Über die quantenausbeute der kettenspaltung von polystyrol in lösung bei bestrahlung mit wellenlängen λ ≧ 270 nm

Values of the mean number of chain scissions per macromolecule and the quantum efficiency of chain scission processes are presented for systems studied in our previous works, in which the photodegradation of polystyrene in solutions irradiated with mercury light (λ ≧ 270 nm) was investigated and changes of the weight-average molecular weight M?_w were considered to be a measure for chain scission. The presented values of the number of scissions were obtained as follows: the molar mass distributions were determined for the investigated polystyrene samples by dynamic (quasielastic) light scattering experiments, before and after irradiation, the number-average molecular weight values M?_n were calculated from these distributions and the mean number of scissions was obtained from the changes of the M?_n values.     

Polystyrene as an inert medium in the synthesis of the styrene/divinylbenzene/acrylonitrile copolymers

Samples of styrene/divinylbenzene/acrylonitrile macroporous copolymers were prepared, using polystyrene as inert medium. The initial viscosity average molecular weight of the polystyrene samples were: M?_v.i=87000, 98000, 117000 and 218000. The polystyrene samples with the initial molecular weights M?_v.i=87000 and M?_v.i=117000 were reused as inert media, for many times, until they lost their capacity to produce permanent porosity of the copolymers. The macroporous copolymers were characterized by their permanent porosity and volume swelling. If a polystyrene sample is used for many times, the molecular weight of the polystyrene removed (extracted) is gradually diminished and therefore the permanent porosity of the macroporous copolymers decreases step by step. The reasons responsible for this behaviour are:

• during the copolymerization process a polystyrene with a smaller molecular weight is formed.
• polystyrene parts of high molecular weights are included in the network structure of the macroporous copolymers.

The evidence for this was given by plotting the differential and integral molecular weight distribution curves for six samples of polystyrene.     

Viscoelastic properties of mixtures of polystyrene with low-molecular-weight poly[oxy(2,6-dimethyl-1,4-phenylene)]

A series of poly[oxy(2,6-dimethyl-1,4-phenylene)]s (PPE) (trivial names: polyphenylenether, polyoxyxylene, polyphenyleneoxide) with narrow molecular weight distribution were prepared by polymerization of 4-bromo-2,6-dimethylphenol and subsequent fractionation. The molecular weight dependence of the glass transition temperature obeys the Fox-Flory equation. Polystyrene (PS)/PPE blends (PS: number-average molecular weight M?_n = 144 000, ratio of weight- to number-average molecular weight M?_w/M?_n = 1,05) were prepared using PPE samples with molecular weights below the entanglement spacing of PPE, in order to obtain information about the influence of specific interactions on the linear viscoelastic properties in the plateau and terminal region. The iso-free-volume state turned out to be the most appropriate reference state to compare samples of various compositions. Low-molecular-weight PPE essentially acts as a solvent for polystyrene. The concentration dependence of the zero-shear viscosity η₀ is proportional to ?^3,6_PS, ?_PS being the volume fraction of PS, and the temperature dependence of the logarithmic shift factor log a_T indicates that interactions, which are responsible for the thermodynamic miscibility in this system, do not alter the linear viscoelastic properties of PS. The concentration dependence of the plateau modulus (G⁽⁰⁾_N ∝ ?^1,2 for PS/PPE-1500) blends is explained by an additional small elastic contribution of the short PPE chains to the plateau modulus at higher frequencies.     

Volumes spécifiques de polystyrènes en étoile à l'état liquide

Specific volume measurements carried out on linear and star-shaped liquid polystyrene versus the number average molecular weight, M_n scaling between 5000 and 2.10⁶, are in good agreement with a review of the experimental results of others. These results confirm the occurrence of a loss of volume per monomeric unit above a molecular weight of 10000 already observed for polystyrene in solution. We attribute the influence of this specific volume variation against M_n on the thermal dilatometric coefficient α = (1/v)dv/dT and the temperature of vitrous transition. We also attempted to give an explanation for this phenomenon.     

UV-Photometrische Analyse kationisch erzeugter Polystyrole, 2. Quantitative Bestimmung von Endgruppen in Polystyrolen,dargestellt mit Acylperchloraten

Acyl perchlorates generated in styrene without a solvent by acyl chlorides and silver perchlorate gave polystyrenes with covalently bonded acyl groups. In order to gain secured values their number average relative molecular masses (M?_n) were determined by different methods. The polystyrenes could be hydrogenated with hydrogen and Raney nickel at room temperature and under atmospheric pressure without attacking the phenolic nuclei. In addition IR data and a UV absorption at 294 nm of the polystyrenes revealed the presence of and olefinic bond, which was also found in a polystyrene obtained by polymerisation with perchloric acid. Also the quantitative evaluation of the hydrogeneation by UV absorption data gave number average relative molecular masses (M?_n,H), which are in accordance with other M?_n values. Furthermore, the UV absorption data of the polystyrenes gave correct M?_n values (M?_n,e) in combination with the molar absorption coefficients (ε) of model compounds. The number of covalently bonded acyl groups in a polystyrene sample could be determined by quantitative measurement of the UV absorption in combination with the ε-values of model compounds and the M?_n values. This number was found to depend on the nature of the acyl perchlorate and it amounts to one acyl containing molecule per four to hundred molecules without an acyl group.     

Dilute solution properties of high molecular weight poly(isobutyl methacrylate). III. Effect of centrifuging on various parameters

Three high molecular weight samples of poly(isobutyl methacrylate(designated as 937, SW 63/0082, and SW 62/0298 were obtained from Edgewood Arsenal, Maryland. Sample 937 has been fractionated and described^l,2) earlier. Initial investigations have shown that the solution viscosities were shear dependent. The three samples were subjected to centrifugation at constant velocity for various times. The intrinsic viscosity and molecular weight (M?_w) dropped slightly for sample 937, but dropped drastically for the other two samples. The number average molecular weight (M?_n) remained constant for each sample under these conditions. In this presentation we have also shown the necessity for taking measurements at low angles daring light scattering measurements in order to obtain the correct molecular weight (M?_w) for these high molecular weight species.     

Molecular weight determination of isotactic polypropylene by high-sensitivity ebulliometry

The use of a new differential ebulliometer and the determination of the number average molecular weight of unfractionated isotactic polypropylenes is described; the results were reproducible and of satisfactory accuracy. Application of a thermopile with 150 junctions and of suitable devices for the regularity of boiling allowed measurements of number average molecular weights M?_n up to 100000 in good agreement with results obtained by other methods. In this way it is possible to measure M?_n directly, e.g. for reliable determinations of M?_w/M?_n also for polymer samples with low molecular weights and/or wide molecular weight distributions.     

Experimental verification of effects of conditions of solutional fractionation on molecular weight distribution of the first fraction by atactic polystyrene/methylcyclohexane system

The solutional fractionations were carried out experimentally on lowering the temperature of solutions of atactic polystyrene in methylcyclohexane. The concentration of the initial solution and the relative amount of the polymer dissolving in the polymer-lean phase (i.e., the amount of the fraction) were systematically changed. Gel permeation chromatography was applied to determine the molecular weight distribution (MWD) of the first fractions and the original polymer. In addition, polydispersity parameters including the ratio of the weight average molecular weight to the number average molecular weight, M _w/M _n, and the standard deviation, σ′, were calculated from MWD curves. Effects of the fractional conditions on the MWD for the first fractions were compared with those obtained by the computer simulation as well as the experimental results obtained in the case of the precipitational fractionation. The validity of the theoretical conclusions on the solutional fractionation, reached from the computer simulations, was definitely confirmed from the experiments.     

Synthesis and characterization of aliphatic-aromatic poly(ether amide)s

Four aromatic diamines containing aliphatic spacers and Meta and para oriented oxyphenylene rings, and their corresponding hydrochlorides, were combined with isophthaloyl chloride (IPC) and terephthaloyl chloride (TPC) to give high molecular weight polyamides by interfacial and low-temperature solution methods. The synthesis and characterization of monomers and polymers are reported, and the differences observed in polycondensation yields, molecular weights and molecular weight distributions, as a function of the method of synthesis, are discussed. Values of number-average molecular weight (M?_n) up to 8 × 10⁴ g/mol and weight-average molecular weight (M?_w) up to 1 × 10⁵ g/mol could be measured by gel permeation chromatography using aromatic polyamide standards, and values of M?_n up to 2 × 10⁵ g/mol and M?_w up to 3.6 × 10⁵ g/mol by using polystyrene standards.     

Determination of network structure by extraction and random degradation, 2. Experimental results: Functionality,inhomogeneity and efficiency of crosslinking

Experiments on networks crosslinked by peroxides show that the amount of extracted molecules as well as the time needed for a dissolution of a network during random degradation and the molecular mass

1 “Relative molecular mass” (systematic IUPAC name) is shortened to “molecular mass” throughout this paper.

of high molecular mass degradation products may be used to determine previously inaccessible structural details, such as molecular mass of the network chains, weight fraction of chains with one free end, functionality of the crosslinks, and inhomogeneity of crosslinking, i.e. the amount, the diameter, and the concentration of crosslinking units of anomalously and strongly crosslinked regions. In crosslinking of polydienes, chain splitting is negligible, but the functionalities of the crosslinks are abnormally high for low peroxide concentrations, because the peroxide radicals may connect more than two chains by polymerization. A relatively high spatial inhomogeneity of the concentration of crosslinking units occurs with polybutadienes, presumably because the radicals of this polymer have especially long life-times so that they can polymerize sequences of polyfunctional crosslinks via kinetic chains with transfer reactions. In crosslinking of polyisoprene the apparent efficiency of this peroxide is about 1,0 if one takes into account not only the number of crosslinks, but also that of loops, and if one neglects transfer. The efficiency of this peroxide is ? 1 in the crosslinking of polybutadiene, because of pronounced transfer reactions.     

On the molecular weight determination by vapor pressure osmometry (VPO), 2. Molecular weight average obtained by VPO

Provided that in molecular weight determinations by vapor pressure osmometry (VPO) the relationship between M and the measured quantity (δV/c)_c=0 obeys a calibration function of the type (δV/c)_c=0 = KM^?a, the kind of molecular weight average M?_VPO delivered by this method is derived. The deviation of M?_VPO from the true number average molecular weight M?_n is estimated from its dependence on the polydispersity and the exponent a of the calibration function.     

Micellisation de copolymères séquencés polystyrène-polyvinylpyridinium, 3. Influence de la concentration en sel et de la température

The effects of the salt concentration and temperature on the micellization phenomenon of polystyrene-poly(4-vinyl-N-ethylpyridinium bromide) block copolymers in dilute solution are investigated in solvents selective for the polyelectrolytic part (water-methanol-LiBr mixtures). The polystyrene moiety being in non-solvent media remains rather collapsed whatever temperature and salt concentration. On the contrary, the latter parameters modify strongly the conformation of the soluble polyelectrolytic chains and therefore determine the “quality” of the solvent essentially towards the polyvinylpyridinium blocks. Consequently an increase of the temperature or a decrease of the salt concentration have the same effect on the behaviour of the copolymers. In the case of a copolymer with a small molecular weight polystyrene block (M_w = 2 700), the unimer-multimer (single molecules/micelles) equilibrium is easily shifted in favour of the single molecules by increasing the temperature or decreasing the ionic strength. On the contrary, if the polystyrene moiety is longer (M_w = 6 000 – 13 000) the micellar weight of the system is little or even not at all influenced by the ionic strength and the temperature. These results emphasize that, for the investigated systems, it is the “insoluble” blocks which essentially govern the micellization phenomenon.     

Synthesis and characterization of ABA-triblock copolymers with polystyrene and main-chain liquid crystalline polyester segments

This paper reports on the synthesis and characterization of polystyrene-block-poly(2,2′-dimethyl-4,4′-biphenylene phenylterephthalate)-block-polystyrene. The ABA-triblock copolymers were synthesized by condensation reactions of telechelic poly(2,2′-dimethyl-4,4′-biphenylene phenylterephthalate) with anionically prepared ω-hydroxy polystyrenes. Three different lengths of the liquid-crystalline polyester (M?_n = 2650, 5 500, 10 100 g/mol) were used as central block B. The number-average molecular weight M?_n of the polystyrene segments was varied in the range of 690 to 10 000 g/mol. The liquid crystalline behavior and the transition temperatures are discussed with respect to the molecular weight of the polystyrene segments and the block copolymer composition. A comparison with the corresponding polymer blends is given and first results on the morphology of the block copolymers are presented.     

Synthèse et caractérisation de copolymères coordinés par des sels métalliques

The anionic block copolymerisation of isoprene and 2-vinylpyridine (2VP) followed by a coordination with iron (III) chloride, leads to thermoreversibly crosslinked copolymers. These copolymers are character+ed by a low polydispersity (M?_w/M?_w≈1,1) between the coordination nodules of poly(2-vinylpyridine). The study of the swelling ratio at the equilibrium in benzene shows that such a polymeric network does not reach the equilibrium state expected from the thermodynamic analysis of the system. The presence of 2VP in the copolymer induces a screening effect which prevents the solvent diffusion through the polyisoprene network.     

Control of Macromolecular Architecture of Polyamides by Poly‐Functional Agents, 1. Theoretic and Experimental Approaches to Star‐Branched Polyamides

In this first paper of the series, a statistical model for star‐branched polycondensation of AB type monomers in the presence of a polyfunctional agent RA_f was completely developed. The analytical expressions obtained for the number‐average (DP_n) and weight‐average (DP_w) degree of polymerization, and the dispersion index (D) for whole polymer species, linear and star macromolecular chains, were derived as a function of the conversion of the functional group of RA_f. An important molecular parameter, mole fraction of star‐branched polymer, was introduced. Numerical examples are reported on the relationship between molecular parameters and conversion of the functional group of RA_f. It is illustrated that the molecular weight properties of the linear and star‐branched polymers in the mixture of the products are very important factors for the application of this kind of polymeric materials. Polymerization of 6‐aminocaproic acid was carried out in the presence of terephthalic (T2) and trimesic (T3) acids as tri‐ and bifunctional agents. The molecular weights calculated are in good agreement with those obtained by size exclusion chromatography (SEC).     

Uncrosslinked epoxide-amine addition polymers, 44. Linear arylamine/2,2-bis[4-(2,3-epoxypropoxy)phenyl]-propane addition polymers — synthesis and properties

The addition polymerization of aromatic disecondary diamines and 2,2-bis[4-(2,3-epoxypropoxy)phenyl]propane (DGEBA) leads to linear high molecular weight epoxide-amine addition polymers with number-average molecular weights ranging from 10 000 to 20 000 g/mol. Depending on the amine structure, their glass transition temperatures were estimated between 80 and 140°C. The fractionation of the high molecular weight addition polymers allows the separation of cyclic oligomers and the separation of polymers with narrow molecular weight distribution (M?_w/M?_n = 2.4–2.8). In dilute solution, predominantly cyclic oligomers were formed. Hence, they were prepared in such solutions and isolated by means of column chromatography. Their cyclic structure is proved by combination of M? values and ¹³C NMR spectra.     

Lithium alkylnickelate and alkylpalladate bimetallic “ate” complexes as initiators for anionic polymerization of methyl methacrylate

Anionic-coordinative polymerization of methyl methacrylate (MMA) was carried out in the presence of new bimetallic initiators based on lithium alkylnickelates and alkylpalladates in tetrahydrofuran, at ?78°C. Well-defined poly(methyl methacrylate), PMMA, with molecular weights increasing linearly with conversion and relatively narrow polydispersities (M?_w/M?_n = 1,26 to 1,4) were prepared by initiation with some of the “ate” complexes. In the presence of lithium “ate” Ni-based complexes, PMMA with enhanced syndiotacticity [(rr) = 73 to 75%] was formed.     

Determination of network structure by extraction and random degradation, 1. Theory

The weight fraction and the molecular mass

1 “Relative molecular mass” (systematic IUPAC name) is shortened to “molecular mass” throughout this paper.

of polymeric material extracted from a polymer network, the time needed for the dissolution of the network during random degradation, and the molecular mass of the high molecular mass degradation products can be utilised for the determination of previously inaccessible structural details of the network, e.g. the value of the molecular mass of network chains, the chain end correction term, the functionality of the crosslinks, and the inhomogeneity of crosslinking, i.e. the amount, the diameter, and the crosslink concentration of anomalously and highly crosslinked regions.     

Stereocomplex‐ and Homo‐Crystallization and Phase‐Transition Behavior of Relatively High‐Molecular‐Weight Linear One‐ and Two‐Armed and Star‐Shaped Four‐Armed Poly(l‐lactide)/Poly(d‐lactide) Blends

Relatively high‐molecular‐weight linear one‐ and two‐armed and star‐shaped four‐armed poly(l ‐lactide) and poly(d ‐lactide) are synthesized and the multiplicate effects of arm‐number (branching architecture, coinitiator moiety), crystallization temperature (T _c), and number‐average molecular weight (M _n) on stereocomplex (SC)‐ and homo‐crystallization and phase‐transition behavior are investigated. For nonisothermal and isothermal crystallization, in addition to SC crystallites, homo‐crystallites are formed in the blends with higher M _n values, irrespective of arm number. For isothermal crystallization, the transition T _c ranges below which in addition to SC crystallites, homo‐crystallites are formed depended on M _n per one arm‐determining melting temperature or thickness of homo‐crystallites. The transition M _n ranges above which in addition to SC crystallites, homo‐crystallites are formed are not affected by arm number. The high molecular weight disturbs the change of crystalline growth mechanism of one‐ and two‐armed blends, whereas the branching architecture inhibits the change of crystalline growth mechanism of four‐armed blends.     

N‐oxyl mediated free radical donor‐acceptor co‐ and terpolymerization of styrene,cyclic maleimide monomers and n‐butyl methacrylate

The N‐oxyl mediated donor‐acceptor copolymerization of styrene as a donor and the maleimides N‐phenylmaleimide (NPI), N‐benzylmaleimide (BMI), and N‐cyclohexylmaleimide (CMI) as acceptor monomers is studied, using 2,2,6,6‐tetramethylpiperidine‐N‐oxyl (TEMPO) as reversible capping agent and benzoyl peroxide (BPO) as initiator. These copolymerizations are characterized by high polymerization rates and very short induction periods. In bulk, a control of the molecular weights and the polydispersity is only possible for the weakest acceptor CMI. For the stronger acceptors BMI and NPI the polymerizations have to be performed in solution (anisol) to realize a linear increase of the molecular weight with conversion and polydispersities below M_w/M_n 1.55. The polymerization rates (NPI > BMI > CMI), the induction periods (CMI > BMI > NPI) and the total number of polymer chains (NPI > BMI > CMI) of the TEMPO mediated free radical donor‐acceptor copolymerizations are a function of the acceptor strength of the maleimide monomers. As the main reason for the observed high reactivity, an “acceptor depending self‐initiation”, proceeding via a Diels‐Alder reaction mechanism, is discussed. Additionally, the concept of the “acceptor depending self‐initiation” is used for the rate of acceleration of S/BuMA copolymerizations leading to poly(S‐co‐BuMA‐co‐maleimide) terpolymers with well‐controlled molecular weights and narrow molecular weight distributions.