Determination of residual levels of unsaturation in partially hydrogenated poly(2,3-diphenyl-1,3-butadiene) using thermogravimetry

The thermal degradation characteristics of head-to-head poly(styrene) (HHPS) should provide insight with respect to the impact of head-to-head placement on the thermal stability of the traditional atactic head-to-tail polymer (HTPS). The synthesis of head-to-head poly(styrene) must be accomplished indirectly. The HHPS is most satisfactorily obtained by dissolving metal reduction of poly(2,3-diphenyl-1,3-butadiene) (PDBD) generated by radical polymerization of the corresponding diene monomer. Full saturation of the polymer mainchain requires several iterations of the reduction procedure. Since the decomposition of PDBD is prominent at 374 °C and that for HHPS is similarly facile at 406 °C, it seemed feasible that TGA of partially hydrogenated PDBD might be utilized as a convenient means of monitoring the extent of hydrogenation. This has been demonstrated for various levels of unsaturation remaining—from approximately 90 to less than 10%. Within this range the peak areas from the DTG plots of the partially hydrogenated polymer provide a good reflection of the ratio of unsaturated to saturated units in the polymer. Even low levels of unsaturation in the polymer may be detected by the asymmetry of the decomposition peak for the polymer.     

Head-to-Head Polymers. XXVIII. Attempted Syntheses of Linear Head-to-Head Polyisobutylene

2,2,3,3-Tetramethyl-1,4-dibromobutane, when used as monomer for polymerization by Wurtz-type polycondensation, gave head-to-head polyisobutylene which is branched. Under similar conditions, 2, 5-dimethyl-2, 5-dibromohexane gave no polymer. Copolymerization of ethylene with tetramethylethylene under various conditions gave polyethylene of modest molecular weight with about 5% tetramethylene units in the polymer. 1,1,4, 4-Tetramethyl-1,3-butadiene (2,5-dimethylhexadiene-2,4) polymerized with BF₃ initiator to high molecular weight trans- 1,4-poly-(1,1,4,4-tetrarnethylbutadiene-1,3). The polymer could not be hydrogenated with soluble hydrogenation catalysts and only partially by chemical reduction with diimide. Under forcing conditions, incorporation of portions of the decomposition products of the precursor of the diimide was observed.     

The utilization of TG/GC/MS in the establishment of the mechanism of poly(styrene) degradation

General purpose poly(styrene) is a large volume commodity polymer used in a variety of applications. It is widely used in food packaging, particularly for baked goods. In this application, the presence of styrene monomer, which has a distinctive taste and aroma, cannot be tolerated. Processing of the polymer and forming of the food container at an unacceptably high temperature leads to the formation of styrene monomer and finished articles with unacceptable aroma characteristics. An examination of the thermal degradation of poly(styrene) has revealed the origin of monomer formation. The thermal decomposition of poly(styrene) has been widely studied. However, most studies have been carried out at high temperature (>300°C) where many processes are occurring simultaneously. Degradation at lower temperature, 280°C, occurs in two well-defined steps. The first is thermolysis of a head-to-head bond present in the mainchain as a consequence of polymerization termination by radical coupling. This generates macroradicals which smoothly depolymerize to expel styrene monomer. The nature of the degradation is readily apparent from kinetic analysis of the isothermal thermogravimetry (TG) data and the identity of the single volatile product may be readily established by gas chromatography/mass spectrometry (GC/MS) analysis of the effluent from the TG analysis.     

Thermal and radiation-induced dehydrochlorination of poly(vinyl chloride). II. Head-to-head structures

The mechanism of dehydrochlorination of 2,3-dichlorobutane and chlorinated polybutadiene which are model compounds of head-to-head poly(vinyl chloride) has been investigated by pyrolysis, thermal, and ultraviolet-induced decomposition. The activation energy of dehydrochlorination for head-to-head poly(vinyl chloride) in nitrogen was 23 kcal/mole at temperatures of 150–190°C, which is slightly smaller than that (29 kcal/mole) for head-to-tail poly(vinyl chloride). The conjugated double bonds were formed by thermal and radiation decomposition of head-to-head poly(vinyl chloride), similar to head-to-tail poly(vinyl chloride). The probability of polyene formation by radiation-induced dehydrochlorination is larger than that by thermal decomposition and is affected by the conformation and the molecular motion of the main chain. This may be due to the alternative mechanism of dehydrochlorination in the thermal and radiation decomposition. The amount of head-to-head linkage of poly(vinyl chloride) samples prepared with various catalysts is dependent on polymerization temperature rather than the kinds of catalyst. Commercial poly(vinyl chloride) has 6–7 head-to-head linkages per 1000 monomeric units.     

Thermal properties of some hydrogenated poly(α-methyl styrenes)

The Synthesis of poly(isopropenyl cyclohexane) via the hydrogenation of poly(α-methyl styrene) is described. Depending on the reaction time and catalyst system a homopolymer or a copolymer is obtained. Under the conditions of synthesis both materials are highly syndiotactic. For the pure hydrogenated homopolymer (>99.9%) the glass transition temperature was found to be 185.4°C, about 20°C above T_g of poly(α-ethyl styrene). Contrary to expectations, the glass transitions of the 92/8, 33/67 poly(isopropenyl cyclohexane-co-methyl styrene) and poly(α-methyl styrene) are almost identical, as are the decomposition temperature ranges. Thermal data indicate that the decomposition mechanism of the copolymers and hydrogenated homopolymer is random scission. The thermogravimetric curves also indicate that the copolymers are random. Thus, chain stiffness appears not to increase rapidly with hydrogenation of this highly syndiotactic polymer.     

The reactions of germenes generated thermally from pivaloyl- and adamantoyltris(trimethylsilyl)germane with 1,3-butadienes

The thermolysis of pivaloyl- and adamantoyltris(trimethylsilyl)germane in the presence of 2,3-dimethyl- and 2,3-diphenyl-1,3-butadiene gave the respective adducts derived from [2+4] cycloaddition of the germenes with butadienes in good yields.     

Head-to-head polymers—I. The preparation and some properties of head-to-head polypropylene

Samples of head-to-head polypropylene have been prepared by the hydrogenation of two polydienes; 1,4-poly(2,4-hexadiene) and 1,4-poly(2,3-dimethyl-1,3-butadiene). Glass transition temperatures were found to be marginally lower than for conventional polypropylene suggesting that the head-to-head placements in the chain increased the polymer flexibility.     

Electron-transfer photochemistry of 2,3-diphenyl-1,3-butadiene

Photoinduced electron-transfer (ET) reaction of 2,3-diphenyl-1,3-butadiene 1 resulted in the formation of [4+2] dimer 8, [4+4] dimer 4, and its secondary product bicyclooctadiene 9. The ET induced dimerization of 1 is suggested to proceed through a stepwise mechanism involving a bis-allylic intermediate 10.     

Dicobalt octacarbonyl-catalyzed tandem cycloaddition reaction between diyne and diene under CO

Treatment of 1,7-diphenyl-1,6-heptadiyne and a symmetric butadiene such as 2,3-dimethyl-1,3-butadiene and 1,3-cyclohexadiene with Co(2)(CO)(8) (5 mol%) in CH(2)Cl(2) at 110 degrees C under 30 atm CO for 18 h afforded a 5.5.6 tricyclic enone in high yields. For unsymmetrical dienes such as 2-methyl-1,3-butadiene, 2-methyl-1, 3-pentadiene, and 3-methyl-1,3-pentadiene, two separable regioisomers were obtained. The catalytic reactions described are experimentally quite simple and provide a very useful synthetic procedure for the syntheses of [5.5.6] tricyclic enones.     

Cycloaddition of Alkenes and Alkynes to the P-centered Singlet Biradical [P(μ-NTer)]2

The reaction of biradical [P(μ-NTer)]₂ ( 1 , Ter = 2,6-bis(2,4,6-trimethylphenyl)phenyl) towards different alkenes (R = 2,3-dimethyl–butadiene, 2,5-dimethyl-2,4-hexadiene, 1,7-octadiene, 1,4-cyclohexadiene) and alkynes (R = 1,4-diphenyl-1,3-butadiyne) was studied experimentally. Although these olefins can react in different ways, only [2+2] cycloaddition products ( 1R ) were observed. The reaction with 2,3-dimethylbutadiene also led to the [2+2] product ( 1dmb ). Thermal treatment of 1dmb above 140 °C resulted in the recovery of biradical 1 upon homolytic bond cleavage of the two P–C bonds and the release of 2,3-dimethylbutadiene. In contrast to this reaction, all other [2+2] additions products ( 1R , R = 1,7-octadiene, 1,4-cyclohexadiene, 1,4-diphenyl-1,3-butadiyne) began to decompose at temperatures between 200 °C and 300 °C. Only unidentified products were obtained but no temperature-controlled equilibrium reactions were observed. Computations were carried out to shed light into the formal [2+2] as well as the possible [4+2] addition reaction.     

Thermal stability of poly(styrene) containing no head-to-head units

General purpose poly(styrene) prepared by conventional radical techniques contains a head-to-head unit as a consequence of polymerization termination by radical coupling. As has been previously demonstrated, thermal stress promotes homolysis of the bond linking the head-to-head components. The macroradicals generated depolymerize rapidly to generate styrene monomer. This decomposition during processing can lead to finished articles containing objectionable levels of styrene monomer, particularly for food packaging applications in which even low levels of monomer can promote objectionable taste and aroma. Polymer containing no head-to-head units should not be prone to this facile decomposition. In this instance, poly(styrene) has been prepared by nitroxyl-mediated polymerization of styrene monomer followed by reductive removal of nitroxyl end groups. Polymer prepared in this manner contains no head-to-head units and displays thermal stability much greater than that observed for conventional poly(styrene). A direct comparison of the stability for the two polymers is readily available by thermogravimetric techniques. A quantitative reflection of the difference in stability is available from the rate constants for the respective decomposition.     

A simple synthesis of heterocyclic ring systems containing the 1,3-oxazine nucleus

An easy, one-step conversion of aldol adducts 1 into spiro-derivatives of partially hydrogenated [1,3]oxazino[2,3-a]isoquinoline 5 , [1,3]oxazino[2,3-a]phthalazine 6 and [1,3]oxazino[3,2-a]quinoline 7 is reported.     

Calorimetric determination of head-to-head defect in poly(vinylidene fluoride)

Differential scanning calorimetric analyses were conducted on samples of poly(vinylidene fluoride) polymerized in an autoclave by tributylborane-oxygen by free-radical initiation at low temperature (-70-0°C). The peak melting points and the percent head-to-head defect in each polymer sample were determined by a reported calorimetric method. A commercial sample showed a melting temperature in the range 157–162°C and a percent head-to-head defect of 7.7%; whereas two experimental samples showed melting temperatures in the range 172–179°C with a percent head-to-head defect of 4.4 and 4.9%. The calorimetric procedure was modified by reducing annealing times to only 2 h, which saves time and, as shown in this study, avoids thermal polymer degradation.     

Hydrocarbon polymers containing six-membered rings in the main chain. Microstructure and properties of poly(1,3-cyclohexadiene)

The relationship between the microstructure and the properties of poly(1,3-cyclohexadiene)s, obtained by living anionic polymerization with an alkyllithium/amine system, and their hydrogenated derivatives are reported. The 1,2-bond/1,4-bond molar ratio of poly(1,3-cyclohexadiene) was determined by measuring 2D-NMR with the H H COSY method. The glass transition temperature of poly(1,3-cyclohexadiene) was found to rise with an increase in the ratio of 1,2-bonds to 1,4-bonds or with an increase of the number average molecular weight. The 1,2-bond of the polymer chain gives a high flexural strength and heat distortion temperature. Hydrogenated poly(1,3-cyclohexadiene) has the highest T_g (231°C) among all hydrocarbon polymers ever reported. 1,3-Cyclohexadiene–butadiene–1,3-cyclohexadiene triblock copolymer and 1,3-cyclohexadiene–styrene–1,3-cyclohexadiene triblock copolymer have high heat resistance and high mechanical strength. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1657–1668, 1998     

A systematic study of stereochemical effects in homologous poly(alkenamer)s: Dewar benzene versus norbornene

Two diastereomeric derivatives of norbornene, dimethyl (1R,2R,3S,4S)-bicyclo[2.2.1]hept-5-ene-2,3-dicarboxylate and dimethyl (1R,2S,3S,4S)-bicyclo[2.2.1]hept-5-ene-2,3-dicarboxylate, were synthesized and polymerized using ring-opening metathesis polymerization (ROMP). For comparative purposes, diastereomeric derivatives of Dewar benzene, dimethyl (1R,2S,3R,4S)-bicyclo[2.2.0]hex-5-ene-2,3-dicarboxylate and dimethyl (1R,2S,3S,4S)-bicyclo[2.2.0]hex-5-ene-2,3-dicarboxylate, were also synthesized and polymerized using ROMP. The polymerization reactions proceeded in a controlled manner as evidenced in part by linear relationships between the monomer-to-catalyst feed ratios and the molecular weights of the polymer products. Chain extension experiments were also conducted which facilitated the formation of block copolymers. Although the poly(norbornene) derivatives exhibited glass transition temperatures that were dependent on their monomer stereochemistry (cis: 115°C vs. trans: 125°C), more pronounced differences were observed upon analysis of the polymers derived from Dewar benzene (cis: 70°C vs. trans: 95°C). Likewise, microphase separation was observed in block copolymers that were prepared using the diastereomeric monomers derived from Dewar benzene but not in block copolymers of the norbornene-based diastereomers. The differential thermal properties were attributed to the relative monomer sizes as reducing the distances between the polymer backbones and the pendant stereocenters appeared to enhance the thermal effects.     

Grafting of polymers onto and/or from silica surface during the polymerization of vinyl monomers in the presence of γ‐ray‐irradiated silica

The effects of radicals on silica surface, which were formed by γ‐ray irradiation, on the polymerization of vinyl monomers were investigated. It was found that the polymerization of styrene was remarkably retarded in the presence of γ‐ray‐irradiated silica above 60 °C, at which thermal polymerization of styrene is readily initiated. During the polymerization, a part of polystyrene formed was grafted onto the silica surface but percentage of grafting was very small. On the other hand, no retardation of the polymerization of styrene was observed in the presence of γ‐ray‐irradiated silica below 50 °C; the polymerization tends to accelerate and polystyrene was grafted onto the silica surface. Poly(vinyl acetate) and poly(methyl methacrylate) (MMA) were also grafted onto the surface during the polymerization in the presence of γ‐ray‐irradiated silica. The grafting of polymers onto the silica surface was confirmed by thermal decomposition GC‐MS. It was considered that at lower temperature, the grafting based on the propagation of polystyrene from surface radical (“grafting from” mechanism) preferentially proceeded. On the contrary, at higher temperature, the coupling reaction of propagating polymer radicals with surface radicals (“grafting onto” mechanism) proceeded to give relatively higher molecular weight polymer‐grafted silica. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2972–2979, 2006     

Some cycloaddition reactions of halomethylenecyclopropanes

Bromo-,chloro- and ethoxymethylenecyclopropane 3–5 undergo head to head dimerzations at 185–195° to give the corresponding 7,8-disubtituted dispiro[2.0.2.2]octanes 6–8 in high yields. Chloromethylenecyclopropane 4 undergoes cross cycloaddition reactions with near equimolar amounts of 3 and 5 to give about 50% of the corresponding mixed 7,8-disubstituted dispiro[2.0.2.2]octanes together with equal parts of 6 and 7 or 6 and 8. Bromo- and choromethylenecyclopropane also undergo similar cross cycloaddition reactions with methelene-cyclopropane to give the 7-halodispiro[2.0.2.2]octanes, but in relatively poor yields. At 190°, 4 reacts with 1,3-cyclopentadiene, furan, and 1,3-cyclohexadiene to give the products of (2+4) cycloaddition 12–14. With 2,3-dimethyl-1,3-butadiene at 190° ,4 gives the unusual products 18–20 in yields of 35%, 8% and 13%, respectively, and with acryloionitrile 4 gives exclusively 21, the product of (2+2) cycloaddition. Relative reactivities of 4 with furan, 2,3-dimethyl-1,3-butadiene, 1,3-cyclohexadiene, acrylonitrile and 1,3-cyclopentadiene were estimated as 1:2.5:2.5:4:and 50,respectively.     

Comparison of Birch with electrochemical reduction of 2,3-diphenyl-1,4-diazaspiro[4.5]deca-1,3-diene

Reduction of 2,3-diphenyl-1,4-diazaspiro[4.5]deca-1,3-diene is investigated both voltammetrically (glassy-carbon electrode, 20 °C, non-aqueous-solvents) and using dissolving-metals (sodium, ?78 °C, tetrahydrofuran (THF)/NH₃(l)). Remarkably, electro-reduction furnishes two two-electron processes, whilst only a four-electron product results from Birch synthesis.     

Synthesis of thermally stable aromatic poly(spiroorthocarbonate)s having a Cardo or bent structure

Novel poly(spiroorthocarbonate)s [poly(SOC)]s having a Cardo or bent structure were synthesized by polycondensation of several bis‐catechols having fluorene (BCFL), spirobisindane (BCSPI), or spirobischromane (BCSPC) in the structure with 2,2,6,6‐tetrachlorobenzo[1,2‐d:4,5‐d’]bis[1,3]dioxole (4ClBD). Synthesis of poly(SOC)s was confirmed by NMR and IR spectrometry. The poly(SOC)s obtained from BCFL or BCSPC were soluble in common organic solvents. The glass transition temperature of the poly(SOC)s was not detected by differential scanning calorimetry (DSC) in the range of 50–300 °C. The 10 wt % decomposition temperature of the poly(SOC)s was found to be above 400 °C. These results indicated the high thermal stability of the poly(SOC)s. Soluble poly(SOC)s could be possessed to form a film on a glass plate by the spin coat method. The obtained polymer films were 0.2 μm in thickness with 95% light transmission in the optical wavelength range. These results suggested that the Cardo or bent structure may block the packing of the main‐chain of the structure, which improves the solubility of the polymers, increases transparency, and enhances the thermal stability of SOCs. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1409‐1416     

旋光性聚{(+)-甲基丙烯酸-2,5-二[4′-((S)-2-甲基丁氧基)苯基]苄酯}的合成与表征

设计、合成了一个带有横挂三联苯侧基的手性乙烯基单体——(+)-甲基丙烯酸-2,5-二[4′-((S)-2-甲基丁氧基)苯基]苄酯,进行了普通自由基和原子转移自由基聚合反应.所得聚合物具有比单体低30°左右的比旋光度,且在侧基的紫外吸收处呈现明显不同于单体的Cotton效应,说明其主链可能形成了具有相反旋光方向的螺旋构象.在所研究范围内,聚合条件对聚合物的旋光度没有明显的影响.在分子量较小时,聚合物的比旋光度随着分子量的增加而降低,说明主链螺旋构象的贡献在增大,而当分子量达到一定值后,聚合物的比旋光度不再随分子量的增加而显著变化.