Block copolymers, PMMA

Table 13. Relaxation times characterizing the intramolecular mobility of the polymer chain, for the homopolymer and the block of the corresponding chemical structure and molecular weight M in three-block copolymers (PMMA-PS-PMMA) and (PS-PMMA-PS) at 25 °C ij,ed 0.38 cP. a) ratMA, b) PS. The polymer concentration in solution is 0.005% the component under investigation with a luminescent marker is denoted by ( )...

Living anionic polymerization can also be used to produce well-controlled block copolymers. For PMMA, the best procedures need temperatures below O C and are therefore unlikely to be commercially attractive. Hiey are, furthermore, largely unsuccessful for the controlled polymerization of acrylates, which are far too reactive. The use of tetraalkyl ammonium ate complexes, in conjunction with an appropriate aluminum catalyst, solved fhis problem [225]. The function of the ammonium counterion is to promote dissociation of the complex ion to form the reactive ate complex of the aluminum enolate of the ester (Scheme 6.176). Thus, polymerization was initiated by the lithium enolate of isobutylate in the presence of the ate complex of Me3Al-R3NCl. A controlled block copolymer (PMMA-block-... 

Tri-block copolymers of MMA-styrene-MMA were characterized by SEC, TLC and PGC [79]. SEC was applied first to fractionate the copolymers according to molecular size. These fractions were subjected to PGC to obtain their composition. These fractions were also separated into block copolymer and homopolymers (PS and PMMA) by TLC. Using these three techniques, MMA (or styrene) percentage, and concentrations of block copolymer, PMMA homopolymer and PS homopolymer as a function of SEC retention volume could be obtained. 

PMMA US 1.8kD-305kD CR 0.7kD-12kD THF /n-hexane 82/ 18wt. S/N Nucleosil, 120°A, 5 pm, 15x0.4cm, Nucleosil 300°A, 5 pm, 25x0.4cm 0.5 ml/min 25 pi uv, ELSD Block copolymers PMMA-PtBMA, two-dimensional separation. Falkenhagen J, Much H, Stauf W, Muller AHE [55]... 

The average molar masses of components of block copolymers PMMA-PtBMA estimated by LC under critical conditions (for polymer eluted in SEC mode) agree very well with values SEC obtained by subtracting the molar mass of the PtBMA precursor from that of the block (deviation 2-4 %) [55]. Agreement up of individual component ratio of 1 5 was found. On the other hand, Lee et al. [39,78] have found systematic difference 0-33% between by critical conditions measured the molar mass of precursor and expected molar mass of precursor. Differences between measured, and expected, molar masses increased with the concentration of the invisible part of copolymers (i.e. part of copolymer under critical conditions). Additional studies are needed to generalize this phenomenon. 

The first reported controlled polymerization based on the OMRP-RT principle appears to have been presented by Minoura in a series of articles starting in 1978, where the redox initiating system BPO/Cr was used for the polymerization of vinyl monomers.Not only were the kinetics different than in free-radical polymerization (very low reaction orders in Cif and BPO), but also the polymerization was observed to continue after all Cr had been converted by the peroxide to Cr and the degree of polymerization was found to increase with monomer conversion at low temperatures (<30 0). These studies included the report of a block copolymer (PMMA-b-PAN). Polydispersity indexes were not reported for these studies. Minoura formulated the mechanistic hypothesis of the formation of a metal complex with the free radical and stated that "the recombination of free radicals formed by the dissociation of the complexed radicals competes with a disproportionation of free radicals". However, these studies did not have a great impact in the polymer community, being cited only a handful of times before 1994. A few subsequent contributions reported the application of similar conditions to other metals but well-controlled polymerizations were not found."- " ... 

Using novel asymmetric difunctional initiators containing TEMPO and 2-bromopropanoate or 2-bromo-2-methylpropanoate groups, block copolymers can be prepared via combination of ATRP and STRP [147,148]. For example, asymmetric difunctional initiator, CLI-25 was used in the ATRP of MM A with CuCl/N, N, N , N ,N -pentamethyldiethylene-triamine (PMDETA) as catalyst. The low initiator efficiency (i.e. 0.8) may be related to the side reactions that occur in the initiation step. Subsequently, the TEMPO-terminated PMMA was used as the macroinitiator in the nitroxide-mediated radical polymerization of St at 125 °C. A series of block copolymers, PMMA-6-PSt [147], PrBA-6-PSt [147] and PtBA-6-PMMA-Zi-PSt [148] have been obtained, an example of which is shown in Scheme 3.36. 

There has also been active interest in blends of PBT with other polymers. These include blends with PMMA and polyether-ester rubbers and blends with a silicone/polycarbonate block copolymer. 

The main experimental techniques used to study the failure processes at the scale of a chain have involved the use of deuterated polymers, particularly copolymers, at the interface and the measurement of the amounts of the deuterated copolymers at each of the fracture surfaces. The presence and quantity of the deuterated copolymer has typically been measured using forward recoil ion scattering (FRES) or secondary ion mass spectroscopy (SIMS). The technique was originally used in a study of the effects of placing polystyrene-polymethyl methacrylate (PS-PMMA) block copolymers of total molecular weight of 200,000 Da at an interface between polyphenylene ether (PPE or PPO) and PMMA copolymers [1]. The PS block is miscible in the PPE. The use of copolymers where just the PS block was deuterated and copolymers where just the PMMA block was deuterated showed that, when the interface was fractured, the copolymer molecules all broke close to their junction points The basic idea of this technique is shown in Fig, I. 

The polymers initiated by BP amines were found to contain about one amino end group per molecular chain. It is reasonable to consider that the combination of BP and such polymers will initiate further polymerization of vinyl monomers. We investigated the photopolymerization of MMA with BP-PMMA bearing an anilino end group as the initiation system and found an increase of the molecular weight from GPC and viscometrical measurement [91]. This system can also initiate the photopolymerization of AN to form a block copolymer, which was characterized by GPC, elemental analysis, and IR spectra. The mechanism proposed is as follows ... 

Recently, various polyesters such as poly(ethylene adipate), poly(tetramethylene adipate), poly(caprolac-tone), and poly(aliphatic carbonate), having terminal hydroxyl groups, were reacted with ACPC to give corresponding macroazoesters and their thermal behaviors were observed by DSC [14]. The block copolymers of these polycondensation polymers with addition polymers such as PSt and PMMA were synthesized [14]. 

Polyarylate (PAR)-b-PSt and PAR-b-PMMA for compatibiiizers are described 135,39,40). The addition of PAR-b-PSt (1-10 parts) to 100 parts of a blend of PAR-PSt (7w-3w) resulted in improvement of the tensile and flexural modulus (Fig. 4), and PSt dispersed particles were diminished from 1-5 microns to an order that is undetectable by SEM, indicating the excellent, compatibilizing effect of the block copolymer. The alloy thus formed exert the characteristic of PAR, an engineering plastic, as well as easy processability of PSt. Addition of PAR-b-PMMA (3 or 8 parts) to 100 parts of a blend of PAR-polyvinylidenefluoride (PVDF) (7w-3w) resulted in improved microdispersed state of PVDF due to compatibility of PMMA with PVDF, while segregation of PVDF onto the surface was controlled. 

PDMS macromonomer was used as a component of block segment to obtain a graft block copolymer with PMMA (Scheme 1) [51-53]. This graft block copolymer is characteristic of surface water repellence, easy peeling, and weatherability superior to simple graft copolymers of the same members. PDMS-b-PVC film also shows long life surface water repellency with weatherability and very low coefficiency of abrasion [18,54]. 

PSt or PMMA, respectively, was coupled with polymethacrylate having a PEG side chain or methylammo-niumchloride side chain to prepare a block copolymer for giving a hydrophilic surface [55]. Also, PSt-b-PVP [36,37], PSt-b-(hydrophilic vinyl copolymer) [56], PSt-b-po y(sodium acrylate) (PNaA) [57], and PSt-b-PNaA-b-(polyperfluoroacrylate) (PFA) [58] were synthesized for the same application. 

Block copolymers with materials such as a polyester (PE) (qv) can be prepd by the reaction of diisocyanate-terminated polyesters with hydroxyl-terminated PMMA according to Wilkes and Grezlak (Ref 21). The basic structure was found to be PMMA-PE-FMMA, with a mw of from 7500 to 47000. The purpose of the work was to produce a stronger copolymer (in terms of stress-strain) by tailoring the amt of each monomer used to produce the copolymer Further information on polymerization can be found in Refs 2a 6a... 

Yijin X. and Caiyaun P., Block and star-hlock copolymers by mechanism transformation. 3. S-(PTHF-PSt)4 and S-(PTHF-PSt-PMMA)4 from living CROP to ATRP, Macromolecules, 33, 4750, 2000. Feldthusen J., Ivan B., and Mueller A.H.E., Synthesis of linear and star-shaped block copolymers of isobutylene and methacrylates hy combination of living cationic and anionic polymerizations. Macromolecules, 31, 578, 1998. 

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. 

In the past, ionomers have generally consisted of 10-12 mole percent of ions and it is our intention to be consistent with the corresponding random ionomers previously discussed in the literature. In addition to gel permeation chromatography (GPC), H and 3C NMR can readily be utilized to verify the relative amount of monomer successfully incorporated into the block copolymer. For example, the composition of a PMMA-PTBMA diblock can be verified by H NMR ratioing the methyl ester integration (3.5 ppm) to the t-butyl ester integration (1.36 ppm). Figure 1 depicts the t-butyl ster chemical shift which appears reproducibly at 1.J6 ppm. C or FTIR can be utilized in certain instances when H NMR chemical shifts overlap. For... 

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. 

The alignment of a lamellar microstructure by electric fields has been reported [64], The electric fields were applied across a melt of a PS-PMMA block copolymer and were maintained throughout cooling down to below the glass transition point. SAXS studies show persuasive evidence that the microstructure was aligned by an electric field. 

Narrow molecular weight distribution PMMA-fc-poly(2-perfluorooclyle-thyl methacrylate) block copolymers (Scheme 2) were synthesized in THF at... 

The direct synthesis of poly(3-sulfopropyl methacrylate)-fr-PMMA, PSP-MA-fr-PMMA (Scheme 27) without the use of protecting chemistry, by sequential monomer addition and ATRP techniques was achieved [77]. A water/DMF 40/60 mixture was used to ensure the homogeneous polymerization of both monomers. CuCl/bipy was the catalytic system used, leading to quantitative conversion and narrow molecular weight distribution. In another approach the PSPMA macroinitiator was isolated by stopping the polymerization at a conversion of 83%. Then using a 40/60 water/DMF mixture MMA was polymerized to give the desired block copolymer. In this case no residual SPMA monomer was present before the polymerization of MMA. The micellar properties of these amphiphilic copolymers were examined. 

A combination of ATRP and ROP was employed for the synthesis of PLLA-fr-PS block copolymers and PLLA-fr-PS-fo-PMMA triblock terpoly-mers [120]. Styrene was initially polymerized using the functional initiator /3-hydroxyethyl a-bromobutyrate, HEBB, and the catalytic system CuBr/bpy. 

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