Zu-Ren Pan

Free radical copolymerization and kinetic treatment of styrene with N‐phenylmaleimide

The copolymerization of styrene (M1) with N-phenylmaleimide (M2) in chloroform with 2,2′-azobis(isobutyronitrile) as an initiator was investigated. The kinetic parameters, such as reactivity ratios, overall activity energy, and the effect of molar fraction of monomers on the initial copolymerization rate, were determined. The bimolecular termination of the copolymerization was proved. The treatment method proposed by Yoshimura and colleagues was used to estimate quantitatively the contribution of the charge-transfer complex (CTC) and the free monomers in the copolymerization process. The propagation reactivity ratios of CTC and free monomers were calculated by a new method.

Effects of water solubility of acrylonitrile on vinylidene chloride/acrylonitrile/styrene suspension polymerization

The water solubility of acrylonitrile (AN) and its effects on vinylidene chloride/acrylonitrile/styrene (VDC/AN/St) suspension copolymerization were investigated in this study. It shows that the VDC/St ratio and the presence of suspending agent have no obvious influences on AN phase partition between the monomer and aqueous phases, whereas the water solubility of AN increases as temperature increases. Polymerization in the aqueous phase occurs extensively with azobis(isobutyronitrile) (AIBN) as initiator, whereas with lauryl peroxide (LPO) as initiator, polymerization in the aqueous phase is negligible. Theoretical analysis and experimental results indicate that transport of the monomer molecule is possible during polymerization. Both VDC and AN transfer from the monomer phase to the aqueous phase when AIBN is used as initiator. AN transfers from the aqueous phase to the monomer phase for the polymerization system initiated by LPO. Sodium nitrite (NaNO2), but not sodium sulfide (Na2S), can be used to effectively inhibit polymerization in water and exerts less influence on the polymerization in the monomer phase.

PREPARATION AND CHARACTERIZATION OF MMA-BA-DMAEMA TERPOLYMER LATEX

Abstract The terpolymer latex of methyl methacrylate (MMA)/butyl acrylate (BA)/dimethylaminoethyl methacrylate (DMAEMA) was prepared by batch and semi-continuous emulsion copolymerization. The effects of emulsifier type and concentration, polymerization temperature, and feed policy of emulsified monomers on process stability of the copolymerization and properties of the terpolymer latex were studied systematically. The results suggest that the selection of emulsifier should not be based on the HLB values for the DMAEMA-containing systems. The co-emulsifiers suitable for stabilizing the copolymerization process are in the order of SDS/OP>SDBS/OP>OT/OP. The results also indicate that an increase in amount of the co-emulsifiers, sodium dodecyl sulfate (SDS) and octyl phenol polyoxyethyl ether (OP), improves the process stability, decreases the surface tension and particle size of latices; however, it has little influence on the electrolyte stability when SDS/OP ratio is unchanged. A decrease in reaction temperature improves the process stability of polymerization but decreases the electrolyte stability of latices. The DMAEMA content does not affect the process stability significantly under investigated conditions but contributes to improve the electrolyte stability of latices. Compared to the batch polymerization process, the semi-continuous polymerization with a lower monomer feed rate provides better process stability for the polymerization and better electrolyte stability for the latices.

Micron-size uniform poly(methyl methacrylate) particles by dispersion polymerization in polar media. IV. Monomer partition and locus of polymerization

Abstract A thermodynamic model has been proposed for the simulation of monomer partition between the particles phase and the continuous phase in the dispersion polymerization of methyl methacrylate in methanol/water medium. The monomer concentrations in the polymer particles and in the continuous phase decrease as the polymerization proceeds. It is strongly dependent not only on initial monomer concentration but also polymerization temperature. The partition coefficient of methyl methacrylate between the polymer particles phase and continuous phase is almost constant in limited range with increasing conversion. There are two polymerization loci in dispersion polymerization, namely the continuous and particle phases, based on the molecular weight and its distribution, and the monomer partition study.

Semicontinuous thermal bulk copolymerization of styrene and maleic anhydride: Experiments and reactor model

Thermal bulk copolymerization of styrene (St) and maleic anhydride (MAH) has been carried out at 110-130°C and up to around 55 wt % conversion in a stirred tank reactor with an anchor impeller to prepare the random copolymer of St-MAH (R-SMA). A series of experiments in semicontinuous monomer adding process were done to investigate the effects of operating condition on monomer conversion, copolymer composition, and its uniformity. It has been shown that a random copolymer with constant composition can be obtained by semicontinuous copolymerization. A reactor model was developed to simulate the copolymerization processes. The numerical method in which the gel effect on the copolymerization is incorporated has exhibited excellent agreement between the model calculation and the experimental data. However, when using the assumption that (1) k 22 = 0; (2) k 21 [M 1 ] » k 12 [M 2 ]; and (3) (R 1 / 2k t ) 1/2 is a constant, an analytical solution to the model was found to be available also.

Continuous thermal bulk copolymerization of styrene and maleic anhydride

Thermal bulk copolymerization of styrene (monomer 1) and maleic anhydride (monomer 2) was carried out in a continuous stirred tank reactor (CSTR) with a double helical ribbon-anchor impeller. A series of experimental runs under different operating conditions (average residence time, reaction temperature, and the composition in the inflow stream) were done, which showed that steady states could be approached. The effect of operating conditions on monomer conversion and copolymer composition was discussed. A CSTR model was established and the model parameters from the semicontinuous tests were used to predict conversions and copolymer compositions of the continuous process under transient and steady states. Kinetics from the semicontinuous bulk copolymerization were transferable to the continuous process. The modeling work for the continuous process showed that the same result as in a semicontinuous process could be obtained; the numerical method in which the gel effect on the copolymerization was incorporated exhibited excellent agreement between the model calculation and the experimental data. However, when using the assumption that k22 = 0, k21[M1] ≫ k12[M2], (RI/2kt)1/2 is a constant, and V is a constant, the predictions from the analytical solution to the model were in good agreement with the actual process data.

Effects of acrylonitrile water solubility on limiting conversion and copolymer composition in suspension polymerization

Abstract The effects of acrylonitrile (AN) water solubility on the limiting conversion and copolymer composition of the AN and AN/vinylidene chloride (VDC) suspension polymerization were investigated. It was found that AN dissolved in aqueous phase does not transfer back to oil phase in AN suspension homopolymerization but partially does in AN/VDC suspension copolymerization, and thus the limiting conversion is lowered and decreases with water/oil ratio increasing in both AN and AN/VDC suspension polymerization. For the continuous transport of AN in aqueous phase to oil phase during suspension polymerization, the composition distribution of AN/VDC copolymer prepared by suspension polymerization is narrower than that by bulk polymerization. The calculated composition of AN/VDC suspension copolymer with considering AN water solubility is consistent with the experimental data.

Structure–property relationships of lightly chemical crosslinked poly(vinyl chloride) thermoplastic elastomer

Chemical crosslinked poly(vinyl chloride) (C-PVC) was synthesized by vinyl chloride suspension polymerization in the presence of diallyl phthalate (DAP) and plasticized to prepare poly(vinyl chloride) (PVC) thermoplastic elastomer (TPE) materials. The chemical crosslinking and physical crosslinking structure in chemical crosslinked PVC-TPE were investigated. It showed that the gel fraction and the crosslinking density of gel increased as the feed concentration of DAP increased. C-PVC prepared by VC/DAP copolymerization was lightly crosslinked as compared with irradiation crosslinked PVC. Physical entanglements would greatly influence the crosslinking density of gel when the gel fraction was high. Chemical crosslinking had little influence on the recrystallization behavior of PVC. A structure model of chemical crosslinked PVC-TPE was proposed, in which chemical networks acted with physical networks cooperatively. It also showed that chemical crosslinking and physical crosslinking influenced the processability and mechanical properties of chemical crosslinked PVC-TPE cooperatively. Although the processability of PVC-TPE deteriorated with chemical crosslinking, the dimension stability and elasticity of PVC-TPE were improved as the permanent chemical networks were introduced.

Studies on the microstructure of vinyl/N-phenylmaleimide copolymers by NMR and their applications

The micro- and stereostructures and sequence distribution of methyl methacrylate (MMA)/N-phenylmaleimide (PMI) and styrene (St)–PMI copolymers were studied in detail with NMR spectroscopy. The MMA–PMI copolymer was in a random sequence distribution and the St–PMI copolymer was alternating in structure. Some micro- and stereoinformation of the MMA–PMI copolymers could be obtained from 1H-NMR spectra. The average number sequence length obtained from the copolymer triad by 13C-NMR spectra was in agreement with that calculated from the reactivity ratios measured by an elemental analyzer. From the triad fraction of the copolymer measured by 13C-NMR, the copolymer chain of MMA–PMI was proved to be a one-order Markov chain. More suitable propagation reactions were proposed from the deviation of sequence distribution of the St–PMI copolymer.

Synthesis of chemically crosslinked poly(vinyl chloride) by vinyl chloride/divinyls suspension copolymerization

Abstract Vinyl chloride (VC)/divinyl derivative copolymerization was carried out in the suspension process for preparing chemically crosslinked poly(vinyl chloride) (PVC). Effects of the reactivity ratios and concentration of divinyl, polymerization temperature and conversion on the structure of crosslinked PVC (such as the gel fraction, polymerization degree of sol and crosslinking density of gel) were investigated. It showed that the crosslinking behavior of various divinyls was different. The crosslinking efficiency of diallyl maleate (DAM) was higher than that of diallyl phthalate (DAP) and ethyl glycol dimethyl acrylate (EGDMA). The crosslinking efficiency of EGDMA was very low due to its high probability of homopolymerization. The gel fraction and crosslinking density of gel increased as the concentration of DAP increased, and decreased with the increase of polymerization temperature for VC/DAP copolymer. Polymerization degree of sol of VC/DAP copolymer decreased with the increase of concentration of DAP and varied with polymerization temperature. The crosslinking density of gel increased gradually with the increase of the gel fraction at lower gel fraction stage, and increased rapidly at higher gel fraction stage. The concentration of double bonds of VC/DAP copolymerization system increased as polymerization proceeded, which resulted in the increase of gel fraction of VC/DAP copolymer as conversion increased.