Liquid crystalline,highly luminescent poly(2,5-dialkoxy-p-phenyleneethynylene)

A high-molecular-weight poly(2,5-dialkoxy-p-phenyleneethynylene) derivative has been prepared by the Heck reaction of 1,4-bis(2-ethylhexyloxy)-2,5-diiodobenzene and 1,4-diethynyl-2,5-dioctyloxybenzene. The highly luminescent polymer exhibits excellent solubility and can readily be processed into high-optical-quality films. The weight-average molecular weight M̄_w was 240000 g · mol⁻¹, with a polydispersity index of 2.9. Thermal analysis revealed a glass transition around 90°C, and an onset of chemical crosslinking at 130°C. The high M̄_w and the remarkable solubility enabled the preparation of liquid crystalline solutions of the new PPE.     

Crosslinking Index,Molecular Weight Distribution and Rubber Equilibrium Shear Modulus During Polyfunctional Crosslinking of Existing Polymer, 6. Primary Polymer with a Schulz–Zimm Distribution of Molecular Weights

A network model for the crosslinking of already existing polymer molecules with a so‐called Schulz–Zimm distribution of their molecular weights is presented. It is an extension of previously developed statistical network models applied to the crosslinking of primary polymers with several other molecular weight distributions and with crosslinks of any functionality. The model results in the possibility to obtain more insight into the structure of polymers, especially those with narrow distributions of the molecular weight. In more detail, the model can give a perspective on structural network parameters such as the weight fractions of ideal network, of dangling polymer ends, and of those molecules not connected to the network, i. e., the sol fraction, the number of crosslinks in which a polymer molecule is bound, the functionality of the crosslinks, or the average molar mass of the polymer molecules in between the crosslinks M̄_c. Results of calculations are shown for a hypothetical crosslinking process of polymers with various molecular weight distributions. Moreover, the dependency of the network parameters on the polydispersity index and the type of molecular weight distribution is shown. Finally the increase of the functionality of the crosslinks during the ageing process of a 9.9% poly(vinyl chloride) gel as a function of the polydispersity index of the molecular weight distribution is presented.     

PC及PC/ABS共混物的疲劳裂纹扩展研究

研究了聚碳酸酯(PC)和PC/ABS高分子材料的疲劳裂纹扩展规律,利用改进柔度法测量其裂纹扩展速率,采用扫描电子显微镜(SEM)观察其断口形貌,分析疲劳裂纹扩展机理.在较大裂纹扩展速率(10-6～10-3mm/cycle)范围内,PC/ABS的疲劳裂纹扩展速率可以用Paris公式da/dN=9·5587×10-5(ΔK)2·88381来描述.高分子材料PC的疲劳裂纹扩展速率约为高分子材料PC/ABS的3倍.高分子材料PC/ABS疲劳裂纹面上的特征以韧窝为主,较低裂纹扩展速率对应较小的韧窝,较高裂纹扩展速率对应较大的韧窝.高分子材料PC疲劳裂纹面有明显的不连续裂纹扩展带,其裂纹面相对较平.     

Determination of crack growth kinetics in non-reinforced semi-crystalline thermoplastics using the linear elastic fracture mechanics (LEFM) approach

The aim of this study was to find a satisfactory method to characterize the fatigue crack growth behavior of non-reinforced, semi-crystalline thermoplastic polymers using linear elastic fracture mechanics (LEFM). For this, crack growth curves (crack length versus cycle number) as well as crack growth kinetics curves (crack growth rate da/dN versus amplitude stress intensity factor ΔK) had to be generated. As methods suggested by ISO 15850 and ASTM E 647-11 failed to provide satisfactory results for the crack growth curves, a more advanced method was searched for and finally found in the literature. Regarding the crack growth kinetics curve, the idea of the calculation was based on methods recommended in ISO 15850 and ASTM E 647-11. However, these methods had to be considerably modified and improved in order to get accurate results with little scatter. The whole methodology was developed and verified with fatigue crack growth tests on two semi-crystalline thermoplastics (polyoxymethylene POM and polyetheretherketone PEEK).     

Free-radical polymerization of a reducing vinyl sugar ester in dimethylformamide and water

To develop a new synthetic polymer containing sugar branches, radical polymerization of the reducing vinyl sugar ester 6-O-vinyladipoyl-D -glucose ( 1 ) was performed in an organic solvent or in water. The polymers obtained with several azoinitiators in dimethylformamide (DMF) showed comparatively low average molecular weight (M̄_n ≈ 4500). In contrast, the use of a redox initiator (FeSO₄ and H₂O₂) in water gave polymers of higher average molecular weight (M̄_n ≈ 33000) in higher yield (90%), followed by crosslinking at high conversions.     

Synthesis and characterization of multiarm star-branched polyisobutylenes: Effect of arm molecular weight

A series of star-branched polyisobutylenes with varying arm molecular weights was synthesized using the 2-chloro-2,4,4-trimethylpentane/TiCl₄/pyridine initiating system and divinylbenzene (DVB) as a core-forming comonomer (linking agent). The resulting star-branched polymers were characterized with regard to the weight-average number of arms per star molecule (N̄_w) and dilute solution viscosity behavior. As the molecular weight of the arm (M̄_{w, arm}) was increased, dramatically longer star-forming reaction times were needed to produce fully developed star polymers. It was calculated that N̄_w varied from 50 to 5 as the M̄_{w, arm} was increased from 13,000 to 54,000 g/mol. The radius of gyration, R_g, of the star polymers was observed to increase as M̄_{w, arm} was increased. The solution properties of the star polymers were evaluated in heptane using dilute solution viscometry. It was determined that the stars had a much higher [η] compared to the respective linear PIB arms, but a much lower [η] compared to a hypothetical linear analog of an equivalent molecular weight. The dependence of [η] on temperature for the stars and linear arms was very small over the temperature range 25 to 75°C, with only a very slight decrease with increasing temperature. [η]_star was also determined to increase with increasing M̄_{w, arm}, but decrease with increasing M̄_{w, star}. The branching coefficient, g′, calculated for the stars at 25°C, increased as N̄_w decreased and agre ed well with literature values for other star polymer systems. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3767–3778, 1997     

The grafting of acrylamide onto poly(ε‐caprolactone) and poly(1,5‐dioxepan‐2‐one) using electron beam preirradiation. II. An in vitro degradation study on grafted poly(ε‐caprolactone)

Acrylamide was graft polymerized onto the surface of a biodegradable semicrystalline polyester, poly(ε‐caprolactone). Electron beam irradiation at a dose of 5 Mrad was used to generate initiating species in the polyester. The degradation in vitro at pH 7.4 and 37°C in a phosphate buffer solution was studied for untreated, irradiated and acrylamide‐grafted polymers. In the case of poly(ε‐caprolactone), all materials showed similar behavior in terms of weight loss. No significant decrease in weight was observed up to 40 weeks, after which the loss of weight accelerated. The main differences in degradation behavior were found for the average molecular weights, M̄_n and M̄_w. Virgin poly(ε‐caprolactone) maintained M̄_n and M̄_w up to about 40 weeks, whereas the irradiated and grafted poly(ε‐caprolactone) showed similar continuous declines in M̄_n and M̄_w throughout the degradation period. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1651–1657, 1999     

NMR relaxation study of crosslinked cis-1,4-polybutadiene

Proton relaxation measurements have been used to investigate the effects of crosslinking on the segmental motion in cis-1,4-polybutadiene samples. The temperature dependence of proton spin–lattice relaxation time T₁ and spin–spin relaxation time T₂ at 60 and 24.3 MHz are reported in cis-1,4-polybutadiene (PB) samples with different crosslink density including uncrosslinked PB and samples with 140, 40, and 14 repeat units between crosslinks. In addition, spin-lattice relaxation times in rotating coordinate frame, T_1p, have also been determined. The relaxation data are interpreted in terms of the effects of crosslinks on segmental chain motions. Because of their sensitivity to low-frequency motion, T₂ data are of major interest. At temperatures well above the T₁ minimum the small T₂ temperature dependence resembles solidlike behavior reflecting the nonzero averaging of dipolar interactions due to anisotropic motion of the chain segments between crosslinks. The magnitude of T₂ at 60°C is found to be proportional to the average mass between crosslinks.     

Synthesis and ring-opening polymerization of new 1,4-anhydro-glucopyranose derivatives

Three new 1,4-anhydro-glucopyranose derivatives having different hydroxyl protective groups such as 1,4-anhydro-2,3,6-tri-O-methyl-α-D -glucopyranose (AMGLU), 1,4-anhydro-6-O-benzyl-2,3-di-O-methyl-α-D -glucopyranose (A6BMG), and 1,4-anhydro-2,3-di-O-methyl-6-O-trityl-α-D -glucopyranose (A6TMG) were synthesized from methyl α-D -glucopyranoside in good yields. Their polymerizability was compared with that of 1,4-anhydro-2,3,6-tri-O-benzyl-α-D -glucopyranose (ABGLU) reported previously. The trimethylated monomer, AMGLU, was polymerized by a PF₅ catalyst to give 1,5-α-furanosidic polymer having number-average molecular weights (M̄_n) in the range of 2.8 × 10³ to 6.8 × 10³. The ¹³C-NMR spectrum was compared with that of methylated amylose and cellulose. Other anhydro monomers, A6BMG and A6TMG, gave the corresponding 1,5-α furanosidic polymers having M̄_n = 17.1 × 10³ and 1.8 × 10³, respectively. Thus, the substituents at the C2 and C6 positions were found to play an important role for the ring-opening polymerizability of the 1,4-anhydro-glucose monomers. In addition, debenzylation of the tribenzylated polymer gave free (1 → 5)-α-D -glucofuranan. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 841–850, 1998     

Highly heterotactic polymerization of methacrylates — Higher order stereoregulation and stereochemical significance

A combination of tert-butyllithium (t-BuLi) and bis(2,6-di-t-butylphenoxy)methylaluminium (MeAI(ODBP)₂) was found to be an efficient initiator for heterotactic living polymerization of certain alkyl methacrylates in toluene at low temperatures. The polymerization of methyl methacrylate (MMA) with t-BuLi/MeAI(ODBP)₂ (AI/Li=5 mol/mol) in toluene at −78°C gave heterotactic-rich poly(methyl methacrylate) (PMMA) with narrow molecular weight distributions (MWDs) (heterotactic triad fraction mr = 68%, ratio of weight- to number-average molecular weights M̄w/M̄n = 1.06-1.17). Other alkyl methacrylates also gave heterotactic polymers under the same conditions; in particular, ethyl and butyl methacrylates gave polymers with heterotactic triad fractions of 87%. The highest triad heterotacticity of 91.6% was obtained for the polymerization of ethyl methacrylate at −95°C. Some characteristic features of this stereospecific polymerization were discussed based on the polymerization results combined with other structural information of the polymer such as chain-end stereostructure and stereosequence distribution in the main chain.     

Cationic 1,2-vinyl addition polymerization of cyclic ketene acetals initiated by conventional acids

Pure 1,2-addition polymers, poly(2-methylene-1,3-dioxolane), 1b , poly(2-methylene-1,3-dioxane), 2b , and poly(2-methylene-5,5-dimethyl-1,3-dioxane), 3b , were prepared using the cationic initiators H₂SO₄, TiCl₄, BF₃, and also Ru(PPh₃)₃Cl₂. Small ester carbonyl bands in the IR spectra of 1b and 2b were observed when the polymerizations were performed at 80°C ( 1b ) and both 67 and 138°C ( 2b ) using Ru(PPh₃)₃Cl₂. The poly(cyclic ketene acetals) were stable if they were not exposed to acid and water. They were quite thermally stable and did not decompose until 290°C ( 1b ), 240°C ( 2b ), and 294°C ( 3b ). Different chemical shifts for axial and equatorial H and CH₃ on the ketal rings were found in the ¹H NMR spectrum of 3b at room temperature. High molecular weight 3b (M̄_n = 8.68 × 10⁴, M̄_w = 1.31 × 10⁵, M̄_z = 1.57 × 10⁵) was obtained upon cationic initiation by H₂SO₄. Poly(2-methylene-1,3-dioxane), 2b , underwent partial hydrolysis when Ru(PPh₃)₃Cl₂ and water were present in the polymer. The hydrolyzed products were 1,3-propanediol and a polymer containing both poly(2-methylene-1,3-dioxane) and polyketene units. The percentages of these two units in the hydrolyzed polymer were about 32% polyketene and 68% poly(2-methylene-1,3-dioxane). No crosslinked or aromatic structures were observed in the hydrolyzed products. The molecular weight of hydrolyzed polymer was M̄_n = 5740, M̄_w = 7260, and M̄_z = 9060. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3707–3716, 1997     

Effect of the mixture t - BuCl/SnCl4 on the cationic polymerization of isobutylene

The polymerizations of isobutylene initiated with the system tert-butyl chloride (t-BuCl)/SnCl₄ and carried out in CH₂Cl₂ at −20°C and −78°C were investigated. The results obtained demonstrate that the presence of t-BuCl in the polymerizing system gives rise to a PIB product with a distinctly bimodal MWD. The higher-molecular weight (HMW) PIB, M̄_n = 20000, I=M̄_w/M̄_n ∼ 2.5, is the result of existence of the protogenic initiation with residual water in the reaction system. The lower-molecular weight (LMW) PIB, M̄_n < 600, M̄_w/M̄_n ≤ 1.4, is the product of polymerization initiated presumably with a complex t-BuCl-SnCl₄-H₂O. To elucidate the reaction mechanism of the polymerization initiated with the complex, a series of similar isobutylene polymerizations using the initiation system 2,5-dichloro-2,5-dimethylhexane (DDH)/SnCl₄ was run and the oily LMW PIB samples were investigated by ¹H-NMR. A new polymerization mechanism describing the role of DDH and t-BuCl is suggested.     

Thermal polymerizations of alkali 4-(2-bromoethyl)benzoates in bulk

Thermal polymerizations of alkali 4-(2-bromoethyl)benzoates (2-BEBAs) were investigated. The polymerization of the lithium salt at 220°C for 2 h under reduced pressure in bulk, followed by esterification, produced poly(methyl 4-vinylbenzoate), having a number-average molecular weight (M̄_n) of 9500 in a 54% yield. Thus, elimination of hydrogen bromide to form a double bond occurred, followed by vinyl polymerization. In contrast, polymerization of the potassium salt at 200°C for 2 h afforded poly(oxycarbonyl-1,4-phenylene-ethylene) (polyester 1), having an inherent viscosity of 0.19 dL g⁻¹ in a 95% yield: i.e., polycondensation proceeded to afford the polyester. Reaction of the sodium salt at 220°C for 2 h produced polyester 1 having M̄_n of 4000 in a 28% yield as well as 4-vinylbenzoic acid in a 9% yield. In the reaction of the sodium salt, both polycondensation and double bond formation occurred. Thus, these polymerizations depended on the counter cations of 2-BEBAs. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2055–2060, 1999     

Cationic polymerization of vinyl ethers as synthetic path to diphylic polymers and potential complexants

The polymers of universal solubility like dimethyl ether of ethylene glycol and dioxane are synthesised by cationic polymerization of cis-1,2-dimethoxyethylene and p-dioxene. Some specific features of polymerization, going on long-lived active centers, are observed. In the case of polymerization of cis-1,2-dimethoxyethylene, conducted under usual conditions, the possibility of obtaining polymers with molecular weights as high as 10⁶ and M̄_w/M̄_N<1.5 is shown. Improved procedures of cyclopolymerization of divinyl ethers of mono-, di-, and triethylene glycols are described. Some solution properties of polymers obtained, including conformational transitions and metal ion complexing, are discussed.     

Highly stereospecific protonation of stereoregular living PMMA anions with several alcohols

Living and highly isotactic poly(methyl methacrylate) (PMMA) anion (M̄n = 2.5 × 10³) prepared with t-C₄H₉MgBr as an initiator was protonated with phenol in toluene at −78°C. The reaction was stereospecific toward meso addition, and the meso/racemo ratio at the chain-end of the resultant polymer was 89/11. Addition of 1,4-dioxane to the living isotactic PMMA anion in toluene at −78°C remarkably reduced the viscosity of the system, and protonation of the PMMA anion with phenol in the presence of 1,4-dioxane enhanced the meso-specificity to 94%. On the other hand, the protonation reaction of the living syndiotactic PMMA anion (M̄n = 2.5 × 10³), which was generated by t-C₄H₉Li/(n-C₄H₉)₃Al in toluene at −93°C, with t-butanol was found to be 97% racemo-specific. These highly stereospecific protonation reactions of the stereoregular PMMA anions were in contrast to the protonation of the anions with methanol or benzyl alcohol which was almost non-stereospecific.     

Thermodynamic properties of linear polyurethanes based on 1,6-hexamethylenediisocyanate with butane-1,4-diol and hexane-1,6-diol in the temperature range from T → 0 to 460 K

The temperature dependences of the heat capacity of partially crystalline linear polyurethanes based on 1,6-hexamethylenediisocyanate with butane-1,4-diol and hexane-1,6-diol were studied for the first time in a temperature range of 6–460 K by the methods of adiabatic vacuum and dynamic calorimetry. Physical changes in the state of polyurethanes were revealed and characterized; the standard thermodynamic functions, namely, C _p °(T), H°(T)-H°(0), S°(T), and G°(T)-H°(0), were calculated from the obtained experimental data in the temperature range from T → 0 to 460 K for the polymers in the crystalline, glassy, highly elastic, and liquid states. The energies of combustion of the polymers were measured by the bomb calorimetry method, and the standard thermodynamic characteristics of their formation at 298.15 K were calculated. The thermodynamic characteristics of bulk polycondensation of 1,6-hexamethylenediisocyanate with butane-1,4-diol and hexane-1,6-diol to form linear aliphatic polyurethanes-{4,6} and-{6,6} were determined in the range from T → 0 to 350 K at p° = 0.1 MPa. The thermodynamic properties of the polyurethanes under study and polymers of isomeric structure were compared. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 817–823, May, 2006.     

New processes and designed polymers by cationic techniques

The most important recent development in cationic polymerizations is the emergence of living polymerizations leading to a variety of new potentially useful well-defined macromolecules under conventional laboratory conditions. Three requirements have to coexist for living carbocationic polymerization to occur: Controlled initiation controlled chain-transferless propagation and controlled (quasiliving) termination. The first part of this presentation will briefly discuss the road to these three key requirements. The second part will concern practical consequences and select systems. The synthesis of narrow-molecular-weight-distribution (M̄_w/M̄_n = 1.1 - 1.3) tert-chlorine telechelic polyisobutylenes over a wide molecular weight range (M̄_n from ∼1000 to ∼125, 000 g/mole) will be outlined together with recent work on aromatic olefins, e.g., styrene, tert-butylstyrene and p-chlorostyrene. These developments led to the combination of these living systems for the synthesis of block copolymers by sequential monomer addition. Tri- or higher block copolymers comprising glassy outer segments and rubbery inner segments, for example, poly(styrene-b-isobutylene-b-styrene, poly(p-chlorostyrene-b-isobutylene-b-p-chlorostyrene), have been prepared. These new thermoplastic elastomers exhibit phase-separated microstructures and an interesting combination of physical-mechanical properties.     

Well-defined side-chain liquid-crystalline polysiloxanes

A route to well-defined side-chain liquid-crystalline polysiloxanes (ratio of weight-to number-average molar masses M̄_w/M̄_n < 1.2 is reported. Anionic ring-opening polymerization of pentamethylvinylcyclotrisiloxane yielded a poly(dimethylsiloxane-co-methylvinylsiloxane) backbone. A flexible disiloxane spacer was used to connect 4-(ω-alkenyloxy)-4′-cyanobiphenyl mesogenic molecules to the vinyl groups which belong to the backbone, leading to a side-chain liquid-crystalline polysiloxane (SCLCP) which has its mesogens distributed regularly along the main chain. Preliminary measurements indicate an electro-optic switching time τ_s = 1 min at 20°C and 7 s at 32°C (dc, 5 V/μm)).     

Synthesis of a novel starch-derived AB-type polyurethane

Starting from 1,4:3,6-dianhydrosorbitol (DAS, 1 ), a five step monomer synthesis led to 2-deoxy-1,4:3,6-dianhydro-2-isocyanato-L -iditol, 9 , which by catalytic polyaddition gave polyurethane 13 . A second route required the synthesis of 2-azido-5-O-chloroformyl-2-deoxy-1,4:3,6-dianhydro-L -iditol, 11 . During catalytic hydrogenation, the intermediate 2-aminochloroformyl derivative 12 underwent spontaneous polycondensation. The structure of 13 was characterized by ¹H and ¹³C NMR, IR spectroscopy and elemental analyses. Gel-permeation chromatography showed M̄_n = 8 000–12 000 corresponding to a degree of polymerisation up to 70. Differential scanning calorimetry revealed the polyadduct to be semicrystalline with a glass transition at T_g = 118°C and a melting range of 190–200°C. The polycondensation product was found to be crystalline with a melting range of 140–180°C.     

Polymerization of Methyl Methacrylate Initiated with Organomanganate Reagents

Organomanganate reagents [R₃Mn]^–Li⁺ (R = Bu, Me) were found to polymerize methyl methacrylate in the presence of potassium tert‐butylate. A conversion of the tacticity of the resulting poly(methyl methacrylate)s from heterotactic (mr = 54%) to isotactic (mm = 58%) was observed upon changing the R group of the initiator from Bu to Me. The addition of triisobutylaluminium was found to efficiently control M̄_w and M̄_w/M̄_n of the resulting polymers.