Polymerization two-step

A two step polymerization involving formation of oligomeric phos-... 

Figure 24.3 Two-step polymerization process for the manufacture of polyethylene terephthalate ...

Figure 3.13 shows the variation of the gel conversion of the limiting reactant as a function of the stoichiometric ratio. For r > 3, no gel is formed and the polymer remains in the liquid state after complete reaction of epoxy groups. If the amount of epoxy monomer necessary to obtain a stoichiometric system is added in a second step, polymerization restarts, leading to gelation and the formation of a network. The two-step polymerization is the basis of several commercial thermosetting polymers. 

The copolymers were prepared by the two-step polymerization MMA, EMA, and BMA were partially polymerized for 1.5 h... 

Sequential polymerization of two acrylic monomers was discussed in Sections VI.E.4, VI.E.7 and VI.F. This technique was extended to three comonomers with formation of ABC-type triblock copolymers. For example, PMMA-fcZoc -PtBMA- Zoc -PMMA triblock copolymer was synthesized by the sequential DPFlLI-initiated polymerization of MMA, tBMA and MMA, respectively . Symmetrical BAB-type diblock copolymers were also prepared in two steps, polymerization of the A monomer being first initiated by a difunctional compound. The B blocks formed in the second step necessarily have the same average degree of 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). 

Gallos et al. [6] synthesized stereocomplexed polylactide using reactive extrusion process. The stereocomplexed PLA obtained in a two-step polymerization of L-lactide and D-lactide process to yield poly-L,D-lactic acid multiblocks. In the first step, DSM Micro 15... 

In contrast in the two-step polymerization technique (Fig. 1.6), in the first step of the reaction a prepolymer is produced through the reaction of a SS oligomer with an excess of diisocyanate, followed by chain extension with a short diol(urethane or ester) or a diamine (urea, urethaneurea, amide, or ester-amide) to form the HS and also to increase the overall molecular weight of the polymer. 

Fig. 1.6 Schematic of the PUs two-step polymerization synthesis route based on diol chain extenders.

Eceiza et al investigated a series of thermoplastic PUs synthesized in bulk by two-step polymerization, obtained with the isocyanate-chain extender couple MDI-BG and various SS macrodiols. The chemical structure, the SS molecular weight and the HS content were varied. The effects on the thermal and mechanical properties were investigated [77]. The changes in the macrodiols in the case of PUs based on MDl-BG, resulted in a modulus curve that showed a plateau indicating the existence of physical crosslinks because of the increase in the size and inter-connectivity... 

As a second step, we explored the possibility of a two-step polymerization reaction to enhance the structural control necessary to arrive at complex polymer architectures. By carefully selecting a precursor monomer that provides the encoding of the selective and sequential reaction sites, we rationally controlled a hierarchical two-step reaction process. 

Polyimides are class of polymers generally prepared from organic diamines and organic tet-racarboxylic acid dianhydrides by condensation polymerization. There are mainly two synthetic routes for polyimides one-step and two-step polymerization. Scheme 3.1 shows a generalized route of polyimide synthesis from an aromatic dianhydride and an aromatic diamine. 

In two-step polymerization, initially the polyamic acid is formed from an equimolar mixture of dianhydride and diamine in a polar aprotic solvent such as A,A-dimethylacetamide (DMAc) or A,A-dimeth-ylformamide (DMF). The reaction pathway for the formation of poly(amic acid) involving intermediates is presented in Scheme 3.2. The reaction mechanism involves nucleophilic attack of the amino group to the electrophilic carbonyl carbon of the anhydride group. This opens the anhydride ring to form an amic acid group. Formation of the poly(amic acid) is an equilibration reaction in which the forward reaction... 

Wu DC, Fu RW (2006) Synthesis of organic and carbon aerogels from phenol-furfural by two-step polymerization. Microporous Mesoporous Mater 96 115-121. 

Polycondensation. Oligocarbonate with molecular weight of less than 1x10 was formed by lipase CC-catalyzed polycondensation of carbonic acid diphenyl ester with bisphenol A (206). Diethyl carbonate was poljmierized with 1,4-butanediol by lipase CA catalyst (207,208). The successive two-step polymerization, the prepoljTnerization under ambient pressure, followed by the polymerization under vacuum (0.5 mm Hg), produced poly(tetramethylene carbonate) with Mw of more than 4x 10 . 

Pyo and Reynolds (52,53) reported the selective releasing of ions, such as adenosine 5 -triphosphate and heparin respectively, from conducting polymer bilayer structures. Piro and co-workers (54) successfully incorporated oligonucleotides into conducting polymer films using a two-step polymerization process. The release of these trapped oligonucleotides was also investigated, where the... 

Polyimides (PI) exhibit very good chemical, mechanical and dielectric stability at temperatures from -150 to 250 C. These rigid polymers with a high glass transition temperature are mostly used in (micro)electronics, aircraft industry, space exploration and as polymeric separation membranes. Linear polyimides (LPI) are traditionally prepared by the two-step polymerization. The polyimideprecursor, polyamic acid (PAA) (the most often a solution in N-methyl-2-pyrrolidone), is prepared from an aromatic dianhydride and an aromatic diamine. This precursor is transformed into a polyimide using thermal or chemical imidization (Figure 2) [5]. 

In this process, it is thought that a two-step polymerization reaction is involved [11]. In the first step an adduct of the catalyst and a growing polycarbonate chain is formed in the organic phase, e.g. ... 

The highest conductivities in lithium salt doped systems have been achieved in plasticized systems (13-17). These are characterize by relatively high ionic conductivities (up to 10 S/cm at room temperature) and transparency for up to 30 mass% of PMMA where PMMA has been used (13,14). A two step polymerization of glyddyl methacrylate (GMA) in the presence of propylene carbonate (PC) and a lithium salt (IS), the use of small molecule cyclotriphosphazenes in... 

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