Copolymers, block alkyl methacrylates

By employing anionic techniques, alkyl methacrylate containing block copolymer systems have been synthesized with controlled compositions, predictable molecular weights and narrow molecular weight distributions. Subsequent hydrolysis of the ester functionality to the metal carboxylate or carboxylic acid can be achieved either by potassium superoxide or the acid catalyzed hydrolysis of t-butyl methacrylate blocks. The presence of acid and ion groups has a profound effect on the solution and bulk mechanical behavior of the derived systems. The synthesis and characterization of various substituted styrene and all-acrylic block copolymer precursors with alkyl methacrylates will be discussed. 

Various substituted styrene-alkyl methacrylate block copolymers and all-acrylic block copolymers have been synthesized in a controlled fashion demonstrating predictable molecular weight and narrow molecular weight distributions. Table I depicts various poly (t-butylstyrene)-b-poly(t-butyl methacrylate) (PTBS-PTBMA) and poly(methyl methacrylate)-b-poly(t-butyl methacrylate) (PMMA-PTBMA) samples. In addition, all-acrylic block copolymers based on poly(2-ethylhexyl methacrylate)-b-poly(t-butyl methacrylate) have been recently synthesized and offer many unique possibilities due to the low glass transition temperature of PEHMA. In most cases, a range of 5-25 wt.% of alkyl methacrylate was incorporated into the block copolymer. This composition not only facilitated solubility during subsequent hydrolysis but also limited the maximum level of derived ionic functionality. 

Although the potassium superoxide route can be universally applied to various alkyl methacrylates, it is experimentally more difficult than simple acid hydrolysis. In addition, limited yields do not permit well-defined hydrophobic-hydrophilic blocks. On the other hand, acid catalyzed hydrolysis is limited to only a few esters such as TBMA, but yields of carboxylate are quantitative. Hydrolysis attempts of poly(methyl methacrylate) (PMMA) and poly(isopropyl methacrylate) (PIPMA) do not yield an observable amount of conversion to the carboxylic acid under the established conditions for poly(t-butyl methacrylate) (PTBMA). This allows for selective hydrolysis of all-acrylic block copolymers. 

Brown and White employed this approach to prepare block copolymers of styrene and mcthacrylic acid (6). They were able to hydrolyze poly(styrene-b-methyl methacrylate) (S-b-MM) with p-toluenesulfonic acid (TsOH). Allen, et al., have recently reported acidic hydrolysis of poly(styrene-b-t-butyl methacrylate) (S-b-tBM) (7-10). These same workers have also prepared potassium methacrylate blocks directly by treating blocks of alkyl methacrylates with potassium superoxide (7-10). 

Our requirements for certain applications called for the preparation of block copolymers of styrene and alkali metal methacrylates with molecular weights of about 20,000 and methacrylate contents of about 10 mol%. In this report we describe the preparation and reactions of S-b-MM and S-b-tBM. In the course of our investigation, we have found several new methods for the conversion of alkyl methacrylate blocks into methacrylic acid and/or metal methacrylate blocks. Of particular interest is the reaction with trimethylsilyl iodide. Under the same mild conditions, MM blocks are completely unreactive, while tBM blocks are cleanly converted to either methacrylic acid or metal methacrylate blocks. As a consequence of this unexpected selectivity, we also report the preparation of the new block copolymers, poly(methyl methacrylate-b-potassium methacrylate) (MM-b-MA.K) and poly(methyl methacrvlate-b-methacrylic acid) (MM-b-MA). 

We also explored the direct conversion of S-b-tBM to S-b-MA.K. Hydrolysis under basic conditions (KOH in refluxing aqueous THF) was again resulted in unchanged S-b-tBM. The reaction with potassium trimethylsilanolate for 1 hr in refluxing toluene gave very little reaction. Only 10% of the expected amount of potassium was found by ICP, and the NMR and IR spectra were little changed from those of the starting copolymer. This difference in reactivity between S-b-MM and S-b-tBM parallels that observed for the reaction of alkyl methacrylate blocks with potassium superoxide (7-10). 

Block copolymerization was carried out in the bulk polymerization of St using 18 as the polymeric iniferter. The block copolymer was isolated with 63-72 % yield by solvent extraction. In contrast with the polymerization of MMA with 6, the St polymerization with 18 as the polymeric iniferter does not proceed via the livingradical polymerization mechanism,because the co-chain end of the block copolymer 19 in Eq. (22) has the penta-substituted ethane structure, of which the C-C bond will dissociate less frequently than the C-C bond of hexa-substituted ethanes, e.g., the co-chain end of 18. This result agrees with the fact that the polymerization of St with 6 does not proceed through a living radical polymerization mechanism. Therefore, 18 is suitably used for the block copolymerization of 1,1-diubstituted ethylenes such as methacrylonitrile and alkyl methacrylates [83]. 

Spijker and colleagues (2005) synthesized nucleobase-functionalized block copolymers containing thymine via ATRP of a thymine methacrylate monomer from a poly(ethylene glycol) (PEG) macroinitiator. This polymer was introduced into the polymerization of an adenine containing an alkyl methacrylate... 

Pioneering work from Hatada and co-workers [8] has illustrated the molecular weight dependence of the chemical composition of block and random (alkyl) methacrylate copolymers, for example ... 

Two reports in the patent literature claim the invention of CFI additives specifically designed to improve the cold weather performance of biodiesel (Scherer and Souchik, 2001 Scherer et al, 2001). Block copolymers of long-chain alkyl methacrylates and acrylates were effective as PPD and flow improv-... 

Scherer, M., Souchik, J., and Bollinger, J. M. 2001. Block Copolymers of Long-Chain Alkyl Methacrylates as Lubricating Oil and Biodiesel Additives. PCT Int. Patent Appl. WO 0140339 (Jun. 7). 

Block copolymers of 23b and alkyl methacrylates [158] and diblock copolymers of 23b with 2-(diethylamino)ethyl methacrylate (23b-DEAEM), 2-(diisopropylamino)ethyl methacrylate (23b-DIPAEM), or 2-(N-morphoHno) ethyl methacrylate (23b-MEMA) exhibited reversible pH-, salt-, and temperature-induced micellization in aqueous solution under various conditions. The micelle diameters were 10-46 nm [238]. The micelles of these hydropho-bically modified polybetaines consist of coronas from 23b and cores from polyDEAEM, polyDIPAEM, or polyMEMA. In aqueous solution, the 23b-MEMA diblock copolymers form micelles with cores of polyMEMA above an upper critical micelle temperature of about 50 °C, and reversibly betainized-DMAEM core micelles below a lower critical micelle temperature of approximately 20 °C [239]. 

Block copolymers between alkyl or related methacrylates (B-1,132 198,357 B-2,198 and B-3115,146,148) were prepared via the ruthenium-, copper-, and nickel-catalyzed living radical polymerizations. These block copolymers can be synthesized both via sequential living radical polymerizations and via the living radical polymerization initiated from isolated polymers. For example, the ruthenium-catalyzed sequential living radical polymerization of MMA followed by nBMA affords AB block copolymers B-1 with narrow MWDs (Mw/Mn = 1.2), which can be extended further into ABA block copolymers B-2 with similarly narrow MWDs (Mw/Mn = 1.2).198 Star block copolymers with B-1 as arm chains were similarly synthesized but with multifunctional initiators.357... 

Poly(acrylates) and (alkyl acrylates). - Structured nanopore films of poly(styrene-block-methyl methacrylate) copolymers have been made with controlled spectral sensitivity, such that each block is sensitive to a specific degradation wavelength. In copolymers of 2,2,2-trifluoroethyl methacrylate with vinyl ethers, the photosensitivity is controlled by the vinyl ether units. Photodegradation occurs at the tertiary positions of the ether units followed by lactone formation and chain scission processes. Furthermore, the fluorinated side chains have been found to inhibit cyclization reactions. 

Microreactors have also been used for ionic polymerization or polycondensation processes. Nagaki et al. [136] have synthesized polystyrene-poly(alkyl methacrylate) block copolymers by butyllithium initiated anionic polymerization in an integrated flow microreactor system. A high level of control of molecular weight was achieved at temperatures between -28 and +24 °C due to fast mixing, fast heat transfer, and residence time control. Santos and Metzger... 

PIT Pitsikalis, M., Siakah-Kioulafa, E., and Hadjichristidis, N., Block copolymers of styrene and n-alkyl methacrylates with long alkyl groups. Micellization behavior in selective solvents, J. Polym. Sci. Part A Polym. Chem., 42,4177, 2004. 

This interesting behavior of the ABA triblock copolymers is not a unique feature of the styrene-diene stmcture, but can be found in the case of other analogous chemical structures. Thus thermoplastic elastomers have been obtained from other triblock copolymers, where the dienes have been replaced by cyclic sulfides (Morton et al., 1971), cyclic siloxanes (Morton et al., 1974), or alkyl acrylates (Jerome, 2004) poly(alkyl methacrylate) end blocks have also been investigated (Jerome, 2(X)4). 

Nagaki A, Miyazaki A, Yoshida J (2010) Synthesis of polystyrenes-poly(alkyl methacrylates) block copolymers via anionic polymerization using an integrated flow microieactor system. Macromolecules 43 8424—8429... 

The preparations by anionic mechanism of A——A type block copolymers of styrene and butadiene can be carried out with the styrene being polymerized first. Use of alkyl lithium initiators in hydrocarbon solvents is usually a good choice, if one seeks to form the greatest amount of c/s-1,4 microstructure [346]. This is discussed in Chap. 4. It is more difficult, however, to form block copolymers from methyl methacrylate and styrene, because living methyl methacrylate polymers fail to initiate polymerizations of styrene [347]. The poly(methyl methacrylate) anions may not be sufficiently basic to initiate styrene polymerizations [345]. 

Kuroki, M. Nashimoto, S. Aida, T. Inoue, S. Sequential addition-ring-opening living polymerizations by aluminum porphyrin. Synthesis of alkyl methacrylate-epoxide and -lactone block copolymers of controlled molecular weight. Macromo/ec Ze 1988, 21, 3114—3115. 

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... 

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