ISSN:1042-7147    

DOI:10.1002/pat.1994.220051201

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractBased on previous work, where it was shown that 4‐urazoylbenzoic acid (U4A) groups, which are attached statistically to polybutadiene, form ordered supramolecular arrays in the unpolar polymer matrix, the present work describes the synthesis of a new molecular building block capable of self‐assembling in the unpolar polymer matrix. 5‐Urazoylisophthalic acid (U35A) groups attached to 1,4‐polybutadiene chains cause the formation of a thermoplastic elastomer of improved properties. The clusters of functional groups show an endothermic transition. The melting temperature increases for low levels of modification from 130°C up to 190°C. The mechanical properties (stress–strain and dynamic mechanical) reveal excellent rubbery characteristics and a rubbery plateau which is considerably flatter than those of technical grade thermoplastic elastomers. The IR data indicate that the U35A groups are tetrafunctional with respect to supramolecular self‐assembling. Based on detailed knowledge of the structure of the self‐assembled domains in U4A groups, a model is developed which describes the observed material propertie

ISSN:1042-7147    

DOI:10.1002/pat.1994.220051202

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractA series of thermotropic polyethers synthesized from 1‐(4‐hydroxyphenyl) ‐ 2 ‐ (2 ‐ methyl ‐ 4 ‐ hydroxyphenyl) ‐ ethane and α,ω‐dibromo‐n‐alkanes with odd numbers of methylene units (MBPE‐n = odd) shows monotropic mesophase behavior. In isothermal differential scanning calorimetry (DSC) experiments, two—sometimes even three—exothermic transition processes can be observed when the crystallization temperature is below the mesophase transition temperature, while only one exothermic process is present above the mesophase transition temperature. The melting behavior of the crystals grown from the mesophase and from the isotropic melt states is different. The crystals grown from the mesophase state exhibit a larger overall heat of transition and a higher transition temperature compared with those grown from the isotropic melt. This may be attributed to the molecular interfacial connections between the crystal and amorphous regions when MBPEs crystallize from the mesophase state. The difference in morphology between the crystals grown from the different states has also been studied with polarized light microscopy (PLM) and transmission electronic microscopy (TEM). The structures of the crystals grown from the different states are, however, the same, as evidenced through wide‐angle X‐ray diffraction (WAXD) measurements. From the banded morphology of MBPE samples observed from PLM, the defect textures observed through TEM and the results of WAXD experiments, this mesophase can be identified

ISSN:1042-7147    

DOI:10.1002/pat.1994.220051203

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractHeat capacities of a series of thermotropic polyethers consisting of a semiflexible mesogen [1‐(4‐hydroxyphenyl) ‐ 2 ‐ (2 ‐ methyl ‐ 4 ‐ hydroxyphenyl)ethane], with n methylene flexible spacers (n = 4–12) (MBPE‐n) have been measured by DSC and fitted at low temperature to an approximate frequency spectrum, as well as at high temperature to a general equation for the liquid MBPE‐n. The latter equation is:Cp= n(17.33 + 0.04551T) + (280.9 + 0.3839T) where n is the number of methylenes in the polyether spacer. The calculated vibration‐only heat capacities start to show deviations from the measured heat capacities below the melting temperature, reflecting contributions from conformational disorder and motion in methylene spacers. It is suggested that part of this increase in heat capacity can be looked upon as a glass transition of the partially conformationally disordered crystals. Solid state13C–NMR studies showed similarly that over the range of temperature some of the CC bonds in the spacer are in a rotational state similar to that in the melt. The equilibrium heats of fusion (ΔH 0m) and the changes of heat capacity (ΔCp) for the amorphous polymer at the glass transition temperature, Tg, were determined by WAXD and DSC. Based on the discrepancy of ΔCpit is concluded that these phenylene containing polyethers have a certain amount of rigid amorphous polymer. Thermodynamic functions H, S and G for all of the po

ISSN:1042-7147    

DOI:10.1002/pat.1994.220051204

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractPoly(dialkylsiloxane)s and poly(dialkylsilane)s form a similar type of columnar mesophase. Although, the polysilanes are stiffer than polysiloxanes, both classes of polymers may be considered to be flexible due to the ability to form chain‐folded crystals. Chain flexibility rather than the presence of chain stiffness determines whether the columnar mesophase is formed. A certain amphiphilic character does not appear to be required, as polysiloxanes with short side groups, e.g. polydiethylsiloxane display the same mesophase behaviour as polydialkylsilanes with long side chains and other nonpolar flexible chain molecules. The importance of the entropy gain upon conformational disordering is reflected in the increase in temperature stability with increasing alkyl side group length and the absence of mesophase behaviour in the case of the dimethyl substituted polyme

ISSN:1042-7147    

DOI:10.1002/pat.1994.220051205

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

ISSN:1042-7147    

DOI:10.1002/pat.1994.220051206

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractThe main approaches that have been taken to chemically modify polymer surfaces are introduced and reviewed. These are wet chemical oxidation, plasma treatment, classical organic chemistry, and attachment of polymer chains. The extent to which each of these approaches can produce the specific modifications desired is discussed, and any unwanted effects that commonly occur are cited. Finally, the need for using several methods of surface analysis in concert to obtain adequate surface characterization is described.

ISSN:1042-7147    

DOI:10.1002/pat.1994.220051207

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractThe utility of high‐strength, high‐modulus polyethylene fibers in fiber‐reinforced composites is limited due to its poor interfacial adhesion to various polymeric matrices. One way to overcome this limitation is to introduce reactive functionalities on the fiber surface capable of covalently bonding to matrix resins. Ultra high‐strength polyethylene (UHSPE) fibers were treated with chlorosulfonic acid. The surface acid groups were found to considerably improve the interfacial adhesion between polyethylene fibers and epoxy resins as shown by the microbond test. These surface functionalities were found to improve the fiber wettability, as shown by contact angle measurements using the Wilhelmy balance method. Colorimetric measurements of methylene blue absorption were used to quantify the surface concentrations of the acid groups. It was possible to functionalize the UHSPE fiber surfaces using this method to obtain fibers that formed a stronger adhesive bond with epoxy resins; this was achievable without sacrificing other fiber mechanical pro

ISSN:1042-7147    

DOI:10.1002/pat.1994.220051208

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractThe surface‐grafting of polymers onto aramid, poly(p‐phenylene terephthalamide), powder surface by the reaction of acyl chloride groups on the surface with functional polymers having terminal hydroxyl and amino groups was investigated. The introduction of acyl chloride groups onto the aramid powder surface was achieved by the reaction of the aramid powder with adipoyl dichloride: the acyl chloride group content of the surface was estimated to be1.14mmol/g (0.17mmol/m2) by elemental analysis. It was found that by the reaction of acyl chloride groups on the surface with functional polymers, such as terminal diol‐type poly(propylene oxide) (PPG) and terminal diamine‐type poly(dimethylsiloxane) (SDA), these polymers were grafted onto the aramid powder surface; the percentage of surface grafting of PPG and SDA onto the aramid powder was16.7and22.4%, respectively. The thermogravimetric curve of PPG surface‐grafted aramid powder exhibited an initial weight loss at about250°C and a second weight loss at about500°C. This indicated that the grafting of PPG is limited to the powder surface. The wettability of the aramid powder surface turned from hydrophobic to hydrophilic by the surface‐grafting of PPG ont

ISSN:1042-7147    

DOI:10.1002/pat.1994.220051209

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

Abstract“Surface‐photografting” with UV‐irradiation of polypropylene (PP) fiber and film and high‐strength polyethylene (HSPE) yarn has been made with acrylic acid (AA) and acrylamide (AM) as monomers and benzophenone (BP), 4‐chlorobenzophenone (4‐BCP) and hydroxylcyclohexylacetophenone (HHA) as photoinitiators using a new continuous method. The grafting reaction occurs in a thin liquid layer on the fiber or film substrate, which is presoaked in a solution containing initiator and monomer. After irradiation with a highpressure mercury lamp, HPM 15 (2 kW) from Philips, for 5–20 sec at about 50°C the fiber and film surface is completely covered with a 2–8 nm thick layer of grafted polymer, analyzed by electron spectroscopy for chemical analysis. The grafting efficiency is 70–80%, i.e. only 20–30% of the polymer is homopolymer which can be removed by extraction. The grafted layers are so thin that they cannot be analyzed as weight increase (<0.1% of fiber weight). Absolute values for the amount of grafted AA polymer is analyzed by microtitration of the COOH groups at the fiber surface. The results agree well with the relative ESCA values. Grafting of commercial PP yarn with AA increases the adsorption of Crystal Violet dye with a factor of about 6. Grafting the same yarn with AM increases the adhesion to epoxy resin by a factor of 3–4 without affecting the mechanical properties of the fiber more than a few percent. For comparison, strips of blown PP film (5 mm wide) are modified by “surface‐photografting” with AM. With increasing grafting, the contact angle for drops of distilled water decreases from 90° to 20°, indicating extensive wetting. The adhesion to epoxy resin increases from about 0.35 to 1.7 N/mm2, i.e. with a factor of about 5 when the film surface is completely covered. Other comparisons are made with grafting of commercial HSPE yarn. Grafting with AA increases the adsorption of Crystal Violet dye by a factor of about 6. Grafting with AM increases the adhesion to epoxy resin from 0.25 to 1.3 N/nm2, i.e. with a factor of 5. The bulk mechanical properties of the HSPE filaments are not affected by the grafting measured as tensile strength 2.7±0.1 GPa, elongation at break 4.8±0.3%, and Young's modulus 55±3 GPa, both befor

ISSN:1042-7147    

DOI:10.1002/pat.1994.220051210

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY