Mechanism of fracture in glassy polymers. II. Survey of crazing response during crack propagation in several polymers

Of nine glassy polymers so far investigated, eight yield evidence that fracture propagation involves the formation and breaking of craze material. All eight produce fracture surfaces exhibiting interference colors to one extent or another and even the colorless areas cause low angle x-ray scattering. Ranked in terms of decreasing ease of colored surface formation, these polymers are poly(methyl methacrylate), poly(ethyl methacrylate), polystyrene, acrylonitrile—styrene copolymer, poly-α-methylstyrene, poly(vinyl acetate), a polyhydroxy ether, and polycarbonate. Only rigid poly(vinyl chloride) has failed to show evidence of precrack craze formation.     

Determination of coisotacticities of some alternating styrene–acrylic copolymers by NMR spectra

Coisotacticities σ for some alternating copolymers were determined through the analyses of their CH₃O, CH₃ and CH₂ proton NMR spectra; styrene–methyl methacrylate (σ = 0.56), styrene-methyl acrylate (σ = 0.53), styrene–methyl α-chloroacrylate (σ = 0.69), styrene–methacrylonitrile (σ = 0.19), styrene–methacrylamide (σ = 0.16), α-methylstyrene–methyl methacrylate (σ = 0.21), and α-methylstyrene–methyl acrylate (σ = 0.53) were studied. It was found that a terminal model or Bernoullian trial prevails in these complexed copolymerizations with diethylaluminum chloride. The influence of monomer structure on σ values is discussed.     

Synthesis of Vinyl Polymer—Poly (α-Amino Acid) Block Copolymers by End-Reactive Oligomers

In order to synthesize block copolymers consisting of segments having dissimilar properties, vinyl polymer - poly (α-amino acid) block copolymers were synthesized by two different methods. In the first method, the terminal amino groups of polysarcosine, poly(γ-benzyl L-glutamate), and poly(γ-benzyloxycarbonyl-L-lysine) were haloacetylated. The mixture of the terminally haloacetylated poly (α-amino acid) and styrene or methyl methacrylate was photoirradiated in the presence of Mo (CO)₆ or heated with Mo(CO)₆, yielding A-B-A-type block copolymers consisting of poly(α-amino cid) (the A component) and vinyl polymer(the B component). The characterization of block copolymers revealed that the thermally initiated polymerization of vinyl compounds by the trichloroacetyl poly(α-amino acid)/Mo(CO)₆ system was most suitable for the synthesis of vinyl polymer - poly-(α-amino acid) block copolymers. In the second method, poly (methyl methacrylate) and polystyrene having a terminal amino group were synthesized by the radical polymerization in the presence of 2-mercaptoethylammonium chloride. Using these polymers having a terminal amino group as an initiator, the block polymerizations of γ-benzyl L-glutamate NCA and e-benzyloxycarbonyl-L-lysine NCA were carried out, yielding A-B-type block copolymer. By eliminating the protecting groups of the side chains of poly(α-amino acid) segment, block copolymers such as poly(methyl methacrylate) with poly(L-glutamic acid) or poly(L-lysine) and polystyrene with poly(L-glutamic acid) and poly(L-lysine) were successfully synthesized.     

Graft copolymers of polyethylene by atom transfer radical polymerization

Poly(ethylene‐g‐styrene) and poly(ethylene‐g‐methyl methacrylate) graft copolymers were prepared by atom transfer radical polymerization (ATRP). Commercially available poly(ethylene‐co‐glycidyl methacrylate) was converted into ATRP macroinitiators by reaction with chloroacetic acid and 2‐bromoisobutyric acid, respectively, and the pendant‐functionalized polyolefins were used to initiate the ATRP of styrene and methyl methacrylate. In both cases, incorporation of the vinyl monomer into the graft copolymer increased with extent of the reaction. The controlled growth of the side chains was proved in the case of poly(ethylene‐g‐styrene) by the linear increase of molecular weight with conversion and low polydispersity (M_w /M_n < 1.4) of the cleaved polystyrene grafts. Both macroinitiators and graft copolymers were characterized by ¹H NMR and differential scanning calorimetry. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2440–2448, 2000     

Graft copolymers from star‐shaped and hyperbranched polystyrene macromonomers

Branched polystyrene macromonomers were synthesized by the slow addition of a stoichiometric amount of either 4‐(chlorodimethylsilyl)styrene or vinylbenzyl chloride as a coupling agent to living polystyryllithium. Star‐shaped macromonomers were produced by the addition of the coupling agent alone, and hyperbranched macromonomers resulted from the addition of the coupling agent along with styrene monomer. Star and hyperbranched graft copolymers were produced by the copolymerization of the macromonomers with styrene and methyl methacrylate. The copolymers were characterized by gel permeation chromatography coupled with multi‐angle laser light scattering, ¹H NMR spectroscopy, and Soxhlet extraction to determine that the macromonomers were incorporated in high yields into the copolymers. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3547–3555, 2001     

Radical block polymerization of vinyl chloride. II. Synthesis and characterization of vinyl chloride block copolymers

Peroxidized polypropylene has been used as a heterofunctional initiator for a two-step emulsion polymerization of a vinyl monomer (M₁) and vinyl chloride with the production of vinyl chloride block copolymers. Styrene, methyl-, and n-butyl methacrylate and methyl-, ethyl-, n-butyl-, and 2-ethyl-hexyl acrylate have been used as M₁ and polymerized at 30–40°C. In the second step vinyl chloride was polymerized at 50°C. The range of chemical composition of the block copolymers depends on the rate of the first-step polymerization of M₁ and the duration of the second step; e.g., with 2-ethyl-hexyl acrylate block copolymers could be obtained with a vinyl chloride content of 25–90%. The block copolymers have been submitted to precipitation fractionation and GPC analysis. Noteworthy is the absence of any significant amount of homopolymers, as well as poly(M₁)n as PVC. The absence of homo-PVC was interpreted by an intra- and intermolecular tertiary hydrogen atom transfer from polypropylene residue to growing PVC sequences. The presence of saturated end groups on the PVC chains is responsible for the improved thermal stability of these block polymers, as well as their low rate of dehydrochlorination (180°C). Molecular aggregation in solution has been shown by molecular weight determination in benzene and tetrahydrofuran.     

Spectroscopy of irradiated vinyl chloride–propylene copolymers

Spectra of vinyl chloride—propylene copolymers irradiated at low temperature in vacuum have been obtained at selected temperatures in the range 130–335°K. Copolymers and PVC homopolymer pass through identical intermediate states of dehydrochlorination in which alkyl, allyl, and polyenyl radicals are observed. Substantial spectral differences between copolymers and PVC appearing in the final states of dehydrochlorination after warming above room temperature are consistent with shorter average polyene lengths in the copolymers. This probably results from termination of polyene growth by propylene comonomer. Spectral differences at long wavelength between copolymers with varying amounts of propylene are minor compared to the basic changes between copolymer and homopolymer.     

Synthèse de copolymères greffés à base de polyéthylène—1

Polyethylene macromolecular free radical initiators, obtained by ozonization, are used to prepare graft copolymers with methyl methacrylate, styrene and vinyl chloride. The reactions parameters are the number of initiator groups (found by DPPH), peroxide and hydroperoxide proportions (respectively 36 and 64%), decomposition rate (K_d at 90° 10⁻¹sec⁻¹) and monomer concentration. The molecular structure of these copolymers is defined.     

Synthesis of tritium labelled monomers and polymers

The use of P₂O₅ for promoting the tritiation of various monomers and polymers has been investigated. Methyl methacrylate and vinyl acetate may be labelled at ambient temperatures by this procedure which is also applicable to labelling polystyrene and poly(α-methylstyrene). Exchange labelling of polymer substrates is most conveniently carried out in chlorinated hydrocarbons. The rate of tritium exchange increases with solvent polarity and temperature. Monomers of high radiochemical purity may be derived from the thermal depolymerization of tritiated polystyrene, poly(α-methylstyrene) and poly(methyl methacrylate).     

Aggregation and protein binding of sodium maleate copolymers with varying hydrophobicities

Copolymers of sodium maleate with methyl methacrylate, styrene, or vinyl acetate have been synthesized and studied in aqueous NaCl solutions of various ionic strengths. The polymers are polyelectrolytes with varying hydrophobicities, and their solution properties have been studied using static and dynamic light scattering. Copolymers containing methyl methacrylate or styrene were shown to aggregate in water upon increasing salt concentration. Copolymers of sodium maleate and vinyl acetate do not associate with increasing ionic strength. The binding of bovine serum albumin and cytochrome C to the sodium maleate copolymers was also investigated by light scattering. It was observed that cytochrome C forms complexes with the copolymers containing methyl methacrylate or vinyl acetate whereas albumin does not bind to any of the copolymers studied. Copyright © 2004 John Wiley & Sons, Ltd.     

Metal‐catalyzed living radical graft copolymerization of olefins initiated from the structural defects of poly(vinyl chloride)

Commercial poly(vinyl chloride) (PVC) contains allyl chloride and tertiary chloride groups as structural defects. This article reports the use of the active chloride groups from the structural defects of PVC as initiators for the metal‐catalyzed living radical graft copolymerization of PVC. The following monomers were investigated in graft copolymerization experiments: methyl methacrylate, butyl methacrylate, tert‐butyl methacrylate, butyl acrylate, methacrylonitrile, acrylonitrile, styrene, 4‐chloro‐styrene, 4‐methyl‐styrene, and isobornylmethacrylate. Cu(0)/bpy, CuCl/bpy, CuBr/bpy, Cu₂O/bpy, Cu₂S/bpy, and Cu₂Se/bpy (where bpy = 2,2′‐bipyridine) were used as catalysts. Living radical polymerizations initiated from 1‐chloro‐3‐methyl‐2‐butene, allyl bromide, and 1,4‐dichloro‐2‐butene as models for the allyl chloride structural defects and from 3‐chloro‐3‐methyl‐pentane and 1,3‐dichloro‐3‐methylbutane as models for the tertiary chloride defects were studied. Graft copolymerization experiments were accessible in solution, in a swollen state, and in bulk. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1120–1135, 2001     

Polymerization of coordinated monomers. XVIII. Sequence distribution in methyl acrylate–styrene copolymers prepared in the presence of zinc chloride

Methyl acrylate and styrene have been copolymerized in the presence of zinc chloride either by photoinitiation or spontaneously. The copolymerization mechanism is investigated by analyses of copolymers composition and monomer sequence distribution. The resulting copolymers are not always alternating, their composition being dependent especially on the monomer feed ratio. Appreciable deviation to higher methyl acrylate unit content from an equimolar composition occurs at monomer feed fractions of methyl acrylate over 0.7. The larger deviation is induced by higher temperature, by photoirradiation, and by greater dilution of the reaction mixture with toluene. The ¹³C-NMR spectrum of the alternating copolymer shows a sharp singlet at the carbonyl region, whereas the spectra of random copolymers prepared by benzoyl peroxide initiation at 60°C show a triplet splitting at the carbonyl carbon region, irrespective of copolymer composition. The relative intensities of the triplet peaks for the random copolymers are in good correspondence to the contents of triad sequences calculated by means of conventional radical copolymerization theory. These results clearly indicate that the carbonyl splitting is caused predominantly by variation of the monomer sequence and not by variation of the stereosequence. The monomer sequence distribution in the copolymers is thus directly and quantitatively measured from the split carbonyl resonance. Although the same triplet splitting appears in the spectra of methyl acrylate–rich copolymers prepared in the presence of zinc chloride at high feed ratios (>0.7) of methyl acrylate, the relative intensities of the split peaks do not fit the sequence distributions of random copolymers calculated by means of the Lewis–Mayo equation. The copolymerization yielding these peculiar sequences and the alternating sequence in the presence of zinc chloride is fully comprehended by a copolymerization mechanism proceeding between two active coordinated monomers, i.e., the ternary molecular complex composed of zinc chloride, methyl methacrylate, and styrene, and the binary molecular complex composed of zinc chloride and methyl methacrylate.     

Synthesis of PP graft copolymers via anionic living graft-from reactions of polypropylene containing reactive p-methylstyrene units

In this article, we discuss a new chemical route for preparing polypropylene (PP) graft copolymers containing a PP backbone and several (polar and nonpolar) polymer side chains, including polybutadiene, polystyrene, poly(p-methylstyrene), poly(methyl methacrylate), and polyacrylonitrile. The new PP graft copolymers had a controlled molecular structure and a known PP molecular weight, graft density, graft length, and narrow molecular weight distribution of the side chains. The chemistry involves an intermediate poly(propylene-co-p-methylstyrene) copolymer containing few p-methylstyrene (p-MS) units. The methyl group in a p-MS unit could be lithiated selectively by alkylithium to form a stable benzylic anion. Because of the insolubility of the PP copolymer at room temperature, the excess alkylithium could be removed completely from the lithiated polymer. By the addition of the anionically polymerizable monomers, including polar and nonpolar monomers, the stable benzylic anions in PP initiated a living anionic graft-from polymerization at ambient temperature to produce PP graft copolymers without any significant side reactions. The side-chain length was basically proportional to the reaction time and monomer concentration. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 4176–4183, 1999     

Cationic polymerization of α-methylstyrene from polydienes. I. Synthesis and characterization of poly(butadiene-g-α-methylstyrene) copolymers

The preparation of poly(butadiene-g-α-methylstyrene) copolymers was investigated with three different alkylaluminum coinitiators. The alkylaluminum compounds in conjunction with polybutadiene which contained a low concentration of labile chlorine atoms initiated the polymerization of α-methylstyrene to produce graft copolymers. Trimethylaluminum gave higher grafting efficiencies than diethylaluminum chloride at comparable monomer conversions. Triethylaluminum produced only very low monomer conversions (<5%), even at long reaction times, and for this reason was not studied extensively. The number of grafts per polybutadiene backbone was determined for a number of copolymers and found to increase slightly as the allylic chlorine concentration in the polybutadiene backbone was increased. In all cases, however, only a low percentage of the available labile chlorine sites along the polybutadiene backbone resulted in grafted α-methylstyrene side chains. The addition of small quantities of water to the polymerization solvent greatly enhanced the grafting rate and ultimate monomer conversion during the synthesis of these poly(butadiene-g-α-methylstyrene) copolymers. The mechanistic role of water during these grafting reactions is unknown at the present time.     

Formation of block copolymers from polyurethanes containing reactive disulfides

Block copolymers containing polyether segments and segments of a vinyl polymer have been synthesized. A low molecular weight polyether terminated with isocyanate groups was condensed with bis-(β-hydroxyethyl disulfide) to give polyurethanes containing reactive disulfide linkages. When this polymer was photolyzed in the presence of a vinyl monomer such as styrene, methyl methacrylate, or acrylonitrile, homolytic cleavage of the disulfide polymerized the monomer, giving block copolymers. The mechanical properties of the products were investigated by means of modulus–temperature measurements.     

The thermal degradation of polychloroprene-III degradation of polychloroprene/poly(methyl methacrylate) mixtures

The mechanism of dehydrochlorination has been studied by examining the degradation of polychloroprene/poly(methyl methacrylate) blends, using thermal volatilization analysis and infrared spectroscopy; the behaviour has been compared with that previously found for PVC/PMMA blends. Unlike the latter system, the polychloroprene blends did not show any increased production of methyl methacrylate monomer in the early stages of breakdown. The stabilization effect on PMMA due to reaction of ester groups with hydrogen chloride, on the other hand, is much more evident in the case of polychloroprene blends than for PVC, PVC dehydrochlorination is retarded by the presence of PMMA, but evolution of hydrogen chloride from polychloroprene is unaffected to any significant extent. It is concluded that the dehydrochlorination of polychloroprene is not a radical chain process. A unimolecular mechanism is suggested.     

Microstructure and Thermal Properties of Ethylene/Vinyl Chloride Copolymers

Abstract

The microstructure of ethylene/vinyl chloride (E/VC) copolymers, prepared by partial reduction of PVC with a variety of reagents, was analyzed using carbon-13 NMR spectroscopy. The effect of the reduction mechanism on the microstructure and stereochemistry of the copolymers was studied. The reduction with tri-n-butyltin hydride (TBTH) produced copolymers with higher degrees of alternating monomer units than copolymers obtained by reduction with lithium aluminum hydride (LAH). Reduction with lithium triethylborohydride (SH) produced blockier copolymers. The correlation of monomer sequence and distribution with thermal stability and dehydrochlorination rate in these copolymers was investigated. Partial reduction of PVC by all reagents was shown to produce E/VC copolymers with improved thermal stability compared to PVC. In the series of copolymers produced by TBTH reduction, improvement in thermal stability increased with an increase in E content and reached a maximum at 40% E content but dropped steadily thereafter. All copolymers from SH reduction showed a considerable drop in their dehydrochlorination rate compared to PVC. The stabilization effect reached a maximum at ～7 mol% E content and stayed constant throughout.     

Separation of copolymers by adsorption liquid chromatography

Binary random copolymers of styrene with butadiene, methyl methacrylate, and t-butyl methacrylate, and styrene-methyl methacrylate-acrylonitrile random terpolymers were separated by adsorption chromatography. The HPLC conditions required for the sample to adsorb to the stationary phase are discussed. Sequence length as well as composition affected the elution volume of block and graft copolymers of styrene and butadiene. A mixture of terpolymers having different composition was separated to each component by cross-fractionation using two types of adsorption chromatography.     

1:1 alternating copolymers of 1-bicyclobutanecarbonitrile with styrene

High molecular weight, 1:1 alternating copolymers of 1-bicyclobutanecarbonitrile with styrene were prepared in tetramethylenesulfone solution by complexing the electron-poor bicyclobutane monomer with zinc chloride. Methyl 1-bicyclobutanecarboxylate under these conditions gave copolymers containing a slight excess of styrene units (ratio 1:1.3 to 1:1.8). High molecular weight homopolymers of 1-bicyclobutanecarbonitrile and of methyl 1-bicyclobutanecarboxylate were prepared similarly. The tendency of the bicyclobutane nitrile to form 1:1 alternating copolymers is as great as that of its vinyl analog, acrylonitrile, and the synthesis of other alternating copolymers from this monomer should be possible.     

β-蒎烯嵌段、接枝共聚物的合成

分别使用苯乙烯 HCl加成物 (a)和 2 氯乙基乙烯基醚 HCl加成物 (b)作为引发剂 ,TiCl4 Ti(OiPr) 4(3∶1mol mol)为活化剂 ,在nBu4NCl存在下 ,- 40℃、CH2 Cl2 中 ,通过顺序活性阳离子聚合 ,合成了 β 蒎烯与苯乙烯、对甲基苯乙烯的嵌段共聚物 .又用带丙烯酰氧功能基的引发剂c [CH3CH (OCH2 CH2 X )Cl,X =OCOC(CH3)CH2 ]引发 β 蒎烯活性阳离子聚合 ,合成了 β 蒎烯大分子单体 .该大分子单体在AIBN引发下与甲基丙烯酸甲酯进行自由基共聚 ,获得主链为聚甲基丙烯酸甲酯、侧链为聚 β 蒎烯的接枝共聚物