Showing papers in "Macromolecular Chemistry and Physics in 1986"

Molecular design of multicomponent polymer systems, 13. Control of the morphology of polyethylene/polystyrene blends by block copolymers

Abstract: As investigated by optical and electron microscopy, the observed morphology of the meltblended polyethylene/polystyrene pair unambiguously supports the interfacial activity of poly(hydrogenated butadiene-b-styrene) copolymers. The phase size is significantly reduced, the interfacial adhesion is dramatically increased and the phase dispersion is firmly stabilized against coalescence during subsequent processing. Diblock copolymers with a balanced composition are the most efficient interfacial agents in such an extent that only small amounts (1–2 wt.-%) are required to obtain homogeneous and stable phase dispersions. The emulsification concept applied to melt-blended immiscible polymers appears to be a powerful technique to prepare valuable polymer alloys.

Liquid crystalline elastomers based on liquid crystalline side group, main chain and combined polymers

Abstract: Covalently crosslinked liquid crystalline networks with elastic properties were prepared in isotropic solution from linear liquid crystalline polymers. As linear precursors for the networks were used: (i) polymers with the mesogenic groups in the side groups (polyacrylates and polymethacrylates), (ii) polymers with the mesogenic groups in the main chain (polymalonates) and (iii) polymers with the mesogenic groups in main chain and side groups (“combined liquid crystalline polymers”). In all crosslinked polymers the liquid crystalline phases of the linear polymers are retained. For low degrees of crosslinking (≤2 mol-%) the phase transition temperatures remain nearly unchanged. These elastomers are very soft above Tg and can be easily stretched for more than 100%. For higher degrees of crosslinking the phase transition temperatures are reduced.

Polylactones, 8. Mechanism of the cationic polymerization of L,L-dilactide

Abstract: Various acidic compounds were tested as potential initiators of the cationic polymerization of L,L-dilactide. Regardless of solvent and temperature only trifluoromethanesulfonic acid and methyl triflate proved to be useful initiators. With methyl triflate as initiator L,L-dilactide polymerizes faster than diglycolide, whereas diglycolide is more reactive when anionic or complexing initiators are used. Initiation with methyl triflate yields poly(L-lactide) with methyl ester endgroups indicating that the chain growth proceeds via cleavage of the alkyl-oxygen bond. At polymerization temperatures > 100°C the resulting poly(L-lactide) is 100% optically active indicating that the chain growth does not proceed via free carbenium ions, but via triflate ester endgroups. All attemps to identify cyclic dioxocarbenium ions as reaction intermediates failed, because propagation is much faster than initiation. However, in nitromethane oligomers with triflate ester endgroups were detected. For comparison the reaction of γ-valerolactone with methyl triflate was studied by means of IR and 1H NMR spectroscopy. Methylation of the exocyclic oxygen yielding a cyclic dioxocarbenium ion was found to be the sole reaction.

Anionic ring-opening polymerization of 2,2-dimethyltrimethylene carbonate

Abstract: The anionic ring-opening polymerization of 2,2-dimethyltrimethylene carbonate in solution with sec-butyllithium as initiator was found to result under suitable conditions in a bimodal molecular weight distribution, vic. cyclic oligomers and a high-molecular-weight polymer. The concentration of cyclic oligomers approaches that of a ring chain equilibrium. In the kinetically controlled regime high polymer yields were obtained. Optimum reaction conditions for a polymer yield of 85 – 95% are a temperature of −10°C, an initial monomer concentration of 10 weight-% and toluene as solvent. In THF the ring chain equilibrium is achieved readily. The ceiling temperature was determined to be ≈ 30°C. The homopolymer was characterized by spectroscopic, thermoanalytical and viscosity measurements. A high degree of crystallinity was observed.

Phase structure and compatibility studies in poly(ethylene oxide)/poly(methyl methacrylate) blends

Abstract: Morphology, crystallinity, and melting behaviour of solution-cast films of poly(ethylene oxide) (PEO)/poly(methyl methacrylate) (PMMA) blends were investigated as a function of composition, using optical and scanning electron microscopy, differential scanning calorimetry, and dilatometry. Up to a content of about 40 wt.-% of PMMA the blend films are completely filled with PEO spherulites, no separated domains of PMMA being observed. This observation suggests, in agreement with small angle X-ray scattering analysis, that for such compositions the PMMA molecules are incorporated in interlamellar regions of PEO spherulites. Blends with higher content of PMMA show islands of crystalline PEO within a matrix of PMMA; large amorphous regions coexist with not well developed PEO spherulites. Addition of PMMA strongly increases the nucleation density for PEO crystals. The solubility parameters δ of PEO and PMMA were calculated from specific volume values as a function of temperature. It was found that at temperatures higher than that of PEO melting the difference δ(PEO) - δ(PMMA) is very low suggesting that the two polymers are compatible in the melt. Compatibility of PEO and PMMA was also predicted by using a theoretical approach which allows to calculate the free energy of mixing as a function of composition and temperature.

Synthesis and properties of polyurethanes derived from diaminodianhydroalditols

Abstract: The readily accessible 1,4:3,6-dianhydroalditols with D-gluco- (1), L-ido- (5) and D-mannoconfigurations (6) were efficiently transformed into the 2,5-diamino-1,4:3,6-dianhydro-2,5-dideoxyalditols with D-gluco- (10), D-manno- (13), and L-ido-configuration (16). Interfacial polycondensation of these chiral heterocyclic diamines as well as ethylene- and tetramethylene diamine with the bis(chloroformate) 3 derived from 1,4:3,6-dianhydro-D-sorbitol gave the polyurethanes 17 to 21. Their number-average molecular weights were determined to be Mn ≈ 3000 corresponding to an average degree of polymerisation Pn ≈ 20. Inherent viscosities were measured, and 1H NMR spectroscopy as well as DSC gave informations about the molecular structure and some polymer properties.

Poly(ethylene glycol)s containing enzymatically degradable bonds

Abstract: The possibility to use poly(ethylene glycol) (PEG) as a synthetic, water-soluble polymeric carrier of biologically active compounds was investigated. The relationship between structure of oligopeptide (amino acid)-PEG conjugates and their hydrolysis catalyzed by chymotrypsin was studied. Two types of derivatives were synthesized: Derivatives of PEG 2000, containing an oligopeptide sequence terminating in p-nitroaniline (drug model) and higher molecular weight derivatives of PEG 2000 containing in the main chain enzymatically and hydrolytically degradable bonds. The rates of chymotrypsin catalyzed release of p-nitroaniline at pH 8,0 and 25°C were determined over a range of substrate concentrations to derive values for kcat and KM. The influence of the length and detailed structure of the oligopeptide sequence on the rate of hydrolysis was demonstrated. Comparison with copolymers of N-(2-hydroxypropyl)methacrylamide and poly(maleic anhydride-co-vinylpyrrolidone) showed that the sterical hindrance of the formation of the enzyme-substrate complex is much less pronounced in the PEG-oligopeptide conjugates. The latter conclusion is also valid in the case of cleavage of PEG derivatives which contain enzymatically degradable bonds in the main chain. The incorporation of a single amino acid residue (phenylalanine) into the main PEG chain is sufficient to make the polymer susceptible to chymotrypsin catalyzed hydrolysis.

Composition-properties relationships in propene-ethene random copolymers obtained with high-yield Ziegler-Natta supported catalysts

Abstract: The crystallization and thermal behaviour of crystallizable random propene/ethene copolymers (P-co-E) was systematically investigated. Index of crystallinity and, index of γ-form, enthalpy and entropy of fusion, equilibrium melting temperature, spherulite growth rate, and overall kinetic rate constant were determined and correlated with the overall ethene content and with the concentration of specific chemical defects as determined by 13C NMR analysis (PEP, EPP, EPE triads). The samples of the copolymers, obtained with very-high-yield Ziegler-Natta catalysts, were characterized by IR, 13C NMR, wide angle X-ray scattering, and differential scanning calorimetry.

Lyotropic mesophase of imogolite, 1. Effect of polydispersity on phase diagram

Abstract: The acidic aqueous solution of imogolite is proposed to be an ideal lyotropic system. No temperature dependence was marked on the two phase boundary concentrations (A and B points) of imogolite solutions as predicted by the theories of Flory and Onsager. A satisfactory quantitative agreement was observed with Onsager's theory. The polydispersity of rod lengths was found to shift the A point towards lower concentrations than expected from theory.

Polymerization of propene in the presence of MgCl2-supported Ziegler-Natta catalysts, 2. Effects of the co-catalyst composition†

Abstract: As a part of a study on the polymerization of propene in the presence of MgCl2-supported catalysts, new results were obtained when polymerizing at variable ethyl benzoate (EB)/alkylaluminium and alkylaluminium/Ti mole ratios. The pre-treatment of MgCl2 with the Lewis base is essential to achieve high stereoregularities without an unacceptable decrease of polymerization rate, apparently because it prevents the formation of nonstereospecific active sites of low Lewis acidity, which require high EB/alkylaluminium mole ratios in the co-catalyst in order to be poisoned. The data may be explained in the framework of a model of catalytic sites preliminarily presented in Part 1 of this series.

Rheological properties of liquid-crystalline side-group polymers in the isotropic, nematic, and smectic states

Abstract: The melt viscosity of seven liquid-crystalline side-group polymers with polyacrylate and polysiloxane main chains is measured as a function of shear rate and temperature. In the isotropic and also in the nematic phase none or only a very small dependence of the melt viscosity on shear rate is observed for the shear rates investigated. The melt viscosity in the nematic phase is higher than that in the isotropic phase. This is contrary to the results for liquid crystalline mainchain polymers and points to the fact, that there is no resulting orientation in shear flow of liquid-crystalline side-group polymers in the nematic phase. In the smectic phase the melt viscosity is very high and strongly shear-rate dependent. These results are compared with dielectric relaxation measurements on polymethacrylates and a polychloroacrylate.

Phase transitions and defect structure in the lamellar surface of polyethylene and n-alkane crystallites. Magic angle spinning 13C NMR studies†

Abstract: Variable temperature magic angle spinning 13C NMR experiments on linear alkanes and low molecular weight polyethylene allowed the observation of up to six carbon atoms at the chain ends near the surface of the lamellar crystallites. Conformational order-disorder and intermolecular packing effects are reflected by the spectra. The effects are discussed with regard to the peculiar phase behaviour of the n-alkanes and the fringed micella model for low molecular weight polyethylene. The solid-solid transitions of nonadecane and hexatriacontane appear to be correlated with the occurrence of specific non-liquid-like conformational disordering. Thus, conformational defects were observed for the “rotator phase” which depend on the chain length and which vary along the chain. Whilst the center part of the chain remains all-trans ordered, significant gauche defects were observed for the bonds at the chain ends. For a polydisperse low molecular weight linear polyethylene as well as for monodisperse octahexacontahectane reversible liquid-like conformational disordering of the terminal chain segments could be detected when the melting point was approached. Hence, in this case the NMR spectra indicate pre-melting of the lamella surface, while in case of the shorter n-alkanes the occurrence of end-gauche defects is correlated with solid-solid transitions.

Comparison of the cationic polymerization of octamethylcyclotetrasiloxane and hexamethylcyclotrisiloxane

Abstract: Some features of the cationic polymerization of hexamethylcyclotrisiloxane (D3) and octamethylcyclotetrasiloxane (D4) in methylene chloride in the presence of a strong protonic acid (CF3SO3H) were compared. The polymerizations of both these monomers show many similarities, which are taken as evidence for analogies in their mechanisms. In particular, in both cases the reaction is affected by the addition of a small amount of water. The role of water is interpreted in terms of its direct participation in some elementary reactions of the process. The addition of water affects also the state of hydrogen bonding association in the system. Some experimental results together with comments concerning the mechanism of ring formation in the polymerization system are included.

Synthesis of antitumor‐active conjugates of adriamycin or daunomycin with the copolymer of divinyl ether and maleic anhydride

Abstract: Polymeric conjugates of adriamycin (ADR) (2) or daunomycin (DM) (3) were synthesized by reaction of the drugs with the copolymer of divinyl ether and maleic anyhdride (DIVEMA) (1). The content of ADR moieties in the DIVEMA conjugate (4) could be varied depending on the reaction conditions up to 35,8 wt.-%. Considering the low toxicity and the high possibility of renal excretion, DIVEMA with Mw of 7000 and Mw/Mn = 1,6 was used for the conjugation. The rate of drug release from the conjugate was determined under physiological conditions by reversed phase HPLC. Within 14 days only 15% of the attached ADR was released from conjugate 4. The antitumor activity of the conjugates was tested in vitro and in vivo against mouse P388 leukemia. Conjugate 4 proved to be 28 times less active than ADR in vitro, which could be explained from the slow drug-release. On the contrary 50% of the leukemic mice treated by 4 survived more than 60 days, whereas no mice given ADR alone or the admixture of ADR and DIVEMA survived 30 days. An antitumor activity of the polymeric conjugate better than that of the free drug was also observed in vivo with DM. Such a polymeric effect can be attributed either to the change in body distribution, the difference in pharmacokinetics, or the slow drugrelease.

Biologically active polycations, 6. Polymeric pyridinium salts with well‐defined main chain structure

Abstract: Polyesters and polyamides with pendant N-alkylpyridinio-4-ylmethyl groups and definite spacer length between the pyridinio groups were prepared. It was found that the polyesters generally exhibit higher antibacterial activity than the corresponding monomers. Furthermore, the longer the alkyl chain length attached to the nitrogen of the pyridine ring, the higher is the antimicrobial activity. Polyamides with various spacer length were fractionated by gel filtration chromatography to obtain samples with comparable average molecular weights. Antimicrobial assessment of the fractionated polyamide samples demonstrated the existence of an optimum spacer length for lethal action.

Studies on the β‐form of isotactic polypropylene, 1. Characterization of the β‐form and study of the β‐α transition during heating by wide angle X‐ray diffraction

Abstract: The conditions for the formation of the β-form of isotactic polypropylene in the presence of a β-nucleator and the β-α transition during heating were studied by wide angle X-ray diffraction. A conditional crystallinity of the β-form, X′β, and a structural disorder parameter, S, deduced from WAXD data were defined for the characterization of the β-form in addition to the K value. The results show that X′β and S obviously depend on the content of β-nucleator, and that the β-α transition during heating essentially consists in the melting of the β-form and the successive recrystallization to the α-form.

Equilibria in the anionic polymerization of methyl methacrylate, 1. Chain‐length dependence of the rate and equilibrium constants

Abstract: The rate constants of polymerization and cyclization and the equilibrium constants of polymerization are calculated from kinetic data of the anionic oligomerization of methyl methacrylate initiated by methyl α-lithioisobutyrate in THF at 25°C, and of the “disproportionation” of living oligomers. The numeric method reported earlier was improved. The rate constants of cyclization decrease with chain-length, due to increasing steric hindrance. The rate constants of polymerization depend on the concentration of active centres, due to the formation of associates. Rate and equilibrium constants of polymerization decrease with chain-length. This is discussed in terms of intramolecular coordination of the counterion with ester groups of the chain.

Polymerization of propene in the presence of MgCl2‐supported Ziegler‐Natta catalysts, 3. Catalyst deactivation

Abstract: The different trends of polymerization rate as a function of time observed when polymerizing propene, ethylene and mixtures thereof in the presence of MgCl2-supported catalysts are explained assuming that catalyst deactivation is due to the reduction of Ti (III) by alkylaluminium to lower, polymerization-inactive oxidation states, and that ethyene polymerization is diffusion-controlled. A possible route for Ti reduction is also presented, which might give the reason for the observed kinetics of polymerization rate decay.

Influence of hydrogen bonding on the properties of elastomers and elastomeric blends

Abstract: Polybutadienes and polyisoprene are modified using 4-phenyl-1,2,4-triazoline-3,5-dione. The resulting urazole moieties give rise to the formation of hydrogen bonds. From the temperature dependence of the dilute solution viscosity as well as from GPC it can be deduced that intra- and intermolecular hydrogen bonds are formed. The intermolecular hydrogen bonds can be used to overcome the demixing tendency in blends of polybutadiene and polyisoprene. DSC measurements indicate enhanced miscibility depending on the degree of modification.

Liquid crystalline polyurethanes, 1. Polyurethanes based on 4,4′‐[1,4‐phenylenebis(methylidynenitrilo)]diphenylethanol

Abstract: Polyurethanes were synthesized from 4,4′-[1,4-phenylenebis(methylidynenitrilo)]diphenylethanol (3) with diisocyanates such as hexamethylene diisocyanate (4a), 4,4′-methylenedicyclohexyl isocyanate (4b), 1,3-cyclohexylenedimethyl isocyanate (4c), 2,4-toluylene diisocyanate (4d) and 4,4′-methylenediphenyl isocyanate (4e), and their thermal properties were investigated. The resulting polymers show a liquid crystalline state at 206–230, 160–216, 186–226 and 144–204°C, respectively, and the polymer obtained from 4e has a melting point at 272°C, determined by DSC and polarizing microscopy.

Lyotropic mesophase of imogolite, 2. Microscopic observation of imogolite mesophase

Abstract: Imogolite, though achiral, forms cholesteric spherulites in the anisotropic phase as shown by the regular striations arranged in a swirl-like or fingerprint pattern observed through a polarizing microscope. Electron microscopy revealed the raft-like imogolite sheet floating in the anisotropic phase. The structure of the imogolite sheet was deduced from periodicities observed by an electron microscope using various imaging conditions. The origin of the twisting force to maintain the cholesteric ordering is also discussed.

Addition polymerization of 1,4‐diethynylbenzene with 1,4‐benzenedithiol and properties of the resulting copolymer

Abstract: A novel addition polymerization of 1,4-diethynylbenzene (1) with 1,4-benzenedithiol (2) was studied under UV-irradiation in toluene solution at −20°C. The addition polymerization was found to proceed rapidly and a pale-yellowish polymer precipitated with the progress of the reaction (Mn = 7500). A soluble polymer was recovered from the toluene solution by evaporation. Its Mn value was estimated to be 3000. When an excess amount of 2 was used (mole ratio 1:2 = 2:3), the yield of the insoluble polymer increased. TG of the polymer indicated its decomposition point to be ≈500°C in air. The electroconductivity of the insoluble and soluble polymers was found to be 10−2 S · cm−1 and 10−5 S · cm−1 when doped with I2 at room temperature, respectively, and the conductivity was reversibly increased with increasing temperature up to 90°C. At T > 90°C the iodine was released and the conductivity decreased.

Solution and membrane properties of zwitterionic polymers

Abstract: The aqueous solution properties of poly(4-vinylpyridinium sulfopropylbetaine) (PVPyPS, systematic name: poly{1-[1-(3-sulfonatopropyl)pyridinium-4-yl]ethylene} (1)) and poly(3-methacryloylethoxycarbonylpyridinium sulfopropylbetaine) (PMAPS, systematic name: poly{1-methyl-1-[2-[1-(3-sulfonatopropyl)pyridinium-3-ylcarbonyloxy]ethoxycarbonyl]ethylene} (2)) are investigated. Polymers 1 and 2 are soluble only in salt solutions and their intrinsic viscosity increases with increasing salt concentration, this being a common property of poly(sulfobetaine)s. Hydrogel membranes containing PVPyPS are opaque in pure water but become transparent in salt solution.

Anionic polymerization of 4-methyl-2-oxetanone

Abstract: Potassium solutions, obtained by contacting the metal mirror with a THF solution of a crown ether were found to initiate the anionic polymerization of 4-methyl-2-oxetanone (1) (β-butyrolactone). The tacticity of the resulting polymer 2 was established by means of 13C NMR spectroscopy. The results indicate that living polymers of 1 were formed, and the polymerization proceeds without abstraction of hydrogen from the monomer and no termination and transfer reactions take place.

Dynamic mechanical behaviour and phase separation of mixtures of polysulfone with bis[4‐(4‐ethynylphenoxy)phenyl]‐sulfone or poly(phenylene sulfide)

Abstract: The dynamic mechanical behaviour and microphase-separation structure of polysulfone blends with bis[4-(4-ethynylphenoxy)phenyl]sulfone and with poly(phenylene sulfide) were investigated using torsional braid analysis and scanning electron microscopy. The experimental results showed that the size and shape of dynamic mechanical damping peaks and the structure characteristics of polysulfone blends with sulfur-containing polymers do not only depend on the chemical and physical nature and the weight fractions of the two components but also on conditions of thermal treatment leading to cross-linking reactions. In these multi-component polymer systems, the initially compatible mixture turns into an incompatible two-phase system during heating.

Dielectric properties of a liquid crystalline siloxane copolymer

Abstract: An investigation on the molecular dynamics of a liquid crystalline side chain polymer using the dielectric relaxation method on oriented samples in the frequency range of 0,1 to 10 000 kHz is presented. The compound under investigation is a polysiloxane copolymer with two different mesogenic side chains and a phase sequence glassy-smectic A-nematic-isotropic. Three main relaxation processes are found and assigned to the rotation of the side chains around the main chain, the glass transition process coupled with side chain motions, and a local motion in the glassy state, respectively. Evidence is found for a layered arrangement of the polymer main chain in the smectic phase and for a parallel correlation between the transverse components of the dipole moments.

High molecular weight chitosan 6‐O‐sulfate. Synthesis, ESR and NMR characterization

Abstract: Selective sulfation of the primary hydroxyl group of chitosan was performed by means of the pyridine-SO3 complex after the positions 2 and 3 of the aminoglucopyranosidic ring were protected by coordination with copper ions. The requirements for complexing copper ions were investigated as a function of the pH and Cu(II)/chitosan mole ratio of the starting solution. Cu(II)-chitosan complexes were characterized by ESR and 13C NMR CP-MAS investigations; two different paramagnetic Cu(II) species were observed, whose relative quantity changes by changing the pH of the starting solution. The g tensor values (species I: g1‖ = 2,28, g1‖ = 2,06, A2‖ = 160 G; species II; g2‖ = 2,24, g2‖ = 2,06, A2‖ = 160 G) are consistent with a CuN2O2 chromophore. The sulfation reaction was studied in the range of 25 to 75°C using 2 : 1 to 6 : 1 pyridine-SO3/Cu(II)-chitosan mole ratios. Under optimized reaction conditions, a selective 6-O sulfation was obtained in more than 90% yield.

A new chain transfer reaction in the anionic polymerization of 2,3-epoxypropyl phenyl ether and other oxiranes

Abstract: Carbonyl groups were found to be present in polymers of 2,3-epoxypropyl phenyl ether obtained by anionic polymerization. On the basis of quantitative analyses these groups were assumed to be formed in a reaction involving chain transfer to the monomer which proceeds in a manner different from that reported in the literature. Results of the present study were compared with those referring to the polymerization of methyloxirane, phenyloxirane and some chlorophenyl 2,3-epoxypropyl ethers.

Molecular weights and molecular dimensions of perfluoropolyether fluids

Abstract: The weight-average molecular weights of a series of fractions from two structurally different types of perfluoropolyether fluids were determined by low-angle laser light scattering. The limiting viscosity numbers of both sets of fractions were measured in Freon TF® and related to molecular weights. By using established polymer solution theory, the coil dimensions of the molecules were calculated. Samples from both sets of fractions were subjected to analysis by gel permeation chromatography and the coil dimensions were derived by using the principle of universal calibration. Results from both methods agree well. Bulk viscosities and molecular weights were correlated.

Polylactones, 7. The mechanism of cationic polymerization of β-propiolactone and ϵ-caprolactone†‡

Abstract: Homopolymerisations of β-propiolactone and ϵ-caprolactone, initiated by means of methyl trifluorosulfonate, triethyloxonium tetrafluoroborate or acetylium perchlorate, were investigated Both 1H and 13C NMR spectra proved that the alkylating initiators yield polyesters with alkyl ester end groups, indicating a chain growth via alkyl-oxygen cleavage of the lactone At temperatures below 100°C cationic polymerizations initiated by alkylating reagents were found to proceed via end groups which may cause degradation due to back-biting When ϵ-caprolactone was reacted with excess methyl triflate, high concentration of triflate ester end groups were formed, whereas in the case of β-propiolactone active end groups were not detectable by 1H NMR spectroscopy Initiation with acetylium perchlorate yielded a polyester with acetate end groups Acetate end groups were also obtained, when “living” polymers, initiated with methyl triflate, were reacted with acetic anhydride It could be shown that the formation of acetate end groups does not indicate an electrophilic attack at the endocyclic oxygen Furthermore, it is discussed that any experimental evidence for a cationic chain growth via acyloxygen bond cleavage is lacking