Effects of crosslinking by quinones on dyeing of irradiated films of copolymers bearing photobase generating groups

Films of copolymers of methyl methacrylate and O-acryloyl acetophenone oxime (AAPO), which is a monomer bearing photobase generating groups, were UV-irradiated and dyed in the presence of p-benzoquinone or 1,4-naphthoquinone. Acyloxyimino groups in AAPO units were transformed into pendant amino groups on irradiation, and films became well dyeable with an acid dye. The quinones in the films caused crosslinking, which reduced the damage of the films during the dyeing processes compared to those without quinones. Sublimed p-benzoquinone was also introduced into heated films after irradiation, which resulted in the success of lowering the surface roughness of the films during the dyeing processes. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 1177–1184, 1998     

Effects of crosslink density on mechanical properties of high glass transition temperature polycyanurate networks

Polycyanurate networks of different architecture were synthesized using different curing cycles. Networks with a variable extent of reaction were obtained; the small variation of the cyanate conversion (0.8 to 1) corresponds to a large variation of glass transition temperature (150–290°C) and crosslink density. The mechanical behavior at small and large deformations and the fracture toughness were examined at room temperature and related to the network structural parameters. To explain the puzzling variation of the yield stress and yield strain with the cyanate conversion, recovery experiments were conducted to discriminate anelastic deformation from plastic deformation. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 2471–2479, 1997     

Analysis of the variation of molecular parameters of NR during vulcanization in the frame of the conformational tube model

The network structure of natural rubber (NR) achieved during vulcanization was analyzed using the model of rubber elasticity based on the tube concept, applied to the treatment of the stress-strain measurements. This theory allows the separation of constraint and crosslink contributions. Also, network parameters can be calculated. The crosslink level of the material was changed using different times and temperatures of cure. The change in the molecular parameters of the model with the degree of cure was estimated. The present research is useful for the precise determination of the chemical crosslink density of the NR network. The values were compared with those obtained by means of equilibrium volume swelling measurement. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1085–1092, 1997     

Analysis of variation of molecular parameters of natural rubber during vulcanization in conformational tube model. II. Influence of sulfur/accelerator ratio

A natural rubber (NR) with a conventional sulfur cure system and a ratio of sulfur/accelerator (Ω) equal to 3 was investigated. The network structure of the NR during vulcanization was analyzed using a model of rubber elasticity based on the tube concept, which was applied to the treatment of the stress–strain measurements. The influence of cure time and temperature on the chemical crosslinks density was analyzed. The values were compared with those obtained by means of an equilibrium volume swelling measurement. The differences between samples of NR cured with Ω = 3 and 1.5 were analyzed. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2747–2755, 1999     

Pore memory of macroporous styrene–divinylbenzene copolymers

The variation of the pore structure of styrene–divinylbenzene (S–DVB) copolymer beads with the drying conditions was investigated. Macroporous S–DVB copolymer beads with various DVB contents were prepared in the presence of toluene‐cyclohexanol mixtures as a diluent. It was found that the pores of 10¹‐nm radius, corresponding to the interstices between the microspheres, collapse upon drying of the copolymers from toluene. The collapsed pores reexpand if the copolymers were dried from methanol. The collapse–reexpansion process of the pores was found to be reversible, indicating that the actual pore structure formed during the crosslinking copolymerization is memorized by the copolymer network. The magnitude of the pore structure variation increased on worsening the polymer–diluent interactions during the gel formation process due to the simultaneous increase in crosslink density distribution. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1055–1062, 1999     

马来酸酐改性蓖麻油制备交联型水性聚氨酯

以马来酸酐与蓖麻油制备含碳碳双键的三羧基蓖麻油(MACO)作为内交联剂,合成改性蓖麻油水性聚氨酯乳液(MACO-WPU)。采用FT-IR和XRD对改性聚氨酯的结构进行表征,证实MACO被成功引入到聚氨酯大分子链中且分子链呈现无序状态。通过对力学性能、吸水率、粒径、热重分析等研究了MACO用量对聚氨酯乳液及胶膜性能的影响,结果表明:当w(MACO)=3%时,乳液外观和稳定性好,平均粒径为48.45 nm; 胶膜的拉伸强度和断裂伸长率分别为13.15 MPa、195%;与未改性WPU相比热稳定性略有提高。     

添加剂改性壳聚糖膜性能的研究进展

壳聚糖膜具有良好的吸附性、抗菌性、生物相容性和生物降解性,因此应用非常广泛。通常交联剂能有效地提高壳聚糖膜的机械性能,减缓壳聚糖的降解速率和影响壳聚糖膜的吸附性;增塑剂可以改善壳聚糖膜的柔韧性,降低机械强度。壳聚糖与酯类复合,与高聚物共混改性,也可以明显改善壳聚糖膜的性能。本文综述了不同添加剂对壳聚糖膜的机械性能、吸附性和生物可降解性等的影响。     

纳米氧化锌对天然胶乳膜干燥及硫化性能影响研究

采用失重法和溶胀法研究了普通氧化锌和纳米氧化锌活化的天然胶乳膜的干燥动力学,以及干燥过程中胶乳膜交联密度变化.结果表明:天然胶乳厚胶膜在成膜后仍含有大量水分并且去除困难.纳米氧化锌活化胶膜的干燥速率明显高于普通氧化锌胶膜.干燥温度对干燥过程影响显著,干燥时间随干燥温度升高明显降低.随着干燥的进行,2种氧化锌活化的胶乳膜的交联密度均迅速上升,在相同条件下,纳米氧化锌活化胶乳膜交联密度均比普通氧化锌的大.纳米氧化锌对天然胶乳膜的干燥及硫化过程均有促进作用.     

MOLECULAR WEIGHT EFFECTS OF THE SOFT SEGMENT ON THE ULTIMATE PROPERTIES OF LIGNIN-DERIVED POLYURETHANES

Polyurethane (PU) films were prepared by solution casting using a three-component system, namely a novel semi-rigid solvolytic lignin, soft segment and a co-monomer. In the present study, the effects of varying the chain length of polyethylene glycol (as the soft segment) were investigated to produce lignin-based polyurethanes with variable thermal and mechanical properties. An important objective was to incorporate as much lignin as possible. The polyethylene glycol (PEG) studied included 5 different molecular weights (200, 400, 1000, 1500 and 2000 g/mol). The polyurethane films, prepared by solvent casting, were evaluated for crosslink density, and ultimate mechanical and thermal properties. Results showed that the films derived from the PEG 200 were either too weak or brittle to be tested. It was found that the PEG (400, 1000, and 1500) are better choices for producing polyurethanes from the solvolysis lignin studied. Crosslink densities of PU films using the 400, 1000 and 1500 were determined to be in the range of 0.8–2.6 mmol/cm³, which is a lower range than those of films from PEG 2000, namely 2.4–2.8 mmol/cm³. Also, the ultimate tensile strength decreased from about 50 MPa at high lignin content for PEG 400, 1000 and 1500 to about 18 MPa for PEG 2000 at low content of lignin. Ultimate strain also decreased from the 30.9–62.7% range for the PEG 400 to 1500 series at low lignin content down to about 4% for PEG 2000 at high lignin content. Young's Modulus varied from a high of 2 GPa (PEG 400, lignin content = 30 wt%) down to 0.6 GPa (PEG 2000, lignin content = 20 wt%). The glass transition temperature was found to decrease from 108°C to about 45°C with increasing molecular weight of PEG for a lignin content of 30 wt% and an NCO/OH of 1.2. The data are consistent with the percolation theory approach to network formation, as well as the notion that the network itself consists of relatively large and stiff islands, each comprising many branch points, held together by a soft and pliable matrix.