Homopolymerization reaction conditions

Tanaka and Kakiuchi (6) proposed catalyst activation via a hydrogen donor such as an alcohol as a refinement to the mechanism discussed by Fischer (7) for anhydride cured epoxies in the presence of a tertiary amine. The basic catalyst eliminates esterification reactions (8). Shechter and Wynstra ( ) further observed that at reaction conditions BDMA does not produce a homopolymerization of oxiranes. 

Each set of experiments was carried out under the same reaction condition except using different comonomers, i.e. p-methylstyrene, o-methylstyrene, m-methylstyrene and styrene, respectively. The compositions of copolymers were determined by H NMR spectra, and the thermal properties (melting point and crystallinity) were obtained by DSC measurements. Overall, all comonomers show no retardation to the catalyst activity. In fact, the significantly higher catalyst activities were observed in all copolymerization reactions (runs 2-5), comparing with that of ethylene homopolymerization (run 1). Within each set (runs 2-5 and 6-9) of comparative experiments, p-methylstyrene consistently shows better incorporation than the rest of comonomers, i.e. o-methylstyrene, m-methylstyrene and styrene. Both catalysts with constrained mono- and di-cyclopentadienyl ligands are very effective to incorporate p-methylstyrene into polyethylene backbone. In runs 2 and 6, more than 80 % of p-methylstyrene were converted to copolymer within one hour under constant (- 45 psi) ethylene pressure. On the other hand, only less than half of styrenes (runs 5 and 9) were incorporated into ethylene copolymers under the same reaction conditions. The significantly... 

The homopolymerization reactions of impure TGDDM (MY720) in the presence and absence of a BF3 NH2C2H5 catalyst and, also, pure TGDDM were monitored by FTIR as a function of cure temperature from 177 to 300 °C. The intensities of the epoxide, hydroxyl, ether and carbonyl bands at 906, 3500, 1120 and 1720 cm-1 respectively were determined from spectral differences and are plotted as a function in cure conditions in Figs. 10,11,12 and 13 respectively. The 906,1120 and 1720 cm-1 band intensities were normalized to the 805 cm-1 band and the 3500 cm-1 to the 1615 cm 1 band. The 805 and 1615 cm-1 bands are associated with the phenyl group which is assumed to chemically unmodified during the homopolymerization reactions. 

In the homopolymerization of dioxolane below 30°C. tertiary oxonium ions exist exclusively (2, 5). Otherwise hydride transfer would occur (carbonium ions abstract hydride from monomeric cyclic formats) (II, 16). In trioxane polymerization, however, at least some of the active chain ends are carbonium ions they cause hydride transfer and elimination of formaldehyde (9, II, 13). Thus, in copolymerization we must expect two different kinds of structures for cationic chains with terminal trioxane unit. Oxonium ions (I) and carbonium ions (II) may have different reactivity ratios in the copolymerization, but hopefully this does not cause severe disturbance since I and II seem to be in a fast kinetic equilibrium with each other (3). Hence, we expect [I]/[II] to be constant under similar reaction conditions. 

Up to now we have not found reaction conditions permitting exclusive production of insoluble copolymer, which is the desired product in commercial copolymerization of trioxane. Conversion of a large portion of the dioxolane into soluble copolymer could not even be avoided by slow and gradual addition of the comonomer to a homopolymerization run of trioxane in methylene dichloride (9). The same result was obtained in solution copolymerization of trioxane with 8 mole % of 1,3-dioxacycloheptane (dioxepane), and even 1,3-dioxane—which is not homopolymerizable and is a very sluggish comonomer—formed a soluble copolymer in the initial phase of copolymerization (trioxane 2.5M 1,3-dioxane 0.31M SnCb 0.025M in methylene dichloride at 30°C.). 

Figure 2 shows a series of cloud-point curves determined for the system ethylene-2-ethylhexyl acrylate-poly(ethylene-co-2-ethylhexyl acrylate). Each cloud-point curve corresponds to one stationary copolymerization condition in CSTR1. The compositions and concentrations referring to the five monomer-polymer mixtures, including one ethylene homopolymerization reaction (Experiment 1), are listed in Tab. 1. FA is the concentration of the acrylate units within the copolymer (in mole-%),/P and/A denote the concentrations of polymer and of acrylate monomer in the monomer-polymer mixture, respectively. As can be seen from Fig. 1 and from Tab. 1, increasing acrylate content in the copolymer lowers the cloud-point pressure. 

The reactivity of a polar monomer can be considerably enhanced in copolymerization with a species of the opposite polarity. Maleic anhydride does not homopolymerize under normal free-radical reaction conditions but it forms 1 1 copolymers with styrene under the same conditions and even reacts with stilbene (7-6), which itself will not homopoloymerize. 

Several methods can be used to synthesize block copolymers. Using living polymerization, monomer A is homopolymerized to form a block of A then monomer B is added and reacts with the active chain end of segment A to form a block of B. With careful control of the reaction conditions, this technique can produce a variety of well-defined block copolymers. This ionic technique is discussed in more detail in a later section. Mechanicochemical degradation provides a very useful and simple way to produce polymeric free radicals. When a rubber is mechanically sheared (Ceresa, 1965), as during mastication, a reduction in molecular weight occurs as a result of the physical pulling apart of macromolecules. This chain rupture forms radicals of A and B, which then recombine to form a block copolymer. This is not a preferred method because it usually leads to a mixture of poorly defined block copolymers. 

Polymerization of vinyl or methacrylic monomers (especially in conjunction with crosslinking monomers) within the wood often results in an autoacceleration during the latter phase of the polymerization this phenomenon is known as the Trommsdorff or gel effect in homopolymerization reactions (Duran and Meyer, 1972 Trommsdorff et a/., 1948). The gel effect arises from a decrease in the termination rate of the free radical polymerization, caused in turn by the effect of the local viscosity on the diffusion rates of the growing polymer chains. Since the heat of polymerization cannot be removed rapidly enough to maintain isothermal conditions, autoacceleration is characterized by a strong exotherm the intensity of the exotherm depends on the catalyst level, as illustrated in Figures 11.4 and 11.5 (Siau et al., 1968). 

Acrylic acid produces an alternating copolymer with 1,3,3-trimethyl azetidine below 80° C, but long acrylic acid sequences above this temperature, since, under these reaction conditions, acrylic acid homopolymerizes already at 150°C to poly(i8-propiolactone) with the monomeric unit - -O—CHz — CH2 —CO But the joint polymerization of 1,3,3-trimethyl azetidine with... 

Several recent studies have demonstrated ATRP reactions within microfluidic devices. An initial study demonstrates the use of a thiolene polymer based reactor with rectangular microchannels (500 x 600 j,m) [86]. The device consists of two inlet channels, an active mixing chamber containing a magnetic stir bar and one outlet channel. Homopolymerization of 2-hydroxypropyl methacrylate (HPMA) by ATRP was demonstrated in this device and it was shown that the kinetics and product properties were similar to those for experiments performed in a batch reactor. This technique provides a fast way of screening various ATRP reaction conditions while using a minimum of raw materials. 

Pig. 6. Termination rate coefficients in bulk methyl acrylate (MA) and dodecyl acrylate (DA) homopolymerizations as a function of monomer conversion. The reaction conditions were 40°C and 100 MPa. 

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