Dynamic Loss Peak Research Articles

Aminated polyacrylonitrile blends with cellulose acetate

Polyacrylonitriles (PANs) were synthesized and aminated with ethylene diamine (2DA), hexamethylene diamine (6DA), and dodecane diamine (12DA), followed by blending with cellulose acetate (CA). Effects of amination and chain length of diamine on the miscibility of the aminated PAN with CA were studied. Scanning electron microscopy (SEM) micrographs of cryogenically fractured surfaces of the blends showed coarse elliptical dispersions of CA in PAN. The dispersed CA domains decreased in size with an increase in aminated PAN content. The dispersed domain size further decreased with increasing chain length of diamine. and eventually the morphology became almost homogeneous with 12DA-modified PAN blends. With increasing chain length of the diamines, the dynamic loss peak temperature of PAN in blends showed a movement toward that of CA. Fourier transform infrared (FTIR) measurements showed that the specific interaction between the aminated PAN and cellulose acetate is the hydrogen bonding between aprotic hydrogen in aminated PAN and the ester carbonyl of CA, the interactions being increased with increasing chain length of diamine.

Effects of alkylation of silicas on interfacial interaction and molecular motions between silicas and rubbers

The interactions between rubbers and silicas were studied by means of bound rubber determination, vulcanizate swelling procedure, and tensile retraction measurement. The mobilities of rubber chain segments in mixture with silicas were investigated by thermomechanical and dynamic mechanical analyzers. The results show that when the untreated silica was incorporated into rubbers, the strong interaction of rubber with the silica apparently constrains the segmental motions of the rubber molecules, resulting in the decrease in the dynamic loss peak and the thermal expansion coefficient, and the increase in the glass transition temperature. The alkylations on silica surfaces weaken the interfacial interaction between rubbers and silicas, and the mobilities of the rubber molecules become less restricted. Furthermore, proton spin–spin relaxation time (T2) measurements by the pulsed NMR on the insoluble bound rubber, indicate that there are two relaxing regions: an immobile (or a tight) region and a relatively free (or a loose) one. The types of the rubbers and the activities of the silica surfaces have influences on the relaxation process of the two bound rubber components. © 1996 John Wiley & Sons, Inc.

Morphology and properties of thermoset blends made from unsaturated polyester resin, poly(vinyl acetate) and styrene

Blends containing an unsaturated polyester resin, poly(vinyl acetate) (PVAc) and styrene monomer in various proportions were cured using benzoyl peroxide as initiator. The morphology of the cured blends was studied using scanning electron microscopy. Polyester resin formed the matrix at low PVAc concentrations and at low styrene contents. A co-continuous phase morphology was observed in blends containing PVAc concentrations ⩾6% and styrene levels ⩾40%. Increasing the styrene content over the range 20% to 80% caused a narrowing of the principal dynamic loss peak, and an increase in peak height: peak temperature reached a maximum at 40% styrene. The change from particulate PVAc to co-continuous structure was associated with a sharp drop in G Ic and K Ic. Parallel studies have shown this transition to be important in ‘low-profile’ behaviour.

Toughening tetrafunctional epoxy resins using polyetherimide

Toughened epoxy resins have been prepared by dissolving polyetherimide (PEI) in a tetraglycidyl-4,4′-diaminodiphenyl methane (TGDDM) based resin with 30 p.h.r. diaminodiphenyl sulphone (DDS) as curing agent. The polyetherimide forms a separate phase, with a dynamic loss peak which varies between 200 and 212°C. The loss peak of the resin occurs at about 265°C. Three-point bend tests show a linear increase in K IC with PEI content, from 0.5MPa√m in the parent resin to 1.42MPa√m at 25 p.h.r. of PEI. Young's modulus at 23°C shows a modest reduction from 3.6 to 3.5 GPa over the same composition range.

Properties of Random and Block Copolymers of Butadiene and Styrene. I. Dynamic Properties and Glassy Transition Temperatures

Abstract The effect of monomer sequence on physical properties was investigated for butadiene—styrene solution copolymers made by organolithium initiation. The polymers varied from random copolymers of uniform composition along the polymer chain to ideal block polymers of specific block sequence arrangement and included rubbers of intermediate degrees of randomness. Uniform composition random copolymers exhibit a single glass transition temperature and a very narrow dynamic loss peak corresponding to this transition. The glass transition can be predicted from the styrene content and the microstructure of the butadiene portion of the rubber. Random copolymers in which composition varies along the polymer chain, and to some extent between molecules, exhibit a single glass transition, but the dynamic loss peak is broadened. The extent of this broadening is shown to be compatible with the sequence distribution, polymer segments of various compositions losing mobility at different temperatures. This indicates a tendency for association between segments of different chains which are similar in composition. Block copolymers display two transitions, corresponding to Tg for each type of block. The position and width of the dynamic loss peaks are related to block length and compositional purity of the blocks.

The effects of various monomer addition methods on the emulsion copolymerization of vinyl acetate and butyl acrylate

AbstractVarious monomer addition methods were applied to the emulsion co‐polymerization of vinyl acetate and butyl acrylate of which polymerization reactivities are very different from each other. The grafting efficiency and homogeneity of copolymer were determined by the fractionation and measurement of dynamic viscoelasticity of emulsion polymers. As the content of the second fraction of acetone‐soluble part increased and that of the third fraction decreased, then the homogeneity of the copolymer increased, In this case, only one dynamic loss peak existed near 0°C. The result showed that homogeneous copolymers were obtained by continuous monomer addition methods and heterogeneous copolymers were obtained by initial addition of total monomers or stepwise monomer addition methods. Homogeneity of copolymer had great influence on various properties, e.g., hardness and adhesive properties. Film hardness was the lowest for homogeneous copolymer and it was the highest for heterogeneous copolymer. Homogeneous copolymer was best for adhering plywood and poly(vinyl chloride). It is remarkable that copolymers of vinyl acetate and butyl acrylate with very different properties were obtained by changing only the monomer addition methods.

Properties of random and block copolymers of butadiene and styrene. I. Dynamic properties and glassy transition temperatures

AbstractThe effect of monomer sequence on physical properties was investigated for butadienestyrene solution copolymers made by organolithium initiation. The polymers varied from random copolymers of uniform composition along the polymer chain to ideal block polymers of specific block sequence arrangement and included rubbers of intermediate degrees of randomness. Uniform composition random copolymers exhibit a single glass transition temperature and a very narrow dynamic loss peak corresponding to this transition. The glass transition can be predicted from the styrene content and the microstructure of the butadiene portion of the rubber. Random copolymers in which composition varies along the polymer chain, and to some extent between molecules, exhibit a single glass transition, but the dynamic loss peak is broadened. The extent of this broadening is shown to be compatible with the sequence distribution, polymer segments of various compositions losing mobility at different temperatures. This indicates a tendency for association between segments of different temperatures. This indicates a tendency for association between segments of different chains which are similar in composition. Block copolymers display two transitions, corresponding to Tg for each type of block. The position and width of the dynamic loss peaks are related to block length and compositional purity of the blocks.