Selective Grafting of Block Copolymers, 3a. Multigraft Copolymers

Double‐grafted copolymers, poly(hydrogenated isoprene)‐block‐{polystyrene‐graft‐[poly(4‐methylstyrene)‐graft‐polystyrene]} and poly(hydrogenated isoprene)‐block‐{polystyrene‐graft‐[poly(4‐methylstyrene)‐graft‐poly(tert‐butyl methacrylate)]}, were prepared using a procedure consisting of two steps. The starting block copolymer, poly(hydrogenated isoprene)‐block‐polystyrene, was metallated using a sec‐butyllithium/N,N,N ´,N ´‐tetramethylethylenediamine complex. The multi‐metallated intermediate produced served as a multifunctional initiator for the anionic polymerization of 4‐methylstyrene, giving rise to the corresponding graft copolymer. The similar grafting‐from procedure was again applied to the synthesized graft copolymer. Using phenylpotassium superbase as the metallating agent and styrene or tert‐butyl methacrylate as the monomers to be grafted, enabled the corresponding double‐grafted copolymers to be prepared.     

Block copolymers by radical polymerization 3. Block copolymers of styrene,methyl acrylate,n-methyl-n-vinylacetamide, 1-vinyl-2-pyrrolidone

A polyazoinitiator obtained from 2,2′-azoisobutyronitrile (AIBN) and a diol is used to prepare block copolymers according to the Smets procedure. Partial decomposition of the polyazoinitiator in presence of a monomer results in an azogroup-containing prepolymer. Block copolymers are obtained decomposing the remaining azo groups in presence of a second monomer. Examples investigated are styrene/methyl acrylate, styrene/N-methyl-N-vinylacetamide, methyl acrylate/N-methyl-N-vinylacetamide, 1-vinyl-2-pyrrolidone/acrylonitrile. Homopolymers are produced simultaneously. Up to 70% of block copolymers are formed in these reactions. Block copolymers of styrene/methyl acrylate have hard/soft segmented molecules. It is an elastic material with spherical, cylindrical and lamellar, resp. domain structures, depending on the composition.     

Miscibility behavior in blends of poly(2,6-dimethylphenylene oxide) and random or block copolymers of styrene with methyl methacrylate

The Miscibility in blends of poly(2,6-dimethylphenylene oxide)

1 Systematic IUPAC name: poly[oxy(2,6-dimethyl-1,4-phenylene)].

(PPO) with random or block copolymers of styrene and methyl methacrylate (MMA) was studied by light microscopy and glass transition temperature measurements. Blends of PPO and the random copolymers were found to be miscible up to a copolymer content of 18 wt.-% MMA. The transition from miscibility to immiscibility in these blends in independent of temperature in the range 100 to 350°C. From these data, the segmental interaction parameter between units of the homopolymer and MMA, χ_PPO/PMMA is estimated to be about 0,5. Blends of PPO and the block copolymers of styrene and MMA used behave essentially as the corresponding homopolymers in terms of miscibility.     

Simple Photochemical Route to Block Copolymers via Two‐Step Sequential Type II Photoinitiation

A simple method for the preparation of block copolymers by a two‐step sequential Type II photoinitiation is described. In the first step, amine functionalized poly(methyl methacrylate) (PMMA‐N(Et)₂) is prepared by photopolymerization of methyl methacrylate at λ = 350 nm using benzophenone and triethyl amine as photosensitizer and hydrogen donor, respectively. Subsequent benzophenone‐sensitized photopolymerization of tert‐butyl acrylate using PMMA‐N(Et)₂ as hydrogen donor yielded poly(methyl methacrylate)‐block‐poly(tert‐butyl acrylate). The obtained hydrophobic block copolymer is readily converted to amphiphilic polymer by hydrolysis of the tert‐butyl ester moieties of the block copolymer as demonstrated by contact angle measurements. All polymers are characterized by NMR, Fourier transform infrared and UV–vis spectroscopies, and differential scanning calorimetry (DSC) thermal analyses.     

Triblock copolymer based thermoplastic elastomeric gels of a large service temperature range: preparation and characterization

Poly(methyl methacrylate)-block-polybutadiene-block-poly(methyl methacrylate) (MBM) triblock copolymers and their hydrogenated counterparts with poly(ethylene-co-1,2-butylene) midblock (MEBM) were swollen by an aliphatic oil of high boiling point which is a selective solvent for the central block. Thermoreversible gels are accordingly formed by both MBM and MEBM copolymers above a critical polymer content (Cr), which depends on the nature of the midblock and not on the copolymer molecular weight, at least in the investigated range. Cr has been found to be 5 wt.-% for an MBM block copolymer and 2 wt.-% for MEBM copolymers of various molecular weights. Gels of MEBM triblock copolymers exhibit interesting mechanical properties, such as high elongation at break (up to 870%) and high tensile strength (32 kPa). The most interesting feature of the MEBM gels is an upper service temperature as high as 170°C, thus more than 100°C higher than the value (47°C) reported for gels of an SEBS copolymer (S = polystyrene) of comparable molecular weight (100000) and composition (ca. 30 wt.-% hard block). The morphology of MEBM gels was studied by scanning electron microscopy (SEM) and found to be cocontinuous in case of a gel containing 20 wt.-% copolymer.     

Graft efficiency

Polystyrenes carrying tert-butyl peracrylic side groups have been synthesized by copolymerization of styrene with acrylyl chloride, partial esterification of the acid chloride units with tert-butyl hydroperoxide, and, finally, methylation of the remaining free carboxylic groups. The weight percent of perester units varied from 0.9 to 3.4, that of methyl acrylate between 14 and 18%. These copolymers were used at 75 °C. in benzene solution for initiating the polymerization of methyl methacrylate; this second step polymerization obeys the square-root law with respect to the initiator concentration, and is proportional to the monomer concentration. The graft efficiency, i.e. the ratio of the amount methyl methacrylate bonded as grafts to that of homopolymer, has been determined by carrying out fractionation of the several reaction products, using the precipitation method with chloroform as solvent and methanol as precipitant. The graft efficiency decreases from 1.52 to 0.77 when the monomer concentration increases from 1.91 to 7.54 mole· 1^?1; it is however unsensitive to the macroinitiator concentration, unsensitive to the bulk viscosity of the reaction medium as well as to the presence of non-solvent (methanol) in this medium. The perester-content of the macroinitiator exerces a slight influence, the efficiency being higher when this content increases. The temperature affects strongly the efficiency ratio; this ratio increases from 0.53 to 1.11 when the temperature rises from 55 ° to 75 °C.; this effect stresses the strong influence of the nature of the radical with respect to their ability of monomer addition.     

Polymerizations of 1-(9-anthryl)ethyl methacrylate and charge-transfer complex formations with its polymers

1-(9-Anthryl)ethyl methacrylate (9AEMA) was prepared by condensation of 1-(9-anthryl)ethanol with methacryloyl chloride. The rate of AIBN initiated polymerization of 9AEMA in benzene at 60°C was intermediate between the polymerization rates of styrene and methyl methacrylate. 9AEMA/styrene copolymerization studies at 60°C resulted in the copolymerization parameters r_9AEMA = 0,42±0,07 and r_st = 0,37 ± 0,08. Charge transfer complexes are formed between p- chloranil and the 9AEMA homo- and copolymers. The absorption maxima of the CT-complexes shifted to higher wavelengths with increasing 9AEMA content of the copolymers, whereas the equilibrium constant of the CT-complex formation was independent of copolymer composition. Both the complex formation enthalpies and entropies decreased with increasing 9AEMA content of the copolymers.     

The Synthesis of Liquid Crystalline Copolymers with Block Copolymer Grafts

The synthesis of novel copolymers consisting of a side‐group liquid crystalline backbone and poly(tetrahydrofuran)‐poly(methyl methacrylate) block copolymer grafts was realized by using cationic‐to‐free‐radical transformation reactions. Firstly, photoactive poly(tetrahydrofuran) macroinimers were prepared by cationic polymerization of tetrahydrofuran and subsequent termination with 2‐picoline N‐oxide. Secondly, the macroinimers and acrylate monomers containing different spaced cyanobiphenyl mesogenic groups were copolymerized to yield the respective graft copolymers. Eventually, these were used for indirect photochemical polymerization of methyl methacrylate by UV irradiation in the presence of anthracene as a photosensitizer leading to the final copolymers with block copolymer grafts. The liquid crystalline, semicrystalline, and amorphous blocks were micro‐phase separated in the graft copolymers.     

Protection and polymerization of functional monomers, 23. Synthesis of well-defined poly(2-hydroxyethyl methacrylate) by means of anionic living polymerization of protected monomers

Anionic polymerizations of 2-[(trimethylsilyl)oxy]ethyl methacrylate ( 1 ), 2-[(tert-butyldimethylsilyl)oxy]ethyl methacrylate ( 2 ), and 2-[(methoxymethyl)oxy]ethyl methacrylate ( 3 ), the protected forms of 2-hydroxyethyl methacrylate (HEMA), were carried out in THF at ?78°C with 1,1-diphenylhexyllithium or 1,1-diphenyl-3-methylpentyllithium in the presence of LiCl. The resulting poly( 1–3 )s were found to possess predictable molecular weights and very narrow molecular weight distributions. The sequential polymerizations of tert-butyl methacrylate with the anionic propagating ends of poly( 1–3 ) gave block copolymers in quantitative efficiency. Thus, the anionic polymerizations of 1–3 proceeded without transfer and termination reactions to afford stable living polymers. Complete hydrolysis of the protective groups of poly( 1–3 )s produced linear poly(HEMA) quantitatively. Novel well-defined di- and triblock copolymers containing hydrophobic [polystyrene, poly(4-octylstyrene), polyisoprene] and hydrophilic segments [poly(HEMA)] were also prepared by sequential polymerization of the corresponding hydrophobic comonomers with 1 , followed by deprotection.     

Block copolymers by sequential group transfer polymerization: poly(methyl methacrylate)-block-poly(2-ethylhexyl acrylate) and poly(methyl methacrylate)-block-poly(tert-butyl acrylate)

Poly(methyl methacrylate)-block-poly(2-ethylhexyl acrylate) (PMMA-block-PEHA) and poly(methyl methacrylate)-block-poly(tert-butyl acrylate) with a methacrylate/acrylate unit ratio of 1:1 and 1:3, 16000 < M _n < 44000 and 1,9 < M _w/M _n < 2,5, were prepared by sequential group transfer polymerization using (1-methoxy-2-methyl-1-propenyloxy)trimethylsilane as initiator and tetrabutylammonium fluoride monohydrate as a catalyst in tetrahydrofuran at ?30°C, PMMA being the first block. The increase in M _n during the successive addition of monomers is linearly dependent on the (co)polymer yield and size-exclusion chromatography (SEC) curves are shifted towards higher molecular weights in comparison with PMMA macroinitiators. The block structure of the copolymers was also proven by extraction experiments. The presence of homopolymers in the copolymers was not detected. When the former copolymer is prepared in a reverse way (PEHA segment being the first), the MMA polymerization ceases at ≈ 43–45% conversion.     

Radical and spontaneous thermal polymerizations of some captodative-substituted acrylates

The polymerization of some captodative-substituted acrylates was examined in the presence and absence of 2,2′-azoisobutyronitrile (AIBN) at 60 °C. Methyl acrylates, substituted by acetoxy, methoxy and ethylsulfenyl groups in α-position, and tert-butyl α-methoxyacrylate homopolymerized with and without this initiator. The rate of AIBN-initiated homopolymerization of methyl α-acetoxyacrylate was as high as that of methyl methacrylate in spite of the captodative-substituted monomer, and these acrylates also gave polymers spontaneously in remarkably high yield even under conditions under which styrene and methyl methacrylate are not polymerized. Copolymers of these monomers with styrene also were obtained in the presence and in the absence of AIBN. The mechanism of the initiation of the spontaneous thermal polymerization is discussed on the basis of ESR spectra, reaction intermediates and radical inhibition experiments.     

Miscibility in blends of random copolymers of styrene and acrylontrile with block copolymers of styrene and methyl methacrylate

Phase behavior in blends of random copolymers of styrene and acrylonitrile with block copolymers of styrene and methyl methacrylate was studied by light scattering, light microscopy and glass transition temperature measurements. The results are compared with those of respective blends containing random copolymers of styrene and methyl methacrylate. In terms of macrophase separation, the block copolymers display a more extended miscibility domain with styrene/acrylonitrile copolymers than the random copolymers. However, the extent of the miscibility domain varies as a function of temperature. Unlike the random copolymer blends, all blends containing block copolymers exhibit lower critical solution temperature behavior. Finally, it is established that the systems studied here undergo spinodal decomposition leading to macrophase separation.     

Living radical polymerization of styrene and its block copolymerization with methyl methacrylate

The existence of living polymer radicals in emulsion polymerization with a macromolecular heterogeneous initiator has been ascertained by preparing block copolymers of styrene with methyl methacrylate. Polymerization of styrene initiated by oxidized polypropylene and triethylenetetramine (3,6-diaza-1,8-octanediamine) proceeds even after the removal of the initiator from the emulsion, reaches 100% conversion, and methyl methacrylate newly added to the system undergoes further polymerization. The molecular weight of polystyrene and of the block copolymer increases with the conversion. The yield of pure block copolymer is about 90% under optimal conditions. The turbidimetric titration curve of the block copolymer shows a characteristic plateau region and suggests monodispersity of the copolymer. Reasons for the absence of termination in this system are presented. This type of living radical polymerization offers some advantages for the preparation of block copolymers, as compared with the anionic living polymerization.     

Synthesis and free radical ring-opening polymerization of 2-methylene-4-phenyl-1,3-dioxolane

The cyclic ketene acetal, 2-methylene-4-phenyl-1,3-dioxolane ( 3 ), was shown to undergo free radical ring-opening polymerization to produce the polyester, poly[γ-(β-phenyl)butyrolactone]. The monomer 3 was synthesized by an acetal exchange reaction of chloroacetaldehyde dimethyl acetal with styrene glycol in an 87% yield followed by dehydrochlorination of the resulting cis and trans-2-chloromethyl-4-phenyl-1,3-dioxolane ( 2 ) with potassium tert-butoxide in tert-butyl alcohol in a 70% yield. 3 was shown to undergo essentially quantitative free radical ring-opening at all temperatures from 60–150°C and also nearly complete regioselective ring-opening with cleavage to give the more highly stable secondary benzyl free radical. Even in free radical copolymerization with styrene, methyl methacrylate, vinyl acetate, or 4-vinylpyridine, 3 gives essentially complete ring opening to introduce an ester groups into the backbone of the addition copolymer. The structures of the polymers were established by elemental analysis and ¹H and ¹³C NMR spectroscopy.     

Living Anionic Polymerization of Functionalized Monomers, 2. Anionic Polymerization of p‐Alkenylstyrene Derivatives

A study has been carried out on the anionic polymerization of eight p‐alkenylstyrene derivatives. The monomers used are p‐(2‐propenyl)styrene ( 1 ), p‐(2‐propenyl)‐α‐methylstyrene ( 2 ), p‐(2‐butenyl)styrene ( 3 ), p‐(2‐butenyl)‐α‐methylstyrene ( 4 ), p‐(2‐methyl‐2‐propenyl)styrene ( 5 ), p‐(2‐methyl‐2‐propenyl)‐α‐methylstyrene ( 6 ), 8‐(p‐vinylphenyl)‐1‐octene ( 7 ), and 2‐methyl‐7‐(p‐vinylphenyl)‐1‐heptene ( 8 ). The anionic polymerizations of 1 – 4 were accompanied by competitive side reactions presumably due to the proton abstraction from their allyl groups. Furthermore, significant degrees of the propagating chain‐end carbanions derived from 1 , 3 , and 4 were deactivated in THF at –78°C after 1–2 h. In contrast, the polymerizations of 5 – 8 proceed in a living manner in THF at –78°C to afford polymers with predictable molecular weights and narrow molecular weight distributions. Novel well‐defined block copolymers of 5 – 8 with styrene or 2‐hydroxyethyl methacrylate were successfully prepared.     

Block copolymers of narrow molecular-weight distribution with a side-chain liquid-crystalline polymeric block as one component

Syntheses of block copolymers have been undertaken by photo-polymerization of 6-{4-[4-(butoxyphenoxy)carbonyl]phenoxy}hexyl methacrylate ( 1 ) using the living propagating chain end of poly(methyl methacrylate) as an initiating species. The latter was derived from photo-polymerization of methyl methacrylate (MMA) in the presence of methyl(5,10,15,20-tetraphenylporphinato)aluminium. The polymerization of 1 proceeded from the propagating end of poly(MMA) with high blocking efficiency to produce poly(MMA)-block-poly( 1 ) with narrow molecular-weight distribution. The length of the block chain could be controlled by varying the amounts of monomers. An endothermic peak of the block copolymer with higher mass of liquid-crystalline chain was observed at almost the same temperature region as that of poly( 1 ) on differential scanning calorimetric analyses, which suggests that the former has a structure with microphase separation.     

New thermo-crosslinking reactions of copolymers of phenyl methacrylates by use of polyfunctional epoxy compounds

Successful new thermo-crosslinking reactions of copolymers of various phenyl methacrylates by use of polyfunctional epoxy compounds were carried out in the film state at 100–150°C in presence of quaternary ammonium salts, quaternary phosphonium salts, tert-amines, or the crown ether dicyclohexyl-18-crown-6/potassium salt systems as a catalyst. Addition reactions of 4-nitrophenyl, 4-chlorophenyl or phenyl ester groups in the copolymers with ethylene glycol diglycidyl ether (EGGE) result in gel compounds without other side reactions. The rate of gel production of the copolymer having electron-attracting groups such as the 4-nitro group on phenoxide is faster than that of the other copolymers. It was also found that the rate of gel production of the copolymer is affected by the amount of phenyl methacrylate component in the copolymer, the glass transition temperature (T_g) of the copolymer, the structure of polyfunctional epoxy compounds as a crosslinking reagent, the length of alkyl chain in the catalyst, and the kind of counter anion of the catalysts, respectively.     

Diblock Copolymers with Azobenzene Side‐Groups and Polystyrene Matrix: Synthesis,Characterization and Photoaddressing

Summary: Diblock copolymers with a photoaddressable dispersed phase containing p‐methoxy substituted azobenzene side groups and a polystyrene matrix were synthesized and characterized. The block copolymers were prepared by a sequential living anionic polymerization of butadiene and styrene. The poly(1,2‐butadiene) segment was hydroborated and the hydroxy‐functions converted by a polymeranalogous reaction with the azo chromophore as side groups. The block copolymers were synthesized with different compositions by varying the length of the polystyrene segment and the length of the functionalized segment in order to obtain different morphologies. In this paper, for the first time a comparison of the cis‐trans photo‐isomerization behavior and photoaddressing with respect to different morphologies of the block copolymers is presented. To complete the comparison, the corresponding homopolymer and a statistical copolymer were also synthesized and investigated. A different photoaddressing behavior between homopolymer, statistical copolymer and the block copolymers was observed. One principal difference and advantage for photo addressable block copolymers is the lack of a formation of surface gratings which occurs in homopolymers and statistical copolymers.

TEM of a poly(1,2‐butadiene)‐block‐polystyrene copolymer containing azobenzene side‐groups.     

Stability of helical conformation and reactivity of optically active poly(triphenylmethyl methacrylate) in solution

The stability of the helical conformation in optically active poly(triphenylmethyl methacrylate) (PTrMA) was investigated by heating the polymer solutions at 100°C. The optical rotation slowly disappeared with time, and some preliminary experiments showed that this phenomenon is not due to a typical racemization process, as it is accompanied by a loss of triphenylmethyl (Tr) groups due to secondary reaction. Experimental results in the presence of methanol indicated that the decrease of optical activity occurs according to first-order kinetics and qualitatively methyl triphenylmethyl ether was isolated from the final solution. In order to explain the above results, full characterization of copolymers obtained by interrupting the methanolysis at different conversions was performed. As a working hypothesis, it was assumed that the reaction starts at the end of the helices with a Tr-oxygen bond fission and the reaction proceeds along the chain mainly with formation of block copolymers consisting of one block of PTrMA and one block of a probably random methacrylic acid anhydride/methacrylic acid copolymer.     

Liquid-Crystalline side-chain AB block copolymers by direct anionic polymerization of a mesogenic methacrylate

AB block copolymers with a liquid-crystalline and an amorphous block are synthesized by anionic copolymerization of 4-[4-(4-methoxyphenylazo)phenoxy]butyl methacrylate ( 1 ) with either styrene or methyl methacrylate (MMA). The polymerization of 1 proceeds from polystyrenelithium capped with 1,1-diphenylethylene to produce polystyrene-block-poly( 1 ), while poly( 1 )-block-PMMA is prepared by addition of MMA to the “living” poly( 1 ) anion. A large variety of block copolymers is obtained with narrow molecular weight distribution and definite composition. The mesophase behaviour of these samples is analyzed with respect to the chain length of the liquid-crystalline block. Electron microscopy of a high-molecular-weight polystyrene-block-poly( 1 ) provides direct evidence for a microphase-separated structure composed of spherical polystyrene domains embedded in a liquid-crystalline matrix. For the corresponding poly( 1 )-block-PMMA, however, electron microscopy indicates no structure, although dynamic mechanical analysis proves microphase separation.