CARBON-13 NMR STUDY ON MOLECULAR MOTION OF 1, 2-POLYBUTADIENE——TEMPERATURE DEPENDENCE OF MOLECULAR MOTION

Proton-decoupled, ~(13)C FT-NMR (operating at 50.3 MHz) is used to determine spin-latticerelaxation time (T_1), nuclear Overhauser enhancement (NOE), linewidth and chemical shift of 1,2-polybutadiene as a function of temperature in CDCl_3 solution and the temperature dependence ofmolecular motion of 1,2-polybutadiene has been investigated with these NMR relaxation parameters.It is found that jumps of NOE and linewidth vs. temperature appear between-1℃and -30℃. Theminimum of nT_1 vs. temperature for all carbons occur at about -45℃.     

STUDY OF THE MOLECULAR MOTION IN POLYEPICHLOROHYDRIN BY HIGH RESOLUTION NMR

The molecular motion in polyepichlorohydrin (PEPCH), in solution and bulk, was studied by high resolution NMR by means of line width, spin-lattice relaxation time T_1 and nuclear Overhauser effect NOE. The results show that the VJGM model can describe the main chain motion of PEPCH in solution perfectly. In bulk state, the relationship between the line width and the temperature is consistent with WLF equation, but that between the high frequency molecular motion correlation time (in T_1 scale ) and temperature is consistent with Arrhenius equation. The motion parameters of PEPCH in both states were calculated. The internal rotation motion of side—CH_2Cl group was analyzed by using equal three-site jump and diffusion internal rotation model in both states.     

THE CRYSTAL STRUCTURE OF BAYLEYITE

The bayleyite crystallizes in monoclinic space group C_2~5h-P2_1/c with a=6.499(1), b=15.235(5), c=26.513(6), β= 92.92(2)°, Z=4. Intensities of 3430 independent reflections are collected with diffractometer using MoKα radiation. The crystal structure has been solved by the Patterson method and refined by block least square refinement for positional parameters and isotropic temperature factor of non-hydrogen atoms. The final R factor is 0.038.The result of crystal structure analysis shows that the structure consists of discrete [UO_2(CO_3)_3]~(4-) ions and Mg~(2 ) cations are between slab-like units, but they are not in a slablike unit. Its crystal struture is different from that of liebigite which was determined by Appleman. Complexes and cations between slab-like units and in a slab-like unit are connected by hydrogen bonds formed by water molecules.     

CORRELATION BETWEEN GLASS TRANSITION OF POLYMERS AND ENERGY OF ROTATIONAL ISOMERIZATION OF MOLECULAR CHAINS

It has been shown that the free volume fraction at T_g is not a universal parameter for linear polymers of different molecular structure. The reason is that the volume expansion at T_g is partially contributed from the change of the numbers of conformations of isolated molecular chains due to internal rotation. In this paper, glassy transformation was connected with internal rotation of isolated molecular chains, and the relationship between free volume fraction of polymers at T_g and energy e of rotational isomerization of isolated molecular chains was formulated, e=-k·T_g·In (△α·T_g/1-△α. T_g). The values of calculated from the above formula are in good agreement with those published in the literatures. Thus, the method described in this paper can be used to estimate a parameter for the flexibility of isolated molecular chains.7     

STUDY OF THE MOLECULAR MOTION AND COMPATIBILITY IN AB-CROSSLINKED POLYMER BASED ON POLYURETHANE AND POLYSTYRENE-co-ACRYLIC ACID BY SOLID STATE HIGH RESOLUTION NMR

The ~(13)C T_(1s) of --CH_3 side group in PPU/P (St-co-AA), AB-crosslinked polymers (i. e.ABCP) was studied by using high resolution solid state NMR. The rotation motion of --CH_3 sidegroup in PPU was analyzed by means of the average spectral density functions of internal rota-tion. The results showed that the rotation of the --CH_3 side group is related closely to the com-patibility between the two components. The compatibility was studied by analyzing the protonspin-lattice relaxation in rotating frame, spin-spin relaxation and spin-diffusion. The resultsshowed that the hydrogen bonds between the components play a major role in determining thecompatibility. Through spin diffusion studying, the soft phase domain size was calculated. Bystudying proton spin-spin relaxation, the content of each component in each phase and that ofeach phase in the samples can be obtained. The result shows that the content of interphase is related closely to the compatibility.     

STUDIES ON THE ~(13)C-NMR SPECTRA OF ALTERNATING COPOLYMERS OF CONJUGATED DIENES WITH METHYL ACRYLATE

The ~(13)C-NMR spectra of alternating copolymers of conjugated dienes, butadiene (BD), isoprene(IP) and chloroprene (CP), with methyl acrylate (MA) were studied. It is proved that they are allalternating copolymers. The BD units in Poly (BD-alt-MA) are joined to MA mainly in the formof trans 1,4-structure. The contents of trans 1,4-, cis 1,4-and 1,2-structure are 88, 7 and 5%, res-pectively. The IP and CP units in Poly(IP-alt-MA) and Poly(CP-alt-MA) exist essentially as trans1,4-configuration and connect with MA units in "head to head" arrangement predominantly, whileCP-CP units present in Poly(CP-alt-MA) in a small quantity.     

A NEW PEAK (T_4) IN THE ~(13)C-NMR SPECTRUM OF POLYBUTADIENE

A new peak at 39.0 ppm in the ~(13)C-NMR spectrum of polybutadiene (PBD) was discovered. This peak is assigned to the fourth peak (T_4) of trans-1,4-sequence marked with an asterisk as shown in Fig. 3 in the text.The occurrence of T_4 carbon nuclei is strongly affected by their neighboring 1,2-units. So long as both contents of trans-1,4- and 1,2-units attain their proper amounts the peak (T_4) with appear in the ~(13)C-NMR spectrum of PBD.     

CRYSTAL AND MOLECULAR STRUCTURE OF N, N-PLATINUM-DIETHYL-DICHLORIDEDI-L-ASPARTATE

This paper reports the crystal and molecular structure of title compound. 3978 three-dimensional independent reflections were collected by Syntex R3 four circle diffractometer. The crystal is monoclinic with space group P2_1, a=8.074(1), b=11.309(4), c=27.793(9), β=106.84°(2), Z=4. The molecular formula is Pt(C_8 H_(15)O_4N)_a Cl_2. The crystal structure was solved by Patterson method and refined by block matrix least squares refinement techniques. The final R factor is 0.039.The result of crystal structure analysis shows that Pt(Ⅱ) has a dsp~2 hybrid orbital and square coordination. Two C1 atoms are located oppositely to two diethyi-dichloride-di-L-aspartare. N atoms have sp~3 tetrahedral hybrid configurations and form the coordinate bonds with Pt(Ⅱ) atom using their lone pair electrons. By reason of molecular packing and due to the formation of inner hydrogen bonds in the complex molecule, the configuration of L-aspartic acid in the title complex is more twisted than that of L-and DL-aspartic acid     

THE CHAIN STRUCTURE OF 1,2-POLYBUTADIENES PREPARED WITH MOLYBDENUM CATALYST SYSTEMS

The chain structure of 1,2-polybutadienes prepared with molybdenum catalyst systems has been studied by IR, ~(13)C-NMR and T_g method, and the method to regulate the chain structure investigated. It was found that some polar additives, e. g., allyl halides, are able to regulate not only the content of 1,2-units in the polymer, but also its configuration and sequence distribution. Attempt has been made to estimate the sequence length of stereo-isomers of 1,2-units by statistical theory.     

ASSIGNMENT OF ~(13)C NMR SPECTRA OF POLYMER WITH SEMIEMPIRICAL METHOD——SURVEY OF SPECTRUM OF SECONDARY CARBON OF 1, 2-PBD

In chain molecules of 1, 2-PBD, there are two kinds of gauche arrangements, which is the cause of making the spectrum of the secondary carbon in main chain of the polymer split. In such a complex system, the gauche arrangements of the secondary carbon and the tertiary carbon occupy an important position. Hence, the contribution of the tertiary carbon to the chemical shifts of the secondary carbon has a decisive effect on the sequence structure distribution. In comparison the contribution of vinyl groups is much less. The γ values are: γ_1=-6.37～-6.41 ppm represents the effect of the tertiary carbon and γ_2=0.0～-1.56 ppm the contribution of vinyl. The mean square errors are 0.364 and 0.166×10~(-2) ppm~2, respectively in the two cases of considering the effect of vinyl and vice versa. In this paper, we discuss the effects of model chain type, chain length and temperature on the bond probability. Meanwhile, it is pointed out that there exist a few cases, which are not in accord with the usual distrib     

DIELECTRIC PROPERTIES OF 1, 2-POLYBUTADIENES

The dielectric permittivity and loss tangent of 1,2-polybutadienes with different chain structures were determined as a function of temperature from-180℃ to 100℃ at different frequencies, and the frequency and structure dependence of the dielectric propertie of 1,2-polybutadienes have been investigated. It is found that a maximum of the permittivity occurs in the glass-transition region. The width of the glasstransition peak increases with increasing frequency while its height has little change. With a rise in the content of 1,2-units, the permittivity decreases and the height of the glass-transition peak slightly grows. A maximum of the width of the glass-transition peak appears when the content of 1,2-units is about 45%. Both the permittivity and dielectric loss drop down as the growth of the content of syndiotactic 1,2-units.     

MOLECULAR STRUCTURE AND ABSOLUTE CONFIGURATION OF SUBEROGORGIN

In the present paper it is reported that the molecular structure and absolute configuration of poisonous suberogorgin are determined by using X-ray diffraction method. The crystal of suberogorgin belongs to orthogonal system with space group D_2~4-P2_12_12_1. The crystallographic parameters are: a=16.135, b=13.189, c=12.901, Z=8. The initial model of the crystal structure was solved by the direct method. The refinement of the strueture parameters was carried out by using the least square method and led to a final R-factor of 0.056. In accordance with the molecular structure of suberogorgin mentioned above, the solvent effect of NMR has been further discussed and the relationship between the molecular structure of suberogorgin and its toxicity has also been preliminarily investigated.     

PREPARATION AND CHARACTERIZATION OF cis-,4-POLYBUTADIENE CONTAINING A FRACTION OF trans-1,4-POLYBUTADIENE

Polymerization of butadiene catalysed first with V(acac)_3-Al(i-Bu)_2Cl, then with Co(acac)_3-H_2O-Al(i-Bu)_2Cl has been studied. The polymer obtained was identified to be a new variety of cis-1,4-polybutadiene which contained a fraction of trans-1,4-polybutadiene chemically bonded to the cis-1,4-polybutadiene chains. Its molecular weight and trans-1,4 content can be regulated by varying the catalyst composition and concentration as well as other polymerization conditions. The trans-1,4 fraction, although it presents only in 9—16%, forms a crystalline phase in the matrix at room temperature and facilitates the crystallization of the polymer.     

Synthesis of hydroxyl-terminated polybutadiene possessing high content of 1,4-units via anionic polymerization

<正>The hydroxyl-terminated polybutadiene(HTPB) possessing high content of 1,4-units was synthesized by anionic polymerization of butadiene,using alkyllithium containing silicon-protected hydroxyl group as initiator and cyclohexane as solvent.The polymers were characterized by GPC,IR and ~1H-NMR.The mechanical properties of cured films were also evaluated.The results show that the content of 1,4-units for HTPBs made by anionic polymerization reaches up to 90%.The molecular weight distribution is very narrow(≤1.05).The functionality of hydroxyl groups approaches 2.Compared with free radical HTPB,the elongation at break of anionic HTPB films increased by 70%,while the tensile strength remained nearly unchanged.This new HTPB can be very useful in solid propellant.     

~(13)C-NMR STUDY ON THE EQUIBINARY (cis-1,4;1,2) POLYBUTADIENE POLYMERIZED WITH IRON CATALYST

The (cis-1,4 and 1,2) polybutadiene polymerized with iron catalyst was investigated by ~(13)C-NMR. Assignments have been made on the spectra for all peaks of the aliphatic and olefinic carbons using chemical shift corrective terms together with Furukawa parameters. The relative intensities of peaks were calculated from the Bernoulli distribution of cis-1,4 and 1,2 units.Quantification of cis-1,4 and 1,2 contents, sequence distribution, alternation pattern of cis-1,4 and 1,2 units, and the chain propagation mechanism were discussed as a result of the detailed study of the spectra.     

MODIFICATION OF NYLON-6 WITH POLYORGANOSILOXANE

Nylon-6 has been modified by polyorganosiloxane. It was realized by radical addition of caprolactam to the vinyl group of silicone and anionic polymerization of the monomer in the presence of the silicone macromer. The mechanical properties of the modified plastics are not far from that of the unmodified one whereas its frictional properties are significantly improved.     

SYNTHESES OF ETHYL PERFLUOROACETYLENIC ESTERS AND STEREOCHEMISTRY OF A NOVEL ACETYLENIC ESTER-VINYL ETHER REARRANGEMENT

The intramolecular Wittig reaction has been applied to the syntheses of ethyl trifluoro-but-2-ynoate (2a) and ethyl heptafluoro-hex-2-ynoate (2b). Treatment of 2a and 2b withaqueous sodium hydroxide, followed by acidification, affords 3-ethoxy-4,4,4-trifluoro-2-bu-tenoic acid (3a) and 3-ethoxy-4,4,5,5,6,6,6-heptafluoro-2-hexenoic acid (3b) respectively. Anovel acetylenic ester to vinyl ether rearrangement takes place as thc corresponding methylestors. Their structures are ascertained by elemental analysis and IR and NMR spectra.The stereochemistry of this novel acetylenic ester to vinyl ether rearrangement has been studied.On the basis of ~1H NMR data, we find that the reaction is highly stereoseleetive and the Z-isomer predominated to the extent of above 94% in all cases. The results of the solventeffect of benzene and NOE enhancement in NMR spectroscopy further confirm the configura-tion of the Z- and E-isomer.     

SYNTHESIS AND NMR CHARACTERIZATION OF PRECURSORS OF EPOXY NETWORK AS POLYMER HOST FOR SOLID ELECTROLYTE

To raise the room temperature ionic conductivity and improve the mechanical strength of a PEO-based polymer electrolyte, a noncrystalline two-component epoxy electrolyte system has been prepared. The diglycidyl ether of polyethylene glycols as precursors of the system were synthesized by a two-step process. The presumed structure of the product was characterized, by ~(13)C, ~1H NMR and IR spectroscopy. It was found that a side-reaction occurred between the secondary hydroxyl group of PEG-chlorohydrin and epichlorohydrin in some degree, resulting in a by- product containing—CH_2Cl side group. By selecting a characteristic signal, which is undistorted by the increase in the length of CH_2 CH_2—O segment, a ~1H NMR approach of determining the equivalent epoxy weight (EEW) was proposed. The method is valid to specimens even though the EEW is as high as 2,000. The examination of the specimens by DSC showed that epoxidation greatly depressed the crystallinity of the PEG's, whereas the T_g was raised.     

A STUDY OF POLYBUTADIENE SYNTHESIS WITH MoCl_n(OR)_(4-n)-(i-Bu)_2AlOPh AS A CATALYST

The catalytic effect of Mo Cl_n (OR)_(4_n)-(i-Bu)_2AlOPh on the polymerization of butadiene inhydrogenated gasoline is studied (R is alkyl, cycloheptyl, phenyl of C_(4_16)). In this system, the solu-bility and the catalytic activity of the catalyst do not depend on whether the number of carbon atomsin R group is odd or even. The R group with the primary and secondary carbon atom has a fairlygreat influence on the catalytic activity. When R is an alkyl, the catalytic activity increases and therange of Al/Mo values that keeps higher conversion of butadiene is broadened as the size of the Rgroup increases. The content of 1,2-units in the polymer hardly varies with the size of the R group.     

PARTICLE MORPHOLOGY OF POLY(VINYL CHLORIDE)RESIN PREPARED BY SUSPENDED EMULSION POLYMERIZATION

Suspended emulsion polymerization was used to prepare poly(vinyl chloride) (PVC) resin. Fine PVC particleswere formed at low polymerization conversions. The amount of fine panicles decreases as conversion increases anddisappears at conversions greater than 30%. Scanning electron micrographs show that PVC grains are composed of looselycoalesced primary particles, especially for PVC resins prepared in the presence of poly(vinyl alcohol) dispersant. The size ofprimary particles increases and porosity decreases with the increase of conversion. In view of the particle features of PVCresin, a particle formation mechanism including the formation of primary particles and grains is proposed. The formationprocess of primary particles includes the formation of particle nuclei, coalescence of particle nuclei to form primary particles,and growth of primary particles. PVC grains are formed by the coagulation of primary particles. The loose coalescence ofprimary particles is caused by the colloidal stability of primary particles and the low swelling degree of vinyl chloride in the primary particles.