Preparation of poly(urethane/vinyl) block copolymers initiated by polyurethane-type macroazo initiators

Poly(urethane/vinyl) block copolymers (PU-PV) were obtained in high yields by the polymerization of vinyl monomers (butyl methacrylate (BMA), ethyl acrylate (EA), and methyl methacrylate (MMA)) in the presence of polyurethane-type macroazo initiators (PUMAI). PUMAI was prepared via addition reaction of azodialcohol, dipropylene glycol and hexamethylene diisocyanate. The PU-PBMA's, as typical examples of PU-PV's were purified by solvent extraction. Characterization of the purified PU-PBMA's by ¹H NMR, IR, together with extraction behavior, supported the block nature of PU-PBMA. Film tensile strength and elongation measurements in comparison with the corresponding blend samples also supported the block nature of PU-PV.     

Synthesis of block copolysaccharides by ring-opening polymerization of anhydro sugar derivatives

Ring-opening polymerization of anhtydro sugar derivatives was carried out with Lewis acid catalysts to produce block copolysaccharides. Polymerization of 1,4-anhydro-2,3-diO-tert-butyldimethylsilyl-α-D -ribopyranose (ADSR) with boron trifluoride etherate proceeded linearly and rapidly within 1 h to give silylated 1,5-α-D -ribofuranan in almost quantitative yield. Although the molecular weight distribution of the polymers was not narrow (M?_w/M?_n = 1.61 ～ 1.73), the relationship between monomer conversion and number-average molecular weight was linear, indicating livingness of the ring-opening polymerization. Thus, an AB block copolysaccharide composed of two different polysaccharide chains was synthesized for the first time in the two-stage polymerization of ADSR and 1,4-anhydro-2,3-di-O-benzyl-α-D -ribopyranose (ADBR) at ?40°C. Block copolysaccharides having different stereoregular monomeric units (i.e., ribopyranosidic and ribofuranosidic units) were obtained by block copolymerization of 1,4-anhydro-2,3-O-benzylidene-α-D -ribopyranose (ABRP) and ADBR. In addition, a block heteropolysaccharide consisting of (1 → 5)-α-D -xylofuranan and (1 → 5)-α-D -ribofuranan was prepared from 1,4-anhydro-2,3-di-O-tert-butyldimethylsilyl-α-D -xylopyranose (ADSX) and ADBR by making use of this polymerization technique. The GPC curves of block copolymers shifted toward the higher molecular weight region, maintaining the molecular weight distributions of the corresponding homopolymers in the first stage of polymerization. The number-average degree of polymerization of the polyADSR-block-polyADBR was estimated to be 113 for ADSR and 221 for ADBR unit. The ¹³C NMR spectra of the resulting block copolymers were different from those of the random copolymers.     

Polysiloxane-Containing triblock copolymers via cationic ring-opening polymerization of cyclic siloxanes

A novel original method allowing the synthesis of polydimethylsiloxane (PDMS)-containing triblock copolymers is described. The synthetical procedure is based on the use of ω-silyl triflate-terminated polymers serving as macroinitiators for cyclic siloxane polymerization. Due to the continous interchange reactions between the siloxane linkages and the reactive cationic sites, triblock copolymers are obtained. This method was applied to the synthesis of triblock copolymers with a central PDMS block and either two polystyrene or two poly(ε-caprolactam) rigid external blocks. Another method, the well-known “end-blocker” technique, was unsuccessful for obtaining block copolymers.     

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.     

Polymerizability of cycloalkenes in a living ring‐opening metathesis polymerization initiated by Schrock complexes, 1. Effect of the solvent on the polymerization kinetics

The solvent influence was studied on the polymerizability of norbornene, whereby a Mo‐based Schrock complex was used as the initiator due to its ability to generate a persistent active center. The polymerizations were performed in solvents of differing coordinating power with the aim to look at their effect on the reactivity of the system. Cyclohexane, toluene, and tetrahydrofuran (THF) were chosen as solvents taking into account that cyclohexane has only a diluent effect whereas both toluene and THF should be able to coordinate to the complex. The competitive binding character of both monomer and solvent was established from kinetic data for ring‐opening metathesis polymerization (ROMP) performed in pure and mixed solvents (cyclohexane/THF). Independent of the solvent, first‐order kinetics with respect to the initiator suggest that most organometallic species form monosite propagating species. The kinetic order with respect to the monomer depends on the THF concentration of the reaction medium; the kinetic order is equal to one in pure THF and zero in pure cyclohexane. To explain this behavior, a kinetic scheme of the polymerization process is proposed, considering that the actual active species are monomer‐bonded metala‐alkylidenes. The respective equilibrium constants of monomer and of THF complexation to alkylidenic species were estimated showing the stronger binding of norbornene compared to that of THF and the strong influence on the polymerization kinetics.     

Syntheses of biodegradable and biorenewable polylactides initiated by aluminum complexes bearing porphyrin derivatives by the ring-opening polymerization of lactides

Three aluminum alkyl complexes bearing porphyrin derivatives were synthesized by pyrrole derivatives and benzaldehyde derivatives. These complexes were characterized by NMR and elemental analysis. These complexes are used for racemic-lactide polymerization. In the ring-opening polymerization of racemic lactide, complex 3(2,3,7,8,12,13,17,18-octamethyl-5,10,15,20-tetraphenylporphyrin aluminum methyl, R₁=H, R₂=Me in Scheme 2) with isopropanol showed the highest stereoselectivity, and an isotactic polylactide with a P_m of 0.68 was obtained. The polymerization kinetics with complex 3 as catalyst was studied in detail. The kinetics of the polymerization data indicated that the rate of polymerization initiated by complex 3 had first-order dependency on monomer and catalyst. There is a linear relationship between lactide conversion and the number average molecular weight of PLA.     

Living ring-opening polymerization of lactones using cationic zirconocene complex catalysts

Living cationic ring-opening polymerization of ?-caprolactone (CL), δ-valerolactone (VL) and 1,3-dioxepane-2-one ( 6 ) was achieved at room temperature by using zirconocene borate complex catalysts. Respective block copolymerization of CL with VL or with cyclic carbonate 6 was also successfully performed. The mechanism of the present cationic living polymerization is discussed.     

Preparation of graft and block copolymers by means of amide linkages

Based on the reaction between acid chlorides and amines, two techniques were developed to prepare graft and block copolymers. In the first method poly(methyl methacrylate), (PMMA), containing chloroformyl groups was reacted with 2,2′-azodiisobutyramidine ( 1 ) or 2,2′-azobis[2-(2-imidazolin-2-yl)propane] ( 2 ) to give a polymeric initiator which, on thermal activation in the presence of acrylamide, produced graft and block copolymers, according to the position of the chloroformyl group on the PMMA backbone. In the second method, PMMA containing one terminal chloroformyl group was directly reacted with polyacrylonitrile containing two terminal amidine groups to produce a block copolymer.     

Studies on mechanism of tetrahydrofuran polymerization initiated by a heteropolyacid

Polymerization mechanism of tetrahydrofuran initiated with H₃PW₁₂O₄₀ in the presence of ethylene oxide (EO) was studied by means of NMR, GC and GPC. The polymerization stopped after complete consumption of EO, but could be re-initiated when a further portion of EO was added. A part of EO was converted into dioxane in the beginning of polymerization in the presence or absence of water, but the formation of dioxane was suppressed by addition of a low molecular weight diol. All the polymer chains were started with EO moieties, and the percentage of hydroxyl group attached to EO moieties at the polymer chain ends was higher than 50% of the total hydroxyl end groups and increased with conversion. Kinetic experiments were performed with successive addition of EO, indicating that the concentration of propagating species and the chain propagation rate constant remained unchanged during polymerization after each addition of EO. The rate constant of the reaction of EO with the propagating species in EO homopolymerization was determined by GC to be 3.6×10^–2 L·mol^–1·s^–1 at 0°C. The high reactivity of EO offered the possibility of tetrahydrofuran polymerization via dormant dioxanium species. The molecular weight distribution index of the product decreased with conversion, in some runs it was lower than 1.3 at a conversion as high as 46.9%.     

Polymers from 2-allyloxymethyl-2-ethyltrimethylene carbonate and copolymers with 2,2-dimethyltrimethylene carbonate obtained by anionic ring-opening polymerization

2-Allyloxymethyl-2-ethyltrimethylene carbonate ( 1 ) was polymerized in toluene with sec-butyllithium as initiator. The resulting product exhibits a bimodal molecular weight distribution. The low-molecular-weight fraction consists mainly of cyclic oligomers and to a minor portion of acyclic oligomers. With 2,2-dimethyltrimethylene carbonate ( 2 ) as a comonomer, statistical and block copolymers were obtained upon addition of the initiator to a mixture of the monomers or upon consecutive addition of the monomers to the initiator, respectively. The primary structure of these copolymers was unambiguously determined by means of ¹³C NMR spectroscopy of especially the carbonyl region, since the carbonyl carbon atom is a sensitive probe for structural changes in its neighbourhood. All polymers were crosslinked upon using di-tert-butyl peroxide as a source of radicals. The thermal behaviour of the polymers before and after crosslinking was studied.     

Vinyl polymerization by a cobalt complex

The rate of decomposition of the complex, sodium bis(diethanolamine)cobaltate octahydrate was studied at pH 7 and pH 1,6, respectively. This complex was found to initiate the vinyl polymerization (polymerization of acrylamide and methacrylamide) at pH 1,6 in aqueous medium. There was no polymerization at pH > 4. The dependences of the rate of polymerization on monomer concentration, initiator concentration, temperature, and pH were studied. The overall activation energy of the polymerization reaction was calculated. A kinetic reaction scheme is proposed on the basis of the experimental data.     

Ring opening polymerization of L-lactide initiated by creatinine

L-lactide was first successfully ring-opening polymerized in bulk using creatinine initiator. Poly(L-lactide)(PLLA) synthesized possesses a moderate molecular weight (MW) (Mn = 1.56 x 10(4)) and pretty narrow MW distribution (PDI = 1.28). Influence of temperature, time and creatinine dosage on the polymerization and formed PLLA's properties were examined. The polymerization mechanism is postulated according to (1)HNMR characterization of the propagation species and the synthesized PLLA product.     

Vinyl polymerization by metal complexes, 17. Effect of nitriles on the vinyl polymerization initiated by imidazole-copper (II) complex

Polymerization of vinyl monomers initiated by the imidazole-copper(II) complex was studied in dimethyl sulfoxide solution. Different from the case of acrylonitrile, the polymerization of styrene and methyl methacrylate did not proceed, even in the presence of various sort of nitriles. From these findings and the copolymerization behaviour of acrylonitrile with styrene and methyl methacrylate, together with the spectroscopic data, the presence of acrylonitrile monomer is essential for generating active species to initiate the polymerization.     

Radical polymerization and block copolymerization initiated with ceric salt/aldehyde redox system

Aldehyde compounds exhibit very high reactivities towards ceric salt in initiating polymerization of acrylamide. In the presence of aldehyde compounds, the rate of polymerization is 8 times as high as the rate initiated by ceric salt alone. In nitric acid solution, the rate of polymerization decreases, but the accelerating effect of aldehyde compound becomes more obvious. Polyether prepolymer with aldehyde and groups also shows high activity towards ceric salt, with a relative rate of polymerization up to ca. 15, which can initiate acrylamide polymerization to form a block copolymer. The polymerization of acrylonitrile and methyl methacrylate initiated with ceric salt/aldehyde were also investigated.     

Linear polymerization of endo-dicyclopentadiene initiated by metathesis catalysts

The polymerization of endo-dicyclopentadiene

1 Systematic name of endo-dicyclopentadiene is: tricyclo[5.2.1.0^2,6]deca-3,8-diene.

(endo-DCP) by the metathesis catalyst ReCl₅/(CH₃)₄ Sn gave a substantial yield of a linear polymer with high molecular weight and high content of cis double bonds. The kinetics of the early stage of the reaction was studied by calorimetry. The polymerization proceeds via an oligomerization reaction followed by the formation of polymers. A mechanistic scheme is proposed to explain the generation of the primary active species and the two-step polymerization process.     

Cationic polymerization of tetrahydrofuran initiated by multifunctional initiators

A series of multifunctional cationic initiators was synthesized from 1,5,9-cyclododecatriene and from methylbenzenes by the Wohl-Ziegler reaction with N-bromosuccinimid. The initiators were treated with silver perchlorate to prepare star-shaped polytetrahydrofurans with three to six arms.     

Preparation of ABCBA-type block copolymers by use of macro-initiators containing peroxy and azo groups

Some new macroinitiators ( 5 ) containing azo and peroxy groups were synthesized by transformation of esters of poly(ethylene glycol) ( 1 ) (PEG) of different molecular weight with hydroxyl end groups and an azo group in the middle into the corresponding polymers with tert-butylperoxycarbonyl end groups by reaction with terephthaloyl chloride and subsequently with tert-butyl hydroporoxide. Decomposition in the presence of styrene at 60°C or with 3,6,9-triazaun-decane-1,11-diamine in presence of methyl methacrylate gave the corresponding ABA block copolymer 6 and the ABBA block copolymer 7 , respectively. Both block copolymers were used as polymeric initiators. The ABCBA block copolymer 8 was synthesized from 6 and methyl methacrylate or from 7 and styrene by thermally induced polymerization at 80°C. The resulting block copolymers were separated from the homopolymers by selective solvent extraction and characterized by spectroscopic and fractional precipitation methods.     

Kinetics of interfacial radical polymerization initiated by a glucose-oxidase mediated redox system

The reaction and coating kinetics for the glucose oxidase initiated interfacial polymerization are elaborated. The interfacial film grows rapidly and linearly with time, producing time-dependent controllable conformal coating thicknesses of up to a millimeter in less than 4?min. Bulk polymerization was only observed when the immersing media was stirred to induce higher mass transport rates. The dramatically different film thicknesses observed between different concentrations of glucose in the hydrogel and iron in the bulk media are demonstrated to be a result of an initial rapid growth phase following which the film grows at the same rate nearly independent of either the glucose or iron concentration. The polymerization rate and hence the thickness growth rate in this initial phase saturate at glucose and iron concentrations above 0.8?M and 0.63?mM, respectively. At iron concentrations above 0.05?mM, the film thickness at the end of 3?h of reaction monotonically decreased with increasing iron concentration from 5.7?mm to 4.2?mm. The glucose oxidase is trapped by the growing polymerization front and can be used as the sole enzymatic precursor to coat a second polymeric layer. However, the rate of film growth of the second layer is 14-fold lower than the rate of film growth when bulk enzyme is present during the second stage coating process.