摘要:

AbstractThis question was addressed using various methods to monitor the process of curing and state of the final network. Attention was particularly focused on the possible inhomogeneous network formation as a consequence of the crosslinking process. An analysis of experimental data has revealed that some cured resins can be considered as homogeneous as the corresponding uncrosslinked materials. Resins cured by simple stepwise alternating chemistries, with good compatibility of components, usually fulfill the criterion of homogeneity. A family of epoxy resins cured with polyamines belongs to this category. Nodular structures seen by electron microscopy are a result of interaction of the electron beam or etching. Such structures are also observed for uncrosslinked polymers investigated under the same conditions. Formation of inhomogeneities in a number of thermoset systems is due to (a) chainwise mechanism of network formation with fast propagation inducing cyclization and steric volume exclusion and (b) poor compatibility of components of the system made stronger by increasing molecular weights and crosslinking during curing. Networks formed by freeradical polymerization and copolymerization of polyvinyl monomers can serve as an example of crosslinking‐driven formation of inhomogeneitie

ISSN:0003-3146    

DOI:10.1002/apmc.1996.052400101

出版商:Hüthig&Wepf Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractAn Aramid‐CTBN block copolymer was added to a Bisphenol‐A type epoxy resins modified with CTBN. With the addition of the copolymer, the impact strength of the CTBN‐modified systems was about twelve times higher than that of the unmodified system. Transmission electron micrographs of the block copolymer‐epoxy system showed that the diameter of CTBN‐dispersed phase decreased and a number of fine CTBN phases were dispersed in the matrix. The deformability of matrix in these systems increased with a dispersion of the fine CTBN phase. It is concluded that the improvement of toughness of the cured resins is due to the increases in the ductility of epoxy matrix by the incorporating of the dispersion of the fine CTBN phase in t

ISSN:0003-3146    

DOI:10.1002/apmc.1996.052400102

出版商:Hüthig&Wepf Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractThe Young's modulus E and Poisson's ratiovof various thermosets, including 6 amine crosslinked epoxies, one anhydride crosslinked epoxy, one styrene crosslinked polyester and one styrene crosslinked vinylester, were determined from tensile tests in the 220–393 K temperature range and 1.6710−4−1.6710−2s−1strain rate range. The bulk (B) and shear (G) modulus were calculated from E andv. Some observations about structure‐property relationships can be derived from these data and their comparison with corresponding ones relative to linear polymers. B appears to depend essentially of the cohesion and packing density and does not depend, practically, of temperature and strain rate. In contrast, G depends sharply of the local molecular mobility, this latter being affected by an antiplasticization mechanism. The Poisson's ratio seems to be systematically higher for thermosets than for line

ISSN:0003-3146    

DOI:10.1002/apmc.1996.052400103

出版商:Hüthig&Wepf Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractA new Monte Carlo (MC) algorithm is reported which enables RAfa+RBfbpolymerisations to be simulated. It is based on the random reaction of pairs of groups for intermolecular reaction, with intramolecular reaction weighted according to Gaussian statistics and the size of ring structure being formed. The algorithm countsallthe ring structures formed and enables polymerisations to be simulated efficiently up tocompletereaction. Gel point and modulus results from trifunctional and tetrafunctional polyurethane‐forming polymerisations are modelled, with particular emphasis on the effects on modulus of network defects at complete reaction. More in keeping with experiment, higher reductions in modulus at complete reaction are predicted using the the present algorithm than using Biosym MC software. However, it is shown that quantitative agreement with experiment cannot be obtained unless relationships defining the entropies of various ring structures are elucidated and more accurate modelling of the chain statistics governing the intramolecular reaction forming ring structures of various sizes is use

ISSN:0003-3146    

DOI:10.1002/apmc.1996.052400104

出版商:Hüthig&Wepf Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractThe attractive physical properties of cyanate ester resins make these materials an important class of high‐performance polymer thermosets for applications such as electro‐optic coatings and thin film dielectrics. Triazine networks have been used as insulating materials for over 25 years; however, in order to meet future requirements such materials must exhibit appropriate glass transition temperatures, high thermal stability, high moduli, good adhesion at elevated temperatures, low dielectric losses, and a low coefficient of thermal expansion (CTE). With our approach to thermoset design and processing we are able to directly control their mechanical and physical properties by curing new liquid crystalline cyanate ester resins in electric fields. Combining new LC materials with non‐LC cyanate monomers leads to a variety of novel ordered network structures and is a convenient method for modifying and controlling their chemical and physical properties. Studies of the new LC thermosets and their mixtures with non‐LC materials will be de

ISSN:0003-3146    

DOI:10.1002/apmc.1996.052400105

出版商:Hüthig&Wepf Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractStandard epoxy resins have good mechanical properties, but their prolonged low temperature curing time limits their potential use in clinical applications as well as in many industrial applications. A fast‐curing epoxy‐episulfide resin has been developed. The gel time of epoxy‐episulfide made from EPONTrade mark of Shell Chemical Company.828 ranges from 2 to 10 minutes by changing the ratio of the ingredients. The heat of reaction of this system is low, resulting in low cure shrinkage. Water absorption of the episulfide network is low. The epoxy‐episulfide system cured with polyamide curing agent V‐40exhibits two transition temperatures, at about 85°C and 130°C, as shown in dynamic mechanical analysis data. In order to solve the long term stability problem of the above episulfides, and also the mixing problem, a lower viscosity resin, Eponex, was used to make Eponex‐sulfide. Eponex‐sulfide systems show promise in that they remain in a stable liquid form without epoxy. The other advantages appear

ISSN:0003-3146    

DOI:10.1002/apmc.1996.052400106

出版商:Hüthig&Wepf Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractThe base and transition metal catalyzed isomerization of allyl and crotyl ethers affords a facile, high yield route to the preparation of a variety of mono‐, di‐, and multifunctional 1‐propenyl and 1‐butenyl ethers. Employing this novel method, monomers containing epoxide, ester, ether carbonate and urethane groups can be prepared from their readily available allyl and crotyl precursors. In general, these monomers display very high reactivity in cationic polymerizations. In our work, we have focused on photoinduced cationic polymerizations of these monomers using diaryliodonium and triarylsulfonium salt photoinitiators. To study these very fast photopolymerizations, extensive use of real‐time infrared spectroscopy was made. Employing this technique, the effects of monomer and photoinitiator structure on the rates of polymerization wer

ISSN:0003-3146    

DOI:10.1002/apmc.1996.052400107

出版商:Hüthig&Wepf Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractThe present investigation concerns acrylic/silicone polymer networks formed by the hydrosilylation reaction. Acrylic polymers containing alkenyl groups have been obtained by radical polymerization of a monomer having an alkenyl group and other vinyl monomers. Also a silicone polymer containing SiH groups has been prepared by the equilibrium reaction in presence of sulfuric acid. They are compatible with each other and can be crosslinked by the hydrosilylation reaction. The cured films are approximately of uniform structure and their acid resistance is excellent.

ISSN:0003-3146    

DOI:10.1002/apmc.1996.052400108

出版商:Hüthig&Wepf Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractStructure and properties of microgels prepared by emulsion copolymerization depend on the composition and concentration of the monomers at the reaction sites, on the reactivity ratios and on the solubility of the comonomers in water. By separate and joint solubilization of 1,4‐divinyl benzene and various comonomers of different solubility it could be shown, that the diffusion control of the copolymerization rate is favoured by crosslinking, by a high concentration of an oil‐soluble initiator and of the emulsifier and by a low solubility of the comonomer in wa

ISSN:0003-3146    

DOI:10.1002/apmc.1996.052400109

出版商:Hüthig&Wepf Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractThis paper describes studies on the formation of microgels from high functionality mixtures of monomers which are able to polymerise by a step‐growth process to polyurethanes in the specially selected solvent butan‐2‐one. Using the reactants poly(ethylene glycol) 6000, 1,2,6‐hexanetriol and biscyclohexylmethane‐4,4′‐diisocyanate in formulations made to comprise exactly one isocyanate group per hydroxyl, it was found that microgels of number average molecular weight, as determined by Gel Permeation Chromatography, of less than 20,000 were obtained up to the Critical Gelation Concentration which ranged from w/w reactant to solvent concentrations of from ∼ 0.24 to 0.74 at PEG/HT ratios of 1:4 to 4:4 respectively. These polymerisations surprisingly, went to complete conversion without gelation and produced 95 – 99% yields of microgel product after precipitation into a non‐solvent. Intrinsic viscosity determinations on the microgels dissolved in chloroform were determined and used to obtain estimates of the swollen coil densities at infinite dilution from which the critical packing concentration of these swollen coils in the solvent used for the solvent could be estimated. The critical packing concentration was in all cases well below the Critical Gelation Concentration. It was thus clearly demonstrated that the formation of “soluble” microgels is progressing in spite of the system being critically packed. This is a surprising observation and especially so when it is combined with the very low measured weight average molecular weights and high conversions of the products in the critically packed region. The GPC molecular weights decreased at the higher concentrations which is contrary to expectations. The ability to form microgels above critical packing confirms the results obtained and reported previously by us, that a similar phenomenom occurs in the case of the polymerisation of polyfunctional free‐radically polymerised monomer systems. These observations will need to be taken into account when formulating mathematical analyses of the gelation process. This class of products are able to be crystallised from organic solvents and are soluble in water. They are potentially useful as components of pharmaceutical formulations for the controlled release of drugs, high molecular weight active materials

ISSN:0003-3146    

DOI:10.1002/apmc.1996.052400110

出版商:Hüthig&Wepf Verlag    

年代:1996

数据来源: WILEY