Sheng-kang Ying

Synthesis of fluorine-containing block copolymers via ATRP 1. Synthesis and characterization of PSt-PVDF-PSt triblock copolymers

A technique is described for the synthesis of polystyrene-block-poly(vinylidene fluoride)-block-polystyrene (St-VDF-St) triblock copolymers through a poly(vinylidene fluoride) macroinitiator. The bromine terminated poly(vinylidene fluoride), which was prepared by radical telomerization of vinylidene fluoride with 1,2-dibromotetrafluoroethane, initiated polymerization of styrene in presence of copper(I) bromide and α,α′-bispyridine complexes. It was found that molecular weights increased linearly in styrene conversion and polydispersities were low. The macroinitiator and block copolymers were characterized by g.p.c. and n.m.r.

Synthesis of fluorine-containing block copolymers via ATRP 2. Synthesis and characterization of semifluorinated di- and triblock copolymers ☆

Abstract A series of semifluorinated fluorocarbon/hydrocarbon di- and triblock copolymers were prepared by atom transfer radical polymerization (ATRP). The mono- and difunctional macroinitiators, which were obtained from bulk ATRP of styrene, butyl acrylate and methyl acrylate, initiated solution ATRP of 2-[(perfluorononenyl)oxy]ethyl methacrylate and ethylene glycol mono-methacrylate mono-perfluorooctanoate, respectively. The formation of the block copolymer was confirmed with size exclusion chromatography and 1 H NMR spectrum.

Controlled radical polymerization of methacrylates at ambient temperature and the synthesis of block copolymers containing methacrylates

The controlled radical polymerization of methyl methacrylate (MMA) and 2-hydroxy ethyl methacrylate (HEMA) were successfully performed at ambient temperature. MMA was polymerized in acetonitrile with ethyl-2-bromopropionate (EPN-Br)/CuCl/2, 2′-bipyridyl (bpy) at 40°C. The final polymer was with a narrow molecular weight distribution (Mw/Mn<1.5) and controllable molecular weight. The controllable nature might have been contributed mainly by the high value of dielectric constant of acetonitrile. The bulk polymerization of HEMA, a monomer with a high value of dielectronic constant, can be well controlled with EPN-Br/CuCl/ bpy at 20°C. The halogen terminated PMMA and PSt were then used as macroinitiators to copolymerize with some other monomers. As a result, some block copolymers, such as PMMA-b-PSt, PMMA-b-PHEMA and PSt-b-PHEMA, were synthesized.

Controlled/living polymerization of MMA promoted by heterogeneous initiation system (EPN-X-CuX-bpy)

The polymerization of methyl methacrylate (MMA) promoted by heterogeneous initiation system (ethyl-2-halopropionate (EPN-X)–CuX–2,2′-bipyridyl (bpy), where X = Br or Cl) is studied in detail. The results show that ethyl-2-bromopropionate (EPN-Br) is an efficient initiator as expected, and that CuCl–bpy, instead of CuBr–bpy, is a better catalyst for the controlled polymerization of MMA. The solvents with a high value of dielectric constant (e) will lead to fast initiation and narrow molecular weight distribution (MWD). As a result, the controlled, living polymerization of MMA with EPN-Br–CuCl–bpy can be got in ethyl acetate (EAc) at 100°C and in acetonitrile at 80°C. All results suggest that the initiation reaction is a controlling step in the controlled polymerization of MMA. The relationship between the UV spectra of CuCl–bpy and the performances of the polymerization in EAc or acetonitrile suggest that the formation of bis-bpy complex, [Cubpy2]X−, will lead to fast initiation and good control of the polymerization.

Hydrogen bonding and crystallization behaviour of segmented polyurethaneurea : effects of hard segment concentration

Abstract I.r. spectroscopy, d.s.c., WAXD and optical microscopy were employed to investigate the differences between hydrogen bonding and crystallization behaviour depending on hard segment concentration in polyether- and polyester-based polyurethaneureas (PUUs). It has been found that the hard segment crystallization behaviour of polyether-based PUU is higher than polyester-based PUU for the same hard segment content. Hydrogen bonding in polyether-based PUU is formed mainly between hard segments, which promotes crystallization of hard segments. Hydrogen bonding in polyester-based PUU is formed mainly between soft and hard segments, which hinders the crystallization of hard segments.

Effect of ionic group on the behaviour of polyurethaneurea emulsion

A novel linear polyurethaneurea emulsion was synthesized from poly(propylene oxide) diol, toluene diisocyanate, dimethylol propionic acid, 2-methyl-1,3-propane diol and ethylenediamine. The effect of the fraction of and the distribution of ionic group on the properties of polyurethaneurea emulsion was investigated by infrared spectroscopy (i.r.), differential scanning calorimetry (d.s.c.), transmission electron microscopy (TEM), a rotary viscometer, etc. In polyurethaneurea investigated, hydrogen-bonds existed not only in the hard segment but also in the soft segment. With increasing the fraction of ionic groups, microphase separation was enhanced and the polyurethaneurea emulsion viscosity increased. In addition, the synthetic method has a profound effect on the distribution of ionic groups, and the emulsion having well-distributed ionic groups is more stable in storage.

The synthesis of ABA block copolymers by means of ‘living’/controlled radical polymerization using hydroxyl-terminated oligomers as precursor

ABA block copolymers with well-defined structure were synthesized by the combination of the end-group transformation of prefabricated hydroxyl-terminated oligomers and atom transfer radical polymerization (ATRP). The hydroxyl-terminated oligomers, such as polyether diol, polyester diol and hydroxyl-terminated polybutadiene, were reacted with chloroacetyl chloride to form α,ω–bichloroacetyl oligomers (P–Cl). After the P–Cl was characterized by IR and chlorine content analysis, it was used as macro-intiator in the bulk polymerization of styrene in the presence of CuCl/bpy, which led to a series of ABA block copolymers. The formation of block copolymers was proved by 1H-NMR. The molecular weight of the block copolymers could be designed up to 105 according to the consumed monomer and the amount of feeding P–Cl. The kinetic study showed that the relationship between the logarithm of monomer concentration and the reaction time was linear, and an induction period was observed. It suggested that the initiation is slow and the concentration of active species was constant after initiation. Moreover, the experimental molecular weight increased linearly with the monomer conversion; simultaneously, the molecular weight distribution (MWD) of the block copolymer was close to the MWD of the macro-initiator (P–Cl). The results demonstrate the polymerization is a ‘living’/controlled process.

Study on sequence distribution of segmented poly(urethane urea)s by 13C-NMR spectroscopy: Effect of polymerization procedures

The segmented poly(urethane urea) copolymers were synthesized by one- and two-step polymerization procedures. The copolymers were based on 4,4′-diphenylmethane diisocyanate, 3,5-diethyltoluene diamine, and ethylene oxide-capped poly(propylene oxide) diol. The mean sequence lengths of polyurethane soft block and polyurea hard block as well as the sequence distribution of the hard block in the copolymers were estimated from the signals of aromatic carbons in 13C-NMR spectra. The results indicated that two-step polymerization led to longer mean sequence lengths and broader hard block sequence distribution than one-step polymerization did.

Phase separation in segmented poly(urethane urea) copolymers during reaction injection molding (RIM) polymerization

In situ experiments were performed with a portable RIM (reaction injection molding) minimachine interfaced to an FTIR spectrophotometer to follow the reaction chemistry and monitor phase separation of copoly(urethane urea)s during RIM polymerization. The PUU copolymers were based on ethylene oxide-capped poly(propylene oxide) polyether diol, 3,5-diethyltoluenediamine (DETDA), and uretonimine liquefied 4,4′-diphenylmethane diisocyanate. The effect of catalyst concentration on the degree of phase separation in the as-molded RIM PUU copolymers was investigated by using differential scanning calorimetery and scanning electron microscopy as supplementary methods. The results suggested that an increase of degree of phase separation and a decrease of the size of hard-segment-rich domains take place with a rise of catalyst concentration. The morphological feature was a consequence in combination with the increase in relative rate of urethane formation and the ordering of hydrogen bonding through urea groups.