聚氨酯的后交联研究进展

通过交联可以将线型聚合物连接成三维网状结构,适度交联后聚氨酯的拉伸强度、模量、耐溶剂性、耐高温性等许多性能都能得到大幅提高,而交联方法、交联的种类及交联密度的大小都是重要的影响因素,因此对交联方法、交联密度的测定、交联密度与聚氨酯性能之间的关系研究对于聚氨酯的质量控制非常重要。本文首先详细介绍了聚氨酯后交联的常用方法,然后对聚氨酯交联密度的测定方法进行了分析比较,在此基础上进一步介绍了国内外关于聚氨酯交联密度与其性能的关系方面的研究进展。     

可生物降解交联聚合物的研究进展

交联聚合物具有稳定的三维网络结构,可以提高药物缓释载体的尺寸稳定性。本文综述了可生物降解交联聚合物的研究进展,主要介绍了可生物降解交联聚合物的制备方法,包括交联剂交联、辐照交联、光致交联以及过氧化物交联在制备可生物降解交联聚合物中的应用,详细介绍了交联剂的种类及结构对交联效果的影响、交联后聚合物性能的变化等。最后总结了可生物降解交联聚合物在组织工程支架、药物缓释材料、神经再生修复材料以及形状记忆材料等生物医用领域的应用。     

新型环氧生物降解交联剂的制备及交联壳聚糖膜的性能

新型环氧生物降解交联剂的制备及交联壳聚糖膜的性能;生物降解材料;环氧;交联剂;壳聚糖     

硬链段浓度对RIM交联聚氨酯结构和性能的影响

用l-MDI/1,4-BDO/PPO-EO快反应体系,考察硬段浓度对聚氨酯结构与性能的影响。发现样品的交联度、模量和抗张强度随硬段浓度增加而提高,交联趋向均匀,断裂伸长率在浓度30％处出现最大值。ATR-FTIR和DSC分析表明,微相分离程度随硬段浓度增大而降低。     

高醚化三聚氰胺甲醛树脂交联水性聚氨酯的制备与表征

合成了高醚化三聚氰胺甲醛树脂(HMMM)交联改性含聚乙二醇单甲醚(Ymer N120)亲水基团的阴离子型水性聚氨酯。 通过全反射红外(ATR-FTIR)、差示扫描量热仪(DSC)、电子拉力机等技术手段表征了改性后的水性聚氨酯胶膜结构、热性能和力学性能。 结果表明,随着HMMM质量分数的增加,聚氨酯胶膜中氢键相互作用减弱,胶膜耐热性、耐水性、拉伸强度、粘接性均有所提高;当HMMM为8%时,聚氨酯胶膜的拉伸强度增加了125%,T-型剥离强度增加了7.4 N/cm,硬段最大热分解速率对应温度增加了38 ℃。 此外,交联水性聚氨酯胶膜的耐水性也得到了很大程度的提高。     

对苯二异氰酸酯基聚氨酯弹性体交联度对其形态与摩擦性能的影响

聚氨酯弹性体的摩擦性能在诸如船舶、汽车、生物医用等领域具有十分重要的意义,而通过化学修饰策略实现该类材料摩擦性能的精细设计,仍具有十分迫切的研究需求和广泛的应用前景。 本工作以对苯二异氰酸酯(PPDI)与聚四氢呋喃醚二醇(PTMG)为原料,通过调节1,4-丁二醇与三羟甲基丙烷两种扩链交联剂的混合比例,采用预聚体法合成了具备不同交联度的PPDI基聚氨酯弹性体。 其中,傅里叶变换衰减全反射光谱(FTIR-ATR)、广角X射线衍射(WAXD)、差示扫描量热仪(DSC)等表征结果表明,聚氨酯弹性体中硬段和软段的结晶度随交联度的提升均呈下降趋势。 同时,力学测试表明,材料的弹性模量随之降低,而PPDI基聚氨酯弹性体摩擦系数则明显增大。 此外,滞后回环曲线表明,交联度的改变影响了PPDI基聚氨酯弹性体的阻尼特性,而聚氨酯弹性体阻尼的差异在其摩擦性能对速率的依赖关系中则有所体现。 本工作由此提出,利用不同交联度下PPDI基聚氨酯中软硬段结晶度的变化,在对材料弹性模量和损耗模量进行可控调节的同时,能够实现对其摩擦性能的改变,为PPDI基聚氨酯弹性体的摩擦性能调控提供了一种简单有效的途径。     

二氧化碳共聚物为基的聚氨酯生物降解性能研究

以CO2为起始物合成出聚碳酸亚乙酯（PEC）二醇，进而合成以PEC为预聚物的聚氨酯。对该聚氨酶的力学性能、降解性能等进行了测试。结果表明，该聚氨酯同时具有良好的力学性能和良好的生物降解性能。     

侧链为光敏感基团的可生物降解聚氨酯的合成及表征

设计合成2-甲基-2-肉桂酰氧甲基-1,3-丙二醇(MCO)作为扩链剂,并以聚乳酸二醇(PLA diol)为软段,异佛尔酮二异氰酸酯(IPDI)和MCO为硬段制备了一系列侧链含有肉桂基团的可生物降解聚氨酯.结果表明MCO具有较高的反应活性,可满足制备高分子量聚氨酯的要求.聚氨酯结构中的肉桂双键可在紫外光和光引发剂的共同作用下,发生快速的交联反应,短时间内形成交联结构.软段结构相同时,凝胶含量随MCO含量的增加而增加.硬段结构相同时,凝胶含量随软段分子量的增加而减少.适度的交联可提高拉伸强度和形变回复率.     

交联聚氨酯水分散体的合成

将硅氧烷封端的含亲水基团的线性聚氨酯预聚体分散于水中 ,获得稳定的聚氨酯分散体 .由于硅氧基团水解、缩合 ,在分散体粒子内产生扩链交联反应 ,生成了交联水基聚氨酯分散体 .透射电子显微镜研究表明分散体粒径小、分布宽 .扫描电子显微镜研究了成膜结构及成膜性能与粒径的关系 .溶胀实验计算获得的两交联点之间的平均分子量与理论平均分子量相符 .研究还发现此分散体膜在干燥过程中可进一步交联 .膜的水溶胀及机械性能表明 ,此分散体具有极大的工业应用价值 .     

基于抗菌性壳聚糖/羧甲基纤维素复合药物涂层的聚氨酯敷料

以抗菌性壳聚糖和羧甲基纤维素为涂层主体材料,通过层层自组装成膜技术,利用抗菌性苦参碱为功能药物,构建了基于抗菌性壳聚糖/羧甲基纤维素复合药物涂层的聚氨酯敷料。再通过分子间化学交联改变了聚合物内部结构,提升涂层的机械稳定性。分别在硅片和聚氨酯敷料上成功制备了复合药物涂层。在模拟的生理条件下,分析了交联(CHI/CMC)₂₅涂层、空白聚氨酯基底和交联(CHI/CMC)₁₀涂层修饰的聚氨酯基底对苦参碱的药物装载和释放性能,三者的载药量分别为27.8、285.2和330.0μg/cm²。相较于交联(CHI/CMC)₂₅涂层和空白聚氨酯基底,聚氨酯基底(CHI/CMC)₁₀交联涂层的载药量分别提升了10.9倍和20%,聚氨酯基底不仅具有良好的药物装载能力,还具有延缓药物释放速度的作用。交联(CHI/CMC)₁₀涂层可以增强基底的力学性能,相较于原始的聚(对苯二甲酸乙二醇酯-1,4-环己二烯二亚甲基对苯二甲酸酯)(PETG)板,PETG板-交联(CHI/CMC)     

Filler-elastomer interactions: influence of silane coupling agent on crosslink density and thermal stability of silica/rubber composites

In this work, the crosslink density and thermal stability of the silica/rubber composites treated by silane coupling agents, i.e., gamma-aminopropyl triethoxysilane (APS), gamma-chloropropyl trimethoxysilane (CPS), and gamma-methacryloxypropyl trimethoxysilane (MPS), were investigated. The chemical structures of modified silicas were studied in term of solid-state 29Si NMR spectroscopy. The crosslink density of the composites was determined by swelling measurement. The development of organic functional groups on silica surfaces treated by coupling agents led to an increase in the crosslink density of the composites, resulting in increasing final thermal stability of the composites. The composites treated by MPS showed the superior crosslink density and thermal stability in these systems. The results could be explained by the fact that the organic functional groups of silica surfaces by silane surface treatments led to an increase of the adhesion at interfaces between silicas and the rubber matrix.     

The effects of crosslink density and crosslink type on the tensile and tear strengths of NR,SBR and EPDM gum vulcanizates

The effects of crosslink density and crosslink type on the tensile and tear strengths of gum NR, SBR and EPDM vulcanizates have been studied. Over a wide range of crosslink densities, sulphur vulcanizates for these rubbers have higher strengths than the peroxide vulcanizates. These results show that crystallizability of the rubbers is not an important factor in producing separate curves in the strength vs crosslink density plots. Tear strengths appear to be more sensitive to crosslink structures than tensile strengths. A composite plot shows that tensile strengths are approximately proportional to tear strengths for all three rubbers.     

Modelling of crosslinking and cyclization in free-radical copolymerization of vinyl/divinyl monomers

The Tobita-Hamielec kinetic model of the crosslink density distribution is further elaborated and extended to incorporate divinyl loop formation. Divinyl loop formation, primary and secondary cyclization, and their effects on the elastically effective crosslink density distribution are extensively examined as a function of cyclization parameters and double bond reactivities. Under conditions of equal double bond rectivity and negligible cyclization, primary chains born at different conversions have the same crosslink density. The variance of the crosslink density distribution is mainly due to unequal reactivities of double bonds and secondary cyclization. Divinyl loop formation and primary cyclization contribute neither to gelation nor to network elasticity and have an insignificant effect on the variance of the crosslink density distribution.     

Effect of crosslink density on some properties of electron beam-irradiated styrene–butadiene rubber

Crosslink densities of electron beam (EB)-irradiated styrene–butadiene rubber (SBR) samples were measured by using a novel magnetic resonance crosslink density spectrometer (MRCDS). With 1,1,1-trimethylolpropane triacrylate (TMPTA) loading increasing, the crosslink density of EB-irradiated SBR increases up to a certain level, and then decreases in the irradiation dose range 50–200 kGy. Tensile strength, elongation at break, thermal stability and pyrolysis products of the EB-irradiated SBR samples with different crosslink densities were also studied in this paper.     

Influence of microstructure on the tensile behavior of acrylic copolymers

Uniaxial tensile properties were determined for two series of copolymers: ethyl acrylate–acrylic acid and butyl acrylate–acrylic acid. The comonomer ratio was varied from 85/15 to 95/5 and various molar ratios of a difunctional carboxylate epoxy crosslinker were used. The master modulus curves indicated that increasing the amount of crosslinker and/or increasing the number of crosslink sites per chain caused both the equilibrium modulus and the transition temperature to increase while increasing the bulk of the side groups decreased both the modulus and transition temperature. All the master ultimate strain curves exhibited a maximum value corresponding to some value of reduced time τ_c and exhibited a shape analogous to a lognormal distribution function with nonzero asymptotes. The maximum ultimate strains were found to be a nonlinear function of the crosslink density and to occur at higher values of temperature and/or lower values of strain rate when either the amount of crosslinker or the relative frequency of the crosslink sites increased. Replacing the pendant ethyl group with a butyl group caused the maximum ultimate strains to occur at temperatures about 60°F lower than the corresponding ethyl acrylate copolymer. This replacement also decreased the magnitudes of the maximum ultimate strains associated with the same crosslink density. It was concluded that the chemical efficiency of the crosslink sites decreases with decreasing relative frequency of the crosslink sites along the prepolymer. Furthermore, the crosslink efficiency decreased as the length and flexibility of the nonreactive side groups increased. The dependency of the actual crosslink density was found to be critically influenced by the chemical crosslink efficiency. A molecular model involving both chain entanglements and chemical corsslinks is postulated which explains qualitatively the observed behavior of the master ultimate strain data.     

Effects of the type of crosslink on viscoelastic properties of natural rubber

The viscoelastic properties of various crosslinked natural rubbers, NR, were investigated by mechanical spectroscopy. The glass transition temperature, T_g, was found to be dependent on both the crosslink density and the crosslink type. Higher values of T_g were obtained for sulfur-crosslinked NR than for peroxide-crosslinked NR at the same crosslink density. The greater influence of the sulfur content on T_g may be attributed to polysulfidic crosslinks and cyclic sulfide structures favored at high sulfur contents. Sulfur-vulcanized NRs with monosulfidic crosslinks, favored at relatively high accelerator/sulfur ratios, have properties more similar to the peroxide-cured NR with simple carbon(SINGLE BOND)carbon crosslinks covalent bonds, resulting in only small shifts in T_g. A qualitative analysis of monosulfidic crosslinks and polysulfidic structures was performed with ¹³C solid-state NMR spectroscopy. The storage modulus, E′, in the rubbery plateau region increased with increasing crosslink density. However, the crosslink type did not influence the moduli values as much as it influenced the T_g values. Different methods of detecting the crosslink density were also discussed. © 1996 John Wiley & Sons, Inc.     

Pyrolysis-mass spectrometry correlations of crosslink density in natural rubber vulcanizates

A set of twelve natural rubber vulcanizates was analyzed by Curie-point pyrolysis-mass spectrometry (Py-MS). Multivariate analysis successfully correlated the Py-MS data with either total or polysulfidic crosslink density measurements. (Polysulfidic means two or more sulfurs.) The principal correlation observed was an increase in the ratio of monomer to dimer pyrolyzate yield with an increase in crosslink density. The feasibility of using Py-MS for total crosslink density determination has thus been demonstrated. The Py-MS data, however, did not allow us to distinguish different types of crosslinks.     

Chemorheology of allophanate-cured polyurethane rubber

Chemical stress relaxation (CSR) of allophanate-cured polyurethane (PU) was measured under two kinds of degradation conditions: (1) degradation in butylamine (BuNH₂)/dimethyl sulfoxide solution; (2) degradation at high temperature in nitrogen. The allophanate groups of the crosslink sites in PU networks are selectively cleaved by BuNH₂, and CSR is not influenced by the crosslink density within experimental error. This suggests the validity of Tobolosky's method for distinguishing between random scission along network chains and the cleavage of crosslinks from the dependence of CSR on crosslink densities. In addition, CSR of PU samples degraded at high temperature in nitrogen was also found to be independent of the crosslink density. It follows that thermal degradation of PU networks occurs by the cleavage of crosslink sites in the same manner. CSR is compared with the relative degree of thermal degradation of PU sample, determined by-the amine-decomposition method and the swelling method. Consequently, the total (or residual) crosslink density of degraded PU networks corresponds essentially to the intermittent CSR.     

The relationship between crosslink system, network structure and material properties of carbon black reinforced EPDM

The crosslink density and sulfur-ranks of crosslinks formed during vulcanization of a carbon black reinforced ENB–EPDM compound are analyzed as a function of the selected curing system: Conventional, Semi-Efficient, Efficient and Nitrosamine-safe. Each vulcanization system results in a specific crosslink concentration and sulfur-rank distribution: mono-, di- and polysulfidic of nature. Tensile properties, tear strength and compression set of the vulcanized materials turn out to practically only depend on overall crosslink density, as resulting from the particular curing systems and vulcanization times. All trends in properties coincide when plotted as a function of the overall crosslink density. Surprisingly, the crosslink distribution: the ratios of mono- to di- and polysulfidic crosslinks, has only a minor effect on these properties. The differences in sulfur-rank as a function of the chosen vulcanization system turn out to be too small for EPDM to have a significant effect.