Block and graft copolymers by selective cationic initiation. III. Synthesis and characterization of bigraft copolymers

The synthesis and characterization of new bigraft copolymers poly[(ethylene-co-propylene-co-1,4-hexadiene)-g-styrene-g-α-methylstyrene] (Nordel-g-PSt-g-PαMeSt) and poly[(ethylene-co-propylene-co-1,4-hexadiene)-g-isobutylene] (Nordel-g-PSt-g-PIB) are described. The synthesis involves the use of a polyhydrocarbon backbone containing allylic chlorines and bromines (chlorobrominated Nordel) in conjunction with a suitable alkylaluminum compound to initiate selectively the polymerization of a monomer (generally styrene) from the chloride sites and subsequently to initiate the polymerization of another monomer (α-methylstyrene or isobutylene) from the bromide sites. Conditions conductive to selective and sequential initiation have been worked out. The pure bigrafts are obtained by selective solvent extraction and their homogeneity (by gel permeation chromatography), overall composition (by nuclear magnetic resonance spectroscopy) and molecular weight (by osmometry) are determined.     

Block and graft copolymers by selective cationic initiation. II. Synthesis and characterization of styrene-isobutylene block copolymers by use of chlorobrominated alkanes

The synthesis and characterization of a new block copolymer, poly(styrene-b-isobutylene) (PSt-b-PIB), is described. The synthesis involves the initiation of an isobutylene polymerization by a polystyrene molecule containing a terminal tertiary bromine (PSt-Br), in conjunction with diethylaluminum chloride coinitiator. The species PSt-Br is in turn synthesized by initiating the polymerization of styrene selectively by the tertiary chlorine of the 2-bromo-6-chloro-2,6-dimethylheptane/Et₃Al initiator system in the absence of chain transfer. The conditions conducive for selective initiation by tertiary chlorine have been worked out. The pure block copolymer, PSt-b-PIB, is obtained by selective extraction and some of its properties were determined, e.g., solubility and film behavior, T_g, and intrinsic viscosity versus temperature. The intrinsic viscosity (in toluene) exhibits a maximum and a minimum in the temperature range from 15 to 55°C.     

Block and graft copolymers based on cationic ring-opening polymerizations

The highly living character of a number of cationic polymerizations has been used to synthesize new, well defined, segmented copolymers. This has been achieved by sequential monomer additions, by grafting reactions, by macromonomer copolymerizations as well as by transfer to polymer. In the present report, a number of examples of such polymers will be presented. The new materials are based on tetrahydrofurane (THF), alkyloxazolines (ROx), cyclic amines, cyclic acetals and cyclic sulfides.     

Synthesis,characterization, and properties of block and bigraft copolymers

The syntheses of poly(styrene-b-isobutylene), poly[(ethylene-co-propylene-co-1,4-hexadiene)-g-styrene-g-α-methylstyrene], and poly[(ethylene-co-propylene-co-1,4-hexadiene)-g-styrene-g-isobutylene] have been accomplished by using the principle of selective sequential initiation. This method makes use of the large differences in initiation rates that exist between labile organic chlorides and bromides when these halides interact with alkylaluminum compounds. Synthesis conditions have been worked out which allow composition control. These new AB blocks and bigrafts exhibit unusual mechanical and solubility properties, some of which will be described. For example, the Nordel-g-PSt-g-PIB bigraft exhibits only one low temperature transition (DSC, Rheovibron), suggesting an intimate aggregation of Nordel and polyisobutylene phases.     

Preparation and characterization of some cellulose graft copolymers. Part IV. Some properties of isolated cellulose acetate–styrene graft copolymers

A series of purified graft copolymers of cellulose acetate and polystyrene, which were prepared and characterized during the course of an earlier investigation, have been used for some initial property studies. Grafts with high molecular weight backbones and low molecular weight side chains and vice versa, and with both side chains and backbones of high and low molecular weights, were prepared. The graft polymers were found to be insoluble in most solvents but soluble in dimethylformamide and pyridine and in mixtures of solvents for each component. Films cast from mixtures of the grafts and homopolymers showed that the grafts were compatible with the homopolymer of the component with a higher molecular weight. A graft copolymer with high molecular weight backbone and side chains was found to be compatible with both homopolymers separately and with a mixture of both across a wide range of compositions. A blend of the high and low molecular weight grafts was also found to be highly compatible with both homopolymers. The permeability, diffusion, and sorption of gases and water vapor in the grafts and in the corresponding homopolymers was also studied. In the case of water vapor, the sorption in cellulose acetate was much higher than in polystyrene whereas the diffusion was much lower. It was found that the graft polymers showed both diffusion and solution behavior closer to that of cellulose acetate, whereas the permeability constants were more intermediate between those of the two homopolymers. The gas permeability and diffusion constants were found to be intermediate between the values obtained with the two homopolymers.     

Block and graft copolymers of 2-oxazolines

The cationic ring-opening polymerization of 2-oxazolines is known to be initiated by alkyl halides, Lewis acids and esters of strong acids. The polymerization proceeds by a living mechanism. Numerous block and graft copolymers have already been described. Recently it was found that chloroformates (R-O-CO-CI) are also useful initiators. The mechanism of the initiation and propagation is discussed. This type of initiators allows the synthesis of different novel two-block and three-block copolymers, star-shape polymers, and a graft copolymer with a polyvinylacetate backbone.     

Structure and properties of cellulose graft copolymers. III. Cellulose–methyl methacrylate graft copolymers synthesized by the ceric ion method

The ceric ion-initiated graft copolymerization of methyl methacrylate onto wood cellulose was found to depend on the concentrations of initiator, monomer, and cellulose. The structure of cellulose—methyl methacrylate graft copolymers was studied by hydrolyzing away the cellulose backbone to isolate the grafted poly(methyl methacrylate) branches. The molecular weights and molecular weight distributions of the grafted poly(methyl methacrylate) were determined by using gel-permeation chromatography. The number-average (M?_n) molecular weights ranged from 36 000 to 160 000 and the polydispersity ratios (M?_w/M?_n) varied from 4.0 to 7.0. The grafting frequency or the number of poly(methyl methacrylate) branches per cellulose chain calculated from the per cent grafting and molecular weight data varied from 0.38 to 3.2. The structure of cellulose—methyl methacrylate graft copolymers and the effect of stepwise addition of initiator on the structure are discussed.     

Morphologies and bridging properties of graft copolymers

Morphologies and bridging properties of graft copolymers in the bulk state were studied by using a real-space algorithm of self-consistent field theory in two dimensions. The phase transition from cylindrical to lamellar phase can be triggered by changing the position of graft points and the number of branches. The fraction of bridged conformation, f(bridge), shows a tendency to decrease with increasing the length of free end blocks, tau1, and the number of branches, m. The value of f(bridge) has a discontinuous drop when the transition from cylindrical to lamellar phase takes place. The relationship between m and the number of bridged chains per unit area, nb, which is associated with the mechanical properties of copolymers, was also examined. It was found that nb increases with increasing m in the cylindrical phase. However, in the lamellar phase, nb decreases when m increases. It is proposed that the position of graft points and the number of branches are two important parameters for material design.     

Synthesis and characterization of bigraft copolymers based on grafted type peracid polymer

In this study, a radiation-induced copolymer, namely, polyethylene-g-acrylic acid and EVA-g-acrylic acid, in the form of a membrane, particulate, or tube was used as a substrate. The carboxyl groups of the grafted acrylic chains were oxidized into peracids. Optimal conditions for the oxidation, including the catalyst, reaction time, and temperature were investigated. Novel bigraft copolymers were then synthesized from the grafted polymeric peracid. A third component (e.g., 2-hydroxyethyl methacrylate) was grafted through the decomposition of peracid groups. Abnormality in morphology of the acrylic acid grafted and HEMA bigraft membrane was investigated by SEM and TEM observation, which showed the levelling effect of the third component and manifested a third circular domain generated inside the membrane at high degree of grafting.     

Amphiphilic graft copolymers - preparation and interfacial properties

Amphiphilic graft copolymers containing poly(ethylene oxide) (PEO) grafts have been prepared by various methods, for example, by coupling of reactive hydrophobic backbone polymers with end-functionalised PEO, by macromonomer copolymerisation, and by anionic graft polymerisation of EO onto polymer backbones carrying functional groups as initiator precursors. The graft copolymers are amphiphilic and were shown to accumulate at surfaces and interfaces in solution and in the solid state. Amphiphilic starch derivatives were prepared by reaction of amylose and starch with aliphatic α-epoxides.     

Synthesis and properties of polystyrene/polydimethylsiloxane graft copolymers

Polystyrene-graft-polydimethylsiloxane (PS-g-PDMS) copolymers with different PDMS content were synthesized by the radical bulk copolymerization of PDMS macromonomer and styrene. The copolymers were characterized by Fourier transform infrared (FT-IR), ¹H-nuclear magnetic resonance (NMR), thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), transmission electron microscopy (TEM) and the mechanical properties of the copolymers were also carried out. It was indicated that the notched impact strength and elongation at break of the polymers increased with the increase of PDMS content. The thermal stability of PS-g-PDMS is better than that of PS. __________ Translated from Journal of East China University of Science and Technology 2005, 31(2) (in Chinese)     

Synthesis of polystyrene-based cationic copolymers and their colloidal properties in water

A series of polystyrene-based cationic copolymers was synthesized by two different methods: (1) solution copolymerization of styrene and vinylbenzyl trimethylammonium chloride (VBTMAC) in ethanol, and (2) surfactant-free emulsion copolymerization of styrene and vinylbenzyl chloride in water followed by reaction with trimethylamine. The results indicated that the different synthesis methods would result in different polymer structures and, therefore, affect the solubility and colloidal properties of the copolymers in water. For the copolymers prepared by method 2, partial crosslinking was observed. The copolymers made by this method are almost water-insoluble. In contrast, the copolymers made from direct copolymerization of styrene and VBTMAC in ethanol are water-soluble or dispersible, but the solubility and the particle size of microaggregates formed by these copolymers in water strongly depend on charge density and temperature. One of the important results from this study is that uniform colloidal particles with a very small particle size (30–50 nm) can be obtained by dispersing polystyrene-based cationic copolymers in water without adding any surfactants. Received: 29 July 1998 Accepted in revised form: 28 September 1998     

New developments in the synthesis of block and graft copolymers via anionic and cationic methods

Ionic living polymerization methods are well suited for the synthesis of macromolecules of known structure, molecular weight and composition, and exhibiting low fluctuations in composition and in molecular weight. They were the first to allow the synthesis of well characterized block and graft copolymers. The present paper discusses a number of recent developments concerning these syntheses based on anionic or cationic living polymerization.     

Block and Bigraft copolymers by Carbocation Polymerizaation

The recent observation that the rate of methylation of t-BuCl by Me₃Al is several orders faster than that of t-bubr, Which in turn is much faster than that of t-BuI, Provides the basis of a new synthetic method for the preparation of block and bigraft copolymers. This presentation concerns the synthesis and characterization of the first well-defined block and bigraft copolymers produced by the carbenium ion mechanisum i. e., poly(styrene-b-isobutylene), poly[(ethylene-co-propylence)-gStyrence-g-α-methylstyrence)]. The synthesis of the block copolymers involved three key steps: 1)the synthesis of a chlorobrominated alkane initiator, 2) the selective initiation of styrence polymerization by the chlorobrominated alkane in conjunction with alkylayuminum halide under conditions of no chain transfer, and 3)selective initiation of isobutylence polymerization by the polystyrence-Br in conjuction with alkylaluminum halide. Selective solubility, DSC, and GPC data indicate pure block copolymer. The effect of temperatute on the intrinsic viscosity of poly(styrence-b-isobutylence) exhibited peculiarities characterstic of block copolymers. The bigraft was synthesized by chlorobrominating an ethylene-propylene copolymer and selectively initiating first the polymerization os styrence and subsequently that of α-methylstyrence of isobutylene by the chlorobrominated copolymer plus an alkylaluminum compound.     

Organosilane polymers. III. Block copolymers

Chloro- and lithio-terminated diorganosilylene oligomers were coupled to form block copolymers that were soluble in common solvents and deposited coherent films from solution. Copolymer UV (ultraviolet) spectra showed a red shift in absorption maxima attributed to increased silicon chain length and phenyl-silicon spine interactions.     

Living cationic isomerization polymerization of β-pinene. III. Synthesis of end-functionalized polymers and graft copolymers

α-End-functionalized polymers and macromonomers of β-pinene were synthesized by living cationic isomerization polymerization in CH₂Cl₂ at −40°C initiated with the HCl adducts [ 1; CH₃CH(OCH₂CH₂X)Cl; X = chloride ( 1a ), acetate ( 1b ), and methacrylate ( 1c )] of vinyl ethers carrying pendant substituents X that serve as terminal functionalities. In conjunction with TiCl₃(OiPr) and nBu₄NCl, these functionalized initiators led to living β-pinene polymerization where the carbon–chlorine bond of 1 was activated by TiCl₃(OiPr). Similarly, end-functionalized poly(p-methylstyrene)-block-poly(β-pinene) were also obtained. ¹H-NMR analysis showed that the polymers possess controlled molecular weights (DP _n = [M]₀/[ 1 ]₀) and number-average end functionalities close to unity. The end-functionalized methacrylate-capped macromonomers form 1c were radically copolymerized with methyl methacrylate (MMA) to give graft copolymers carrying poly(β-pinene) or poly(p-methylstyrene)-block-poly(β-pinene) as graft chains attached to a PMMA backbone. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 1423–1430, 1997     

Block copolymers of ethylene. I. Butadiene

Block copolymers of ethylene and butadiene have been prepared to study their properties. The method of preparation of polybutadiene, polyethylene, and block copolymers of ethylene and butadiene with n-butyl lithium-tetramethyl ethylene diamine complex is outlined. Kinetic studies have been reported elsewhere and these are assessed to determine that suitability of the system to produce monodispersed “living” chains so that simple correlations between physical properties and molecular weight can be made. The properties were somewhat restricted by the 1,2-microstructure of the butadiene block.     

Liquid crystalline block copolymers by sequential cationic or promoted cationic and free-radical polymerizations

The scope for the study of the synthesis and properties of liquid crystalline (LC) block copolymers is briefly outlined. While there are many approaches to the synthesis of LC block copolymers, the use of azo macroinitiators is very versatile and allows one to produce diverse block copolymer architectures. Azo macroinitiators are prepared by cationic or promoted cationic polymerization of tetrahydrofuran (1) or cyclohexene oxide (2), and are then used to initiate the free-radical polymerization of various methacrylates 3,4 or acrylates 5–9 containing mesogenic azobenzene or biphenyl units thereby yielding block copolymers. The AB or ABA block copolymers are microphase-separated and form smectic and/or nematic mesophases similar to the respective LC homopolymers.     

Block copolymers derived from azobiscyanopentanoic acid. IV. Synthesis of a polyamide–polystyrene block copolymer

Polyamides 6.10 and 6.6 (PA^* 6.10 and 6.6) containing small amounts of ? N?N? units in the main chains were prepared by interfacial polycondensation between hexamethylenediamine and sebacoyl chloride or adipoyl chloride with addition of azobiscyanopentanoyl chloride. Polyamide–polystyrene block copolymers (PA-b-PSt) were then prepared by decomposition of the ? N?N? units of PA^*, initiating radical polymerization of styrene in m-cresol. The average PA block length of PA-b-PSt thus formed was longer than that expected from the initially present PA segments between the ? N?N? units. This is probably due to recombination of PA radicals whose initiation efficiency is as low as 15%. The PSt blocks also had higher molecular weight (7000–79,000) in comparison with homopolystyrene produced from monomeric azobiscyanopentanoic acid used as an initiator due to higher viscosity of polymerization system. Variation of intrinsic viscosity and turbidimetric titration behavior along with the change in composition were also discussed.