交联网络和浓溶液中高分子链运动的NMR研究：Ⅲ.质子自旋—晶格 …

用自旋－晶格弛豫研究了溶胀的交联聚丙烯酰胺－丙烯酸网络和线型聚苯乙烯溶液中质子的弛豫行为。交联网络中，随着交联度增大，Ｔ１ＣＨ／Ｔ１、ＣＨ２的值由１．１７逐渐趋于１；，而线型聚苯乙烯溶液中，Ｔ１ＣＨ／Ｔ１ＣＨ２的的值由最稀浓度下的１．７过渡到１。     

交联网络和浓溶液中高分子链运动的NMR研究 Ⅱ质子自旋-自旋弛豫与凝胶和浓溶液体系中高分子链段运动

用自旋－自旋弛豫时间考察了线型聚苯乙烯溶液与溶胀交联聚丙烯酰胺－丙烯酸凝胶的质子弛豫行为。发现在溶胀交联体系中，不论交联度高低，聚丙烯酰胺－丙烯酸质子的弛豫时间弛豫都呈现出双指数衰减特征；而在线型溶液体系中，聚苯乙烯质子的弛豫时间弛豫符合单指数衰减特征。说明在线性聚苯乙烯溶液中，高分子的链段运动是一种均匀行为，而在溶胀交联聚丙烯酰胺－丙烯酸体系中，不论交联度高低，高分子链段运动始终存在快慢不同的两部分。     

交联网络和浓溶液中高分子链运动的NMR研究：Ⅱ质子自旋—自旋？…

用自旋－自旋弛豫时间考察了线型聚苯乙烯溶液与溶胀交联聚丙烯酰胺－丙烯酸凝胶的质子弛豫行为。发现在溶胀交联体系中，不论交联度高低，聚丙烯酰胺－丙烯酸质子的弛豫时间弛豫都呈现出双指数衰减特征；而在线型溶液体系中，聚苯乙烯质子的弛豫时间弛豫符合单指数衰减特征。     

交联网络和浓溶液中高分子链运动的NMR研究：I.NMR质子线型分析

用质子ＮＭＲ谱对交联凝胶高分子（聚丙烯酰胺－丙烯酸）网络与线型高分子（聚苯乙烯）浓溶液体系的ＮＭＲ线型进行了比较研究，结果表明，两种体系中高分子链段运动具有不同的特征。在充分溶胀的交联凝结胶高人子网络中，交联点间的链段运动比较自由，交联点的运动则比较慢，使其质子谱呈现“超洛伦兹”线型；而在线型高分子浓溶液中，缠结点间链段与缠结点一样，运动并不自由，使谱线呈现出类似固体的宽线宽的高斯线型。     

交联网络和浓溶液中高分子链运动的NMR研究Ⅰ.NMR质子线型分析

用质子ＮＭＲ谱对交联凝胶高分子（聚丙烯酰胺－丙烯酸）网络与线型高分子（聚苯乙烯）浓溶液体系的ＮＭＲ线型进行了比较研究。结果表明，两种体系中高分子链段运动具有不同的特征：在充分溶胀的交联凝胶高分子网络中，交联点间的链段运动比较自由，交联点的运动则比较慢，使其质子谱呈现“超洛伦兹”线型；而在线型高分子浓溶液中，缠结点间的链段与缠结点一样，运动并不自由，使谱线呈现出类似固体的宽线宽的高斯线型     

辐射交联顺1,4-聚丁二烯的NMR研究

用１３Ｃ ＮＭＲ方法,测定了辐射交联顺１,４ 聚丁二烯在室温下的自旋 晶格弛豫时间（Ｔ１）,核Ｏｖｅｒｈａｕｓｅｒ因子（ＮＯＥ）,和１３Ｃ ＮＭＲ线宽．以及凝胶本体１Ｈ ＮＭＲ的Ｔ１和Ｔ２弛豫时间,结果表明,辐射交联顺１,４ 聚丁二烯体系中,随着凝胶含量的增加各碳核质子的Ｔ１值变化很小,而—ＣＨ２—核的ＮＯＥ因子明显降低和１３Ｃ ＮＭＲ线宽增宽．以及１Ｈ ＮＭＲ的Ｔ１和Ｔ２表现的双指数弛豫特性反映了交联体系中大分子链段长程运动受阻以及饱和交联叔碳核—ＣＨ对链段运动的影响．     

辐射交联顺1,4-聚丁二烯的NMR研究

用１３ＣＮＭＲ方法,测定了辐射交联顺１,４聚丁二烯在室温下的自旋晶格弛豫时间（Ｔ１）,核Ｏｖｅｒｈａｕｓｅｒ因子（ＮＯＥ）,和１３ＣＮＭＲ线宽．以及凝胶本体１ＨＮＭＲ的Ｔ１和Ｔ２弛豫时间,结果表明,辐射交联顺１,４聚丁二烯体系中,随着凝胶含量的增加各碳核质子的Ｔ１值变化很小,而—ＣＨ２—核的ＮＯＥ因子明显降低和１３ＣＮＭＲ线宽增宽．以及１ＨＮＭＲ的Ｔ１和Ｔ２表现的双指数弛豫特性反映了交联体系中大分子链段长程运动受阻以及饱和交联叔碳核—ＣＨ对链段运动的影响．     

高聚物溶液中大分子链尺寸的研究（Ⅲ）—一种测算高分子…

将高聚物溶液中大分子链尺寸对浓度的依赖关系与Ｚｉｍｍ稀溶液第二维里系数的统计力学硬球模型相结合，借助聚合物的特性粘数、Ｍａｒｋ－Ｈｏｕｗｉｎｋ方程或分子量，计算聚合物－溶剂体系在稀溶液浓度范围内π／Ｃ或Ｈ·Ｃ／τ的模拟实验值。再以π／Ｃ或Ｈ·Ｃ／τ与浓度线型回归中的始斜率求体系的第二维里系数Ａ２，计算了３０种聚合物－溶剂体系的２９５个不同分子量的Ａ２值，结果均与其实验值吻合较好，且明显优于其它理论     

用核磁共振方法研究弱交联高分子体系的微观运动状态及微观结构特征

用核磁共振１３Ｃ自旋－自旋弛豫时间Ｔ２表征了以离子微区为表观交联点的以甲基丙烯酸丁酯－丙烯酸共聚物为基础的弱交联高分子体系的微观链运动特征，及体系中溶剂分子的运动特征，结果表明：聚合物主链表现为快、慢两种运动状态，聚合物体系存在多相结构；溶剂分子也表现出两种不同的运动状态，从而间接反应了聚合物体系的微观结构。     

交联共聚丙烯酰胺-丙烯酸水凝胶溶胀态分子动力学的NMR弛豫研究

用反相悬浮聚合法制备了交联度分别为10％、7．5％、5％、1％、0．5％及0．25％的丙烯酰胺-丙烯酸P（AAM－NaAA）交联共聚水凝胶，用HNMR驰豫方法测定了水及聚合物主链上（－CH2CH－）基团中质子的自旋-自旋驰豫时间（T2），并结合质子线型分析，研究了交联凝胶在溶胀态下的内部分子运动，讨论了不同交联度下谱线线宽及驰豫变化的机制。结果表明，由于交联使凝胶内部各向异性相互作用增强，存在有残余的偶极-偶极相互作用，质子语具有特征的超Lorentz线型；质子线宽比非交联态时加大，水及主链的T2随交联度的加大而减小，反映了内部分子运动由强变弱的过程；水的T2驰豫不是单纯的单指数驰豫行为，表明凝胶内部有较强的键合束缚水存在，与DSC实验的结论一致。     

High-resolution NMR of crosslinked polymers: Effects of crosslinked density and solvent interaction

Measurements have been made of the dependence of nuclear magnetic resonance bandwidths of polymers on the degree of crosslinking. Poly(methyl methacrylates) and poly(hexadecyl acrylates) were studied. Three regions of behavior are apparent: (1) in lightly crosslinked materials, bandwidths are quite insensitive to the degree of crosslinking, and the networks behave almost as linear polymers in solution; (2) in moderately crosslinked material, bandwidths are significantly affected by the degree of crosslinking; and (3) in highly crosslinked materials, bandwidths are extremely sensitive to crosslink density, and the polymer peaks become so broad that they disappear almost completely. These results indicate that segmental motion of a polymer in solution is not a function solely of its molecular weight, and that a certain degree of crosslinking is required to restrict polymer motion at the segmental level. The solvent (benzene) peak is always a singlet in swollen poly(methyl methacrylate) systems with swelling ratios up to 6.4 (regions 1 and 2, above) but as the swelling ratio further decreases to 3.5 (region 3), the solvent peak splits into a doublet; this phenomenon may indicate the existence of two different arrangements of solvent molecules in the swollen network, for which interchange is not sufficiently rapid to produce a single line.     

The Effects of Polymer Properties and Solution Composition on the Distribution,Properties, and Amount of Water in Swollen Ion Exchangers

The effects of the composition and concentration of an external solution on the swelling degree of polystyrene-based ion exchangers crosslinked with different amounts of divinylbenzene have been analyzed within the heterophase model of polymer gel structure. It has been confirmed experimentally that, upon variations in the composition of the external solution, the swelling degree of polymers is determined by the content of “sorbed” water alone. Therewith, the volume of the external solution incorporated into the swollen polymer remains constant; i.e., it depends neither on an ionic form of an ion exchanger nor the concentration and composition of the external solution, but rather depends linearly on the polymer crosslinking degree. An algorithm has been proposed for calculating the volume of water in a polymer gel and some quantitative estimates have been presented.     

A comparative study on the cooperative binding of surfactants with solubilized polymers and networks

The cooperative binding of a linear as well as a crosslinked polyelectrolyte with an oppositely charged surfactant has been analyzed theoretically and experimentally. The experimental results showed that the presence of crosslinkage significantly enhances the initiation process but strongly suppresses the cooperation of the binding. In the theoretical analysis, the hydrophobic interaction has been treated using the nearest-neighbor interaction model, while the electrostatic interaction has been calculated using a rodlike model. The general formulas derived on the basis of the free energy minimum principle demonstrated that the crosslinkage enhances the initiation process but strongly suppresses the cooperation owing to the osmotic pressure in the network domain. The theoretical results showed fairly good agreement with the experimental data, confirming the essential features of the theory.     

The role of the orientation tensor in the rheology of flexible polymers

The stress-strain relations for transversely isotropic deformations of linear and branched polymer melts as well as of (crosslinked) rubbers are discussed in terms of the orientation tensor. It is shown that orientation and network strand extension are decoupled, and that the relative tube diameter and its inverse, the molecular stress function f, can be extracted directly from experimental data, if the effect of network orientation is accounted for by the order parameter. The tension of the average network strand increases with increasing deformation. This is caused by an increasing restriction of lateral movement of polymer chains due to deformation. At small strains, f² is found to be linear in the average stretch for melts as well as for rubbers, which corresponds to a constant volume of the tube. At large strains, melts show maximum molecular tension, depending on the degree of longchain branching, while rubbers show maximum extensibility.     

Molecular weight distribution in random crosslinking of polymer chains

The molecular weight distribution (MWD) of crosslinked polymer molecules formed during polymeric network formation is the sum of the fractional MWDs containing 0, 1, 2, 3, … crosslinkages. The MWD for polymer molecules containing ?? crosslinkages is investigated for the random crosslinking of polymer chains whose initial MWD is given by the Schulz-Zimm distribution. For a very narrow initial MWD, each fractional MWD with ?? = 0, 1, 2, … is independent and a multimodal distribution is obtained for the whole distribution. When the initial MWD is uniform, the average crosslinking density within the polymer fraction whose degree of polymerization is r, ρ_r is simply given by ρ_r = ρ_gel,c – 2/r irrespective of the extent of crosslinking reaction where ρ_gel,c is the crosslinking density within gel fraction at the gel point. On the other hand, the MWDs with ?? crosslinkages overlap each other with different ?? values significantly for the broader initial distributions, and ρ_r increases with the progress of crosslinking reactions. The value of ρ_r increases with increasing r but levels off asymptotically at large r. The average crosslinking density of polymer molecules containing ?? crosslinkages ρ_?? is an increasing function of k but soon reaches a plateau; sooner for the broader initial MWDs. For ?? ≥ 1, ρ_?? is always larger than the average crosslinking density of the whole reaction system ρ in the pregelation period, i.e., in terms of the crosslinking density, the difference between polymer molecules with and without crosslinkage is most significant. In general, the average crosslinking density ρ, which is convenient to use in describing the nature of the whole reaction system, cannot be considered as a characteristic degree of crosslinking for polymer molecules containing at least one crosslinkage. Consideration of the bivariate distribution of r and k reveals important aspects of the polymeric network formation that have been obscured in the conventional theories in which the averages including linear polymers are solely considered. © 1995 John Wiley & Sons, Inc.     

Interaction of crosslinked polyethylenimine with a homologous series of methyl orange derivatives in aqueous solution

Polyethylenimine (PEI) was crosslinked with dichloroethane, glyoxal, or glutaraldehyde and polymers of various degrees of crosslinkage were made. The insoluble polymers obtained were examined for their ability to bind methyl orange and its homologs, methyl, ethyl, propyl, and butyl orange at 5, 15, 25, and 35°C, respectively, in an aqueous solution. PEI crosslinked with glutaraldehyde showed markedly increased binding affinity toward these cosolutes compared with the polymers crosslinked with dichloroethane or glyoxal. The extent of the binding increased with an increase in the degree of crosslinkage. These results suggest that the enhancement of the binding by the crosslinking is due mainly to a dual effect, introduction of hydrophobic moieties and proximity of neighboring polymer chains. The first binding constants and the thermodynamic parameters that accompanied the binding were calculated. The thermodynamic data show that the binding process is athermal and is stabilized entirely by the entropy term. Water-soluble PEI exhibited stronger cooperative interactions than the crosslinked polymer because the mobilities of the chains of the former are greater than those of the latter.     

Influence of the bulk and surface morphology on adhesion of polystyrene-inter-poly-cross-2-ethylhexyl-methacrylate films and particles

The adhesion behavior of semi-interpenetrating polymer networks (semi-IPNs) of linear polystyrene (PS) in crosslinked poly-2-ethylhexylmethacrylate (EHMA) was studied by variation of the bulk and surface morphology, i.e., domain size, continuity, and concentration in the domains. Semi-IPNs were prepared by liquid-liquid demixing upon cooling of a homogeneous solution of PS in methacrylate monomer, followed by gelation of the PS-rich phase and UV polymerization of the methacrylate resin. Welding of films allowed the preparation of larger objects provided that (1) the samples were phase separated to a high degree and contained domains with a high PS concentration (>90%) and (2) polystyrene was present at the interface. For semi-IPN films, a linear dependence of the adhesion strength on the (crack healing time)^1/4 was obtained. Based on these considerations, a process was developed to obtain melt-processable semi-IPN particles, by quenching droplets of the polymer solution into a cold liquid. These particles obtained a PS-rich skin layer and showed good adhesion after blending with a thermoplast. © 1996 John Wiley & Sons, Inc.     

Anomalous freezing point depression of solvents in a swollen homogeneous rubber network

The freezing point depression of a solvent, imbibed by crosslinked polyisoprene networks, was studied. It is argued that in a swollen vulcanizate, polymer chains subdivide the solvent, creating zones too small for nucleation on cooling to occur at the normal freezing point of the solvent. The freezing point of the solvent is identified with the temperature at which nuclei can form in the swollen network. A linear relationship between freezing point and the volume fraction of rubber in the swollen gel is predicted for a uniformly crosslinked network. Such a relationship is shown to hold for gamma-irradiated polyisoprene, but not for peroxide-cured samples, where deviations from linearity are interpreted as indicative of nonuniformity in the network. © 1993 John Wiley & Sons, Inc.