Modified two-step polymerization

This book introduces a modified two-step polymerization technique. Partial urethane chains are employed as the soft segment phase. Such modified two-step polymerization can improve the molecule fiexibility of the SMPU. After the modified two-step polymerization, short polyols and rigid 4,4 -diphenylmethane diisocyanate (MDI) form the soft segment phase. To further improve the phase separation, rigid chain extenders can be used. 

High performance type shape memory polymers prepared by modified two-step polymerization... 

Muller and coworkers prepared disc-like polymer Janus particles from assembled films of the triblock copolymer SBM and, after hydrolysis of the ester groups into methacrylic acid units, used these as Pickering stabilizer in the soap-free emulsion polymerization of styrene and butyl acrylate [111]. Armes and coworkers described the synthesis of PMMA/siUca nanocomposite particles in aqueous alcoholic media using silica nanoparticles as stabilizer [112], extending this method to operate in water with a glycerol-modified silica sol [113, 114]. Sacanna showed that methacryloxypropyltrimethoxysilane [115] in the presence of nanosized silica led to spontaneous emulsification in water, which upon a two-step polymerization procedure afforded armored particles with an outer shell of PMMA [116]. Bon and coworkers demonstrated the preparation of armored hybrid polymer latex particles via emulsion polymerization of methyl methacrylate and ethyl methacrylate stabilized by unmodified silica nanoparticles (Ludox TM O) [117]. Performance of an additional conventional seeded emulsion polymerization step provided a straightforward route to more complex multilayered nanocomposite polymer colloids (see Fig. 14). 

Heat-resistant ABS resins can also be produced by polymerizing styrene with modified nitriles, such as fumaronitrile and maleonitrile. Fumaronitrile can be produced from acrylonitrile (Figure 15.7) in a two-step process involving the addition of hydrogen cyanide followed by oxydehydrogenation over metal oxide catalysts. The compatibility of styrene-co-acrylonitrile-co-fumaronitrile (SANF) terpolymers and SAN has been studied [75]. High-gloss, heat-resistant... 

Co(acac)3 is frequently used as a probe for enantioseparation efficiency of col-umns " . A monolytic capillary silica gel column was functionalized with methacrylate residues in two steps, as shown in equation and then it was impregnated with cellulose or amylose (51a, b) which was modified so that 30% of the R groups were the methacrylate group 52 and the rest was identical to R (53). For further stability of the column, the polymeric modifier was immobilized on the silica gel by in situ copolymerization with an olefinic monomer such as 2,3-dimethylbutadiene. Only the column containing cellulose modified as in 51a was able to separate the Co(acac)3 racemic mixture, whereas neither cellulose nor amylose modified as in 51b did, although they were successful in resolving other racemic mixtures ° °. ... 

An example related to the polymeric route has been given by Roger et al. [72] in which a tin alkoxide is modified in order to create a residual porosity in the matrix formed from this modified precursor. These compounds were prepared from a tin (IV) alkoxide modified with difunctional carboxylate ligands. Formation of the final porous material is obtained through a two step process. The first... 

Another strategy consists in the use of QDs coated with a cysteine acrylamide, a polymerizable stabilizer [304]. Successful incorporation of hydrophilic cysteine-acrylamide-stabilized QDs into 80-200 nm fluorescent latexes was achieved via emulsion polymerization, as reported by Sherman et al. [308], using two different procedures. In the first, a two-step shot growth surfactant-free emulsion polymerization of styrene and NaSS was performed in the presence of a solution of hydrophilic cysteine-acrylamide-stabilized CdS or CdSe/CdS QDs. In the second approach, CdSe/CdS QDs were first electrostatically modified by vinylbenzyl(trimethyl)-ammonium chloride and subsequently copolymerized with styrene in the presence of SDS. A third approach was also described in this paper coating of cationic PS particles with anionic poly(cysteine acrylamide)-coated QDs through electrostatic-driven interactions. 

Commercial PBI is a proprietary product (Celanese) made from 3,3, 4,4 -tetra aminobiphenyl (TAB) and diphenyl isophtalate in a two step, melt/solid polymerization [190]. A modified PBI structure such as poly(2,5)-benzimidazole (ABPBI) (see Fig. 6.10) has been synthesized by condensation of 3,4-diaminobenzoic acid (DABA) monomer in polyphosphoric acid [191]. 

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