Zhixue Weng

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.

Effect of Oleic Acid-modified Nano-CaCO3 on the Crystallization Behavior and Mechanical Properties of Polypropylene

Abstract Oleic acid (OA)-modified CaCO 3 nanoparticles were prepared using surface modification method. Infrared spectroscopy (IR) was used to investigate the structure of the modified CaCO 3 nanoparticles, and the result showed that OA attached to the surface of CaCO 3 nanoparticles with the ionic bond. Effect of OA concentration on the dispersion stability of CaCO 3 in heptane was also studied, and the result indicated that modified CaCO 3 nanoparticles dispersed in heptane more stably than unmodified ones. The optimal proportion of OA to CaCO 3 was established. The effect of modified CaCO 3 nanoparticles on crystallization behavior of polypropylene (PP) was studied by means of DSC. It was found that CaCO 3 significantly increased the crystallization temperature, crystallization degree and crystallization rate of PP, and the addition of modified CaCO 3 nanoparticles can lead to the formation of β-crystal PP. Effect of the modified CaCO 3 content on mechanical properties of PP/CaCO 3 nanocomposites was also studied. The results showed that the modified CaCO 3 can effectively improve the mechanical properties of PP. In comparison with PP, the impact strength of PP/CaCO 3 nanocomposites increased by about 65% and the flexural strength increased by about 20%.

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.

Morphology, Rheology, and Mechanical Properties of Polylactide/Poly(Ethylene-co-octene) Blends

Polylactide (PLA)/poly(ethylene-co-octene) (POE) blends containing ethylene-glycidyl methacrylate copolymer (EGMA) as a compatibilizer were prepared by melt blending. An immiscible, two-phase structure with POE dispersed in the PLA matrix was observed by scanning electron microscopy. It was found that the POE particle size was significantly decreased by the addition of EGMA, and the POE particle size and distribution decreased with the increase of the compatibilizer content up to 2% EGMA, beyond which the POE particle size and distribution remained unchanged. The reactions between the epoxy groups of EGMA and carboxylic or hydroxyl groups of PLA were elucidated by the Fourier transform infrared spectroscopy. Rheological results showed that the G′(ω), G″(ω), and complex viscosity of PLA/POE blends significantly increased at low frequencies with the addition of EGMA. The failure mode changed from brittle fracture of the neat PLA to ductile fracture of the PLA/POE blends.

Thermosensitive Poly(N-isopropylacrylamide-co-acrylonitrile) Hydrogels with Rapid Response

Abstract Acrylonitrile (AN) was copolymerized with N -isopropylacrylamide (NIPA) to synthesize thermosensitive hydrogels, and the on-off switch behavior of poly(NIPA-co-AN) hydrogels with different fraction of hydrophobic component (AN) was investigated. It is found that the lower critical solution temperature (LCST), the swelling ratio at certain temperature and the reswelling rate of poly(NIPA-co-AN) hydrogels decreased as AN unit fraction in copolymers increased. In order to improve the responsive rate of poly(NIPA-co-AN) hydrogels, they were further treated by surface crosslinking using N , N′-methylene bisacrylamide (BIS) as a crosslinking agent. The swelling and deswelling behaviors of these copolymers were compared with those of the untreated hydrogels. The results indicated that the responsive rate of poly(NIPA-co-AN) hydrogel was improved by surface crosslinking. The resulting hydrogels bearing cyano groups with fast response have potential applications in the field of drug-controlled release and immobilization of biomolecules.

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.

Thermal Degradation Behavior and Flame Retardancy of Polycarbonate Containing Poly[(phenylsilsesquioxane)-co-(dimethylsiloxane)] and Potassium Diphenyl Sulfonate

The synergistic effect of poly[(phenylsilsesquioxane)-co-(dimethylsiloxane)] (PPSQDS) and potassium diphenyl sulfonate (KSS) on the thermal degradation and flame retardancy of polycarbonate (PC) was studied. The flame retardancy of PC was improved by the combination of PPSQDS and KSS, and a V-0 rating for 1.6 mm thickness sample was successfully obtained. The thermal degradation of the flame retarded PC was characterized by thermogravimetric analysis (TGA) and the degradation activation energy (E a) was calculated according to the Kissinger and Flynn-Wall-Ozawa (F-W-O) methods. The E a value of PC was decreased by the combination of PPSQDS and KSS, indicating that the synergistic effect of PPSQDS and KSS facilitates the thermal degradation of PC and accelerates char formation.

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.