are characterized by GPC. The kinetics of poly(tert‐butylmethacrylate) chain growth on a PI macroinitiator under ATRP conditions are studied. The results obtained provide evidence for the controlled character of the ATRP process and the regular structure of the synthesized graft‐copolymers. It is shown that PI‐g‐PMAA PI brushes are significantly more efficient intracellular delivery agents for the potential photosensitizer [tetra(4‐fluorophenyl)tetracyanoporhyrazine free base] than are the commonly used PEG‐micelles. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 4267–4281     

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry analysis of atom transfer radical polymerization macroinitiators derived from poly(3-ethyl-3-hydroxymethyloxetane)

The matrix-assisted laser desorption/ionization time-of-flight analysis of macroinitiators for atom transfer radical polymerization prepared by the functionalization of a multihydroxyl, highly branched polyether, poly(3-ethyl-3-hydroxymethyloxetane), allows the exact determination of the macroinitiator functionality, providing information on the number of bromine atoms in individual macromolecules, in contrast to NMR analysis, which gives average values. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 608–614, 2004     

Synthesis of sugar‐based macromolecules via sono‐ATRP in miniemulsion

Ultrasound‐mediated atom transfer radical polymerization (sono‐ATRP) in miniemulsion media is used for the first time for the preparation of complex macromolecular architectures by a facile two‐step synthetic route. Initially, esterification reaction of sucrose or lactulose with α‐bromoisobutyryl bromide (BriBBr) is conducted to receive multifunctional ATRP macroinitiators with 8 initiation sites, followed by polymerization of n‐butyl acrylate (BA) forming arms of the star‐like polymers. The brominated lactulose‐based molecule was examined as an ATRP initiator by determining the activation rate constant (k_a) of the catalytic process in the presence of a copper(II) bromide/tris(2‐pyridylmethyl)amine (Cu^IIBr₂/TPMA) catalyst in both organic solvent and for the first time in miniemulsion media, resulting in k_a = (1.03 ± 0.01) × 10⁴ M^?1 s^?1 and k_a = (1.16 ± 0.56) × 10³ M^?1 s^?1, respectively. Star‐like macromolecules with a sucrose or lactulose core and poly(n‐butyl acrylate) (PBA) arms were successfully received using different catalyst concentration. Linear kinetics and a well‐defined structure of synthesized polymers reflected by narrow molecular weight distribution (M_w/M_n = 1.46) indicated 105 ppm wt of catalyst loading as concentration to maintain controlled manner of polymerization process. ¹H NMR analysis confirms the formation of new sugar‐inspired star‐shaped polymers.     

Influence of macroinitiator’s glass transition temperature on the response times of polymer dispersed liquid crystals

Glass transition temperature (T_g), an important parameter of polymer, was reported to have great influence on the electro-optical properties of polymer dispersed liquid crystals (PDLCs). In this study, macroinitiators with different T_g were synthesised by reversible addition fragmentation chain transfer polymerisation, and used to prepare PDLCs with different T_g block chains. The effect of different T_g of the block chains on response times was investigated. It was found that rise time decreased and decay time increased with the decrease of the block chain’s T_g. We proposed a possible mechanism by which T_g of the block chains influence response times.     

Surface active azogroup-containing polymers and their use in emulsion polymerization

Polymeric azoinitiators have been obtained by the acidcatalyzed polyreaction of azobisisobutyronitrile (AIBN) with tetraethylene glycol (TEG) and 1.6-hexanediol resp. The kinetics of decomposition of these polyazoesters were investigated by differential scanning calorimetry (DSC) resulting in an activation energy of E_a=124.5 KJ/mol and a frequency factor of A= 3.6 · 10¹⁴ sec^–1.The polyazoesters were used to initiate radical polymerization of acrylamide limiting the decomposition of the initiator to 37%. The resulting polyacrylamides containing azogroups had molecular weights between 50 000 and 250 000 g/mol. They are surface active polymers having a critical micell concentration of 0.1 to 0.3 g./l. By use of these polyacrylamides as an emulsifying initiator system stable emulsions of polymers were obtained without additional use of a tenside. Polymethacrylic acid containing azogroups can be used as well as an emulsifying initiator.The latex particles are stabilized by a solvated shell of a polymer. Thus it is possible to obtain stable emulsions in organic solvents by use of an azogroup-containing prepolymer which is soluble in that solvent. An emulsion of polyacrylamide in methanol ohtained by use of an azogroup-containing polyvinylacetate is an example.Dedicated to Professor F. H. Müller.Thanks are due to Dr. R. Menhold, Bayer AG, Leverkusen for performing the electronmicroscopic investigations. Financial support by Deutsche Forschungsgemeinschaft and Fonds der Chemischen Industrie is gratefully acknowledged.