Diene-acrylic block copolymers

Excellent reviews on micelles formed in organic solvents have been published by Hamley [2], Chu et al. [86], and Riess [14]. From these overviews it appears that a wide range of styrene-, (meth)acrylates-, and dienes-based block copolymers were investigated and that the formation of micelles in organic solvents can generally be considered as an entropy-driven process. AB diblock and ABA triblock architectures were systematically compared. All these previous investigations have been summarized by Hamley [2], We will therefore not perform an extensive review of all these systems, since this information has already been provided by others, but we will briefly outline some selected examples. 

NR, styrene-butadiene mbber (SBR), polybutadiene rubber, nitrile mbber, acrylic copolymer, ethylene-vinyl acetate (EVA) copolymer, and A-B-A type block copolymer with conjugated dienes have been used to prepare pressure-sensitive adhesives by EB radiation [116-126]. It is not necessary to heat up the sample to join the elastomeric joints. This has only been possible due to cross-linking procedure by EB irradiation [127]. Polyfunctional acrylates, tackifier resin, and other additives have also been used to improve adhesive properties. Sasaki et al. [128] have studied the EB radiation-curable pressure-sensitive adhesives from dimer acid-based polyester urethane diacrylate with various methacrylate monomers. Acrylamide has been polymerized in the intercalation space of montmorillonite using an EB. The polymerization condition has been studied using a statistical method. The product shows a good water adsorption and retention capacity [129]. 

The additional complexity present in block copolymer synthesis is the order of monomer polymerization and/or the requirement in some cases to modify the reactivity of the propagating center during the transition from one block to the next block. This is due to the requirement that the nucleophilicity of the initiating block be equal or greater than the resulting propagating chain end of the second block. Therefore the synthesis of block copolymers by sequential polymerization generally follows the order dienes/styrenics before vinylpyridines before meth(acrylates) before oxiranes/siloxanes. As a consequence, styrene-MMA block copolymers should be prepared by initial polymerization of styrene followed by MMA, while PEO-MMA block copolymers should be prepared by... 

ADMET is a step growth polymerization in which all double bonds present can react in secondary metathesis events. However, olefin metathesis can be performed in a very selective manner by correct choice of the olefinic partner, and thus, the ADMET of a,co-dienes containing two different olefins (one of which has low homodimerization tendency) can lead to a head-to-tail ADMET polymerization. In this regard, terminal double bonds have been classified as Type I olefins (fast homodimerization) and acrylates as Type II (unlikely homodimerization), and it has been shown that CM reactions between Types I and II olefins take place with high CM selectivity [142], This has been applied in the ADMET of a monomer derived from 10-undecenol containing an acrylate and a terminal double bond (undec-10-en-l-yl acrylate) [143]. Thus, the ADMET of undec-10-en-l-yl acrylate in the presence of 0.5 mol% of C5 at 40°C provided a polymer with 97% of CM selectivity. The high selectivity of this reaction was used for the synthesis of block copolymers and star-shaped polymers using mono- and multifunctional acrylates as selective chain stoppers. 

With the purpose of increasing the range of available block copolymers, comonomers other than methacrylates and acrylates can also be involved in sequential polymerization, provided that they are susceptible to anionic polymerization. Dienes, styrene derivatives, vinylpyridines , oxiranes and cyclosiloxanes are examples of such comonomers. The order of the sequential addition is, however, of critical importance for the synthesis to be successful. Indeed, the pX a of the conjugated acid of the living chain-end of the first block must be at least equal to or even larger than that of the second monomer. Translated to a nucleophilicity scale, this pK effect results in the following order of reactivity dienes styrenes > vinylpyridines > methacrylates and acrylates > oxiranes > siloxanes. 

The following sections detail the literature reports pertaining to the synthesis of block copolymers using nitroxide-mediated polymerization techniques. The sections are organized according to monomer type and generally follow the historical development of the particular subsection. Most literature on nitroxide mediated preparation of block copolymers is found for the styrene-based monomers, and is summarized first. This is followed by acrylates and dienes, as they were the next monomers to be studied. These sections are followed by more recent work with vinyl pyridine, acrylamides, and maleic anhydride. The final section deals with methacrylates. This is presented last to stress the importance of developing new nitroxides that can successfully be used for the homopolymerization of methacrylate-based monomers. 

TMPAH was used successfully for the homo-, co-, and block polymerizations of IP. In this case, due to the less reactive diene monomer, no additional free nitroxide was necessary to control the polymerization and both low and high molecular weight polymers (Mn=4500 to Mn=100,000) with narrow molecular weight distributions (Mw/Mn= 1.07-1.3) were synthesized [159]. Copolymers with various styrene and (meth)acrylate derivatives, including acrylic acid and HEMA, were obtained, with the content of isoprene varying from 10% to 90% in the comonomer feed. Block copolymers were also produced, starting from either ptBA or pSt macroinitiators however, the alternate order of blocks (i.e., starting from a pIP macroinitiator) was only achieved with St. Chain extension with tBA resulted in inefficient initiation [159], as had been found for pSt-pnBA block copolymers [71]. 

Nitroxides have been used to prepare numerous block copolymers. Initially, using the TEMPO moiety, only styrene-based monomers could be incorporated into copolymers, but with the use of new nitroxides like DEPN and BPPN, the list has expanded to include acrylate-type monomers, as well as dienes, something that previously could only be accomplished through ionic mechanisms. Unfortunately, chain extension of either St or diene-based macroinitiator with an acry-... 

Orientations in elongated mbbers are sometimes regular to the extent that there is local crystallization of individual chain segments (e.g., in natural rubber). X-ray diffraction patterns of such samples are very similar to those obtained from stretched fibers. The following synthetic polymers are of technical relevance as mbbers poly(acrylic ester)s, polybutadienes, polyisoprenes, polychloroprenes, butadiene/styrene copolymers, styrene/butadiene/styrene tri-block-copolymers (also hydrogenated), butadiene/acrylonitrile copolymers (also hydrogenated), ethylene/propylene co- and terpolymers (with non-conjugated dienes (e.g., ethylidene norbomene)), ethylene/vinyl acetate copolymers, ethyl-ene/methacrylic acid copolymers (ionomers), polyisobutylene (and copolymers with isoprene), chlorinated polyethylenes, chlorosulfonated polyethylenes, polyurethanes, silicones, poly(fluoro alkylene)s, poly(alkylene sulfide)s. 

It was shown that p-hydrogen-containing nitroxides promote the controlled polymerization of not only styrenic monomers but alkyl acrylates and dienes as well. Taking this into account, a novel ttifimcdonal alkoxyamine (Scheme 28, 7) based on N-t Tt-butyl-1 -diethylphosphono-2,2-dimethylpropyl nitroxide (Scheme 28, 8) was developed for the synthesis of 3-arm PS and poly(n-butyl acrylate) (PnBuA) stars along with (PnBuA-b-PS)3 star-block copolymers. ... 

Shell Oil Co. EB/UV radiation cure of composition comprising a monoalkenyl arene/conjugated diene block copolymer, tackifying resin, and a di-tetra functional acrylate or methacrylate selected from the group consisting of acrylic and methacrylic acid esters of polyols. Improved high-temperature properties and solvent resistance. PSA properties,... 

Fully methacrylic triblocks, containing a central rubbery poly(alkyl acrylate) block and two peripheral hard poly(alkyl methacrylate) blocks, are potential substitutes for the traditional styrene-diene-based thermoplastic elastomers (TPEs), which have relatively low service temperatures. Fully methacrylic triblock copolymers are able to cover service temperatures due to the varying Tg from — 50 C (poly(isooctyl acrylate)) to 190 C (poly (isobornyl methacrylate) [210]. Poly(methyl methacrylate)-Z)-poly(n-butyl acrylate)-Z)-poly(methyl methacrylate) triblock copolymers, which are precursors for poly(methyl methacrylate)- -poly(alkyl acrylate)-Z)-poly(methyl methacrylate) via selective transalcoholysis, have been synthesized by a three-step sequential polymerization of MMA, ferf-butyl acrylate (t-BuA), and MMA in the presence of LiCl as stabilizing ligand [211,212]. Various diblock copolymers, such as poly(methyl methacrylate)-Z)-poly( -butyl acrylate) and poly(methyl methacrylate)-Z)-poly( -nonyl acrylate), have been synthesized... 

Scheme 3 Acrylic acid as key component in the Passerini-3CR for synthesis of diversely substituted acrylate monomers left) [23]. Formation of unsymmetric a,o)-dienes and subsequent ADMET polymerization with PEG acrylate to yield amphiphilic block copolymers in a one-pot reaction right) [24]...

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