Formation Of Hyperbranched Polymers Research Articles

Model of hyperbranched polymers prepared via polymerization of AB2 and core C3 monomers in a continuous-stirred tank reactor

The formation of hyperbranched polymers (HBPs) generated by the stepwise polymerization of AB2 monomers with the addition of trifunctional core monomers in a continuous-stirred tank reactor, CSTR, was investigated by a kinetic model. The dependency of the degree of polymerization (DP), the degree of branching (DB), and conversion on the Damköhler number (Da) were calculated by a generating function method. When using the polymerization system without the core monomers, the process could be halted due to the production of larger molecules at the conversion of group A, α(A), of approximately 0.44. The addition of core monomers with high reactivity in the CSTR could retard the growth of polymers. Consequently, the reduced weight-average DP and DB could reach 1000 and 0.51, respectively, at a high α(A) of 0.91. Moreover, the amount of unreacted monomers remaining in the flow exiting the CSTR was much less than that without the addition of the core monomers.

One-Step Synthesis of Thermally Curable Hyperbranched Polymers by Addition–Fragmentation Chain Transfer Using Divinyl Monomers

Free radical bulk and solution polymerizations of a divinyl monomer, ethylene glycol dimethacrylate (EGDMA), in the presence of methyl 2-(bromomethyl)acrylate as an addition–fragmentation chain transfer agent were investigated to synthesize thermally curable hyperbranched polymers by a one-step reaction. Soluble polymers were obtained up to high conversion of EGDMA, and the molecular weight and molecular weight distribution of the polymers increased with increasing EGDMA conversion. 1H NMR and MALDI-MS analyses revealed that the soluble polymers were obtained after the consumption of a considerable amount of the pendant methacryloyl groups, and one polymer chain contained a number of end groups indicating the formation of hyperbranched polymers. The isolated hyperbranched polymers underwent thermal curing above 110 °C without curing agents, and the polymers having a large number of pendant methacryloyl groups resulted in a significant increase in glass transition temperature, i.e., from around room temperature to above 210 °C.

Formation of hyperbranched polymers in atom transfer radical copolymerization of MMA and DVB

Hyperbranched poly(methyl methacrylate)s (HPMMAs) have been successfully prepared by atom transfer radical copolymerization of MMA and divinylbenzene (DVB). Kinetic study shows complete consumption of the initiator in 0.5 h, and relatively low polymerization rate when DVB content in the feed was high. By analyzing MALDI-TOF spectra of the resulting copolymers, the linear A n B* (n = 0, 1, 2, 3) oligomers were formed in 0.5 h of polymerization, and then the oligomers reacted each other to form dimers, further reactions produced HPMMA. The SEC and NMR spectroscopies were used to trace the polymerization, and the results demonstrate that small amount of the branching reactions occur in the initial polymerization, and the branched polymers are significantly generated past a certain conversion depending upon the feed ratios. Raising the content of DVB in the monomer mixture can increase the pendent vinyl groups of the linear oligo-inimers, leading to gelation at low MMA conversion.

Initiator-fragment incorporation radical polymerization of diallyl phthalate: Kinetics, formation of hyperbranched polymer, and iridescent porous film thereof

Diallyl phthalate (DAP) was polymerized in toluene using dimethyl 2,2′-azobisisobutyrate (MAIB) of high concentrations (0.1–0.9 mol/L) as initiator. The polymerization of DAP of 1.50 mol/L with MAIB of 0.50 mol/L proceeded homogeneously at 80°C without gelation to give soluble polymers in a high yield of 93%. Kinetic results of the homogeneous polymerization at 80°C suggest significant contributions of the degradative chain transfer and the primary radical termination as shown by the rate equation, Rp = k [MAIB]0.8[DAP]1.0 (Rp = polymerization rate). The polymer formed in the polymerization of DAP (1.30 mol/L) with MAIB (0.50 mol/L) at 80°C for 8 h consisted of the DAP units with (17 mol %) and without (47 mol %) double bond and the methoxycarbonylpropyl group (36 mol %) as MAIB-fragment. The large fraction of the incorporated initiator-fragment as terminal group indicates that the polymer has a hyperbranched structure. The film cast from a solution of the hyperbranched poly(DAP) in tetrahydrofuran showed an iridescent color. The confocal scanning laser microscope image of the film revealed that the iridescent film contained the pores of about 1 μm arranged in an ordered array. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 408–415, 2006

Studies on the atom transfer radical polymerization of a maleimide AB* monomer and modification of the halogen end groups

The atom transfer radical polymerization (ATRP) of an AB* monomer, N-(4-α-bromobutyryloxy phenyl)maleimide (BBPMI), was conducted using the complex of CuBr/2,2′-bipyridine as catalyst. The study of kinetics of polymerization and the growth behavior of macromolecules show that the polymerization proceeds rapidly in first 1 h and then slows down. The decrease in the rate of polymerization is ascribed to the poor reactivity of maleimide radicals from A* to initiate the polymerization of maleimide double bonds. The molecular weight of the resulting polymer also increases with the dosage of catalyst. The coincidence of molecular weight determined by hydrogen proton nuclear magnetic resonance spectroscopy ( 1H NMR) and gel permeation chromatography (GPC) proves that the resulting polymer is of linear structure, which is further verified by 13C NMR measurement and high performance liquid chromatography (HPLC) analysis of the hydrolysate of the resulting polymer. The stabilization modification of the halogen end groups of the resulting polymer by free-radical chain transfer reaction was attempted under ATRP condition. Isopropyl benzene was employed as the chain transfer agent. Indeed, the modified polymer with carbon–bromine bonds conversion of 40.7% shows enhanced thermal stability. The initial weight loss temperature has been increased from 193 to 243 °C. On the other hand, the atom transfer radical copolymerization of BBPMI with styrene resulted in the formation of hyperbranched polymer.

Dendritic polymers containing a dimethylsilyl linked dihydroxybenzyl alcohol backbone: divergent synthesis, aggregation, functionalization, and an evaluation of their applications in catalysis

A divergent synthetic approach to the construction of dimethylsilyl linked dihydroxybenzyl alcohol based dendrimers via acid–base hydrolytic chemistry of bis(dimethylamino)dimethylsilane with 3,5-dihydroxybenzyl alcohol, is reported. The peripheral OH groups lead to significant aggregation that was studied using FT-IR and UV-Vis spectroscopies, light scattering and transmission electron microscopy. Different generations of dendrimers could be easily functionalized at the periphery with phosphorus donor groups that were subsequently bound to RhCl(1,5-C8H12). Such organometallic dendrimers were found to be active and recoverable catalysts for hydrogenation of decene. The catalytic efficiency was found to be dependent on the number of generations and reaction time. An uncontrolled reaction of Me2Si(NMe2)2 with 3,5-dihydroxybenzyl alcohol in a multi-step addition process or one-pot reaction, led to the formation of hyperbranched polymers in which the build-up of the polymeric backbone was found to be dependent on the preferential reactivity and sterics at the benzylic center, as observed during dendrimer construction.

Hyperbranched Polymers Made from A2 and BB‘2 Type Monomers. 1. Polyaddition of 1-(2-Aminoethyl)piperazine to Divinyl Sulfone

A new strategy for synthesis of hyperbranched polymers from commercially available A2 type and BB‘2 type monomers has been developed. In the first part of this series, hyperbranched polysulfone−amine with multiamino groups is prepared by polyaddition of 1-(2-aminoethyl)piperazine (BB‘2) to divinyl sulfone (A2) without any catalysts. The products are soluble in water and organic solvents such as N,N-dimethylformamide, chloroform, and N-methyl-2-pyrrolidone. The polymerization mechanism has been investigated with FTIR, HPLC, and MS. During the reaction, secondary amino groups of 1-(2-aminoethyl)piperazine react rapidly with vinyl groups of divinyl sulfone within 15 s, forming dominant dimers and some other species. The dimer can be considered as a new AB‘2 type of monomer. Further reactions among AB‘2 molecules and AB‘2 with other species result in the formation of hyperbranched polymers. The degree of branching of the resulting polymer is higher than 50%. No gelation occurs in solution polymerization when the A2 to BB‘2 ratio equals 1. Similarly, there is no gelation in solution polymerization if the feed ratio of A2 to BB‘2 is 3/2; however, gelation does occur when the resulting polymer is separated from the solution. There are both terminal amino groups and vinyl groups in the hyperbranched polysulfone−amine if the feed A2 to BB‘2 ratio is 3/2, which further react with each other in bulk state resulting in a cross-linked material. If the terminal amino groups are protected by hydrochloride acid in advance in the solution, then no gelation can be observed after the product is separated from the solution.