摘要:

Elastic modulusE1of crystalline regions in the direction parallel to the chain axis has been measured for various kinds of polyethylene (PE) with different microstructures, such as ultrahigh-modulus PE, linear low-density PE, high-pressure-crystallized PE, and a heat-drawn PE whose crystallite size exceeds its long period, etc., by x-ray diffraction. TheE1value, which corresponds to the initial slope of stress-strain curve for the crystal lattice, is 235 GPa for all kinds of PE irrespective of the estimation method of the diffraction peak shift for the (002) plane owing to the constant stress applied. This indicates that the assumption of “homogeneous stress distribution,” that is, stress in the crystalline regions was equal to the stress applied to the sample, is proved experimentally at least for PE. TheE1value at −155°C is obtained as high as 254 GPa. The x-ray diffraction method is considered to be the most proper method to evaluate theE1value.

ISSN:0022-2348    

DOI:10.1080/00222349108245780

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The thermal behavior and structure of poly(hexamethylenep,p′-biben-zoate) (BB-6)/poly(tetramethyleneoxide) (PTMO) block copolymers (BB-6/PTMO) were studied using differential scanning calorimetry, polarizing optical microscopy, and wide-angle and small-angle x-ray diffractometry. As the PTMO fraction increases, BB-6 liquid crystallinity decreased and two transition temperatures [Tc→M (crystal-mesophase) andTm→i (mesophase-isotropic melt)] move to lower temperatures. BB-6/PTMO containing less than 20 mol% of PTMO retains liquid crystallinity. The isotropic melt-mesophase transition exotherm of BB-6/PTMO in the cooling process moves to lower temperature with increasing PTMO. Contrary to the isotropic melt-mesophase transition, the mesophase-crystal transition exotherm moves to higher temperature, indicating that PTMO segments favor the molecular mobility of BB-6 segments. As the mole fraction of BB-6 increases, the texture indicative of the smectic liquid crystal is gradually disorganized. BB-6/PTMO containing more than 30 mol% of PTMO no longer forms the texture indicative of smectic liquid crystals.

ISSN:0022-2348    

DOI:10.1080/00222349108245781

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Radiation-induced crosslinking of poly(methyl methacrylate) (PMMA)-poly(methylene oxide) (PEO) blends was studied. It was found that PMMA in PMMA-PEO blend can be crosslinked in the range of certain doses (1∼20 × 104Gy) and composition (PMMA% = 30∼70) under the absence of oxygen. Moreover, it was also found that the crosslinking degree of PMMA in the blend in which the content of PMMA is 70% is the largest. The crosslinking degree of PMMA in the blend is closely related with the polymer miscibility. The crosslinking degree of the blend prepared at 60°C is far higher than one at ambient temperature.

ISSN:0022-2348    

DOI:10.1080/00222349108245782

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The elastic modulusE1of crystalline regions of isotactic poly(4-methyl-1-pentene) (P4M1P) in the direction parallel to the chain axis and its temperature dependence were investigated by x-ray diffraction.E1values for the (001) and (007) planes of P4M1P agreed well at 4.1 GPa at room temperature. This smallEvalue could be attributed both to the contracted helical conformation (7/2 helix) and to a large cross-sectional area of P4M1P in the crystalline regions. Though the lattice distortion of the first kind increased and partial destruction of crystallites occurred with increasing stress, the stress-strain curve for the crystal lattice was linear up to 80 MPa. However, theE1value remained unchanged up to 150°C. The lattice spacing for the (007) plane increased monotonously with increasing temperature, with a thermal expansion coefficient of 0.9 × 10−4K−1. These phenomena were in contrast with the temperature dependence ofE1values of various polymers previously reported, in whichE1decreased in the temperature region where the thermal expansion coefficient changed. It is considered for P4M1P that the axail thermal molecular mitions which cause the decrement of E1do not take place and that the deformation mechanism of the chain molecules remains unchnaged in the crystalline regions over the temperature and stress range studied.

ISSN:0022-2348    

DOI:10.1080/00222349108245783

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The monoclinic form of crystal in cold-drawn high-density polyethylene has been examined by infrared spectroscopy and x-ray diffraction. The IR results show that the monoclinic form of crystal exists in samples drawn at room temperature at high rates up to 8.5 mm/s. The x-ray diffraction photographs also show that the monoclinic form exists in the high-rate cold-drawn PE samples. The quantitative determination shows that the draw ratio has a primary effect on the content of the monoclinic form in cold-drawn PE samples. The results are explained by a “localized melting” model.

ISSN:0022-2348    

DOI:10.1080/00222349108245784

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

We report a conformational change observed in poly-n-butyl isocyanate (PBIC) dissolved in carbon tetrachloride (CCl4) with temperature. This change was detected by measuring the reduced viscosity of the polymer solution with a Zimm-Crothers type viscometer of very low shear rate; we found a reversible jump in reduced viscosity whose amplitude depends on concentration, but its position is only molecular weight dependent. This jump goes from lower to higher values of reduced viscosity when we increase the temperature, corresponding to an increase in the hydrodynamic volume of the chain. The largest size of the jump we found was about 3.5% of the viscosity value, and the jump decreased when the concentration approached the overlap concentrationc*.

ISSN:0022-2348    

DOI:10.1080/00222349108245785

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The change of molecular mobility during the phase transition of PHB/3-C1-PHB copolymer (5:1) from the orthorhombic modification II into an orthorhombic modification which is close to hexagonal chain packing was investigated by means of2H-NMR. It is shown that a flipping of the benzene rings takes place at temperatures far below the transition temperature. The phase transition starts after more than 60% of the benzene rings are flipping. Even in the newly formed phase close to the hexagonal chain packing, at temperatures up to 300°C, free rotation of the benzene rings can be excluded.

ISSN:0022-2348    

DOI:10.1080/00222349108245786

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

During gel spinning/drawing of PVA fiber, a series of bands with ∼1 μmspacing are formed at angles of 75–90° to the fiber axis. Band angle varies depending on drawing temperature. The banded structure can be interpreted in terms of a model in which molecular axes are alternatively kinked from band to band. The stress-strain curve during drawing-contraction suggests that the formation of the banded structure is due to contraction strain of the deformed fiber, which is induced during stress relaxation. It is suggested that crystallographic, (101)⟨010⟩ slip plays an important role in the formation of the banded structure of gel-drawn PVA fibers.

ISSN:0022-2348    

DOI:10.1080/00222349108245787

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

An equimolar mixture of poly(L-lactide) and poly(D-lactide) was crystallized into a stereocomplex whose crystal system is triclinic (P1) with cell dimensions:a= 0.916 nm,b= 0.916 nra,c(chain axis) = 0.870 nm, α = 109.2°, β - 109.2°, and γ = 109.8°. In the unit cell, a poly(L-lactide) segment and a poly (D-lactide) segment are contained as a pair and packed laterally in parallel fashion. The L- and D-poly(lactides) in the complex take a 31helical conformation, which is a little extended from a 103helix in the homopolymer crystal with the α-form. Homopolymers are also able to take the 31helical conformation and form the β-form crystal. The 31helix in the homopolymer crystal is less stable than the 103one, and hence the β-form is easily transformed to the α-form by annealing.

ISSN:0022-2348    

DOI:10.1080/00222349108245788

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Successive differential and integral sorptions of water vapor into the polyelectrolyte complex of poly (sty renesulfonic acid) / poly(4-vinyl-N-ethylpyridinum bromide) have been measured; films of stoichiometric (1/1 molar ratio) and nonstoichiometric (2/1 molar ratio) complex were employed in the experiments. Sorption isotherms have been also determined by using the values obtained from integral sorption experiments. The sorption data have suggested the following. (i) The rearrangement of polymer chains plays a relatively unimportant role in sorption of water. (ii) The relaxation motion of network chains is suppressed. (iii) The change of morphological structure caused by vapor sorption is obscure. (iv) The ionic character of the 1/1 complex is higher than that of 2/1 complex. (v) A small amount of water can be dispersed on specific polymer sites, but the sorption of a large amount of water is accompanied by an expansion of network structure. Points (i)-(v) have been consistently interpreted on the basis of the network structure and ionic character of this complex.

ISSN:0022-2348    

DOI:10.1080/00222349108245789

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor