Synthesis of biodegradable poly-epsilon-caprolactone microspheres by dispersion ring-opening polymerization in supercritical carbon dioxide

A series of fluorinated diblock and triblock copolymers of poly(epsilon-caprolactone) and poly(heptadecafluorodecylacrylate) were prepared by combining ring-opening polymerization of epsilon-CL and atom transfer radical polymerization of the acrylate. These copolymers with well-controlled molecular weight and composition were characterized by (1)H NMR spectroscopy and used as stabilizers for the dispersion ring-opening polymerization of epsilon-CL in supercritical carbon dioxide. The effect of composition and architecture of the polymeric stabilizers on the stabilization of PCL microspheres was investigated. Finally, purification of PCL was successfully implemented by reactive supercritical fluid extraction of the tin catalyst.     

Synthesis and solution behavior of poly(ε-caprolactone) grafted hydroxyethyl cellulose copolymers

Trimethylsilylated hydroxyethyl cellulose (TMSHEC) was synthesized by using hexamethyldisilazane (HMDS) as silylated agent. With the partial protection of hydroxyl groups of HEC by silylation, the novel poly(?-polycaprolactone) (PCL) grafted HEC (HEC-g-PCL) copolymers were successfully prepared by homogenous ring-opening graft polymerization and deprotection procedure. The structure of HEC-g-PCL copolymers was characterized by FTIR and 1H NMR. Fluorescence spectrum of HEC-g-PCL copolymer dilute solution indicated that copolymers could associate and form hydrophobic microdomains in aqueous solution. With the increasing of grafted PCL content, the critical association concentration (cac) of HEC-g-PCL copolymers decreased. The surface tension of HEC-g-PCL copolymers decreased dramatically with the increasing of the concentration and then approached to a plateau value when concentration was above the cac of HEC-g-PCL copolymers. The hydrodynamic radius of the aggregate of copolymer in dilute solution was found to increase with the increasing of the grafted PCL content. When the concentration of copolymer was above the cac, the zero-shear viscosity of the copolymer increased sharply and became much higher than that of HEC at the same concentration.     

Monohydroxylated poly(3-hydroxyoctanoate) oligomers and its functionalized derivatives used as macroinitiators in the synthesis of degradable diblock copolyesters

The presence of a hydroxyl group at the end of poly(3-hydroxyoctanoate) oligomers, noted PHO oligomers, is required to prepare diblock copolymers with improved properties by ring-opening polymerization of cyclic monomer as epsilon-caprolactone. Several chemical methods such as basic hydrolysis, acid-catalyzed reaction with APTS, and methanolysis were used to prepare well-defined low molar masses PHO oligomers. The methanolysis reaction was allowed to proceed for 10-60 min to produce PHO oligomers with Mn values ranging from 20,000 to 800 g mol-1 with low polydispersity index. Detailed analysis of the MALDI-TOF mass spectra of the obtained oligomers has revealed the presence of linear structures bearing methyl ester on one side and hydroxyl end group on the other side. The same procedure was applied to poly(3-hydroxyoctanoate-co-3-hydroxyundecenoate), PHOU, a poly(3-hydroxyalkanoate) containing unsaturated units in its side chains. These oligomers were further used to initiate the polymerization of epsilon-caprolactone by varying the PHO (or PHOU) and PCL lengths. By copolymerization with epsilon-caprolactone, the properties of PHO or PHOU have been improved. The crystallinity of the obtained copolymers was modified by controlling the length of the two different blocks. The unsaturations in the side chains of the PHOU block were oxidized in acid carboxylic functions to obtain a novel artificial biopolyester. Moreover, degradation was followed to study the influence of carboxylic groups on the hydrolysis of the copolymers.     

Poly(carbonate-ester)s of dihydroxyacetone and lactic acid as potential biomaterials

The synthesis of new polymeric biomaterials using biocompatible building blocks is important for the advancement of the biomedical field. We report the synthesis of statistically random poly(carbonate-ester)s derived from lactic acid and dihydroxyacetone by ring-opening polymerization. The monomer mole feed ratio and initiator concentration were adjusted to create various copolymer ratios and molecular weights. A dimethoxy acetal protecting group was used to stabilize the dihydroxyacetone and was removed using elemental iodine and acetone at reflux to produce the final poly(lactide-co-dihydroxyacetone) copolymers. The characteristics of the copolymers in their protected and deprotected forms were characterized by (1)H NMR, (13)C NMR, GPC, TGA, and DSC. Hydrolytic degradation of the deprotected copolymers was tracked over an 8-week time frame. The results show that faster degradation occurred with increased carbonate content in the copolymer backbone. The degradation pattern of the copolymers was visualized using SEM and revealed a trend toward surface erosion as the primary mode of degradation.     

Design and synthesis of self-degradable antibacterial polymers by simultaneous chain- and step-growth radical copolymerization

Self-degradable antimicrobial copolymers bearing cationic side chains and main-chain ester linkages were synthesized using the simultaneous chain- and step-growth radical polymerization of t-butyl acrylate and 3-butenyl 2-chloropropionate, followed by the transformation of t-butyl groups into primary ammonium salts. We prepared a series of copolymers with different structural features in terms of molecular weight, monomer composition, amine functionality, and side chain structures to examine the effect of polymer properties on their antimicrobial and hemolytic activities. The acrylate copolymers containing primary amine side chains displayed moderate antimicrobial activity against E. coli but were relatively hemolytic. The acrylate copolymer with quaternary ammonium groups and the acrylamide copolymers showed low or no antimicrobial and hemolytic activities. An acrylate copolymer with primary amine side chains degraded to lower molecular weight oligomers with lower antimicrobial activity in aqueous solution. This degradation was due to amidation of the ester groups of the polymer chains by the nucleophilic addition of primary amine groups in the side chains resulting in cleavage of the polymer main chain. The degradation mechanism was studied in detail by model reactions between amine compounds and precursor copolymers.     

Enzymatic preparation of novel thermoplastic di-block copolyesters containing poly[(R)-3-hydroxybutyrate] and poly(epsilon-caprolactone) blocks via ring-opening polymerization

Enzymatic modification of a microbial polyester was achieved by the ring-opening polymerization of epsilon-caprolactone (CL) with low-molecular weight telechelic hydroxylated poly[( R)-3-hydroxybutyrate] (PHB-diol) as initiator and Novozym 435 (immobilized Candida antarctica Lipase B) as catalyst in anhydrous 1,4-dioxane or toluene. The ring-opening polymerization was investigated at different conditions with two different types of PHB-diols: PHB-diol(P), containing a primary OH and a secondary OH end groups, and PHB-diol(M), consisting of 91% PHB-diol(P) and 9% PHB-diol containing two secondary OH end groups. The reactions were followed by GPC analyses of the resulting polymers at different time points, and the optimal conditions were established to be 70 degrees C at a weight ratio of CL/enzyme/solvent of 8:1:24. The ring-opening polymerization of CL with PHB-diol(M) (Mn of 2380, NMR) at the molar ratio of 50:1 under the optimal conditions in 1,4-dioxane gave the corresponding poly[HB(56 wt %)-co-CL(44 wt %)] with Mn (NMR) of 3900 in 66% yield. Polymerization of CL and PHB-diol(P) ( Mn of 2010, NMR) at the same condition in toluene gave the corresponding poly[HB(28 wt %)-co-CL(72 wt %)] with Mn (NMR) of 7100 in 86% yield. Both polymers were characterized by (1)H and (13)C NMR and IR analyses as di-block copolyesters containing a PHB block with a secondary OH end group and a poly(epsilon-caprolactone) (PCL) block with a primary OH end group. NMR analyses and control experiments suggested no formation of random copolymers and no change of the PHB block during the reaction. The enzymatic ring-opening polymerization was selectively initiated by the primary OH group of PHB-diol, whereas the secondary OH group remained as an end group in the final polymers. The thermal properties of the di-block poly(HB-co-CL)s were analyzed by DSC, with excellent T g values for the elastomer domain: poly[HB(56 wt %)- co-CL(44 wt %)] with M n (NMR) of 3900 demonstrated a T g of -57 degrees C, Tm of 145, 123, and 53 degrees C; and poly[HB(28wt%)-co-CL(72wt%)] with Mn (NMR) of 7100 gave a Tg of -60 degrees C, Tm of 147 and 50 degrees C. Thus, the selective enzymatic ring-opening polymerization with PHB-diol as macro-initiator provides a new method for the preparation of PHB-based block copolymers as biomaterials with good thermoplastic properties and novel structures containing functional end groups.     

Gel formation driven by tunable hydrophobic domain: design of acrylamide macromonomer with oligo hydrophobic segment

Nowadays, biomaterials with amphiphilic properties are undergoing remarkable development. Here, we present one such development, in which we prepared amphiphilic graft copolymers, with a main chain composed of hydroxyethyl acrylamide (HEAA), to introduce hydrophilicity, and a side chain composed of poly(trimethylene carbonate) (PTMC) to introduce tunable hydrophobicity. These macromonomers were created with a novel molecular design, which introduced a ring-opening polymerization by the hydroxyl end group of HEAA in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene, and were analyzed by (1)H NMR and gel permeation chromatography. The amphiphilic graft copolymers were shown to form a hydrogel, the swelling ratio of which was greatly influenced by the number of trimethylene carbonate units. These copolymers also exhibited the Tyndall phenomenon in aqueous solution; they aggregated spontaneously due to hydrogen bonding and hydrophobic interactions, and a sodium 8-anilino-1-naphthalenesulfonate (ANS) fluorescence probe was introduced into the hydrophobic domain. The solution property of ANS in the polymer solution was analyzed by fluorescence measurement and (1)H NMR. The maximum fluorescence wavelength of ANS shifted to shorter wavelengths as the degree of polymerization of the hydrophobic PTMC, the composition of the macromonomer, and the concentration of the copolymer increased. The resulting copolymer formed a polymer micelle structure due to the tunable hydrophobic domain formation in selected solvents. Therefore, these amphiphilic graft copolymers containing a PTMC segment are excellent candidates for use as hydrophobic drug delivery carriers.     

Enzymatic synthesis and characterization of novel biodegradable copolymers of 5-benzyloxy-trimethylene carbonate with 1,4-dioxan-2-one

Enzymatic ring-opening copolymerization of 5-benzyloxy-trimethylene carbonate (BTMC) and 1,4-dioxan-2-one (DON) was investigated for the first time. Immobilized porcine pancreas lipase (IPPL) on silica particles was selected to perform the copolymerization. A series of novel biodegradable copolymers with different compositions were characterized by (1)H NMR, (13)C NMR, and GPC. The influences of reaction conditions such as polymerization time and catalyst concentration on the yield and molecular weight of the copolymers were also studied. The copolymerizations of different monomer feed ratios were carried out in bulk at 150 degrees C with 4.5 wt per thousand IPPL as a catalyst for 24 h. With the increase of the BTMC molar feed ratio from 20% to 79%, the M(n) of the resulting copolymers increased from 5600 to 63400. Water uptake and static contact angle experiments showed that the hydrophilicity of copolymers could be improved with increasing DON content in the copolymers. Moreover, the in vitro drug release rate (ibuprofen as the model drug) of the resulting copolymers also increased along with the DON content in the copolymers.     

Decisive role of hydrophobic side groups of polypeptides in thermosensitive gelation

Thermosensitive hydrogels based on PEG and poly(l-glutamate)s bearing different hydrophobic side groups were separately synthesized by the ring-opening polymerization (ROP) of l-glutamate N-carboxyanhydrides containing different alkyl protected groups, that is, methyl, ethyl, n-propyl, and n-butyl, using mPEG(45)-NH(2) as macroinitiator. The resulting copolymers underwent sol-gel transitions in response to temperature change. Interestingly, the polypeptides containing methyl and ethyl showed significantly lower critical gelation temperatures (CGTs) than those bearing n-propyl and butyl side groups. Based on the analysis of (13)C NMR spectra, DLS, circular dichroism spectra, and ATR-FTIR spectra, the sol-gel transition mechanism was attributed to the dehydration of poly(ethylene glycol) and the increase of β-sheet conformation content in the polypeptides. The in vivo gelation test indicated that the copolymer solution (6.0 wt %) immediately changed to a gel after subcutaneous injection into rats. The mass loss of the hydrogel in vitro was accelerated in the presence of proteinase K, and the MTT assay revealed that the block copolymers exhibited no detectable cytotoxicity. The present work revealed that subtle variation in the length of a hydrophobic side group displayed the decisive effect on the gelation behavior of the polypeptides. In addition, the thermosensitive hydrogels could be promising materials for biomedical applications due to their good biocompatibility, biodegradability, and the fast in situ gelation behavior.     

Synthesis, characterization, and degradation behavior of amphiphilic poly-alpha,beta-[N-(2-hydroxyethyl)-L-aspartamide]-g-poly(epsilon-caprolactone)

A series of biodegradable amphiphilic graft polymers were successfully synthesized by grafting poly(epsilon-caprolactone) (PCL) sequences onto a water-soluble poly-alpha,beta-[N-(2-hydroxyethyl)-L-aspartamide] (PHEA) backbone. The graft copolymers were prepared through the ring-opening polymerization of epsilon-caprolactone (CL) initiated by the macroinitiator PHEA with pendant hydroxyl groups without adding any catalyst. By controlling the feed ratio of the macroinitiator to the monomer, the copolymers with different branch lengths and properties can be obtained. The successful grafting of PCL sequences onto the PHEA backbone was verified by FTIR, 1H NMR, and combined size-exclusion chromatography and multiangle laser light scattering (SEC-MALLS) analysis. The hydrolytic degradation and enzymatic degradation of these graft copolymers were investigated. The results show the hydrolytic degradation rate increases with increasing content of hydrophilic PHEA backbone. While the enzymatic degradation rate is affected by two competitive factors, the catalytic effect of Pseudomonas cepacia lipase on the degradation of PCL branches and the hydrophilicity which depends on the copolymer composition. In situ observation of the degradation under polarizing light microscope (PLM) demonstrates the different degradation rates of different regions in the polymer samples.     

Synthesis and characterization of poly(dimer acid-brassylic acid) copolymer and poly(dimer acid-pentadecandioic acid) copolymer

Poly(dimer acid-brassylic acid) [P(DA-BA)] copolymers and poly(dimer acid-pentadecandioic acid) [P(DA-PA)] copolymers were prepared by melt polycondensation of the corresponding mixed anhydride prepolymers. The copolymers were characterized by Fourier transform infrared (FTIR), gel permeation chromatography (GPC), differential scanning calorimetry (DSC), wide angle x-ray powder-diffraction, and thermal gravimetric analysis (TGA). In vitro studies show that all the copolymers are degradable in phosphate buffer at 37 degrees C, and leaving an oily dimer acid residue after hydrolysis for the copolymer with high content of dimer acid. The release profiles of hydrophilic model drug, ciprofloxcin hydrochloride, from the copolymers, follow first-order release kinetics. All the preliminary results suggested that the copolymer might be potentially used as drug delivery devices.     

Chitosan grafted with macrocyclic polyamines on C-2 and C-6 positions as nonviral gene vectors: preparation, characterization, and in vitro transfection studies

Chitosan grafted with macrocyclic polyamines (Cs-g-MCPA) on the C-2 or the C-6 position was synthesized by a simple method. Four copolymers prepared were characterized by (1)H NMR, (13)C NMR, Fourier transform infrared spectra (FTIR), X-ray diffraction (XRD), and gel permeation chromatography (GPC). Circular dichroism spectra (CD), fluorescence spectra and agarose gel electrophoresis assay showed that Cs-g-MCPA copolymers had good binding ability to DNA. By modification of the MCPAs, the copolymers showed low cytotoxicity and high transfection efficiency as new gene vectors. It was found that Cs-g-MCPA copolymers with different grafted positions showed different properties: copolymers grafted on the C-2 position showed higher cytotoxicity and higher transfection efficiency than those grafted on position C-6.     

Synthesis and characterization of hydroxypropyl methylcellulose and ethyl acrylate graft copolymers

The synthesis of hydroxypropyl methylcellulose-g-poly (ethyl acrylate) was carried out by potassium persulfate induced graft copolymerization in homogeneous aqueous medium. By varying the reaction conditions, graft copolymers with different percentage of grafting were prepared. These graft copolymers were characterized by fourier transform infrared spectra (FTIR), transmission electron microscopy (TEM), scanning electron microscopy (SEM), thermogravimetric analyses (TGA), X-ray diffraction analysis (XRD), and dynamic light scattering (DLS) methods. The molecular weight of grafted and ungrafted polymer chains determined by gel permeation chromatography (GPC) increased with increasing monomer and matrix concentration but decreased with increasing initiator concentration and reaction temperature. The mechanical properties of graft copolymers were measured as function of the percentage of grafting. In addition, the equilibrium humidity adsorption behavior and the disintegration time of the grafted copolymer films were also studied.     

Resorbable and highly elastic block copolymers from 1,5-dioxepan-2-one and L-lactide with controlled tensile properties and hydrophilicity

New resorbable and elastomeric ABA tri- and multiblock copolymers have been successfully synthesized by combining ring-opening polymerization with ring-opening polycondensation. Five different poly(L-lactide-b-1,5-dioxepan-2-one-b-L-lactide) triblock copolymers and one new poly(L-lactide-b-1,5-dioxepan-2-one) multiblock copolymer have been synthesized. The triblock copolymers were obtained by ring-opening polymerization of 1,5-dioxepan-2-one (DXO) and L-lactide (LLA) with a cyclic tin initiator. The new multiblock copolymer was prepared by ring-opening polycondensation of a low molecular weight triblock copolymer with succinyl chloride. The molecular weight and the composition of the final copolymers were easily controlled by adjusting the monomer feed ratio, and all of the polymers obtained had a narrow molecular weight distribution. It was possible to tailor the hydrophilicity of the materials by changing the DXO content. Copolymers with a high DXO content had a more hydrophilic surface than those with a low DXO content. The receding contact angle varied from 27 to 44 degrees. The tensile properties of the copolymers were controlled by altering the PDXO block length. The tensile testing showed that all the polymers were very elastic and had very high elongations-at-break (epsilon(b)). The copolymers retained very good mechanical properties (epsilon(b) approximately 600-800% and sigma(b) approximately 8-20 MPa) throughout the in vitro degradation study (59 days).     

Nanocapsules based on linear and Y-shaped 3-miktoarm star-block PEO-PCL copolymers as sustained delivery system for hydrophilic molecules

Well-defined amphiphilic Y-shaped miktoarm star-block copolymers of PEO and PCL were synthesized by ring-opening polymerization of ε-caprolactone initiated by a PEO-bound lysine macroinitiator. The copolymers were characterized by (1)H NMR, SEC, DSC, and WAXD techniques. Separate PCL and PEO crystalline phases occur in melt-crystallized copolymers when their segmental lengths were comparable and the PCL content was ≤80 wt %. Self-assembling of these copolymers in aqueous medium led to nanoaggregates with low critical aggregation concentration values (0.35 to 1.6 mg·L(-1)) and size depending on composition. Despite the fact that copolymers were not prone to self-organize in vesicles, once processed by a novel w/o emulsion-melting-sonication technique, they gave nanocapsules with a water core and a hydrophilic surface. A macromolecular fluorescent dye was effectively loaded and released at sustained rate by optimizing nanocapsule formulation. The results demonstrate that amphiphilic block copolymers can be assembled in different kinds of nanomorphologies independently of their hydrophilic/hydrophobic balance and architecture through specifically designed preparation techniques.     

Copolymers from unsaturated macrolactones: toward the design of cross-linked biodegradable polyesters

The enzymatic synthesis of a series of random copolyesters by ring-opening polymerization of unsaturated macrolactones like globalide and ambrettolide with 1,5-dioxepan-2-one (DXO) and 4-methyl caprolactone (4MeCL) was investigated. (13)C NMR diad analysis confirmed the randomness of all copolymers irrespective of the comonomer ratios. Thermal investigation showed that incorporating the comonomers lowered the melting points of the polymers as compared with the macrolactone homopolymers. The decrease was dependent on the comonomer ratio. The unsaturated copolymers were thermally cross-linked using dicumyl peroxide, which resulted in completely amorphous insoluble networks. It was found that 10% incorporation of the unsaturated macolactone was sufficient to obtain a gel content of 95 wt %. Preliminary degradation tests confirm that the cross-linked copolymers are enzymatically degradable and that the incorporation of hydrophilic comonomers like DXO enhances degradation.     

Multiblock copolymers of L-lactide and trimethylene carbonate

Sequential copolymerizations of trimethylene carbonate (TMC) and l-lactide (LLA) were performed with 2,2-dibutyl-2-stanna-1,3-oxepane as a bifunctional cyclic initiator. The block lengths were varied via the monomer/initiator and via the TMC/l-lactide ratio. The cyclic triblock copolymers were transformed in situ into multiblock copolymers by ring-opening polycondensation with sebacoyl chloride. The chemical compositions of the block copolymers were determined from (1)H NMR spectra. The formation of multiblock structures and the absence of transesterification were proven by (13)C NMR spectroscopy. Differential scanning calorimetry (DSC), wide-angle X-ray scattering (WAXS), and dynamic mechanical analysis (DMA) measurements confirmed the existence of a microphase-separated structure in the multiblock copolymers consisting of a crystalline phase of poly(LLA) blocks and an amorphous phase formed by the poly(TMC) blocks. Stress-strain measurements showed the elastomeric character of these biodegradable multiblock copolymers, particularly in copolymers having epsilon-caprolactone as comonomer in the poly(TMC) blocks.     

Poly(L-lysine)-graft-chitosan copolymers: synthesis, characterization, and gene transfection effect

Polypeptide/polysaccharide graft copolymers poly(L-lysine)-graft-chitosan (PLL-g-Chi) were prepared by ring-opening polymerization (ROP) of epsilon-benzoxycarbonyl L-lysine N-carboxyanhydrides (Z-L-lysine NCA) in the presence of 6-O-triphenylmethyl chitosan. The PLL-g-Chi copolymers were thoroughly characterized by 1H NMR, 13C NMR, Fourier transform infrared (FT-IR), and gel permeation chromatography (GPC). The number-average degree of polymerization of PLL grafted onto the chitosan backbone could be adjusted by controlling the feed ratio of NCA to 6-O-triphenylmethyl chitosan. The particle size of the complexes formed from the copolymer and calf thymus DNA was measured by dynamic light scattering (DLS). It was found in the range of 120 approximately 340 nm. The gel retardation electrophoresis showed that the PLL-g-Chi copolymers possessed better plasmid DNA-binding ability than chitosan. The gene transfection effect in HEK 293T cells of the copolymers was evaluated, and the results showed that the gene transfection ability of the copolymer was better than that of chitosan and was dependent on the PLL grafting ratio. The PLL-g-Chi copolymers could be used as effective gene delivery vectors.     

Novel synthesis of functionalized poly(3-hydroxybutanoic acid) and its copolymers.

Novel feasibility of fuctionalized poly(3-hydroxybutanoic acid), PHB, and its copolymers synthesis via ring-opening of beta-butyrolactone (ROP) mediated by activated anionic initiators or enzymes in vitro is presented. Using these new synthetic approaches, PHB with defined chemical structure of the end groups as well as block, graft and random copolymers have been obtained and characterized by IR, NMR, ESI-MS and GPC techniques. The relationship between the structure and properties of the novel polymeric materials prepared is discussed.     

Synthesis and self-assembly of well-defined poly(amino acid) end-capped poly(ethylene glycol) and poly(2-methyl-2-oxazoline)

Poly(ethylene glycol) (PEG) and poly(2-methyl-2-oxazoline) (PMOx) are water-soluble, biocompatible polymers with stealth hemolytic activities. Poly(amino acid) (PAA) end-capped PEG and PMOx were prepared using amino-terminated derivatives of PEG and PMOx as macroinitiators for the ring-opening polymerization of γ-benzyl protected l-glutamate N-carboxyanhydride and S-benzyloxycarbonyl protected l-cysteine N-carboxyanhydride, respectively, in the presence of urea, at room temperature. The molecular weight of the PAA moiety was kept between M(n) = 2200 and 3000 g mol(-1). PMOx was polymerized by cationic ring-opening polymerization resulting in molecular weights of M(n) = 5000 and 10,000 g mol(-1), and PEG was a commercial product with M(n) = 5000 g mol(-1). Here, we investigate the self-assembly of the resulting amphiphilic block copolymers in water and the effect of the chemical structure of the block copolymers on the solution properties of self-assembled nanostructures. The PEG-block-poly(amino acid), PEG-b-PAA, and PMOx-block-poly(amino acid), PMOx-b-PAA, block copolymers have a narrow and monomodal molecular weight distribution (PDI < 1.3). Their self-assembly in water was studied by dynamic light scattering and fluorescence spectroscopy. In aqueous solution, the block copolymers associate into particles with hydrodynamic radii (R(H)) ranging in size from R(H) 70 to 130 nm, depending on the block copolymer architecture and the polymer molecular weight. Larger R(H) and critical association concentration values were obtained for copolymers containing poly(S-benzyloxycarbonyl-l-cysteine) compared to their poly(γ-benzyl-L-glutamate) analogue. FTIR investigations revealed that the poly(γ-benzyl-L-glutamate) block adopts a helical conformation, while the poly(S-benzyloxycarbonyl-L-cysteine) block exists as β-sheet.